Phytoplankton population dynamics and the underlying physicochemical variables, during the summer / autumn transition (February – May 2018) in Ryder Bay, Antarctica.

Supervisors: Corina Brussaard, Ella Wesdorp (NIOZ Royal Netherlands Institute for Sea Research).
Global warming and its possible effects on the polar regions are currently being studied. The Western Antarctic Peninsula has been warming faster than any other region of the world with an increase in sea surface temperatures of > 1 ℃ between the early 1960s and 2000s. This is most pronounced by shortening of sea ice cover due to later onset in autumn. As Antarctic ecosystems are hugely dictated by seasonality and the presence of sea ice, changes in these may have unprecedented consequences on community structure. Samples for microbial abundance, viral lysis and microzooplankton grazing rates and molecular analysis were collected in Ryder Bay, Antarctica. My research focuses on the physicochemical variables, chlorophyll-a concentrations and fresh phytoplankton abundances enumerated on site using flow cytometry. It aims to use changes in the physicochemical variables as the driving forces between the changes in dominance of phytoplankton groups throughout the sampling period. Chlorophyll-a was seen to peak throughout February and mid-March and was predominantly microphytoplankton dominated, while the remainder of the season was dominated by nanophytoplankton. Flow cytometry analysis of phytoplankton revealed a large abundance of picophytoplankton, consistently contributing the most in terms of relative abundance. Flow cytometry yielded eight phytoplankton groups. A correspondence analysis of these groups and the sampling points showed a tendency of certain groups to dominate during different sampling points. For example, sample points 3 and 4 were most influenced by group Crypto Nano II. Wind speed was found to be significantly correlated with the most phytoplankton groups. However, changes in wind speed may have a cascading effect on other physicochemical parameters which affected phytoplankton growth and changed between favorable conditions of the different groups. With the changing climate, these changes may become more prominent and have more pronounced effects on the phytoplankton community composition, with shifts beginning to be observed from dominance of larger to smaller phytoplankton groups. Such shifts in phytoplankton could have further impacts on the food web.