Summer Jellyfish Blooms in the Northern California Current: Modeling the Impacts upon Fish Production and Evaluating the Evidence

What are the consequences should jellyfish consume an increasingly greater share of plankton production? Jellyfish may play a role shaping energy flow through pelagic food webs by diverting plankton production away from higher trophic levels. In the Northern California Current, scyphozoan jellyfish obtain high biomasses during summer months, but their abundance is variable from year to year. Do large jellyfish blooms have an observable impact on the rest of the ecosystem? Scenario analyses with an end-to-end ecosystem model were used to examine the potential effects of increased jellyfish production upon higher trophic levels. These analyses suggest that salmon are particularly sensitive. Although jellyfish and young salmon feed at different trophic levels, they may be indirect competitors for plankton production. Pelagic surveys off Oregon and Washington were used to examine the relationship between the dominant jellyfish (Chrysaora fuscescens) and salmon production. There was a significant, negative correlation between C. fuscescens abundance and the strength of salmon returns to the Columbia River in subsequent years. Further examination showed that juvenile salmon stomachs were less full at locations with higher C. fuscescens biomass. Though we did not study processes regulating jellyfish blooms, we do see evidence of their negative impact on fish production.