The community of marine alveolate parasites in the Atlantic inflow to the Arctic Ocean is structured by season, depth, and water mass

Elianne Egge, Daniel Vaulot, Aud Larsen, Bente Edvardsen

Abstract

The marine alveolates (MALVs) are a highly diverse group of parasitic dinoflagellates, which may regulate populations of a wide range of hosts, including other dinoflagellates, copepods, and fish eggs. Knowledge on their distribution and ecological role is still limited, as they are difficult to study with morphological methods. In this work, we describe the taxonomic composition and seasonal and depth distribution of MALVs in the Arctic Ocean west and north of Svalbard, based on 18S V4 rRNA metabarcoding data from five cruises. We recovered amplicon sequence variants (ASVs) representing all major groups previously described from environmental sequencing studies (Dino-Groups I–V), with Dino-Groups I and II being the most diverse. The community was structured by season, depth, and water mass. In the epipelagic zone, the taxonomic composition varied strongly by season; however, there was also a difference between Arctic and Atlantic water masses in winter. The spring and summer epipelagic communities were characterized by a few dominating ASVs present in low proportions during winter and in mesopelagic summer samples, suggesting that they proliferate under certain conditions, e.g., when specific hosts are abundant. Mesopelagic samples were more similar across months, and may harbor parasites of deep-dwelling organisms, little affected by season.