Autotrophic picoplankton of Lake Baikal: composition, abundance and structure

Abstract

Investigations of Baikalian phytoplankton in 1960s showed that some very small blue-green algae with a cell diameter of 1.5 lm develop in great abundance in Lake Baikal in summer. They were described as a new endemic species -Synechocystis limnetica Popovsk. S. limnetica was found as mass dominant species of the autotrophic picoplankton. Knowledge on species composition of Baikalian picoplankton is limited to this species. Autotrophic picoplankton (APP) communities were studied monthly from 1997 to 2001 at the monitoring station in southern Lake Baikal. Microscopic examinations of picoplanktonic samples based on the fluorescence of pigments, cell morphology and ultrastructure revealed that Lake Baikal is dominated by chroococcoid phycoerythrin-rich cyanobacteria of genus Synechococcus. Cyanobacteria of this genus were represented by various morphotypes throughout the study: coccoid and ellipsoid Synechococcus spp. 0.85 Â 1.1 lm by size, constituting the main mass of autotrophic picoplankton, their proportion varying during the year from 74 to 97%; Synechococcus-species with short and long rod-shaped form of cells, reach maximum (8-18%) in the autumnal period. Endemic species of Lake Baikal -S. limnetica contribute 1-4% in APP communities. Baikalian APP was found to include free aggregated cells of Synechocystis-and Synechococcus-type, to 5% in autumn, as well as the colonial species Aphanothece clathrata f. brevis, the contribution of which to total autotrophic picoplankton fraction changes significantly in seasonal and annual aspects. Picoplanktonic green algae are not especially abundant in Lake Baikal, and, on average did not exceed 8% of the total APP. The sizes of picoalgae are 1.25 Â 1.75 lm, both single cells of green algae; aggregated forms are noted in the picoplankton. Maximal abundance of autotrophic picoplankton was registered in a near-surface layer in late July (7.36 Â 10 5 cells ml )1 ), and the minimum number (2.03 Â 10 4 cells ml )1 ) in May, during the period of spring isothermal mixing.

Size fractionated phytoplankton production in two humic shallow lakes with contrasting coverage of free floating plants

“…On the other hand, in LGL, the P A dynamics was strongly influenced by temperature and irradiance seasonality and, in particular, temperature explained the P A fluctuation along the year for picoplankton. This observation has also been reported in several studies regarding picoplankton abundance (Belykh et al, 2006;Mózes et al, 2006).…”

Trophic coupling of the microbial and the classical food web in Lake Baikal, Siberia

“…In natural prey assemblages, calanoid copepods frequently prefer ciliates over nanoflagellates (Burns & Schallenberg, ; Yoshida et al., ), and consume very few APP because of their small size (Sommer & Sommer, ). Although aggregated cells of APP are ingested by marine copepods (Wilson & Steinberg, ), such aggregates are rare in the top 50 m of Lake Baikal (Belykh et al., ), and they were seldom seen in our samples. Finally, an early experiment exploring feeding rates of E. baikalensis suggested this copepod is bacterivorous (Afanasyeva & Messeneva, ), but the lack of replication compromised the results, and subsequent experimental work concluded that grazing rates of Epischura on bacteria are low (Stom et al., ).…”

“…However, large mucous‐bound colonies (60–130 μm greatest axial linear dimension [GALD]), probably the cyanobacterium Microcystis , were not enumerated because they were assumed to be unsuitable for grazing due to their large size and gelatinous matrix (Sommer & Sommer, ). Cells within APP aggregates averaged nine to 14 cells, but they were not included in total APP counts because they occurred in <15% of the fields of view, and they contribute a negligible proportion (1%–2%) to total APP abundance throughout most of the year in Lake Baikal (Belykh et al., ). Because a trophic cascade might alter the size of APP cells (Zöllner, Santer, Boersma, Hoppe, & Jürgens, ), we also measured the diameter (μm) of 10 APP cells on one to three microscope slides from each of the Control and EPI treatments per experiment.…”

Phylogenetic diversity of T4-like bacteriophages in Lake Baikal, East Siberia

“…The filters for bacteria counting were stained with 4 0 ,6-diamidino-2-phenylindole (DAPI) solution. Picoplanktonic cyanobacteria were detected using the phycobilin autofluorescence as described previously (Belykh & Sorokovikova, 2003).…”