MEPS 191:207-216 (1999)  -  doi:10.3354/meps191207

Influence of prey detection on capture success for the ctenophore Mnemiopsis leidyi feeding upon adult Acartia tonsa and Oithona colcarva copepods

J. H. Costello*, R. Loftus, R. Waggett**

Biology Dept., Providence College, Providence, Rhode Island 02918-0001, USA
*E-mail: **Present address: Marine Science Institute, University of Texas at Austin, Port Aransas, Texas 78373-1267, USA

ABSTRACT: Although the lobate ctenophore Mnemiopsis leidyi is known to be an important copepod predator, the mechanistic basis for its predatory success is not well understood. We directly observed and recorded predation by free-swimming M. leidyi ctenophores on Acartia tonsa and Oithona colcarva copepods (n = 349 encounters, 25 different ctenophores) in the laboratory using videographic methods. Overall capture success was relatively high (74%) following copepod contact with M. leidyi. However, average retention of copepods initially contacting the interior surfaces of the oral lobes (the major capture sites) was considerably lower (34%). Average retention was low because copepods most frequently collided head-first with the oral lobes and bounced away without being captured. Escape success for copepods declined rapidly during ensuing contacts, and most captures (57%) involved multiple contacts within an encounter. Our most novel finding was that almost half (49%) of the encounters involved alterations of oral lobe positions which preceded, or anticipated, actual contact with a copepod. Anticipatory responses were cued to fluid disturbances created by swimming copepods. Anticipation of prey contact allowed ctenophores to shift oral lobe positions and reduce copepod escape avenues, thereby increasing the number of contacts per encounter and significantly increasing capture efficiency.

KEY WORDS: Foraging · Escape · Hydrodynamic cues · Anticipation · Behavior · Selection · Ambush

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