NEARSHORE GULF ECOSYSTEM Diagram and Documentation by William B. Brogden Stephen N.~James preriared for The General Land Office of Texas Bob Ar mstrong, Conmissioner August 31, 1979 The authors would like to t l:ianl: the follm1ing people for their assistance during the research and preparation of this report: Hr. Hike Litwin for his accurate literature search and assistance in reviewing the ~iagran! Mr. Paul Carans elo for his assistance in revie"1ing the diagraw and his valuable discussions of ecosystem functions; ~-1r. Tmmny Barnes for the final dr.?.fting of the dia3rar.i; and a special thank you to irrs. Ruth Grundy, librarian at the University of Texas Marine Science Institute at Port Aransas, Te~as, for her invaluable assistance in obtaining much of the literature used in this re~ort. TABLE OF CONTEi'!! S -NEA?SHO!'E (:;TTLF ECOSYSTEr.f I . Ir1TRODUCTION -PURPOSE 0F THIS DOCtn'!E!JT ..•...•.•.•.•..••.• 1 II. Stn1HARY A_JD OVERVIEH OF THE NSG ECOSYSTDJ DIA~RAJ',f •• • •••.•• 1 A. Physical descrintion................................1 B. Primar:-1 energetics..................................1 C. Maj or regulating factors ............................l D. Imnortance to man of organisms ......................2 E. Types of i~pacts anticipated.............•..........2 III. DETAILED DESCRI PTION •••..••.•••••••••.••...••••.••••••..•• 2 A. Introduction and physical descrintion ...............2 B. Energy inputs .......................................3 1. Sunligl1t ....................................3 2. ~~lind energy.................................3 3. Gulf circulation and tides.................•4 4. Offshore 't·Javes . .............................4 C. Ph:rsical attributes ................................. 4 1. Salinit3l....................................4 2 . Current energ~r . ... . .........................5 3. 1.Jave energy. ................................5 LL Suspended solids ............................ 5 5 . Sediri.en t s o 1 i ds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. \·later depth .................................5 7. Seditl'..ent texture . ...·........................6 8. Dissolved and susnended toxics ............. . 6 9. Sedir.ient toxics . ... . ........................6 10. Dissolvec'l and sus0ended nutrients ...........fi 11. Sedinent nutrients.......................... 7 12. Dissolved oxy;:en ............. .... ........... 7 13. Sedinent dissolved oxy~en......... . ......... 7 14. Aquatic organi c matter/~icrobes . ··~··· ......8 15. Sedi~ent organic matter/microbes ......•.....8 D. Import/Exuort of Physical Attributes................8 1. \Vave energy export. ......................... 8 2. Salinity iI:l.port/exnort......................9 3. Suspended solids inport/export..............9 4. Toxics import/ex~ort . . ..... . ................9 5. Organic matter import/export................9 6. Nutrient inport/export...........•......... 10 7. Atmosoheric oxy~en exchange................10 8. Dissolved oxygen inport/exnor t ............ . 10 E. Biotic Attributes ..................................10 1. Ph,1tonl(1nl12 dcscrioes the t:1e~r::r, net~10ds or construction a11d e::2np l es of di20ra:-~s for otl:.er co.::.st.:J.l cco::;yste:-is . ':"hi s :--eport \.Jas ~~G}!Ctrct1 ~ji t~1 s:i~:;ort fro~ t:.1e ~e::.12~0..l I-:~:-:cl ~· :Zfice of '".Le::..J.s . r-·-; ­ II. 1·, v:··.,-.1....·T_ -·__..r: .:~ A. Physical Description For the purposes of this docUl::ent, the :·~ears:10:::-e Gulf is considered to be that portion of the inner continental shelf of Te:~as tlwt lies j_nsi de of the t hree l e acue line, outsic::e of the surf zone and outside of t h os e areas at t~1c: rJoutfts of ri,1ers and t l1e nrincipal -;:>c.sses t;nicl1 are considered 11Inlet-':L'idal Del t A.11 sys teDs. i~2ter-depth along the inner boundary is about 5 meter-s , \·.Jhile the outer boundary lies i11 between 13 to 30 r:i.eters of uater. B. Prir.:1:;.r'r Ener;.:e tics The r:ios t i:-TJorta:-it ei.1er gy ill-puts to tnis sys teo are s~11li~l1t, ~·1ind all. G \.Jav e en'3~0:/ . ;;_~:1.lir;~1t dri~.1cs ~: e ?l10tos:111thesi::; by 0~1ytoplanl:to~1 uhic:1 forr1s t:1c bas·2 of t~1c food ueb. ~:ir:d and ·waves provide t i e oi:~i:ig ener-c-'.r uhic'.:1 brings ret;enerated nutrients from the botton ._and lc~;e:::-uater column U? to t~1e photic zone. La r ge ai-::ounts of ;;1av e enQr[;y are exported to t he Upper Shoreface. C. liaj or ::.e;:::ulatin;; r actors i:utricnts and organic rr:atte r fron t~1c: rivers and estuaries clearly exert a ~ajor influence on t he base of t h e food \·7eo throuc;h pric2r7 productivity and detritus supp l:r. s:isr:ei:ded s?l~ds may al~o play . a. si;:;nificant role b:1 liraiting lig~t penetration. Salinity appears t o be a c ~ ~-i·=~c"nt yaru 1ato-O~ ~~e ~i -rat~oI~ o= or vJ.. 0 c .L -1 ­ .J... 1 lv 1L l...L a. t:.) ~ · '-... "' J..l-:_j . J. -[, ~an~sJ... " . 