Surveys were conducted to evaluate and compare assemblage
structure and trophodynamics of ichthyoplankton, and their variability, in an estuarine transition zone.
Environmental gradients in the saltfront region of the Patuxent River subestuary, Chesapeake Bay, were hypothesized to define spatiotemporal distributions and assemblages of ichthyoplankton. Larval fishes, zooplankton,
and hydrographic data were collected during spring through early summer 2000 and 2001. Larvae of 28 fish species were collected and species richness was similar each year. Total
larval abundance was highest in the oligohaline region down-estuary of the salt front in 2000, but highest at the salt front in 2001. Larvae of anadromous fishes were most abundant at or up-estuary of the salt front in both years. Two ichthyoplankton assemblages were distinguished: 1) riverine—characterized predominantly by anadromous species (Moronidae and Alosinae); and 2) estuarine—characterized
predominantly by naked goby (Gobiosoma bosc) (Gobiidae). Temperature, dissolved oxygen, salinity-associated
variables (e.g., salt-front location), and concentrations of larval prey, specifically the calanoid copepod
Eurytemora affinis and the cladoceran Bosmina longirostris, were important indicators of larval fish abundance. In
the tidal freshwater region up-estuary of the salt front, there was substantial diet overlap between congeneric
striped bass (Morone saxatilis) and white perch (M. americana) larvae, and also larvae of alewife (Alosa
pseudoharengus) (overlap= 0.71–0.93). Larval abundance, taxonomic diversity, and dietary overlap were highest
within and up-estuary of the salt front, which serves to both structure the ichthyoplankton community and control trophic relationships in the estuarine transition zone
