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R. Eliot Crafton - Invasions Ecology Lab

Williams College, Mystic, CT

Shallow water as refuge against predation for the white

fingered mud crab, Rhithropanopeus harrisii

Predation pressure on Rhithropanopeus harrisii was studied in the Rhode River, a sub-estuarine tributary of the Chesapeake Bay. The sample site was located on the southern portion of Canning House Bay, at a location of bare sediment with no woody debris present. The samples consisted of tethering R. harrisii and deploying at two depths to determine if a shallow water refuge was present.  In addition crab size and physical parameters were recorded and the crabs were checked at 4, 8, and 24 hours. Results for the tethers showed that predation rate was high, averaging about 92 percent after 24 hours. With regard to depth, predation rate was similar at 4 hours, but showed a significant difference at 8 and 24 hours, with a lower predation rate at the shallower site. This result suggests that shallow water is acting as a refuge for R. harrisii. Size was inconclusive due to an unequal sample size. Further study would be needed to better understand the extent of the depth influence and size influence on predation pressure.

Funding provided by the National Science Foundation - REU