R. Waggett et Jh. Costello, Capture mechanisms used by the lobate ctenophore, Mnemiopsis leidyi, preying on the copepod Acartia tonsa, J PLANK RES, 21(11), 1999, pp. 2037-2052
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.