A CONCEPTUAL ECOSYSTEM MODEL OF THE CORPUS CHRISTIBAYNATIONALESTUARY PROGRAM STUDYAREA by Paul A. Montagna, Jian Li, and Gregory T. Street FINALREPORT "ACONCEPTUAL ECOSYSTEMMODEL OF THE CORPUS CHRISTI BAY NATIONAL ESTUARY PROGRAM STUDY AREA” Paul A. Montagna, Ph.D. Jian Li, Ph.D. and Gregory T. Street, B.A. TheUniversityofTexasatAustin,Marine ScienceInstitute 750 Channelview Drive, Port Aransas, Texas 78373 Telephone; (512)749-6779 Fax: (512)749-6777 E-mail; paul@utmsi.zo.utexas.edu Submitted to: Corpus Christi Bay National Estuary Program TAMU-CC, Campus Box 290 6300 Ocean Drive Corpus Christi, Texas 78412 UTMSI Technical Report Number 95-001 A CONCEPTUAL ECOSYSTEM MODEL OF THE CORPUS CHRISTI BAY NATIONAL ESTUARYPROGRAM STUDY AREA TABLE OF CONTENTS 1 EXECUTIVE SUMMARY I. INTRODUCTION 3 6 11. METHODS 111. ESTUARINE PROCESSES 10 Background 10 12 Bay System Sources 12 15 Storage 19 Subsystems 20 Summary Producers 20 24 Summary Representative Producer 24 24 Synthesis 29 Respiration 29 Reproduction Predation / Grazing 29 Natural death 29 Summary 30 Consumers 30 Summary 33 33 Representative Consumer Intake 36 Assimilation 36 Respiration 37 Excretion 38 Reproduction 38 Predation 38 Natural death 40 Migration 40 40 Summary Mineralizers 41 Aerobic respiration 41 42 Anaerobic respiration 45 Summary 45 Representative Mineralizer 45 Increasing biomass Decomposition 45 Other factors 46 Summary 46 IV. HABITATS 49 Seagrass Bed Habitat 52 Salt Marsh Habitat 55 AlgalMatHabitat 58 Beach Habitat 59 Water Column Habitat 62 Open Bay, Sandy Bottom Habitat 65 Open Bay, Muddy Bottom Habitat 68 Oyster ReefHabitat 74 Scale ofBenthic Invertebrates 75 Summary 75 V. ESTUARIES OF THE CCBNEP AREA 79 Laguna Madre Estuary 79 Mission-Aransas and Nueces Estuaries 81 VI. ANTHROPOGENIC PROCESSES 83 Summary 83 83 Water and Sediment Quality Management Living Resources Management 90 Pollutants 90 Summary 90 VII. PRIORITY PROBLEMS 96 Altered Freshwater Inflow Into Bays and Estuaries 96 Loss ofWetlands and Estuarine Habitats 98 Condition ofLiving Resources 98 DegradationofWater Quality 101 Altered Estuarine Circulation 103 Bay Debris 105 Public Health Issues 107 Summary 109 VIII. INFORMATION GAPS 110 IX. REFERENCES 11l A CONCEPTUAL ECOSYSTEM MODEL OF THE CORPUS CHRISTI BAY NATIONALESTUARYPROGRAM STUDY AREA by Paul A. Montagna, Jian Li, and Gregory T. Street EXECUTIVE SUMMARY The ofthisprojectistodevelopaconceptualmodeltodescribemechanistic purpose relationships among biotic, abiotic, and anthropogenic components ofthe estuarine ecosystems contained within the Corpus Christi Bay National Estuary Program (CCBNEP) area. A conceptual model is a presentation ofthe ecosystem components and linkages among schematic format. The model also includes components for socioeconomic and components in a management policy mechanisms. Therefore, the conceptual model will be useful to environmental managersintheresolutionofCCBNEPpriorityproblems. The conceptual model was developed using a hierarchical structure. The CCBNEP area can be viewed asasingleunitwithcomponents;thecomponentsarecomposedofsubcomponents,and soon.Ifallthedetailsofan ecosystemarepresentedinonelargemodel,thenitisnearly impossible to identify relationships among components. The hierarchical view allows us to the broadest picture ofthe CCBNEP area first, then into details of zoom begin focusing on specificsubcomponentsofinterest. Anotheradvantageofthehierarchicalnatureofthemodelis that a reader can continue to focus down to finer details depending on the reader’s expertise and interest. Theconceptualmodelispresentedinbothatechnicalandpublicformat. Thetwodifferent formatsaretailoredtoaudiences ofdifferentlevelsoftechnical expertise, i.e.,resource managers, scientists and engineers versus the general public. The technical format presents the model using energy circuit language, which is a standard format for presenting ecosystem diagrams. The public format presents the same information that is in the technical format, but it is in “cartoon form”. Therefore, words, names, or relationships that may not be familiar to the lay person obstacle to understanding the underlying concepts being presented. are not an The model These three encompasses the three major ecosystems ofthe CCBNEP study area. systems are the Baffin Bay-upper Laguna Madre Estuary, the Nueces Estuary, and the Mission-Aransas Estuary. The generic processes that occur in the CCBNEP study area are included in the model as all these occur The relative importance ofsome ofthe processes in each system. on the environmental characteristics that processes changes among the ecosystems based may differ among the three ecosystems. These differing characteristics are primarily freshwater inflow, oceanic exchangewiththeGulfofMexico (bothofwhich are greaterin the Nueces and Mission-AransasEstuariesthaninLagunaMadre) andarealextentofspecifichabitattypes within the three estuaries. A CONCEPTUAL ECOSYSTEM MODEL OF THE CORPUS CHRISTI BAY NATIONAL ESTUARY PROGRAM STUDY AREA Paul A. Montagna, Jian Li, and Gregory T. Street I. INTRODUCTION Characterization Phase. The Characterization Phase will increase the understanding ofestuarine problems, probable causes, and recognize management implications. wayto understand and present The Corpus Christi Bay National Estuary Program (CCBNEP) is currently in a One thecomplexprocessesthat occurinestuariesistohave aconceptualmodeloftheecosystems. The goal ofthis project is to compile existing information regarding conceptual modeling for estuaries, and develop a conceptual (qualitative) model, both pictorial and narrative, ofthe CCBNEP study area. A conceptual model demonstrates ecosystem linkages at all trophic levels and all habitat types, and provides a Conceptual framework that can be used to assess environmental impacts (both episodic and cumulative) associated with external influences. Theconceptualmodel theentireCCBNEPareatoenablecomparisonofthe encompasses region’s three major ecosystems. The study area covers about 125 kilometers ofthe southeast Texas coast and includes all marine and estuarine waters behind the surf-line from the eastern edgeofMesquiteBaytotheLandCutofLagunaMadre,andthe12associated countiesofthe Coastal Bend Council ofGovernments. This includes three distinct ecosystems (Fig. LI): the Baffin Bay-upper Laguna Madre Estuary, the Nueces Estuary, and the Mission-Aransas Estuary The Nueces Estuary includes Nueces, Corpus Christi and Redfish Bays. The Mission-Aransas Estuary includes Mesquite, Copano, and Aransas Bays. The models developed apply to all bays and estuarine ecosystems. The goal in developing the conceptual model is to describe biotic, abiotic, and anthropogenic components ofthe CCBNEP estuarine ecosystems, and the functional relationships among the components. Such a model would provide the conceptual framework to incorporate socioeconomic issues into environmental management policy. This is necessary to enable resolution ofCCBNEP priority problems. Therefore, the conceptual model is didactic, that is, it Fig. 1.1. Map ofstudy area including three estuaries. Mission-Aransas, Nueces and Laguna Madre Estuaries, and their primary bays, secondary bays, rivers, and creeks. teaches as well as demonstrates, ecosystem components and linkages. The conceptual model should be understandable to a broad audience including the lay public, as well as environmental experts. There were five objectives that were accomplished by this project: (1) To develop a systems model to describe the mechanistic relationships among abiotic, biotic, and anthropogenic components ofthe estuarine ecosystems contained within the CCBNEP area. (2) To incorporate socioeconomic and management policy mechanisms, where possible, to enable resolution ofthe CCBNEP priority problems. (3)Toprovide aconceptualcharacterizationoftheCCBNEP area. (4) Todevelopatwo-layeredmodeltailoredtoaudiencesofdifferentlevelsoftechnical expertise. (5) To compare ecological differences between the three distinct ecosystems within the two ecotonesoftheCCBNEP studyarea. 11. METHODS Manyconceptual andquantitativemodeling studiesofestuaries havebeen completed duringthe last 30 The first task ofthe currenl project was to review this information to assure that all years. ecosystem components found in other models were incorporated, where appropriate, into the CCBNEP conceptual model. However, we did not simply “cut and paste” existing literature. Rather, we tried to be creative, and develop a different, but accurate view ofthe estuaries in South Texas. All models developedforestuarine ecosystems describe componentsofthe ecosystem and the interrelationshipsamongthecomponents. Manygobeyondthequalitativestateandalsoprovide mathematicalrelationshipsfortheflowofmaterialamongthecompartments orforchangesin the standing stocks (or amounts) contained in the compartments. Although the current project limitedtodevelopingthequalitative relationships,we providemostofthe basic mathematical equations necessary to model most ecological processes. The equations will enhance thepresentationofthe conceptualmodeltothetechnically trainedreader. was Thepresentationofmodelsoccursinavarietyofdifferentschematicformats. Themost common format, and the only one that comes close to being a standard format, is based on energy circuit language and was developed and refined by H.T. Odum (1972). The conceptual models in this report are drawn using this format. Models consist ofa series ofdiagrams and figures showing the biotic and abiotic components ofthe ecosystems and the functional linkages present (i.e., the flow ofmaterials between the components). One innovation presented here is to present the CCBNEP model as a series ofhierarchical, conceptual models. The conceptual models presented here include three hierarchical levels; the estuarine trophic component, food web subsystem components, and processes for each component (Fig. 11. 1). The conceptual model also includes habitat components. Essentially, we started at the highest level, and focused down to detailed levels. This approach was adopted so thatwewouldnotproduce onefigurewithanindecipherable amountofinformation onit. Models are like examining specimens from the macroscopic to microscopic levels. For example, imagine viewing the ecosystem from an airplane, then a boat, then a microscope. This hierarchical view is the technique we used to develop the conceptual submodels. Fig. 11. 1. Theconceptual models described in this study The three estuaries ofthe CCBNEP area share many similarities, but differ in some significant It would be redundant to simply repeat each model three times. The the models ways. way changeforeachsystem, isinthequantitativeaspectsofthesizesofthecompartments andflows ThisIslargelycontrolledbythe sizesoftwovariables:thefreshwater among the compartments. inflow balance, and the area ofspecific habitats or geological features. Therefore, one common However, specific differences are discussed in section V. view suffices for all three ecosystems. Including biotic and abiotic components into conceptual models is a relatively simple task. However, humans are also an important component in the CCBNEP ecosystems. Incorporating humanactivitiesismorecomplex,andrarelyperformed. Thereareavarietyofanthropogenic influences that are important, such as effects on water quality and supply, resource utilization (e.g., fishing and hunting), and habitat alteration (e.g., channelization, altering circulation, or Some activities “act like a switch.” For example, fishing yield is translated habitat destruction). into dollars, but for some fisheries (e.g. shrimp), the season is either open or closed, which is analogous to turning on or offa switch. Other management strategies “act like a dial,” to increase or decrease flows. In this there are variable settings and not just “on or off.” For case, recreational finfishery can be increased or deceased by a range values by on a example, pressure changing the size and bag limits on the species. Human impacts and management policies have been incorporated into models through the switches and dials that alter flows between our compartments. Conceptual models presented using energy circuit language are easily understood by people with ahighdegreeoftechnicalandquantitativeskills. Thelanguage,becauseitistechnicaljargon, contains many shorthand notations that convey detailed information about the system being described. However, the jargon used in these technical models may be an obstacle to the lay public or to members ofthe Management Conference without specific training in ecosystem science. Therefore, all models have also been presented in a second, pictorial format, which should be relatively easy for people from any background to understand. In some cases, important relationships are emphasized, and the less important relationships are deleted. The pictoral formats are described in lay terms in “summaries” that follow the sections describing each energy circuit model. Energy circuit language and scientific models demonstrate the principlesoftheinteractionswithinecosystems. Additionalfiguresor“cartoon”viewsofthe models will ensure that the final product will be useful to scientists, engineers, managers, and the general public. The lay person who has no interest in the technicl details is encourage to skip a “B” directly to the sections labled “Summary” and figures with as a suffix. Theremainderofthisreporthassixsections. Thefirstofthesesectionsdescribestheecological thatoccurwithinestuariesoftheCCBNEParea. Thedescriptionofecological processes processes is a typical format for conceptual models. Many ofthe processes are modified or have unique pathways in different habitats. Therefbie, we have also identified the major habitats and unique pathways in these habitats in the next section. The third section describes the relative differences in the ecological processes among the three estuaries within the CCBNEP study area. The next section describes the anthropogenic influences upon ecological processes within the estuaries. The next section describes the “Priority Problems” identified by the CCBNEP as potentialproblemsworthyoffurtherscientificinvestigation. Thefinaltaskwastoidentifydata andinformationneeds,andthisisthesubjectofthelastsectionofthecurrentreport. Therewill begapsintheunderstandingoftheseecosystems. Theconceptualmodelidentifiesthe compartments that exist and the arrows identify the existing linkages. Other CCBNEP characterization reports can be used to determine which compartments are well known, and for which information is lacking. 111. ESTUARINEPROCESSES Background Communitiesoforganisms, considered togetherwiththeirphysical settings orhabitats, are known as ecosystems. The flow ofenergy through an ecosystem is very complex, involving manydifferenttypesofenergysources,interactionsand sinks. Aconvenientwaytorepresent energy flow through an ecosystem is by using energy circuit diagrams. Models based on energy circuit diagrams, developed by Odum (1971, 1972 and 1983), symbolically represent the thermodynamic constraints, feedback mechanisms and energy flows in ecosystems. energy An circuit diagram is used to divide an ecosystem into its component parts and illustrate the relationships and connections among those parts. The symbols used in energy circuit diagrams include paths, sources, storage tanks, interactions, heat sinks, switches, transactions and subsystems (e.g., producers, mineralizers and consumers) (Fig. 111. 1). Paths, represented by arrows,showthedirectionofenergyflowthroughanecosystem. Sources,representedbyopen circles, are energy inputs from outside the ecosystem, such as sunlight. There are two, basic, trophic processes: production and consumption. Producers are represented with a bullet. Consumers are represented with a hexagon. These two process symbols are shorthand notation for the that occur within the symbol, e.g., storage, interactions and processes energy flow. Storage tanks, represented by shields, are temporary depositories for energy. Living things can be considered storage tanks, because ofthe tied in living tissue. energy up Interactions,represented byarrowboxes, occurbetweentwoormoretypesofenergyflow. For example,temperature hasaninteractionwiththebiologicalprocessofrespiration. Energysinks, represented by shrinking parallel lines are the energy losses in an ecosystem. Uneaten food that becomes buried, and therefore inaccessible, is a common energy sink. Switches, illustrated by concave boxes,reflectsomemanagement controlontheflowofenergyfromoutsidethe ecosystem. Transactions, represented by a rhombus, occur when there is feedback from an energy path to an energy source. Subsystems are smaller units within the main ecosystem. For example,thegeneralcategoryof“producers” canbebroken downintospecifictypesof producers, such as plankton and seagrass. There are different ways in which an ecosystem may be represented by using an energy circuit diagram. One approach is to model different trophic levels, such as the producer subsystem, Fig. 111.1.Thesymbolsusedforpartsofanecosystem. consumer subsystem, or mineralizer subsystem. Ecosystems can also be portrayed as different habitat subsystems, such as beaches, intertidal and shallow subtidal flats, deeper areas, and deltas. Biotic habitats include salt marshes, oyster reefs, mussel beds or seagrass beds. Inthis report, we piesent models using both approaches to cover both general and specific information. Bay System Like all ecosystems, the CCBNEP bay ecosystem consists ofthe system itselfand its input sources and output targets (Fig. HI.2A). The bay area ecosystem receives energy from external sources.Theprimarysourceofenergyforthebayisthesun. Energyalsocomesfromrivers, groundwater and terrestrial runoff, which provide nutrients for primary producers and detritus for consumers and mineralizers. Energy is exchanged between the coastal ocean and bay as current, wind and tide movements ofnutrients and detritus, and the migration ofsome consumers, such as fish and shrimp. Energy leaves the bay ecosystem through a heat sink, returns to land through human fishing and hunting or else is transferred to the coastal ocean (Fig. III.2B). Themainstructureofthebaysystemincludes sixenergysources,sevenstoragetanksandthree subsystems(Fig. 111.3A).Sun,wind,tide,river,runoffandoceanaretheenergysources.The storage tanks are salinity, temperature, carbon dioxide (CO2 ), water (H2O), nutrients, kinetic energy, oxygen and detritus. Three main subsystems (ecological processes) are: producers, consumers, and mineralizers. All processes require input from sources that are modified by storage systems. Sources Irradiance from the sun increases the temperature ofthe whole ecosystem (Fig. 111.3A), which, in turn, affects the physiology ofevery producer, consumer and mineralizer. Sunlight provides the energy for photosynthesis, the biochemical pathway used by almost all producers to increase theirbiomass, andindirectlygainenergy(Parsonsetal. 1984). Heat from the sun also creates wind. Warm air is less dense and tends to rise upward in the atmosphere. Cool air is more dense and sinks through the atmosphere. The movements ofthese parcelsofairareknown asaircurrents,oronamorelocalscale,wind. Inthebay Fig. 111.2A.Thelandscapeand seascapeoftheCorpusChristiBayNationalEstuaryProgram studyareaintermsofinputandoutputfromtheBayAreaSystem. 