New Phytoplankton Communities Revealed in Coastal Antarctica Using a Citizen Science Approach

The nearshore waters of the western Antarctic Peninsula (WAP) are one region subject to the fastest rates of warming in the world. This region is known for large phytoplankton blooms associated with melting glaciers and as such, fjords along the WAP coast have been proposed as hotspots of biodiversity with krill and whale aggregations and abundant benthic fauna fueled by primary production. Seasonal and inter-annual variability in freshwater influx is expected to favor different phytoplankton assemblages and shift the timing of blooms. Testing this hypothesis in such a remote harsh environment is extremely challenging requiring time series data collection. This study represents the first attempt to understand phytoplankton succession in relatively unexplored nearshore sites during the austral growth season (November to March). Sampling was conducted through a citizen science project – FjordPhyto – in collaboration with the International Association of Antarctica Tour Operators vessels. Results from the first year were unexpected. Different from the existing observations of diatom dominance in this region, the blooms encountered were from flagellated taxa: Pyramimonas sp., a cryptophyte, and an unarmored small dinoflagellate. The latter does not coincide with previously described Antarctic species and represents, as far as we know, the first record of a dinoflagellate bloom in the WAP. Seasonally, cryptophytes were more abundant in early summer, nanophytoflagellates dominated in December to January, and prasinophyceans dominated in late summer. Results highlight the importance of nanophytoflagellates in nearshore Antarctic waters. The range in cell size and carbon content of the different dominant taxa provide a first approximation of how much organic matter enters the food web through the phytoplankton communities sampled along the Antarctic growth season. A shift away from diatoms – the predominant food source of Antarctic krill – could have ramifications to the carbon available to upper trophic levels.