Larval fish assemblage dynamics in the York River estuary, Virginia, U.S.A.

The York River estuary (Chesapeake Bay) ichthyoplankton assemblage is described based on weekly sampling at a single site from 2007 to 2015. Larvae of 39 estuarine, marine, and diadromous taxa (24 families) were collected and patterns for 5 taxa (Atlantic menhaden [Brevoortia tyrannus], Atlantic croaker [Micropogonias undulatus], common anchovies [Anchoa spp.], American eel [Anguilla rostrata], and summer flounder [Paralichthys dentatus]) were analyzed. The most abundant taxa (collectively 92.6% of larvae encountered) were Anchoa spp., naked goby (Gobiosoma bosc), green goby (Microgobius thalassinus), Atlantic croaker, and Atlantic menhaden. Two distinct assemblages were present each year—a warm season assemblage (May to August) and a cool-season assemblage (September to April). Model-based predictions of mean species richness across the time series varied, with greatest richness from 2007 to 2009. Predicted mean seasonal species richness also varied, with stable richness from October to May and elevated richness from June to September. Analogous predictions of mean annual and seasonal Simpson’s inverse diversity generally followed patterns of species richness. Predicted annual mean densities were relatively lower during the middle years of the time-series for Atlantic menhaden and summer flounder, consistently declined for Anchoa spp. and Atlantic croaker, and were generally constant for American eel. Seasonal patterns in predicted mean densities of those taxa reflected seasonality of spawning.