1 ~) . I nporto.nce to ~'.an :iany of the prominent estuarine orr.;anis~;1s spend p;:irt of their life cvcles within the ~earshore Gulf . Thia includes t he Penaeid shrimp and o any of the n ajor sport and co:Tu-::ercial organisn s such as ?,edfish, Bla cl~ l'-:-uD, f launder, and 3lue Crabs. l~any species of forage fish, uhich are major food items for the sport and cor.i.~ercial fish, also spend part of their life cycles in the ~Tearshore Gulf. E. Types of Iupacts Anticipated :fajor activities affectinr; the Ilearshore Gulf ;:it t h e present time include: dred3ing and spoil disposal , petroleum e:{ploration and developoent, comr:iercial fishing , SiJort fishing , and nodification of fresh water and nutrient inputs. Temperature :1as been lef t out of t-.c diagr.::i.n in spite of its major regulatory role because none of man's activities are expected to si; nif icantly alter the temperature of the Nearshore Gulf. Although there is currently no evidence of toxic effects on organisr.:.s in the lTearshore Gulf ecosys ten , provisions have been r:l~de in the ~ia~ran for tracins toxic effects. III. DETAIL:t::D DESCEI PTinn A. Introduction and Physical Des cJ;."iption The ":·Tearshorc G ..L.. .-... ....:> .. -l--.I. • -.!.. . .. ..L C. -l \;.,;. ..L.. C..1. -'-~ L .1. ..L.. J_ L. ., .J,_. ..:..> .J .J -....,; -..... i·rnul c, 'l)e t~1e "inner continental shelf". '.Lhe de;:it~1 ranr;e~ froo 5 to 9 1.leters (15 to 30 feet) on the inner bo'undary-to 13 to 30 meters (42 to 96ft.) at the t!l.ree league line. The greatest depths, at the three league line, occur along the southern third of the Texas coast, Hhile the shallouest occur offshore fron Sabine Lake. The substrate of the Fearshore Gulf Ecosysten is primarily sand and !'Jud. It is disturbed infrequently during norr:lal ueather, but can be extensively eroded during storns. Althour;h the :Tearshore Gul f ecos;steD's productivity is based on phytoplanl:ton, the estuaries and rivers s trongl~r influence the systeD with respect to nutrients , organic detritus , sus;;e:-ided solids, and thi:= r:iir,r a tion of oc.ny organis~s. The ~~ear.shore Gul f is of particular inporto.nce as 2 t~ie spmmin~ 3round of nany sports a:id co:--:.-::i:=rc L':ll 1~1 ir::~rnrtant or;:;;r;iisn s u'.1ici.1 S?end part of ~~ 1eir life cyc le in t:1e estuaries. :3ecLJ.u::;e of 6ieir oven.''.12l r::in;:: i::-:r:;ortance to cout.12rcial fisl1in: i~1 J.exas , ~articul.:.r 2.ttenti.o'!:l 11,1s bee:-i p~i~ (in t~e diasran ) to the life cyc le of the Penaeid s nri1.1p . The concept that biotic cor..JDunities on the continei.1tal shelf c'..1ange uith depth is uell 1-:nrnm. f_lthough diff eren t aut~ors suggest slig~tly differ2nt dept~ li~its, t~1ere appear s to t e a distinct "inshor e " fauna e:~tencli:ir, f ron roug~ly 3 or 4 uete rs (10 to 13 ft.) out to roughly 20 to 27 neters (65 to 89 ft.) of water denth. Chittenden and licEachran (1976) ca ll this the "Hhite Shrinp \-:::-ounds" £auna i n contrast to t h2 " Brrn·m Shriup Grounds" fauna 1:.;rhich occur fron ab out 22 Det e rs (72 ft.) out to ab out 91 neters (300 ft.) of 1·rnter depth. ':i:'his inshore faunal area corres ponds •;.1e 11 ·Hi th tl.1e ":,;earshore Gulf" ecosys ten of this report. J:an' s activities can have both direct and indirect effects on this ecosysten. ~he direct effects, such as shriEJ.p trm;ling , dred8ing , spoi 1 dunpine;, pipeline co·1s truetioa, offshore oi1 D l a tforr., cons truetion and operation, and oil spills ar e obvious; but nay be of less si.;nificance than tl1e indi rect effects . ':i:'l:e indirect ef~ects ste~ uai n l y ~roo raodi f ication of the inputs of nutrients, suspended solids, and other inputs fron the rivers and estuaries. B. Energy Inputs 1. Sunli .n;'1t Solar energy inout is t'1e nos t inporta11t sin8le .eneq~y source for t h e nea~shore rrul f ecos~rs ten. T:1e or;;anic matter famed by photosynthesis, together uith sP.1aller amounts of organic matter from the rivers and estuaries, provide the base of the food web. Solar energy which is not absorbed by phytoplankton is stored and released as heat. Heat is not explicitly represented on the Nearshore Gulf ecosystem dia3ram since it is unlike l y to be altered by n an's activities. 2. \:Tind I:nerr;y \Jind cner t,y is one of 61e najor factors controllin':" .. -., ,... ~ ) circulation and uave acti on in t11e . :e.::.rsnorc:: r:ulr sys ten. This enersy input varies seasonally, both in direction and r.1a; nitude. J..ecent studies U3Eli t~1 19 75 and 1973) h~ve s hmr.1 Current velociti es on t~1e inn2r sh2l f to be ap;Jro~~ino. tel·1 15 to 25 cr../sec (0 .3 to 0.5 l::.nots) c:urin[; the uii1ter and ar~und l :J c01/sec (0.2 l;:.nots) durin[ the sun_':ler. '.':'he current air e ction corrlates 1:·1ell 'i7ith the wind direction over 1 to 2 we ek periods. Hind energy is ultinately derived fron solar energy , but since this connection should not be altered by Gan's activities , i t is not repr esented on the dia0ran . 