A survey of the terrestrial tardigrades inhabiting soil, algae, lichens, and mosses was conducted during the austral summer of 1990 at the Australian Research Station at Mawson and other localities on the Mawson Coast. Five genera and six species of tardigrades were recovered: Echiniscus jenningsi, Diphascon sanae, Hypsibius antarcticus, Macrobiotus blocki, Macrobiotus stuckenbergi, and Milnesium tardigradum. Males have seldom been reported in the genus Echiniscus, but constituted about 40% of the population of E. jenningsi. Such a high concentration of males suggests a sexually reproducing population of E. jenningsi on the Mawson Coast. Patterns, obstacles, and strategies of dispersal, reproduction, and survival are discussed relative to the harsh, sparse, and insular environment of East Antarctica. Additional key words: sexual dimorphism, dispersal, distribution In the harsh environmental conditions of Antarctica there are few truly terrestrial ecosystems. Mosses, lichens, and a few algae are scattered over the small areas of unfrozen land that ring the edge of the continent or protrude through the ice as nunataks. These plants and the rudimentary polar soils are inhabited by bacteria, yeasts, fungi, unicellular algae, rotifers, nematodes, tardigrades, and mites (Heatwole 1983; Heatwole et al. 1989); this biota is depauperate compared to that of the milder Antarctic Peninsula. The occurrence of tardigrades in Antarctica has been well known (see review by Miller et al. 1988), but details of the distribution of species are only beginning to emerge. We have studied tardigrades of the Mawson Coast, East Antarctica, for which there are no previous records. Tardigrades have been reported from other sites in East Antarctica, including Gaussberg (Richters 1907), the Japanese station at Syowa on the Prince Olav Coast (Morikawa 1962; Sudzuki 1964, 1979), the Bungar Hills (Sudzuki 1979), the Vestfold Hills near the Australian Research Station at Davis on the Ingrid Christensen Coast (Everitt 1981; Miller et al. 1988), the Russian base at Molodezhnaya in Enderby Land (Dastych 1984), the Australian Research Station at Casey (Dastych 1989; Miller, Miller, & Heatwole aPresent address: 1710 Lakeshore Dr., Mahomet, IL 61853, USA. b To whom correspondence should be addressed. 1994), Robertskollen, western Dronning Maud Land (Ryan et al. 1989), and the Larsemann Hills (Miller et al. 1994). Study area. Mawson Base is an Australian Antarctic Research Station on the east coast of Antarctica (Fig. 1), at 67?36' S, 62?52' E (Betts 1981), located about 700 km west of the Australian base of Davis. It lies on a horseshoe-shaped rocky outcrop 1 km long and slightly more than 0.5 km wide, rising to an elevation of 33 m (Filson 1966); the area is free of ice in summer. The substrate consists of smoothly scoured Mawson Charnockite, a granite with occasional crevices (Harrington 1965; Filson 1966) and strewn with patches of gravel, soil, and pebbles. The flora is reasonably rich, comprised of 18 species of lichens and 2 mosses (Filson 1966). Patches of moss occurred in cushions up to 3 cm thick on soil, while boulders had up to a 25% cover of lichens. The nitrophilic alga Prasiola crispa grew in places containing feathers and guano of penguins. Mawson Base has been inhabited since 1954 and has over 30 buildings (Betts 1981). The human population is 25-30 in winter and expands in summer to about 90. Scattered snowbanks persist throughout summer and together with the adjacent ice cap provide sufficient runoff to form meltwater channels and seepages. Soil accumulates mainly in sheltered places and usually maintains a relatively high moisture content. Field Rocks is a seasonally exposed, rocky outcrop This content downloaded from 207.46.13.85 on Fri, 18 Nov 2016 04:15:35 UTC All use subject to http://about.jstor.org/terms