The Influence of a Deep-Water Intrusion on the Distribution of Chrysaora melanaster in the Southeastern Bering Sea

Abstract

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 composed 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 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 east of Unimak Island in both sampling periods. The current pattern revealed by an acoustic Doppler current profiler showed that cold, deep water from Bering Canyon flowed onto the shelf east of Unimak Pass. Differences in the strength of this cross-isobath, deep-water intrusion were observed during the two sampling periods. This flow may have influenced the distribution of C. melanaster by constraining the mixed coastal water near of Unimak Island in June-July and by transporting medusae westward, into deeper water in September, after the deep-water intrusion weakened. The present study provides a new mechanistic understanding of how regional-scale ocean variability in the SEBS affects C. melanaster distribution.