Ecology of Mangrove Crabs: Predation, Physical Factors and Refuges

The relative importance and interactions of biological and physical factors as influences on microhabitat utilization of crabs in mangrove forests in Florida Bay is examined. Two experimental approaches were taken: (1) Estimation of the relative risk of predation among microhabitats in the mangrove on a tidal, seasonal, and annual basis, (2) Measurement of responses of crabs to exposure in microhabitats in the field. Florida Bay mangroves are intertidal soft-sediment habitats in which four species of mangrove crabs broadly overlap in habitat utilization and share periodic shifts in microhabitat selection. Aratus pisonii is an arboreal crab; Eurytium limosum, Sesarma curacaoense, and Uca thayeri live in burrows and holes on the mud surface and occasionally climb mangrove prop roots. Field predation tethering experiments found a differential risk of predation among microhabitats and strong tidal and seasonal differences in predation rates. In field experiments that tested tolerance to exposure in various microhabitats species exhibited different responses to temperature and relative humidity conditions in each microhabitat. The unique physiognomy and characteristics of mangroves provide a habitat that ameliorates environmental conditions and provides varied structural refuge from predation for crabs. The differential physiological suitability of refuges and risk of predation among microhabitats means that crabs must balance the constraints of physiological tolerances and the avoidance of predation in a system that has a seasonally variable risk of predation and environmental conditions