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

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 "0) 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.

Stealth predation and the predatory success of the invasive ctenophore Mnemiopsis leidyi

“…Most often the escape attempt fails and the trapped prey eventually becomes enmeshed upon the sticky inner surface of the lobe (19). As a result, M. leidyi captures most copepods (a > 70%) that enter the region between the lobes (19). Most captures result from the copepod jumping into the inner lobe surfaces and only a small proportion of prey are captured on the tentillae surrounding the mouth (18).…”

“…At that point, the copepod may detect the high deformation rate and respond with one or more escape jumps. Most often the escape attempt fails and the trapped prey eventually becomes enmeshed upon the sticky inner surface of the lobe (19). As a result, M. leidyi captures most copepods (a > 70%) that enter the region between the lobes (19).…”

“…Low deformation rates enable ctenophores to transport copepods unwittingly into the capture zone between the oral lobes. In this region, M. leidyi is capable of detecting copepods and closing the lobe opening before the copepod reaches the high deformation regions (19). By closing the oral lobes around a copepod M. leidyi envelopes a package of water containing the copepod.…”

“…Despite some identified mechanoreceptive abilities (19), prey do not appear to be detected by the ctenophore until the prey have entered the region encompassed by the oral lobes (defined as the capture zone). Prey are captured only after contacting either the tentillae or the inner surface of the oral lobes (18,19) (Fig. 1B).…”

Fluid Interactions That Enable Stealth Predation by the Upstream-Foraging Hydromedusa Craspedacusta sowerbyi

“…However, post-encounter escape behavior of prey will greatly reduce the percentage of the encountered prey that are actually ingested (termed capture efficiency). High capture efficiencies can occur with some gelatinous predators, such as the ctenophore Mnemiopsis leidyi (Costello et al, 1999). However, capture efficiencies for upstream-foraging medusae feeding on copepods appear to be low.…”