Transformation of Phytoplankton Communities in the High Arctic as They Move North. Ecological Properties of Species

During the 84th cruise of the R/V Akademik Mstislav Keldysh in August 2021, patterns of phytoplankton composition transformation were revealed along a northward gradient. The study involved three transects in the Fram Strait and adjacent Arctic waters: a southern transect (from the Barents Sea shelf to the Greenland shelf), a central transect across the Fram Strait, and a northern transect along the ice edge. Ten species of diatoms and eleven of dinoflagellates were identified, and their ecological preferences were characterized by determining the minimum, maximum, mean, and median values for abundance, biomass, depth of the biomass maximum, salinity, temperature, and the concentrations and ratios of nitrogen, phosphorus, and silicon. All identified species are of Atlantic origin. In summer, within the relatively warm Atlantic Waters, phytoplankton biomass was dominated by dinoflagellates of the genus Tripos and Protoperidinium depressum. Diatoms contributed insignificantly, with Stephanopyxis turris, Navicula planamembranacea, and Thalassiosira gravida being the most frequently observed. Northward, towards the Fram Strait, the dinoflagellate community shifted to include Protoperidinium breve, Protoperidinium brevipes, and Prorocentrum cordatum, while diatoms were increasingly represented by Thalassiosira rotula, Chaetoceros borealis, and Rhizosolenia styliformis. A further decline in temperature and salinity favored the dominance of the dinoflagellates Protoperidinium pellucidum and Gyrodinium lachryma, and the diatoms Eucampia groenlandica, Rhizosolenia hebetata f. semispina, and Rhizosolenia hebetata f. hebetata. The dinoflagellates Protoperidinium granii and Protoperidinium islandicum, along with the diatom Porosira glacialis, thrived at the lowest temperatures and salinities. Diatoms generally grew at silicon concentrations of 1–3 µM and nitrogen concentrations above 1 µM, except for R. hebetata f. semispina, R. hebetata f. hebetata, and Porosira glacialis. The dinoflagellates P. depressum, P. islandicum, P. brevipes, P. breve, and Gyrodinium lachryma were associated with lower nitrogen concentrations (< 2 µM), while others preferred higher levels. Diatom biomass was regulated by ambient nitrogen concentration, whereas dinoflagellate biomass was correlated with the biomass of small flagellates.