The fall emigration of stone crabs Menippe mercenaria (Say) from an intertidal oyster habitat and temperature's effect on locomotory activity

The population structure of stone crabs Menippe mercenaria (Say) inhabiting an intertidal oyster habitat in the northern Gulf of Mexico, was monitored during monthly spring low tide periods from May 1983 to May 1984. Seasonal density fluctuations indicated crabs moved subtidally during the fall and early winter and returned to the intertidal region the following spring. The torpid state and occasional mortality of non-emigrants in the winter suggest that movement to subtidal regions is important for survival. To test a proximate stimulus that may trigger emigration, we experimentally exposed crabs to water temperature fluctuations that simulated conditions in the field during autumnal weather fronts. Water temperatures were lowered from 27°C to 20°C over 24 h and were rewarmed to 27°C several days later. Crab activity was recorded by a time-lapse video camera that continuously scanned four 2000-liter tanks. The distances walked by experimental crabs increased following the treatment, whereas, the frequency of other behaviors did not change. Control crabs held at a constant 27°C did not change their walking distances during the experiment. The increase in locomotory activity in experimental crabs suggests temperature fluctuations may influence the onset of fall emigrations from the intertidal habitat by stone crabs.