3. Gul~ Circu lation and Tides 7he affects of circulation and tides iTl the open Gulf or1 t~1e :Tearsl1oi.. e Gulf are definitel:l snaller tl1an tl1c direct •.Jind input, but are still r:J.easurable. Cl1ant;es in wat er l evel in the Gulf as a whole are of signi~icance nainly in tl1e shal lrn1er sys ter;1s and are not shmm on th is diagram. 4. Offshore P aves Uaves generated by wind in the open ~ulf are of r::aj or s i ;:;nificance as a source of mi~dnc: ener[;v ui t hin t~1e systen . 7his enerGY input is hi~hly ~~riable , boci1 seasonally and daily . C. Phvsica l ~ttributes 1. Salinity Salinity in the ~7earsb.ore Gulf e cosys ten is nuc~1 less v2ria-o l e t~w:l it i s '.:7ithin t~1e estuar:i_nc 3ystews , :10-r;1ever, si3nifica11t variatio!l.s do occur. In adcli tior: to t:1e runoff fro:-:1 'l'e:~as' rivers, the influence of the "fresh" 'dater nlune fror:1 the 'I:Iississippi ~aver is frequentlv observable in eastern portions of the Te:~as i'!earshore Gul f durine the late sprin8 (Smith, 1979). Salinity values in the J.Jearshore Gulf ecosys tern may rant;e froEl 36. 5 ppt, characteristic of the open Gulf, to bclou 20 pp t around "Inlet-'lidal Jelta" ar eas. The lm7er va lues are core typical of tne norti1eas te rn Texas coast, 'd:1ere the rivers ar e larzer and tl1e influe11ce of t:ie l tississ i ppi ::'..iver is s tronGer. 2orizontal and/or vertical salinity gradients of a fm1 parts per thousand are not un cor.u:1on i n the !:iearshore Gul:: (Sn ith , 1979 ; Jones, Copeland and lioese , 196 5) . 2 . Current Ener~v C·.irrents in · the . Je1t. In ti1e Jears!rnre Gulf syster-i., nitrate :-iitro;-;er~ is consi c1.ercd to be t~1c l i r:i.itinc; r:.ut::-ien~. This is incicat ed L; t:-1e fact t :1at it is e:::1aus t ec1. ~2fore :lhos11~1ate er silico.tc C:.urin:::; ;:;hyto~il o_n;: ton b l oo::.1s (S 2cl~ct t ~;1d ~rool~s, 19 70) . ~!utrients na~r e::ist in both di ssolved for:-:: and ad.:;orbed to t l1e surface oE particles. Sedinentatio:-i o:: ;;a:::-ticlcs , , .. • , .. 1 • , , p.1otosyntnetic upt a,:e and e}':Cc1anr;e u i t n ot,1er sys t ens can rer.10ve nutrients fron the i:1ater colur:m. ':::'l1e deconposi tion of organic natte~ by bacteria , the netabolis::: of hi zher organisms , the release of nutrients fron the sedin ents and the exchange of nutrients uith other systens can add nutrients to t h e \Jater colui:fil. 11. Sedin ent ~:utrients ':!:'he interstitial uater and t:-12 solid particles in the sediments contain nutrients in both solid and dissolved forms. The s l m: deconpos i tion of or[:,anic oatter by mi cro-orGani sns and t~e activities of bcnthic or~anisns causes the rel ease of nutrients suc~1 as anr1onia, p:10sphate and trace metals. 1hese nutrients can be released to the ·wa ter by diffusion or by turbulent ni:~ing o:f the sedinents. This recyclin8 of nutrients from the sedinents i s extremely i o.? ortan.t to t~1e fu11ctionins of t:-ie ::c:r1rshore G11l f ccosyste:-:i . ; l• <; t;0 1 V"' u-1 :j~·V""P'Y"I 12 • -............. ..r... .. _ . .. .. , {,'--.!.. E:zch.::i.n:::;e of ox~13e:-i uit h the atnos p'here t ends to l~eep dissolved o:~y0en l evels near saturci.tion i n t he -;:2 ters of t ::1e ~:earshore Gulf sys ten . S2.c::ett and Brooks (19 79) found t hat aver ..i.. ~..1. · ._ ·, J.. .._. -,.)c,.1...-· c.. .. 1-. ,.10.t. 1 c:;..; ...___ c_ t:;.\.~ values r0.ng2cl fron 100 to 112 . erc ent sntur <:.tion. ':::'!:is i ndicate s t~at tenperature and salinity tended to control dissolved oxy13en concentration . 13. Sedi o ent Dissolved Ox,yzen _ 1..-' Uo direct rneasureraents of t h is par aneter in t he Gulf of : [exico l1ave been found. l~os t ob servations of s edinen t indicate t1rnt the surface deposits are o::y13en;i_ted but the lower layers are anaerobic as evidenced by the presence of oethane (Sackett and Brooks , 1979). The biotic connonent "n2-crooes" is vartiall7 co::1bined with t j_1e S:';.rnboi repr eser:ting dissolved and suspended or;;anic natter in the 1,1ater. r: :~perience has shmm that this co2biu.ed symbol greatly sil:1plifies the diagran without any loss of ability to analyze potential impacts. Dissolved organic matter is present in the waters of the Nearshore Gulf at levels on the order of 1.0 to 3.7 ID8 of organic carbon per liter Cfaurer and Parker, 19 72). The bacteria are the most i noortant of the microbes in the decooposition of orcranic matter in the ~·Tearshore Gulf. The po~ulations of bacteria respond rapidly to organic matter inflm,·s and rapidly colonize or3anic particles. Thus, populations of micorbes are hi gher near the shore and near Inlet-Tidal Delta systems. Typical numbers nay ranr.r,e fron 500 to 155,000 cells per liter of \·7ater (Oujesky and 'lan Auize:-i , 1979). Si;:;11ificant nuwbers of fungi have also been found in the lJearshore Gulf ecosystem (Szaniszlo, 1979). 15. Sedi!llent Organic l!atter/Microbes Because t:1e action of i:.raves tends to l:eep organic particles suspended in the 11atcr colur.m , t he concentration of organic matter in lTearshore Gulf secir:ients is relatively low. Jones (1960) found a mean concentration of 0.52 percent organic carbon in surface sediments. The nur.:bers of bacteria found in the sedir.1ents range from 0. 