1.Energyforprimary producers from sun. 2. Energy input from land through rivers, groundwater and runoff, which providenutrientsforprimaryproducers,organicmatterforconsumers andmineralizers, and output to people through human fishing or hunting. 3. Energy input and output through coupling with the coastal ocean including currents, wind and tide carrying out nutrients and organic matter, and migration ofmacrofauna. 4. Energy sink in the form ofheat to produce C0 and 2 H O. Fig. 111.28. SummaryoftheCorpus ChristiBayNationalEstuaryProgram(CCBNEP)BayArea System. The Bay Area includes rivers, marshes, primary and secondary bays, lagoons and the coastal ocean. The natural in the Bay Area are processes driven by the sun and exchange with the landand ocean.Humans usetheBayAreaforavarietyofuses,includingmanyshownhere. However, manyoftheseactivitiesalso havethepotentialtonegativelyimpacttheBayArea. and from the air into water. Energy ecosystem, wind transfers kinetic energy oxygen pressure leavesthebaysystemthroughsedimentationandsubsidenceoforganicmatteraswell. Tides originatefromthegravitationalforcesofthesunandmoon. Dependinguponmanyfactors, including latitude, weather, and local geography, different places on the planet have different tidalzones(rangingfromafewcentimeterstotensofmeters) and adifferentnumberoftidesin aday(usually 1or2). Tidesbehavemuchlikelarge,slowwaves;theycantransferkinetic and transport nutrients and detritus between the ocean energy and bay systems. Riversareindirectlyaproductofthesunandgravity. Riverwateristheproductofprecipitation Precipitationresults fromatmosphericwatervapor thatisitself theproductofevaporation from the ocean. Rivers provide kinetic and transport nutrients and detritus from land to the energy bay ecosystem. Runoff is fresh water that originates from sources other than rivers. Typically, this is drainage from the land directly into the bay. However, we also include non-river such as return sources, flow from a city sewer system, and direct rainfall onto the bay surface. Runoff can transport nutrients and detritus from land to the bay ecosystem. Finally, the ocean provides energy for the bay ecosystem. Upwelling currents can bring up nutrients and detritus from the sea bottom. Water currents, waves, and tides act to transfer between the ocean into the bay energy and bay. Migrating consumers can also transport energy ecosystem. Typically,theneteffectofmigratingconsumersistotransportenergy and nutrients outofthe estuary. Storage Thebayecosystemhassevenmainstoragetanks(Fig.111.3A). Storagetanksinanecosystem are nonliving things that stand for an energy storage level, or can energy be transferred into an storage level in an ecosystem. The storage tank is passively accumulated or lost due to the effects ofenergy sources or a living component’s processes in the system. Inside a living component, the biomass can be defined as a storage tank accumulated or lost due to biological processes (see the following section: Representative Producer). Fig. 111.3A. The Bay Area System Components. The diagram represents the energy flow and transformation inside the Bay Area System. Fig. 111.38. Summary ofthe CCBNEP Bay Area System components. The arrows illustrate a simplifiedflowofenergywithintheBayArea.Producers,such asthisdiatom,requiresunlight and nutrients to grow. Consumers, such as this fish, survive by eating producers. Dead plants and consumers and their waste products sink to the bottom, where they are decomposed by other consumersandbacteria. Decompositionalsoresultsinrecyclingofnutrientsthatcanbere-used by producers. New nutrients can enter the bay from rivers and terrestrial runoff. Because a bay is directly connected to the ocean, everything from nutrients to consumers can be exchanged between thetwobodiesofwater. Temperaturestorageisaproductofsolarradiation. Heatislostthroughseawaterevaporationto air or conduction to the deep sediment layer. Water loss by evaporation has a cooling effect on anymoistsurface(585calorieslostg'1ofwaterevaporatedat20°C)(Prosser, 1991). Temperature increase may increase physiological processes, such as photosynthesis, energy intake, respiration, excretion, natural death, migration and reproduction. The relationship between temperature and physiology is usually represented by the term QQis the factor by lO. lO which reaction velocity is increased by a rise of 10 °C: k “r~ Where k and k 2 are velocity constants corresponding to temperatures t and t 2. lx Salinityisdetermined bytheinfluencesoffreshwaterfromrivers andrunoff(0ppt)andthe influence ofseawater from the ocean (36 ppt). Salinity is also determined by evaporation. Salinity in bays is usually between about 5 and 25 ppt, but can become much lower in times of flooding, or much higher, saltier than the in periods oflow rainfall. Salinity even areas or ocean, limits some physiological processes, such as photosynthesis, natural death, respiration, reproduction, excretion, and migration. Carbondioxide(CO)andwater(HO)areneededforphotosynthesis chemosynthesis,and or 22 are produced by respiration. Photosynthesis and chemosynthesis are biological processes that convertinorganiccarbonintoorganiccarbon(C) andproduceoxygen(02).Respiration,onthe other hand, consumes oxygen, converts organic carbon into inorganic carbon, and releases energy for cellular functions. By definition, consumers can only respire, but producers both respire and synthesize. Autotrophic production occurs by photosynthesis or chemosynthesis. Nutrients, such as, nitrogen (N) and phosphorous (P), are also needed by producers. Ammonia (NH+),nitrates(N=),andnitrites(NO)aresourcesofN,whichisneededtoconstructsome 4 032 organic molecules, particularly proteins and fatty acids. Phosphorus, which comes from phosphates (PO), is important for cell membranes making nucleic acids and in molecules that 4 transfer energy through the tissues, such as adenosine triphosphate (ATP). Mineralizers and consumers break down tissue and release nutrients back into the ecosystem, a process called recycling. Kinetic energy originates from wind, river, tide, runoff and ocean currents. Kinetic energy refers tothemovementofwaterinthebay. Thehigherthekinetic ofwater,themoreoxygen energy and nutrients it is able to contain. 0 is necessary for respiration. 0 is used to help break down organic carbon bonds to release the 22 for use by tissues. The oxygen-carbon molecules that are released as a by-product of energy respirationareintheformofC0 Consumerscannotgeneratetheirown0 andmustrelyon . 22, the 0generated from producers. Producers generate 0through photosynthesis by removing22 the carbon from C0 The carbon is used to form organic molecules such as carbohydrates, 2 proteinsandlipids,whiletheremaining0 isreleased. Theamountof0 inthewateris 22 0 affected by physical factors, such as, wind, tide, rivers, and kinetic energy. 2 solubility in water is also affected by salinity, temperature and pressure. Detritus is nonliving, decomposing organic material, including fresh leaves sloughed from seagrassormarshgrass,fecalmatterfromanimals,anddeadanimalandplanttissue. Particulate material from the water column, such as dead phytoplankton or zooplankton, also forms detritus. Detritus is classified as autochthonous, detritus that originates from within the ecosystem, or allochthonous, detritusthatistransportedintotheecosystem. Becauseofgravity,detritus usually sinks to the sediment, where it is either decomposed or becomes buried. Detritus is decomposed by bacteria that convert the detritus into nutrients and energy through a process called mineralization. In addition to bacteria, other animals, including meiofauna and macrofauna invertebrates, affect the amount of detritus in the sediment. For example, can an abundance ofnematodes can increase the decomposition ofsalt marsh leaves (Alkemade et al., 1993). Because oftheir small size, nematode defecation cannot significantly affect detritus levels (Li, et al., in press). However, defecation from larger animals have greater affects on the may amount of detritus in an ecosystem. Subsystems There are three main trophic subsystems withinthe bay ecosystem: producers, consumers and mineralizers (Fig.III.3A). Producers can generate biomass and energy from sunlight and atmospheric carbon, and are commonly known as plants or autotrophs. Consumers, including animalsandmostbacteria,areincapableofgeneratingtheirownenergy biomass,andmusteat or or producers other consumers; these organisms are called heterotrophs. Consumers also require 0 for respiration. Mineralizers are a specific kind of consumer. Mineralizers include microscopic bacteria that respire by decomposing detritus. They liberate C0 from the organic 2 2 matterintheprocess,hencethenamemineralizer. Therearetwomaincategoriesof mineralizers. Aerobes use 0 as terminal electron acceptors that are essential to the oxidation of 2 organic matter as an energy source. Anaerobes use compounds other than 0 such as, sulfate 2, (sod. Summary Life in the bay is dependent upon the sun (Fig. III.3B). Producers, such as, phytoplankton, require sunlight, carbon dioxide and nutrients to grow and produce energy. Consumers, such as, fish, receive the carbon by eating producers, and the oxygen they need from water. Non-living organicmatterisproducedfromproducers andconsumers,and“rainsdown”uponthebottomof the bay. In the sediment, bacteria use oxygen to break down the organic matterto receive Bacteria also release nutrients energy. Like consumers, these bacteria produce carbon dioxide. back into the water. and The three living subsystems in the bay, producers, consumers mineralizers,aredependentuponavarietyofnon-livingfactorsthat operateonthebay. For example, new nutrients enter the bay from rivers or as runoff from cities, farms, and other adjacent landscapes. Another factor that affects the bay ecosystem is the ocean. Energy, nutrients, oxygen and living organisms are all exchanged between the bay and ocean. The rate ofexchange is determined by the number and size ofpasses and by the intensity ofthe wind and tide. Producers Producers in the bay ecosystem can be classified as photoautotrophs (salt marsh, mangrove, or seagrass, phytoplankton, benthic macroalgae and microbenthos) chemoautotrophs (bacteria) (Fig. III.4A). Photoautotrophs receive energy from sunlight, and include familiar plants such as, saltmarshcordgrass(Spartinaalterniflora),mangroves(Avicenniagerminans), seagrasses (Halodule wrightii, Halophila englemannii and Thalassia testudinum ), phytoplankton, benthic macroalgae, and microphytobenthos. Chemoautotrophs are groups ofbacteria, such as, sulfur, hydrogen, or methane bacteria. These organisms can satisfy their primary energy requirement by using simple inorganic compounds. In the bay, chemoautotrophs live primarily in the sediment, especially at the oxic-anoxic interface. All benthic autotrophs are food sources for deposit feeding benthos. consumers. Fig. 111.4A.TheProducer Subsystem. Theenergyflowsfromproducersto Fig. lIL4B. There are six different types ofproducers in the CCBNEP Bay Area. Phytoplankton are microscopic, one-celled algae that live in the water. Marsh live at the margin grasses betweentheshoreandthebay. Sometypesofbacteriaarecapableofphotosynthesis. Thereare also one celled algae that grow sediment called microalgae or microphytobenthos. Larger on producers include seagrasses and macroalgae, also known as “seaweed.” Consumers eat most and marsh and marsh types ofproducers, except for seagrasses grasses. However, seagrasses grassesareimportantsourcesoforganicmatterand ashabitatsformanyanimalspecies. Saltmarshesdevelopadjacenttothewatermargin. Theyarebedsofintertidal,rooted vegetation, particularly grasses, that are alternately inundated and drained by tides. Because they have adapted to a life ofsun, salt, and wind, these plants are tough, difficult to digest, and generally are poor food sources for consumers. However, salt marsh plants can be ar? important input of detritus sources to the bay ecosystem. Mangroves are typically adapted to loose, wet soils, a dominantly saline habitat, and periodic, submerged tides (Davis, 1940). Because they are alsodifficulttodigest,generallyonlythewoodypartsofmangroves areconsumedbyafew boring isopods such the root-boring Sphaeroma tenehrans the wood-boring Limnoria as or lignoria. The boring isopods increase the carbon flow from mangrove to decomposing materials. Mangrove detritus can be important to the ecosystem in situtations where these isopods are dominant plant in the CCBNEP area but are found in isolated are not a found. Mangroves areas, particularly after several ofmild winters. years Seagrasses exist in habitats similar to salt marshes, but exist entirely underwater, growing in shallow estuarine sediments. The contribution ofseagrass production to estuarine carbon budgets can range from negligible to almost 50% ofthe total production within an estuary (Day contribute carbon to the detritus pool, and not are et al. 1989). Like salt marsh plants, seagrasses usually consumed by herbivores except for a few exceptions, such as diving ducks. Seagrasses areextremelyimportanthabitatsforavarietyofinvertebratesand fish. Phytoplankton are tiny, single-celled algae, such as flagellates, dinoflagellates, diatoms and nannoplankton (summarized by Parsons et al., 1984). Plankton have limited movement capabilities,andareusuallycarriedaboutwiththemotionofthewater. Phytoplanktonarevery productive,andcansupportahighabundance anddiversityoftheirmainconsumer,zooplankton (see next section, “Consumer”). Small phytoplankton are the dominant producers in the open ocean. Benthic macroalgae, such as brown algae and other seaweed, grow in sea water in the shallow water or subtidal area. Because they have no root system, many macroalgae need a hard substrate for attatchment. For this reason, macroalgae are not a dominant producer in the CCBENP study area. Unlike sea grasses and mangroves, macroalgae are easily digestible, and are eaten by some herbivorous benthos or fish. Microphytobenthos include single-celled algae, particularly diatoms, that live on the sediment surface. Microphytobenthos are very productive in shallow water, and are food sources for herbivorous and deposit-feeding benthos, such as some gastropods, most harpacticoid copepods, and many polychaetes and free-living nematodes. Summary There are five main components ofthe producer subsystem (Fig. III.4B). Marsh grasses grow on theedgeofthebay. Theyarenotdirectlyeaten,butmaycontributesubstantiallytothepoolof decomposing matter. Seagrasses are a dominant feature in shallow water in the bay. Like marsh tough, fibrous tissue. grasses, seagrasses are very productive but difficult to eat, due to Macroalgae,includingthelargebrown,red andgreen“seaweeds,” areeatenbybenthic herbivores, such as grass shrimp and amphipods. Microalgae, particularly small diatoms, are very productive, and live on the sediment surface. Microalgae are eaten by grazing herbivores, such as shrimp, but are also eaten by deposit feeding animals, such as polychaete worms and brittle stars. The same deposit feeders also eat chemoautotrophs, small, sediment-dwelling bacteria. In the water column are other small plants, the phytoplankton. These organisms are eaten primarily by zooplankton, small animals that include tiny crustaceans and the larvae of larger shrimp, crabs and fish. All producers are important contributors to the pool of decomposing matter. Representative Producer Thebiomassofasingleproducerisbalancedbyseveralphysiologicalprocesses(Fig. 111.5A). Producers increaseinbiomass, eitherbygrowthorreproduction,i.e.,synthesisofnewbiomass. Biomass is lost from the producer compartment through respiration, natural death and consumption by herbivores. Synthesis Both photoautotrophs and chemoautotrophs synthesize inorganic carbon (C), C0 into organic 2, carbon, n(CH2O), and produce 0 as a by-product through the reaction; 2 nC0 +2nH 0=*n{CH0)+rO+nH0 2 2 222 Photosynthesisincludes:(1)productionofATPandmolecular0 fromadenosinediphosphate 2 (ADP) through the cytochrome system, and reduction ofnicotinamide adenine dinucleotide (NAD); and (2) fixation ofC0 using ATP and production ofNAD. The difference between 2 ofthe reduce NAD. Photosynthesis uses light energy for this purpose; whereas, chemosynthesis photosynthesis and chemosynthesis depends upon the source energy to produce ATP and uses chemical reducing power produced through dehydrogenization (Gundersen, 1968). Dehydrogenization occurs through the reaction: nAH +nH o=*nA O +4n[H*+e ] 22 Where AH2 represents simple inorganic compounds, such as NH + methane (CH), or N0 or 4, 42, elements, such as ferrous iron, hydrogen gas, or water-insoluble amorphous sulfur. AO is the oxidizedend-product. Thereducingpower{[H++e'J)isutilizedforproducingATPand reducing NAD. - The effectsoflightintensity onphotosynthesis canbe representedbythelightlimitation(Light L) equation; - Light-L= exp(l +r) lopt lopt1opt 1opt Where I is mean light in the water column, calculated from; m C , _/(l-e 2) m Cz WhereI isaveragevisiblelightatthesurfacethatmaybetakendirectlyfromfield s measurementsor obtained bymultiplying an estimateoftotalincidentlight,by0.45toeliminate long-wave radiation. Cis the diffuse attenuation coefficient (or extinction coefficient), per meter, zisthicknessofthewaterlayer.Itislightintensityatwhichphytoplanktongrowthis maximum, ris a correction factor allowing for a negative change in biomass at very low light levels(I<0.01l)(Carradaetal.1983). m op Temperature effects on photosynthesis (Aruga, 1965) can be represented by the temperature limitation {Temperature-L) equation (Li, et al., in press): ( T-MAT) 10 Temperature-L=Qlo whereQlO comesfromthetemperatureeffectsonphysiology(seep.18,above). Tis which the lives have their maximal temperature, andMATis the maximalactiontemperature, at physiological action. Inadditiontolightandtemperature,productioninproducerscanbelimitedbyconcentrations of nitrogen, phosphorus, and silicate in the water and sediment. The uptake of carbon, nitrogen, silicate and phosphorus by weight, generally occurs according to the ratio of 106:16:15:1, respectively (Redfield, 1934;Parsons et al. 1961). A different nutrient maybe limiting at a differenttimeoftheyear,such as,isthe caseforphosphorousinthespring andnitrogeninthe summer for Delaware Bay (Pennock and Sharp, 1994). The limitation ofproduction by a nutrient (Nutrient-L) can be represented by the equation: [NH,*NO] poj ­ Ar,,...., 3s Nutrient-L=Mwimum( ) +NO, , PKN+[NH] PKP+[POJ PKSi+[Si(OH)J 43 where PKN, PKP and PKSi represent the half maximum production rates for concentrations of nitrogen(NH+N0),phosphorus(PO4)andsilicate(Si(OH)4),respectively(Carradaetal. 