• 
• 
COMPARISON OF ECOSYSTEM STRUCTURE 
AND FUNCTION OF CREATED AND NATURAL 
SEAGRASS HABITATS IN LAGUNA MADRE, 
TEXAS 

• 
Paul A. Montagna, Principal ·investigator 
Cooperative Agreement No. X-00658801-0 
Technical Report Number TR/93-007 
• • • • • • 
• MARINE SCIENCE LIBRAR~ 
The University ofTexas at Austm 
750 Cbannelview Drive 
Port Aransas , TX 78373 
U.S.A. 
• 
• 

FINAL REPORT 
• 
COMPARISON OF ECOSYSTEM STRUCTURE AND FUNCTION . 
• 
OF CREATED AND NATURAL SEAGRASS HABITATS 
IN LAGUNA MADRE, TEXAS 
• 
by 
• 
Paul A. Montagna, Principal Investigator 
from 
• 
University of Texas at Austin 
Marine Science Institute 
P.O. Box 1267 Port Aransas, Texas 78373 
• 
to 
Dr. James H. Ratterree, Project Officer 
• Water Management Division (6W-QM) 
U.S. Environmental Protection Agency, Region 6 
1445 Ross Avenue Dallas, Texas 75202-2733
• 
Cooperative Agreement No. X-00658801-0 
The University of Texas Marine Science ljistitute Technical Report Number • TR/93-007 
November 3, 1993 
• 
• 

COMPARISON OF ECOSYSTEM STRUCTURE AND FUNCTION OF CREATED 

• 
AND NATURAL SEAGRASS HABITATS IN LAGUNA MADRE, TEXAS 
TABLE OF CONTENTS 
• LIST OF FIGURES II 
LIST OF TABLES iii 
• ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
INTRODUCTION 2 
• 
METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Study Design ........... . ..... . ................. .. .... ·; . . 5 Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Study Site Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .·. 6• Hydrographic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 
Geological Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Chemical Flux Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Biological Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9• Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 
RESULTS ............................. , . . . . . . . . . . . . . . . . . . . . 12 Synoptic Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 • Temporal Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 
• ACKNOWLEDGEMENTS 46 
I 
REFERENCES 47 
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LIST OF FIGURES 
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Figure 1. Upper Laguna Madre. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Figure 2. Northern part of Upper Laguna Madre. . . . . . . . . . . . . . . . . . . . . . . . 4 Figure 3. Sediment composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 4A. Sediment eH profiles. Vegetated stations. . . . . . . . . . . . . . . . . . . . 20 
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Figure 48. Sediment eH profiles. Unvegetated stations. . . . . . . . . . . . . . . . . . 21 Figure 5. Sediment organic matter at two depths. . . . . . . . . . . . . . . . . . . . . . 22 Figure 6. Sediment organic matter components. . . . . . . . . . . . . . . . . . . . . . . 23 Figure 7. Oxygen flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 
Figure 8. Total dissolved inorganic nitrogen flux. . . . . . . . . . . . . . . . . . . . . . . 25 Figure 9. Ammonia flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 10. Nitrite flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 11. Nitrate flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
• 	Figure 12. Phosphate flux. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 13. Silicate flux. . ......................................~ . 30 Figure 14. Macrofauna abundance at two sediment depths. . . . . . . .. . . . . . . . 31 Figure 15. Macrofauna biomass at two sediment depths. . .............. . 32
• Figure·16. Macrofauna taxa abundance. 33 Figure 17. Macrofauna taxa biomass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 18. Macrofauna species principal factor analysis. . . . . . . . . . . . . . . . . . 35 Figure 19. Macrofauna species diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36• Figure 20. Macrofauna species evenness. . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 
Figure 21. Relationship be~een species diversity and evenness. . . . . . . . . . . 38 Figure 22. Sediment organic matter at two sediment depths over one year. . . . 39 Figure 23. Sediment organic matter components over one year. . . . . . . . . . . . 40• Figure 24. Macrofauna abundance at two sediment depths over one year. . . . . 41 Figure 25. Macrofauna biomass at two sediment depths over one year. . . . . . . 42 
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• 	ii 
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• Table 1. Table 2. Table 3. Table 4. 
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Table 5. Table 6. Table 7. Table 8. Table 9. 
LIST OF TABLES 
Sampling locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Hydrographic measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Sediment grain size in Laguna Madre. 53 Eh profiles in sediment cores. 54 Oxygen measurements in sample incubations. . . . . . . . . . . . . . . . . . 55 Nutrient measurements in sample incubations. . . . . . . . . . . . . . . . . . 59 Vertical distribution of macrofauna in April 1992. . . . . . . . . . . . . . . . 63 Species distributions in April 1992. . . . . . . . . . . . . . . . . . . . . . . . . . 66 Laguna Madre Diversity and Evenness. . . . . . . . . . . . . . . . . . . . . . . 71 
Table 10. Temporal changes in sediment organic matter. 
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. . . . . . . . . . . . . . . . 72 

• 

COMPARISON OF ECOSYSTEM STRUCTURE AND FUNCTION OF CREATED • AND NATURAL SEAGRASS HABITATS IN LAGUNA MADRE, TEXAS 
ABSTRACT 
• 
• There is increasing demand to mitigate the loss of submerged wetland habitats. This project is designed to identify the criteria for a successful mitigation project, and the time for a created seagrass bed to become a functional habitat. Two approaches are taken. The first is a synoptic study of mitigated sites of different ages, the second 
• 
• 
is monitoring of a recent mitigation site for one year. Ecosystem structure and function is assessed by measuring select variables. Community metabolism and nutrient regeneration are key variables, which indicate the functioning of an ecosystem. Benthic community structure is a key variable that indicates the habitat utilization of an ecosystem. The mitigation sites are compared to three natural reference sites. Above­ground, the mitigation sites resembled natural sites in terms of biogeochemical f~.mction, but there were large differences below-ground. The mitigation sites lack sufficient organic material in the sediment for the environment to be fully functional. Benthic 
community structure at the mitigation sites resembled disturbed environments with high number, diversity, and low evenness. There was also a discernible trend among sites of different ages, that suggest it may take longer than 14-17 years to fully recover. Since this is such a long time, monitoring for one year did not reveal these differences . • Future projects to transplant seagrasses for mitigation should consider adding organic 
matter to the soil to speed the time it takes for the habitat to become fully functional. 
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• 1 
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INTRODUCTION 
• 
• Seagrass habitats are important to desirable fish and wildlife species (Kikuchi, 1974). Yet, numerous seagrass habitats have been damaged or destroyed by discharges, dredging and marine construction in our nation's bays and estuaries. There have been many projects to mitigate these adverse impacts on fish and wildlife. The 
• 
general · goal of mitigation programs is to replace habitat or repair damage. National Marine Fisheries Service recommends that mitigation projects should attempt to reestablish wetland fishery habitats and their ecological function (Thayer et al., 1986). Mitigation projects generally include the restoration or creation of new seagrass habitats, but monitoring or evaluation of the success of these projects is rarely done. 
• 
When it is performed it is usually limited to describing the success of the plantings. For example, in south Texas estuaries four out of seven mitigation projects planted between 1978 and 1983 were judged successful (Cobb, 1987). Success was determined by comparing percent cover in the mitigated area versus a control area. Much less is not 
known on whether these mitigated habitats are functioning like natural s~agrass habitats. Biological interactions between plants, animals, and microbes have a profound • effect on the success of any habitat creation project. After initial construction or planting, there is a succession of events leading to the climax, mature seagrass community. This process includes colonization of the unvegetated or transplanted area by microbes, epiphytes, and benthic invertebrates. The microbial community is• important in maintaining the balance of available nutrients, which are necessary for plant growth. Invertebrate bioturbation plays an important role in irrigating sediments with water and oxygen, which can enhance nutrient cycling rates. Finally, a luxuriantly vegetated benthos can provide the habitat for a variety of vertebrate and invertebrate • species. All these processes must occur before the mitigated environments become a functioning habitat in the sense of an ecosystem. The objective of this study is to compare benthic metabolism, nutrient regeneration, and habitat utilization of created seagrass habitats of different ages with • natural habitats. The goal of collecting this data is to determine how, and when created 
• 
habitats become functioning ecosystems like natural systems. This information is neces~ary to define measures of success, and delineate how long it takes a planted system to provide the ecological functions that are provided by naturally occurring seagrass systems. This information can alsb be used to. develop new criteria or 
methods for projects to create, enhance or restore seagrass habitats . 
• 2 
• • • • • 
• 
Figure 1. Upper Laguna Madre. Natural reference sites are in Baffin Bay 
(6), and the Laguna Madre (189). Mitigation sites are between the shorelines of the cities of Flour Bluff and Padre Isles . 
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• 3 
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Is I es 
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_­
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20 
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e 
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• Figure 2. Northern part of Upper Laguna Madre. Location of mitigation sites. Channels are shown in dashed lines . 
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METHODS 
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Study Design 
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Two studies were performed. One study was a synoptic sampling of 13 stations to compare community structure and rates of biogeochemical processes at natural, old 
• 
and recent mitigation sites. Three stations were naturally vegetated sites, nine stations were in mitigation sites and one was in a muddy bottom of an open bay. Two of the mitigation sites were constructed in the mid-1970's and are about 14-17 years old. These are called "old sites". Three of the mitigation sites were constructed between 
• 
1990 and 1991 and were 1-2 years old when s~mpled. These are called "new sites". It is reasonable to assume that natural sites are much greater than 20 years old, so the natural sites represent the oldest sites. An important feature of the study design is that we are replicating sites,· that is replicating at the treatment level to avoid 
• 
pseudoreplication. The 13 stations used for the synoptic study were sampled in April 1992. The second study was performed to monitor seasonal variability in community structure at a natural and mitigation site. Four stations, two natural and two mitigation, were sampled quarterly throughout a one-year period. 
Study Area 
• 	Ten study sites were chosen in the Upper Laguna Madre and Baffin Bay (Table 
1). Two of the sites have been visited since 1989 as part of a long-term research project to determine the importance of seagrass beds in maintaining a productive finfishery (Figure 1). These sites are 189 in the southern upper Laguna Madre and 6• in Baffin Bay (Table 1). Eight of the sites were located in a small area in the northern Upper Laguna Madre between the Flour Bluff and Padre Isles shorelines (Figure 2). In most cases there is only one station per site. At three sites, there are two paired station locations. One station is located in the grass bed, and one station is• adjacent in a bare patch. These paired stations are located in sites 189, TS and GI. The suffix (-G) for the grass and (-S) for sand patch is used to name each site: 189G, 189S;··'TSG, TSS, GIG, and GIS. Only station 6, which was in mud, does not have a suffix added to the station name. ·· 
~
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All stations were sampled during the synoptic study in April 1992. Four stations (189G, 189S, TSG and TSS), one at a natural site (189) and the other at a mitigated site (TS) were sampled in each of the four seasons during the temporal study. 
I' 
• 	5 
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Study Site Descriptions 
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Gulf Isles Limited (GI_), project #9009(08) is located east of lntracoastal Waterway Marker 49. The project scraped down a spoil island and created an area of submerged habitat approximately 320 m x 168 m with six circulation channels in April, 
• 
1991. Seagrass planting was not required. Natural colonization by Ruppia maritima, 
• 
Ha/odule wrightii and Ha/ophila engelmannii appears to have been successful. Two stations were sampled in the southern end of the excavation site at a depth of 0.4 m. One station was in a mixed bed of H. enge/mannii and R. maritima (GIG) and the other was an adjacent bare sand patch (GIS). The sediment was firm in both areas composed of approximately 90% sand, 5% rubble, 2% silt and 3% clay. 
• 
Padre Isles Natural Site #1 (Pl 1 G) was lo'cated in an open area east of the Gulf Isles site and west of the Padre Isles development. This site is protected from high wave action due to the surrounding land resulting in a low energy area. Most of this area is covered with a mixture of H. wrightii and R. maritima with few bare patches. 
Core samples were taken from a bed of H. wrightii at a depth of 0.5 m. The sE1diment was very soft and smelled of H2S when disturbed. The upper 3 cm of sediment was composed of 10% rubble, 55% sand, 10% silt, and 25% clay while from 3 to 10 cm • depth sand increased to 90%. Padre Isles Natural Site #2 (Pl2G) was located in the center of a seagrass flat east of the spoil islands adjacent to lntracoastal Waterway Marker 63 and west of Padre Island. The dominant seagrass at this site is H. wrightii. Samples were taken • at a depth of 0.75 m in a bed of H. wrightii. The sediment was firm compared to Pl1 with more rubble 14% and sand 74% and less silt 25% and clay 10%. The deeper sediment (3-10 cm) had higher sand content (89%). Transco scrape-down (TS_) project #18853 is located in state land tract 64 on • a spoil island east of lntracoastal Waterway Marker 55. Submerged habitat was developed by scraping down an existing spoil island, cutting three circulation channels and planting H. wrightii. Samples were taken from H. wrightii (TSG) and bare sand (TSS) in a water depth of 0.4 m. The sediment was very firm composed primarily of • sand in the grass (88%) and the bare patches (95%) . Transco pipeline (TPG) project #18853 was an attempt to establish seagrass, 
H. wrightii, on the bare shoulders of a pipeline extending from Padre Island in state land tract #17 4, and 64 under the lntracoastal Waterway near Marker 59, and through state tracts 48, 47, 25 and 134 to the mainland~ The site sampled was located east of the spoil islands adjacent to marker 59 near the area where the pipeline crossed the state tract boundary between state tracts 64 and 174. The water depth was 0.6 m and the dominant grass along this section of the pipeline was R. maritima. The sediment l' 
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was firm composed of 95% sand. 
Central Power and Light Company (CPG) project #10444 is located on the west Laguna Madre shoreline adjacent to the CP&L mariculture ponds. The project resulted in the removal of dredged material covering submerged seagrasses and was described as being successful. The project site is in a small cove formed by a point of land to the north with the opening facing the southeast. The predominant southerly winds deposit dead seagrass along the shoreline and on the bottom. Ruppia maritima was the dominant seagrass and was sparse. The water depth was 0.55 m and the sediment was very soft. The upper 3 cm of sediment sampled was 9% rubble, 70% sand, 12% silt, and 9% clay and the 3-10 cm sediment layer was 10% rubble, 79% sand 1 % silt and 10% clay. 
Skyline Equipment, Inc. (SKG) project #12004 (03) is located on the west Laguna Madre shoreline just north and adjacent to the Central Power and Light project. The project created 0.14 ha (0.34 acre) of submergent habitat from uplands in 1978 . The site is located on a point and is exposed to high energy southeast and northerly winds resulting in minimal dead seagrass deposition. The bottom was cove~ed with approximately 25% Ruppia maritima, 25% Ha/odule wrightii and 50% bare sand. Core samples were taken in H. wrightii at a depth of 0.35 m. The sediment was composed mainly of firm sand (92%). 
Marker 189 (189_) is a natural reference site in an open grass flat to the west of lntracoastal Waterway Marker 189. This site is vegetated with Halodu/e wrightii with scattered bare patches and very little drift algae and dead seagrass debris. The water depth is 0.8 m. Samples were taken from the grass (189G) and an adjacent bare patch (189S). The sediment in th~ bare patch sampled was firm composed of 21 % rubble, 61% sand, 3% silt and 15% clay. The grass sediment was similar with 21% rubble, 50% sand, 4% silt and 19% clay. The amount of clay increased with depth (35%) in the sandy bare patches and the seagrass. 
Genesis Petroleum (GES) project #15844 is located between two dredge spoil islands east of lntracoastal Waterway Markers 67. Approximately 0.4 ha (0.9 acre) of submerged wetland was created from the emergent spoil island. The site is in a small cove which faces southeast into the prevailing wind. Dead seagrass and detritus collect along the shoreline and on the bottom. Although H. wrightii was planted following the scrape-down, no living seagrass was found at the site. The water depth was 0.9 m. The surface sediment was 63% ..sand and 31%_. clay. Below 3 cm the 
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sediment was 94% sand. 
Marker 6 (BB6) is a control site located approximately 180° off of Marker 6 at the mouth of Baffin Bay. This site is in the open bay in 2.2 m water depth without seagrass. The sediment is soft mud predominantly silt (15%) and clay (81 %). 
7 
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Hydrographic Measurements 
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Salinity, conductivity, temperature, pH, dissolved oxygen, and redox potential were measured at each station during each sampling trip with a multiparameter instrument (Hydrolab Surveyor II). The sonde unit was lowered to just beneath the • surface and to the bottom. The instruments allows us to collect a variety of water 
• 
quality parameters rapidly. The following parameters are read from the digital display unit (accuracy and units): temperature (± 0.15 °C), pH (± 0.1 units), dissolved oxygen (mg/I ± 0.2), specific conductivity (± 0.015 -1.5 mmhos/cm depending on range), redox potential (± 0.05 mV), depth (± 1 m), and salinity (ppt). Salinity is automatically corrected to 25°C. 
Suspended sediments are measured as turbidity in nephelometric turbidity units (NTU) with a Hach photometer. Turbidity can be converted to suspended sediment concentration by making a standard curve of turbidity versus dry weight of filtered• sediments. In most Texas bays there is a linear relationship between suspended sediment and turbidity (R2 =0.99): suspended sediment (mg-ml-1) =0.038xNTU + 0.085 (Montagna, 1989). 
• Geological Measurements 
Sediment grain size analysis was also performed. Sediment core samples were taken by diver and sectioned at depth intervals 0-3 cm and 3-10 cm. Analysis followed • standard geologic procedures (Folk, 1964; E. W. Behrens, personal communication) . 
• 
Percent contribution by weight was measured for four components: rubble (e.g. shell hash), sand, silt, and clay. · A 20 cm3 sediment sample was mixed with 50 ml of hydrogen peroxide and 75 ml of deionized water to digest organic material in the sample. The sample was wet sieved through a 62 ΅m mesh stainless steel screen 
using a vacuum pump and a Millipore Hydrosol SST filter holder to separate rubble and 
sand from silt and clay. After drying, the rubble and sand were separated on a 125 ΅m 
screen. The silt and clay fractions were measured using pipette analysis . 
• Chemical Flux Measurements 
Biogeochemical fluxes were measured in the same 6.7 cm diameter core tubes 
• 
that were used to sample macrofauna. Samplrs were taken _by hand to a depth of 1 O 
cm by divers. Three replicates were taken within a 2 m radius. The water level was 
brought to the top with added station water. After settling for about 1 O minutes the initial water subsample was taken. Then the cores were closed with rubber stoppers 
• 8 
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that had an oxygen probe and a relief valve so that a tight seal could be o~tained. • Cores were incubated in the dark for two hours. Ice chest coolers were used as incubation chambers. The coolers had station seawater circulated through them, via a pump, to maintain the temperature as near to ambient conditions as possible. Three replicate cores were used to determine sediment metabolism and nutrient regeneration. • One station water sample was incubated as a control for oxygen metabolism, and two control samples were incubated for nutrient regeneration. The controls were used to represent changes in the overlying water that were not due to the presence of the sediment. 
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Oxygen concentration changes were measured every 15 min using pulsed 
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oxygen electrodes (Endeco, Inc., Marion, MA). ~hese electrodes are of a recent design in which the measurement of oxygen concentration is flow-insensitive (Langdon, 1984). The electrodes are connected to a Pulsed D.0. Sensor™ that controls the timing of the electrical pulses sent to each probe. Data is interpreted by the Pulsed 0.0. Sensor 
• 
and logged automatically on a portable computer. Oxygen changes per unit time were estimated using linear regression analysis. Water subsamples were taken from the overlying water in the cores after the two hour incubation period to measure changes in other chemical constituents. Dissolved 
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inorganic nitrogen (DIN) concentrations of ammonia, nitrate, and nitrite and phosphate and silicate were measured from the water subsamples using highly precise autoanalyzer techniques (Whitledge et al., 1986). Nutrient changes were estimated as the difference from initial and ending values. The mean of two replicates was used as the control value. 
The flux (FLUX) for both oxygen and nutrients is calculated a function of the chemical change (CHANGE) with ·respect to time minus a control value, and was adjusted for the area of sediment (FACTOR) covered by the core and the volume • (VOLUME) of water contained in the core: 
FLUXmmol·m-2·h-1 =VOLUME I x CHANGE mmol·l-1 ·core-1 ·h-1 x FACTORm-2/core (1) 
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Biological Measurements 
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Sediment was collected from the same 6. 7 cm diameter core tube, that was used 
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to measure chemical flux. The macrofauna were sectioned at depth intervals of 0-3 cm 
and 3-10 cm (Montagna and Kalke, 1992). Samples were preserved with 5% buffered formalin, sieved on 0.5 mm mesh screens, sorted, identified, and counted . 
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Each macrofauna sample was also used to measure biomass. Individuals were • combined into higher taxa categories, i.e., Crustacea, Mollusca, Polychaeta, Ophiuroidea, and all other taxa were placed together in one remaining sample. 
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Samples were dried for 24 h at 55 °C, and weighed. Before drying, mollusks were placed in 1 N HCI for 1 min to 8 h to dissolve the carbonate shells, and washed with fresh water. 
Sediment organic matter was also measured from each core. The seagrass stems, roots, and detritus from each sample was collected on a 0.5 mm sieve, dried and weighed . 
• Statistical Analyses 
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Macrofauna diversity is calculated using Hill's diversity number one (N1) (Hill, 1973). It is a measure of the effective number of species in a sample, and indicates the number of abundant species. It is calculated as the exponentiated form of the 
Shannon diversity index: 
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N1 =eH' (2) As diversity decreases N 1 will tend toward 1. The Shannon index is the average uncertainty per species in an infinite community made up of species with known 
proportional abundances (Shannon and Weaver, 1949). The Shannon index is calculated by: 
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l 

