Summer Ichthyoplankton Assemblage Diversity Within a Southeastern United States Estuary

Abstract

We evaluated spatial, short-term, and decadal-scale variability in the summer ichthyoplankton assemblages within the North Inlet-Winyah Bay estuarine system, Georgetown County, South Carolina, USA. Ichthyoplankton were collected weekly from late May to early September 2016 on nighttime flood tides using a 1-m diameter, 1-mm mesh plankton net at three sites of varying salinity and proximity to inlets. Nearly 30,000 fishes representing 59 taxa were collected from all three sites over the 14-week study period. Gobiidae and Anchoa spp. dominated the overall community, composing between 69 and 94% of the total catch at each of the three sites. Weekly densities of all taxa combined did not vary between sites, yet diversity metrics (richness, evenness, Shannon-Weiner index, and Simpson’s index) were greatest at the highest salinity site, and overall assemblage composition significantly varied among sites. Non-metric multidimensional scaling suggested a shift in the assemblage at all sites corresponding to an increase in water temperature throughout the summer. Differences in family-level assemblage composition between this study and previous work from the 1980s were detected, differences which may be indicative of regional-scale environmental change. Overall, the summer ichthyoplankton assemblages resembled those from other estuaries along the southeastern US Atlantic coast and temperate regions worldwide, generally dominated by a few taxa and composed of a mixture of estuarine-, estuarine and nearshore-, and continental shelf-spawning taxa.