43 1983). The values ofPKN, PKP and PKSi are different for different producers since the required ratio for nutrients are different, e.g., diatoms and flagellates have different Si;N requirement ratios (Sommer, 1994). Synthesis by a producer can be estimated by the formula; Production-B-R '(Light-L}(Temperature -L) •(Nutrient-L) M whereBisbiomass,RMisthemaximalsynthesisrate. Thisequationincludesfeedbackfrom biomass to photosynthesis, because biomass is involved in producing more biomass (Fig. III.5A). Nutrient limitation also come from competition between producers. For instance, may the uptake ofinorganic carbon by seagrass can be reduced significantly by microalgal growth on leaf surfaces (Sand-Jensen, 1977). Fig. 111.5A. Representative producer subsystem. The Energy flows and controlling processes inside a single producer subsystem. The input is through synthesis by either photoautotrophs or chemoautotrophs, and the output includes predation, respiration and natural death. Fig. 111.58. Summary ofa representative producer, a red algae. The alga gains energy and biomass from light and nutrients and loses biomass through natural death or by being eaten by consumers. The algae are also affected by the temperature and salinity ofthe surrounding water. Respiration Producers gain biomass by synthesizing new organic matter using energy and simple carbon molecules. Stored energy from photosynthesis is released by respiration. Respiration involves breaking down carbon bonds (nCH,O) to produce energy. Respiration requires 0 and produces 2, C0 andHO: 22 nCH 0+rO ~^nC0 +nHp -henergy 2 22 Therateoftherespirationprocessisincreased astemperatureincreases toapoint,because up the rate at which catalytic enzymes work is increased. Respiration can also be affected by environmental conditions, such as an unfavorable salinity or the presence oftoxic chemicals. Stressed organisms must respire faster to keep cells functioning properly. Reproduction In addition to increasing their own biomass, producers can also produce offspring. Like all organisms, producers reproduce through the process ofcell division. Reproductive and early life stages ofmost organisms are often very sensitive periods. Therefore, reproduction may be greatly affected by stressful environmental conditions, such as the presence oftoxins or unsuitable temperature or salinity. Predation / Grazing Producers lose biomass to consumers. When a consumer eats a producer, it is usually called herbivory, grazing, or foraging. Zooplankton graze on phytoplankton. Herbivores graze on microphytobenthos and benthic macroalgae. Deposit-feeding benthos consume microphytobenthos and sediment bacteria by incidental ingestion of sediment or by the selection ofspecificparticles. Thegrazingactionofconsumersisaffectedbyenvironmentalconditions, such as temperature and kinetic energy (see following section Consumers). Natural death Whereas smaller producers, such as phytoplankton, usually die only through grazing, larger organisms may die “naturally”. Seagrass blades become senescent and fall offduring the late summer and early fall. Environmental changes, such as salinity change or high turbidity may also kill or stress producers. Summary Producers, such as macroalgae, are dependent upon sunlight for photosynthesis (Fig. III.5B). Photosynthesis is the process by which a producer may create biomass from sunlight, carbon dioxide and nutrients, releasing oxygen inthe process. To utilize the energy that is stored during photosynthesis, producers use oxygen and produce carbon dioxide in the process called respiration. Someofthebiomassproducedbyanorganismmaybeusedtorepairdamageor increase the plant’s own size. Additional biomass and energy are used to reproduce. Producers lose biomass either through respiration, natural death or by being partially or totally by an eaten herbivore. Manyofthebiochemicalreactionsthatoccurinaproducer’scellsareaffectedbythe temperature and salinity ofthe surrounding water. Consumers Theconsumer subsystemoftheCCBNEP areaincludeszooplankton,herbivorous benthos, deposit-feedingbenthosandpredators(Fig.HI.6A). inthebaysystemhave Different consumers different energy inputs, that is, they live off different resources. Thezooplanktoncommunityiscomposedoftinyanimalsthatliveinthewatercolumn. There are two typesofzooplankton; holoplanktonspend theirentirelivesinthewater column, meroplanktonspendonlytheirlarvalformsinthewatercolumn. Examplesofholoplankton includecalanoidcopepodsandsmalljellyfish. Examplesofmeroplanktonincludelarvalshrimp, crabs, worms or fish. Almost all zooplankton derive their energy from grazing on phytoplankton or other zooplankton. Herbivorous benthos include those animals that graze on phytoplankton, macroalgae, epiphytic algae, or microphytobenthos. Some herbivorous benthos are filter feeders, such as oysters, whereas others the sediment surface, as do Animals such as graze some mudflat-dwelling snails. amphipods and other rock-dwelling snails graze on macroalgae, while small harpacticoid copepods and nematodes graze on benthic microalgae. Most herbivores are invertebrates that live in association with the bottom, either epifaunally or infaunally, and are either motile or sessile. There are, however, also some herbivorous fishes. Fig. 111.6A. The Consumer Subsystem. The energy flows from food sources to consumers. Fig. 111.68. There are several different kinds ofconsumers in the CCBNEP Bay Area. Zooplankton, smallcrustaceansandthelarvaeoflargeranimals,eatmainlyphytoplankton. Deposit feeders, such as polychaete worms and some clams, eat decomposing matter (also called detritus). Benthic herbivores, such as shrimp and amphipods, eat a variety ofplants. Secondary consumers, such as many fish, are predators that eat other consumers. Tertiary consumers, such as large fish, humans and birds, eat secondary consumers. Deposit-feeding benthos, such as most polychaete worms, include those animals that derive their food sources from organic matter in sediment. Organic matterthat is processed by these animals can include detrital material, bacteria, or microbenthos, such as ciliates and flagellates. Some deposit feeders all the sediment they encounter and arc called “non selective deposit process feeders”. Others seek out organic matter specifically, and are called “selective deposit feeders.” Atthetopofthefoodchainarepredators. Predators,such ascrabs,feedonbenthicorganisms, while some fish, such as, red drum and black drum, feed on crabs. Some fish prey on zooplankton. There are also predators that eat other predators, such as, the largest fish, as well as birds and humans* Summary Consumers areanimalsthatcannotsynthesizeinorganicmatterintoorganicmatter(Fig.III.6B). Those consumers that eat plants, including algae and microphytes, are called herbivores, and includegrassshrimp. Thoseconsumersthatfeedonbacteriaororganicmatterinthesediment arecalleddepositfeeders,andincludemanytypesofpolychaeteworms. Smallconsumersthat live in the water column and feed on phytoplankton are called zooplankton. There are also consumersthateatotherconsumers. Asmallfishthatfeedsonzooplanktonmayitselfbecome to larger fish, such as seatrout or red drum. These large fish may, in turn, be eaten by a prey terrestrialpredator,such asahumanorbirdof prey. Representative Consumer Biomass that is stored by a consumer is balanced by several physiological processes (Fig. III.7A). Processes that contribute to increases in biomass storage include assimilation and reproduction. The thatcontributetoalossofbiomassincluderespiration,excretion, processes predation, and natural death. The loss ofbiomass also includes the thermodynamic heat loss due to biological processes like searching for food, ingesting food, assimilation, respiration, excretion and escaping from predators. Some consumers gain or lose biomass from their populations duetomigrationofindividuals between thebay and ocean. Fig. 111.7A. Representative Consumer Subsystem. The energy flows and controlling processes inside a single consumer system. The food sources and consumers are different for different consumers asshowninFig. 111.6A.Migration occursonlyforsomeconsumergroups. Fig. 111.78. Summary ofa representative consumer, the menhaden. The fish gain energy by eating prey, in this case, calanoid copepods. This energy can be used for growth or for reproduction. The menhaden lose energy by natural death or by being eaten by a predator, such as a redfish. Menhaden can move from the bay to the ocean or back by migration. Like most organisms, these fish are affected by the temperature and salinity ofthe surrounding water. Furthermore, because they cannotphotosynthesize, all consumers oxygen. need Intake In order to gain energy, a consumer must encounter and assimilate The chance that a prey. consumerwillmeetafoodunitperunittimeandtheingestionspeedofthe consumerr.rckey factors that affect intake. Some consumers may actively search for food. For these consumers, such as most fish, movementand ingestion speeds are more important factors than food concentration. For sessile animals that do not actively search for food items, such as oysters, food concentration and kinetic in the water will be more important. The intake energy process is, therefore, not only controlled by the food concentration and consumer density, but also by the current speed and the consumer’s own physiology. Water temperature may increase a consumer’sphysiologicalactions, such asrateofingestionand swimmingspeed,therefore increasingthechancesofsuccessfullyassimilatingfood. Theintakerate(IK)canbeexpressed by the Michaelis-Menten equation (Carrada et al. 1983): MRFC j£_ ~ FC+HMRFC WhereMRisthemaximalintakerate unittime,whichdependsuponingestionspeedand per stomach capacity, the FC is the food concentration, which be a function ofcurrent speed for may passivelyfeedingconsumers, andHMRFCistheone-halfmaximumfoodconcentration thata consumer can process. The total intake is also dependent on the consumer population level, which is a feedback from the biomass to the intake interaction; Intake =D-IR the biomass ofa consumer whereDisthedensityor dependentontheunitofIR. Assimilation Once food is ingested, it is assimilated into the cells through a series ofbiochemical reactions with digestive enzymes, through which the consumer transforms the energy from a food source into its body (Prosser, 1991). Many consumers only assimilate part ofa food source. The unassimilated part is excreted and becomes detritus. Assimilation rates are controlled by food For quality. Consumers have different requirements, leading to differences in assimilation rates. instance, nematodes feeding on diatoms have higher assimilation rates than those feeding on participate organic matter (POC), because the nutritional quality of diatoms is higher than that ofPOC (Li et al., in press). Many aquatic invertebrates extract organic molecules directly from solution (Allendorf, 1981), without the use of a capturing or ingesting process. For instance, the parasitic animals in rich a environment ofhost tissue do not require special digestive structures. Their body surfaces resembleintestinalepitheliainsurfaceareaandtransportmechanisms(Prosser, 1991). Many free living cnidarians, molluscs, echinoderms, annelids, and arthropods also extract some organic substances directly from solution. The result is that these animals excrete less organic matter, which means that their assimilation rates are higher than other animals. Respiration a consumer The respiration rate ofis dependent upon its physiological activity. Fast swimming These animals would have much higher respiration rates per unit time than slowly moving animals, like many snails, or nonmotile animals, such as sponges. Respiration per unit time is normally described in apowerrelationtoitsbodysize(Zeuthen, 1970;Banse, 1982): fish, including many predators, may require high quality foods, rather than POC. Respiration-aV b h’ wheretherespirationrateisreportedinunitsoftheconsumptionofoxygen(nl0 1ind.•'),V\s 2 body volume (nl ind.’1), proportional to the mean individual biomass, ais a parameter indicating themetabolicintensity(SchiemerandDuncan 1974)orreflectingtheinternalmetabolismofthe organism (Zeuthen, 1970) due to different feeding habits, b is a parameter that approximates the body volume to body weight. It is different for different species, for example, differences among tropical, temperate, and boreal species (Ikeda, 1970). Usually, b is less than one. For example, a meiobenthicnematodewithadryweightof0.3jigandarespirationrateof0.6nl0 h’1ind.’1has 2 1 aweight-specificrespirationof2nl0 h’pg’1whilebisabout0.75(Heipetal.,1985).Itis 2 clear that the smallest animals have the highest metabolic rate (since the b is less than one and therespirationrateR/V=aVb1Thetransformationofoxygenconsumptionto ' ). energy usage may be estimated using the conversion factors: 1 ml 0 2 20.2 J (Schiemer, 1982) and 1 mg 48.26 = C= J (Sikora et al., 1977). The respiration rate ofan animal is highly variable due to variations in temperature (Comida, 1968), food availability (Ivlev, 1945), and biological activity (Heyraud, 1979; Vidal, 1980). Excretion excess Excretion maintains the body’s internal constancy (homeostasis) by the elimination of Such substances substances (or their metabolic byproducts) that enter the body. may be water, salts, andby-productsofcellular activity, especially nitrogenouswastes(Ruppert&Barnes, 1993). This is because animals cannot store excess amino acids, unlike carbohydrates and lipids, which can be stored as glycogen and triglycerides (Krebs, 1972). For instance, nematodes have high C:N ratios (8:1 to 12:1) in comparison with their food, such as bacteria, (3:1 to 4:1) and thus must release N as a waste product (Anderson et al. 1983). Nitrogen excretion is dependent on body size and costs energy (Wright and Newall, 1980). The representation by a mathematical formula can be similar to the one for respiration. A nematode of 1 pg wet wt. would excrete 1.92pmolNh' 1g'1;inmammals,1gofnitrogenexcretedcorrespondsto5.94102respired. Mammals and other large animals, such as echinoderms, molluscs, and some crustaceans, have excretory systems, such as metanephridial organs that help to maintain a body less salty than the surrounding sea water. Animals can also excrete salt through a metanephridial system that dependsonthesalinityoftheenvironment,whichinahighsalineenvironment canincreasethe speed ofnitrogen excretion. Reproduction Reproduction for a consumer is similar to that for a producer. Reproduction is affected by the physical factors, such as temperature and salinity. Some consumers, like fish, produce a large numberofeggs,buthavehigheggmortalityorpredationlossrates. Otherconsumers,such as dolphins and other mammals, are viviparus. Although they produce very few young, those that are produced have a lower mortality, because there is a high investment ofparental care. Having youngthatdevelopinternallyisnotlimitedtomammals. Forinstance, eggsofthenematode, Anoplostoma viviparum, characteristically contain developing larvae (Platt and Warwick, 1983). Predation Some consumers are eaten by other consumers. For example, zooplankton and herbivorous benthos (e.g., copepods) are consumed by fish; deposit feeding meiobenthos (e.g., nematodes) are eaten by deposit-feeding macrobenthos (e.g., polychaetes); small fish are eaten by large fish, and large fish are eaten by ducks, humans and other mammals. Many consumers are both predatorsand prey. Apinfishmayeatsmallshrimp,butisitselfpreyeduponbyreddrum. the chance ofthe interaction between the predator and the prey, and the predator’s ingestion speed and the stomachcapacity. Thechanceoftheinteractionisaffectedbythedensityofbothpredatorand prey,mobilityofpredatorand prey, and thetypeofspatialdistributioninthehabitat,(e.g, a contagiousorrandomdistribution,Elliot, 1971). Alinearrelationship betweentheprey Thepredationrateofapredator orpredationmortalityofpreyis dependent on survival rate and the predator abundance is the well known “Lotka-Volterra Model” (Lotka, 1925). It can be applied to those non-moble or infrequently moving predators, such as filter feeding of plankton by bivalves: J{N^)=\~crP: - Wheref(N„P)isthepreysurvivalrate{predationmortality=\ survivalrate)attimet,aisthe predationrateofthepredator,Ntistheprey’sabundance atthetimetandP,isthepredator’s abundance at the time t. A non-linear relation between the survival rate prey and the predator’s abundance, e.g., “Nicholson-Bailey Model” (Nicholson and Bailey, 1935), can be used lor moving predators who actively search for food sources (i.e., fish feeding on grass shrimp): ~°'P AN,J>)=e ' For prey that aggregate, such as nematodes, Li et al. (in press) suggested using an exponential relationship between prey abundance to their predation mortality: _k_ N N=P -P-e ' r rt WhereNistheprey’spredationmortalityduetoallP andPistheprey’spredationmortality r hr duetoeachsinglepredatorand£isaparameter. Theexponentialterm,e^0,istheeffectthatis due to the aggregate distribution ofwhich exponentially decreases predatory mortality prey, when its abundance is low. In the field, the relationship between prey and predator is not always this simple. Many predators share more than one prey population. Most prey populations have more than one predator (Kerfoot, 1987). Obviously, predation is not quite as simple as it is represented by these equations. Natural death In this context, “natural death” refers to causes of death other than predmom. In general, the life-spanofanimalscorrespondstobodysize. Therateofrging, i e .derthperunittime,fora population is dependent on The representation by a the total biomass. nathemaiical formula is similar Some small animals, such as most meiofama, have a short life- to that for respiration. spanofafewdaystoafewmonths. Largeranimals,such asmostmacr:faumaandfish,have longer life-spans ofa few months to a few years. An unfavorable environment, such as unsuitable temperature or salinity may prevent an animal from reaching is maximum possible life-span. Migration Migration between the bays and the ocean occurs in many large, swimming animals, such as red AninrJs drum (.Sciaenops ocellatus) and blue crabs (Callinectes sapidus). may migrate to reproduce, find better food sources, or escape unfavorable environment!! conditions. Therefore, environmental parameters such as temperature, salinity and the behavioral ecology ofthe species all affect migration. For example, some species require specific emTommems for reproduction and nurseries for developing larvae, e.g., the migration ofrad drumlarvae or shrimp larvae back into the bays. can Summary Consumers must ingest prey items in order to increase their own biomas amd reproduce (Fig. m.78).Aconsumermustfirstassimilate apreyitem,andthenrespiretogainenergyfromthe ingested tissue. Both assimilation and respiration are dependent on the temperature and salinity ofthe environment. An increase in An increase in temperature speeds up enzymatic activity. salinitywilldivert reservesastheanimalisforcedtoadjustwaterconcentrationsto energy compensate for a change in salt concentrations. Consumers can lose bkmass and energy when they excrete organic material, die, or are eaten by larger consumers. Bitmaps can be transferred from one ecosystem to another ifthe consumers migrate from bay to ocsan or back. Mineralizers The process ofmineralization is important in transforming organic matterin an ecosystem, becausemineralizers decompose andreduce the organicmatterbackinto nutrients. Mineralizers aremicroscopicbacteriaandfungithatgaintheirenergyfromdetritus(Fig. 111.8A). The degradationoforganic matteris afunctionoftherateofexoenzymatic hydrolysis whichis proportionaltothebiomassofbacteria(BillenandLancelot, 1988).Mineralizingbacteriacan be classified as aerobes and anaerobes based on how organic matteris reduced (Parsons et al., 1984). Aerobes use oxygen as an electron acceptor to reduce detritus. They reduce 0 to C0 22 and H2O. Anaerobes include nitrate reducers, sulphate reducers and methanogens. Anaerobes use other compounds, such as N0 = and N0 ‘, sulphate (SCV), and C0 as electron acceptors to 322 reduce detritus. The nutrients that are produced by anaerobes include ammonia (NH4+), nitrous oxide (N2O) and nitrogen (N 2), reduced sulfide (H2S and S"), and methane (CH), respectively. 