(3) 
Where ni is the number of individuals belonging to the ith of S species in the sample • and n is the total number of individuals in the sample. Richness is an index of the number of species present. The obvious richness index is simply the total number of all species found in a sample regardless of their abundances. Hill (1973) named this index NO. Another well known index of species • richness is the Margalef (1958) index (R1). R1 is based on the relationship between the number of species (S) and the total number of individuals (n) observed: 
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R1-S-1 ' 
(4)
ln(n) 
)
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Although common, this relationship presupposes that there is a functional relationship 
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between S and n. This assumption may not be justified in all cases. Evenness is an index that expresses that all species in a sample are equally 
abundant. Evenness is a component of diversity. Two evenness indices, E1 and E5, have been calculated. E1 is probably the most common, it is the familiar J' of Pielou (1975). It expresses H' relative to the maximum value of H': 
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Et=_!!!_= ln(N1) 
(5)
In(S) ln(NO) 
• E1 is sensitive to species richness. E5 is an index that is not sensitive to species 
richness. E5 is a modified Hill's ratio (Alatalo, 1981): 
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E5 (1/A.)-1 Nt-1 
5 n(n.-1)
where,A.= L ' ' (6) 
i-1 n(n-1) 
• .A is the Simpson (1949) diversity index. E5 approaches zero as a single species 
becomes more and more dominant. 
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Statistical analyses to reveal differences among sampling periods, stations and sediment depths were performed using general linear model procedures (SAS, 1985). • Analyses were performed on chemical flux and species abundance, biomass and diversity measurements. Two-way analysis of variance (ANOVA) models were used where sampling dates and stations were the two main effects or where stations and sediment depth were the main effects. One-way ANOVA was used to compare stations • during the synoptic study of natural and mitigation sites in April 1992. Grthogonal linear 
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contrasts were used to test five a priori hypotheses about the structure and function of the habitats studied (Kirk, 1982). The first hypothesis is that there is a difference between the means of all vegetated and all nonvegetated stations. The second hypothesis is that among seagrass stations, there is a difference between the means 
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of the natural and mitigation sites. The third hypothesis is that there is a linear or temporal difference among ages of seagrass bed habitats; the natural sites are considered the oldest, CPG and SKG are considered the same age and designated "old" mitigation sites; and TPG, GIG, and TSG dre considered -as "new" mitigation sites. 
The fourth hypothesis is that there are differences among the means of the old and new mitigation sites. The fifth hypothesis is that there is a difference between the TRANSCO scrapedown (TSG) and pipeline seagrass sites (TPG). Tukey multiple 
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comparison procedures were used to find a posteriori differences among sample means (Kirk, 1982). The stations means are reported in a Tukey test, and those that are not 
different to the 0.05 level are joined by underlining. Multivariate ANOVA was used to test for treatment effects on species data. Factor analysis with rotated and unrotated factors was used to determine if communities were similar in different stations . 
• RESULTS 
Synoptic Experiment 
• 
• The stations were all hydrographically similar in April 1992 during the synoptic study (Table 2). Salinity and temperature averaged 24.6 ppt and 24.0 °C respectively at all stations. Dissolved oxygen and pH averaged 7.54 mg.i-1 and 8.97 respectively. There were some differences in oxygen concentration due to site differences and sampling at different times of the day. Baffin Bay was the only site with high turbidity. 
There was considerable difference in sediment composition at all sites (Table 3; Figure 3). Baffin Bay was the only site dominated by mud, having a high silt ~nd clay content. In the natural site of the southern part of the study area, station 189, sand • composed half of the content of sediments. The southern natural site, 189, was no more than 55% sand. All the northern stations, natural and mitigation, were composed of at least 73% sand. Within sites, bare patches had 5-10% higher sand content than vegetated sediments. The seagrass obviously promotes settling of fine particles, since • there was a higher amount of silt and clay at these stations. Eh decreased with sediment depth at all stations (Table 4; Figure 4). There were dramatic differences among sites in sediment Eh profiles. Vegetated sediments (Figure 4A) were always much more negative than bare-patch sediments within sites • (Figure 4B). There was a gradient of electronegativity from recent mitigation sites to older mitigation sties to natural sites. The two new sites (GI_, TS_, and TP) had almost no vertical differences in Eh. This indicates that there is a lack of reducing power in sediments of recent mitigation sites. • There was a considerable amount of seagrass-derived organic matter in all samples, except for the unvegetated sediments (linear contrast, P=0.0001, Figure 5). In the natural and old mitigation sites, most of this material was associated with the surface of the sediment (Figure 5). There w.as more material in natural sites (934 g.m-) than in mitigation sites (438 g.m-2) (line~r contrast, P='0.0001). There was also 
• 2 
a significant difference with age of the mitigation site (linear contrast, P=0.0001). Old sites had 619 g.m-2, but new sites had only 317 g.m-2• New sites had proportionately 
_
...
lesser amounts of all components (Figure 6), but especially less below-ground material, 
• 12 e.g., roots and detritus. The new total amount of material at new mitigation sites was not significantly different from unvegetated sediments (Tukey test). The general trend was for higher amounts of organic material in natural and newer mitigation sites and higher amounts in seagrass stations (mean dry weight in g.m-2, station name, and Tukey test): 
985 952 876 793 445 357 326 267 220 165 18 12 5 Pl1G Pl2G 189G SKG CPG TPG TSG GIG 189S GES GIS TSS 6 
Oxygen measurements collected from the oxygen electrodes for calculating oxygen metabolism is given in Table 5. Mean oxygen flux was calculated using equation 1 and is presented in Figure 7. The average oxygen flux is negative indicating that the sediments were consuming oxygen in the dark. Seagrass bed samples had the greatest oxygen demand, -8.0 mmol 0 2 · m-2 · h-1 compared to -1.1 mmol 0 2 . m-2. h-1 in non-vegetated sediments, because of the high biomass of the seagrasses themselves (linear contrast, P=0.0001). Average flux (mmol 0 2 -m-2 .h-1) at natural stations was -10.4, old mitigation sites was -7 .2, and new sites was -6.5). There was a trend of higher oxygen consumption with age of the habitat (linear contrast, P=0.0001 ). The sand and mud stations were not significantly different from one another. The general trend was for higher amounts of oxygen consumption at seagrass stations, and less at mitigation sites (mean flux in mmol 0 2 . m-2. h-1, station name, and Tukey test): 
0.1 -0.9 -1 .4 -1.7 -1.9 -4.8 -5.1 -5.4 -7.1 -7.7 -7.8 -9.7 -16.4 GIS GES 6 189S TSS CPG GIG TSG Pl2G TPG 189G SKG Pl1G 
Nutrient measurements for calculating nutrient regeneration is given in Table 6. Flux for all nitrogen components, DIN, phosphate and silicate were calculated. Total DIN flux was near zero at most stations (Figure 8). There was a great deal of sediment nitrogen uptake in the southern stations. However, variability was so great, that is it difficult to detect differences among stations (average flux in mmol DIN-m-2 -h-1, station name, and Tukey test): 
13 

