Shifting Patterns of Ribbed Mussel Distribution and Ecosystem Services in Response to Sea Level Rise

Throughout the salt marshes of the US Atlantic Coast, ribbed mussels (Geukensia demissa, Dillwyn, 1817) and smooth cordgrass (Spartina alterniflora Loisel) form an important mutualistic relationship. Spartina provides habitat and promotes settling of ribbed mussels, which, in turn, stabilize and fertilize the Spartina and sediment. This relationship, however, is at risk of interruption due to sea level rise, erosion, and coastal development. Among the most at-risk segments of the marsh, the front (waterward) edge of the marsh is also where ribbed mussels and their ecosystem services are concentrated. Despite their importance of ribbed mussels to the salt marsh ecosystem, very little is known about the spatial distribution. in order to address these questions, we had the following objectives: 1) to identify spatial factors influencing mussel distribution across the landscape, 2) to quantify the contribution of ribbed mussels to nitrogen removal in the presence of Spartina, and 3) to assess how the distribution of the population and its ecosystem services are likely to change by the year 2050. We conducted field work in the summers of 2015 and 2016 to survey ribbed mussel populations in 30 marshes around the Chesapeake Bay. Ribbed mussel population density and distribution was positively related to the number of Spartina stems, the exposure of the site, and to a minor degree, the amount of agriculture within 300 m. The amount of forested land cover within 60 m was negatively related to ribbed mussel density. With these factors, we built a model to estimate ribbed mussel populations in the first two meters (edge) of the marsh, and estimated the presence of 805 million mussels along the edges of Virginia\u27s marshes. Sediment core incubations revealed that when ribbed mussels are integrated with Spartina, the ammonium and particulate removal is enhanced, relative to when mussels occur separately, but that the overall rates vary dramatically by the location of the marsh whence the cores were collected. Spatial application of a 0.62 m sea level rise scenario and local erosion rates altered the distribution of both marshes and ribbed mussels. Overall, ribbed mussel abundance declined by 3.6% between 2018 and 2050; however, most locations saw moderate to large declines, while a very few locations saw very large increases (\u3e 100%). Declines in abundance were greatest in urban areas dominated by fringing marsh and extensive shoreline armoring, while gains were greatest in agricultural areas with extensive marshes. The projected redistribution of mussels by 2050 will have important implications for water quality improvement goals that will need to be addressed by local and state authorities. This dissertation has focused on the seascape ecology and management of ribbed mussels in the Chesapeake Bay. The work has demonstrated the importance of applying spatial techniques to study and understand organisms and ecosystems at the interface between land and water. Only through further study and proactive planning will we be able to plan for and address the coming impacts of anthropogenic climate change and sea level rise

Impacts of Projected Sea Level Rise on Diamondback Terrapin Nesting Habitats in Virginia

Diamondback terrapins face a variety of ecological and human pressures. As an estuarine species reliant on the availability of optimal nesting sites, the effects of climate change and sea level rise are important to consider when determining appropriate conservation methods for terrapins. My research focuses on the potential impacts of sea level rise on diamondback terrapin nesting locations along tidal shorelines in Virginia. Utilizing GIS and maximum entropy modeling (MaxEnt), I have edited and analyzed spatial data to determine optimal nesting habitats and how these locations will change as rising sea level forces land use shifts. Through my analysis, I determined that essential nesting habitat factors include: distance to beaches, distance to core habitat (the marsh habitat terrapins occupy when not nesting), salinity, and placement of roads. Using this information, I have created a model displaying the current distribution of terrapin nesting habitat throughout Virginia. My results demonstrate how future terrapin nesting habitat will likely decrease across Virginia shoreline. With this information, conservation efforts can be focused on the current terrapin nesting habitat most threatened by rising waters

Johns Point Landing Living Shoreline – Ecological Monitoring : Final Report to Gloucester County

