The distribution of Chrysaora melanaster and hydrographical conditions in the southeastern Bering Sea in 2018

Scyphozoan jellyfish are conspicuous components of marine ecosystems, which during a bloom, can impact food web structure and economically important fisheries. Jellyfish biomass in the southeastern Bering Sea (SEBS) is primarily comprised of Chrysaora melanaster and has varied widely over the past four decades, yet the underlying causes of these biomass fluctuations remain unclear. The present study investigated the spatial and seasonal dynamics of C. melanaster along the Alaska Peninsula in the SEBS using an Adaptive Resolution Imaging Sonar (ARIS) system and nets in June-July and September 2018. The abundance of C. melanaster was high in coastal waters near the Alaska Peninsula, with peak densities occurring north of Unimak Island in both sampling periods. The current pattern revealed by an acoustic Doppler current profiler (ADCP) showed that cold deep water from Bering Canyon flowed onto the shelf north of Unimak Island and influenced the distribution of C. melanaster by constraining the mixed coastal water to areas north of Unimak Island, flowing northeast along the Alaska Peninsula. The present study provides a new mechanistic understanding of how large-scale ocean variability in the SEBS affects C. melanaster distribution.