Phytoplankton community structure in the Western Subarctic Gyre of the Pacific Ocean during summer determined by a combined approach of HPLC-pigment CHEMTAX and metabarcoding sequencing

The Western Subarctic Gyre (WSG) is a cyclonic upwelling gyre in the northwest subarctic Pacific, which region with high concentration of nutrients but low chlorophyll. We investigated community structure and spatial distribution phytoplankton this area by using HPLC-pigment CHEMTAX (a chemotaxonomy program) metabarcoding sequencing during summer 2021. showed significant differences between two methods. analyses identified eight major marine assemblages. Cryptophytes were contributors (24.96%) to total Chl , followed pelagophytes, prymnesiophytes, diatoms, chlorophytes. eukaryotic OTUs obtained categorized into 149 species 96 genera 6 groups (diatoms, chlorophytes, cryptophytes, dinoflagellates). Dinoflagellates most abundant group, accounting for 44.74% obtained, cryptophytes pelagophytes. Sixteen out 97 annotated as harmful algal species, Heterocapsa rotundata Karlodinium veneficum Aureococcus anophagefferens assigned group (i.e., at least 0.1% reads). Nutrients more important shaping than temperature salinity. 24 stations divided southern northern regions along 44°N according k -means method, former being dominated nutrients. Although different assemblages analyzed methods various relationships environmental factors, common feature was that dinoflagellate proportion significantly negative correlation positive .