VIMS monitoring activities consisted of three components: • Monitoring of marsh vegetation establishment after planting • Documenting ribbed mussel and oyster recruitment and growth in experimental bags of oyster shell at the living shoreline • Monitoring infaunal communities prior to and after living shoreline implementatio

Impact Assessment and Management Challenges of Key Rural Human Health Infrastructure Under Sea Level Rise

Accelerating sea level rise in Virginia, United States, will significantly increase the flooding threat to low-lying roads, residences, and critical infrastructure as well as raise the water table, allowing saltwater intrusion into well water and threatening the function of septic fields. Although most of the adaptation work in Virginia has focused on urban economic centers, the majority of the coastline is rural and faces different threats and opportunities to address them compared to urban areas due to their reduced economic assets and their reliance on private infrastructure. In this case study, we assess the potential for geospatially quantifying impact to septic systems and adjacent water ways due to sea level rise. The case study found that the data necessary to reliably quantify these impacts on a state-wide scale are lacking and collection of that information needs to be prioritized given the potential for extensive sea level impacts

Large Projected Population Loss of a Salt Marsh Bivalve (Geukensia demissa) from Sea Level Rise

Salt marshes and their inhabitants are being displaced by climate change and human development along the coastline. One inhabitant, the ribbed mussel (Geukensia demissa), forms a mutualistic relationship with smooth cordgrass, Sporobolus alterniflorus, along the US Atlantic Coast. Ribbed mussels stabilize the marsh, remove particulate matter from the water column, and promote denitrification, thereby improving local water quality. To quantify the potential effects of SLR on ribbed mussel abundance and resulting impacts on water quality functions, we compared the current and projected future (2050) spatial distributions of ribbed mussels in Chesapeake Bay assuming an intermediate SLR for the region. We found that ribbed mussel abundance was reduced by more than half due to a combination of drowning marshes, coastal squeeze, and a shift from higher to lower quality habitat. Mussel losses were greatest along the mainstem of the Chesapeake Bay, with modest gains in the headwaters. Our results highlight the importance of permeable land cover (including living shorelines) in the future tidal extent to promote marsh transgression for future mussel populations. The projected mussel abundance reductions will result in a \u3e 50% reduction in mussel-mediated filtration and nitrogen processing, ultimately reducing the resilience of marshes in the system

Comparison of Nutrient Accrual in Constructed Living Shoreline and Natural Fringing Marshes

Living shoreline marshes are coastal wetlands constructed as alternatives to “hardened shorelines” (e.g., bulkheads, riprap) to mitigate erosion and to allow for landward migration of intertidal habitat as sea level rises. Living shorelines are designed to mimic natural fringing marshes and over time should be sinks for carbon and other nutrients. We collected soil cores and aboveground plant material from 13 pairs of natural fringing marshes and living shoreline marshes of different ages and degree of isolation from more extensive marsh shorescapes to compare nutrient pools and accrual. Although the nutrient content of plants was similar within and between marsh types, soil nutrients were variable from both living shorelines aged 2–16 years and long-established natural marshes. Most—but not all—living shoreline marshes had lower soil organic content, higher bulk density, and lower soil % carbon, nitrogen and phosphorus than their natural marsh pair. Variation in soil nutrients from living shorelines was not strongly correlated with either marsh age or degree of isolation in the estuarine shorescape. Assuming constant accrual within individual marshes, we estimated soil nutrient levels in living shorelines would approach those observed in their paired, natural fringing marshes over timescales from less than 10 years to many decades. Living shoreline marshes are on trajectories to match natural marsh function with respect to carbon and nutrient storage in estuarine systems

Ribbed mussel Geukensia demissa population response to living shoreline design and ecosystem development