• 

2.0 ·1.2 1.1 0.2 -0.8 -0.3 -0.9 -1.0 -1.0 -1.6 -5.7 -16.7 -26.3 • GIG TSS Pl1G TSG TPG Pl2G CPG 189S SKG GES GIG 189G 6 
Ammonia flux was the greatest constituent of DIN. Ammonia flux was similar at all stations (Figure 9, average flux in mmol NH4. m-2. h-1, station name, and Tukey test):
• 
2.3 2.3 2.2 0.9 0.1 0.07 -0.2 -0.3 -1.0 -1.1 -1.4 -16.8 -26.0 TSS GIG TSG Pl1G 189S TPG GIS Pl2G CPG SKG GES 189G 6 
• 
Nitrite flux generally, was near zero, but on average there was efflux (0.084 mmol N02 .m-2 .h-1). The only stations with a large amount of nitrite regeneration were the mud and natural seagrass station in southern Laguna Madre (Figure 10). Because of the high value at the mud site (station 6), there was more nitrite regeneration in 
• 
• unvegetated stations (0.20 mmol N02 .m-2.h-1) than in vegetated sediments (0.012 mmol N02 .m-2 .h-1) (linear contrast, P=0.0096). Except for the high values at 6 and 189G, there were little differences among stations (average flux in mmol NQ2.m-2 .h-1, station name, and Tukey test): 
1.12 	0.64 0.09 0.03 0.03 0.02 -0.03 -0.04 -0.05 -0.06 -0.08 -0.28 -0.29 6 189G TSG Pl1G TPG GIS TSS 189S CPG GES GIG SKG Pl2G 
• 
Nitrate flux was also generally near zero, but on average there was uptake by 
sediments (-0.77 mmol N03 -m-2-h-1) (Figure 11). The only stations with a significant 
amount of nitrate uptake were generally unvegetated stations (-1.60 mmol N03 .m-2 .h-1),
• 	which were different from vegetated stations (-0.26 mmol N03 •m-2. h-1} (linear contrast, P=0.0001 ). The only station with a large amount of nitrite flux was GIS (Figure 11, average flux in mmol NQ3.m-2 .h-1, station name, and Tukey test): 
0.43 0.30 0.13 0.11 -0.16 -0.17 -0.21 -0.37 -0.52 -1.06 -1.08 -2.11 -5.33 SKG Pl2G CPG Pl1G GES TPG GIG 6 189G 189S TSS TSG GIS 
-..
• 
Phosphate flux was not significantly different at any of the 13 stations (P=0.3206, one-way ANOVA). The mean flux was -0.265 mmol P04 .m-2.h-1, and was not different from zero (Figure 12). On average silicate was generated by sediments (5.1 mmol 
• 	14 
• 

Si04 -m-2 -H1) (Figure 13). Silicate regeneration was higher in the natural seagrass sites 
• 
(16.0 mmol Si04 -m-2 -h-1) than in the mitigation seagrass stations (2.4 mmol Si04 -m-2 -h­
• 
1) (linear contrast, P=0.0001). Silicate flux was high in seagrass bed stations (7.5 mmol Si04 -m-2 -h-1) and low in non-vegetated stations (1.1 mmol Si04 -m-2 -h-1) (linear contrast, P=0.0001). This trend was driven by large fluxes at two natural stations (Figure 13, average flux in mmol Si04 -m-2 -h-1, station name, and Tukey test): 
34.4 15.5 6.9 4.7 3.7 3.3 1.9 0.8 0.7 -0.3 -1.4 -2.0 -2.5 189G Pl1G 6 GIG TSG TPG GES TSS CPG SKG GIS Pl2G 189S 
• 
Macrofaunal invertebrates were much more abundant in the top 3 cm of surface sediment (Table 7, Figure 14). There were on average 19,994 animals-m-2 in top 3 cm, and 3,831 animals-m-2 in the 3-10 cm depths. There were significant interactions • among sediment depths and stations (2-way ANOVA, P=0.001), so it is difficult to determine if mitigation affected the vertical distribution of organisms. The percent of organisms present in the top 3 cm of sediment was calculated and a 1-way ~NOVA indicated there were station differences (P=0.0069). Total percent abundance in • surface was higher (linear contrast, P=0.0006) at all the seagrass sites (85%) than at 
• 
the unvegetated sites (72%). The average biomass at all stations in the top 3 cm of sediment was 5.11 g-m-2, and 5.84 in the 3-10 cm section. Differences in vertical profiles among stations were found for biomass (Figure 15, 1-way ANOVA, P=0.0003). Again there was a higher percentage of the biomass found in vegetated sediments 
• 
(63%) than in unvegetated sediments (38%) (linear contrast, P=0.0004). Natural sites had a higher percentage of the biomass in surface sediments (75%) than mitigation sites (55%) (linear contrast, P=0.0159). There was also an increased percentage of biomass in surface sediments with age of the seagrass bed; the old mitigation sites had 
66% of the biomass in the surface, and the new sites had 48% at the surface (linear contrast, P=0.0228). The following is a Tukey test of the percent of biomass in the surface sediment: 
• 87.5 82.1 80.2 73.0 61.1 58.6 55.9 49.2 45.0 39.1 26.7 24.7 11.3 Pl2G Pl1G 6 -CPG TPG SKG 189G GIS GIG TSG 189S GES TSS 
In general, vegetated sediments had higher total abundances to a depth of 10 cm (32,229-m-2) than unvegetated sediments (10,098-m-2) (linear contrast, P=0.0001) . 
• 15 
• 

• 
Natural sites had higher abundances (40,781.m-2) than mitigated sites (27,097.m-2) (linear contrast, P=0.0005). Although there was no difference among old (28,932.m-2) 
• 
and new sites (25,874.m-2) (linear contrast, P=0.4824), the trend of natural to old to new is significant (linear contrast, P=0.0006). Total macrofaunal density was highest in the vegetated (natural sites of the northern part of the study area (Tukey test, average numberx10 3 .m-2 to a depth of 10 cm, and station name): 
55.8 41.1 29.0 28.8 27.1 27.0 25.4 25.4 25.1 9.1 6.1 4.3 3.8 Pl2G Pl1G SKG CPG GES TSG GIG 189G TPG 189S GIS 6 TSS 
• 
The average infauna! biomass in the top 10 cm of sediment was different only • among vegetated and unvegetated sediments (Figure 15, linear contrast, P=0.0245) . Although infauna! biomass varied by an order of magnitude there were few stati.stically significant differences among the stations (one-way ANOVA) (average biomass ;;in g.m-2 to a depth of 10 cm, and station name): 
• 
21.3 19.1 18.8 16.4 14.2 13.3 10.6 9.6 5.2 4.6 4.2 2.6 2.5 TSS GIG SKG TSG CPG 189G TPG Pl1G Pl2G 189S GIS GES 6 
• Community structure, in terms of major taxa, was different among the stations sampled (Figure 16). There were large differences among vegetated and unvegetated 
I 
• 
sediments (MANOVA, P=0.0001). Natural and mitigation sites were also different (MANOVA, P=0.0003). There were significant differences with respect to age of the vegetated sites (MANOVA, P=0.0006). The differences among sites was driven by 
• 
changes in polychaete density, since they generally dominated the communities in all stations. Polychaetes generally dominated biomass also (Figure 17). Differences similar to abundance were found among vegetated and unvegetated sediments (MANOVA, P=0.0017), natural and mitigation sites (MANOVA, P=0.0053), and with 
respect.. to age of the vegetated sites (MANOVA, P=0.0146) . 
.,.·Community structure, in terms of species distributions was also different among 
the stations (Table 8). The most obvious factor.that is related to changes in community 
• 
structure is whether the station is vegetated o~ unvegetated ·(Figure 18). This factor, 
factor 1 in Figure 18, accounted for 53% of the variability in species distributions. The second factor, which accounts for 23% of the variability, seems to be related to the age 
of the mitigation site. All natural stations, the oldest mitigation stations (CPG and 
• 16 
• 

• 
SKG), and the pipeline site (TPG) group together in the center and left side of the second factor axis. The newer sites (TSG and GIG) group together with unvegetated 
sites on the right side of the second factor axis. 
• 
Species diversity is highest in seagrass systems (Figure 19, Table 9). The average N1 diversity for seagrass beds was 10.4 species compared to a 6.3 species for unvegetated stations (linear contrast, P=0.0001 ). Species diversity is highest in the 
• 
recently disturbed environments. Natural sites had a lower average diversity (8.0) than mitigation sites (11.0) (linear contrast, P=0.0001). Diversity declined with age of the habitat (linear contrast, P=0.0001; new mitigation sites had a diversity of 12.6, old sites were 10.7, and natural sites were 8.0. The small difference between new ~nd old sites 
was significantly different (linear contrast, P=0.0453). The average diversity at each site follows (N1, station name, and tukey test): 
• 
16.8 12.2 11.8 11.0 10.9 9.2 9.2 8.1 7.1 6.0 5.8 4.2 2.5 
TSG SKG GIG 189G 189S CPG TPG TSS Pl1G GIS Pl2G GES 6 
• Species evenness was different among stations (1-way ANOVA, P=0.0001, Figure 20, Table 9). The average E1 evenness index for seagrass beds was 0.80, which was not different from 0.77 for unvegetated stations (linear contrast, P=0.1173). Natural sites had a lower average evenness (0.70) than mitigation sites (0.82) (linear • contrast, P=0.0002). Evenness declined with age of the habitat (linear contrast, P=0.0003; new mitigation sites had an evenness of 0.83, old sites were 0.79, and natural sites were 0.70. The average evenness index at each site follows (E1, station name, and tukey test): 
• 
0.97 0.91 0.88 0.85 0.83 0.83 0.80 0.77 0.76 0.74 0.68 0.62 0.57 TSS 189S TSG GIG GIS SKG 189G TPG CPG 6 Pl1G Pl2G GES 
• 
Evenness and diversity were correlated (Figure 21 ). As diversity increases evenness increases, i.e., dominance decrease-;s. There appears to be a phase shift, • or two separate relationships, for the non-vegetated sites versus the vegetated sites. The non-vegetated sites have higher evenness values than the vegetated sites. This indicates that there may be less dominance at n~n-vegetated sites . 
• 17 
• 
Temporal Study 
• 
• Two paired stations, one natural (189) and one created (TS), were monitored for one year to determine if change in the newly created habitat were discernible. There was always more material in the natural sediments (189) than in the mitigation site (TS) (Table 10, Figures 22-23). The relative proportion of organic matter in the surface 0-3 
• 
cm and bottom 3-10 cm sections of sediment did not change much over the year of monitoring (Figure 22). In general, the higher proportion of organic matter in the natural station (189) was due to higher amounts of material in both sections (Figure 22). At both sites, the organic material at the sand stations (-S) was composed entirely of 
detritus (Figure 23). There was much more detritus in the natural grass station (-G) than at the mitigation station (Figure 23). There was very little change at any station from April through October 1992. 
• 
• 
Seasonal fluctuations in macrofaunal abundance (Figure 24) and biomass (Figure 25) did occur. The interaction between stations and dates was significant for biomass (2-way ANOVA, P=0.0428) and abundance (P=0.0028), indicating that changes in abundance and biomass were different at the mitigation and the natural site. Abundance at the natural sites increased throughout the year, but at the mitigation site there was a large decline during the spring and then a rise for the remainder -of the 
year . 
• 
• 
• 
• 
• 18 
• • • • • 
• Figure 3. Sediment composition. Per cent dry weight of sediment 
components in each station. Samples taken in April 1992 . 
• 
• 

•· 
• 
• 

• 19 
• • • • • • • • • • • 
Laguna Madre Sediment Composition (% dry weight) Percent 
100-,,-,.,.-,,.-...,.--.-~,..--r-~~~-n-:~-=-?TT-r~-=--r--n-~-,.,--n--77"-r-t7J'~~~--,.,.r--rr-»--"7r"T--i-7r-=-~~/7'1 
90 
80 
70 
60 
50 
40 
30 

20 
10 
0 189G 189S 6 CPG GES GIG GIS Pl1 Pl2 SKG TPG TSG TSS 

Station Clay ts<S000<S?J Silt VZIZJ Sand V77J Rubble
IComponent 
' 
... 
• 
• 

• 
• 
• 

• 
Figure 4A. Sediment eH profiles. Vegetated stations. Vertical distribution 
of eH measurements within each station. Samples were taken at each cm horizon. Samples taken in April 1992. 
• 
• 
• 
• 
• 20 
• 
• 	Laguna Madre eH Profiles 
Habitat= Seagrass 
z .--~~~~~~~~~~~~~~~~~~~~-----.--~~~----, 
o-4-~~~~~~~~~~~~~~~~~~~~~~-+-~~~---t 
-500 -400 -300 -200 -100 0 100 • eH 
Station 	6 A A 189G E E E CPG o o o GIG • • • Pl1G D D D Pl2G I I 1· SKG. ** ** ** TPG o o o TSG 
• 

... 
• 

• • • • • 
• Figure 48. Sediment eH profiles. Unvegetated stations. Vertical distribution of eH measurements within each station. Samples were taken at each cm horizon. Samples taken in April 1992 . 
• 
• 

• 
• 

• 21 
• 
• 

• z 
0 -1 
• -2 
-3 
• 
-4 
-5 
• 
-6 
-7 
• 
-8 
-9 
• 
-10 
. -11 -500 
• 
IStation 
• 

Laguna Madre eH Profiles 
Habitat= Unvegetated 

-400 -300 -200 -100 0 100 
eH 
6 6 6 189S E E E 6 o o o GES 
• • • GIS 
o o o TSS 
.,. 
.; 
• • • • • 
• Figure 5. Sediment organic matter at two depths. Average from 3 replicate cores taken at each station in April 1992. Cores were sectioned into 0-3 cm 3-10 cm sections . 
• 
• 
• 
• 

... 
~ 
• 22 
• 
• 

Laguna Madre Sediment Organic Matter (g · m-2)
• 
Dry Wt. 
• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS '!'· Station 
Section (cm) .... 3-1 0 l\\\'3 0-3 

.,. 
• 

• • • • • 
• 
Figure 6. Sediment organic matter components. Average from 3 replicate 
cores to a depth of 10 cm. Samples taken at each station in April 1992. Plant material and detritus retained on a 0.5 mm sieve . 
• • • • 
... 
\ 
.; 
• 23 
• 
• 

Laguna Madre Sediment Organic Matter (g · m -2)
• • • • • • 
• 
189G 1895 6 CPG GES GIG GIS Pl 1 G Pl2G SKG TPG TSG TSS ~, Station 
Co~ponent .... Detritus [\\\"] Roots ™ Seagrass 
• 

\' 
• • • • • • 
• Figure 7. Oxygen flux. Average flux from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• • • • 
• 
24 
• 
• 
• 

Flux 
1 0 • -1 
-2 -3 
• 
-4 -5 -6 • -7 -8 
• 
-9 -10 -11 
-12 -13 
• 	-14 -15 -16 -17 
• 
• 

Laguna Madre Oxygen Flux (mmol · m -2 · h -1) 

189G 189S  6  CPG  GES  GIG  GIS  Pl1 G  Pl2G  SKG  TPG  TSG  TSS  
Station  
MARINESCIENCELIBRAK i The University ofTexas at Austin 1SO Channelview Drive Port Aransas, TX 78373 U.S.A.  