4 Thebreakdown oforganicmatterprovides apathwayforburied energy toberecycled intothe bay ecosystem. The compounds that can be used by respiring organisms form a vertical sequence in their main activity within sediments. The respiratory compounds are electron acceptors that carry the detrital Thedistributionofthesecompoundsfollowsthefollowingsequencewith energy. respect to depth in sediments: oxygen, nitrate, sulphate, and carbon dioxide. The distribution is determinedbyacombinationoffactors,such as;differencesinrequirementsforspecificredox levels, differences in energy yield ofthe respiration types, competition for electron donors, and differences in the concentration and distribution patterns ofthe electron acceptors (Jorgensen, 1989). Theenergyyieldfromrespirationofthissequenceofcompoundsdecreasesfromoxygen tonitratetosulphatetocarbondioxide astheelectronsacceptorsbecomelessoxidizing. Concordant with this decrease in the organisms become increasingly restricted in the energy, range ofsubstrates that they can utilize (Jorgensen, 1980). The aerobes and denitrifiers energy are very versatile with respect or organic energy sources, but the sulphate reducers and methanogens aredependent onsubstratesthataretheproductsoffermentationprocessesinthe reducing sediments (Jorgensen, 1980). Aerobic respiration Aerobes require oxygen and undergo the familiar process ofaerobic respiration. The respiration ofsubstrates, e.g., carbohydrates is represented by the formula: C 6H 0 +60 6C0 +6H2O 126 2 2 Aerobic respiration requires oxygen and is only possible in oxic waters and sediments. Typically this can occur at deeper depths in sandy than muddy sediments. However, it is restricted to the top few mm in mud and top few cm in sand. The change in oxidation level using oxygen as an electron acceptor is -4. Anaerobic respiration Anaerobic respiration occurs in anoxic environments and is also called fermentation. Anaerobes require compounds other than oxygen as electron acceptors to decompose organic matter. Therefore, energy flow is decoupled from carbon flowin anaerobic environments. Energy flow be traced through the nitrogen and sulphur cycles in anaerobic sediments. can The changing chemistry ofsediments is reflected in changes in “redox potential” and pH (Malcolm and Stanley, 1982). The redox potential (Eh) generally decreases (i.e., becomes more negative) in sediments as organic matteris destroyed. Eh measurementsgenerally indicate the extentoforganicmatterdecompositioninanaerobic sediments. Thereareprimarilythree respiratory processes, denitrification, sulfate reduction, and methanogenesis. Denitrification is the respiration ofsubstrates, e.g., carbohydrates, using nitrate in anoxic environments. Typically this can occur below the top few cm of sediment. The change in oxidation level using nitrate as an electron acceptor is -5, and is represented by the formula: 5C6H 0 +24 +24H+~>30C0 +l2 O N 2 +42 H2 126 2 Sulphatereductionistherespirationofsubstrates,e.g.,carbohydrates, usingsulfateinhighly reduced sediments. Sulfide production via this is responsible for the familiar “rotten process eggs” smell common in many organically enriched marine environments, such as salt marshes. Typically sulphate reduction well below the top few cm ofsediment. The change in occurs oxidation level using sulphate as an electron acceptor is -8, and is represented by the formula: CH,20+3so;+6H+-*•6C0 +3HS+6HO 66 22 2 Carbonatereduction,ormethanogenesisisaformofrespirationinthedeepest sediments. Fig. HI. BA. The Mineralizer subsystem. The energy flows through mineralizers via aerobic or anaerobic respiration. Fig. 111.88. Some bacteria live in sediment and decompose organic material. Some ofthese bacteriauseoxygenfortheirdecomposition. However,ifoxygenisdepletedfromthesediment, other compounds can be used for this purpose, including sulfate and nitrate. These bacteria are veryimportanttothebayecosystembecause theyreturnmanyofthesenutrientstothewater, where they can be used by producers. m or so of sediment. The change in oxidation Methanogenesis typically occurs below the top level using carbonate as an electron acceptor is -8, and is represented by the formula: + 2 42 C0+4H2> CK 2HO Summary Mineralizers are bacteriathatconvertdecomposing matterinto energy usingdifferent biochemical respiration pathways (Fig. HL8B). Mineralizers that use oxygen to decompose detritus are called aerobes. When the oxygen is depleted from the sediment, a second group of bacteriatakesover. Thesebacteriareducenitrogen,convertingnitrateandnitritetoammonium. Whennitrogenisdepleted,anothergroupofbacteriareducessulfatetosulfide. Afinalgroup simplydecomposestheorganiccarbonindetritusintomethane. Allofthemineralizersproduce carbon dioxide as a by-product oftheir activities as well certain nutrients, such as ammonium, as that can be recycled back into the bay system. These bacteria are essential to an ecosystem because they process organic matter and regenerate nutrients. Representative Mineralizer Increasing biomass The biomass storage tank ofa mineralizer increases through the decomposition of detritus. Like other organisms, mineralizers can reproduce, creating new bacterial cells. Processes such as natural death, respiration, and predation decrease the biomass storage tank ofmineralizer (Fig. a m.9A). Decomposition Mineralizingbacteriagettheirenergythrough decompositionoforganicmatterinthedetritus pool. The turbulence ofwater or sediment by kinetic energy may accelerate the decomposition process. Thehighdefecationrateofnematodes,orotherinvertebrates,mayalsoacceleratethis process. For example, the maximum mineralization rate can be doubled by adding only ten nematodes per 10 cm2 (Findlay & Tenore 1982). A high temperature can also increase the physiological activity ofbacteria, increasing their uptake action. For example, there can be a significant differencein therateofdegradationofplant detritusin deep-sea sediments between spring and summer (Poremba 1994). Other factors a Factors affecting the respiration rate ofmineralizer are similar to those affecting a consumer. Respiration is limited by oxygen for aerobes, and other potential electron acceptors for anaerobes. an oxic environment for aerobes Reproductionofmineralizingbacteria islimitedto andanoxicenvironmentforanaerobes. Thus,disruptionofthesedimentmayaffectmineralizers whenturbulenceremovesorresuspendsaspecificsedimentlayer. Thepredationofmineralizing bacteria is predominantly due to grazing ofsediment by deposit-feeding fauna, such as nematodesorpolychaetes. Thelife-spanofmineralizingbacteriaisprobablymuchshorterthan smallinvertebrates,suchasmeiofauna. Becauseofthesmallsizeofbacteria,andthedifficulty ofculturingall speciesofbacteriainthelab,thereisnotalotofinformationavailableaboutthe lifespan ofindividial cells. Summary Like consumers, mineralizing bacteria are limited by sources of energy, and by death and predation (Fig. III.9B) . However, for bacteria, the food source is sediment detritus and predation is by deposit-feeding animals. Furthermore, not all bacteria require oxygen. Sulfate reducing bacteria utilize sulfate, and release hydrogen sulfide into the environment. The “rotten egg”smellthatoccursinsomepartsofCorpusChristiBayduringthe summeriscaused by sulfide released by these bacteria. However, without these organisms, important nutrients, such as nitrogen, phosphorous, and sulfur would be buried in the sediment and lost from the ecosystem. Fig. 111.9A. The Mineralizer Subsystem. The energy flows and controlling processes inside a representive mineralizer. Fig.111.98.Summaryofarepresentativebacteria,acolonyofsulfatereducingbacteria. These bacteria utilize sulfates, which are abundant in the sediments, to decompose organic material, such as this seagrass. The bacteria gain energy from the organic matter, and the sulfate is converted into hydrogen sulfide (which is easy to smell on hot, summer days). Like producers and consumers, bacteria are affected by temperature and salinity. Bacteria also have their own predators, particularly polychaete and nematode worms. IV. HABITATS Another to characterize ecosystems, in addition to considering energy flow for each trophic way level, is to consider each habitat within an ecosystem. Habitats are the elements ofan environment that sustain an organism or a specific community oforganisms. The populations of differentspeciesoforganismslivinginahabitatiscalled acommunity. InaTexasbay ecosystem, typical habitats include riverine, salt marsh, algal mat, seagrass bed, water column, open bay bottom, oyster reef, beach and oceanic habitats (Fig. IV. 1A IV. IB) (Day et al. 1989). - Energy can be transferred among habitats by physical movementofthe water, or by movement ofthe organisms between habitats. The interaction habitats is partly responsible for the among high productivity that is characteristic ofestuaries. structure. Like other Texas estuaries, the CCBNEP estuaries have a common Ocean water exchangewiththeGulfofMexicooccursthrough abreakinthebarrierislandcalled a pass. Beach habitat faces the ocean or barrier island. There is only one continously open inlet, AransasPass,thatconnectsCorpusChrist!andAransasBaystotheGulfofMexico. Corpus Christi and Copano Bays have a bottom that is predominantly a muddy habitat. However, there arepatchyareasofsandybottomoroysterreefs. Oysterreefhabitatsoccurmostlyinsecondary bays, such as Nueces or Copano Bays, because oysters depend upon freshwater brought by rivers. The rivers empty into the secondary bays; sometimes there are tertiary bays or lakes associated with the river, e.g., Mission Lake, which empties into Copano Bay. Marshes line the riversourcesoftertiaryandsecondarybays. Lagoonsrunparalleltothebarrierislands,and perpendicular to primary bays. Primary bays are connected by the lagoons; therefore, lagoons are important for transport ofmaterials and recruitment between systems. Lagoons are long and narrow,withashortfetch.Furthermore,lagoonsareintheleeofthebarrierisland. Therefore, the water in a lagoon is calm and clear, relative to the primary bays. Seagrass beds develop well in this habitat. Algal mats develop on broad, supratidal tidal flats. Within the CCBNEP Bay Area System, all different habitat types can be found in all three estuaries. However, the area ofeach habitat varies within each estuary. The muddy bottom is typicalofthebays,butthereareregionswithasandybottom,particularlynearshore. Theoyster reef and salt marsh habitats are common in the Mission-Aransas Estuary. The oysters inthis estuary are an important commercial harvest. The algal mat, and grass bed habitats are common inLagunaMadre. TheLagunaiswellknownforitspopulationsoffish,due,inparttothe nursery habitat provided by the extensive seagrass beds. The Nueces Estuary is intermediate Fig.IV.IA. HabitatsubsystemsoftheCCBNEPareaecosystem. Fig. IV. 18. Habitat subsystems ofthe CCBNEP Bay area System. Water column refers to water thatfillsthethreeestuaries. Whilethereisalotofsurfaceareaforthishabitat,itisnotvery The most common benthic deep, and is less productive than the vegetated benthic habitats. habitats are muddy bottoms in Nueces Estuary and Mission-Aransas Estuary, and seagrass beds in Laguna Madre. Sandy bottoms occur in patches in all three estuaries, particularly near shorelines. Oyster reefs are common in Copano Bay and Nueces Bay. Salt marshes occur along muchofthe shorelineoftheCCBNEPBayArea,butareparticularlyabundant intheNueces Delta. Algal mats are a unique supratidal habitat that occurs in patches around the Bay Area, particularlyalongBaffinBay. Beachesoccuralongtheoceansideofthebarrierislandsofall three estuaries. betweentheothertwoestuaries, becausetheextentofalgalmat,grassbed,beach, oysterreefand salt marsh habitats are intermediate in size. The open bay bottom, therefore, is a large habitat in the Nueces Estuary. The Nueces Estuary has a gradient from muddy to sandy bottom from Nueces to Corpus Christi Bay. The nutrient storage in Nueces Bay k much higher than in Corpus Christi Bay because the Nueces River and marsh provide Nueces Bay with intermittent fresh water (Whitledge, 1989). Although there are more nutrients in Nueces Bay, chlorophyll a per unit area is higher in Corpus Christi Bay (Stockwell, 1989). Correspondingly, a higher zooplankton abundance is also found in Corpus Christi Bay (Buskey, 1989). The sandier Corpus ChristiBayhashigherabundance andspeciesdiversityofbenthicmollusksthanthemuddier NuecesBay. However,theCorpusChristimolluskstend tobesmallerthanthoseinNuecesBay (Montagna and Kalke, 1995). Seagrass Bed Habitat MuchoftheLagunaMadre, andshallow,fringingareasofNuecesBay,RedfishBayand Copano Bay are covered with beds ofseagrasses (Fig. IV.2A 1V.28). There is also a large - seagrass bed in Corpus Christi Bay (i.e., East Flats). There are five species ofseagrasses, but the thin-bladed shoal Halodule wrightii, and the thick-bladed turtle Thalassia grass, grass, testudinum, are the most common. Halodule grows rapidly in disturbed areas, but is usually out- competed by Thalassia over time. The areas in which seagrasses grow are characterized by strong currents and a shallow bottom. The sediments range from sandy to fine, and are usually reducing just below the surface due to high oxygen consumption rates ofdecomposers. ofcarbon Seagrass beds support a very diverse and productive foodweb by providing a source for the food web, and a place for fish and invertebrates to The high amount hide from predators. ofbiomass fromtheseplants leadstohighratesofgrossprimaryproductivityand netcommunity productivity. Seagrassisdifficulttodigest,becauseofstructuralcompounds.However, seagrass is an important contributor to the detrital foodweb. Seagrass is also a substrate for epiphytic algae (e.g., microalgae that on seagrass blades) and animals (e.g., crustaceans grow and polychaete worms). Seagrass beds serve an important role as nursery grounds for larval fish and invertebrates. They also serve as buffers against storms and can help filter contaminants fromthe water. Fig.IV.2A. ThecomponentsoftheSeagrassHabitatSubsystem Fig.1V.28. SeagrasshabitatoftheBayArea. Seagrassesprovideanimportanthabitatformany fishandinvertebrates, andcontributeamajorcomponentofthedecomposingmatterthatfeeds depositfeeders.2 Spirorbissp.,2 Palaemonetessp.(grassshrimp),3 Tozeumacarolinese - (grass shrimp), 4 Hippolyte pleuracanthus (grass shrimp), 5 -CerUhium lutoswn, 6 Diastoma Grandidierella bonneroides 8 9 ­ varium, 1 Caecum pulchellumHaploscoloplos foliosus, 10 ,, - Capitella capitata11 Clibinarius vittatus (hermit crab), 12 Callinectes sapidus (blue crab), , - 13 Lagodon rhomboides (pinfish), 14 ducks. - can be found in the meadows. Among these are the tiny polychaete worm Many species seagrass be Spirorbis sp., which filters plankton and organic matter from the water column. Spirorbis can seen blades as a small, white coil or circle. Grass shrimp graze on epiphtyic algae on seagrass ariddetritalmatter. Therearethreetypesofgrassshrimp,thedominantPalaemnmte*sp.(Fig. 1V.28.2), the arrow shrimp, Tozeuma zostericola (Fig. 1V.28.3), and the broken backed green, shrimp, Hippolyte carolinensis (Fig. 1V.28.4). The epiphytic algae is grazed by small snails, such as the white, sharp-pointed Cerithium lutosum (Fig. 1V.28.5) and the brown, round­ knobbed Diastoma varium (Fig. 1V.28.6). Many animals are supported by detrtitus trapped by the blades or beneath the sediment. seagrass These include the tube-building amphipod, Grcmdidierella bonneroides (Fig. 1V.28.7), small snails, such as Caecumpulchellum (Fig. 1V.28.8) and burrowing polychaetes. These polychaetes, such Haploscoloplosfoliosus(Fig.1V.28.9)andCapitellacapitata(Fig. as IV.2B.10),processbulksediment, extractingorganicmatterfromnon-organicmud. Atthetopofthefoodwebareseveralgeneralistcrustaceans,such asthestripedhermitcrab, Clibinarius vittatus (Fig. IV.2B.11), and the blue crab, Callinectes sapidus (Fig. 1V.28.12). These animals eat everything they can find, from detritus to grass shrimp and worms. Many kinds offish live inthe seagrass meadows, but particularly visible are the pinfish, Lagodon rhomboides (Fig. 1V.28.13). In the winter, a variety of duck species move into the seagrass meadows (Fig. 1V.28. 