Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7407
Title: Seasonal food web models for the Oregon inner-shelf ecosystem: Investigating the role of large jellyfish
Author: J. J. Ruzicka, Thomas C. Wainwright
Publication Year: 2007
Journal: California Cooperative Oceanic Fisheries Investigations Reports
Volume: 48
Pages: 107-128
Keywords: marine ecosystems,trophic structure,food webs,California Current,jellyfish

We developed two seasonal food-web models, spring and summer, within the Ecopath framework for the Oregon upwelling ecosystem to investigate the role of large jellyfish as competitors for zooplankton prey. We used information about fish and jellyfish biomass, dis- tribution, and diet derived from pelagic trawl survey data. Information about lower trophic-level production was acquired from zooplankton survey data. The mod- els indicate that in spring, jellyfish are a modest con- sumer of zooplankton, and forage fishes dominate the system in terms of biomass and consumption. By late summer, jellyfish become the major zooplankton con- sumers, and they consume 17% of the summer zoo- plankton production while forage fish consume 9%. Jellyfish appear to divert zooplankton production away from upper trophic levels. Only 2% of the energy con- sumed by jellyfish is passed to higher trophic levels. However, the role of jellyfish as competitors may be moderate; a large proportion of zooplankton produc- tion (40%–44%) is not consumed but lost to detritus.