• 

• 
• 
• 

• 
• 

• Figure 8. Total dissolved inorganic nitrogen flux. Average flux from 3 
replicate cores taken at each station. Samples taken in April 1992 . 
• 
• 

• 
• 
... 
\ 
.: 
• 25 
• 
• 

• 2
Laguna Madre Dissolved Inorganic Nitrogen Flux (mmol · m-· h-1) 
Flux 

• 
189G 189S 6 CPG GES GIG GIS Pl 1 G Pl2G SKG TPG TSG TSS 

Station 
• 
• 

• 
• 
• 
• 
• 

• Figure 9. Ammonia flux. Average flux from 3 replicate cores taken at 
each station. Samples taken in April 1992 . 
• • • • 
l' 
• 26 
• 
• 

Laguna Madre Ammonia Flux (mmol · m -2 · h -1)
• 
Flux 

• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 
Station 
• 

• • • • • 
• Figure 10. Nitrite flux. Average flux from 3 replicate cores taken at each 
station. Samples taken in April 1992 . 
• 
• 
• 
• 

• 27 
• 
• 

Laguna Madre Nitrite Flux (mmol · m -2 · h -1)
• 
Flux 
1.2 
• 
1. 1 

• 
0.8 

• 
0.5 

0.3 

• 
0.2 


1.0 
0.9 
0.7 
0.6 
0.4 
0.1 
0.0 
• -0.1 
-0.2 
-0.3 

• 

• 

• 


• 
• 
• 
• 
• 

• Figure 11. Nitrate flux. Average flux from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• • • • 
t' 
; 
• 28 
• 
• 

• 2
Laguna Madre Nitrate Flux (mmol · m-· h-1) 

• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 
Station 
• 
• 
• 
• 
• 
• 

• 
• Figure 12. Phosphate flux. Average flux from 3 replicate cores taken at 
each station. Samples taken in April 1992 . 
• 
• 

• 
• 29 

• 
• 

2
Laguna Madre Phosphate Flux (mmol · m-· h-1)
• 
Flux
0.4 
--.--~~~~~~~~~~~~~~~~~~~~~~~~~~-----, 
0.3 
0.2 
0.1 
• 
• 

189G 1895 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 
Station 
• 
• 
• 
• 
• 

• Figure 13. Silicate flux. Average flux from 3 replicate cores taken at each 
station. Samples taken in April 1992 . 
• • • • 
• 30 
• 
• 

2
Laguna Madre Silicate Flux (mmol · m-· h-1)
• 
Flux 

• 
1 89G 189S 6 CPG GES GIG GIS Pl 1 G Pl2G SKG TPG TSG TSS 

Station 
• 
• 

• • • • • 
• Figure 14. Macrofauna abundance at two sediment depths. Average number of individuals from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• 
• 
• 

!• 
• 31 
• 
• 

Laguna Madre Macrofauna Abundance (n · m -2)
• 
Number 
60,000 
• 
50,000 
• 40,000 
• 30,000 
20,000
• 
10,000 
• 
0 
• 
• 
• 


• • • • • 
• 
Figure 15. Macrofauna biomass at two sediment depths. Average dry 
weight from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• 
• 
• 

• 32 
• 
• 

Laguna Madre Macrofauna Biomass (g · m -)
• 2
189G _189S 6 CPG GES GIG GIS Pl 1 G Pl2G SKG TPG TSG TSS . • Station Section (cm) (\\\3 0-3 
-·3-10 
• 

• 
• 

• 
• 
I 
I• 
• Figure 16. Macrofauna taxa abundance. Average number of individuals from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• • • • 
• 
33 
• 
• 

• 
Laguna Madre Macrofauna Abundance (n · m-2) 

Number 
60,000~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-, 
• 
50,000 
• 40,000 
• 
30,000 
20,000 
• 
10,000 
• 
0 189G 189S 6 CPG GES GIG GIS Pl 1 G Pl2G SKG TPG TSG TSS 

Station
• Taxa Crustacea l\\\1 Mollusca lS09<.SOO?J Others VZ//J Polychaeta 
• 

• 

• 
• 
• 
• 
• 

• Figure 17. Macrofauna taxa biomass. Average dry weight from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• .._ 
• 
• 
• 

34 


• 
• 

Laguna Madre Macrofauna Biomass (g · m -2)
• 
Dry Wt.
40 
• 
30 
• 
20 
• 
• 10 • 0 s s 
1 1 T T 1 1 T T 1 1 T T 1 1 T T Station 8 8 s s 8 8 s s 8 8 s s 8 8 9 9 G s 9 9 G s 9 9 G s 9 9 G s G s G s G s G s 
• 
~ JAN92 --1 ~ APR92 --1 ~ JUL92 --1 ~ OCT92 --1 Date 
Section (cm) 3-10 [""-"""'-Sl 0-3 
• 
• 
• 
• 
• 
• 
• 

• Figure 18. Macrofauna species principal factor analysis. Samples taken in April 1992 . 
• • • • 
• 35 
• 
• 

Laguna Madre Macrofauna Biomass (g · m -2)
• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 

• Taxa ~~Crustacea tsOOOQO(j . Others 
Station 
l\\\1 Mollusca VZ//] Polychaeta 
• 

• 
• • • 
• Figure 19. Macrofauna species diversity. Average Hill's index, N1, from 3 replicate cores taken at each station. Samples taken in April 1992 . 
• 
• 
• 

~~CIENCEL1BRAR'₯ 150 tty of~exes at Austin
• Port ~lvicwDrive 
~aoaas • TX 18373 
U.S.A. 
• 36 
• 
• 

Laguna Madre Macrofauna Species Principal Factor Analysis 
• 
Factor 1 
-

1.0 -
• 
0.8 
-
0.6 • ­
0.4 
-
0.2 
• 0.0 
-
-0.2 
• ­
-0.4 -0.6 
-
• 
-0.8 ­
-
-1.0 
PIVi
TPG
CPG 
M189G 
SKG 
GIG 
M1 B9S 
TSG
Pl2G 
GIS 
, 
GES 
TSS 
M6 
-· 

I I I I 
• 
I T I I I 
I I I I I I
I I T I I 
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 
Factor 2 
• 
• 

• • • • • 
• Figure 20. Macrofauna species evenness. Average Hill's index, E1, from 
3 replicate cores taken at each station. Samples taken in April 1992 . 
• • • • 
• 37 
• 
• 

Laguna Madre Macrofauna Diversity
• 

• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 
Station 
• 
• 

• • • • • 
• Figure 21. Relationship between species diversity and evenness. Average Hill's index, E1 and N1, from 3 replicate cores taken at each station. Samples taken in April 1992. 
• 
• 
• 

. . 
:--..
. 
• 38 
r--------------------------------­
• 
• 

Laguna Madre Macrofauna Eveness 
• 
E1 

• 
189G 189S 6 CPG GES GIG GIS Pl1 G Pl2G SKG TPG TSG TSS 
Station 
-· 
• 
• 
• • • • 
• 
Figure 22. Sediment organic matter at two sediment depths over one 
year. Average number of individuals from 3 replicate cores taken at three 
stations . 
• 
• 
• 
• 

• 
39 
• 
• 

Laguna Madre Diversity and Eveness 
• 	E1 


1.0 ­
TSS 
• 	189S 
0.9 	­TSG 
GIG GIS SKG
• 	189G
0.8 ­
TPG CPG 6 
• 
0.7 ­
PMG 
Pl2G 
• 
0.6 ­GES 

0.5 ­
• 
• 

• • • • • 
• Figure 23. Sediment organic matter components over one year. Average dry weight from 3 replicate cores taken at three stations . 
• 
• 
• 

• 
• 40 

• 
• 
Laguna Madre Sediment Organic Matter (g · m-2)
• 
Dry Wt. 
1900~~~~~~~~~~~~~~~~~~~~~~~------. 
• 
1800 
1700 

1600 
1500 
1400 

• 
1300 1200 1100 1000 

• 
• 
900 800 700 600 500 400 


300 
200 
100 

1  1  T  T  
8  8  s  s  
9  9  G  s  
· G  s  
~  OCT92~  

Station 8 8 s s 8 8 s s 8 8 s s 
9 9 G S 9 9 G S 9 9 G s 
G S G S G s 
1 1 T T 1 1 T T 1 1 T T
• 0 
• Date
~ JAN92 ~ ~ APR92 ~ ~ JUL92 ~ 
Section (cm} 
3-10 [""'""'""'~ 
0-3 

• 
• 

• 
• 
• 
• 
• 

• 
Figure 24. Macrofauna abundance at two sediment depths over one year . 

Average number of individuals from 3 replicate cores taken at three stations . 
• 
• 
• 

• 
• 
41 

• 
• 
Laguna Madre Sediment Organic Matter (g · m -2)
• 
Dry Wt. 
1900~~~~~~~~~~~~~~~~~~~~~~~-, 
1800 
• 
1700 1600 1500 1400 

• 	
1300 1200 1100 1000 

900 
800


• 
700 600 500 400 300 200 100 
• 


Station
1 1 T T 1 1 T T
• 0 
8 8 s s 8 8 s s 
9 9 G S 9 9 G s 
G S G s 

• 
Date~ JAN92 -i ~ APR92 ~ 
DetritusCof!lponent 
1 1 T T 1 1 T T 
8 8 s s 8 8 s s 
9 9 G s 9 9 G s 
G s 	G s 
~ JUL92 -i ~ OCT92-i 
l\\S'\I Roots IS9@0?J Seagrass 
• 

• 

• 
• 

• 
• 
• 

• Figure 25. Macrofauna biomass at two sediment depths over one year. Average dry weight from 3 replicate cores taken at three stations . 
• 
• 
• 
• 
• 42 
• 
• • • • • • • • • • 
Laguna Madre Macrofauna Abundance (n · m -2) Number 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 0 1 1 T T 1 1 T T 1 1 T T Station 
8 8 s s 8 8 s s 8 8 s s 
9 9 G S 9 9 G S 9 9 G S 

G S G S G S 
~ JAN92 -i t-APR92 ~ ~ JUL92 -i Date Section (cm) .... 3-1 o l'\SS"\1 0-3 

• 

• 

• • • • • • • 
• 

DISCUSSION 
There is increasing demand to mitigate the loss of wetland habitats. Wetland loss is a recognized problem nationwide. Texas alone has lost over 240,000 ha of its original wetlands primarily to dredge and fill operations (Gosselink and Bauman, 1980). The problem is acute for seagrass beds, which are a submerged wetland habitat. Currently there is about 68,500 ha of seagrass beds in Texas estuaries (Duke and Kruczynski, 1992). Many of these habitats are at risk due to geomorphological changes by hurricanes, subsidence due to groundwater and hydrocarbon extraction, dredging for channels, filling and other development activities. Risk for seagrass loss is apparently higher in the northeastern Texas coa~t, because of higher population density and greater amounts of subsidence (White et al., 1985). For example, in Galveston Bay, Texas, 95% of the seagrass beds have been lost since 1979 (Pulich and White, 1990). In contrast, seagrass beds in the southwestern coast, which includes the Laguna Madre, have changed less. Since 1965, there has been a gain of 130 km2 of Halodule wrightii seagrass cover in the upper Laguna Madre, and a 330 km2 los,s in the lower Laguna Madre for a net loss of 200 km2 (Quammen and Onuf, 1993). Current state and national policy requires mitigation for new habitat losses . 
Mitigation projects have not always been successful. Of eight recent seagrass mitigation projects in south Texas, four failed to be effective (Cobb, 1987). Projects in this evaluation were judged as effective if seagrass grew back by either transplantatiqn or natural revegetation. Recently, concern has been raised that these created or restored habitats may have grass cover, but are not functioning like a normal seagrass habitat (Quammen, 1986; Fonseca et al., 1990). A new definition of "success" is the replacement of lost wetland function based on judgements that can withstand scientific review (Pacific Estuarine Research Laboratory, 1990). However, this could be difficult to implement. Any monitoring or sampling effort would be of limited duration and could be distorted by a R-selected or disturbance species, and we probably cannot replace the complex interactions that took up to centuries to evolve (Pacific Estuarine Research Laboratory, -1990). Much ecological research will be needed before we know what to measure, and how to interpret our measurements. We will also expect this research to provide recommendations for better planning of mitigation projects. 
·· The current research is designed to identify some criteria for a successful mitigation project, and the time for a created or resto~ed_ se~grass bed to become a functional habitat. Two approaches were taken. The first was a synoptic study of 10 mitigation sites of different ages, the second is monitoring of a recent mitigation site for a one year period. No one study can possibly examine all, or even most, of the 
43 

• • • • • • • • 
complex interactions in any ecosystem. These interactions can be grouped into two categories: structure and function. Structure refers to the composition of the ecosystem. The components are both biotic and abiotic. Function refers to the characteristic behavior of the system. Energy flow, trophic relationships and biogeochemical cycling are functional components that are unique to specific ecosystems. Seagrasses are benthic plants, so the creation or restoration of a seagrass habitat must duplicate the structure and function of an undisturbed benthic environment. In seagrass ecosystems, Ecosystem structure and function is assessed by measuring select variables. Community metabolism and nutrient regeneration are key variables, which indicate the functioning of an ecosystem. Benthic community structure is a key variable that indicates the habitat utilization of an ecosystem. The six mitigation sites are compared to three reference sites with seagrass and one open bay station. 
Below ground, the Eh profiles show dramatic differences among natural and mitigation sites, and also suggest trends with mitigation site aging (Figure 4). Eh is a measure of the total electronegativity of the sediment. Reduced ions, e.g., NH 4 and H2S are major contributors to Eh. These ions are evolved via anaerobic respiration during the decomposition of organic matter. So, Eh can be thought of as the total number of available electron donors. Low Eh values were typical of sediments in recent mitigation sites. This indicates there is might be low organic content in the mitigation sediments. This indication is supported by the measurements of sediment organic matter (Figures 5 and 6). Total oxygen consumption was also lower in mitigation sites (Figure 7). Both organic matter and oxygen flux exhibited increasing trends with habitat age. , The mitigated ecosystems are not functioning biogeochemically like a natural ecosystem. The mitigation sites lack sufficient organic material in the sediment for the environment to be fully functional. It appears as if it may take up to 14-17 years for enough organic matter to accumulate at these sites for the processes to be occurring at similar rates to natural sites. 
Above-ground, the mitigation sites differed from natural sites in terms of community structure. Utilization of mitigation sites by benthic macrofauna increases with age of the habitat (Figures 14-17). Both abundance and biomass increase along the gradient of new mitigation, old mitigation, and natural sites. Benthic community structure at the mitigation sites resembled disturbed environments with high diversity, and low evenness (Figures 19-21 ). There was also a qis~ernible trend in diversity and evenness among sites of different ages. As with the biogeochemical data, the benthic invertebrate data suggests it may take longer than 14-17 years to fully recover. Since this is such a long time, monitoring for one year did not reveal these differences. 
44 

