Spatial, seasonal and diel distribution patterns of two species of mojarras (Pisces: Gerreidae) in a Mexican tropical coastal lagoon

Abstract

Instituto de Ciencias del Mar y Limnologi´a, Universidad Nacional Auto´noma de Me´xico, Me´xico, D.F., Me´xicoSummarySpatial, seasonal and diel distribution patterns were analysedover a 2-year period for Diapterus auratus and Eucinostomusmelanopterus in Pueblo Viejo lagoon, a tropical coastal lagoonin Veracruz, Mexico. A total of 216 samples were collectedwith 329 individuals of D. auratus and 170 of E. melanopterus.Diapterus auratus individuals were captured throughout awider range of environmental conditions, and consequently itsspatial niche breadth was significantly greater (P < 0.001)than that of E. melanopterus. In general, more individuals werecaptured at localities with submerged vegetation (Ruppia mar-itima), with 70% for D. auratus and 87.2% for E. melanopte-rus, although only the latter species showed significant spatialdifferences. A spatial segregation influenced by distance fromthe lagoon inlet and salinity was observed between the species.It is considered that this segregation may allow resourcepartitioning and minimize interspecific competition. A relat-ively low niche overlap (4.9%) was observed for the twospecies. Seasonal capture peaks of D. auratus were related torainfall and the productivity pattern in the lagoon system.Seasonal fluctuations in monthly mean number of D. auratuswere correlated with preceding variations in local rainfall(r ¼ 0.86, P < 0.02). Moreover, seasonal capture peaks ofD. auratus coincided with ecosystem primary productionpeaks. Although E. melanopterus exhibited no significantseasonal differences, its maximum numbers also coincidedwith an ecosystem primary production peak and recruitmentpatterns. In 24-h cycle analysis, both species were capturedmainly around mid-day, with minor peaks at dawn and/or atdusk. Generally, few individuals were collected during hours ofdarkness. It was proposed that diel abundance variation ofgerreids might be related to both light penetration in the watercolumn and feeding activity. Food availability within PuebloViejo lagoon appears to be an important factor influencing fishabundance.IntroductionThe Gerreidae family (mojarras) is mainly marine, with about40 species described worldwide (Nelson, 1994). Twelvemarine species exist in the Western Atlantic, plus onefreshwater species in the watersheds of Mexico and Guate-mala. There are approximately nine confirmed species recor-ded for the coastal waters of the western Gulf of Mexico(Robins and Ray, 1986; Deckert and Greenfield, 1987;Matheson and Gilmore, 1995). Members of this family arevery abundant in tropical and subtropical coastal lagoons,and are among the dominant species in estuarine systems ofthe northern (Aguirre-Leo´n and Ya´n˜ez-Arancibia, 1986;Stoner, 1991; Matheson and Gilmore, 1995) and southernWestern Atlantic (Garzo´n-Ferreira, 1989; Teixeira and Fal-cao, 1992; Rami´rez-Villarroel, 1994; Chaves and Bouchereau,1999), making an important contribution to commercialfisheries (Arau´jo and Santos, 1999).In spite of their importance, few studies have been conduc-ted exclusively on the biology and ecology of the mojarraspecies. Most published information consists of incidentalrecords or notes in general surveys (Cyrus and Blaber, 1983).Studies from tropical and subtropical estuaries of the westernAtlantic are limited and typically concentrate on feeding habits(Austin, 1971; Kerschner et al., 1985; Arenas-Granados andAcero, 1992), with little attention given to the spatial andtemporal distribution of the mojarras.The present study aims at increasing the knowledge ongerreid ecology by studying the distribution patterns ofDiapterus auratus Ranzani, 1840 and Eucinostomus melano-pterus (Bleeker, 1863) in Pueblo Viejo lagoon, Mexico. Theobjective was to analyse the spatial, seasonal and dieldistribution patterns, and their relationship with the mostimportant environmental conditions.Materials and methods