Abstract
Decapod crustaceans are predominately meroplanktonic, spending their early life stages in the water column as zooplankters before settling onto benthic habitat. Planktonic decapods are subject to influence by natural and anthropogenically altered freshwater inflow in estuaries. In order to capture both spatial and temporal variability in decapod zooplankton abundance and distribution in Estero Bay, sixteen stations were sampled monthly, from January 2005 through December 2006, using plankton tows at open bay sites, near tidal passes, and along the lower reaches of the main tributaries. Seasonal variability of freshwater inflows influenced the distribution of decapod plankton in the bay by structuring the bay's salinity regime, which affected various species differently. The majority of decapods exhibited peak abundances in spring and summer months with precipitous declines at the onset of the wet season in each of the two study years, indicating a response to freshwater inflow and/or decreased salinities. Densities of the mud crab, R. harrisii, indicate a geographical association with tributary (lower salinity) stations, while other common species exhibit greatest densities at open bay and near pass stations. Multivariate statistical analysis of the larval decapod densities reveal significant difference in community structure between stations within the influence of high-flow tidal tributary stations (lower salinity) and all other stations (higher salinity). The influence of freshwater inflow and resultant salinities on decapod distribution and community structure was strongest in the northern and southern portions of the Bay where the greatest freshwater inflows exist. When examining community structure along the main estuarine axis, higher rates of change were identified at each end of estuarine salinity gradient.