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Examining effects of sea level rise and marsh crabs on Spartina patens using mesocosms
Citation:
Hanson, Alana, K. Szura, C. Wigand, R. Mckinney, A. Oczkowski, E. Davey, AND J. Gurak. Examining effects of sea level rise and marsh crabs on Spartina patens using mesocosms. Coastal & Estuarine Research Federation (CERF) 23rd Biennial Conference, Portland, OR, November 08 - 12, 2015.
Impact/Purpose:
The goal was to analyze the effects of multiple stressors, but most particularly, sea level rise and crab burrowing and herbivory on Spartina patens plants in a controlled greenhouse setting. Accelerated sea level rise and is already impacting salt marshes in the northeast, and we hypothesize that as sea level increases, the habitat of the high marsh plant Spartina patens will be threatened as habitat is lost in the low marsh. The role of native salt marsh crabs, Uca pugilator and Sesarma reticulatum is less well studied, and the greenhouse allows us to control for examining just their effects coupled with sea level rise on targeted marsh plants.
Description:
Coastal salt marshes provide essential ecosystem services but face increasing threats from habitat loss, eutrophication, changing precipitation patterns, and accelerating rates of sea level rise (SLR). Recent studies have suggested that herbivory and burrowing by native salt marsh crabs could be impacting degrading marsh conditions in southern New England, U.S. We conducted a greenhouse mesocosm experiment to examine the interactive effects of SLR and marsh crabs, Uca pugilator (sand fiddler crab) and Sesarma reticulatum (purple marsh crab) on the marsh plant Spartina patens. Spartina patens is a native salt marsh plant that resides in the high marsh, an area which is threatened by SLR and watershed development. In each mesocosm tank, we placed pots filled with local salt marsh soil and S. patens plugs at elevations representing the high marsh and low marsh and filled tanks on semidiurnal tides with Narragansett Bay seawater. Each elevation consisted of three treatment pots: fiddler crabs, purple marsh crabs, and no crabs (control). Over the course of one summer we found significantly greater above- and belowground biomass at the high marsh elevation than the low marsh elevation. There were no differences in plant biomass between fiddler crab and control pots, indicating fiddler crabs may not pose a great threat of plant herbivory on southern New England, U.S. salt marshes. Pots with either fiddler or purple marsh crabs had significantly less macro- and filamentous algae, which in previous studies have been shown to contribute to dieback of marsh plants. This suggests that herbivory by the crabs lessen the severity of algal blooms. We also observed a nearly complete loss in above- and belowground plant material due to destruction from the purple marsh crab. Our results show similarities to recent studies demonstrating increased marsh degradation by the purple marsh crab linked to SLR and marsh loss.