14). The ducks feed on small meiofauna, grass shrimp, or the roots and rhizomes ofthe seagrass itself. Larger predatory fish, such as a redfish, black drum, and spotted seatrout feed on the smaller fish and larger invertebrates that congregate in meadows. seagrass Salt Marsh Habitat Saltmarshes areshalloworintertidalregionsofthebay,oftennear asourceoffreshwaterinput, - that are dominated by marsh grasses and plants, particularly Spartina alterniflora (Fig. IV.3A 1V.38). In the CCBNEP Bay Area System, salt marshes can be found along the shores of all three estuaries, but are particularly abundant near river mouths in secondary bays. Nueces Bay has an extensive salt marshin theNuecesDelta/Rincon Bayou area.CopanoBay also supports salt marshes in Mission and St. Charles Bays. Along the eastern coast ofthe United States, salt marshes extend for kilometers. In contrast, Texas has very small tidal ranges, so salt marshes in the CCBNEP Area only extend for a few meters from the shoreline. In more Fig.IV.3A. ThecomponentsoftheMarshHabitatSubsystem. Fig.1V.38. SaltmarshhabitatoftheBayArea. Marshesoccuralongtheshoreline,particularly nearthemouthsofriversandcreeks. Marsh contributeorganicmatttertotheBayArea. grasses 1 Streblospio henedicti, 2 Mediomastus sp., 3 -Chironomidae (midge) larvae, 4 Corixidae - Fundulus Uca crab), 8 -Assiminea succinea 9 -Littorina irrorata (marsh periwinkle). - (water boatmen), 5 sp. (killifish), 6 -rails and other marsh birds, 7 -sp. (fiddler , tropical regions, mangroves, such as Avicennia germinansgradually replace salt marsh grasses. , TheCCBNEPAreaisnearthenorthernextentofmangroves’ range. However, intheperiod following several mild winters, mangroves are quite common, particularly along Redfish Bay. Intertidal wetlands act as sediment traps, where soft sediment and peat become trapped between the salt marsh plants. Beneath the plants are strong reducing conditions, and often low oxygen levels. Areas with a higher fresh water inflow have higher producer diversity, higher rates of primaryproduction andhighernetcommunityproduction. Becauseoftheamountofdeadand decaying plant matter, the detrital foodweb is important in salt marshes, and other habitats near salt marshes. Biomass ofproducers and consumers can be high, but species diversity can be low because offluctuating salinity. seagrass beds, salt marshes are important nursery Like and feedinggroundsfor avarietyofinvertebrates and fish. be found in salt marshes. Streblospio filters plankton from the water browses detritus with its tentacles. Another The übiquitous polychaete, Streblospio henedicti (Fig. 1V.38.1), can or polychaete, common in salt marshes, and many other habitats, is the deposit feeder, Mediomastus sp. (Fig. 1V.38.2). Unlike most marine habitats, salt marshes also support some insects, particularly when salinities are low. Midge larvae (Chironomidae) behave much like polychates, feeding on detritus from their tubes (Fig. 1V.38.3). Water boatmen (Corixidae) active are swimmers, but feed mostly on detritus (Fig. 1V.38.4). Many small fish can be found in salt marshes. Themanyspeciesofkillifish(Fundulussp.)feedontheabundantsoft-bodied invertebrates in the marsh (Fig. 1V.38.5). These fish and their invertebrate prey are eaten by the diverse array of shore birds that frequent salt marshes, including rails, herons, egrets and ibis be found Uca the fiddler crabs (Fig. 1V.38.6). Scurrying about on land, with the birds, can sp., (Fig.1V.38.7). Ucadigburrowsinthesoftmudinthehighintertidalzone. Theyfeedonalgae and detritus that they collect by scooping up the mud into a feeding ball and scraping organic matteron offoftheballwiththeirmouthparts. Theepiphyticalgaethatgrow Spartinaare grazedbyseveral speciesofsnail,includingthesmall,whiteAssimineasuccinea(Fig.1V.38.8) and the larger, striped periwinkle, Littorina irrorata (Fig. 1V.38.9). Algal Mat Habitat Algal mats are unusual features ofthe supratidal zone that occur in some locations around the CCNEP Bay Area. They occur when rain or wave surge collects in low spots near the shore, often in areas with higher elevation than salt marshes. The trapped water is very shallow, and oftenbecomesquitehotandsaline. However,thewateralsoallowsabloomofphotosynthetic the sediment surface. fix bacteria, called cyanobacteria or blue-green algae, that live on These producers are very important to the bay ecosystem, because they have the ability to atmospheric nitrogen (N 2) into a form more usable by other producers and bacteria (NH N0 or 3, 3 N02).Whenthismaterialgetstransportedbackintotheestuaries,itrepresents nutrientspike a that can enhance primary productivity in the estuary. However, aside from the cyanobacteria, there are not many species that are endemic specifically to the algal mats. Beach Habitat - There are two types ofbeach habitat in the CCBNEP Bay Area System (Fig. IV.4A 1V.48). Bay shorelines that are not covered by salt marsh be considered beaches. However, grasses can bay beaches are not as diverse and are not as distinct a habitat as are oceanic beaches. Oceanic beachesarefoundontheGulfofMexicosideofPadre,MustangandSanJoseIslands. While these habitats are not directly connected to the estuaries, there is interaction between the estuary and the adjacent beach. After storms, seagrass can be washed onto the beach, transporting from the bay to the oceanic environment. Also, many mobile animals, such as fish and energy crabs, move freely between the two ecosystems. Tidalpassesandbeachesaredirectlyexposedtostrongcurrentsandwaves. Becauseofthehigh energy imparted by the water, most mud-sized particles have been carried away. Furthermore, beach habitats are well oxidized and have a because ofthe constantexposure tohighenergy, constantoceanicsalinity(about 35ppt). Intheabsenceofmud, andhighorganicdetritus,these habitats are home mostly to filter feeders. The community is often highly diverse and has a high biomass and productivity, due to the transport of food by currents. The larger, more obvious animals include the mole crab, Emerita portoricensisa relative ofthe , hermit crab (Fig.1V.48.1). Emerita buries itselfup to its head in the sand and filters plankton and organicmatterwithitsfeatheryantennae. Somepolychate species, such asthetentacled Scolepis squamata (Fig.1V.48.2), also rely on plankton brought in by the waves. These filter feeders are eaten by many species ofjuveline fish, particularly postlarval jacks (Carangidae) that hide in shallow water to escape predation (Fig.1V.48.3). The small polychaetes are also eaten by larger, predatory polychaetes, such as Lumbrineris sp. (Fig.1V.48.4). Another Fig. IV.4A. The component ofthe Beach Habitat Subsystem. Fig.1V.48.BeachhabitatoftheBayArea. Becahesexperiencehighenergy,butstillsupport many animal species. Emeritaportoricensis (mole crab), 2 -Scolepis squamata, 3 juvenile 1 Carangidae (jack fish) and other fishes, 4 Lumhrineris sp., 5 Donax variablis (coquina clam), 6­ Ocypoda quadrata (ghost crab), 7 Diptera (flies), 8 sandpipers and other shore birds. common andfamiliarresidentofthebeaches is thecolorfulcoquina clam,Donaxvariablis (Fig.1V.48.5). Donax bury themselves using their muscular feet and probe for food with their longsiphons. Becauseofthewavesandtides,alotofdetrituspilesuponthebeachitself This detritus is mostly plant material, particularly Sargassum seaweed or sea grasses that are transportedbytidesoutofthebayareaafterstorms. Whilethisdecomposingmattermaysmell offensive, and is often cleaned from the beaches by humans, it serves as an important source of food for near coastal environments. Detritus is food for animals such as the elusive ghost crab, Ocypodaquadrata(FigJV.48.6),amphipods, meiofaunaorinsects(Fig. 1V.48.7).Someof these smaller animals are eaten by the numerous shorebirds, such as sanderlings, sandpipers, tumstones and seagulls (Fig.1V.48.8). In addition, buried debris can trap sand and is partly responsible for the beach accretion process during the summer and pre-hurricane seasons. Water Column Habitat ThewatercolumnoftheCCBNEPBay Areareferstothewaterthatfillsallthree estuaries(Fig. - IV.5A IV.5B).Althoughthewatercolumncoversahugesurfacearea,itisnotverydeep,and often only as productive as the bay bottom. Water column productivity is much lowere than in vegetated habitats. Typically, in marine environments, such as the GulfofMexico, the water column habitat is very deep, and more productive than the bottom. The water column ofbays can become quite turbid as sediment is resuspended by wind or human activities. Because fresh water mixes with salt water in the bays, the salinities are typically brackish (10-25 ppt). However, when evaporation exceeds fresh water inflow and flushing by the ocean, salinities can become saltier than the ocean (> 35 ppt). The water column is usually well oxygenated. Mixing, duetotheconsistenthighwindspeeds, andshallowdepthscausestratificationofthebaywater columntobearareevent. Thefoodwebconsistsofphytoplankton(onecelledalgae)beingeaten by zooplankton, which are in turnby fish. Primary production by phytoplankton in eaten estuarine water can be relatively high. In temperate zones, there is a strong seasonal change (the spring and fall blooms), which is not as pronounced near the tropics. Therearetwocyclesofenergyinthewatercolumnfoodweb. Oneoftheseiscalledthe “microbial loop.” Small, flagellate algae (Fig.1V.58.1) can photosynthesize, or ingest planktonic bacteria(Fig.1V.58.2). Flagellatesareaverydiversegroupofplanktonthatcantravelshort distances by beating their whip-like flagella. These small phytoplankton are by small eaten zooplankton, such as ciliated protists (Fig.1V.58.3). When the small phytoplankton and Fig. IV. SA. Thecomponents ofthe Water Habitat Subsystem Fig.IV.58. WatercolumnhabitatoftheBayArea. Thewatercolumncontains small many animals and plants that are important food sources for larger animals. flagellate - 1 phytoplankton, 2 -bacteria, 3 ciliate, 4 diatom phytoplankton, 5 Acartia tonsa (calanoid copepod), 6 -Oithona colcarva (cyclopoid copepod), 7 crustacean nauplius (larva), 8 -crab - - zoea (larva), 9 -Anchoa mitchilli (bay anchovy), 10 Mnemiopsis mccraydii (comb jelly or 13 Brevoortia patronus (bay menhaden), 14 Sciaenops ocellatus (red drum) and other large fish. ctenophore), 11 Sagitta sp. (arrow worm or chaetognath), 12 fish larva, - zooplankton die, they may be decomposed by bacteria in the water. Therefore, a small, but rapid foodweb cycle occurs amongthe small phytoplankton, small zooplankton and bacteria. Scientists arestillunsurehowmuchofthisenergyisavailabletootherorganisms,thatis,itis unknown whether the microbial loop is a “link” cr “sink.” A larger foodweb consists ofthe larger phytoplankton, such as diatoms (Fig.1V.58.4), that are eaten by zooplankton. Diatoms have silicate shells that resemble pill boxes or petri dishes, and canbesolitaryorbejoinedtogetherinlongchains. Therearetwotypesofzooplankton, holoplankton, which spend their entire lives as plankton, and meroplankton, which are planktoniconlyaslarvae. Holoplanktonincludemanycopepodcrustaceansoftheorders Calanoida (e.g., Acartia tonsa\ Fig.1V.58.5) and Cyclopoida (e.g., Oithona colcarva\ Fig.1V.58.6). Meroplankton include larval barnacles (or nauplii, Fig.FVSB.7) and larval crabs (orzoea,Fig.1V.58.8). Therearealsolargerfishthat eatphytoplankton,suchasthelarge schoolsofbayanchovy,Anchoamitchilli(Fig.1V.58.9). Somezooplanktonareeatenbylarger zooplankton. The comb jelly, or ctenophore, Mnemiopsis mccraydii (Fig.IV.SB.10), filters out copepodswithrowsofcomb-likeprojections. Combjelliesmay,inturn,beeatenbylarger jellyfish, such the sea nettle, Chrysaora quinquirecha. Another zooplankton predator is the as chaetognath,orarrowworm,Sagittasp.(Fig.IV.SB.11). Manyfishpreyonzooplankton, includingthelarvaeofmanydifferentspecies(Fig.lV.58.12),andtheadultsofspecies such as the menhaden, Brevoortiapatronus (Fig.IV.SB. 13). Large, predatory fish, including the red drum,Sciaenopsocellatus(Fig.IV.SB.14),eattheplantkivourous fish. Open Bay, Sandy Bottom Habitat WhilemostoftheCCBNEP areahas amuddybottom,certainareas,particularlynear shore, - have sandier sediment (Fig. IV.6A 1V.68). Sand can support larger animals that might sink in the soft mud. Sandy bottoms are often accompanied by stronger currents and higher water transparency in comparison with muddy water habitats. Attached algae, such as macroalgae, and benthic diatoms can yield high productivity in sandy bottoms. Because ofthe clear water, there are also many filter feeders in sandy sediment. Oneofthesefilterfeeders isthe sandybottomversionofthetentacledpolychaete,Spiophanes bomhyx (Fig. 1V.68.1). Like its relatives, Spiophanes uses its palps to capture food from the water,orgatheritfromthesedimentsurface. Alarger,strangerpolychaeteisChaetopterus variopedatus (Fig. 1V.68.2). Chaetopterus builds a tube that is completely buried in the Fig.IV.6A. ThecomponentsoftheOpenBaySandyBottomHabitatSubsystem. bottoms Fig.IV.68. SandybottomhabitatoftheBayArea.Althoughnotalargearea,sandy cansupportmanyofthelarge,familiarinvertebrates. 1 Spiophaneshomhyx,2 Chaetopterus variopedatus, 3 phoronid worms, 4 Mercenaria camphechiensis (quahog clam), 5 -Branchiostomaperidium (lancelet), 6 sp., sipunculid worm (in a gastropod shell), 8 - Tellina 7 ­ - Diopatracuprea9 Busyconcontrarium(lightningwhelk),10 Callinectessapidus(bluecrab), , 11 Gohiosoma boscii (naked goby). - sand. The worm stays inside the tube, using highly modified feet to pump in water and filter out organic matter. Another strange, tube worm is the phoronid (Fig. 1V.68.3), that filter feeds by using a U-shaped brush, somewhat like a barnacle. A more familiar filter feeder is the quahog clam, Mercenaria campechiensis (Fig. 1V.68.4). Mercenaria is quite large for a clam, and is capableofremovinglargeammountsofplanktonfromthewatercolumn. northernbays In more Mercenaria can be very common, and is an important shellfishery. In the CCBNEP Area, these clams tend to be rare, occurring only in sandy sediment, but individuals can be quitelarge. Another filter feeder, less well known than the quahog, is the hemichordate, Branchiostoma peridium (Fig. 1V.68.5),that resembles a small fish. There are also deposit feeders in sandy sediment, such as the small clam, Tellina sp. (Fig. 1V.68.6). Another deposit feeder is the sipunculid worm (Fig. 1V.68.7). Sipunculids sometimes live in discarded gastropod shells, much like hermit crabs. The filter and deposit feeders support several invertebrate and invertbrate predators. The many red-gilledworm,Diopatracuprea(Fig. 1V.68.8)buildstubesofshells anddetritusthatareoften found washed the beach. up on Despite the fact that it builds a tube, Diopatra is predatory, emerging from its tube to grab passing prey. The lightning whelk, Busycon contrarium which in , uses Texas, has a backwards-curving shell (Fig. 1V.68.9) is a large, well known snail that the edgeofitsshellandaraspingradulatofeedonlargeclams,suchasMercenaria. Bluecrabs, Callinectes sapidus (Fig. IV.6B.10), can be found in many habitats, including sandy bottoms. They tend to be opportunistic, eating any animals or detritus that they encounter. Another generalistpredatoristhenakedgoby, Gohiosomahocii(Fig.1V.68.11). Open Bay, Muddy Bottom Habitat By far, the most common benthic habitat in the CCBNEP system is the muddy bottom (Fig. IV.7A - 1V.78). Sediment underlying deeper water in Corpus Christi, Nueces, Redfish and Copano Bays is predominantly mud. In the Laguna Madre ecosystem, only Baffin Bay has a muddy bottom. Muddy bottoms occur in portions ofbays where there is a lack of other physical features, such as grasses or oyster reefs. Movement ofthe water over the surface ofthe mud keeps the sediment oxygenated to about one centimeter depth. Below this region is a strongly reduced environment due to the absence ofoxygen-generating producers. Mud is easily resuspended, and muddy bottoms may experience erosion or deposition ofsediment. Therefore, turbiditytendstobehigh,whichrestrictsthepresenceofproducersandfilterfeeders. Deposit feeders, however, can be present in high abundance and diversity. Biomass and metabolism Fig. IV.7A. The components ofthe Open Bay Muddy Bottom Habitat Subsystem. Fig.IV.78.MuddybottomoftheBayArea. Muddybottomsareverycommon,andsupporta diverse array ofspecies. 1 Mulinia lateralis (dwarf, surf clam), 2 -Clymenella torquata - 4 56 (bamboo worm), 3 Streblospio henedicti Mediomastus sp., Tellina sp., Ampelisca , - abdita, 7-ophiuroid(brittlestar),8 Penaeusaztecus(brownshrimp),9-Leiostomusxanthurus - (spot), 10 Pogonias cromis (black drum) shown in background. are also relatively high. Themudybottomecosystem isdrivenbytwosourcesofcarbon:phytoplankton and detrital matter. The filter feeders eat phytoplankton in the water column, or detritus that is may dissolvedinthewater. Oneofthedominantspeciesisthedwarfsurfclam,Mulinialateralis (Fig. 1V.78.1). Mulinia is a small, white clam that can become so dense in certain areas that there is no space between a clam and its neighbors. Other filter feeders present are the bamboo wormsoffamilyMaldanidae,particularlyClymenellatorquata(Fig.1V.78.2). These polychaetes pump water through their tubes and extract food from it. An unusual characteristic ofthesewormsisthattheirheadisatthebottomofthetube. Becausetheypumpwaterdownto thebottomofthetube,theseanimals areimportantinturningoverandaeratingsediment,and returning sediment-bound nutrients to the foodweb. Another polychaete filter-feeder is the übiquitous Streblospio benedicti (Fig. 1V.78.3). Streblospio uses its palps to capture organic matterinthewaterinstrongcurrents collectorganicmatterfromthesurfacesedimentwhen or flowis lower. Detritus, whichcancomefromterrestrialorganic mattertransportedbyfreshwater inflow, marine organic matter derived from marshes or seagrasses, and sedimented phytoplankton are themostimportantsourcesofcarbonformuddybottoms. Therearethreetypesofanimalsthat utilize detritus; non-selective deposit feeders, selective deposit feeders, and omnivores. Non- Mediomastus that resemble earthworms selective deposit feeders include polychaetes such as sp., from the (Fig. 1V.78.4). These polychaetes process bulk sediment, extracting organic matter mud. Selective deposit feeders usually have tentacles to pick and choose specific particles of materialforingestion. IntheCCBNEPArea,the dominantselectivedepositfeedersinclude bivalves, such as Tellina sp. (Fig. 1V.78.5) and Macoma sp., amphipods that build tubes, particularly Ampelisca abdita (Fig. 1V.78.6), and brittle stars (or ophiruoids, Fig. 1V.78.7). Omnivores include animals such as the edible shrimp, Penaeus sp., that eat detritus, microphytes, any small animals they can catch (Fig. 1V.78.8). Many animals, particularly or fish, eat the numerous invertebrates on the bottom. Spot, Leiostomus xanthurus (Fig. 1V.78.9), are wellknownforpickingatanimalsinthesediment, particularlyforbitingoffsiphonsor tentacles without killing the whole organism. Mulinia lateralis is the primary food source for black drum, Pogonias cromis (Fig. IV.7B.10), which collect mouths full ofsediment and grind upshellswiththeirpharyngealteeth. Shrimpareeatenbyadiverseassemblageoffish,such as catfish,Ariusfelis,reddrum,Sciaenopsocellatus, andflatfish. Fig.IV.BA. ThecomponentsoftheOysterReefHabitatSubsystem. Fig.IV.88. OysterreefhabitatoftheBayArea.Inadditiontoprovidinganimportantfishery, oystersprovideahardsubstrateforadiversearrayofotherorganisms. 