LARVAL FISH ASSEMBLAGE RESPONSE TO FRESHWATER INFLOWS: A SYNTHESIS OF FIVE YEARS OF ICHTHYOPLANKTON MONITORING WITHIN NUECES BAY, TEXAS

摘要

The spring season spatiotemporal dynamics of the ichthyofaunal assemblage structure and its relationship to freshwater inflows were investigated in the Nueces Estuary, a secondary bay system along the Texas coast which is heavily influenced by the operation of two reservoirs within its watershed. The study was based on a comprehensive survey consisting of 499 plankton collections from four to six fixed stations over six calendar years. During this study period, the Nueces Estuary experienced hydrological fluctuations spanning from moderate drought to the watershed's flood of record. In total, 265,664 larval and juvenile fishes from 21 families and 51 taxa were collected. Three families (Engraulidae, Gobiidae, and Clupeidae) accounted for 97.6% of the individuals. Despite the widely varying inflow conditions experienced within the estuary, analysis of similarity of the larval fish assemblages revealed that significant differences existed only among the years with the most extreme salinity differences. Temporal trends of maximal abundance in the plankton during the mid- to late spring were similar across years. Peak abundance and composition of the ichthyoplankton were temporally modified by the timing of the inflow events. Taxonomic diversity of the ichthyofauna also responded to the inflow events, with greatest phylogenetic diversity present during a springtime-coincident flood event. Only during the most extreme inflows (record spring flooding coincident with the peak in fisheries abundance) did the abiotic conditions dramatically alter the larval fish assemblage recorded within the Nueces Estuary.