ABSTRACT
Pelagic copepods are subject to predation throughout much of their planktonic life. As a result, predator detection and avoidance are crucial to the survival of individuals. By using a quantifiable fluid mechanical disturbance we determine the fluid characteristics needed to elicit an escape reaction in Pleuromamma xiphias (Calanoida: Metridinidae). Four different siphon configurations were used to spatially separate regions of maximum flow speed and acceleration from regions with maximum shear surrounding the siphons. The patterns of escapes indicate that the spatial variation in fluid velocity is the proximate cue which elicits the escape reaction in P. xiphias. An average threshold shear value of 15 /s was needed to elicit the escape reaction. These results suggest that small scale fluid motion, such as those caused by a predator’s feeding current, with shear values greater than the 15 /s are more likely to initiate an escape reaction in P. xiphias.