05 to 1. 6 million cells ner cubic centimeter of seclL-o.ent (Schi:,rnrz, 1979). In addition· to the decor::.position of or3anic natter and the release of inor8anic nutrients such as a-:1nonio. and j1l1osp~1ate, the bacteria are believed to produce significant a:~10unts of vitamin B-12 (i''.aurer 2nd ParLer, 1968). D. Import/Export of Physical Attributes 1. ·i:-:ave Energy :::xport During norTial i;1eatl1er , t.1e Nearshore rulf exports most of the wave energy it receives from offshore waves, plus that added by local wind, to the Upper Shoreface or Inlet-7-idal Delta systens. 'l'he anount exported, and to sone extent t he direction of propagation, is strongly influenced by tte water depth, as previously discussed. 8 ,.., 1 . . t -;~ 2 . ~a_ini ·v lcnort ~xport The ~earshore Gulf re ceives low salinity uater fr on the rivers and estuaries via the Inlet-Ti dal f'e 1ta sys ten ,.. -'-1 -•• . . . • 1 . G 1 ,.. ,.. ' < D • and rron L1e l'iJ.ss issippi ...--....iver p ur\le via ,u r or "e:cico currents fron the northeast (Snith, 1979). Generally, the 1 S !'.:> ~T 1 r ,..j d ,-. _,_, ~-1 ,-, 1 ,.. • t' ' • 1 cci.,·, a_(..;. e c;e or L.1e i:earsnore Gu r eJccnanges i:1i n ni g 1er salinity water froEJ. the central Gulf of Iie:dco. Durinc; drought periods , the Laguna :ladre, Corpus Chris ti Bay and Aransas :Gay nay have salinities higher than that in the Gulf, thereby reversin[; t~1e noroal salinity gradient (Collier and Hec13peth, 1950). 3. Susnen' ~~orerar cray ex~or t 11 ae.1 • ..__ 1 ,. J • e sn2 tr~L~S 1 anG ais~oLvea orsanic natter to t:12 ~:eu.rs~10re Gulf . '.!:'hus the net b2lance reli.ai ns unclea r. 6. ~Tutri.ent I r.:port/E:mo;::-t The generally observed p:radient of nutrient concentrations and photosynthetic activity decreas~s goin3 from the estuaries throut:;h the l'earshore Gulf to the offshore ·waters. This gradient indicates that estuaries are sources of nutrients for the ~!earshore Gulf; Hhile it, in turn, is a source for the offshore waters . Em·1ever, the amounts and forns of these nutrients are by no neans clear. The aril.ount of nutrients transnorted in combined form as or ganic matter may greatly ex~eed t he ar:iount transported in inorganic form. In tl ose areas i;.1here rivers C.irectly enter the Gulf ~ithout oassinR throuch an estuarine svsten, the ma gnitude of nutrient supply can be calculated dir~ctly. 7. Atomospheric Oxygen Exchanne \Jave energy pronotes rapid exchange of ox:1;:;en be r.1een t:1e air and \;rater. 'This tends to reduce the 2a3nitude of dissolved oxygen fluctuations causd by ph otosynth esis and respiration. Dissolved oxy2en is exchanged uith adjacent aquatic sv s ter'l.s such as t:1e Inlet-Tidal Delta, Upper Shoref ace and ci ddle continental shelf. Sa.cl:ctt o..nd 3rool~s (19 79) four..d r·a tl1er unifor.:i dis t:::-i~ution o= dis sol vcd m~:;l;-_~cn ove r the '..:'exas conti:-icnt a l s::.elf, indicu.tinc tlw.t e~':cha71ze of \;rater beb,1e en t l1e r1cars:1ore a11 d of~s:1ore are as :1as littlc: ef~cct on dissolved oxy3en concentrations. E. Biotic Attributes 1. Phyt onlankton Photos7nthesis by phytoplanl~ton is by far the greatest source of organic matter for the base of the food chai::i in C:1e ::earshore Gul f . ::any studies have tended to concentrate on tl1e "net" phytopl2nl:ton (ie. th e phytoplankton caut:;l1t in a fine 1:i.esh net) 'i7hich is nainly diator::s suc~1 as Ske letonena co<.s t a tu:-~ . Hou evcr, 10 " nc.nnop lan~: ton" is prob a'.J ly of equal or srea ter ir::portn.:1ce ~o .._:, .... t 1 · .... · · t (" , 1 • ' '" .,.., 1 J 9 7° ) L L,Le LO 2, p::::-oauc L:..vi y . ·J':.i'l~r_:m1s"::::... anu : .'.ln .i.,2a_ei.1., _ ; . Productivit v Peasurenents in t :-ie ~!earsl10n~ (;ulf have included carbon-14, fixation rates and c'..1lorophyll "a" arr.aunts. Kaillyl::.o~·rnki and Van Daalen (19 79) sanpled both paraL:eters repeatedl y alon g a transect fron Port Aransas out into the open Gulf. They found levels of ch lorophyll "a" typic2lly ranging from 1.0 to 4.0 micrograms per liter of water (uz/l) a t inshore stations ex cept for values less than 0.5 U[;/l durinr; June , July and August. The hiijh l evels ·were apparently associated ui th a pulse of nutrients f::-or'.1 sprin3 run-off . Carbon up take rates as hic;h as 2t, milligrar:1S of carbon per cubic neter pe:::-hour (nr;C/r:i.3/hr) uere observed, but most valu es ranged between 4.0 and 16.0 ngC/n3/~r. As shmm in t l-1e diar,ram, p!.1ytoplankton cner ;:.;:-' £lm7 is based on sunliGht , stinulated by nutrients, and decreased oy shadins due to suspended solids and toxic effect::;. Tl:ere is no evidence, in the literature searched, th at indicates toxic effects on phytopl ankton in t }1e Te~::.as ITearshore Gulf at t~1is tine . 2. Herbi vores an2 Letritivor es TI1ere arc a \rari.ety... of or[ tJ.nisT"JS \7~1ict1 fee.cl O:l. phyto~1 lanl:ton ancl or; anic de tritus i n t lic 2"'.earshore Culf ecosvs ten. The s:-.1alles t a.r e t he cil::..2 t ed nrotozoa i:;'1ich D3~ 2:;r upon' the nannopl a:-:::to:1. 