Species composition of cryosestic algae, their seasonality and basic ecological parameters in coastal (maritime) Antarctica (King George Islang, South shetland Islands) were studied during the Antarctic summer season 1995/96. A relatively high species diversity was found. About 17 species of algae were recognised, from which 14 (about 80%) occurred exlusively in snow and glatier biotopes. Although several nontypical cryosestic algae occurred in continually changing conditions on the snow fields, the occurrence of characteristic cryosestic species is exactly determined by their ecological spectra. As the species live at the temperatures from -1 to +5 oC and in narrow spectra of nutrient concentrations, thay can be considered as extremophiles.