Reefs in no-take reserves host more oysters, macroparasites, and macrofauna than harvested reefs across an estuarine salinity gradient

Abstract

No-take reserves and habitat restoration are important management tools for reversing the effects of fishing on coastal habitats, associated faunal assemblages, and host-parasite interactions. Populations of the eastern oyster Crassostrea virginica have declined by 99% in areas of Chesapeake Bay, USA, due to overharvesting, disease, and other factors, and are now the focus of extensive restoration efforts. We surveyed subtidal oyster reefs using classic quantitative approaches and emerging videography methods to contrast pairs of harvested reefs and reefs protected in subtidal no-take marine reserves (oyster sanctuaries) in the Choptank, Great Wicomico, and James River tributaries of Chesapeake Bay. Overall, sanctuary oyster reefs contained more intact habitats and communities. Relative to nearby harvested reefs, sanctuary reefs (1) contained higher densities of oysters, (2) held larger oysters of lower condition, (3) hosted stronger oyster-macroparasite (boring sponge [Cliona spp.] and mud blister worm [Polydora spp.]) interactions, (4) had more complex habitat, and (5) supported a greater richness and abundance of macrofauna. Oyster and mobile macrofauna abundance increased with salinity, whereas macroparasite pre-valence peaked at mesohaline (5-20 psu) sites. Our results suggest that restored, sanctuary-protected oyster reefs are beginning to rebound from the effects of >100 yr of intensive harvest, as indicated by increased oyster density, recovery of host-parasite interactions, improved habitat characteristics, and more mobile macrofauna. Additionally, these patterns, observed across the salinity gradient in Chesapeake Bay, reflect a widespread trend in aquatic ecology: relative to fished areas, unfished areas have more complex habitats and communities, larger and higher densities of hosts, and stronger host-parasite interactions.