Medusae, siphonophores, and ctenophores as planktivorous predators in changing global ecosystems

Medusae, siphonophores, and ctenophores are planktivorous predators operating at higher trophic levels in marine ecosystems of a wide range of productivity. It has been hypothesized that high-productivity ecosystems such as areas of upwelling tend towards food chains dominated by larger phytoplankton, large copepods, and ultimately many species of fish rather than gelatinous predators; ecosystems with lower productivity are characterized by small flagellate phytoplankton, small copepods, and ultimately numerous medusae and ctenophores. Evidence is provided that medusae, siphonophores, and ctenophores are actually important predators in both sorts of planktonic ecosystems, although uneven reporting in the literature may be cause for underestimates of the importance of these carnivores in some systems. As world fisheries begin to experience serious declines, it is relevant to recognize that the carnivorous “jellyfishes” are ubiquitous and are thus opportunistically positioned to utilize secondary production that is ordinarily consumed by fish.