MEPS 510:167-181 (2014)  -  DOI: https://doi.org/10.3354/meps10810

ABSTRACT: As in many regions of the world, the shelf waters of the western United States have experienced large increases and high interannual variability in jellyfish populations in recent decades. The northern California Current (NCC) is a productive upwelling zone that is home to large populations of medusae, particularly during some years. Seasonal trawl surveys in the NCC over 13 yr have documented a substantial biomass of jellyfish consisting primarily of one species, the sea nettle Chrysaora fuscescens, with abundances generally peaking in late summer. Trophic overlap can be high in the NCC with planktivorous species such as Pacific sardines and herring that consume copepods and other zooplankton. In this study, we examine the spatial overlap and co-occurrence of C. fuscescens and Pacific herring Clupea pallasii, northern anchovy Engraulis mordax and Pacific sardine Sardinops sagax in the NCC using spatial analysis tools to determine the species that have the potential to be most affected by high jellyfish biomass and the geographic areas in which these interactions are likely to occur. Significant spatial overlap of C. fuscescens with these pelagic fishes occurred during certain months and years, although the results were highly variable. There was an overall negative relationship between the abundance of C. fuscescens and the catch of the 3 forage fishes for both June and September. End-to-end food web models show that jellyfish have a greater potential to affect production of pelagic forage fishes than the reverse.

KEY WORDS: Scyphomedusae · Planktivores · Spatial overlap · Seasonal variability · Interannual variability · Pelagic fishes