1 Crassostreavirginica - (oyster), 2 Balanus sp. (acom barnacles), 3 serpulid polychaete worms, 4 mussels, 5 tunicates(seasquirts), 6-Thaishaemastoma(rocksnail),7 Crepidulafornicata(slippershell), - 89 10 Corophium sp., nereid polychaete, Libinia dubia (spider crab), 11 -Menippe adina (stone crab), 12 Pogonias cromis (black drum). - Oyster ReefHabitat Oysterreefs areintertidalorsubtidalareasofopenbottomthathavebecomecoveredwiththe living and dead shells ofthe oyster, Crassostrea virginica (Fig. IV 8A IV. 8B). In the CCBNEP - Area,oystersflourishinshallowwaterofintermediatesalinity. InCopanoBayandpartsof Nueces Bay, oysters have formed extensive reefs. These reefs have two dramatic effects on the habitat. Both living oysters and dead shells provide a hard substrate for encrusting fauna, one of the only two natural hard bottom habitats in estuaries ofthe Texas coast. Furthermore, the physical structureofthereefsacts asabarriertowaterflow,whichcancauseorganicmatterto settle outofthewaterontothereefwhereitcanfuel adetrital-based foodweb. Manyspeciesinoysterreefs arefilterfeeders,includingtheoysteritself{Crassostreavirginica; Fig. FV.88.1) and animals that encrust oyster shells. These include many species ofbarnacles, Balamis sp. (Fig. 1V.88.2), crustaceans that live in calcareous shells and filter water using modifiedfeet. Somepolychaetes,suchasthemembersofthefamilySerpulidae(Fig.1V.88.3), extend tentacles from calcaerous tubes. Other filter feeders, that actually pump water through theirbodies,includevarious speciesofmussels(e.g.Brachiodontes exustus)(Fig. 1V.88.4),and tunicates (or sea squirts, Fig. FV.88.5). Like the oysters, mussels filter plankton and organic matteroutofthewaterusingtheirgills asselves. Tunicates, whichresemblelumpy bags with an incurrent and excurrent siphon, trap food from the water column using a fibrous net. as Deposit feeding encrusting fauna are also very diverse. Several mollusks, such the rock snail, Thais haemastoma (Fig. 1V.88.6) and the slipper shell, Crepidulafomicata (Fig. 1V.88.7), attach to the oyster shells. Slipper shells settle on top ofeach other to facilitate reproduction. Slipper shells and rock snails graze on epiphytic algae that grow on oyster shells. Tube-building amphipods, Corophium sp. (Fig. IV.8B.8), feed on detrital material that settles on the reefs. They also use the material to construct their protective tubes. Withsuchahighbiomassanddiversityoffood severalomnivore predatorscanbe - sources, foundinthevicinityofoysterreefs. Nereidpolychaetesandseveralspeciesofcrabspatrolthe reefs searching for food. Nereids (Fig. 1V.88.9) are large, highly developed worms that have well-developed eyes, tentacles, and large jaws. The crabs include the spider crab, Libinia dubia (Fig. IV.BB. 10) and the stone crab, Menippe adina (Fig. IV.BB. 11). Stone crabs use their powerful claws to break open oyster and mussel shells, while spider crabs use their long arms to grabsmallerprey.Fishalsofrequentoysterreefs,eithertohideamongtheshells, tofind or food. The übiquitous black drum, Pogonias cromis (Fig. IV.BB. 12), use their pharyngeal teeth to crush shells ofa variety ofbivalve mollusks. ScaleofBenthic Invertebrates Throughoutthehabitatsectionofthisreport,wehavefocused oninvertebratemacrofauna,the large and more familiar animals, such as polychaete worms, mollusks and crustaceans (Fig. IV.9A. 1V.98.).However,therearealsomanyspeciesofsmallerinvertebratespresentinallof - thehabitatsoftheCCBNEPStudyArea.Muchlessisknown aboutthesesmallerinvertebrates, despitethefactthattheyareveryimportantcomponentsofthefoodweb. Meiofauna arethose animals between 63 and 500 pm in length. Meiofauna are extremely abundant in estuarine sediments, reaching densities of 106 m'2 . They are important food for some macrofauna, fish, such as spot, and birds, such as the green-winged teal and spoonbills. There are two trophic categoriesofmeiofauna,depositfeedersandepigrowthfeeders. Depositfeedersare dominated by nematode worms. In the CCBNEP Area, Sabatieria hilarula and Viscosia macramphida are twoofthemostcommon. Epigrowthfeeders animalsthatfeedprimarilyuponbenthic are microalgae. Epigrowth meiofauna include both nematodes and shrimp-like harpacticoid copepods. In the CCBNEP Area, two typical, epigrowth feeding nematodes are Chromadorita chitwoodi and Molgolaimus turgofrons. Epigrowth feeding harpacticoids are also very diverse, and include such species as Longipedia americana and the Coullana Microfauna are animals sp. smaller than 63 pm, and are typically one-celled. In estuaries, ciliated protists, foraminifera, flagellates, and bacteria are the most These organisms are even more abundant than common. the meiofauna, but even less is known about them. The structure and dynamics ofmeiofauna andmicrofaunacommunities are seriousdatagapsintheCCBNEPBayAreaSystem.Readers should keep in mind that there are hundreds ofundocumented meiofauna and microfauna species present in each ofthe CCBNEP habitats. Summary The different marine habitats in the CCBNEP Bay Area are defined by the physical structures, particularlyvegetation,thatcanbefoundineachhabitat(Fig.IV.IB). Seagrassbedsarevery diverse and productive, and serve as an important nursery ground for larval fish and Fig. IV.9A. Trophic relationships among different sizes ofbenthos. Fig.IV.98. Therelationshipamongthesizesofbenthicinvertebrates.Itisimportantto remember that even though invertebrate macrofauna, such as large mollusks, crustaceans and polychaetewormsarethemostfamiliar,thereisadiverseassemblageofsmallerorganisms as wellthatcanbefoundinalloftheCCBNEPBayAreahabitats. Meiofauna,particularly harpacticoid copepods and nematode worms, have very high productivity because oftheir great numbers and rapid growth rates. Smaller, one-celled microfauna, such as Foraminifera, ciliate protozoans, and even bacteria, are even more abundant. These small animals are important components ofall benthic, marine habitats. invertebrates. Saltmarshes areimportantsourcesoforganicmatter, andservetobuffer shorelines. Beach habitats experience high energy from wave impacts, but are still home to several speciesofanimals. ThewatercolumnreferstoallofthewaterintheCCBNEPArea. Watercolumnorganismsthatareatthemercyofthecurrentsarecalledplankton. Thelarger animals, such as fish, that eat plankton, are called nekton. Sandy bottoms occur near shore, and can support large animals. Muddy bottoms are more common, but support smaller animals. substrate and home for different species. Although each habitat may seem distinct, there are many interconnections amongthe habitats. Water currents, waves and tides transport organic matter, energy and even Oyster reefs are very diverse, because the oyster shells provide a many animals between habitats. Many types ofanimals, such as the blue crab, can move among many different habitats. V. ESTUARIES OF THE CCBNEP AREA The three estuaries in the CCBNEP study area are the Mission-Aransas, Nueces and Laguna Madre Estuaries (Tabie V. 1). Estuarine described in earlier chapters occur in all three processes estuaries. The primary factor affecting biological processes is temperature. Temperature the three changes mostly along latitudinal gradients. Therefore, temperature variation among estuariesissmall, and consequently thereislittledifferenceintheratesofbiologicalprocesses among the estuaries. The largest difference in biological processes among the estuaries is driven by other abiotic factors. The two dominant abiotic factors are undoubtely freshwater inflow and physiography. Freshwater inflow drives many key ecological processes (Figs. IH3A, III.3B). Therefore,differencesinfreshwaterinflowwillhaveagreateffect thehabitatsofeach upon system. Theshapeoftheestuariesisimportantindeterminingthecurrentsandexchangewith theGulfofMexico. Therearebasicallythreebaysystemsandtwolagoonalsystems(Fig.1.1). Laguna Madre links Baffin Bay and Corpus Christi Bay. Red Fish Bay is actually a lagoonal system that links Corpus Christi Bay and Aransas Bay. Bays are dominated by deeper, muddy sediments. Lagoons are shallower, narrower, with less fetch, have clearer water and more beds. These habitat differences cause the ecological differences the three seagrass among Anothergeological differenceisGulfpasses, which areconduits forfisheries systems. recruitment,andtheexchangeofnutrientsandorganicmatterwiththeGulfofMexico. The same basic habitats and processes occur in all three estuaries, with minor differences among them. Laguna Madre Estuary LagunaMadreisthreetimesthesizeoftheothertwoestuaries. Therefore,ithasmoretotal energy flow, from the sun to the bay system and from the bay system to various sinks, than the other two systems (“1” and “4” in the Fig. III.2A). The higher energy flow from the sun to the bay area system for Laguna Madre means more energy input to the producer subsystem (Fig. 111.3A) by increasing the photosynthesis of producers (Fig. IH.SA). Laguna Madre has an average depth that is shallower than the other two estuaries and a larger surface area receiving sun light (Table V. 1). The sun radiation unit water volume is much higher in Laguna Madre per than in the other estuaries, so the temperature storage is higher. This increases the energy flow level transport between subsystem and storage components (Fig. 111.3A), by increasing all such biophysiological process, as synthesis rate, intake rate, decomposition rate, aging rate, respiration rate, migration rate, and reproduction rate (Fig. 111.5A, 111.7 A and III.9A). TableV.l. ComparisonofcharacteristicsofbaysintheCCBNEPstudyarea. Variables Primary Bay Secondary Bays Tertiary Bays Rivers Creeks Size* (km'2) AverageDepth atMid-tideLevel*(m) " Volumeb(km 3) Rainfall0 (cm • y"1) CombinedInflow4(106m •y'1) 3 NetInflow4(106m3 -y"*) SurfaceSalinity* (%o) Bottom Salinity* (%o) AverageFreshwaterInflow*(m3 1 -s' ) MaximalMonthly MeanInflow*(m3 -s' 1) Residence Time(y) OpenBay Bottom8 MarshHabitat 8 Algal MatHabitat8 WaterColumnHabitat8 Grassbed Habitat8 Oyster ReefHabitat8 BeachHabitat8 FinfishCommercialHarvest*1(103kg y"‘) • • ShellfishCommercialHarvest*1(103kg y'1) • MaximalPhytoplankton Abundance(cell ml'*) MaximalZooplankton Abundance(10s ind. 3) • m" * MaximalBenthosAbundance(102ind. m"2) “Orlandoet al., 1993. cLarkin and Bomar, 1983. eLongley, 1994. 8Personal observations. 'Hollandetal., 1975. kHildebrandandKing, 1978. mBuskey and Stockwell, 1993. Mission-Aransas Estuary Aransas Bay Copano Bay Mission Bay St Charles Bay Carlos Bay Mission River Aransas River Copano Creek Chiltipin Creek 540 2 1.08 81 476 190 11.2-17 12.3-19.3 10 15(1964-1990) 3.02e common common rare common rare common intermediate 207 1453 584 1 7* 25' b Nueces Estuary Corpus Christ? Bay Nueces Bay Oso Bay Nueces River Oso Creek 500 2 1 76 841 509 14.8-31 16.6-30.6 30 50(1939-1989) 0.46° common intermediate intermediate common intermediate intermediate intermediate 151 544 1100j 500* 72" Laguna Madre Estuary lMadre aguna BaffinBay Alazan Bay Cayo Del Grullo Laguna Salada Petronila Creek San Fernando Creek JarachinalCreek Los Olmos Creek 1500 1 1.5 69 849 -947 30.3-34.4 31.3-37.0 1 5 (1965-1987) f ~l intermediate rare common common common rare common 834 147 1600k 200 m 130" Texas Department ofWater Resources, 1982. fSee text. Terry Whitledge, per comm. hTexas Parks and Wildlife, 1988. ]Murry and Jinnette, 1976. ’Buskey, 1993. "Montagna and Kalke, 1995 (mollusks only). Volume = surface area x depth d Thehighenergyflowinthiscreatesthehighrateofprimaryproduction. Phytoplanktonprimary production in Laguna Madre ranges from 2.68 to 4.78 gC • m'2 • d" 1, which is more than two timesthatoftheothertwoestuaries(OdumandWilson, 1962;Odumetal., 1963). Thehigh ecological efficiency alsoresultsinthehigh abundancesofthehigher levelconsumers, such as benthicmollusks,andfishes(TableV.1). ThebenthicmolluskabundanceinLagunaMadre (13,000ind. m*2)istwicethatoftheotherestuaries(2,500-7,200ind. *m*2). Thecommercial * harvestoffinfishinLagunaMadre(834 103kg •y'1)isaboutfourtimeshigherthantheothers (151-207 103kg•y'1). Thisbiomassproductivityisprobablyduetooverallhigherprimary production inLaguna Madre. lower LagunaMadreEstuaryhasa energyinputfromrivers,whichprovidenutrients,in comparison with the other two estuaries. Laguna Madre has a negative inflow balance (-947 • 1 106 m 3 • y'), which means the freshwater inflow is less than outflow, e.g., evaporation. The negativebalancealsoaccountsforhypersalinityinLagunaMadre. FlowofwaterfromNueces Estuary keeps the Laguna from evaporating entirely. Residence time for the water in Laguna, however, is very to calculate because ofits shallow depth, “negative” inflow, and its difficultconnection to Nueces Estuary (Table V. 1). Energy flow from ocean to the bay area system is higher for Laguna Madre than for the others (“3” in the Fig. IH.2A), which mainly provides detritus. The detritus storage tank in Laguna Madre is expected to be much higher than in other estuaries, because there is high primary production due to an extensive seagrass habitat. The consumer subsystem is dominated by depositfeedingbenthos. Theinputofseawaterandlessinputfromriveralsomaintainastable high salinity but low nutrients in Laguna Madre. The main limitation on producers’ synthesis maybeonlynutrients(Fig.HI.5A). However,lessinputfrominflowreducesthehumaneffects. So, Laguna Madre Estuary has a higher temperature storage, salinity storage and detritus storage and remains a more natural ecosystem than others. Mission-Aransas and Nueces Estuaries Nueces Estuary and Mission-Aransas Estuaries have a higher level ofnutrient storage, kinetic more inflow storage and oxygen storage in comparison with Laguna Madre Estuary, because of from rivers and creeks perunittime(Fig. 111.3A). However,phytoplanktonprimaryproduction in Corpus Christi Bay is only 0.48-1.26 gC • m‘2 •d 1 (Odum and Wilson, 1962; Odum et al., 1963;Flint, 1984;Stockwell, 1989). Otherlimitationsratherthannutrientlimitationsaremore importantinthisestuary. Mission-AransasEstuaryhasaseriesofoysterreefsintheprimary These reefs increase the kinetic bay, Aransas Bay, and secondary bay, Copano Bay. energy by transfering the energy from river flow and ocean tide to water turbulence through changing the directions oftide, river flow, runoff, and currents. The water, turbulence, and sediment-derived turbidity decrease the available light for producers at the bottom. There is also a large biomass offilter-feeding mollusks (oysters). The high consumer biomass and increased turbulence may explain the fact that Mission-Aransas Estuary has a much lower phytoplankton standing stock (Table V.l), and much lower seagrass standing stock (Dunton, 1994) than the other a two estuaries. Oyster reefs can steer and slow water currents. As currents slow or are diverted, nutrients and organic mattercan settle, or be trapped. The average water depth in Nueces and the Mission-Aransas Estuaries is 2 m (compared to 1 m for Laguna Madre) while the total area is halforone-thirdthat ofLagunaMadre(TableV.l). Theamountofsunradiation unitwater per volume is much lower than in Laguna Madre. This means a lower capacity for temperature storage and lower ecological efficiency than in Laguna Madre. may explain the lower This primaryproductionrates and loweramountofconsumer biomass (TableV.l). The Mission-Aransas and Nueces estuaries have bothriver and creek sources whileLaguna Madre has only creeks. The Mission-Aransas and Nueces Estuaries have an annual inflow • This indicates balance (190-509 106 m 3 • y’1) that is much higher than in the Laguna Madre. that energyflowfromthe landtothebaysystem ishigherthanintheLagunaMadreEstuary (“2” in the Fig. HL2A). However, the flow from the bay area system to ocean is also energy higher (“3” in the Fig. IH.2A). The rainfall ofthe three estuaries decreases from average 11 1 Mission-Aransas (81 cm y' ) to Nueces (76 cm y' ) to Laguna Madre (69 cm y' ) (Table V.l) - Because Mission Aransas recieves less inflow, the residence time ofwater in this estuary (3.02 y)ismuchlongerthaninNuecesEstuary(0.46y)(TableV.1). Thegradientofriverinflowand rainfall cause a lower salinity in the Mission-Aransas (12-19%o) and Nueces (17-3 l%o) average estuariesthaninLagunaMadreestuary(30-37%0). ThesalinityvariationishigherinMission- Aransas and Nueces Estuaries than Laguna Madre. High salinity variation makes these ecosystems more unstable than Laguna Madre (Fig. 111.3A), by affecting population aging rates, respiration rates, reproduction rates and migration rates (Figs. 111.5A, 111.7 A and III.9A). The Mission-Aransas and Nueces Estuaries are also more disturbed because there are more people living on their shores. VI. ANTHROPOGENIC PROCESSES The effects ofhuman beings on a bay ecosystem are regulated by public policies, management of water and sediment, and management ofliving resources (Fig. VI.1A). Policy and management actasswitches dialsbycontrollingforcingfunctions,whichcanstoporchangethepathsof or relevant energy flows. The management ofwater and sediment quality can control the energy transport between the bay system and ocean, and from land to the bay system. The management oflivingresources cancontroltheenergyflowfromthebaysystemtotheland. Summary Human activities can impact the estuarine ecosystem in a variety ofways, most ofwhich tend to have harmfuleffectsontheproductivity ordiversityoftheecosystem(Fig. VI.IB).The specific factors that mayleadtodegradationofthe estuarine ecosystem are discussedinthenextsection (VH.PriorityProblems). However,manyofthesefactorscanberegulated,tosomedegree,by Water and sedimentmanagementcan affectthe influenceoftheriver on resource management. the bay, and the degree ofconnection between the bay and the ocean. Water and sediment management canalso controltheamountofanthropogenic materialthatentersthebay ecosystem. Livingresourcesmanagementcanregulatetheextentofdifferenthabitats, such as saltmarshorseagrassmeadows, andcancontrolthelossofanimals duetocommercialharvests and recreational fishing. Water and Sediment Quality Management The control ofwater quality includes limiting pollutants being transported from land to river and from land to the bay. The control of sediment quality includes the changes in geological structures that may affect riverine input, outfall, runoff between the bay and or currents ocean. Changes in freshwater inflow or circulation within the system affect the level ofenergy in the kinetic and nutrients (Fig. VI2.A). Changes in inflow and circulation can also affect the biotic from human various storage components inthe bay system, such as oxygen, energy, salinity, detritus subsystems ofthe bay ecosystem (Fig.VI. 3A, VI.7A-VI.9A). Pollutants can come activities, such as the waste materials from municipalities, industries, or farms. Pollutants can be classified as non-toxic or toxic pollutants (Fig. VI.3A-VI.SA). The toxic pollutants, including chemical discharges, can affect biotic systems by reducing their reproduction success, and increasingnaturalmortalityand energymaintenance costsduetodetoxificationoftoxinsin Fig. VI.IA. The role ofpublic policy and resource management in the landscape and seascape of the Corpus Christi Bay National Estuary Program study area in terms ofinput and output from the Bay Area System. Policy and management acts as a switch by controlling the forcing functions. Fig. VI. 18. The role ofhumans in the CCBNEP Bay Area System. Human activities can impact the bay ecosystem inavarietyofways, mostofwhichtendtohaveharmfuleffectsonthe productivityanddiversityoftheecosystem. Impoundingriverscutsofffreshwaterinflowto 1 - 2 -kill thebay. Industrycanintroducetoxiccompoundstotheairorwaterthancanstressor manyestuarinespecies. 3-Constructionontheshoreofthebaydestroysproductivemarsh habitats, and can increase turbidity. 4 Runoff from cities can introduce contaminants to the bay - and increase turbidity. 5 -Water treatment can bring high nutrients into the bay that may lead to eutrophication. Motor boats can scar seagrass beds and leak fuel. 7 Trawling and dredging 6 may disturb or kill the organisms living in sediment. Shrimping also produces by-catch. 8 - - Creating or reinforcing passes, channels and causeways can alter estuarine circulation. 9 - Fishing may remove too many top predators from an ecosystem. 