Dominance of microflagellates over diatoms in the Antarctic areas of deep vertical mixing and krill concentrations

Open Access
Publisher Website
Google Scholar
Abstract
Phytoplankton data obtained during six summer Polish expeditions to the Antarctic Peninsula area, are compared with concurrently recorded data on water column stabilities and krill abundance. The results show that flagellates (1.5–20 μm) are numerically dominant over diatoms in the areas of deep vertical mixing and/or extensive krill concentrations. Of 102 stations dominated by flagellates, 85 (83.3%) are located in a well mixed water column (>100 m) and correspond to a mean krill density of 15–346 t Nm−2. In the same areas, estimated flagellate carbon biomass exceeds diatom carbon. On the other hand, of the 40 stations dominated by diatoms, 36 (90%) are located in areas of increased water column stability (upper mixed layer of 10–50 m) and correspond to a low mean krill biomass of 0.34–4.6 t Nm−2. Positive correlations of flagellate to diatom (F:D) cell number ratios with the depth of the upper mixed layer suggest light limitation of diatom growth and an increased sinking rate of diatoms relative to flagellates in the areas of deep vertical mixing. The relationship of the F:D ratio with krill abundance suggests that krill prefer feeding on diatoms and are less efficient in grazing particles of the size of microflagellates (<20 μm). Flagellates exceed diatoms in an unstable water column when the phytoplankton populations are low; both algal groups increase in numbers with growing stability. The results provide field evidence that deep vertical mixing and krill grazing create conditions for the dominance of flagellates over diatoms. Both factors acting together are likely to suppress diatom blooms in the Antarctic.

This publication has 0 references indexed in Scilit: