Copepod sensitivity to flow fields: detection by copepods of predatory ctenophores

Copepods have the mechanoreceptive abilities to detect velocity gradients generated by approaching predators and the ability to respond to these predators within milliseconds. Ctenophores produce a low-velocity feeding current to entrain slow-swimming and non-motile prey. Since cope- pod species vary in their sensitivity to hydrodynamic disturbances, it is possible that species will dif- fer in their ability to distinguish flow-generating ctenophores from the surrounding fluid. Predator- prey interactions were recorded between the ctenophore Mnemiopsis leidyi and 3 copepod species, Acartia tonsa, Paracalanus parvus and Temora turbinata. Although A. tonsa is more sensitive to hydrodynamic disturbances, T. turbinata was most successful in escaping the ctenophore predator. T. turbinata entered the inner lobe area (capture surfaces) of the ctenophore significantly less than either A. tonsa or P. parvus and were better able to escape both encounters and contacts with the inner lobes. These results suggest that sensitivity to velocity gradients may play only a minor role in determining escape success and an intermittent swimming pattern may increase susceptibility to capture by flow-generating predators.

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