PLANKTONIC COMMUNITIES OF MELT PONDS ON THE MCMURDO-ICE-SHELF, ANTARCTICA

The planktonic community of 20 melt ponds on the McMurdo Ice Shelf was investigated to determine taxa abundance and diversity and the contro lling environmental variables. Grazing rates were measured using fluor escent beads to examine trophic interactions between ciliates, bacteri a and phytoplankton. The melt ponds contained a surprisingly varied pl anktonic community with relatively high abundance compared with Antarc tic continental lakes. There was a clear distinction between small, pr oductive ponds dominated by bactivorous small ciliates, hymenostomes a nd heterotrophic cryptophytes and the larger, less productive ponds wh ere these taxa were less abundant. The benthic mats of cyanobacteria a nd diatoms were potentially a source of food for some ciliate species but the majority were bacterivores. The lack of large herbivorous cili ates, the heterotrophic capabilities of cryptophytes and the broad eco logical tolerances contributed to a planktonic community dominated by cryptophytes.