• • • • • • • 
The lack of adequate biogeochemical functioning has been found at other locations. There were low amounts of sulfide and nitrogen in man-made salt marsh sediments of the Sweetwater River Wetlands, San Diego Bay, California (PERL, 1990). Benthic invertebrates were 54-55% less abundant in constructed than in natural habitats. PERL (1990) concluded that the man-made habitat was not functioning like a natural habitat. 
Monitoring to determine success of a project can not be done over a short time scale. Monitoring to determine persistence of seagrass cover should occur for at least three years (Fonseca, 1989). Epifaunal colonization of eelgrass habitats in North Carolina can happen rapidly. Faunal abundances of fish and shrimp in a 1.9-year old transplanted bed and a 6-month old seed-developed bed were indistinguishable from mature natural seagrass beds (Fonseca et al., 1990). This indicates that mobile fauna can establish themselves in mitigated habitats rapidly. In fact, most studies on the utilization of submerged vegetated habitats have focused on use by mobile invertebrates, megaepifauna (e.g., shrimp), or fish (Rozas and Odum, 1987a; 1987b; Fonseca et al., 1990). If mobile species that colonize rapidly are studied then Qne can come to an erroneous conclusion that the ecosystem is functional. The current study focuses on the utilization of these habitats by infauna, and small seagrass epifauna (e.g., amphipods). The lack of mobility and reliance on a dispersal stage by macroinfauna, could explain why utilization of the mitigated habitats in the current study was not comparable to utilization of natural habitats. In Texas, macroinfauna were not as abundant in mitigated habitats that were one or two years old, as they were in natural habitats, or in habitats that were 14-17 years old. Therefore, it appears that monitoring for several year$ would be required to assess utilization by the benthic component. 
A major contributing factor to the loss of seagrass habitats is the issuance of permits by the U.S. Army Corps of Engineers. The reestablishment of wetland fishery habitats and their ecological function is an important national goal of several federal agencies, e.g., the National Marine Fisheries Service (Thayer et al., 1986). Some might argue-, that the spoil islands are a beneficial use of dredge materials since they create bird habitat. However, many of these islands contain few birds, because predators (e.g., coyotes and rattlesnakes) can overrun these islands rapidly. So, there has been a value-judgement that bird habitat may be more valuable than seagrass habitat. In the upper Laguna Madre, where the current_ research took place (Figure 1 ), 6% of the seagrass habitat has been converted to spoil islands and channels (Montagna, unpublished data). This determination was made by calculating the surface area of these environments from aerial photographs. One of the mitigation projects 
45 

• • • • • • • 
studied here (site TS_) is a scrapedown of a spoil island to revert the habitat back to a seagrass bed. This habitat is very well covered by seagrass, and probably will become a functioning habitat in time. Although it will take a long time, this project appears to be a good example of how federal agencies can meet their goals to restore fisheries habitats that have been lost. The restored habitats can contribute to enhanced productivity and fisheries habitats (Thayer et al., 1982), therefore it seems reasonable to convert spoil islands back to their original habitat. 
Recommendations: Future projects to transplant seagrasses for mitigation should consider adding organic matter to the soil to speed the time it takes for the habitat to become fully functional. Currently, without soil emendation, it probably requires 14-17 years for seagrass habitats to become fully functional. Monitoring must be long-term. Short-term monitoring is not the best approach to discern when a habitat acquires functional values. Annual sampling over four years would be a better monitoring plan for the same effort than quarterly sampling over one year. Benthic macrofauna abundance and biomass are good monitoring tools to determine community structure changes, since they are relatively fixed in space and have meaningful temporat scales of response. Total organic matter or Eh profiles are good, cost effective monitoring tools for ecosystem function. It is not useful to make routine measurements of nutrient regeneration, but oxygen consumption will indicate the biogeochemical status of the ecosystem in a relative sense. Comparison with natural undisturbed habitats is essential, but is important to replicate at the treatment level, i.e., replicate natural and mitigation sites are required to find differences related to mitigation success. 
ACKNOWLEDGEMENTS 
I would like to thank Mr. Rick Kalke, the University of Texas Marine Science Institute, for his invaluable help on all aspects of this project. The nutrient samples were analyzed under the direction of Dr. Terry Whitledge. Carol Simanek was responsible·
-for all aspects of data management for the project. This project was funded in part by Cooperative Agreement no. X-0658801-0, from the Water Management Division of the U.S. Environmental Protection Agency, Region 6; and in part by grant no. 3658-264 from the Texas Advanced Technology Program. 
46 

• 

• • • • • 
• 
• 
• 

REFERENCES 

Alatalo, RV. 1981. Problems in the measurement of evenness in ecology. Oikos, 
37: 199-204. 
Cobb, 	R. A. 1987. Mitigation evaluation study for the South Texas Coast, 1975-1986. Report to U.S. Fish and Wildlife Service. Corpus Christi State University, Corpus Christi, Texas, 88 pp. 
Duke, T. and Kruczynski, W.L. 1992. The status and trends of emergent and submerged vegetated habitats of Gulf of Mexico coastal waters, U.S.A. Final Report to the U.S. Environmental Protection Agency, Gulf of Mexico Program, Habitat Degradation Subcommittee. Gulf Breeze, Florida. 161 pp. 
Folk, R. L. 1964. Petrology of sedimentary rocks. Hemphill's Press, Austin, Texas. 155 pp. 
Fonseca, M.S. 1989. 	Regional analysis of the creation and restoration of seagrass systems. In: Kusler, J.A. and M.E. Kentula (eds.). Wetland creation and restoration: the status of the science. Volume I: regional rf]views. 
EPA/600/3-89-038a. Environmental Research Laboratory, Corvallis, Oregon. pp. 175-198 . 
Fonseca, M.S., W.J. Kenworthy, D.R. Colby, K.A. Rittmaster and G.W. Thayer. 1990. Comparisons of fauna among natural and transplanted eelgrass Zostera marina meadows: criteria for mitigation. Marine Ecology Progress Series, 65:251-264. 
Gosselink, J.G. a!1d R.H. Bauman. 1980. Wetland inventories: wetland loss along the United States coast. J. Geomorphol. Supp. 34:173-187. Hill, M. 0. 1973. Diversity and evenness: a unifying notation and its consequences. Ecology. 54:427-432. · 
Kikuchi, T. 1974. Japanese contributions on consumer ecology in eelgrass (Zostera marina L.) beds, with special reference to trophic relationships and resources in inshore fisheries. Aquaculture, 4:145-160. 
Kirk R. E. 1982. Experimental Design. 2nd Ed. Brooks/Cole Publ. Co., Monterey, California, 911 p. Langdon, C., 1984. Dissolved oxygen monitoring system using a pulsed electrode: 
design, performance, and evaluation. Deep Sea Research, 31:1357-1367. 
Margalef, R. 1958. Information theory in ecology. General Systematics, 3:36-71. 
Montagna, P.A. 1989. Nitrogen Process Studies (NIPS): t.he ~ffect of freshwater inflow on benthos communities and dynamics. Technical Report No. TR/89-011, Marine Science Institute, The University of Texas, Port Aransas, TX, 370 pp. 
47 
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Montagna, P.A. and R.D. Katke. 1992. The effect of freshwater inflow on meiofaunal and macrofaunal populations in the Guadalupe and Nueces Estuaries, Texas . Estuaries, 15:307-326. 
Nixon, S. A., C.A. Oviatt, J. Frithsen, B. Sullivan. 1986. Nutrients and the productivity of estuarine and coastal marine ecosystems. Journal ofthe Limnological Society of South Africa, 12:43-71 
Pacific Estuarine Research Laboratory. 1990. A manual for assessing restored and natural coastal wetlands with examples from southern California. California Sea Grant Report No. T-CSGCP-021. California Sea Grant College, La Jolla. 105 
p . 
Pielou, E.C. 1975. Ecological Diversity. Wiley, New York. 
Pulich, W.M., Jr., and W.A. White. 1990. Decline of submerged vegetation in the Galveston Bay system: chronology and relationships to physical process. Report to the Texas Parks and Wildlife Department, Austin, Texas. 27 pp. 
Quammen, M.L. 1986. Measuring the success of wetlands mitigation. National Wetlands Newsletter, 8:6-8. Quammen, M.L. and C.P. Onuf. 1993. Laguna Madre: seagrass changes continue decades after salinity reduction. Estuaries, 16:302-310 . 
Robinson, G. R., R. D. Holt, M. S. Gaines, S. P. Hamburg, M. L. Johnson, H. S. Fitch and E. A. Martinko. 1992. Diverse and contrasting effects of habitat fragmentation. Science, 257:524-526. 
Rozas, LP. and W.E. Odum. 1987a. Fish and macrocrustacean use of submerged plant beds in tidal freshwater marsh creeks. Marine Ecology Progress Series, 38:101-108. 
Rozas, LP. and W.E. Odum. 1987b. The role of submerged aquatic vegetation in influencing the abundance of nekton on contiguous tidal fresh-water marshes . Journal of Experimental Marine Biology and Ecology, 114:289-300. 
SAS Institute, Incorporated. 1985. SAS/STAT Guide for Personal Computers, Version 6 Edition. Cary, NC:SAS Institute Inc., 378 pp. Shannon, C. E. and W. Weaver. 1949. The Mathematical Theory of Communication. University of Illinois Press, Urbana, IL. 
Simpson, E.H. 1949. Measurement of diversity. Nature, 163:688. 
Thayer, G. W., M. S. Fonseca and W. J. Kenworthy. 1982. Restoration of seagrass meadows for enhancement of nearshore productivi!Y· pp. 21-27. In N. L Chao and W. Kirby-Smith (eds.), Proceedings of the lntnl. Symposium on Utilization 
of  Coastal  Ecosystems:  Planning,  pollution  and  productivity.  Fundacao  
Unversidade de Rio Grande, Rio Grand.  MARINE SCIENCE LIBRARY  
The University ofTexas at Austin  
48  1SO Channelview Drive  
Port Aransas , TX 78373  
U.S.A.  

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Thayer, G. W., M.S. Fonseca, W.J. Kenworthy. 1986. Wetland mitigation and restoration in the Southeast United States and two lessons from seagrass 
mitigation. In: Estuarine Management Practices Symposium, Baton Rouge, LA, pp. 95-117. White, W.A., T.R Calnan, RA Morton, RS. Kimble, T.G. Littleton, J.H. McGowen, 
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H.S. Nance and K.E. Schmedes. 1985. Submerged lands of Texas, 
• 
Galveston-Houston area: sediments, geochemistry, benthic macroinvertebrates, 
and associated wetlands. Bureau of Economic Geology, Austin, Texas. 145 pp. 
Whitledge, T.E., Veidt, D.M., Malloy, S.C., Patton, C.J. Wirich, C.D. 1986. Automated 
nutrient analysis in seawater. Brookhaven National Laboratory Report 38990 . 

Upton, New York, 231 pp . 
• • • • • • • 
49 

• 
Table 1. Sampling locations. A. Station identification, location, habitat, date of planting, • and project applicant and U.S. Army Corps of Engineer permit number. B. Locations determined by global positioning system (GPS). Abbreviations: ICW=lntracoastal Waterway, BB=Baffin Bay. 
• 
A. 
Station Location Habitat Date Project 
APR91 APR91 Natural Natural APR90 APR90 APR90 AUG75 
1978 OCT83 Natural Natural Natural 
• • • • 
N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna N Upper Laguna S Upper Laguna S Upper Laguna Baffin Bay 
B. 

