Boreskov

PP‐62THE EXTREME LIFE OF A WATER BEAR (HYPSIBIUS KLEBELSBERGI)IN A HOSTILE HABITATBarbara Post, Birgit SattlerInstitute of Ecology, University of Innsbruck; AustriaThe term „extremophile” is usually applied to certain bacteria that show extraordinarytolerance to conditions which seem to be unpleasant for anthropogenic standards like highor low temperatures, desiccation and radiation, but it is frequently used for multicellulareukaryotic organisms. Among metazoans, only tardigrades, rotifers, and nematodes includetaxa that are extremophiles during their whole life cycle. Hypsibius klebelsbergi Mihelčič,1959, a tardigrade, has the ability to occupy a particular ecological niche on the glaciers.Only this species occurs in a large number in so called cryoconite holes, microcaverns on theice surface in the glacier`s abalation zone. These unique freshwater environments can cover0,1‐10 % of the abalation zone of a glacier and occur globally in glaciated environments. Theholes are caused by absorbtions of solar radiation by dark particles in the ice surface; theyare predominantly water filled and frozen throughout the winter or even during a day‐nightcycle. The living conditions in this extreme habitat are characterized by a high light intensity(UV‐radiation), a low water conductivity (1.9 to 6.0 µS), low temperatures (0,1‐0,2°C), littledissolved oxygen and a lack of nutrients. It is settled by mainly microbial communities(viruses, bacteria, microalgae and protozoa). Depending on the geographic region alsometazoa such as tardigrades, rotifers, nematodes, copepods and insect larvae can be found.Both the microflora and ‐fauna are probably decomposed by fungi and bacteria. 12tardigrade species are known from cryoconite holes (all over the world), excludingquestionable identifications. H. klebelsbergi and H. janetscheki (a Himalayan species), twovery highly pigmented species, have only been reported from the glacier surface. Until nowthe glacier‐dweller Hypsibius klebelsbergi is the only species known from the Alps. Due tothis harsh living conditions this species needs certain adaptation abilities. Tardigrades(except marine Arthrotardigrada), have the ability to form a tun, caused by dehydration. Inthis ametabolic dry stage these animals show no visible sign of life, but become active againif rehydrated. While in anhydrobiosis, tardigrades can be tolerant to a variety of extremeenviromental conditions. The importance of tardigrades and their food preference withinthe food web of cryoconite holes are still unknown. The objectives of this research are the242