7~1e:r are L1 turll. ·feel upon b? -t he lar.;er zoopl ank ton. Johansen (1979) found the protozoan biomas s to be on the or der of 10 to 20 percent of the l3rzer zoopl ankton biomass. Laq;er zoopl ankt on in clude conenods, o,-:; tracods, aophipods, and t h e l arvae of crusta~e~ns, mollusks and fishes. 1.'he extent to which these organisms feed upon phytoplankton and detritus depends on the species and its life sta3e. The biomass of zooplankton in the ~earshore Gul f was found to average 34 .1 mg dry ·wt per cubic meter by Parl: (1979). It ·1:-;as observed to be positively correlated \lith ch lorophyll "a" and salinity. Menhaden and liullet and are the most COD.'Tton herb ivorous fish in the 8earshore Gulf ecosysten. Due to the economic and biological sisnifi cance of Penaeid shrir1p , t~1e liter a ture on t h ese orzanisr_-:s i s 2xtensive. Synopses of the biolor;ical data on the thr ee 1-::iaj or commercial species :1ave recently been pub lished: Lindner and Cook, -(1978) on Penaeus setife::-us (;;ihite sh rimp); Costello and Allen, (1978) on Penaeus c:.uorar un (pink shrimp); c.nd Cook and Lindner, (1978) on _?enneus aztecus (brmm shrimp). The following discussion and the discusson of Adult Shrinp, in a later section, drm; heavily on these papers. Spmming of uhite s hrimD occurs lar3ely in the l~earshore Gulf, uhere the young shrir.lp grou to 6 7 r:im b efore enterin~ tl1e es tuc.ries. Pink sh riw;; spmm further off shore. Brm-m shrir:-q spmm in of fshore i:rnters deeper th a:i 14 meters. The eGgs of all species sinl~ to t~e b ottom, hm,1ever, the larvae ancl post-larvae arc; plank.tonic. The larvae apIJarently feed upon pl1ytoplanl-:ton and so all zoop lanl::ton. 4. Benth ic Infauna For the ;::mrpos es of the ~~earshore Gulf diagr an, the conplex benthic cou111unity has been sinplified into a sin2le conpart:~1ent. Thes e organisn s rane e in size fron ne1";'.atodes to large polychaetes and molluscs. In most studies, the "u eiofauna" 2re separated fron the "n acrofauna" by their ability tc ; ass th rough a 0.5 mn seive~ ~:er::atodes are the nost 2bundant of the weiofauna in lTearshore Crulf sediments (Pequer;nat, 19 79). Other ~roups ob served-include har;?aC tico5. ds, ::in or:1ynchs, foranini fe:::-a, and po 17c~:-iae t e::;. The nacrofauna is doni nated by pol7chaetes (~ollnnd, 19 79). Several aut:1ors have sut,ges ted th.at the benthic fauna of the l:·Tearsl1ore Gulf forn a conr:mnity uhich is distinctly different from th at found further offshore. Cluster analysis of. benthic invertebrates fron grab sanp les indicated five distinct depth related group s of infauna on the continental shel f Ciolland, 1979). Defenbauzh (1979) suggested that t:wre is an "inr.er shelf assenblase" found at depths from 4 to 20 :"Jc;ter.s on the Texas ar.d Lou isianna shelf. lfany env irono ental factors such as salinity , temperature, or3anic matter su;:ply and sedinent texture are positively correlated to Hater depth. Therefore, th is zonation may be related to wnter depth only indirectly. .5. Internedia te Consuners 'I~1is conpartr.ent is used for :)Qtc1 ::ree s>:JE.1::::_n~ · ir.terr:,edi.t':'~'cc con3ur-cers c'.lncl t:1osc: closel~' u.ssoc::..:1~2d ~~:..e1 t:12 bottOT.1 . r.~:1is i:iclud~~ ~ ;....; rL"'} ---:inc::-c O.r: o.,-a . ~......., ,..... ..c __ O_"'"' _ "')I"l-~·1_sll _.._, t,...L ~. --.._L._ .!_CA.!. .(~,·-.L ~ t J <.!. "' ·..> ~ ~ ,..) .L J. i¥L -_. ­ larvae t o iel l vfish . Table :~SG-1 lis ts tl1e S~)ecies and food hab its for_, tile-r;ios t pro;:-:inent interwediate consul::ers. 6 . J\cl1.1 l t S11 r i :-.1-;J Adult Penaeid shrimp spend most of their tiwe in association with the bottom; either buried in the sediwent for protection or searching on the bottom for food. The white shri1ap (P. setiferus) is the most corr.con Penaeid shrimp of the ""Tnsnore continental shelf . But the other Penaeid shrirnn are also found in the I~earshore Gulf sys ten as ti1ey nigrate between t he estuaries and the deeper water. 7. Ton Cons ur:1ers ifawmals such as Porpoises, rentiles such as sea turtles, and many species of fish such as-sharks and most of the i nportant i:;amefish are considered top consUJ."Tlers in the :Tearshore Gulf sys ter:i. Table ::sG-2 lists the major SjJecies found in the Texas Lear.shore Gulf. In most cas es, t:1ese organisms do not n i grate into the estuarine systens. Porpoises , sea turtles and sone sharl:s have been found in es tuarine ~aters. Of course , man also constiutes a Qajor top consu:-.1er; especially of shric.p and ganefish . F. Import/2~Qort of ~iotic Attributes l 'uch of t h e biota of the ::c2.rshore ;r;ul f is closely associated i;;;ith estuarine ecosyste:-.1s. 7hcse speci2s pass into the estuarine systems via -the Inlet-Tidal De lta ecosystem. Because of t h e ease of sanpling, most studies of mi8ration of Nearshore Gulf organisDs have taken pla ce in Inlet-Tidal Delta systems. Examnles include Sim:ions and Hoese's (1959), and Kinz's (1971). studies of Cedar Bayou and Copeland's (1965) study of enigration through .'