10 Agriculture can introduce nutrients to the bay, through fertilizer or simple runoff, or can introduce toxins to the bay in the form ofpesticides. Fig. VI.2A. The role ofthe public management in the living and nonliving resources affecting the Bay Area System Component. Fig.V1.28. Therole ofpublicpolicyandresourcemanagementintheCCBNEPBayArea System. ManyofthenegativehumanimpactsontheBayAreacanberegulatedbypublic Itisdifficulttodirectlyregulatemanyofthesubtle interactionsthat education and management. occur between organisms and their environment (for example, how many prey items a particular predatoreats). However, ofthelargescale thatultimatelyaffectthevarious some processes components ofthe Bay Area can, to some extent, be regulated (for example, the quantity of nutrientsreleasedintoabaybyawastewatertreatmentplant). Managementofwaterand sedimentresources canregulate suchprocessesastheamountoffreshwaterinflowtoabayand theamountofpesticideusedoncrop Managementofliving canregulatesuch land. resources as habitat loss and fishery harvests. processes Fig. VI.3A. The role related to public policy resource management in a producer system. Fig. V1.38. Human impacts upon a producer. Agricultural runoff, dredging and trawling can increasewaterturbidity. Runoffandwastewatereffluentcanincreasenutrientsinthebay. Pesticides and industrial pollutants can increase toxic compounds inthe bay. All ofthese additions can impact producers in the bay. For example, photosynthesis of seagrass can be decreased by increasing water turbidity, or increased by increasing nutrient additions to the bay. However, too many nutrients can also lead to eutrophication, which may deplete the oxygen in thebay. Toxinsinthewaterorsedimentcanincreasetherateofrespiration. Theadditional stress may require the plant to expend more energy, or even kill it. the environment. The non-toxic pollutants, such as nutrient inputs from sewers or increased affect organisms metabolism and food supplies. temperature from power plants, can Living Resources Management Livingresourcemanagementincludestheregulationofrecreational andcommercialfishing (including both finfish and shellfish) (Fig. VI.4A), such as limitations on the number, size, and speciesoffishcaught, limitations onfishingtools(e.g., gillnets) aswellasregulating thefishing season. The studyoffishpopulationbiology and ecology canlead torational fishery management, where people receive the optimal benefit from fishing while maintaining sustainable yields for the future. The optimal fishing season and size class may also be determinedfromthebiologicalstudiesoffishpopulations. Themanagementoflivingresources canalsoinclude theregulationofbioticorabioticcomponentsofthefisheryhabitat(Fig. ( VI.4A). Management may create artificial habitats, or enhance natural habitats, such as oyster reefs, that increase the fish populations by increasing the subsystem that supports a fishery. Pollutants Pollutants can enter the system through human activities, including waste materials from municipalities, industries or agriculture. The non-toxic pollutants, such nutrient additions due as to point sources like sewage outfall, and non-point sources like agricultural runoff, may actually increase ecosystem productivity. However, increases in ecosystem productivity almost always occurcoincidentwithchangesincommunity structureleadingtobloomsofundesirable algal species and lower biodiversity in the ecosystem. When nutrient additions become high, high growthratesofbloomorganisms,suchas,phytoplankton andbacteriawillcauseoxygen This depletion in a marine ecosystem. process is known as hypoxia caused by eutrophication. Summary Human activities have the potential to affect the various subsystems ofthe bay ecosystem (Fig. V1.28). Water and sediment management affect everything from the amount offresh water can inflowandexchangewiththeGulfofMexico,tonutrientandtoxicchemicaladditions. Living resource management can affect the extent ofsome habitats, such as salt marshes, and the Fig. VI.4A. The role related to public policy resource management in a consumer system. Fig. V1.48. Human impacts upona consumer. Consumers are not directly affected by nutrient levels.However,consumers areaffectedbyabundanceanddistributionofproducers,whichare dependentuponnutrients. Consumers areatanevengreaterriskthanproducersfromtoxic compounds through biomagnification. There is also the possibility that the migration, and therefore the reproductive success, ofsome consumers may be altered by extensive changes to theflowofwaterinanestuaryduetochannelsandbarriers. Thegreatestthreatstolarge consumers are over-fishing and loss ofhabitat. Many consumers, such as redfish, have very high take a larval mortality, and take years to reach reproductive age. Therefore, stocks offish may recover even more long time to from losses to over-fishing. The loss ofhabitat is probably of importancetoconsumers. Manyfishandinvertebratesaredependentuponwetlandsforfood andtoprovideanurseryfortheirlarvae. Managementcanaffecttherateoflossofwetlands, andcanalsoregulatefishinglimits, aswell aspointandnon-pointsourcesofpollutants. Fig. VI. SA. The role ofpublic policy resource management in a mineralizer system. Fig. VI.58. Human impacts upon bacteria. Because bacteria are important food sources, break down organic matter, and recycle nutrients, negative impacts upon bacteria can affect an entire ecosystem. Like all organisms, bacteria are sensitive to toxic compounds, such as hydrocarbons andheavymetals. Likeproducers,bacteriamayalsoincreasetheirproductioninthepresenceof increased nutrients. However, too many nutrients can cause eutrophication or nuisance plankton blooms. The metabolism ofbacteria is dependent upon water temperature. Cooling very systems for power plants might significantly increase local water temperature. numbersofindividualsofcertaincommercialorrecreationalspecies. Producerscanreceive increased nutrientadditions duetopointsources, such aswatertreatment,orrunoffofexcess fertilizersappliedtofarmlands(Fig.VI.3B). Whilesomedegreeofnutrientadditioncanbenefit too much can lead to alteration ofthe community structure and producers, such as seagrasses, eutrophication. Eutrophication occurs when a body ofwater contains an excess ofnutrients and Because organic material, to the extent that the ecosystem may deplete all available oxygen. decrease in water Turbidity can be increased by activities such as dredging, trawling, and by the input ofsediment to the bay from terrestrial runoff. The addition ofany toxic chemical, particularly pesticides, heavy metals and hydrocarbons, that might be produced by industry, can either stress producers, causing them to respire at higher rates, or even kill them. producers need sunlight to photosynthesize, any clarity can limit production. While as sensitive to nutrient additions or turbidity (Fig. V1.48), they have anotherproblemduetotheirpositiononthefoodchain. Althoughcontaminantsinthewater consumers are not may enter living tissues, they are often at concentrations too low to be threatening. However, a predator can gradually accumulate the contaminant burden from all different items that it prey eats. Thisphenomenonisknown biomagnification,andbecomesmoreofathreatathigher as trophic levels. In addition to biomagnification, also face losses in the form of some consumers predation from humans. Fishing efficiency can be so high that unrestricted fishing can quickly deplete an entire population past the point from which it may recover in subsequent years of recruitment. Mineralizers can be constantly exposed to sediment-bound contaminants, because oftheir intimateassociationwiththesediment,(Fig.VI.5B).Likeproducers,mineralizers arealso sensitivetonutrientadditions. Aformofpollutionthatisoftennotconsideredisthermal pollution. Anyactivitythatraisesthewatertemperature,suchastheinputofcoolingwaterfrom apower plant, can have anegative impact on the bay environment. High temperatures can quicklydepleteasystemofoxygen,orkillsomesensitive speciesoutright,replacingthemwith more tolerant, opportunistic species. VII. PRIORITY PROBLEMS TheCCBNEP BayArea System islocated in apartofthecountry thatisexperiencing human population growth. Humans already impact the Bay Area in many ways, most ofwhich different This have the potential to decrease the diversity and productivity ofthe estuarine ecosystem. impactwillonlyintensifyasthehumanpopulationgrows. IntheCCBNEPArea,someofthe impacts with a potentially negative effect are associated with estuaries in general, such as eutrophication, while others are specific to the local area, such as hypersalinity. The CCBNEP has identified several “Priority Problems” that affect the three estuaries in the CCBNEP may System. According to the CCBNEP Priority Problem Fact Sheet, “...these are problems in the definitionalsenseoftheword,i.e.,aproblembeingthefocusforfutureinvestigation. Thelists ofconcernsandcontributingfactorsaremeanttobeinclusiveofallpotentialproblems realor - perceived thatareworthyoffurtherscientificinvestigation.” Inmanycases,theactualeffect - that these Problems have on the CCBNEP Bay Area System have not been fully explored by scientific methods, and represent a “data gap” in the CCBNEP, and therefore designing conceptualmodelsto levelofdetailcomparabletotherestofthisreportisnotcurrently a possible. Altered Freshwater Inflow Into Bays and Estuaries TheissueoffreshwaterinflowintoNuecesBayhasreceived agreatdealofpoliticalandmedia attention (Fig. VTI. 1). TheNuecesRiverdoesnottransport agreatvolumeofwatercomparedto other rivers in Texas, and yet is under considerable pressure from the growing population ofthe Coastal Bend and South Texas in general. People need water to drink, clean, water plants (particularly crops), and for industrial production. However, the organisms in Nueces and CorpusChristiBaysalsoneedfreshwatertolive. Manyoftheanimalsthatarecommerciallyor recreationally important, such as shrimp and redfish, thrive in water that is less saline than the open ocean. Fresh water also brings nutrients into the bay that are needed by producers, just as crops and house plants need fertilizer. Seasonal inflow lowers salinity in a short period at time. These events areknown totriggerreproduction andrecruitmentofmanyestuarine species. Another concern specific to Nueces Bay is the alteration offlow ofthe Nueces River so no that it longer feeds into the Nueces Delta. The Delta supports an extensive salt marsh, which is an ofnutrients and programunderwaytoenhance freshwaterflowinto theDeltabyloweringthe banksofthe important source energy to the entire bay. There is currently a restoration Fig. VII. 1. Priority problems: altered freshwater inflow. Brackish water can support more productive organisms than marine water. Therefore, when fresh water inflow to an estuary decreases, the estuary generally becomes less productive. Fresh water can be diverted for a number ofreasons, including industrial, residential and agricultural uses. Although humans need watertoo,itisimportanttorememberthattheonly sourceoffreshwatertoanestuary isthrough rivers and creeks, particularly in an area with low rainfall, such south Texas. as Nueces River. This program should have positive benefits to the marsh and nursery habitat. Loss ofWetlands and Estuarine Habitats There are several reasons that salt marshes and other wetlands, such as seagrass beds, are so important to an estuarine ecosystem (Fig. V11.2). Wetlands: (1) provide critical habitat for fish, shellfish and wildlife, (2) provide a nursery ground for important commercial and recreational fish, (3) support a large and diverse estuarine foodweb, (4) filter and buffer residential, agricultural and industrial wastes, (5) buffer coastal areas against storm and wave damage, and and provide employment from recreational activities. Wetlands, however, (6) generate revenue can be lost through several human activities. Lower fresh water inflow decreases the size ofsalt marshes. Development along the bay shore may also remove salt marshes. Increasing the turbidityofthewatercanharmtheproductivityofseagrasses, orevencausethegrassbedsto disappear. turbidity, including natural factors, such as Several factors contribute to wind. Human activities that can increase turbidity include dredging, trawling, construction and run-off. ThepersistentbrowntideinLagunaMadre alsoincreasesturbidityduetoitshighconcentration. Scientists are still unsure as to whether the brown tide was caused or promoted by human activities. However,itisknownthatthebrowntidethrivesinperiodsofhighammonia, a nutrientthat canbe introducedthrough agriculturalorresidential run-offorwatertreatment. Condition ofLiving Resources The three estuaries in the CCBNEP are very productive, and support many different species. Severalkindsoffish,such asredfish,speckledtroutandflounder,areofeconomicimportanceto the area (Fig. V11.3). Other animals, such as the whooping crane, are threatened species with a limited range. Many ofthese animals are relatively large, and consequently at the top ofthe food chain. Therefore, they are extremely susceptible to changes in the environment that might have effects at any trophic level. For example, black drum are largely dependent upon bivalves for their food. be Ifthe bivalve populations in the CCBNEP Area are compromised, as may happening due to the brown tide, then black drum populations might be consequently impacted. Habitat loss and over-harvesting can also take their toll on estuarine wildlife. Species are adapted to live where they live. Consequently, habitat loss decreases the livable area of a Fig.V11.2.Priorityproblems:lossofwetlandsandestuarinehabitats. Evenifallother conditions are optimal, all estuarine species need a place to live. There are many factors that can limit habitat size. For example, restricting fresh water inflow reduce the size ofsalt marsh can a habitat. Increasing water turbidity can restrict the size ofa seagrass bed habitat. Dredging or trawlingover amuddybottomcanconstantlydisrupttheproductivityoftheorganismsthatlive there. Because some estuarine species are important to the local economy, through tourism, recreational or commercial fishing, loss ofhabitat can have monetary consequences as well. resources. a Fig. VIL3. Priority problems; condition ofliving The CCBNEP Bay Area supports These animals diverseassemblageofwildlife,includingsomeendangered orthreatenedspecies. can decrease in number ifthey lose viable habitat or important food sources. These factors, combined with over-fishing, have cause some fish, such as snook and tarpon, that were once common to become much more scarce. Other animals, such as bottle-nosed dolphins, may be experiencing declines due to disease. species. Over-fishingcanhurtapopulation,becausemanyoftheanimalsrequiremanyyears before they can become reproductive. Fish, such as tarpon and snook, sea turtles, and particularly the whooping crane have all declined in population, probably due to combination a ofover harvesting and habitat loss. Other animals, such as the bottle-nosed dolphin, seem to experience periodic die-offs due to unknown reasons that may include pollution, plankton blooms, disease perhaps old-age. or Degradation ofWaterQuality All organisms that are dependent upon the CCBNEPBay Area System, including humans, can be adversely affected by bad water quality (Fig. V11.4). For example, turbid water decreases photosynthesis by plants, while water that is contaminated by heavy metals can compromise the health ofa variety oforganisms. Water quality be degraded in three main ways: it can can become turbid, contaminated, or eutrophic. Turbidity,intheshallow bays oftheCCBNEP study area,is caused primarilyby wind,but can be exacerbated by dredging or trawling the bottom. There are a variety ofsources for potential contaminants. introduce contaminants in For example, the petrochemical industry alone can many ways, including: drill cuttings, produced waters from oil production, accidents and spills fromtransportingoil,andpipelineleaks.Runofffromindustrialandresidential isamajor areas pathway forthe introduction ofnon-point source contaminants to the bay. In the CCBNEP Area: air pollution may be another main source ofcontaminants to the water. Loss ofwetlands can make contamination worse, because natural wetlands act as filters, removing some harmful chemicals from the water. Eutrophication is caused when excessive nutrients are introduced into the bay. Nutrient sources include: agricultural runoff, water treatment plant effluents, and runoff from residential lawns. Thenutrientscause an initialbloomofalgaeorbacteria.However,bloomsofthismagnitude can deplete the water ofoxygen at night, which can limit secondary productivity or even kill animals such as fish. Toxicityisanotheraspectofthedegradationofwaterquality. Manufacturedchemicals,called xenobiotic compounds, enter the bay from a variety ofsources. Point sources, such as outfalls, discharge pipes, marinas, and platforms are easy to target for monitoring. Non-point sources, such as municipal, industrial, and agricultural runoff difficultquantify. are to Fig.V11.4.Priorityproblems:degradationofwaterquality. Themostproductivemarine ecosystemsthriveinareasofclear,cleanwater. Increasingtheamountofcontaminantsor turbidityinthewatercandecreaseproductivity, Humanactivities,such or even human health. as agriculture, dredging and trawling can increase water turbidity, which limits photosynthesis. Limitingtheflowofwaterinanestuaryorlimitingfreshwaterinflow inhibitthenatural can properties that wetlands have to filter contaminants from water. Many human activities have the potentialtocontaminate water,fromoilspillstorunofffromstreetsfollowing astorm. Atmosphericdeposition isanother sourceofnon-point pollution, andisverydifficulttoquanitfy. The main concern in agricultural and residential runoff is pesticides. Municipal and industrial runoffincludes heavy metals and hydrocarbons. Altered Estuarine Circulation Although the CCBNEP estuaries are connected to the open ocean by passes, these passes allow only asmallamountofwaterthroughthem,relative tothetotalamountofwaterin the estuary. Thisisduetothemicrotidal oftheCCBNEP estuaries. Theresdiencetimeofwaterin range South Texas Estuaries can be as great as several years (Table V.l). Circulation in CCBNEP estuaries is strongly influenced by winds especially the offronts. passages Small changes in the flow ofwater within an estuary in the CCBNEP area can have large effects on theestuary(Fig. V11.5).Forexample,limitingflowinsomeregionsmayprevent contaminants from becoming diluted throughout a bay. Low circulation can be responsible for relatively stagnant water, which can become hypoxic. Also, radically restructuring the pattern of waterflowinabaymayhave aneffect onthemanyanimalsthatmigratebetweenbaysandthe ocean. Theroleoflimitedwaterflow thepersistenceofthebrowntidehasbeenmuch on discussed, but it not completely understood. Under natural conditions, the locations and sizes ofpasses are changed constantly by wind and water currents, particularly during storms or hurricanes. Several channels, such Aransas Pass as and Mansfield Pass have been artificially maintained by granite jetties and regular dredging. However, several other channels that have not been maintained, such as Fish Pass, Newport Pass, Packery Channel, and Yarborough Pass have become closed. The size and location of channels does have an effect on circulation. One reason that Corpus Christi Bay passes may be difficult to maintain is that the deeper Aransas Pass currently directs all the circulation between of freshwater inflowduetorestrictedinflowsoftheNuecesRivertothe NuecesEstuary. theGulfandtheBay. Anotherpotentialcause passessiltingover,isthelowpressureheadof Dredging channels through the bays is also a significant alteration from the natural condition. Dredging makes portions ofthe bays much deeper than they would be naturally. Although cannot in the deep channels, the channels do allow much more water to circulate seagrass grow through abay. Dredging also creates spoil islands, which may inhibit the flow ofwater in some locations,butarealsoimportantroostingand nestinggroundsforavarietyofbirds,such as Fig.VII.5. Priorityproblems:alteredestuarinecirculation. Changingtheflowofwaterinan estuary can have subtle effects uponthe migrational patterns ofsome animals, the concentrations ofcontaminantsinthewater,andevennuisanceplanktonblooms,such asthebrowntide. Creating channels and spoil islands to permit boat traffic creates unnatural features in the relatively shallow and unobstructed Bay Area. The creation ofjetties, bulkheads and seawalls canhavedramaticeffectsonthesedimenttransportbywater. Theconsequencesofaltering estuarine circulation are not well understood, and warrants further scientific investigation. black skimmers and white pelicans. There are two other potential effects on estuarine circulation that are particular to the Nueces Estuary. TheflowoftheNuecesRiverhasbeendivertedandgreatlydecreasedbydams upstream. Therefore,thenetflowofwaterfromtherivertotheseamayhavebeenchanged. Secondly, industrial use ofwater can affect circulation. A CPL power plant draws cooling water in from the ship channel and returns it to Nueces Bay. The power plant in Flour Bluff