Large medusae in surface waters of the Northern California Current: variability in relation to environmental conditions
Blooms of jellyfish around the world have been correlated with climatic variables related to environmental causes. Sizeable populations of large medusae, primarily Chrysaora fuscescens and Aequorea sp., appear annually in shelf waters of the Northeast Pacific Ocean. Previous research has shown that C. fuscescens is abundant seasonally in the inner shelf and exhibits high feeding rates on zooplankton. We examined medusae caught in surface trawls over an 8-year period (2000–2007) using (1) mesoscale surveys sampling 8–10 transects in May, June, and September, and (2) biweekly surveys along two transects from April to August, relating abundance to environmental parameters. C. fuscescens abundances generally peaked in late summer, whereas Aequorea sp. peaked in May or June. General additive models of the mesoscale data indicated that station catches for both species correlated with latitude, temperature, salinity, and distance from shore (and chlorophyll a for Aequorea sp.). Analysis of interannual variability revealed that highest catches of medusae correlated with cool spring–summer conditions, or negative anomalies of the Pacific Decadal Oscillation, and low winter–summer runoff from the Columbia River. Results confirmed our hypothesis of connections between jellyfish populations and regional climate conditions in a region known for strong physical forcing of ecosystem processes.
KeywordsJellyfish Chrysaora Aequorea Climate Upwelling California Current
Thanks to the captains and crew of the FV Frosti, FV Ocean Harvester, FV Sea Eagle, FV Piky, RV Miller Freeman, and RV W.E. Ricker, as well as the many seagoing scientists who participated in the fieldwork component of this project. G. Krutzikowsky, C. Morgan, S. Pool, and C. Bucher helped with database management. E. Casillas, J. Field, C. Rice, J. Purcell and two anonymous reviewers provided helpful comments on earlier drafts of the manuscript. This study was funded by the Bonneville Power Administration, the US GLOBEC Northeast Pacific Program, and the Northwest Fisheries Science Center (NOAA). Completion of this manuscript was supported by the National Science Foundation, while the lead author was working at the Foundation. Any opinion, finding, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
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