Annual variation of ichthyoplankton assemblages in Neritic waters of the southern Gulf of Mexico

Intra-annual variations in larval fish assemblages in the southern Gulf of Mexico are analyzed in relation to the main fluvio-lagoon systems. Zooplankton samples were obtained with Bongo nets, mesh 505 mum, during February, June, September, and November 1992 from 22 sampling stations located at four transects perpendicular to the coast line. Fish larvae were sorted and identified at the lowest possible taxonomic level. Data were standardized to larvae per 100 m(3) and the Bray-Curtis dissimilarity index was applied to determine the larval fish assemblages throughout the annual cycle. The analysis discovered two main larval fish assemblages: Coastal and Neritic. Each assemblage depicted subgroups that varied in location and extension throughout the year. The spawning period and spawning location of the species are the main factors differentiating the Coastal from the Neritic assemblages. However, variations in composition and extension of the subgroups along the year can be attributed to the main circulation patterns, the continental water discharges, and mainly to the mixing process. Similarities between this work and previous ones, regarding hydrography and larval fish assemblages, suggest that assemblages and their variations are recurrent events in the continental shelf of the southern Gulf of Mexico.