Functional biodiversity and seasonal transitions of pelagic protists in Disko Bay, Greenland

Abstract

Environments are changing more and more due to the ongoing climate change. The Arctic is warming up at approximately double the rate than other regions. To understand how the marine ecosystem will be affected by this, it is necessary to understand how it is behaving in the first place. For marine pelagic ecosystems, protists form the basis of the marine food web, encompassing most of the primary producers of biomass. The community usually follows seasonal patterns in abundance and dominance of different taxonomic groups throughout the year. Due to the relative inaccessibility, protist seasonal patterns have not been studied extensively in the Arctic environment before. This study focused on the months leading into and out of the annual spring bloom event in an Arctic environment, and how the local protist community reacted to the changing circumstances. The highly seasonal study area provided the opportunity to investigate several typical Arctic phenomena during two field trips in 2017 and 2018, including seasonal sea ice and very dark periods in winter, and the continuously shining midnight sun in summer. Embedded in contextual data, an approach with state-of-the-art metabarconding was utilized to shed light on the pelagic protist diversity. The winter community (2018) consisted of many mixotrophic, heterotrophic and parasitic organisms, which were displaced by phototrophs towards the spring bloom, especially in the microplankton size fraction. When looking at the transition from spring to summer (2017), pico- and nanoplankton had only a small percentage of phototrophs, but more heterotrophs and mixotrophs. Microplankton shifted from predominantly phototrophs during the spring bloom to mostly mixotrophs in summer. This work contributes to a better understanding of protist organisms in an Arctic context. In the future, this may help to understand the changes that are currently provoked and how they will affect these small but significant organisms.