Effects of floating oyster aquaculture on a Zostera marina dominated bed in Chesapeake Bay

Bivalve aquaculture continues to increase in coastal waters globally as consumer demand increases. Simultaneously, there has been a worldwide effort to restore seagrass beds following large-scale declines of these critical habitats, creating potential use conflicts in many shallow-water environments. In Chesapeake Bay, Virginia, USA, nutrient reductions and seagrass habitat restoration have been a focus for decades, and a precautionary approach to permitting aquaculture operations within seagrass has been the norm. To examine whether the current precautionary approach is too conservative, this study quantified the impacts of floating oyster aquaculture on a Zostera marina (eelgrass)-dominated seagrass bed. Seagrass and macroalgae percent cover and canopy height measurements were taken over 5 yr. Experiments were designed to measure small-scale direct impacts as well as broader farm-scale impacts using a paired before-after control-impact (BACI) design. Small-scale impacts to seagrass under the oyster cages were statistically significant in only one of 5 years. Measurements taken within the farm footprint compared to areas immediately outside the farm found macroalgae to have a higher probability of being present within the farm but no differences in other measured parameters. The impacts of both adding a floating oyster farm to an existing seagrass bed as well as the impacts of removal of a farm were analyzed, with no significant impacts detected. Our work shows that under similar environmental conditions and using the farm practices in the current study, floating oyster aquaculture and Z. marina -dominated seagrass beds can coexist in the Chesapeake Bay.