Differential settlement of ribbed mussels in natural fringe salt marshes and living shorelines in Chesapeake Bay

Ribbed mussels (Geukensia demissa) are secondary foundation species of salt marshes along the Atlantic East Coast, providing ecosystem services such as water filtration, nutrient removal, shoreline stabilization, and sediment accretion. Despite their integral role in ecological and structural marsh processes, it remains unclear whether living shorelines—now widely promoted as a nature-based coastal protection—provide comparable habitat for ribbed mussels as natural fringe marshes. In this study, we compare juvenile ribbed mussel settlement across four living shoreline and natural fringing marsh site pairs in the lower Chesapeake Bay. We deployed artificial substrates for mussel settlement to assess differences across sites and examine relationships with marsh conditions (e.g. cordgrass and mussel density, inundation, connectivity). After a three-month period, juvenile mussel counts were ~11x lower on substrates deployed in living shorelines than in natural marshes. An additional one-week trial revealed less than half the number of settlers at the living shoreline compared to its natural counterpart. Mussel settlement was most strongly affected by site type (living shoreline versus natural marsh) but did not exhibit any detectable relationships with the other marsh metrics. Our findings suggest that the typical marsh-sill living shoreline design may constrain early recruitment of ribbed mussels through interrupted or absent settlement cues, possibly due to altered hydrodynamics (e.g. presence of the rock sill) and/or substrate conditions. Restoration design that incorporates elements critical for larval delivery, settlement, and survival will enhance mussel recruitment, strengthen positive marsh-mussel feedbacks, and improve the resilience and ecosystem service provision of living shorelines.