Virginia Institute of Marine Science
Salt marsh ecosystems have declined globally and are increasingly threatened by erosion, sea level rise, and urban development. These highly productive, physically demanding ecosystems are populated by core species groups that often have strong trophic interactions with implications for ecosystem function and service provision. Positive interactions occur between ribbed mussels (Geukensia demissa) and cordgrass (Spartina alterniflora). Mussels transfer particulate nitrogen from the water column to the marsh sediments, which stimulates cordgrass growth, and cordgrass provides predator and/or heat stress refuge for mussels. Here, we test mussel facilitation of two functions in salt marshes that relate to N removal: microbial denitrification and water filtration. Microcosm experiments revealed that the highest rates of N-2 production and nitrification occurred when mussels were present with marsh vegetation, suggesting that mussels enhanced coupling of the nitrification-denitrification. Surveys spanning the York River Estuary, Chesapeake Bay, showed that the highest densities of mussels occurred in the first meter for all marsh types with mainstem fringing (1207 +/- 265 mussels/m(2)) being the most densely populated. The mussel population was estimated to be similar to 197 million animals with a water filtration potential of 90-135 million L/hr. Erosion simulation models demonstrated that suitable marsh habitat for ribbed mussels along the York River Estuary would be reduced by 11.8% after 50 years. This reduction in mussel habitat resulted in a projected 15% reduction in ribbed mussel abundance and filtration capacity. Denitrification potential was reduced in conjunction with projected marsh loss (35,536 m(2)) by 205 g N/hr, a 16% reduction. Because of the predominant occurrence of ribbed mussels at the marsh seaward edge and because the highest proportional loss will occur for fringing marshes (20%), shoreline management practices that restore or create fringing marsh may help offset these projected losses.
OYSTER CRASSOSTREA-VIRGINICA; GEUKENSIA-DEMISSA; CHESAPEAKE BAY; SPARTINA-ALTERNIFLORA; SHORE LEVEL; ECOSYSTEM SERVICES; NUTRIENT FLUXES; EASTERN OYSTER; FOOD WEBS; POPULATION
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This study was supported by National Science Foundation (Grant Number 1600131), NSF Women in Science and Engineering (WISE), and the David H. Smith Conservation Research Postdoctoral Fellowship (A.R.S). We thank our colleagues at the Center for Coastal Resources Management, Virginia Institute of Marine Science, for field and laboratory support. We also thank Hunter Walker, Iris Anderson, and BK Song for laboratory assistance. This paper is Contribution No. 3622 of the Virginia Institute of Marine Science, College of William & Mary.
Bilkovic, D. M., M. M. Mitchell, R. E. Isdell, M. Schliep, and A. R. Smyth. 2017. Mutualism between ribbedmussels and cordgrass enhances salt marsh nitrogen removal. Ecosphere 8(4):e01795. 10.1002/ecs2.1795