Investigation of freshwater and soil protozoans of Antarctic

Despite extreme environmental conditions, more than 80 ciliate species (unicellular organisms, protozoans) were found in soils and freshwater lakes of the Antarctic continent. This represents an unexpectedly rich diversity. The community of testate amoebae was distinctly less diverse but their species number was still twice as high as previously extrapolated from their occurrence in other areas. Even the unvegetated mineral soil (fellfield), which is exceptionally dry and poor in organic matter (often <1% of soil dry mass), harboured a species-poor but sometimes rather abundant community of specially adapted single- and multicelled organisms (ciliates, testate amoebae, rotifers, nematodes, tardigrades, springtails, mites). The prime environmental factor for the soil biota turned out to be the soil pH. This is in contrast to traditional beliefs, which suggest that low temperature or soil moisture is essential. Most of the about 2% of snow- and ice-free ground on the Antarctic continent consists of raw mineral soil (fellfield, lithosol). It occurs mainly in the coastal regions surrounding the continent where also small lakes and meltpools are located. Many of these freshwater bodies are ice-covered for most of the year but some are ephemeric, i.e. they exist only in the short summer period and then dry up again. As studies on the organisms of these extreme biotopes are scarce, the communities of ciliates and testate amoebae were investigated in various lakes, pools and terrestrial habitats (moss, mineral, ornithogenic and geothermal soils) of the Victoria Land (74S) in co-operation with the Italian National Antarctic Research Programme (PNRA). The dynamics of the active micro- and mesofauna (ciliates, testate amoebae, rotifers, nematodes, tardigrades) were studied in mineral soil in order to elucidate prime environmental factors influencing the populations. Growth and generation times of selected ciliate species were determined at different temperatures in the laboratory to detect temperature adaptations and survival strategies. In total, 83 species of ciliates were identified in more than 70 samples and 50 silver preparations. For example, 23 species were found each in moss and mineral soil, whereas 52 species occurred in the freshwater bodies. At least 5 species and subspecies were new to science and 22 were first records for Antarctica; the new species and several insufficiently known taxa were described. Additional 35 species were found on the sea floor and in sea ice of the Ross Sea. Only 16 species or varieties of testate amoebae were recorded, which occurred mainly in mineral soil. Among these were, however, one new species and four first records for Antarctica. Comparatively more species- rich were four soil samples from sub-Antarctic South Georgia, which contained 19 taxa of testate amoebae. However, only one ciliate species was found there, but this was new to science. The population densities of the active biota ranged on average between 0.3-19 individuals per gram dry mass of mineral soil. These numbers are in the same order of magnitude than those found in other regions of Antarctica but, nevertheless, indicate a distinct faunal pauperization with increasing southern latitude. However, the ciliate community decreased only slightly. The growth experiments showed, that some Antarctic ciliates reach shortest generation times at the lowest temperature (4C), some at the highest (20C) and others multiply almost equally well over this whole temperature range. This suggests that different species use differing survival strategies and some ciliates are particularly well-adapted to the low temperatures. These results are important for further ecological investigations in Antarctica, e.g. for studies concerning global changes.