Joint seasonal dynamics of phytoplankton and zooplankton in the sub-Arctic White Sea

Abstract

The seasonal succession of phytoplankton species composition and biomass plays a pivotal role in driving the seasonal variations in zooplankton community structure and biomass. Our study focused on the seasonal dynamics of planktonic communities in the Chupa Inlet (Kandalaksha Bay, White Sea) to determine if there are distinct complexes of phyto- and mesozooplankton species associated with different seasons, and whether these complexes are interconnected. Four seasonal groups of phyto- and zooplankton samples were revealed, each characterized by a specific composition of typical species. The winter and spring groups of phytoplankton and zooplankton corresponded to each other in their temporal span. Later in the year, this temporal correspondence was disrupted as early copepodite stages of Calanus glacialis dominated the community briefly in late spring, forming the basis of a separate seasonal group. From July until the end of the study period, warmer-water species constituted the community core, shaping the summer-autumn seasonal group. The role of smaller species in both phyto- and zooplankton communities increased during summer and autumn. The size structure and motility of the phytoplankton were found to significantly influence the seasonal succession of the zooplankton. This apparently contributes to better trophic coupling between phyto- and zooplankton throughout the seasonal cycle.