Impacts of Oyster Aquaculture on Subaqueous Soils and Resident Infauna in Rhode Island Coastal Lagoons.

Coastal lagoons are unique estuaries that are experiencing expansion of oyster (Crassostrea virginica) aquaculture in southern New England. Although native shellfish are known to help maintain water quality, few studies have examined the environmental impacts of long-term aquaculture on the benthic environment We assessed the effects of time under oyster aquaculture (0-21 years) on three coastal lagoons in southern Rhode Island, using subaqueous soil properties and resident benthic infauna as indicators of environmental impact. Samples were collected from the upper 20 cm of the soil in aquaculture areas, and in control areas, not previously used for aquaculture practices. Samples were analyzed for bulk density, total carbon and nitrogen, incubation pH (soil sulfide levels), and soil pore-water sulfide levels. Benthic infauna were sorted, identified by species, and assigned to a functional feeding group. Although bulk density, total carbon and nitrogen levels, and incubation pH were significantly different across all sites and depths, these differences were not proportional to time under aquaculture use. Aquaculture sites also had significantly higher total abundance of infauna, populations of deposit and interface feeders, and soil pore-water sulfide levels compared to control sites, however, differences were not proportional to age of aquaculture use. In addition, aquaculture sites had larger populations of opportunistic species (e.g. Capitella capitata and Corophium volutator), which are indicative of disturbance. Our results suggest that continuous aquaculture has few impacts on soil properties over time; however, site specific aquaculture practices and associated soil disturbances appear to increase soil pore-water sulfide levels and cause a significant shift in the total abundance and trophic structure of infauna.