Diversity and Distribution of Free-living Ciliates from High-Arctic Kara Sea Sediments

For the first time, free-living ciliates were studied in sediments from a variety of habitats in the Kara Sea (the Arctic Ocean). Ciliates were found in a wide range of environmental conditions (from the intertidal zone up to depths of 554 m, from salinities ranging from 0 to 34 psu, and from coarse sands and gravel to muddy sediments), with total abundances varying from 1 to 127 ind/cm3. Altogether, 114 species were identified, most of which were widely distributed and were previously reported from other Arctic regions. An unsaturated species accumulation curve and the presence of many rare species indicated that the Kara Sea is potentially as rich in ciliates as other regions. Fine- and medium-grained sands exhibited the richest and most abundant ciliate fauna, with many interstitial forms occurring up to depths of 200 m; whereas both the coarse sands of the exposed intertidal beaches and the sublittoral muds were poorly inhabited by non-specific euryoecious species. The granulometric composition of sediments was suggested to be the main driver controlling the diversity and composition of ciliate communities, while the other factors, such as salinity, water productivity and depth, were of secondary importance.