Behavioral basis of depth regulation in hatching and post-larval stages of the mud crab Eurypanopeus depressus

Abstract

Stage I larvae of the benthic mud crab Eurypanopeus depressus Hay and Shore are negatively geotactic and show high barokinesis at a low response threshold, traits which should promote upward migration. A vertical temperature gradient of 10d C has no inhibitory effect on upward migration of first stage zoeae under laboratory conditions. Vertical stratification in estuarine spawning grounds should not influence movement to the surface of the hatching stage of estuarine brachyurans. Megalopae show a low response threshold to pressure increase, similar to earlier reports for megalopae of swimming crabs, indicating such sensitivity to pressure is probably widespread among brachyuran species. High degree of pressure sensitivity in brachyuran megalopae creates high precision in depth regulation, a trait important in successful recruitment to appropriate adult habitats.