Tintinnids and other microzooplankton along a transect through the Greenland Sea Gyre

The present study investigates microzooplankton (MZP) species richness, vertical abundance, and organism dimensions along a transect through the Greenland Sea Gyre from 2 to 10 September 2021, at the end of the productive season. Total MZP abundance varied from 6.25 ind. L − 1 to 721.5 ind. L − 1 , and total carbon content from 0.01 µgC L⁻¹ to 1.7 µgC L⁻¹. Microzooplankton abundance and biomass decreased drastically in the presence of cold polar water on the Greenland slope. Vertical distribution profiles showed significantly higher organism abundance in the photic zone ( ≤ 100 m) compared to the aphotic zone (> 100 m) across the entire transect. Tintinnids, with a maximum of 613 ind. L − 1 , dominated the MZP assemblage; among them, Acanthostomella norvegica , Parafavella denticulata , Parafavella parumdentata , and Ptychocylis obtusa were the most common species. Tintinnids appeared to play a major role in the photic zone and exhibited small dimensions, with an oral lorica opening between 15 and 35 μm in 84% of the individuals. Consequently, at the end of the productive season, the amount of carbon transferred to higher trophic levels in the Greenland Sea may be constrained by the small size of the organisms, with potential effects on upper trophic levels that critically depend on efficient energy transfer. Due to ongoing changes in the Arctic, there is an urgent imperative for a better characterization and understanding of food web structures, which are key elements of the Arctic pelagic ecosystem.