Summary
Zooplankton and benthic invertebrates are important components of polar lakes and often form the highest trophic level in the aquatic food web. Their biodiversity decreases towards high latitudes, although the two poles have different species composition despite environmental similarities in temperature, habitat structure, and light cycle. Different geological history and accessibility largely explain the faunal differences between the poles. The Arctic, with easier colonization from the south, extensive high-latitude glacial refugia and a milder climate, is more species-rich than the Antarctic. Furthermore, some taxonomic groups occurring in the Arctic are entirely missing from the Antarctic. Whereas some species live close to their environmental tolerance in the cold polar regions, others have adapted to life at low temperatures, short growing season, long periods of ice cover, and low food supply. Their abundance can be as high as at lower latitudes, especially in shallow water bodies where microbial mats increase the habitat complexity and food. Lakes, ponds, rivers, and streams are all inhabited by various and often different communities of zooplankton and zoobenthos. Small-bodied zooplankton grazing on small food particles are dominant in lakes, while large, pigmented species are often found in shallow ponds where they can be exposed to high levels of ultraviolet (UV) radiation. In some coastal saline lakes of Antarctica zooplankton can form the highest biomass in the plankton. In the well-oxygenated polar lakes and streams benthic animals can be found at high abundance. The aim of this chapter is to describe the unique cold-water communities of zooplankton and zoobenthos common to both poles. The chapter reviews the most important factors that define the zoogeography and diversity of freshwater invertebrates in the Arctic and Antarctic. It describes the range of aquatic invertebrate communities in different habitats, and introduces in more detail the ecology and life history of some key zooplankton and aquatic insects. The F nal section considers how climate change, especially elevated temperature and increase in UV radiation, are altering high-latitude aquatic invertebrate communities