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OCEANOLOGICA ACTA. 1982. N° SP

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Ecological characterization

Coaslal lagoon5

E5tllary

System ccology

of Términos Lagoon, a tropical

Lagunes côlières

Esluaire

Écologie

lagoon-estuarine system in the Southern Gulf of Mexico

ABSTRACT

RÉSUMÉ

A. yaiicz-Arancibia·, J.W. Day Jr

b • Univcrsidad Nacional Aut6noma de México, InstÎtuto de Cicncias dei Mar y Limnologia.

Apanado postal

70-305, 04510 México.

b Louisiana Slatc Univer sity, Center for Welland Rcsourccs. Coaslal Ecology Laboratory.

Baton Rouge, Louisiana 70803. USA.

Términos Lagoon was sclcClcd for siudy bccausc of: 1) its biologieal divcrsity, in Icrms of both spccics and habitaiS; 2) ils valuablc fish, oysler, shclUish. and wildlifc rCSOUTces j 3) ils rclationships with Campeche Sound, the mesi important fishcry area in the Gulf of México; and 4) ils proximity to present and proposcd oil industries. The ecological characterization is a description of the imponant components and processes that make up the ecosyslem, stressing functional relations hips and synthesizing cxisting information from the biological, ehemical. ph ysK:al, and cnvironmental sciences. The ecological eharaeterization collates what is known abo ut the natural resourees of the area, describes areas of probable cnvironmcntal impacts. aids in development of mitigation procedures and alternati ves for minimizing environmcntal damage. and hclps idenlify researeh needs.

The lagoon

has a mooerale seasonal pulse of lemperalure and light. and the area has slrong near-permanent physieal gradients and a high diversity of eSluarine habitats. prevailing winds cause a net inflow into the eastern inlet and a net outflow from the weslern inlel, whieh ereales high salinity and elear water conditions in the eastern end of Ihe lagoon. The major river discharge is into the western part of the lagoon, ereating turbid, nutrient-rieh waters with low salinity. An inlet delta is bcing formcd on the lagoon side of the eastern inlet. Most biologieal proccsscs ineluding assemblages of bcnthic and fish populations arc sirongly influenced by these gradients. Extensive grass bcds occ:ur in the northeastern end of the lagoon and a succession from grass beds to mangroves in taking place on the emerging delta. Extensive oyster reds arc located in the weslern pan of the lagoon near the river mouths. Phyloplankton production, chiorophylllcveis. and mangrove lil1er-fall are higher in the riverine area. Nekton larvae and juvenilcs generally enter the lagoon through the eastern inlCI, reflecting prcvailing currents. Peak river discharge is in Octobcr, when the highest primary productivity and entry of juveniJcs occur,

Oceollol. Acta, 1982.

SCORlIABO/UNESCO,

Proceedings International Symposium on coastal

Bordeaux, France,

8·14 Septcmbcr, 1981,431-440.

lagoons, Caractérisation écologique de la lagune de Términos, système lagunaire tropical du Golfe du Mexique.

La lagune de Términos a été choisie pour cette étude en raison de : 1) la diversité des espèces

ct dc! habitats; 2) la qualité des ressources en poissons, huîtres. coquillages; 3) ses relations avec le détroit de Ca mpeche. la plus importante zone de pèche dans le Golfe du Mexique;

4) la proximité de raffineries. La cantctérisation écologique consiste en une description des

composants ct des mécanismes de fonctionnement dc l'écosystème. en mettant l'accent sur les

Contribution n" 2J6 of the InstÎtuto de Cieneias dei Mar y Limnologia, Univcrsidad Nacioonai Aut6noma

de México.

A. yANEZ-ARANCIBIA. J. W. DAY

relations fonctionnelles ct en synthétisant l'information disponible rclati\'e aux sciences biologique, chimiqu e. physiquc ct écologique. La caractérisation écologique fait le point sur les connaissances concernam les ressources naturelles de la zone étudiée, décrit les zones sensibles aux aménagements, aide le développemem de techniques douces d'aménagemem el propose des solutions de remplacement pour sauvegarder l'environnemem: enfin, sen li mettre en évidence des besoins de connaissance.

La température ct la luminosité dans la lagune présentent une certaine stabilité saisonnière;

cette zone est caractérisée par un gradient permanent des facteurs physico-chimiques ct par une grande diversité de biotopes estuariens. Les vems dominams som â l'origine d'un nux cntram d'cau de mer dans la passe Est, et d'un nux sonant dans la passe Ouest, çe qui entraîne de fortes salinit és dans la partie oricmale de la lagune. Les apports fluviaux sont importants dans la partie occidentale de la lagune CI provoquent de fones turbidités ct un enrichissement des caux en nutriments. Dans la passe, un delta est en voie de formation du côté est. La plupart des phénomènes biologiques sont dépendants de ces gradients. Des herbiers très importants s'étendent dans la partie nord-est de la lagune; les herbiers sont progressivement remplacés par la mangrove dans le delta en cours d'émergence. Des bancs d'huîtrcs très

étendus sont situés dans la partie occidentale de la lagune près de l'embouchure de la rivière,

La production phytoplanktonique, les concentrations en chlorophylle ct les quantités de matière organ ique provenant de la mangrove sont plus élevées dans la zone fluviale. Les lalVes ct juvéniles de poissons pénètrent dans la lagune par la passe Est fi cause des çourants dominants. Le débit maximum du neuve sc silue en octobre en même temps que les plus rortes productions primaires et pendant l'immigration de juvéniles. Ouano/. Acta, 1982. AÇles Symposium International sur les lagunes côtières, SCOR/IABO/UNESCO, Bordeaux, 8-14 septembre 1981,431-440.