Grass Sand Grass Grass Grass Sand Grass Grass Grass Sand Grass Sand Mud Gulf Isles Limited 9009(08) Gulf Isles Limited 9009(08) Padre Isles Site 1 Padre Isles Site 2 Transco Scrape-down 18853 Transco Scrape-down 18853 Transco Pipeline 18853 ~ Central Power and Light 100444 Skyline Equipment, Inc. 12004(03) Genesis Petroleum 15844 West of ICW Marker 189 West of ICW Marker 189 North of BB Marker 6 site GIG GIS Pl1G Pl2G TSG TSS TPG CPG SKG GES 189G 189S 6 
Station Latitude (N) . Longitude (W) Error (m) 
• 
97° 15' 0.5'' 97° 14' 49.6" 97° 15' 22.2" 97° 15' 19.6" 97° 15' 9.7" 97° 17' 55.7" 97° 17' 46.1" 97° 16' 3.5" 97° 23' 30.1" 97° 25' 39.2" GI 27° 36' 32.6" Pl1 27° 36' 33.9" Pl2 . 27° 35' 6.3" TS 27° 35' 56.0" TPG 27° 35' 22.8" CPG 27° 36' 28.5" SKG . 27° 36' 40.4" GES 27° 34' 34.0" 189 27° 20' 53. 7" 6 27° 16' 36.6" 
±57 ±74 ±303 ±110 ±81 ±48 ±101 ±20 ±118 ±14 
50 

• 
• 

• 
• • • • 
• 

Table 2. Hydrographic measurements. Abbreviations: ST A=Station, Z=Depth, SAL(R)=Salinity by refractometer, SAL(M)=Salinity by meter, COND=Conductivity, TEMP= Temperature, DO=dissolved oxygen, and ORP=oxidation redox potential. Missing values show with a period . 
Date STA Z SAL(R) SAL(M) COND TEMP pH DO ORP NTU 
(m) (ppt) (ppt) (uS/cm) (oC) (mg.r1) (mV) 
21JAN92 155  0.00  28  28.2  43.70  10.63  8.64  9.53  0.125  
21JAN92 155  1.10  28  28.3  43.70  10.64  8.64  9.47  0.125  
21JAN92 189  0.00  29  29.0  44.70  10.48  8.55  9.62  0.117  
21JAN92 189  1.00  29  29.0  44.80  10.47  8.67  9.50  0.115  
21JAN92 6  0.00  32  32.8  50.00  9.99  8.46  9.29  0.130  
21JAN92 6  2.40  32  34.6  52.50  9.97  8.62  8.16  0.126  
21JAN92 TS  0.00  24  24.7  39.00  12.65  8.52  9.78  0.131  
08APR92 189  0.00  25  25.5  39.70  23.97  8.77  8.83  0.144  
08APR92 189  1.00  25  25.5  39.70  24.00  8.77  8.76  0.142  
08APR92 6  0.00  25  24.4  38.20  21.05  8.31  7.82  0.145  
08APR92 6  2.20  25  24.6  38.70  20.75  8.57  6.30  0.136  
22APR92 GIG  0.00  24  23.4  37.10  22.46  9.19  6.31  0.094  4.4  
22APR92 GIG  0.10  24  23.5  37.20  22.51  9.09  6.25  0.097  4.4  
22APR92 Pl1  0.00  2~  23.2  36.80  26.95  9.81  12.63  -0.055  
22APR92 Pl1  0.20  24  23.4  37.00  26.93  9.93  12.36  -0.026  
23APR92 189  0.00  26  25.5  40.00  26.13  9.27  9.40  0.100  
23APR92 189  0.80  26  25.5  40.00  26.07  9.52  8.92  0.098  
23APR92 6  0.00  24  23.6  37.40  24.33  8.56  7.68  0.137  
23APR92 6  2.20  24  27.0  42.10  23.90  8.85  5.20  0.130  
24APR92 TPG  0.00  26  24.4  38.40  26.27  8.64  6.14  0.126  6.6  
24APR92 TPG  0.60  26  24.5  38.50  26.29  8.77  6.07  0.126  6.3  
24APR92 TSG  0.00  24  23.9  37.70  25.43  8.64  5.72  0.132  6.6  
24APR,92 TSS  0.40  24  23.8  37.70  25.15  8.60  4.21  0.149  6.6  
27APR92 CPG  0.00  25  25.0  39.30  24.17  9.12  8.49  0.089  6.0  
27APR92 CPG  0.55  25  25.0  39.30  24.17  9.12  8.49  0.089  6.0  
27APR92 SKG  0.00  25  24.2  38.20  22.14  8.37  7.30  0.139  5.2  
27APR92 SKG  0.35  25  24.2  38.20  22.14  8.37  7.30  0.139  5.2  

51 

• 

• 
28APR92 GES 0.00 25 24.8 38.30 21.78 9.19 5.13 0.108 19.0 28APR92 GES 0.90 25 24.7 38.30 21.76 8.93 4.96 0.289 19.0 
• 
28APR92 Pl2 0.00 26 25.0 39.20 23.67 9.41 8.40 0.098 28APR92 Pl2 0.75 26 25.0 39.40 23.65 9.44 8.38 0.100 08JUL92 189 0.00 20 18.8 30.40 29.80 9.03 8.25 0.187 08JUL92 189 0.70 20 18.8 30.60 29.80 9.03 8.20 0.182 
• 
08JUL92 6 0.00 18 16.8 27.60 29.14 8.73 8.51 0.208 08JUL92 6 2.00 18 24.4 38.50 28.90 8.34 3.29 0.227 08JUL92 TS 0.00 21 20.5 33.00 32.91 8.80 8.10 0.171 200CT92 189 0.00 36 33.3 53.30 25.37 8.47' 7.35 0.166 200CT92 189 0.90 36 33.3 53.40 25.28 8.60 6.86 0.174 
200CT92 6 0.00 35 33.6 51.00 24.91 8.47 7.28 0.176 
200CT92 6 2.40 35 34.0 51.50 24.68 8.63 5.12 0.172 
200CT92 TS 0.00 38 31.8 48.50 26.45 8.55 8.52 0.177
• 
• 
• 
• 
• 
• 
• 52 
• 

Table 3. Sediment grain size in Laguna Madre. Percent dry weight of each sediment • fraction . 
• 
Date Station Depth Rubble Sand Silt Clay (cm) (%) (%) (%) (%) 
• 
23APR92 6 3 1.4 3.3 14.7 80.6 23APR92 6 10 3.9 8.4 19.8 67.9 23APR92 189G 3 20.7 55.9 3.8 19.6 
23APR92 189G 10 10.3 47.7 7.4 34.5 23APR92 189S 3 20.9 60.7 3.1 15.2 23APR92 189S 10 10.9 50.3 5.2 33.6 23APR92 GIG 3 4.3 83.1 4.2 8.5 
• 
• 
• 23APR92 · GIG 10 2.5 89.3 2.6 5.5 23APR92 GIS 3 5.0 90.7 2.1 2.1 23APR92 GIS 10 4.5 90.3 1.8 3.3 23APR92 Pl1G 3 9.7 54.5 10.1 25.7 23APR92 Pl1G 10 1.0 91.8 1.4 5.8 24APR92 CPG 3 8.8 70.2 12.3 8.7 24APR92 CPG 10 10.4 78.8 1.0 9.8 27APR92 GES 3 0.5 62.7 5.8 31.0 27APR92 GES 10 1.7 94.2 0.1 4.0 
• 
24APR92 Pl2G 3 14.0 73.6 2.1 10.3 24APR92 Pl2G 10 3.9 89.4 1.1 5.6 24APR92 SKG 3 4.0 91.2 0.4 4.5 24APR92 SKG 10 2.2 92.2 3.4 2.2 
24APR92 TPG 3 2.2 94.5 0.4 2.9 24APR92 TPG 10 2.7 94.8 0.6 1.9 24APR92 -TSG 3 4.6 87.6 2.0 5.8• 24APR92 TSG 10 14.6 83.2 0.9 1.3 24APR92 TSS 3 2.4 94.5 1.0 2.0 24APR92 TSS 10 3.7 93.9 1.3 1.1 
53 

• 

Table 4. Eh profiles in sediment cores. Values are the oxidation redox potential in mV • at the sediment depth horizon. Missing values show with a period . 
• 
Sediment Depth (cm) 
Date Station 0 1 2 3 4 5 6 7 8 9 10 
• 
22APR92 GIG 66 30 18 -4 -14 -10 -4 -9 -7 -14 -3 
22APR92 GIS 25 -245 -7 -10 -9 -10 -12 -15 4 6 22APR92 Pl1G 6 -285 -320 -310 -320 -20 -147 -173 -240 
23APR92 6 94 39 21 -18 -400 -484 -451 -431 -432 -422 
• 
23APR92 189S 6 -355 -327 -325 -330 -300 -240 -326 -333 -345 
• 
• 
23APR92 189G-150 -326 -364 -363 -357 -355 -362 -360 -357 -348 -352 24APR92 TSS 22 20 0 -1 0 0 -4 -6 -2 -4 -5 24APR92 TSG 23 20 13 3 -1 -18 -50 -71 -150 -150 -140 24APR92 TPG 22 13 8 -1 -25 -40 -67 -110 -120 -200 -110 27APR92 SKG 40 32 32 29 28 22 17 7 -91 -290 -306 27APR92 CPG 25 -220 -260 -310 -326 -310 -353 -334 -339 -330 -376 28APR92 GES 4 -200 -313 -388 -330 -344 -285 -230 -275 -305 -319 28APR92 Pl2G 48 -9 -275 -350 -343 -347 -333 -336 -334 -340 -342 
54 

• 

• 
Table 5. Oxygen measurements in sample incubations. Oxygen units in ΅mole. r1• Missing values show with a period. Core 4 is a control with just station water. 
• 
Date Station Time Core 1 Core 2 Core 3 Core 4 
• 
• 
22APR92 GIG 10:25 213.9 277.9 359.9 311.2 22APR92 GIG 10:40 183.9 251.0 361.4 347.9 22APR92 GIG 10:55 163.3 226.4 328.9 344.4 22APR92 GIG 11 :10 160.9 201.7 310.4 343.7 22APR92 GIG 11:25 129.8 163.4 281.1 341.5 22APR92 GIG 11:40 104.4 151.0 215.6 338.3 22APR92 GIG 11 :55 102.8 132.6 222.9 339.2 
22APR92 GIG 12:10 109.3 126.8 204.9 336.9 
• 
22APR92 GIS 12:40 304.3 356.9 446.2 400.4 22APR92 GIS 12:55 263.5 352.8 457.9 402.8 22APR92 GIS 13:10 281.0 357.4 456.5 404.7 
22APR92 GIS 13:25 287.5 373.1 474.0 406.4 22APR92 GIS 13:40 299.6 381.0 482.4 405.7 22APR92 GIS 13:55 292.7 379.5 481.4 404.8• 22APR92 GIS 14:10 285.1 375.6 471.5 402.6 22APR92 GIS 14:40 246.0 365.7 459.4 398.3 
22APR92 Pl1G 14:55 313.6 317.6 434.3 380.4• 22APR92 Pl1G 15:10 236.8 220.2 329.8 390.1 22APR92 Pl1G 15:25 176.1 131.0 231.6 395.5 22APR92 Pl1G 15:40 114.3 63.2 162.1 398.5 22APR92 -Pl1G 15:43 87.5 37.3 127.5 399.5 • 22APR92 Pl1G 15:47 78.8 25.8 125.0 399.9 22APR92 Pl1G 16:02 40.8 0.1 111.4 400.3 
23APR92 886 10:42 178.7 279.3 343.1 342.8 23APR92 · 886 11 :12 160.0 263.4 330.7 339.0 23APR92 886 11:27 160.0 260.5 294.7 335.4 23APR92 886 11:42 159.4 259.2 303.7 333.1 
55 
• 

• 
23APR92 886 11:57 160.3 260.3 315.7 331.8 23APR92 886 12:12 157.3 242.8 313.4 332.4 
23APR92 886 12:27 153.5 217.3 292.0 333.9 
• 
23APR92 189G 13:27 305.7 343.8 443.8 382.9 23APR92 189G 13:42 260.4 296.3 412.4 382.8 
• 
23APR92 189G 13:57 177.3 251.3 370.8 382.2 23APR92 189G 14:12 120.4 243.9 290.8 381.5 23APR92 189G 14:27 48.3 243.6 210.7 380.7 23APR92 189G 14:42 40.9 190.1 143.6 380.4 23APR92 189G 14:57 10.1 159.5 128.6 380.7 23APR92 189G 15:12 0.0 162.0 123.2 379.8 
23APR92 189S 15:27 278.7 346.7 457.2 379.0• 23APR92 189S 15:42 256.5 344.7 441.4 378.5 23APR92 189S 15:57 252.5 344.1 437.7 378.3 23APR92 189S 16:12 242.8 338.6 430.8 377.4 23APR92 189S 16:27 234.7 337.4 428.9 377.4 • 23APR92 189S 16:42 227.8 323.5 422.5 376.4 23APR92 189S 16:57 213.7 312.9 408.3 375.1 23APR92 189S 17:12 208.0 310.2 400.2 374.6 
• 24APR92 TSS 9:30 97.3 195.8 291.9 285.1 24APR92 TSS 9:45 85.5 174.8 282.1 280.0 24APR92 TSS 10:00 76.2 165.7 256.8 275.1 24APR92 TSS 10:15 70.8 138.7 260.4 275.2 • 24APR92 TSS 10:30 67.1 141.9 240.3 269.8 24APR92 TSS 10:45 64.9 134.0 227.7 270.0 24APR92 TSS 11:00 65.9 140.2 223.4 280.3 24APR92 TSS 11 :15 58.6 147.4 214.7 281.4 
1. 
• 
24APR92 TSG 11 :30 181.0 265.7 380.2 337.3 24APR92 TSG 11 :45 96.8 142.2 260.9 342.1 24APR92 TSG 12:00 92.1 104.3 219.3 339.9 24APR92 TSG 12:30 32.1 54.5 182.8 329.9 
24APR92 TSG 12:45 24.4 32.8 155.1 328.2 24APR92 TSG 13:00 31.6 19.6 146.7 327.9 
• 56 
• 

• • • • • • • • 
(~ 
-·

. 
• 

24APR92 24APR92 
24APR92 24APR92 24APR92 24APR92 24APR92 24APR92 24APR92 24APR92 
27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 
27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 27APR92 27 APR92 
28APR92 28APR92 28APR92 28APR92 28APR92 28APR92 
TSG 
TSG 

TPG TPG TPG TPG TPG TPG TPG TPG 
SKG SKG SKG SKG SKG SKG SKG SKG 
CPG CPG CPG CPG CPG CPG CPG CPG ·CPG 
GES GES GES GES GES GES 
13:15 
13:30 
13:45 
14:00 
14:15 
14:30 
14:45 
15:00 
15:15 
15:30 
9:54 
10:09 
10:24 
10:39 
10:54 
11 :09 
11:24 
11:39 
11:54 
12:09 
12:24 
12:39 
12:54 
13:09 
13:24 
13:39 
13:54 
9:36 
9:51 
10:06 
10:21 
10:36 
10:51 37.6 
27.4 
182.7 
111.3 
42.4 
23.6 
21.5 
13.0 
3.6 
0.0 
299.6 
218.2 
148.7 
77.8 
35.5 
16.4 
6.7 
9.8 
310.2 
197.6 
188.7 
184.8 
188.5 
160.3 
151.8 
66.4 
52.7 
214.4 
198.3 
201.8 
200.1 
201.0 
199.8 
57 20.5 
19.7 
314.7 
280.0 
230.3 
175.5 
115.4 
76.0 
55.2 
39.3 
368.5 
263.0 
177.6 
125.8 
114.1 
97.4 
76.4 
50.5 
369.7 
317.1 
293.3 
282.9 
272.2 
258.3 
250.5 
235.9 
216.0 
278.8 
256.8 
247.4 
242.8 
239.7 
243.0 148.9 
145.7 
412.2 
221.3 
124.1 
122.2 
149.8 
138.7 
97.2 
73.5 
445.0 
351.5 
273.9 
176.7 
120.1 
77.8 
51.2 
36.7 
482.2 
425.5 
407.3 
381.8 
368.0 
346.9 
325.2 
311.6 
297.9 
397.3 
390.5 
378.8 
382.5 
373.4 
370.7 325.8 
325.4 
367.5 
364.6 
362.1 
358.5 
353.1 
349.9 
348.0 
345.4 
395.9 
391.3 
387.2 
382.6 
379.5 
378.7 
376.5 
374.3 
397.5 
399.7 
401.8 
401.6 
397.3 
398.1 
393.3 
391.6 
390.0 
363.9 
362.4 
359.8 
358.0 
356.0 
353.3 
• 

