Phytoplankton population dynamics in perennially ice-covered Lake Fryxell, Antarctica

Abstract

Phytoplankton were collected over five austral summers (1987–88 through 1991–92) to examine seasonal and annual fluctuations in species composition and biovolume in Lake Fryxell, a perennially ice-covered lake located in the Dry Valleys of South Victoria Land, Antarctica. Lake Fryxell has perennial gradients of salinity, dissolved oxygen and nutrients. We found that algal species diversity was low (56 taxa were collected), confirming the results of previous short-term studies. The phytoplankton consisted primarily of cryptophyte and chlorophyte flagellates, and filamentous cyanobacteria. The presence of filamentous cyanobacteria, which have not been reported as abundant in this lake by previous workers, may represent a significant ecological change. Each austral summer, one dominant species contributed >70% of the total biovolume; Chroomonas lacustris was dominant in 1987–88, while Cryptomonas sp. dominated the phytoplankton in the remaining 4 years. No species succession occurred during the austral summer. Some common taxa were vertically stratified (Oscillatoria limnetica, Phormidium angustissimum, Pyramimonas sp., Oscillatoria sp.), while others showed no distinct vertical stratification (Chlamydomonas subcaudata, Cryptomonas sp.). The stratification of the phytoplankton reflects the gradients of nutrients and light, and the stability of the water column.