INTKODUCTION

Estuarine ecosystems arc dominated by a diversificd physi cal environment. EstuarÎne physical factors include winds, tidal and riverine effects, heavy nutrient loads, high lurbi· dit y Icvels, and turbulence. Moreover, in highcr latitudes there is a si lOng seasonal pulse of lempcrature and sunlight. Much of estuarine ecology is an investigation of the effect of Ihi) variablo.:: at..iulic cnvirollment on the biOla (Day, Yanez

Arancibia, 1982).

Términos Lagoon i5 an excellent site at whkh 10 stud)' physical-biological interaçtions ror a number of reasons:

1) because of ilS tropical location, thçre is no strong

seasonality in sunlight and Icmperature as in higher latitu des. Thus, in effecl. the unique estuarine riverine·tidal interaction is isolated rrom tempcrate scasonal variabililY ;

2) there arc two in lets connecting the lagoon wilh the Gulf

of México. Regional winds and coastal currents cause a net innow through one inlet and a nel outDow through the other, a circulation pattern that leads to strong semi· permanent gradients in salinity, turbidity, sediment lypeS, and nUlrient levcls ; 3) estuarine habitats in the lagoon arc diverse, including mangroves, submerged sea grasses, marsh grasses, oyst er reefs, areas of high sedimentation. and low salinity in the oligohaline zone. The errects of the physical environment can be studied in each casc. THE

PHYSICAL ENVIRONMENT

Regional sdting

Términos Lagoon is a large (:t: 2 500 km!), shallow (mean deplh 3.5 m) coastallagoon bordering the southern Gulf of México in Campeche, Méxiço (Fig. 1). Offshore is located Ihe Bay of Campeche, an area wilh a broad çontinental shcif. This rcgion supports one of the largest marine fishcries in México. The lagoon is at the base of Yucatsn

Peninsula

and boarders two gcologic provinces. To the cast is the Yucatân Peninsula. characterized by Jow rainfall.

OF €

Figure l

Tlrminos JAgoolI 011 CamptcM wast.

sowh(fn Gulf of MlxlCO. sht!"';111 Ih( moill ((ologlcul subsys/(ms.

LQ(ulr"tll's K'lIh

muril/./' ÎlIflUI'IIChumfHlII-Ba/chac:ah, Pt.: Paflzada-del

Es/t'. PA; Pom·AI05/a.

432
calcarcous soils. and I1Q signifieanl surface drainage. To the west and south arc the lowlands of Tabasco and the highla nds of Chiapas and GUaiemala. an area of high rainfall and fluvial soils. The Usumacinra-Grijalva river system (the largesl in México and sccond largest in the Gulf of México) discharges inlo the Gulf about 70 km to Ihe west. Three main rivers enter the lagoon: the Candelada, the Chumpan, and the Palizada (a distributaf)' of the

Grijalva·Usumacinra).

ClImalk IInd c1rtulation patterns

Thcrc are three • scasons" in this region (Fig. 2)_ From

June until

lhe end of Scptcmbcr. there are almost daily aftemoon and evening showers_ From Octobcr inlo MaTch is the scason of. nones" or winter storms. These Slorms are generally strongest and associated with rains during l 'ïl 11 \ "j _ IV . .. '" fi ... '-t--'

1 .....

c ......... ... _p""e"'nl __ •• j 1

Figure 2

rda/iollsMps ill Térmillos Lageoll. Da/a for prtcipi/arioll (it, mm). al/d days will, • 1I0r/tS" IIrt mOll/hly mtllll l'II/lItS (lIdllp/td from Bravo NÛfltl, Y4iitl·Arllrn."ibia, 1979). Wil/d di"l/iol/ a/ld ,'docity IIrt IIItal/ va/lits for tach ollhe 12 dirulions indiealta (adapltd {rom MafICiI/o, Vargol'. 19(0). Rh·tr dDlil art {rom S. H. II. (1976). 433

ECOLOOICAL CHARACTEAlZATION OF TÉAMINOS LAGOON

Novembcr, Dcccmbcr and Januaf)'. February through May is the dry season. Annual precipitation averages 168 cm.

Scasonal precipitation pattems over the

drainage basin arc simil ar to the local pattern. Temperatures in open lagoonquotesdbs_dbs16.pdfusesText_22

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