Pelagic cnidarians and ctenophores as predators: selective predation, feeding rates, and effects on prey populations

Abstract

The following paper reviews predation by the pelagic ctenophores and cnidarians (hydomedusae, siphonophores, and scyphomedusae). In spite of the difficulties in studying gelatinous zooplankton, much has been learned about the tropic ecology of the gelatinous predators. Their feeding 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; predator tentacle width and spacing; predator swimming behavior and resulting water flow; nematocyst/colloblast structure affecting adhesion or penetration, and toxins; sensitivities to chemical and mechanical discharge affecting nematocyst or colloblast discharge; prey escape abilities; and attraction between predator and prey. Feeding rates and effects on prey populations (cope-pods, fish eggs and larvae, and ctenophores) of the cyphomedusan Chrysaora quinquecirrha are given as examples of the potential importance of predation by gelatinous species. At high densities, gelatinous predators can seriously affect populations of zooplankton and ichthyoplankton, and may be determined to fisheries through competition for food with fishes as well as direct predation on the eggs and larvae of fish.