ECOLOGY OF INFAUNAL MOLLUSCA IN SOUTH TEXAS ESTUARIES

The ecology of Texas estuaries is strongly influenced by latitudinal e cotones that exist along the northwestern Gulf of Mexico coastline. Lo ng-term studies were conducted in four of the seven major estuarine ec osystems in Texas. The objective was to determine the role of climatic variability and concordant differences in freshwater inflow among the ecosystems in structuring benthic infaunal communities and maintainin g secondary production. Mollusks are prominent members of the infauna in all benthic habitats of Texas estuaries. The abundance, biomass, an d community structure of mollusks was measured along salinity gradient s within the four south Texas estuaries. Infaunal samples were collect ed by divers using small (6.7 cm diameter) cores (so larger epibenthic mollusks were not collected). Overall, these Texas estuaries had a me an of 14 species of infaunal mollusks, with mean abundance of 7,500 in dividuals/m(2), and mean biomass of 2.4 g/m(2). Freshwater inflow is t he dominant factor regulating variability of molluscan communities. Sa linity is a surrogate for inflow, therefore, there are zoogeographic p atterns within and among estuaries related to salinity patterns. There are seasonal, interannual, and latitudinal patterns of inflow, and th ese patterns are apparently regulating community structure, population dynamics, and secondary production in Texas estuaries. Recent water p rojects to enhance the amount of freshwater flowing into estuaries app ear to have had an effect and have increased the number of mollusks in those areas. However the projects occurred during a naturally wet per iod, so it is difficult to differentiate natural versus anthropogenic changes. The response of mollusks to natural gradients and man-induced changes of freshwater inflow demonstrate the importance of this facto r in regulating benthic communities.