Predicted Changes in Seagrass Cover and Distribution in the Face of Sea Level Rise: Implications for Bivalve Aquaculture in a US West Coast Estuary

Sea level rise (SLR) is changing coastal habitats that support valuable ecological and economic resources. A rise in global mean sea level (GMSL) will lead to changes in water depth in coastal bays and estuaries, affecting the distribution of seagrasses, which provide numerous ecosystem services, but are declining globally. In estuaries along the west coast of the USA, seagrasses often co-occur with shellfish aquaculture and some aquaculture practices negatively influence seagrass. Understanding this interaction and future shifts in seagrass distribution has therefore become a concern for both natural resource managers and aquaculturists. In this study, a model is developed to establish relationships between seagrass presence and seven predictor variables (bathymetric elevation, salinity, distance to estuary mouth, distance to nearest channel, cumulative wave stress, sediment composition and burrowing shrimp density) and then used to predict the distribution of eelgrass ( Zostera marina ) in aquaculture habitats of Willapa Bay, Washington, for the years 2030, 2050 and 2100 under conservative and high rates of SLR. The model predicts Z. marina will increase throughout the intertidal for all SLR scenarios and years, resulting in as much as 34% more eelgrass in Willapa Bay by 2100 and a 40% increase within aquaculture beds. By 2100, Z. marina could increase in as many as 333 of the 458 aquaculture beds examined and the majority of aquaculture beds could experience over 50% Z. marina coverage. Such increases in Z. marina will likely result in future management challenges for aquaculture operations.