Seasonal variations in the diversity,abundance, and composition of species in an estuarine fish community in the Tropical Eastern Pacific,Mexico

The ichthyofauna of the Chacahua Lagoon in the western Oaxaca State of Mexico was sampled every 2 months, using a trawl net over seven sampling cycles. The estuary mouth closed in late January, generating hypersaline conditions in the system. A total of 33 species belonging to 20 families were recorded; most of them marine species, showing tropical and subtropical affinities. The most abundant species were Diapterus peruvianus, Centropomus robalito, Anchovia macrolepidota, Lile stolifera, and Lutjanus novemfasciatus. Total fish abundance and species richness were not significantly affected by the mouth closing, and this was related to the presence of a permanently open entrance channel with an adjacent lagoon, which allowed easy exchange of fish between these two systems. Canonical correspondence analysis (CCA) revealed that salinity and dissolved oxygen were the most important environmental variables in determining the observed variability in fish community composition. Two fish groups were evident: the fish assemblage of the low-salinity period (open-mouth phase), in which Eucinostomus currani, Sciades guatemalensis, Centropomus armatus, Citharichthys stigmaeus, and Caranx caninus constituted the majority of the catch; and the fish assemblage of the high-salinity period (closed-mouth phase), with A. macrolepidota, L. stolifera, and Harengula thrissina as the most abundant species. Multivariate analyses showed differences in the composition of the fish community between both periods. Other species, such as the permanent residents D. peruvianus and C. robalito, which showed the widest range in tolerance of ambient salinity, were caught during both periods. Seasonal succession of fish populations may be related to differences in life cycle and tolerance of the environment among those species adapting to ecological conditions.