• 
28APR92 GES 11 :06 195.1 230.6 373.4 348.9 28APR92 GES 11 :21 188.0 227.8 371.5 345.5 
28APR92 GES 11:36 182.8 232.7 369.8 343.4 
• 
28APR92 Pl2G 12:06 283.8 297.8 441 .3 399.3 28APR92 Pl2G 12:21 222.3 205.8 373.1 402.6 
• 
28APR92 Pl2G 12:36 174.9 133.8 317.3 401.1 28APR92 Pl2G 12:51 132.0 94.5 242.1 399.3 28APR92 Pl2G 13:06 148.9 78.5 249.4 394.2 28APR92 Pl2G 13:21 121.4 56.8 225.9 390.9 
28APR92 Pl2G 13:36 107.4 41 .1 172.0 386.3 28APR92 Pl2G 13:51 86.8 25.1 138.7 384.7 
• • • • • • 

58 

• 
Table 6. Nutrient measurements in sample incubations. Nutrient units in ΅mole.r1 Missing values show with a period. Cores 4 and 5 are controls with just station water. 
• 
Date STA Core Time P04 SI04 N02 N03 NH4 
• 
• 
22APR92 GIG 1 10:20 0.721 141 0.412 0.924 1.960 22APR92 GIG 1 12:20 0.440 143 0.357 0.190 1.622 22APR92 GIG 2 10:20 0.693 141 0.456 0.151 2.507 22APR92 GIG 2 12:20 0.575 143 0.466 0.141 2.361 22APR92 GIG 3 10:20 0.687 141 0.354 0.435 1.819 22APR92 GIG 3 12:20 0.384 143 0.299 0.126 1.577 22APR92 GIG 4 10:20 0.409 142 0.194 1.080 2.202 22APR92 GIG 4 12:20 0.345 141 0.213 0.880 1.095 
22APR92 GIG 5 10:20 0.370 142 0.198 0.955 2.131 22APR92 GIG 5 12:20 0.306 141 0.200 0.771 0.805 22APR92 GIS 1 10:20 0.289 141 0.236 0.006• 22APR92 GIS 1 12:20 0.312 140 0.214 0.332 0.987 22APR92 GIS 2 12:30 0.424 140 0.256 0.169 1.310 22APR92 GIS 2 14:42 0.382 139 0.201 0.466 1.150 22APR92 GIS 3 12:30 0.418 140 0.227 0.319 1.198• 22APR92 GIS 3 14:42 0.299 139 0.205 0.341 0.956 22APR92 GIS 4 12:30 0.433 141 0.264 0.404 1.251 22APR92 GIS 4 14:42 0.347 140 0.241 0.123 1.050 22APR92 GIS 5 12:30 0.503 140 0.267 0.461 1.318 • 22APR92 GIS 5 14:42 0.363 140 0.221 6.335 1.405 22APR92 Pl1G 1 14:52 1.019 138 0.804 5.752 4.504 22APR92 Pl1G 1 16:58 0.651 147 0.553 6.003 2.616 22APR92 Pl1G 2 14:52 1.143 137 0.807 5.748 3.775 • 22APR92 Pl1G 2 16:58 0.872 149 0.516 5.919 2.751 22APR92 Pl1G 3 14:52 1.006 136 0.803 5.753 22APR92 Pl1G 3 16:58 0.833 143 0.519 5.854 2.242 22APR92 Pl1G 4 14:52 0.576 134 0.807 5.810 7.476 
• 
22APR92 Pl1G 4 16:58 0.501 135 0.303 6.010 2.528 
22APR92 Pl1G 5 14:52 0.461 137 0.255 6.300 0.848 22APR92 Pl1G 5 16:58 0.452 135 0.274 6.282 2.389 
• 59 
• 

• 
23APR92 886 1 10:33 2.972 23APR92 886 1 12:33 1.380 
• 
23APR92 886 2 10:33 2.017 23APR92 886 2 12:33 1.422 23APR92 886 3 10:33 1.062 23APR92 886 3 12:33 1.741 
• 
• 
23APR92 886 4 10:33 1.062 23APR92 886 4 12:33 1.125 23APR92 886 5 10:33 1.295 23APR92 886 5 12:33 1.019 23APR92 189G 1 13:18 1.847 23APR92 189G 1 15:18 1.168 23APR92 189G 2 13:18 2.123 23APR92 189G 2 15:18 1.146 23APR92 189G 3 13:18 1.613 
23APR92 189G 3 15:18 1.125 23APR92 189G 4 13:18 0.828 23APR92 189G 4 15:18 0.807• 23APR92 189G 5 13:18 0.764 23APR92 189G 5 15:18 0.764 23APR92 189S 1 15:28 1.231 23APR92 189S 1 17:28 0.807 • 23APR92 189S 2 15:28 0.934 23APR92 189S 2 17:28 1.062 23APR92 189S 3 • 15:28 0.828 23APR92 189S 3 17:28 1.062 • 23APR92 189S 4 15:28 0.807 
• 
23APR92 189S 4 17:28 0.637 23APR92 189S 5 15:28 0.828 23APR92 -189S 5 17:28 0.722 24APR92 TSS 1 9:24 0.442 
i. 
24APR92 TSS 1 11:24 0.566 24APR92 TSS 2 9:24 0.365 24APR92 TSS 2 11 :24 0.501 24APR92 TSS 3 9:24 0.392 
24APR92 TSS 3 11:24 0.447 24APR92 TSS 4 9:24 0.304 
• 60 
168 173 166 168 176 173 161 160 162 159 159 160 159 157 161 162 160 158 185 156 157 155 157 153 156 152 157 156 157 155 171 170 172 172 171 171 171 0.410 
1.000 
0.279 
0.853 
0.779 
1.074 
0.738 
0.681 
0.820 
0.705 
0.500 
0.861 
0.402 
0.828 
0.549 
0. 787 
0.385 
0.312 
0.320 
0.262 
0.713 
0.361 
0.312 
0.640 
0.459 
0.451 
0.262 
0.295 
0.287 
0.295 
0.364 
0.356 
0.395 
0.341 
0.372 
0.354 
0.339 0.554 
0.003 
0.454 
0.027 
0.049 
0.118 
0.184 
0.172 
0.306 
0.133 
0.433 
0.002 
0.300 
0.020 
0.464 
0.047 
0.288 
0.400 
0.448 
0.327 
0.079 
0.362 
0.358 
0.069 
0.197 
0.352 
0.271 
0.711 
0.232 
0.806 
0.402 
0.023 
0.199 
0.334 
0.208 
0.150 
0.070 18.640 
5.287 
7.971 
4.728 
39.448 
8.376 
5.200 
3.924 
4.842 
3.781 
22.794 
6.455 
21.775 
6.542 
9.125 
5.034 
2.060 
1.689 
1.472 
1.302 
4.045 
2.855 
2.681 
4.435 
3.457 
3.905 
0.873 
1.148 
0.888 
1.120 
3.427 
2.778 
2.596 
3.225 
2.738 
3.265 
2.413 
• 

• 
24APR92 TSS 4 11 :24 0.624 24APR92 TSS 5 9:24 0.366 
• 
24APR92 TSS 5 11 :24 0.502 24APR92 TPG 1 13:40 0.604 24APR92 TPG 1 15:40 0.544 24APR92 TPG 2 13:40 0.977 
• 
24APR92 TPG 2 15:40 0.698 24APR92 TPG 3 13:40 0.970 24APR92 TPG 3 15:40 0.529 24APR92 TPG 4 13:40 0.467 
• 
24APR92 TPG 4 15:40 0.430 24APR92 TPG 5 13:40 0.494 24APR92 TPG 5 15:40 0.514 24APR92 SKG 1 9:49 0.694 24APR92 SKG 1 11:49 0.718 24APR92 SKG 2 9:49 0.775 24APR92 SKG 2 11 :49 0.624 24APR92 SKG 3 9:49 0.753• 24APR92 SKG 3 11 :49 1.114 
24APR92 SKG 4 9:49 0.424 24APR92 SKG 4 11 :49 0.406 24APR92 SKG 5 9:49 0.453• 24APR92 SKG 5 11 :49 0.558 27APR92 CPG 1 11 :56 0.833 27APR92 CPG 1 . 13:56 0.703 27APR92 CPG 2 11 :56 0.903 • 27APR92 CPG 2 13:56 0.620 27APR92 CPG 3 11:56 0.677 27APR92 CPG 3 13:56 0.669 27APR92 · CPG 4 11 :56 . 0.573 • 27APR92 CPG 4 13:56 0.412 27APR~2 CPG 5 11:56 0.520 
/ 
• 
27APR92 CPG 5 13:56 0.370 28APR92 GEN 1 9:28 0.766 28APR92 · GEN 1 11 :45 0.493 
28APR92 GEN 2 9:28 2.145 28APR92 GEN 2 11 :45 0.716 
• 61 
170 171 170 193 194 194 194 194 194 195 194 195 194 185 184 185 184 186 186 186 185 185 185 186 186 185 184 185 186 185 185 185 185 182 182 182 182 
0.321 
0.333 
0.334 
0.358 
0.451 
0.427 
0.483 
0.403 
0.376 
0.370 
0.352 
0.374 
0.430 
0.472 
0.385 
0.467 
0.295 
0.353 
0.376 
0.254 
0.269 
0.249 
0.374 
0.541 
0.579 
0.599 
0.489 
0.500 
0.484 
0.276 
0.283 
0.279 
0.263 
0.503 
0.352 
0.490 
0.401 0.637 
0.060 
0.296 
0.106 
0.093 
0.178 
0.046 
0.656 
0.138 
0.205 
0.147 
0.186 
0.054 
0.230 
0.183 
0.221 
0.193 
0.255 
0.303 
0.272 
0.329 
0.605 
0.143 
0.099 
0.030 
0.028 
0.074 . 
0.046 
0.066 
0.121 
0.049 
0.105 
0.056 
0.035 
0.086 
0.042 
0.098 2.109 
3.650 
2.150 
2.880 
2.718 
2.596 
2.738 
2.312 
1.987 
2.251 
1.825 
2.211 
2.434 
0.293 
0.492 
0.670 
0.377 
1.309 
0.817 
0.314 
0.440 
0.230 
0.900 
1.361 
1.288 
1.518 
1.204 
1.413 
2.565 
0.733 
1.926 
0.722 
0.838 
1.014 
1.028 
3.714 
1.455 
• 

• 
28APR92 GEN 3 9:28 1.223 181 0.414 0.043 2.320 28APR92 GEN 3 11:45 0.612 182 0.381 0.044 0.648 
• 
28APR92 GEN 4 9:28 0.680 181 0.347 0.036 0.957 28APR92 GEN 4 11:45 0.468 180 0.313 0.105 0.395 28APR92 GEN 5 9:28 0.494 181 0.271 0.105 0.652 28APR92 GEN 5 11:45 0.466 180 0.222 0.258 0.446 
• 
28APR92 Pl2G 1 12:01 0.485 171 0.224 0.249 0.455 28APR92 Pl2G 1 14:01 0.509 171 0.237 0.204 0.395 28APR92 Pl2G 2 12:01 0.617 175 0.391 0.144 0.851 28APR92 Pl2G 2 14:01 0.650 178 0.381 0.122 1.618 
• 
28APR92 Pl2G 3 12:01 0.554 175 0.308 0.221 0.410 28APR92 Pl2G 3 14:01 0.557 176 0.352 0.144 0.800 28APR92 Pl2G 4 12:01 0.389 171 0.076 0.378 0.607 28APR92 Pl2G 4 14:01 0.557 176 0.352 0.144 0.800 28APR92 Pl2G 5 12:01 0.408 172 0.109 0.406 0.271 
• 
28APR92 Pl2G 5 14:01 0.380 171 0.115 0.300 0.923 24APR92 TSG 1 11:34 0.521 172 0.379 0.221 2.697 24APR92 TSG 1 13:34 0.423 172 0.422 0.117 2.555 24APR92 TSG 2 11 :34 0.460 172 0.439 0.019 3.123 
24APR92 TSG 2 13:34 0.369 174 0.380 0.145 2.312 24APR92 TSG 3 11:34 0.502 171 0.420 0.634 3.407 24APR92 TSG 3 13:34 0.488 171 0.457 0.052 2.839• 24APR92 TSG 4 11 :34 0.610 172 0.396 0.486 2.758 24APR92 TSG 4 13:34 0.320 171 0.323 0.015 2.129 24APR92 TSG 5 11 :34 0.349 173 0.335 0.063 2.393 24APR92 TSG 5 13:34 0.324 171 0.336 2.211 0.143 
• 
• 

• 62 
• 
• 
Table 7. Vertical distribution of macrofauna in April 1992. Mean biomass (g-m-2) and abundance (n· m-2) of taxonomic categories . 
Section 
• 0-3 3-10 
• 
Station Taxa n-m-2 g.m-2 n-m-2 g.m-2 Mean SD Mean SD Mean SD Mean SD 
• 
189G Crustacea 1891 433 0.093 0.026 189 328 0.018 0.031 Mollusca 2742 1845 2.211 1.215 95 164 0.016 0.028 Nemertea 473 433 0.029 0.037 95 164 0.012 0.021 
Polychaeta 13520 2542 3.880 2.496 6429 3059 7.036 6.814 
• 
189S Crustacea 1607 164 0.234 0.156 95 164 0.023 0.039 Mollusca 1040 867 0.414 0.673 0 0 0.000 0.000 Polychaeta 4255 1725 0.652 0.517 2080 912 3.268 2.145 
6 Crustacea 189 164 0.017 0.015 95 164 0.001 0.002 Mollusca 756 164 2.311 1.995 0 0 0.000 0.000• Polychaeta 2458 590 0.108 0.031 851 983 0.084 0.084 
CPG Crustacea 1229 1181 0.062 0.058 567 284 0.049 0.052 Mollusca 1796 1074 7.020 3.706 567 284 0.498 0.738• Others 473 433 0.012 0.011 1324 2293 0.172 0.298 Polychaeta 17018 8608 3.481 1.156 5862 1889 2.890 1.509 
GES Crustacea 1513 819 0.058 0.065 95 164 0.002 0.003 • Mollusca 284 0 0.019 0.023 284 284 0.028 0.044 Polychaeta 16451 3002 0.432 0.109 8131 2869 1.977 1.464 
• 
63 

