Capture mechanisms used by the lobate ctenophore, Mnemiopsis leidyi, preying on the copepod Acartia tonsa

Although the lobate ctenophore Mnemiopsis leidyi is an influential plankton ic predator, the mechanisms enabling it to capture its characteristically w ide range of prey have not been systematically examined. We recorded intera ctions between Gee-swimming M. leidyi and two stages (nauplii, adults) of t he calanoid copepod Acartia tonsa in order to determine a mechanistic expla nation of this feeding process. Prey encounter with Mnemiopsis involved two different processes. The first depended on fluid motions created by the ne arly continuous beating of cilia lining the four auricles. These cilia crea ted a low-velocity flow in which A. tonsa nauplii were entrained (94% of na upliar encounters) and transported past the oral lobes onto the tentillae ( oral tentacles). The nauplii, although capable of rapid escape responses, g enerally appeared to be insensitive to the current in which they were carri ed. The second process relied upon the collision of swimming prey with the inner surfaces of the oral lobes and was not obviously influenced by the au ricular feeding currents. Adult A. tonsa were rarely entrained in the auric ular flow, but, instead, propelled themselves into contact with the oral lo bes (97% of adult encounters). Both prey capture processes functioned simul taneously. The synergistic functioning of these processes probably explains the broad patterns of prey ingestion found by in situ studies of Mnemiopsi s feeding.