Parallel assessment of marine autotrophic picoplankton using flow cytometry and chemotaxonomy

Autotrophic picoplankton (0.2–2 μm) can be a significant contributor to primary production and hence play an important role in carbon flow. The phytoplankton community structure in the Baltic Sea is very region specific and the understanding of the composition and dynamics of pico-size phytoplankton is generally poor. The main objective of this study was to determine the contribution of picoeukaryotic algae and their taxonomic com- position in late summer phytoplankton community of the West-Estonian Archipelago Sea. We found that about 20% of total chlorophyll a (Chl a) in this area belongs to autotrophic picoplankton. With increasing total Chl a, the Chl a of autotrophic picoplankton increased while its contribution in total Chl a decreased. Picoeukaryotes play an important role in the coastal area of the Baltic Sea where they constituted around 50% of the total autotrophic picoplankton biomass. The most abundant groups of picoeukaryotic algae were cryptophytes (16%), chlorophytes (13%) and diatoms (9%). Picocyanobacteria were clearly dominated by phycoerythrin containing Synechococcus. The parallel use of different assessment methods (CHEMTAX and flow cytometry) revealed the share of eukaryotic and prokaryotic part of autotrophic picoplankton. We gratefully thank Dr. Tiit Kutser (Estonian Marine Institute, Uni- versity of Tartu) for organizing the cruises and helping with the sample collection and Karolin Teeveer for providing microscopy counts. This work was supported by Estonian Ministry of Education and Research (IUT 21-02); Estonian Science Foundation (ETF9102, ETF8576); Swiss Grant for Programme “Enhancing public environmental monitoring ca- pacities” and Estonian Doctoral School of Earth Sciences and Ecology. We are thankful for the two reviewers who provided excellent advice to improve this manscript. We gratefully thank Dr. Tiit Kutser (Estonian Marine Institute, Uni- versity of Tartu) for organizing the cruises and helping with the sample collection and Karolin Teeveer for providing microscopy counts. This work was supported by Estonian Ministry of Education and Research (IUT 21-02); Estonian Science Foundation (ETF9102, ETF8576); Swiss Grant for Programme “Enhancing public environmental monitoring ca- pacities” and Estonian Doctoral School of Earth Sciences and Ecology. We are thankful for the two reviewers who provided excellent advice to improve this manscript.