Distribution, abundance, and predation effects of epipelagic ctenophores and jellyfish in the western Arctic Ocean

The Arctic Ocean is undergoing changes at an unprecedented rate because of global climate change. Especially poorly-studied in arctic waters are the gelatinous zooplankton, which are difficult to study using traditional oceanographic methods. A distinct zooplanktivore community was characterized in the surface 100 m by use of a Remotely Operated Vehicle, net collections, and SCUBA diving. The large scyphomedusa, Chrysaora melanaster, was associated with the warm Pacific water at ∼35–75 m depth. A diverse ctenophore community lived mainly above the C. melanaster layer, including Dryodora glandula, a specialized predator of larvaceans, Beroe cucumis, a predator of other ctenophores, and the extremely fragile Bolinopsis infundibulum, which was the most abundant species. Gut content analyses showed that Mertensia ovum selectively consumed the largest copepods (Calanus spp.) and amphipods (Parathemisto libellula); B. infundibulum consumed smaller copepods and pteropods (Limacina helicina). Large copepods were digested by M. ovum in ∼12 h at −1.5 to 0 °C, but by B. infundibulum in only ∼4 h. We estimated that M. ovum consumed an average of ∼2% d−1 of the Calanus spp. copepods and that B. infundibulum consumed ∼4% d−1 of copepods <3 mm prosome length. These are significant consumption rates given that Calanus spp. have life-cycles of 2 or more years and are eaten by vertebrates including bowhead whales and arctic cod.