Abstract
It is well known that gelatinous zooplankton such as chaetognaths, hydromedusae and ctenophores are voracious predators of copepods and the eggs and larvae of fishes. Because gelatinous predators and ichthyoplankton often co-occur within estuaries, changes in environmental factors, many of which are driven by freshwater inflow, can influence zooplankton distribution and abundance, potentially altering trophic relationships. To determine how freshwater inflow shapes ichthyoplankton and gelatinous predator assemblages and the potential interactions between them, zooplankton were collected monthly using oblique plankton tows at 16 stations throughout Estero Bay, Florida from January 2005 through December 2006. Samples were collected from the passes, open bay waters and tidal tributaries. Ichthyoplankton and gelatinous zooplankton were identified to the lowest practical taxon and data were analyzed using contour plots, and correlation and regression analyses. Distribution and abundance of ichthyoplankton were primarily influenced by reproductive timing, water temperature, salinity, prey availability, and freshwater inflow. Gelatinous predator abundances were primarily influenced by water temperature, prey availability, and freshwater inflow. Ichthyoplankton abundances were 2-fold higher in 2005 compared to 2006. Conversely, gelatinous predator abundances were 8-fold higher in 2006 compared to 2005. The high degree of interannual variability in abundances between years was likely related to differences in freshwater inflow. Data suggest flows >0.5 m3 s-1 would be sufficient to prevent a majority of the gelatinous predator taxa identified in this study from entering nursery habitat associated with the tributaries. This would result in less competition for resources and may increase survival rates of larval fishes.
