Bottom-use conflicts in shallow coastal zones: hard clam (Mercenaria mercenaria) aquaculture and restored seagrass (Zostera marina)

Multiple-use conflicts of the marine benthos (“bottom-use conflicts”) are increasing as humans expand use of the coastal zone. These conflicts necessitate balanced management policies that consider the economic and ecological benefits of different bottom uses. In the Virginia coastal lagoons, there is a potential bottom-use conflict between hard clam ( Mercenaria mercenaria ) aquaculture and restored seagrass ( Zostera marina ) meadows. We leveraged two decades (2001–2021) of aerial imagery and environmental data to quantify historic trends in bottom use and conflict, assess the realized niche of seagrass and clam aquaculture across five environmental variables (depth, sand fraction, root mean square [RMS] velocity, fetch, sea surface temperature anomaly), and used random forest models to predict the potential extent of seagrass, hard clam aquaculture, and bottom-use conflict in the future. We found growth in the areal coverage of both bottom uses over the past twenty years with a corresponding increase in bottom-use conflict, though the area of conflict remained relatively minor. We quantified significant but subtle differences in the distribution of seagrass and clam aquaculture across depth, sand fraction, RMS velocity, fetch, and sea surface temperature anomaly. Our random forest models predicted great potential for the expansion of both bottom uses with a relatively small area of predicted spatial overlap under current environmental and regulatory conditions. These results illustrate how species distribution models can be used to understand the spatial impacts of aquaculture on natural ecosystems and inform resource managers and policy makers to create objective policies that balance socioeconomic and ecologic needs.