Coastal communities increasingly invest in natural and nature-based features (e.g., living shorelines) as a strategy to protect shorelines and enhance coastal resilience. Tidal marshes are a common component of these strategies because of their capacity to reduce wave energy and storm surge impacts. Performance metrics of restoration success for living shorelines tend to focus on how the physical structure of the created marsh enhances shoreline protection via proper elevation and marsh plant presence. These metrics do not fully evaluate the level of marsh ecosystem development. In particular, the presence of key marsh bivalve species can indicate the capability of the marsh to provide non-protective services of value, such as water quality improvement and habitat provision. We observed an unexpected low to no abundance of the filter-feeding ribbed mussel, Geukensia demissa, in living shoreline marshes throughout Chesapeake Bay. In salt marsh ecosystems along the Atlantic Coast of the United States, ribbed mussels improve water quality, enhance nutrient removal, stabilize the marsh, and facilitate long-term sustainability of the habitat. Through comparative field surveys and experiments within a chronosequence of 13 living shorelines spanning 2–16 years since construction, we examined three factors we hypothesized may influence recruitment of ribbed mussels to living shoreline marshes: (1) larval access to suitable marsh habitat, (2) sediment quality of low marsh (i.e., potential mussel habitat), and (3) availability of high-quality refuge habitat. Our findings suggest that at most sites larval mussels are able to access and settle on living shoreline created marshes behind rock sill structures, but that most recruits are likely not surviving. Sediment organic matter (OM) and plant density were correlated with mussel abundance, and sediment OM increased with marsh age, suggesting that living shoreline design (e.g., sand fill, planting grids) and lags in ecosystem development (sediment properties) are reducing the survival of the young recruits. We offer potential modifications to living shoreline design and implementation practices that may facilitate self-sustaining ribbed mussel populations in these restored habitats

Ecological equivalency of living shorelines and natural marshes for fish and crustacean communities

Salt marshes provide valued services to coastal communities including nutrient cycling, erosion control, habitat provision for crustaceans and fish (including juvenile and forage fish), and energy transfer from the detrital based food web to the greater estuarine system. Living shorelines are erosion control structures that recreate natural shorelines, such as fringing marshes, while providing other beneficial ecosystem services. Living shorelines are expected to provide fish and crustacean (nekton) habitat, but few comprehensive studies have evaluated nekton habitat use across a range of living shoreline settings and ages. We sampled the intertidal marsh and subtidal shallow water nekton community at 13 paired living shoreline and reference marsh sites, with living shorelines ranging in age from 2 to 16 years from construction. We compared nekton diversity, nekton community abundance, nekton community biomass, forage abundance, and juvenile abundance at reference marshes and living shorelines. Our results indicate that living shorelines are providing suitable marsh habitat for nekton communities, including juveniles and forage base species. The difference in living shoreline construction (rock sill, soil composition) did not appear to diminish habitat quality in the marsh or in nearshore waters, and rock sills may provide enhanced structural shoreline habitat. Living shorelines have the potential to combat marsh habitat loss and provide resilient nekton nursery habitat

Living shorelines achieve functional equivalence to natural fringe marshes across multiple ecological metrics

Nature-based shoreline protection provides a welcome class of adaptations to promote ecological resilience in the face of climate change. Along coastlines, living shorelines are among the preferred adaptation strategies to both reduce erosion and provide ecological functions. As an alternative to shoreline armoring, living shorelines are viewed favorably among coastal managers and some private property owners, but they have yet to undergo a thorough examination of how their levels of ecosystem functions compare to their closest natural counterpart: fringing marshes. Here, we provide a synthesis of results from a multi-year, large-spatial-scale study in which we compared numerous ecological metrics (including habitat provision for fish, invertebrates, diamondback terrapin, and birds, nutrient and carbon storage, and plant productivity) measured in thirteen pairs of living shorelines and natural fringing marshes throughout coastal Virginia, USA. Living shorelines were composed of marshes created by bank grading, placement of sand fill for proper elevations, and planting of S. alterniflora and S. patens, as well as placement of a stone sill seaward and parallel to the marsh to serve as a wave break. Overall, we found that living shorelines were functionally equivalent to natural marshes in nearly all measured aspects, except for a lag in soil composition due to construction of living shoreline marshes with clean, low-organic sands. These data support the prioritization of living shorelines as a coastal adaptation strategy