DETERMINATION OF EUBACTERIAL AND CYANOBACTERIAL SIZE AND NUMBER IN LAKE BAIKAL USING EPIFLUORESCENCE

Chroococcoid cyanobacteria, (mean size = 0.79-mu-m, likely Synchetocystis limnetica POPOVSK) and total eubacteria (mean size = 0.33-mu-m), from Lake Baikal, USSR, were enumerated using epifluorescence microscopy and sized with image analysis. Bacterial densities ranged from 0.44.10(6) cells ml-1 at 250 m to 2.3.10(6) cells ml-1 at the surface. Mean eubacterial abundance was 1.3.10(6) cells ml-1. Cyanobacterial densities were more variable, ranging from 0.42.10(4) cells ml-1 at 250 m to 9.8.10(4) cells ml-1 at the surface, with a mean abundance of 2.7.10(4) cells ml-1. The cyanobacteria, in particular, occurred in clusters resembling "marine snow". Our results indicate that Lake Baikal picoplankton size and density are similar to other large lakes but may have a more diverse community structure than in other large oligotrophic lakes.