Abstract
In order to understand the influence of variable freshwater inflow to estuaries and subsequent fluctuations in salinity on zooplankton community structure and larval recruitment, the distribution and abundance of decapod crustacean larvae in the Caloosahatchee River and Estuary, Florida were quantified using monthly plankton tows for two years. Larvae preferring high salinities (Callinectes sapidus, Dissodactylus spp., Menippe mercenaria, Petrolisthes armatus, and Pinnotheres maculatus) were concentrated near the mouth of the river; euryhaline larvae (Eurypanopeus depressus and Panopeus spp.) occurred abundantly throughout the river; and the low-salinity species Rhithropanopeus harrisii was found upstream. Total larval abundance peaked in late-spring, prior to the onset of the wet season. Additionally, C. sapidus, E. depressus, M. mercenaria, Panopeus spp. and R. harrisii exhibited significant shifts downstream with the onset of the wet season. P. armatus was the only species to demonstrate significant changes in total abundance among calendar seasons, with significant increases occurring during the spring. Species-specific centers of abundance and total abundance demonstrated significant correlations with both average continuous inflow and daily discrete inflow for lags of up to 120 days prior to sampling. C. sapidus, E. depressus, M. mercenaria, P. armatus, Panopeus spp. and R. harrisii were negatively correlated with inflow. Center of abundance and total abundance of Dissodactylus spp. and P. maculatus were positively correlated with daily discrete inflow. These commensal crabs did not respond in the same way to changes in salinity as expected based on the other species surveyed. These results suggest the importance of considering the impacts of freshwater discharges on both the spatial and seasonal variation in larval supply within the estuary.