Ciliated protozoa of two antarctic lakes: analysis by quantitative protargol staining and examination of artificial substrates

Planktonic and artificial substrate-associated ciliates have been identifie d in two perennially ice-covered antarctic lakes of the McMurdo Dry Valleys . Abundances estimated by quantitative protargol staining ranged from <5 to 31690 2cells . l(-1), levels that are comparable to those previously obtai ned using other methods. Nineteen ciliate taxa were identified from these l akes, with the most frequently encountered genera being Plagiocampa, Askena sia, Monodinium, Sphaerophrya and Vorticella. The taxonomic findings compar e favorably with those of previous investigators; however four previously u nreported genera were observed in both Lakes Fryxell and Hoare. The variabi lity in the depth distributions of ciliates in Lake Fryxell is explained in terms of lake physicochemical properties and ciliate prey distributions, w hile factors related to temporal succession in the Lake Hoare assemblage re main unexplained. Local marine or temperate zone freshwater habitats are a more likely source than the surrounding dry valleys soils for present cilia te colonists in these lakes. Although the taxonomic uncertainties require f urther examination, our results suggest that ciliate populations in these a ntarctic lakes undergo significant fluctuations and are more diverse than w as previously recognized.