On the natural history and distribution of oceanic ctenophores

Oceanic ctenophores show aa great diversity in feeding biology, ranging from Leucothea multicornis, which can eat only small copepods, to species of Ocyropsis, which can capture and ingest small fish and euphausiids. The Cydippida capture prey with tentacles, while most of the Lobata use tentacles and their mucus-covered oral lobes. Leucothea multicornis has elaborate oral lobes, which can function independently of one another; Ocyropsis crystallina feeds by trapping prey in its muscular oral lobes, without use of mucus or tentacles. These two species represent extremes in the feeding biology of the Lobata. The Cestida feed by trapping small prey on tentacles that lie over the sides of the body. Several genera of hyperiid amphipods are closely associated with ctenophores, both as parasites and predators. Medusae and heteropods have also been seen to feed on ctenophores. We have encountered oceanic ctenophores often in abundance on about 75% of the 250 dives we have made in the past three years. Our collections from the North Atlantic and Indian oceans suggest that ctenophores are important predators in the upper waters of the open sea. Because most of the species discussed in this paper are never reported from net plankton collections, they constitute a hitherto ignored component of the open ocean ecosystem.