PELAGIC CNIDARIANS AND CTENOPHORES AS PREDATORS - SELECTIVE PREDATION, FEEDING RATES, AND EFFECTS ON PREY POPULATIONS

The following paper reviews predation by the pelagic ctenophores and c nidarians (hydromedusae, siphonophores, and scyphomedusae). In spite o f the difficulties in studying gelatinous zooplankton, much has been l earned about the trophic ecology of the gelatinous predators. Their fe eding is characterized by selectivity; some species specialize on fish larvae, and some specialize on other gelatinous species. Most species have broader diets, but some selection still occurs. Such selectivity in feeding depends on many factors: prey size and swimming speed; pre dator tentacle width and spacing; predator swimming behavior and resul ting water flow, nematocyst/colloblast structure affecting adhesion or penetration, and toxins; sensitivities to chemical and mechanical dis charge affecting nematocyst or colloblast discharge, prey escape abili ties; and attraction between predator and prey. Feeding rates and effe cts on prey populations (copepods, fish eggs and larvae, and ctenophor es) of the scyphomedusan Chrysaora quinquecirrha are given as examples of the potential importance of predation by gelatinous species. At hi gh densities, gelatinous predatora can seriously affect populations of zooplankton and ichthyoplankton, and may be detrimental to fisheries through competition for food with fishes as well as direct predation o n the eggs and larvae of fish.