image: Aerial drone images of a crab-grazed tidal creek on Sapelo Island, GA. view more
Credit: Image credit: Collin Ortals.
A species of crab is reshaping the landscape of marshlands in the southeastern United States, aided by rising sea levels, according to a study. Increased water inundation of coastal salt marshes from sea level rise creates optimal conditions for the burrowing purple marsh crab, Sesarma reticulatum. Sinéad M. Crotty and colleagues conducted aerial imaging and field experiments to study the impact of the crabs, whose extensive burrows and grazing of cordgrass rapidly erode the heads of tidal creeks. The authors compared annual sea levels from 1940 to 2019 with the accretion rate of the marshes, finding that in the last 20 years, the rate of rise has outpaced the accretion rate, leading to marshes being submerged more frequently. Using two decades of aerial images taken at nine sites along coastlines from South Carolina to Florida, the authors found an approximately 240% increase in the prevalence of creekheads denuded by Sesarma burrowing and grazing activity, enhancing creek growth and accelerating marsh drainage. The authors found that grazing was predictable based on landscape characteristics and that mussels along the denuded creekheads are increasingly subject to predation. According to the authors, the study shows how a once-innocuous species, abetted by sea level rise, can reshape the morphology and ecology of a saltmarsh system.
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ARTICLE #19-17869: "Sea-level rise and the emergence of a keystone grazer alter the geomorphic evolution and ecology of southeast US salt marshes," by Sinéad M. Crotty et al.
MEDIA CONTACT: Sinéad M. Crotty, University of Florida, Gainesville, FL; tel: e-mail: <scrotty@ufl.edu>
Journal
Proceedings of the National Academy of Sciences