LIFE AND DEATH IN MOVING FLUIDS - HYDRODYNAMIC EFFECTS ON CHEMOSENSORY-MEDIATED PREDATION

Previous studies in taxonomically diverse marine animals have establis hed the general existence, and importance, of the olfactory sense in a wide variety of behavioral processes. Evidence suggests that the sens e of smell mediates predatory search in many marine animals. Past inve stigations have not, however, been designed to link either the degree of successful olfactory-mediated search or guidance mechanisms with th e hydraulic environment in which predatory activities naturally take p lace. In an effort to examine the interaction between hydrodynamics an d chemoreception, we investigated predatory success and search strateg ies of blue crabs foraging in controlled hydrodynamic environments gen erated in a flume. Hydrodynamics were characterized by quantifying bou ndary layer shear velocity (u) and roughness Reynolds number (Re*), t wo measures that describe the structure of boundary layer flows. Flow properties affected the ability of crabs to orient to odor plumes eman ating from actively pumping infaunal bivalves (Mercenaria mercenaria). High flow speed or large sediment particle size increased boundary la yer turbulence, thereby decreasing the success of crab chemo-orientati on ability. In addition, high flow speed also lessened the probability that crabs contacted odor plumes. Thus, habitats with high flows can provide hydrodynamic refuges from olfactory-mediated predation. Becaus e search ability is contingent on the magnitude of boundary layer turb ulence, olfactory-mediated predation may also be ineffective in slow f lows, if bottom roughness elements can generate sufficient turbulence. Further, search ability in blue crabs is extremely sensitive to small changes in benthic boundary layer structure. The presence of a thick viscous sublayer, dominated by quasilaminar flow, seems especially cri tical for successful location of an odor source by crabs. Benthic estu arine crustaceans inhabit an environment where flows are transitional between smooth- and rough-turbulent conditions. Accordingly, chemosens ory systems appear geared primarily to extracting information from hyd raulically smooth flows. These results indicate that mechanisms govern ing the physical transport of odor signals can have profound influence s, not only on the development of sensory and behavioral mechanisms, b ut also on biotic interactions such as predation, which, in turn, can mediate community structure.