Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer
- 1 August 1994
- journal article
- Published by Oxford University Press (OUP) in Journal of Plankton Research
- Vol. 16 (8) , 945-959
- https://doi.org/10.1093/plankt/16.8.945
Abstract
Autotrophic picoplankton were highly abundant during the thermal stratification period in late July in the pelagic area (water depth 500–1300 m) of southern Lake Baikal; maximum numbers were 2 × 10 6 cells ml −1 in the euphotic zone (˜15 m). Unicellular cyanobacteria generally dominated the picoplankton community, although unidentified picoplankton that fluoresced red under blue excitation were also abundant (maximum numbers 4 × 10 5 cells ml −1 ) and contributed up to ˜40% of the total autotrophic picoplankton on occasions. Carbon and nitrogen biomasses of autotrophic picoplankton estimated by conversion from biovolumes were 14–84 μg C l −1 and 3.6–21 μg N l −1 . These were comparable to or exceeded the biomass of heterotrophic bacteria. Autotropic picoplankton and bacteria accounted for as much as 33% of paniculate organic carbon and 81% of nitrogen in the euphotic zone. Measurements of the photosynthetic uptake of [ l4 C]bicarbonate and the growth of picoplankton in diluted or size-fractionated waters revealed that 80% of total primary production was due to picoplankton, and that much of this production was consumed by grazers in the <20 μ.m cell-size category. These results suggest that picoplankton-protozoan trophic coupling is important in the pelagic food web and biogeochemical cycling of Lake Baikal during summer.Keywords
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