Defining the Zostera marina (Eelgrass) Niche from Long-Term Success of Restored and Naturally Colonized Meadows: Implications for Seagrass Restoration

Seagrass restoration can help reverse global meadow loss and restore ecosystem services, including habitat provision for commercial fish and shellfish, carbon sequestration, and improved water quality. However, restoration projects are generally expensive, and site selection remains a challenge due to uncertainty about how environmental variables affect the survival and spread of seedlings. Long-term Zostera marina (eelgrass) success/failure and expansion data from the Virginia Coast Reserve can be used to determine whether the factors that control seedling survival also explain the regional distribution of seagrass meadows. We tracked plant survival and failure within restoration plots and at natural recruitment sites from 2001 to 2015 and used machine learning methods to identify the relative importance of multiple environmental predictors, including water residence time, fetch distance, water temperature, depth, and sediment grain size. Low water residence time was the best predictor of survival, but short fetch length best explained the natural recruit distribution, consistent with hydrodynamic control of seed dispersal. Restoration plot data suggests that the eelgrass fundamental niche covers > 100 km2 within this system, triple both the current extent and the realized niche predicted by the observed natural spread. Our results corroborate historical records that eelgrass was formerly widespread in areas where it has not spread naturally, likely due to insufficient seed delivery. Additional seeding in these areas would, therefore, increase total seagrass coverage and accelerate recovery. Mapping the total habitable area can help managers maximize the extent of seagrass and other bottom uses, including shellfish aquaculture.