Variations in numbers and biovolumes of microbial populations from two lakes of different trophic levels

Microbial populations were studied in two lakes of different trophic level (oligomesotrophic and mesoeutrophic). The study aimed to determine if funct ional biodiversity of microbial populations varied in relation with the tro phic level of the system. Heterotrophic bacteria picocyanobacteria, and pig mented and unpigmented flagellates were enumerated by epifluorescence micro scopy. Results showed that pigmented organisms were more important in terms of both numbers and biovolumes in the lake from the lowest trophic level. This lake was also the one where functional biodiversity (calculated using the Shannon index) was constantly higher than in the second lake.