1.7 Jellyfish as keystone predators

Bony fish do have very high fecundities. If a species “wins” the lottery and perfectly matches with the onset of energy availability during a seasonal cycle, its larvae and juveniles can monopolize the system.

If the species is a large carnivore, it will deplete the lower levels of the food web. Either large or small as adults, all fish are small when they are eggs and larvae, and all are liable of jellyfish predation. Jellyfish presumably feed on the fish eggs and larvae that are most abundant during their peak, when jellyfish predation is maximal. In doing so, jellyfish reduce the size of the populations of the previous “winners” and release the rest of the nekton guild from their potential monopolization of nektonic biodiversity, as suggested by Piraino et al. (2002). If this were true, as suggested also by Purcell and Decker (2005), carnivorous gelatinous plankton might enhance the diversity of nekton, with a keystone role as a whole guild, and not as a single species.