Predation on Fish Larvae and Eggs by the Hydromedusa Aequorea victoria at a Herring Spawning Ground in British Columbia

Abstract

The importance of soft-bodied zooplankton as predators of fish eggs and larvae was examined during March–June, 1983 in Kulleet Bay, Vancouver Island, British Columbia. The diet of the jellyfish Aequorea victoria was evaluated by gut content analysis of individually collected specimens. Crustacean zooplankters were eaten in lesser proportion, and larvaceans, fish larvae, hydromedusae, and siphonophores were eaten in greater proportion than their presence in the environment. Numerous herring larvae (Clupea harengus pallasi) were consumed, as well as the larvae of fishes in several other families (primarily Pleuronectidae, Cottidae, Scorpaenidae, Stichaeidae, Pholidae, and Gadidae), and the pelagic eggs of flatfish (Family Pleuronectidae). When herring larvae hatched in mid-March, A. victoria medusae in the bay contained an average of 22 herring larvae each, comprising 48% of all ingested prey. The predation rates on herring and other fish larvae were calculated from the numbers of larvae in A. victoria, the digestion times, and the field densities of medusae and larvae. Accordingly, 4 newly-hatched herring larvae∙m−3∙d−1 (0.7%∙d−1) were consumed by A. victoria but few were eaten after April 5–6. Predation on other fish larvae was [Formula: see text] larvae∙m−3∙d−1 during April 5 to May 3, but was not detectable in samples collected during May 9 to June 7. Other soft-bodied predators (ctenophores, chaetognaths, siphonophores, and other hydromedusae) contained few fish larvae.