ICHTHYOPLANKTON COMMUNITY STRUCTURE AND FEEDING ECOLOGY IN THE PATUXENT RIVER ESTUARINE TRANSITION ZONE

Abstract

Surveys were conducted during spring-early summer of 2000 and 2001 to investigate the spatiotemporal structure of ichthyoplankton assemblages, including hatchery-released American shad <i>Alosa<i> <i>sapidissima<i>, and feeding of larval fishes in the Patuxent River, Chesapeake Bay. Ichthyoplankton, zooplankton, and hydrographic data were collected across the Patuxent's estuarine transition zone, including the salt front and Estuarine Turbidity Maximum region. Recaptured American shad larvae cohort mortality (<i>M<i> = 0.20 to 3.01d^-1) and growth (<i>G<i> = -1.28 to 0.87 mmd^-1), low dispersal (±0.4kmd^-1), and feeding habits similar to co-occurring species, suggest that the best production will result from larval shad releases upriver of the salt front in early to mid-May. Two ichthyoplankton assemblages were distinguished: 1) riverine characterized by anadromous species and 2) estuarine characterized by naked goby <i>Gobiosoma<i> <i>bosc<i>. Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and the larval prey <i>Bosmina<i> <i>longirostris<i> (Cladocera) concentrations were indicators of larval abundance. Abundance, taxonomic diversity, and dietary overlap and potential for competition among larval taxa were highest within and up-estuary of the salt front of the estuarine transition zone.