Geospatial variation of ribbed mussel (Geukensia demissa) ecosystem services across the salt marsh landscape
Authors:   , Moody Joshua Andrew , Kilham Susan Soltau , Kreeger Danielle 
Published: July 2021

Salt marshes are a hallmark feature of the Atlantic coastline, where they provide a variety of ecosystem services such as: protection from flooding; nutrient and pollutant sequestration; economic uplift from recreational and commercial ventures; and habitat for a variety of finfish, birds, invertebrates, and mammals. Ribbed mussels (Geukensia demissa) are the functionally dominant animals of Gulf and Atlantic salt marshes, living in facultative mutualism with salt marsh cordgrass (Spartina alterniflora). The cordgrass provides habitat and attachment sites for mussels. In turn, the mussels, through the filtration of seston, provide nutrients for plant production through biodeposition. The magnitude of this pelagic-benthic coupling depends on ribbed mussel population density and the quantity and quality of seston. Since mussels are not evenly dispersed across the salt marsh landscape, their ecosystem services are geospatially variable which may have implications for resource managers interested in sustaining or enhancing mussel-mediated benefits. This dissertation's objective was to quantify the annual variability in particle and nutrient filtration across three habitats of the salt marsh landscape: low marsh habitats along primary tidal channels; intra-marsh creek networks; and vast expanse of high marsh platform. Four representative salt marshes were selected for this study: Dividing Creek, Dennis Creek, and Maurice River in New Jersey along the Delaware Bay; and Coggeshall Cove in Rhode Island in the Narragansett Bay. The relevance of seston filtration data for understanding ecosystem services was demonstrated by estimating the spatial distribution and magnitude of net particulate nitrogen removal and the contribution of biodeposits to vertical marsh accretion. Clearance rates of water by ribbed mussels exhibited little spatial variation, but were dependent on seasonal temperatures. Filtration rates of seston varied with both space and time, since seston quantity and quality was variable at the same scales. Therefore, annual water processing rates can be extrapolated across regions that share similar temperature profiles, but local knowledge regarding seston variability is required to calculate particle filtration services. Annual gross filtration of total suspended solids (TSS) ranged between 4,500 & 11,000 kg ha-1 yr-1 at three locations in New Jersey and 3,800 kg ha-1 yr-1 at one location in Rhode Island. Filtration of particulate nitrogen (PN) ranged between 38 & 92 kg ha-1 yr-1 in New Jersey, assuming 60% of filtered nitrogen was either incorporated into somatic tissue or biodeposited, and 31 kg ha-1 yr-1 in Rhode Island, assuming 43% of filtered nitrogen was either incorporated into somatic tissue or biodeposited. This translated into contributions to vertical accretion between 39 & 93 mm in New Jersey and 26 mm in Rhode Island, if distributed evenly across the salt marsh landscape at the four study sites. The majority of mussel-associated ecosystem services were located in small, mussel-rich, creek networks of both New Jersey (74%) and Rhode Island (69%). However, large discrepancies in mussel density along the primary tidal channels between New Jersey and Rhode Island marshes, resulted in low service provisioning in New Jersey (3%) relative to Rhode Island (28%) in this "shoreline" habitat. The ability to understand the geospatial variation in mussel-mediated services provides natural resource managers with the ability to prioritize areas of high service value for conservation. Additionally, areas where services are underrepresented relative to regional potentials, presumably because of erosion or degradation, can be targeted for restoration or enhancement to maximize ribbed mussel biomass and service potential.