Biogeographic trends in antarctic lake communities

Water bodies that contain liquid water for at least part of the year are a surprisingly common feature of the Antarctic landscape. While these water bodies are generically termed lakes, there is a remarkable variety of types present both on the continent and on subantarctic islands, some of which do not have counterparts in more temperate regions. They range widely in size from cryoconite holes less than a metre across to large lakes with areas over 100 km2, in depth from a few centimetres to over 300 m, in salinity from some of the freshest lakes in the world to others that have salinity approaching that of the Dead Sea and in age from a single summer season to more than 300 000 years. Most of these upper extremes are exceeded by the sub-glacial lakes located deep beneath the Antarctic ice cap. All lakes that have been investigated in Antarctica have been found to contain organisms of some sort. Only in the most saline case - Don Juan Pond in the McMurdo Dry Valleys (see Fig. 1 for a map showing the locations of places mentioned in the text) - is evidence for active metabolism equivocal (Vincent 1988). While some lacustrine plants and animals typically found in more temperate regions are missing from Antarctic lakes and are largely absent from subantarctic islands, notably fish and emergent vegetation, many taxonomic groups, ranging in complexity from bacteria to crustacea, are present (examples of the flora and fauna of Antarctic lakes are presented in Fig. 2). The origins of the Antarctic lake fauna and flora and their position in global biogeography have been of interest since the heroic age of Antarctic exploration (eg Murray 1910, Rühe 1914). Throughout the next 60 years, scattered reports of the biota of lakes in various areas appeared (eg Schmitt 1945, Korotkevich 1958) and slowly a broad picture of the biogeographical patterns emerged (Goldman 1970). This material had wider appeal: Crawford (1974) used the distribution of the cladoceran genus Daphniopsis, which occurs in Antarctica, South America, Australia and Tibet, as evidence for inclusion of all these areas in a greater Gondwanaland. Since 1975 there has been a greater emphasis on lake studies in national programs, which has either directly or indirectly added to our knowledge of lacustrine biogeography. Various reviews have appeared (eg Heywood 1984, Wright and Burton 1981, Ellis-Evans 1996) in addition to a valuable bibliography containing details of many hard-to-get references (Block 1992). In this chapter, we discuss the types and origins of Antarctic lakes and the factors that control biodiversity in these lakes. We review present-day understanding of biodiversity for a series of important taxonomic groups and discuss these data in terms of previous views of Antarctic biogeography.