• 

• 
GIG Crustacea 3120 2473 1.249 1.972 284 491 0.061 0.105 Mollusca 473 590 0.195 0.301 189 328 1.845 3.195 
• 
Nemertea 284 0 0.020 0.020 95 164 0.181 0.313 Others 567 567 0.053 0.059 189 328 0.783 1.356 Ophiuroidea 95 164 0.017 0.029 0 0 0.000 0.000 Polychaeta 18342 4833 5.522 1.012 1796 1456 9.152 7.385 
GIS Mollusca 189 328 1.004 1.739 0 0 0.000 0.000 Polychaeta 4160 1638 0.811 0.404 1702 750 2.327 1.929 
• 
• Pl1G Crustacea 3404 1023 0.471 0.263 851 0 0.076 0.037 Mollusca 189 328 0.071 0.123 189 328 0.002 0.003 Nemertea 1040 819 0.015 0.014 95 164 0.002 0.003 Others 189 328 0.005 0.008 95 164 0.016 0.028 Polychaeta 30917 9360 7.430 1.953 4160 2293 1.544 1.083 
Pl2G Crustacea 20138 15967 1.634 1.419 1324 328 0.135 0.088 Mollusca 567 567 0.678 0.957 0 0 0.000 0.000• Nemertea 945 590 0.042 0.051 0 0 0.000 0.000 Others 2553 983 0.107 0.080 284 284 0.208 0.329 Polychaeta 28459 433 2.132 0.684 1513 433 0.271 0.328 
• SKG Crustacea 4916 2979 0.235 0.195 378 433 0.044 0.070 Mollusca 4916 3691 6.433 6.032 284 0 0.006 0.000 Nemertea 189 328 0.004 0.007 0 0 0.000 0.000 Others 3593 1824 0.357 0.176 95 164 0.350 0.606 • Polychaeta 12575 2412 4.137 1.633 2080 164 7.197 3.723 
TPG Crustacea 5578 1181 0.395 0.067 95 164 0.002 0.003 Mollusca 1135 1474 1.981 2.631 0 0 0.000 0.000 • Others 4822 3485 0.340 0.173 0 0 0.000 0.000 .Polychaeta 12386 9925 2.404 2.071 1135 851 5.446 7.147 
• 
TSG Crustacea 8698 2166 0.253 0.089 378 433 0.019 0.028 Nemertea 473 164 0.013 0.007 95 164 0.003 0.005 
Polychaeta 13331 2735 6.108 1.575 3876 590 9.462 3.427 
64 

• 
• 
TSS Crustacea 662 590 0.056 0.051 0 0 0.000 0.000 Mollusca 189 328 0.165 0.287 95 164 1.077 1.865 
Others 95 164 0.025 0.043 0 0 0.000 0.000 Polychaeta 1607 590 0.999 1.101 1135 567 19.005 18.804 
• 
• 
• 

• 
• 

• 
• 

• 
• 65 
Table 8. Species distributions in April 1992. Average n.m·2 at each station to a depth of 10 cm. 
Taxa 189G 1895 6 CPG GES GIG GIS Pl1G Pl2G SKG TPG TSG TSS 
Cnidaria  
Anthozoa  
Anthozoa (unidentified)  0  0  0  1796  284  851  0  284  2742  3593  4727  95  0  
Platyhelminthes  
Turbellaria  
Turbellaria (unidentified)  0  0  0  0  0  0  95  0  0  0  0  0  95  
Rynchocoela  
Rhynchocoel (unidentified)  567  0  0  0  95  378  0  1135  945  189  0  567  0  
Mollusca  
Gastropoda  
Cerithiidae  
Diastoma varium  0  0  0  284  189  0  0  0  0  95  95  0  0  
Ceritheum Jutosum  567  0  0  1418  0  0  0  0  189  1702  284  0  0  
Caecidae  
Caecum pulchellum  2175  284  0  189  0  0  0  0  189  0  95  0  0  
Caecum glabrum  0  0  0  0  0  0  0  0  0  0  0  95  0  
Pyramidellidae  
SayfJl/a crosseana  0  0  0  0  0  0  0  0  0  95  0  0  0  
Acteonidae  
Rictaxis punctostriatus  0  0  0  0  95  0  0  0  0  0  0  0  0  
Crepidulidae  
Crepidula fomicata  0  0  0  189  0  0  0  0  0  3309  284  0  0  
Nudibranchia  
Nudibranch (unidentified)  0  0  0  0  0  0  0  0  0  0  95  0  0  

66 

Pelecypoda 
Mytilidae Amygdalum papyrium 0 0 0 95 0 0 0 189 95 0 0 0 0 Brachidontes exustus 0 0 0 189 0 0 0 0 0 0 0 0 0 
Tellinidae Tellina texana 95 0 0 0 0 95 95 0 0 0 0 0 0 Tellina tampaensis 0 0 0 0 0 473 0 0 0 0 189 95 284 
Veneridae Anomalocardia auberiana 0 189 0 0 0 95 0 0 95 0 189 0 0 Chione cancellata 0 0 0 0 0 0 0 189 0 0 0 0 0 
Mactridae Mulinia lateralis 0 567 756 0 284 0 95 0 0 0 0 0 0 Annelida Polychaeta 
Phyllodocidae Eteone heteropoda 0 0 0 0 0 0 0 0 0 378 0 378 189 Anaitides erythrophyllus 95 0 0 0 0 95 189 0 0 0 0 0 0 
Pilargiidae Pilargiidae (unidentified) 0 0 0 0 0 95 0 0 0 0 0 0 0 Syllidae 
Sphaerosy/lis cf. sublaevis 567 1418 0 0 284 4444 1229 3687 0 0 284 0 0 Brania furcelligera 945 0 0 2553 0 473 189 2458 567 1418 662 1229 0 Exogone sp. 2458 95 0 284 378 0 0 284 0 0 0 473 0 Sphaerosyllis sp. A 0 0 0 284 0 0 0 0 0 1324 0 2175 284 Opisthosyilis sp. 2553 1324 0 9549 0 378 189 5200 24109 473 4822 378 0 Syllidae (unidentified) 0 0 0 284 95 0 0 0 0 0 0 189 0 
Nereidae Platynereis dumerilii 0 0 0 0 189 95 0 284 378 378 567 662 189 Nereidae (unidentified) 0 0 0 95 0 0 0 0 0 0 0 0 0 
Goniadidae Glycinde solitaria 0 95 95 0 0 0 0 0 0 0 0 95 0 
67 

Dorvilleidae Schistomeringos rudolphi 0 0 0 284 0 0 95 0 0 95 0 0 0 Schistomeringos sp. A 0 95 0 0 0 0 0 0 0 0 0 0 0 
Spionidae Polydora ligni 0 0 0 0 0 0 0 284 0 95 95 189 0 Prionospio heterobranchia 4444 284 0 2931 1324 3215 0 17018 945 6524 3876 4160 0 Scolelepis texana 0 0 0 0 0 0 0 0 0 0 95 0 95 Spiophanes bombyx 0 0 0 0 0 0 0 0 0 0 0 95 0 Streblospio benedicti 284 378 0 95 15884 1135 189 189 0 0 0 756 95 Spio setosa 0 0 0 0 0 0 0 0 0 0 378 189 284 Spionidae (unidentified) 0 0 0 0 0 0 95 0 0 0 0 0 0 
Magelonidae 
Magelona pettiboneae 0 284 0 0 0 0 0 0 0 0 0 0 0 
Chaetopteridae 
Spiochaetopterus costarum 0 0 0 0 0 95 0 0 0 0 0 0 0 
Orbiniidae 
Hap/oscoloplos foliosus 0 0 0 662 95 95 189 0 0 0 0 189 95 Scoloplos rubra 95 378 0 0 0 0 0 0 0 0 0 0 0 Naineris /aevigata 284 0 0 1040 0 0 0 378 2836 378 378 0 0 
Capitellidae Capftella capitata 662 473 284 567 756 3782 2269 0 95 1891 1040 1607 378 Med,iomastus califomiensis 0 0 0 0 0 0 95 0 0 0 0 0 0 Heteromastus filiformis 567 284 0 95 0 0 189 0 0 378 945 1607 662 Mediomastus ambiseta 0 95 2931 0 473 284 189 0 0 0 0 378 0 Maldanidae Branchioasychis americana 378 0 0 0 284 1229 0 0 0 0 95 0 Clymenella mucosa 0 0 0 284 0 2742 662 0 0 473 0 1607 473 
Ampharetidae 
Melinna maculata 189 0 0 0 0 95 0 0 0 95 0 473 0 
68 

Sabellidae Fabricia sp. 0 0 0 0 0 0 0 0 473 284 0 0 
0 Chone sp:· 567 95 0 0 0 1513 0 662 95 473 189 284 
0 Sabellidae (unidentified) 0 0 0 0 0 0 0 0 0 0 95 0 0 Polychaete juv. (unideritified) 0 0 0 95 0 0 0 0 95 0 0 0 0 
Oligochaeta Oligochaete (unidentified) 5862 1040 0 3782 4822 378 95 4444 473 0 0 0 0 Crustacea Ostracoda Myodocopa Sarsiella zostericola 0 0 0 0 0 0 0 0 0 0 95 0 0 Copepoda Cyclopoida Lichomolgidae Cyclopoid (commensal) 0 0 95 0 0 0 95 0 0 0 0 0 0 Malacostraca Natantia Sergestidae Lucifer faxoni 0 0 0 0 0 0 0 0 ·o 0 95 0 0 Hippolytidae Hippolyte zosterico/a 0 0 0 0 0 95 0 0 0 0 0 0 0 Reptanti.a Brachyuran Larvae Megalops 0 0 0 0 0 0 0 0 95 0 0 0 0 Mysidacea Mysidopsis bahia 0 945 189 0 0 0 0 0 0 0 0 0 189 
Cumacea Oxyurostylis sp. 0 0 0 0 95 0 0 0 0 0 0 0 0 Oxyurostylis salinoi 0 0 0 0 0 0 0 0 0 95 0 189 95 
Amphipoda Ampeliscidae Ampelisca abdita 189 473 0 0 1513 378 0 0 0 0 0 756 284 
69 
Gammaridae 
Gammaros mucronatus 0 0 0 0 0 0 0 189 0 0 0 0 0 
Corophiidae·. 
Cerapus tubularis 189 0 0 0 0 95 0 0 0 0 0 3404 0 Grandidierella bonnieroides 284 0 0 95 0 0 0 2647 0 567 95 0 
Caprellidae Caprellid 0 0 0 284 0 851 0 189 284 2269 756 1891 0 Amphilochidae Amphilochus sp. 0 0 0 0 0 0 0 0 1985 0 95 0 0 Amphithoidae 
Cymadusa compta 95 0 0 189 0 945 0 284 473 567 1418 1229 0 
Melitidae Elasmopus sp. 756 95 0 378 0 0 0 0 13047 1229 756 0 0 Melita sp. 0 0 0 0 0 0 0 0 284 0 0 0 0 
lsopoda 
Anthuridae 

Xenanthura brevitelson 0 0 0 0 0 0 0 0 0 0 0 95 95 
ldoteidae 
Edotea montosa 284 189 0 0 0 0 0 284 0 95 0 0 0 Erichsonella attenuata 284 0 0 189 0 0 0 2742 473 567 1229 756 0 
Sphaeromatidae 
Cymodoce faxoni 0 0 0 567 0 1040 0 95 2175 284 662 284 0 
Tanaidacea 
Tanaidae 

Leptochelia rapax 0 0 0 0 0 0 0 378 0 0 0 0 0 
Pycnogonida Pycnogonid (unidentified) 0 0 0 95 0 0 0 0 0 189 95 284 0 Echinodermata Holothuroidea Holothuroid (unidentified) 0 0 0 0 0 0 0 0 95 95 0 0 0
' 
TOTALS 25435 9080 4350 25059 27139 25439 5959 43588 53137 29597 24775 26853 3786 
70 

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Table 9. ·Laguna Madre Diversity and Evenness. Samples from April 1992. Average of 3 replicates . 
Diversity Evenness 
• Station N1 SD HPRIME SD E1 SD E5 SD 
• 
189G 11.0 2.4 2.38 0.23 0.80 0.07 0.73 0.13 189S 10.9 0.1 2.39 0.01 0.91 0.02 1.17 0.20 
• 
6 2.5 1.0 0.87 0.39 0.74 0.10 0.80 0.15 CPG 9.2 1.5 2.21 0.17 0.76 0.03 0.61 0.10 GES 4.2 1.5 1.39 0.34 0.57 0.08 0.52 0.07 GIG 11.8 1.6 2.46 0.14 0.85 0.04 0.80 0.09 GIS 6.0 0.4 1.79 0.06 0.83 0.11 1.09 0.66 
Pl1G 7.1 0.9 1.96 0.13 0.68 0.03 0.56 0.08 Pl2G 5.8 1.4 1.75 0.25 0.62 0.07 0.52 0.11 SKG 12.2 4.2 2.46 0.37 0.83 0.06 0.72 0.11• TPG 9.2 0.3 2.22 0.04 0.77 0.05 0.65 0.13 TSG 16.8 1.8 2.82 0.10 0.88 0.04 0.83 0.17 TSS 8.1 0.5 2.09 0.06 0.97 0.01 2.44 0.93 
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Table 10. Temporal changes in sediment organic matter. Samples from 1992, average of 3 replicates to a depth of 10 cm. 
Dry Weight (g.m-2) 
• Date Station Seagrass Roots Detritus Total 
• 
• 
21JAN92 189G 28 369 525 923 21JAN92 189S 0 0 200 200 21JAN92 TSG 26 57 197 280 21JAN92 TSS 0 0 5 5 23APR92 189G 291 333 251 876 23APR92 189S 0 0 220 220 24APR92 TSG 116 118 92 326 
24APR92 TSS 0 0 12 12 08JUL92 189G 278 270 466 1014 08JUL92 189S 0 0 157 157• 08JUL92 TSG 120 260 134 514 08JUL92 TSS 0 0 3 3 200CT92 189G 306 501 1036 1843 200CT92 189S 0 0 327 327 • 200CT92 TSG 114 300 236 650 200CT92 TSS 0 0 13 13 
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