Autotrophic picoplankton in Lake Baikal: Abundance, dynamics, and distribution

Abstract

The autotrophic picoplankton of Lake Baikal was discovered more than 30 years ago; the productivity of the endemic member of the group, Synechocystis limnetica, is of particular interest. In the course of long-term investigations, the abundance of this species was established using the sedimentation technique. Maximum abundance was reached at 104 cells per ml in summer. In addition to estimating the distribution of this species throughout a defined lake area during the spring-summer period, the character of interrelations with large phytoplankton was revealed. Baikalian autotrophic picoplankton was studied from 1997 to 2000 using epifluorecsence and scanning electron microscopy. The study of seasonal and annual dynamics of picoplankton abundance was conducted monthly at the monitoring station in southern Baikal. The spatial distribution of autotrophic picoplankton was observed in the period when Lake Baikal was free of ice; the lake area was defined by 50 stations. Microscopic examination of planktonic samples revealed that the phycoerythrin-rich cyanobacteria of genus Synechococcus generated the largest biomass of autotrophic picoplankton in Lake Baikal. Morphotype diversity of the representatives of genus Synechecoccus was revealed in the study: Synechococcus spp. of coccoid and ellipsoid forms were dominant by abundance. The coccoid and ellipsoid forms had diameters of 0.9 and 0.7 to 1.3 μm, respectively. The portion of picoplanktonic algae in the Baikalian picoplankton community is not high and does not exceed 10% in the summer time when growth is highest. The autotrophic picoplankton abundance throughout the year in the 0–50 m layer varies by more than one hundred times. Maximal concentration of picocyanobacteria occurs in late July–August at 10 to 25 m depths where it reached 106 cells ml−1. The minimal concentration (103 cells ml−1) was observed in December at the same depths. A small peak of the picoplankton growth occurred in April of each year when the total numbers of picocyanobacteria increased 2 to 4 times after winter. In 1999 the peak rose to 105 cells ml−1 . During the investigation period the highest indices of autotrophic picoplankton numbers were observed in 1999 and the lowest in 1997. The spatial distribution of this group in the whole Baikal aquatorium was characteristically heterogeneous; its abundance varied by 2 to 10 times in different parts of the lake. The largest fluctuation occurred in August and the least in September. The maximum picoplankton abundance was observed in the epilimnion during the periods of thermal stratification. In the course of homothermy a comparably homogeneous distribution of picocyanobacteria was revealed up to 300 m depth, but the highest numbers were found in the upper 30 m layer.

Nutrient limitation of the primary production of phytoplankton in Lake Baikal

“…Picocyanobacteria are the predominant primary producers in pelagic Lake Baikal during summer (Nagata et al 1994;Goldman et al 1996;Belykh and Sorokovikova 2003;Katano et al 2005). A general explanation for the predominance of picocyanobacteria in oligotrophic lakes is that they have an advantage in the uptake of low concentration nutrients because of their high surface-to-volume ratio (Weisse 1993;Raven 1998).…”

“…The vernal maximum biomass of phytoplankton in a Melosira year is about tenfold greater than that in a non-Melosira year (Bondarenko and Evstafyev 2002). Another characteristic of Lake Baikal is the dominance of very small phytoplankton, called picoplankton (formerly called ultrananoplankton) in the biomass and primary productivity of the phytoplankton assemblage (Votintsev et al 1972;Back et al 1991;Nagata et al 1994;Bondarenko et al 1996;Watanabe and Drucker 1999;Belykh and Sorokovikova 2003;Yoshida et al 2003;Katano et al 2005).…”

Resting stages and ecology of the planktonic diatom Aulacoseira skvortzowii in Lake Baikal

“…Also, nutrients decline to undetectable concentrations (Fig. 7a,b), mainly because of picoplankton growth (Nagata et al 1994;Belykh and Sorokovikova 2003;. Therefore, a resting stage helps A. skvortzowii survive these unfavorable conditions but successful sporulation depends on having sufficient time to switch resources and prepare for dormancy.…”

Abundance and pigment type composition of picocyanobacteria in Barguzin Bay, Lake Baikal

“…Several studies on the abundance of picophytoplankton in Lake Baikal demonstrated that picocyanobacteria are also important components in terms of cell density among picophytoplankton (Boraas et al 1991;Nagata et al 1994;Watanabe and Drucker 1999;Belykh and Sorokovikova 2003;Nakano et al 2003;Katano et al 2005b;Belykh et al 2006). Picocyanobacteria are abundant throughout the entire lake during summer (Belykh and Sorokovikova 2003), with a maximum density of 2 9 10 6 cells ml -1 recorded in the southern basin (Nagata et al 1994).…”

“…The cell is of a slightly larger size (ca. 1.25 lm, according to Belykh and Sorokovikova 2003) as compared to unicellular picocyanobacterial cells (0.6-0.8 9 0.8-1.2 lm, according to Nagata et al 1994). Most picocyanobacteria are small unicellular organisms, and their shape is coccoid or that of a short rod (Belykh and Sorokovikova 2003).…”