draws waterinfromLagunaMadre,butreturnsittoOsoBay. Themagnitudeofwatermovedinthis manner is great, but the net flow ofwater from the Laguna to Corpus Christi Bay may not be greatly affected (Cheryl Brown, per. comm.) Bay Debris Debris isthemostvisibleformofpollution: litter,garbage and refusethatis dumped orwashed into the bay (Fig. VIL6). Although it takes a lot ofplastic and other debris to elicit a toxic reasons. response, debris is dangerous for other Debris, particularly plastic, discarded nets and fishing line, can be dangerous to large animals that ingest or become tangled in it. It is said that a lost plastic or nylon net “fishes forever” as an unseen ghost net. Many ofthe gulls and terns that can beseen onthe beachbearvisible signsofbouts withdiscarded, tangled fishingline. Ingestionofplasticisamajorproblemfor turtles.Discardedplasticmayresemblejellyfish,a sea major food component for sea turtles. Necropsies performed on turtles that wash up on the beach frequently reveal the presence ofingested plastic that has blocked the animal’s digestive system (Tony Amos, per. comm.). Humansarealsoaffectedbybay debris. Occasionally,containersoftoxicchemicals arebrought infromtheoceanorfalloffofabay-goingbarges. Medicalwaste,includingdiscardedsyringes, also appear from time to time. Even “harmless” debris can be detrimental to the area. A bay choked with garbage might be much less appealing to tourists, which could eventually hurt the local economy. Some ofthe debris in the bays comes from boats. Recreational vessels, as well as the steady streamoftransportshipsthatentertheCCBNEPBayArea, maycontributetothedebris problem, even accidently. A substantial portion of debris comes from recreational fishing, particularly tangled line, and lost lures and weights. Much ofthis material is accidently discarded when line becomes hung or tangled on rocks, reefs or even power lines. Debris is Fig. VII.6. Priority problems: bay debris. Although not as insidious as chemical contaminants, debriscanhavedetrimentaleffects theBayArea. Thelossofbird,seaturtleandmarine upon mammallifeduetoentanglementinfishinglineoringestionofplastic hasbeenwellpublicized. However,thebuildupoftoomuchbaydebriseven hasthepotentialtoaffecttourism,amajor partoftheeconomyintheCCBNEP BayArea. alsobroughtintotheCCBNEPAreafromtheGulfofMexico.Storms debrisoffof may carry ships or oil platforms, as can be seen from the hard hats and chemical drums that frequently wash up on the barrier islands. Furthermore, because ofprevailing southeasterly winds, the CCBNEP Area also receives a lot oftrash from Mexico and Central America. Not all debris is human made. There is also a lot ofbiological debris, particularly sloughed seagrass. A seagrass die offis a natural phenomenon that occurs in fall or winter. However, storms, heat waves, high turbidity, and algal blooms may also lead to vast quantities of dead seagrass. Because it is organic, seagrass and other biological debris are decomposed by bacteria causing the familiar “rotten eggs” along the Kennedy Causeway. The odor is caused by sulfide. Too much dead matterinthewatercanleadtoalossofortoomuchsulfideandammoniainthewater. oxygen, Sulfide and ammonia in high concentrations are toxic to marine animals. Seasonal freezes, which are periodic but infrequent in the CCBNEP Area, can cause fish kills that can also contaminate muchofthebay asthefishdecompose. Public Health Issues Manyofthepriorityproblems areconcernedwithimpactsupontheestuarinefloraandfaunaof theCCBNEPBayAreaSystem. Obviously,lossofplantandanimallifeisnotinthebest interestofthehumaninhabitantsoftheCCBNEP Areabecauseoflossesinfisheries,tourism, recreational activity, and the qualify oflife for CCBNEP residents. In addition to these indirect concerns, there are also some ways that the bay system may directly affect human health (Fig. VII.7). Thetwomainconcernsforhumansarefromcontaminatedwaterandcontaminated seafood. Althoughdirectdumpingofindustrial andresidentialwasteintothemarineenvironmentisa thing of the past, some dangerous compounds remain in the bay for many years. Bacteria, includingmanywhich arepathogenic, areassociated withsewageandwithrunofffromfarms. Some heavy metals, such as mercury, are toxic in even small doses. Mercury and other metals that are buried in the sediment can become resuspended, especially by dredging and trawling. The most susceptible areas to contamination by hydrocarbons and heavy metals are harbors or otherareasthatreceivealotofboatandshiptraffic. Thehydrocarbonscomefromspilledgas, diesel fuel, and oil. The metals originate from pilings and antifouling coatings. The city of Corpus Christi, and other towns along the CCBNEP Area are fortunate that their harbors are in much more pristine condition than many cities on the East Coast, and even some in the state of Fig. V11.7. Priorityproblems;publichealth. Evenifthepotentiallossofproductionofthe estuariesintheCCBNEPBayAreaisnotconsidered,therearestillseveral issuesconcerning the BayAreathatcanimpacthumanhealth. Illnessandthelossofrevenue duetoshellfish poisoning by a variety of diseases and parasites is one obvious example. Eating seafood that has beencontaminatedbytoxicwastemayalsobeapotentialproblem. Ofcourse,wateritselfmay also become so polluted to be a direct danger to the public, has regrettably happened in as as east coast harbors. many Texas. Another threat to human health may come from all ofthe seafood that is produced in the area, includingfinfish,shrimpandoysters. Becausehumansareatthetopofthefoodchain,weare extremtly susceptible to biomagnification, in which a contaminant becomes more concentrated as predators higher on the foodchain consume their prey. Seafood can also be a source of disease. Fish and shellfish can become infected while alive, or processed seafood may become contaminated during the time between collection and distribution to the consumer. The Vibrio bacteria that infects oyster beds in the summer is a well publicized example ofa disease with the potential to affect humans. Summary The “Priority Problems” outlined by the CCBNEP are issues that have a real or perceived potential to negatively impact the Bay Area System. Many ofthese issues have not been fully explored,andmaybefurtherrefinedanddevelopedbytheCCBNEP asnewinformation becomes available. In general, the greatest negative impacts that humans can have on the from contaminants loss ofhabitat. Contamination from estuarine ecosystem come or may come pointsources,suchaswatertreatmentplants,ornon-pointsources,suchasrunoff. Habitatloss cancomefromalterationofthebaybottom,typicallybydredgingandtrawling, developmentof wetlands and bay shorelines, and restricting fresh water inflow. The main effects ofthese contributing factors, as outlined by the CCBNEP, are altered freshwater inflow into bays and estuaries(Fig.VII.1),lossofwetlandsandestuarinehabitats(Fig. V11.2),conditionofliving resources(Fig. V11.3),degradationofwaterquality(Fig.V11.4),alteredestuarinecirculation (Fig.VII.5),baydebris(Fig.V11.6)andpublichealthissues(Fig.VTI.7). TheCCBNEPwill probably continue to devote resources to defining and refining these priority problems, as well as investigate ways in which people can minimize the negative impacts that they may produce as an important component ofthe estuarine ecosystem. VIII. INFORMATION GAPS Inthisproject,aconceptualmodeloftheCCBNEPBayAreahasbeendeveloped. Inthestrict sense ofa conceptual model, there are few information gaps. There are few biological or ecological processes that are so poorly understood that a simplified conceptual model could not be developed. However, science knows less about microbial and biogeochemical processes than anyothertrophiclevelwithinthe estuaries. Agoodexampleofthekindofproblemthis posesis the brown tide. Why has the brown tide persisted for so long? The answer may lie in the details ofthenitrogencycle. However,inmostcasesthelackofknowledgeaboutthedetailsofspecific elementalcyclesprobablywillnothave agreatinfluence onthe success orfailureofthe CCBNEP. Ontheotherhand,itwouldbedifficulttocreatequantitativemodelsbased onthisconceptual model. The mathematical formulations that would be implied by the relationships between the boxes and arrows in the conceptual model would be a straight forward and relatively easy task. information Parameterizing the quantitative model would be nearly impossible. Only cursory exists on the major standing stocks (represented by storage tanks) in the conceptual models. MostoftheinformationissummarizedinTableV.l. Scantydataareavailableontheratesof processes (represented by bullets and diamonds) in the conceptual model (Table V.l). The data areparticularlyscantyintermsofspatialandtemporalvariability. Virtuallynothingisknown about the transformation coefficients (represented lines and arrows) in the conceptual models. There are few estuaries in the world where quantitative estimates for most ofthese parameters exist. ChesapeakeBayisprobablyoneofthebestknownestuariesintheworld,butitdiffers from South Texas estuaries in fundamental Chesapeake Bay is surrounded by about many ways. 15 forested watersheds, where as Texas estuaries are bordered by only 1 2 agricultural or or grassland watersheds. Municipal development in the CCBNEP area is trivial relative to the northeastern corridor. The Chesapeake is a large, deep, well-flushed, mesotidal system; whereas. South Texas estuaries are small, shallow, sluggish, and microtidal. Using parameters from the Chesapeake ecosystem would unwise. seem Solving the problems identified for the CCBNEP area be may require new quantitative data to collected. The conceptual model can be used to identify the data needed. In some cases the data will be available in other characterization studies that were designed to summarize existing data. IX. REFERENCES Allendorf,P., 1981.Absorptionofdissolvedaminoacidsinthenutritionofbenthicspecies.Kiel. Meeresforsch. 5: 557-565. Alkemade, R., A. Wielemaker and M. A. Hemminga, 1993. Correlation between nematode abundance anddecompositionrateofSpartinaanglicaleaves.Mar.Ecol.Prog.Ser., 99: 293-300. Anderson, R. V., W. D. Gould, L. E. Woods, C. Cambardella, R. E. Ingham and D. C. Coleman, 1983. Organic and inorganic nitrogenous losses by microbivous nematodes in soil. Oikos, 40; 75-80. matter Aruga,Y.,1965.Ecologicalstudiesofphotosynthesisand productionofphytoplankton. 13. Photosynthesis ofalgae in relation to light intensity and temperature. Bot. Mag., Tokyo, 78: 360-365. Banse,K.,1982.Mass-scaledratesofrespirationandintrinsicgrowthin small very invertebrates. Mar. Ecol. Prog. Ser., 9: 281-297. Billen, G. and C. Lancelot, 1988. Modelling benthic nitrogen cycling in temperate coastal ecosystems. In: Blackburn, T. H. and J. Sorensen (eds.). Nitrogen cycling in coastal marine environments. SCOPE. John Wiley and Sons, Chichester: 341-378. Buskey, E. D., 1993. Annual pattern ofmicro-and mesozooplankton abundance and biomass in asubtropicalestuary. J.PlanktonRes., 15:907-924. Buskey, E. J. and D. A. Stockwell, 1993. Effects ofa persistent “brown tide” on zooplankton populationsintheLagunaMadreofSouthTexas.In:Smayda,T. J.andY.Shimizu (eds.). Toxic Phytoplankton Blooms in the Sea: 659-666. Carrada, G., T. Hopkins, Lj. Jeftie and S. Morcos (eds.), 1983. Quantitative analysis and simulation ofMediterranean coastal ecosystems: The GulfofNaples, a case study. Reportofaworkshop onecosystemmodelingIschia,Naples,Italy28Marchto 10April 1981 Organized by the United Nations, Educational, Scientific and Cultural Organization (UNESCO) and the Stazione Zoologica, Naples. p. 158 Comida,G.W., 1968.OxygenconsumptioninDiaptomus.Limnol.Oceanogr., 13:51-57. Davis, J.H.,1940.TheecologyandgeologicroleofmangrovesinFlorida.CarnegieInstitution, Washington, Publ. No. 517; 303-412. Day, J. W., C. A. S. Hall, W. M. Kemp and A. Yanez-Arancibia (eds.), 1989. Estuarine Ecology John Wiley & Sons, 558 p. Dunton, K. H, 1994. Seasonal growth and biomass ofthe subtropical seagrass Halodule wrightii inrelationtocontinuousmeasurementsofunderwaterirradiance.Mar.Biol., 120:479­ 489. Elliot, J.M, 1971.Somemethodsforthe statisticalanalysisofsamplesofbenthicinvertebrates. Freshwater Biological Association, Scientific Publication No. 25, 144 p. Findlay, S. E. G. and K. R. Tenore, 1982. Effect ofa free-living marine nematode (Diplolaimella chitwoodi) on detrital carbon mineralization. Mar. Ecol. Prog. Ser., 8: 161-166. Flint, R. W., 1984. Phytoplankton production in the Corpus Christi Bay Estuary. Contrib. Mar. Sci., 27:65-83. Gundersen,K., 1968.Theformationandutilizationofreducingpower in aerobic chemo­autotrophic bacteria. Zeitschrift. Allg. Mikrobiol., 8: 445-457. Heip, C., M. Vincx and G. Vranken, 1985. The ecology ofmarine nematodes. Oceanogr. Mar. Biol. Ann. Rev., 23:399-489. Heyraud, M., 1979. Food ingestion and digestive transit time in the euphausuiid function ofanimal size. J. Plankton Res., 1:301-311. Meganyctiphanes norvegica as a Hildebrand.H.andD.King, 1978.AbiologicalstudyoftheCayo delOsoandthePitaIsland areaoftheLagunaMadre.FinalRep.toCentralPower andLightCo.from TexasA&I University, Kingsville, 465 p. Holland, J. S., N. J. Maciolek, R. D Kalke, L. Mullins and C. H. Oppenheimer, 1975. A benthos . and plankton study ofthe Corpus Christi, Copano and Aransas Bay systems. Final Rep. to Texas Water Development Board from Univ. Texas Marine Science Inst., Austin. P-Ikeda, T., 1970. Relationship between respiration rate and body size in marine plankton animals asafunctionofthetemperatureofhabitat.Bull.Fac.Fish.HokkaidoUniv., 21:91-112. Ivlev,V.S., 1945.Thebiologicalproductivityofwaters.Usp.Sovrem.Biol.,19:98-120. Jorgensen, 8.8., 1980. Mineralization and the bacterial cycling ofcarbon, nitrogen and sulphur in marine sediment. In; Ellwood, D.C., J.N. Hedger, MJ. Latham, and J.H. Slater (eds.). Contemporary microbial ecology. Academic Press, London: 239-251. Kerfoot, W. C., 1987. Predation; Direct and indirect impacts on aquatic communities. University Press ofNewEngland, 386 p. Krebs, H. A., 1972. Some aspects ofthe regulation offuel supply in omnivorous animals. Adv. Enzyme Regul. 10: 397-420. Larkin,T. J.andG.W.Bomar, 1983.ClimaticAtlasofTexas.TexasDepartmentofWater Resources. Austin, Texas. 151 p. Li, J.,M.VincxandP.Herman,Inpress.AmodelofnematodedynamicsattheWesterschelde Estuary. Ecol. Modeling. Longley, W. L. (ed.). 1994. Freshwater inflows to Texas bays and estuaries; ecological relationships and methods for determination ofneeds. Texas Water Development Board and Texas Parks and Wildlife Department, Austin, TX. 386 p. 460. Lotka, A. J., 1925. Elements of physical biology. Baltimore, Md, Williams & Wilkins, pp. Malcolm, S.J. and S.O. Stanley, 1982. The sediment environment. In: Nedwell, D.B. and C.M. Brown (eds.). Sediment microbiology. Academic Press, London: 1-14. Montagna, P. A. and D. Kalke, 1995. Ecology ofMollusca in the south Texas estuaries. Amer. Malacol. Bull. 11: 163-175. Murray,L. S.andT.S.Jinnette. 1976.StudiesofthermalloadingonNuecesBay,Texas.Rep.to Tex. Water Qual. Bd. from Central Power and Light Co., Corpus Christi. 70 p. Nicholson, A. J. and V. A. Bailey, 1935. The balance ofanimal populations. Part 1. Proceedings ofthe Zoological Society ofLondon, 24: 551-598. Odum, H. T., 1971. Environment, Power, and Society. Wiley Interscience, New York. 331 p. Odum,H.T., 1972.Anenergycircuitlanguage. SystemsAnalysis and SimulationinEcology vol.2. In:B.C.Patten(ed.).AcademicPress,NewYork: 139-211. Odum, H. T., 1983. Systems Ecology. Wiley Interscience, New York, 644 p. Odum,H.T. andR.Wilson, 1962.Furtherstudies onreaerationandmetabolismofTexasBays, 1958-1960. Publ. Inst. Mar. Sci.,U.T., 8:23-55. Odum, H. T., R. P. Cuzon, R. J. Beyers and C. Allbaugh, 1963. Diurnal metabolism, total phosphorus, Ohle anomaly, and zooplankton diversity of abnormal marine ecosystems of Texas. Publ. Inst Mar. Sci., U.T., 9:404-453. Orlando,S.P.,Jr.,L.P.Rozas,G.H.Ward,andC.J.Klein, 1993.SalinitycharacteristicsofGulf ofMexico Estuaries. Silver Springs, MD: National Oceanic and Atmospheric Administration, Office of Ocean Resources Conservation and Assessment. p. 209 Parsons,T.R.,K.Stevensand J.D.H. Strickland, 1961.Onthechemicalcompositionofeleven species ofmarine phytoplankton. J. Fish. Res. Bd., Canada, 18: 1001-1016. Parsons, T. R., M. Takahashi and B. Hargrave, 1984. Biological oceanographic processes (3rd edition). Pergamon Press. 329 p. Pennock, J. R. and J. H. Sharp, 1994. Temporal alternation between light-and nutrient-limitation 275­ ofphytoplanktonproductioninacoastalplainestuary.Mar.Ecol.Prog. Ser.,Ill; 288. Platt, H. M. and R. M. Warwick, 1983. Free-living marine nematodes. Part I British Enoplids. Cambridge University Press. 307 p. Poremba,K., 1994.SimulateddegradationofphytodetritusindeepseasedimentsoftheNE Atlantic (47°N, 19°W). Mar. Ecol. Prog. Ser., 105: 291-299. Prosser, C. L. (ed.), 1991. Environmental and metabolic animal physiology. Comparative animal physiology, 4th ed., John Wiley & Sons, Inc., Publication, pp. 578. Redfield, A.C., 1934.Ontheproportionsoforganic derivativesin seawaterandtheirrelationto thecompositionofplankton. JamesJohnstoneMemorialVolume.Liverpool. 176p. Ruppert, E. E. and R. D. Barnes, 1993. Invertebrate zoology (6th edition). Saunders College Publishing. 1056 p. Sand-Jensen,K., 1977.Effectsofepiphytesoneelgrassphotosynthesis.Aquat.Bot.,3:55-63. Schiemer, F., 1982. Food dependence and energetics offree-living nematodes, I. Respiration, growthandreproductionofCaenorhabditis briggsaeatdifferentlevelsoffood supply. Oecologia (Berlin), 54; 108-121. Schiemer, F. and A. Duncan, 1974. The oxygen consumption offreshwater benthic nematode, a Tobrilusgracilis (Bastian). Oecologia (Berlin), 15: 121-126. Sikora, J.P.,W.B.Sikora,C.W.ErchenbrecherandB.C.Coull,1977.SignificanceofATP, carbon, andcaloric contentofmeiobenthic nematodesinpartitioningbenthicbiomass. Marine Biology, 44: 7-14. Sommer, U., 1994. Are marine diatoms favored by high Si:N ratios? Mar. Ecol. Prog. Ser., 115; 309-315. Stockwell, D. A., 1989. Effects offreshwater inflow on the primary production ofTexas a Coastal Bay System. Nitrogen Processes Study (NIPS) (Final Report), The University of Texas Marine Science Institute, Technical Report No. TR/89-010. 180 p. TexasDepartmentofWaterResources. 1982.Theinfluenceoffreshwaterinflowsuponthe major bays and estuaries ofthe Texas gulfcoast. Vol. 8. Executive Summary (Second 133 Ed.). Texas Department ofWater Resources, Austin, Texas. p. Texas Parks and Wildlife. 1988. Trends in Texas Commercial Fishery Landings, 1977-1987. Management Data Series, No. 149. Texas Parks and Wildlife Department, Coastal Fisheries Branch. Austin, Texas. Vidal,J.,1980.Physioecologyofzooplankton. 111.Effectsofphytoplanktonconcentration, temperature,andbodysizeonmetabolicrateofCalarmspacificus.Mar.Biol.,56; 195­ 202. Whitledge, T. E., 1989.Nutrient distribution and dynamics in the Lavaca, San Antonio and Nueces/Corpus Christi Bays in relation to freshwater inflow. Nitrogen Processes Study (NIPS)(FinalReport),TheUniversityofTexasMarineScienceInstitute, Technical Report No. TR/89-017. 211 p. Wright, D. J. and D. R. Newall, 1980. Osmotic and ionic regulation in nematodes. In: Zuckerman, B. M. (ed.). Nematodes as Biological Models. Vol. 11. Aging and other Models. Academic Press, New York: 143-164. Zeuthen, E., 1970. Rate ofliving as related to body size in organisms. Polskie Archiwum Hydrobiologii, 17; 21-30.