\ransas Pass. In view of the large nunber of species involved, the data 8iven here QUSt neccessarily be limited. The user is referred to the above papers and general uorl~s such as Gunt er (1945) for !:'1ore-· details concerning organisr1 r.:.igr2. t ion . Scientific narr.e FISH '.\1icrooor:on undulatus Ptlantic Croaker A Cynoscion nothus Silver SeAtrout /I , J l Ienticirrhus ao.ericanus Southern Kinp;fish A Arius felis Sea Catfish A Leiostomus xanthurus Snot /i Cvnoscion arenarius Sand SeRtrout /l_ Stenoto8us canrinus Lon0snine Por.,..,~' " , J Svnodus f oetens Inshore Lizardfish A ,.T Syaciur::i 0unteri Shoal Flounder /I , J Centro~ristis nhiladelphicus Pock SeA.ba.ss A,.T Stellifer lanc~olatus Star f'rum /\ , .T Trichiurus leoturus Atlantic Cutlassfish A,J Peprilus burt~ ~ulf Butter-fish .A., J Polydactylus octonemus Atlantic Threadfin A,J I NVEP.TEBf'J\TES Souilla errmusa ~'Antis Shril'n ,h,J Trachvpenaeus similis Broken ~ec~ Shrimp A, ,T Sicvoiiia dorsalis Pock ShriTlT"J .A., J Portunus 0ibbesii Portunid Crr:ib A,J Callinectes si~ilis Blue Crab A,J Callinectes ornatus Blue crab f" J Lolici;o pealei Squi d /\., J Life Star::e: l = :\dul t, J = ~Tuvenile D ­ .,ererences: Chittenden and HcEachran, 1976; Hohlschla.r:, 1979; Holland, 1979; ~1iller, 1965;; Hoese, 1965·; Cnle, 1977; Hoore, Brusher and Trent, 1970 14 Scientific name COl:lrton n;:i.:..e Li::e Stap:e Tursiops truncatus Atlantic Bottlenose A,J Dolphin I'illPTILES Carett a carettR car etta Lozi;perhead A,J Cheloni a mydas nydas Coreen Turtle A,J Lepi dochelys kempi i\tlantic Ei dlev .A ' J Dersochelvs coriacea cori acea Leat~1erb2cl: A,J FISH Carcharinus limbatus Black-tiryned Shark A,J Carcharinus leucas Bull Sharl: A,J Carcharin~s obscurus Dusl::..r Sharl-: A, .J C2rchar inus milberti Sandbar Shark ;\ ' J S')hyrna ti'buro Bonnetheacl. A,J Sphyrna mokarran r.reat Hai"rerhec.d p. , J Galeocerdo cuvieri Ti~er SharV: A,J Ne~anrion brevirostris Lenon. Sharl: A,J SconberoDorus cavalla Kin;; lfackerel _6. , J Scor::beronorus T71aculatus Spanish ~fackerel t\ , J !?or..a torn.us sa l ta tri.· Bl uefish I\ ,J : :er':alo~;s a t L:nticus Tcrpo1 .._ t\ ~ I .._T , Istionhorus e1at yoterus Sai l fish A,J ' :2 '11.,..~ n~ r--,..1c·1nc Jlue "arlin ,l\,J '-' _ j -.. 1 ... c .. ..1... C~ L.-l . ..!... .,,._ c:..t L .,, C2 r 2 n;{ 1--:i p pos Crev.slle J ack f. , J Lif e Sta8e: A = Adult, J = Juvenile ~eferences: Clark and von Schmidt, 196 5; Parker and Bailey, 1979; Hoese and l ·~oore , 1977; Hade , 1962; Raun and ~ehlbach, 1972. Phytoplanl~ton move be t uee21 t he ~:ears~1ore Gul f and the e s t uarine systens via t~e water oass ~oveoent of the Inlet-'I'idal Delta system. 7hey are also exchanged ui th t~:e Upper Shoreface and outer continental shelf syste~s via the ·water cur rents. IL:my of the phytoplanl~ton species f ound in th e Jearshore Gulf sys te~ are also found in these other systems. However, since th e phytoplankton density is higher in the. estuaries and lower in offshore i:'laters (l:ar::rkouski and Van Baalen, 1979), the estuaries act as a net source of phytoplankton i:·;hil e the Nearshore Gulf exports phytoplankton to offshore \:aters . 2. Herbivore and De tritivore lli .crr a tion The StYi?ed ~~ullet Crur-:il ce;:-ihal '...rn) ar:d 'frd.t c : :ulletC·:. curcc:w ) are the u.os t prooinent ner:ibers of t '.:1e ::erb i vore aiiCI ::Jetritivore class, both in t:1e iTear shore ~ulf and in the estuarine systeu.s . z:oore (197 L~) sur:1n.arized the ecolor,ical data on th ese fish. The adults apr>arentl:' nigr a tc to the outer continental shelf to spai:m , and then return to th e :Tearshore Gulf and estuaries. Striped ~ :ullet , the r..os t co!:.1?1on species , spa~fil in fall and uintcr. ;r~-:.ite :·ullet s02-:1:1 3. Larva l I:~ti:u:111 , Cook and ~a:~ter (1969 ) studied t :l.e dis trioution of ~rouns Penc.ei d s:1rin~ neo.r t '.1e entrance t o G2.l ves ton i)u.:1 . I'os tlar'J2.,~ uer e four. cl every r:iont l1 c~:cept ::over:iber and :8ecember , with peak abundance i n 1·arch and \ . 1 .. 1 . . t' 1 . . t-t 1... pr1 _. .:o corre a tJ.on ;;.;i n sa ini ...y or cnp cr.::i. t ure "1:·1as .c • ,­ i:ounu . 