COMMUNITY DYNAMICS OF PHYTOPLANKTON, PROTOPLANKTON AND BACTERIOPLANKTON IN SELECTED WISCONSIN LAKES

Graham, L. E.1, Graham, J. M.2, Lauster, G. H.2, Kent, A. D.2, Yannarell, A. C.2 and Armstrong, D. E.2 1Department of Botany and 2Center for Limnology, University of Wisconsin‐Madison, Madison, WI 53706 USA As part of an NSF‐sponsored Microbial Observatory program at the North Temperate Lakes Long‐Term Ecological Research Site, microbial community dynamics are being monitored in three Wisconsin lakes, representing a trophic spectrum. Bacterioplankton diversity is assessed by automated ribosomal intergenic spacer analysis (ARISA) and dominant members identified by T‐RFLP. Phytoplankton and protoplankton are enumerated in volumes of lake water varying from 5 to 25ml. Surrounded by the city of Madison, eutrophic Lake Mendota is dominated by cyanobacteria throughout the ice‐free seasons. Our intensive counting procedures, however, have revealed an underlying diverse assemblage of chlorophytes, typical of less impacted waters, at low population levels. Dystrophic Crystal Bog in northern Wisconsin has a low diversity of phytoplankton and protoplankton and in summer becomes almost a pure culture of Peridinium limbatum, an event that may be correlated with a dramatic decline in bacterioplankton diversity. In winter the bog is dominated by heterotrophic production as biomass of protozoa exceeds that of phytoplankton. Nearby oligotrophic Crystal Lake has a high species diversity of both phytoplankton and protoplankton, and cyanobacteria and chlorophytes are very diverse. In autumn the lake supports an unusual planktonic grazer, a testate amoeba which captures bacterioplankton and phytoplankton in a net of pseudopodia. Preliminary results indicate that bacterioplankton dynamics may be strongly linked to algal dynamics in the eutrophic and dystrophic lakes but are uncoupled in the oligotrophic lake.