In May 1995, a short-term study on the vertical distribution of phytoplankton in the holomictic, oligotrophic Lake Stechlin revealed a deep chlorophyll maximum (DCM) due to an increase in phytoplankton biomass below the thermocline. The DCM was dominated by centric diatoms, which probably just passed those water layers while sinking to the sediment, and by picocyanobacteria. The DCM was situated well above the 1% level of photosynthetically active radiation, but received almost exclusively light of wavelengths between 500 and 600 nm. The dominant picocyanobacteria were pre-adapted to this environment by the possession of phycoerythrin. The competitive advantage of picocyanobacteria compared with other phycoerythrin-containing phototrophs was probably the most efficient nutrient uptake under low nutrient conditions as a consequence of the small size of picoplankton.
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