1.u:1ever , ...,.eiser , ' 1 , • 1 ( 1 g .., r \ , 1 • ' anG .:LCLTlC l. _ 10 1 oe ieve tt12t larval s~1rir:m use salinitv c;radients to "nav::..r;atc". Lindner and Cook (1() 70) indicat~ that \·Jhite Shri~p enter th e estuaries ·when they are ab out 7 rnm in len8th. I~ing (1971)discusses the correlation beb;een the mi gration of Penaei d shrimp and physical factors, such as \1ater terri.per ature , in det2il. L~ . Internec:iate Consur~er l ~i:;r2. tion lfust of the fish in t~is category in the ~earshore Gulf spend part of their life cycle in th e estuaries. Theytyvically ni2ra te into the estuaries as larvae or juveniles an~ en igrate to th e Gulf as adults. The periods of raicra tion ~ over or r-h :,rear. ~ • •d . ':;" ::J ::> ) e:tend r.1.UCil t . e _·or i nsta:ice , ("__,ope•.!..an' ( l" r ,.. found ::icropor;on unculatus (Atlantic Croal:er) en i0ratin::; over t i.1 e entire :rear. ~ :os t species Herc found in si:: or o ore ;::,on tl1l7 sac.pl es. In zeneral, l:.o~:ever, a s tronz, pulse of eni ;ration was observed in the fall. Si :--'.!:o:.1s and Eoes e (19.5 9) ob served 2 s o:-:-icu11at different patter.1. They found _ icro;:o:-';on un uL:i tus o.nd Leios ton.us ::rnntimrus (Spot) eT".ligra tin[; fror:i Cenar .Gnyou LLainly durini3 :ra:1 and June, ui t h a sccondar1 peak in Septer:1bcr. _\ppar2ntl:r th ere Day be considerab l e vario.tion in the timin3 of niGr a tions of various species due to pres2ntly unl:nO'im or ? Oorly unders toocl factors. E:::.i c;r a tion of Callinectes sa?l clus (Blue Crab)adults, ob served by Copeland (10u5), occurred froo ;\.pril to :-!ove::i.ber, v·Jith a main Deak in i\nril and .. ay. Sir,rmons · and Hoese (1959) ob servect" a strons· pulse of eni0ration of adult Paralich t hys lethosti~ma (Southern f lounder) during t h e tall, wilile juveniles entered the estuaries ':ror".l April throu8h r:ovenber. Dasvatis s abina (Southern Stingray ) breeds in the bays during the suruner. The adults and juveniles emi grate to the Gulf uith the coDi"Tiing of cold weather (Sage et. al., 1972). 5. hdult Shrio n l~rration After several oonths of Rrowth and maturation in the estuarine systeos, adult shrimp Segin to eoi5rate into the Gulf . The rn1ite s:irimp t end to stay in t he ::earshore Cul£ , while t h e Brotm and Pink Shrimp continue out to 3reater ·water dept:1s. SiIJ:,ions and ~-Ioese (1959) cbserved that emi gration through Cedar Dayou occurred only nt night. 7~e elli[;ration lns ted fror.1 i\nri1 to :1ovenber uith the heaviest e:-Jicration occurrin;:; in · Jur..c and Scrltenber. !'. si:"Jilar ext2nciec -,)er ioc oi e:--1i ;_;r .:i tion ~1as ob serve d bv Corye lc.nd (19G 5). 6 . Ton Consw-:1er I'.i~ration Top consuners in th e :T.earshore Gulf include Porpoises, Sea Turtles, Sharks and lar;:;e sport fish. ~ .nny of t h e sharks apparentlly spm,m just outside the surfzone in t l1e Gpper Shoreface (I1arl:er and Bailey, in press). T.... ittle is l:nmm about t he movements of Porpoises in t he '.~earshorc Gulf . Shane (1977) describes populations uhich live in the Aransas Pass area and suggests th at there are separate offshore populations. Sea Turtles spend nost of their life cyc les in t c1e open ocean, only returninz to the Deach to L1y their e;:;r,s. l:'he youn.; nay S?e;:id sone ti:·1e in t:1e :-earshore 1 Gu lf on thei:::-T,rny to the open Sul f a£t er l1a tcl1in~ . ·as t of the lar; e fis~ tiat co~~rise t~e ~ajority of t~e t op consu:-::ers <:i.r2 n°l 2r.·1 c and -,; ,.,.,__,,t r-. cnl-r i"nto t'1r.> o·-01 ,..,ul -'-­ t" ~ 'C -'--'-• -() ~ ~-'-" -J l c -~ i J ._. -" --• 7hey a~e ~o~ d~~~ctl7 dependent on the estuaries for an: part or t~eir li!e c7cles . G. Critical Svsteo Attributes The nos t critical linkas es £or t!:1e continu2d productivity of t}1e l~earsi.1ore Gulf appear to be the linl~s with the estuarine and river systems. ?he supply of nutrients and or[anic matter from the estuarine s7stens and rivers clearly 11elps to maintain a high level of photosynthesis in the Uearshore Gul f . J\:i.on6 tl'1e biota, t~1e Penaeid shri np appear to be a critical stage iYl the food rri . . t 1 1 , , . t t . t' .... . d . cnain . ney r equire sui ao _e naoi a in ne es~uaries urins part of their lif e cycles . IV. LI~ER..i\TURE CITED Chittenuen , I'.E. ,Jr. 2nd J.D. :rcEo.ch ran. 1976. Cor:i:Josition, ecology , and dyn araics of de~ersal ~ish cornosition on the nort~1uestern Gulf of : rexico continentGl shc.lf , u ith a si:nila r syncpsis for the ent ire Gulf . T.1\~~-sr.-76-2J8 . Center for l:a rine Resources. Te:rns /\&1'~ rnivers i ty. Co llege Station, Texas . · Clark , E. and K. von Schoidt. 1965. Shark s of t he Central Cul£ Coast of Florida. Bull. Mar. Sci. 15(1) :13-83. Co le, J. F. 1977. Nunerical analysis of trm:led tenthic fishes from the South Texas Outer Continental Shel£. [fas ters Thesis. University of Texas. Austin, Texos. Cook, H.L. and H.J. Lindner. 1970. S;,mopsis 0£ biolobico.l d2ta on the bro~m sh rinn Penaeus aztecus aztecus ! vcs 1891. FAO Fish. Rep . 57 (4) :1471-149 . Copeland, B.J. 1965. Fauna of t"he Ar2ns2s Pass Inlet, ':'e~ws. I. Emi gration as shmm by tide tran collections. Pub: 1'1ar. Sci. v1J:9-21. Costello, T.J. and D.l·r. P.llen. 1970. Synonsis 0£ biologi cal data on the pink shrii".D Pen,'.leus duor:rrun duoro.rur.i Burkenroad 193 9. FfO ~ ish. Reo . 57 (4) :1499-1537. Defenbaug~. R.E. 1976. A study of the benthic racroinvertebrntes of the continental s'.1elf 0£ the northern Cul£ of ~~exico . PhD dissertation Texas At,M Pr..iversit:r, Colle:::;c St ation, Texas. 