Biodiversity of oyster reef benthic macrofauna at the Virginia Coast Reserve

Within coastal lagoon ecosystems, oyster reefs create structurally-complex intertidal and subtidal habitats that influences the survival, growth, and reproduction of a diverse assemblage of organisms. Species assemblages within these environments may be mediated by a combination of abiotic and biotic factors across spatial scales. Local abiotic factors such as water salinity, and proximity to aquatic vegetation and ocean inlets can determine the type of species present due to species’ tolerances and life history traits. Biotic factors such as predator-prey interactions and competition further influence species abundances. In this study, I characterized the biodiversity surrounding restored oyster reefs in the intertidal and subtidal at two locations (an exposed site and a sheltered site) within the seaside bays of Virginia’s Eastern Shore, USA. To sample fauna, I used artificial benthic habitat units (“habitat trays”) consisting of oyster shell hash within open mesh trays of varying mesh size (coarse vs. fine mesh). I found that mesh size did not affect total fauna counts (no. of individuals per tray), but did alter relative species abundances (though this may have been due to slight seasonal changes that were conflated with trials of different mesh sizes). Additionally, the finer-mesh size increased the proportion of smaller crabs collected. I found that in both mesh sizes, bay locations shared a majority of the same common species of crabs, gastropods, shrimps, and fishes. Species diversity, richness, and evenness were comparable between sites, but we found differences in relative species abundances. Similarities in biodiversity between sites may be explained by similarities in spatial proximity and water quality. When looking across tidal zones, species richness was consistently greater in the subtidal, mainly due to a greater diversity of gastropods and shrimps. We also found differences in species composition between tidal zones, most likely due to a combination of biotic and abiotic factors.