Increases in jellyfish biomass in the Bering Sea implications for the ecosystem

• Published in: Marine ecology. Progress series (Halstenbek) Vol. 233; pp. 89 - 103
• Main Authors: Brodeur, Richard D., Sugisaki, Hiroya, Hunt, George L.
• Format: Journal Article
• Language: English
• Published: Oldendorf Inter-Research 21-05-2002
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Aurelia labiata; Biological and medical sciences; Biomass; Chrysaora melanaster; Cyanea capillata; Food consumption; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Hydromedusa; Jellyfishes; Marine; Marine ecosystems; Marine fishes; Phacellophora camtschatica; Pollock; Predation; Sea water ecosystems; Seas; Synecology; Theragra chalcogramma; Young animals; Zooplankton; Bering Sea; Pacific Ocean; North Pacific; INE, Bering Sea; INE, USA, Alaska, Pribilof Is; Population growth; Theragra chalcogramma; Environmental factor; Trophic relation; Feeding; Marine environment; Coelenterata; Vertebrata; Spatial distribution; Food web; Diet; Animal community; Food intake; Pisces; Trophic cascade; Environment impact; Cnidaria; Dominant species; Invertebrata; Environmental monitoring; Zooplankton; Ecological abundance
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps233089

There has been a dramatic increase in jellyfish biomass over the eastern Bering Sea shelf since the early 1990s, which was previously hypothesized to have been triggered by changing climate and ocean conditions. We examine the hypothesis that the presence of these large carnivores has affected fisheries resources, either through direct predation on larval stages, or through competition for zooplankton prey. In this paper, we explore the impact of this jellyfish increase on zooplankton and fish communities based on field data on the composition of the jellyfish community, and the abundance, size, stable isotopic signatures, and feeding habits of the principal scyphomedusae in the region. These data, together with those on zooplankton biomass, are used to estimate the ecosystem impacts of this increase. The center of jellyfish biomass has shifted from the SE Middle Shelf Domain in the early 1980s to the NW in the late 1990s. In recent years, the species composition of large medusae caught in trawls was dominated (>80% by number and >95% by weight) by the scyphozoanChrysaora melanaster. Dense aggregations of this species occupied the water column in daytime between 10 and 40 m. Their food habits consisted mainly of pelagic crustaceans (euphausiids, copepods, amphipods), although other jellyfish and juvenile pollock were also consumed. Based on stable isotope ratios, the trophic level of this scyphozoan is equivalent to, or higher than, that of Age 0 pollock. Preliminary estimates showed that medusae have a moderate grazing impact on zooplankton in the area around the Pribilof Islands;C. melanasterwas estimated on average to consume seasonally about one-third of the standing stock and 4.7% of the annual production of zooplankton in this region. Daily consumption of Age 0 pollock was estimated to be 2.8% of the standing stock around the Pribilof Islands during 1999. A hypothesis for the increase in jellyfishes observed in the eastern Bering Sea, based on release from competition from planktivorous forage fishes, is proposed.