Abundance and Distributions of Gelatinous Zooplankton in the Northern Gulf of Alaska

Small gelatinous predators have been relatively well-studied for in the Gulf of Alaska for decades, but the seasonal and spatial patterns of gelatinous zooplankton in the Gulf are poorly known, despite suggestion of increased jellyfish populations in Bering Sea and numerous ecosystems globally. We determined gelatinous zooplankton abundances and distributions during July and September of 2018 and 2019, as part of the Northern Gulf of Alaska Long-term Ecological Research (NGA LTER) cruises. We sampled 42 stations along four cross-shelf transects and within Prince William Sound using a 5 m² Methot Trawl. Although scyphomedusae (“true jellyfish”) were our primary focus, hydromedusae and ctenophores were also captured, with a total of eight prominent species across these three taxonomic categories. The hydromedusae Aequorea was most abundant genera and occurred at most stations during both years of sampling. Generally, biomass was greatest in offshore waters, driven by larger individuals. In contrast, near-shore biomass was lower but showed high abundance of smaller individuals. The biomass of these large predators was over an order of magnitude greater than estimates obtained from other sampling methods. These observations will help improve our understanding of the jellyfish composition, spatial and temporal patterns, as well as their ecological importance in the Gulf of Alaska ecosystem.