Rise and fall of jellyfish in the eastern Bering Sea in relation to climate regime shifts

A steep increase in jellyfish biomass, primarily Chrysaora melanaster, over the eastern Bering Sea shelf was documented throughout the 1990s. Their biomass peaked in summer 2000 and then declined precipitously, stabilizing at a moderate level after 2001. The onsets of the outburst and decline coincided with transitions between climatic regimes. Specifically, 1989 marked the beginning of a period of moderate temperatures in the eastern Bering Sea, after the warm conditions of the late 1970s through the 1980s. Very warm conditions came to the eastern Bering after 2000, as evidenced by decreased ice cover in winter and increased total heat content and surface water temperatures in summer. We examined the relationships between jellyfish biomass and temperature, ice cover, atmospheric variables, current patterns, zooplankton biomass, and associated fish biomass in two regions of the Middle Shelf Domain (SE and NW) by use of Generalized Additive Models (GAM). We found density-dependent interactions within and between jellyfish biomass in the two regions related to the flow regime, and demonstrated a linkage between biophysical indices and jellyfish biomass. In particular, ice cover (SE and NW), sea-surface temperature in spring (SE) and summer (NW), and wind mixing (SE) all influenced jellyfish biomass. In addition, the importance of juvenile pollock biomass (SE) and zooplankton biomass (NW) suggest that jellyfish biomass was sensitive to the availability of prey. Since most climate models suggest continued warming is likely in the Bering Sea, the jellyfish populations may remain at moderate levels there but will likely shift northward into the Arctic Ocean.