Seasonal Variability in the Zooplankton Community Structure in a Sub-Arctic Fjord as Revealed by Morphological and Molecular Approaches

Phyto- and zooplankton in Arctic sub-Arctic seas show very strong seasonal changes diversity biomass. Here we document the variability mesozooplankton community structure a fjord Northern Norway based on monthly sampling between November 2018 February 2020. We combined traditional morphological identification with DNA metabarcoding of 313 base pair fragment COI gene. This approach allowed us to provide most detailed species list known for this region across an entire year, including both holo- meroplankton. The was dominated by small copepods throughout period terms abundance relative sequence counts. However, meroplankton diverse group, especially within phylum polychaeta. identified four distinct periods analysis composition. pre-spring bloom (February–March) characterized low biomass zooplankton. spring (April) presence Calanus young stages, cirripedia krill eggs. spring-summer (May–August) succession relatively high genus spp. Finally, autumn-winter (September–December) copepod peak (e.g., Oithona similis , Acartia longiremis Pseudocalanus acuspes elongatus moultoni minutus ). During period, also observed influx boreal warm-water which were notably absent during rest year. Both highly complementary few exceptions showed similar trends structure.