4760. Hoese, H. D. 1965. Spa'¥ming of narinP. fi shes in the Port ;\r;msas, Texas a rea. as detern ined b7 t~e distribution of -;oun~ an d larvae. Di ssertation. Universit7 cf Te::as. L<\us tin, T~:ws. Hoese, H.D. and r_.;I, ~'oorc. 1977. Fishes of th2 Gulf of 1-fe:c::.co. Texas, Louisiana, and Adjacent Hnters. Texas fJ_~~ t:niversi t y Press, College Station, Texas. 327p. Holland, J.S. 1979. Benthic I mvertebrates: n~crofauna and en.i f~una. -in-Environmental Studies, South Texas Outer Continental Shelf, Biolo~y and Chemistr7 . pp 17-l to 17-56. University of Texas, final report for 1977 to the Bureau of Lond Hanager.::ent, Washington, D.C. on contract J\l\550-CT7-ll. Johansen, P.L. 1979. Ciliated protozoa. -in-Environr,en t al Studies, South Texas Continental Shelf, Iliolozv and Chcnistrv. oo 13-l to 13-40 . Gniversity of Texas , final re~ort fo r i977 to the Bureau of Land i~.::marerent , Pas'.1.i nri:ton D.C. on contract AA550-C77-ll . 19 Jones, :!,.S., B.J. Copeland and H. D. rioese. 1965. A study of the hydrogr aph7 of inshorc 1-?a ters in t '.1c Fes tern C'ul E o+: ~rexico off Port Ar ansas, Te:-;:as. Pu'.;. : 1ar. Sci. v l 'J :22-32. Ka8ykowski, D. and C. Van Baalen. 1979. ?hvtonlankton and productivity. -in-Environ~ental S~ud~es South Texos Outer - , Continenta l Shelf, Biolo~y and Che~is try . nn ll-l to ll-57. L'niversity of Texas, f inal renort for 1977 to ~~12 Bureau of Land r~anager:.:ent, Hashington, b.c. on contract L'A551J-CT7-ll. King, B.D. III. 1971. Study of r.igrator,r natterns of !:ish anrl. shellfish through a natural uass. Tech. Series no. 9. Texas Parks and Wildl{fe Dept., Austin, Texas. 54p . Lindner, l·'..J. and H.1.. C:oo1:. 1970. Synopsis of biolorical data on the white shrinp Penaeus setiferus (Linnaeus) 1767. FAO Fish. Rep. 57 (4):1439-1469. Lindner, ~L J. and J. S. Bailev. 196 S. Distribution o~ b rmm. sh:rirT? (Penaeus aztecus az t Qcus Ives) as relc:ite d to turbic1 water ~hotogra~ned fron S?ace. Fis~ery Bull. v67:289-294. }'.:aurer, L.G. and P.L. Parl:er. 196 3 . A stuc:r of t~c ,c;eochcnistry of vitao.in Bl2. Cont. Har. Sci. vl3:29-43. ~~urer, L.G. and P.L. Par ker. 1972. The distribution of dissolve~ or82nic r::.Cltter in the near-shore \1a ters of the: Te::ui.s coast. Cont. ?'.ar. Sci. v l 6 :109 -l24 . r·[iller, J. IL 1965. A trawl survey of the sh.J.llm; Gulf £ishes near Port Aransas, Texas. Pub. Inst. ~',.~tr. Sci. v l '.) : 30-107. Moore, D., ILA. Brusher and L. Trent. 1970. Relative abund::mce, seasonal distribution, and species conpositicn of derersal fishes of£ Louisian2. and Tex3s, l 96 2-l 964. Cont. -r~ar. Sci. Vl5:45-70 . Oujesk~1. II.V. and 0.H. Va.n Aul-::en. 1979. r.ratcr coluT"ln b;:icteriolor-:'r. -in-Environnental Studies, South Texns Outer Continental Shelf, Biology and Chen:1is try . pp 8-1 to 8-12S. l.rniver:; i ty of Texas, final reuort for 1977 to the Bureau of L2nd Management, Washington, D.C. on contract AA550-CT7-ll. Park , E.T. 1979. Zooolankton project. -in-Environnental Sturlies, South Texas buter Con~inental Shelf, Biolo~y and C~enistry . pp 14-1 to 11+-58. University of Texas, f in2.l reoort for 1977 to the Bureau of Land ~ ,.anapenent , 1Jashin0ton, !.". C. on contract AA550-CT7-ll. Parker, F.R. and C. rr . Bailey. 1979. Hassive Ap;p;r eg ations n f Elasuobranchs near t'ust2np: and Pa.dre Islands , Te~:as. Jour.Sci. Vol.~:X! , ~o.3. 20 ~"'.aun, G. G. and F.~. Cehlbac~. 1972. A~~~iLi3ns and ~eotilcs in Te}~as . Dull . l?.O . 2. The S.:illas · ; ru.seur~~ o-!: ;~a.tu~al 1Iisto~~.r. 1 Sackett , .7.l. ~ . and J .>:. Lirool:s. 1979. Lou rolcculnr \:rci--:'.lt hydrocarbons and ~ydro;raphic project . -in-~n~iron~cntal Stud~es, Sout:1 Te~:a s Outer Conti:iental Shelf , Biolor,y 2nd Cheoistry. pp 3-1 to 3-128. Cnivcrsitv of Te~as, fin~l­ report for l 9 77 to the 3ureau cf Land-! ran20cr::cn t, Washington, D.C. en contract Af550-C:7-ll. Sc~1arz, J.R. 1979. Benthic bacteriolopy. -in-~nvironncntol Studies, South Texas Outer Continental Shelf, Biolo;;y and Chenistry. p-v 10-1 to 10-31. Vniversity o:= Te~~as, :!:inal report fer l 9 77 to the Bure;iu n f Land I'an3r:e:ient, Uashington, D.C. on contract AA550-CT7 -ll. Sir:u-:i.ons , E.c;. and II.D. Hoese. 1959. Studies on the hvcrorro.oh'! and f ish n i 3rations of Cedar Bayou, 2 naturai tidnl inlet on the central Texas coast. Pub. Inst. :r2r. Sci. v6:56-8•1. Steele, J.H . (ed) 1970. 1,farine Food Che.ins . 1-'nivc.rsity of Califor:ii.:1 Press, Los An Geles, Cal. 552p. Steele, J.H. 1974. The Structure of 1'arine Ecosystens. }farvard lJniversity Press, 128p . Szaniszlo I r. J. 1979. F.stcr colun n and bcnt~1ic ric:-o'.Jiolor-:r ­r:ticolo~w . -in-Environnen tal S t:..idies, Soeth ':!:'e::3s Outc:::­Contincntal Shelf, Biology and CheQistry. op 9-1 to 9-67. University of Te;~as, finP..l report £or 19 77 to t'.:"le Bureo.u of Land ?~anar;er:1ent, Hashin~ton , D. C. on. contr2ct AA550-CT7-ll. Smith, ~1.P. 1975 . Seasonal variations in nenrshore circulation in the northuestern (;ulf of l~C3~cico . Cont. V:::i.r . Sci. vl9:49-65. Sr::it:1, JJ . P. 1978. Lou -frequenc;r re'10rs