The Antarctic environment comprises diverse habitats and ecosystems that include:
- ice-covered areas
- ice-free vegetated areas and rocks
- saltwater and freshwater lakes and streams
- intertidal areas; sea ice; and mid-water, deepwater and benthic regions of the Southern Ocean.
In the terrestrial environment on the continent, species diversity is low compared with mid-latitudinal or tropical ecosystems; however, many species are abundant. Species that have made the Antarctic continent their home have evolved across very long timescales, and are now highly specialised and able to survive in the extreme conditions of the southern continent and the frigid ocean surrounding it. The most diverse vertebrate groups are flying seabirds (7 species) and penguins (2 species on the continent and 5 on subantarctic islands). Ice-breeding seals (4 species), fur seals (3 species), sea lions (1 species) and elephant seals (1 species) are also part of the Antarctic fauna. Furthermore, several species of baleen and toothed whales forage in the Southern Ocean. Some species of toothed whales appear to remain there throughout the year.
East Antarctica lacks flowering plants, and lower plants such as mosses, lichens and bryophytes live in the few ice-free areas. Algae prosper in the marine environment and in snowfields. The abundance of terrestrial invertebrates varies regionally and depends on the conditions of the local microhabitats—particularly the topography and vegetation (Nielsen et al. 2011). Many invertebrates live under rocks or in the moss beds—Antarctica’s ‘forests’—where moisture is available (Kennedy 1993). Species diversity is low compared with more temperate regions. The most abundant phyla are rotifers (wheel animals), nematodes (worms) and tardigrades (water bears), but mites and springtails are also found (Convey et al. 2008, Nielsen et al. 2011). The terrestrial species diversity of the region pales in comparison with the marine species. Invertebrate taxa living at the continental shelf (0–1000 metres deep) and in the deep ocean (more than 1000 metres deep) encompass more than 3500 species (Brandt et al. 2007). Sea spiders, sea urchins, marine worms, molluscs, sponges and other creatures are highly diverse, with a large percentage of endemic species (Brandt et al. 2007, Rapp et al. 2011).
An international survey of the Southern Ocean, the Census of Antarctic Marine Life of 2007–08, compiled a biogeographical atlas that provides maps of the distribution of at least 6400 benthic species, highlighting the extraordinary biodiversity of the Southern Ocean (Roberts 2013). Many of these species were newly discovered during the census, and questions still need to be answered about their roles in the ecosystem and the reasons for the variability in their distribution (Kaiser et al. 2013). Antarctic fish are often endemic and are dominated by notothenioids (icefish), which make up more than half of the known 320 fish species in the Southern Ocean (Eastman 2005). Marine microbes are highly abundant and constitute most of the biomass in the Southern Ocean. They play a crucial role in nutrient cycling (Hutchins et al. 2009, Pearce et al. 2010).
The species composition on the subantarctic islands is different from that on or near the continent. The fauna of Heard Island and McDonald Islands includes 3 species of penguin not found on the Antarctic continent and 15 species of flying seabirds, including 2 species of albatross, several petrels, skuas and sheathbills. Three different seal species also frequent the island or breed there (BirdLife International 2016a). The vegetation on Heard Island and McDonald Islands covers the ice-free areas and includes a variety of vascular plants (12 species), mosses (44 species), lichens (34 species) and liverworts (17 species) (Hughes 1987, Bergstrom et al. 2002). Heard Island and McDonald Islands are a listed World Heritage Area because of their unique wilderness, which provides examples of biological and physical processes that occur in an environment largely undisturbed by humans. Because the islands support various threatened and endangered seabird species, the International Union for Conservation of Nature (IUCN) has also declared the region an Important Bird Area.
Macquarie Island is home to an estimated 3.5 million seabirds, comprising 13 different species. These include wandering albatross (Diomedea exulans), grey-headed albatross (Thalassarche chrysostoma), a variety of small petrels and 4 species of penguins. In 2011, the IUCN nominated Macquarie Island as an Important Bird Area because of the presence of various threatened and endangered seabird species (BirdLife International 2016b). In terms of vegetation, Macquarie Island supports 45 species of vascular plants and 91 species of moss, as well as many lichens and liverworts (Selkirk et al. 1990). Macquarie Island is listed as a World Heritage Area because of the unique opportunity it provides to study exposed oceanic crust, and its wild natural beauty.
Although generally rich in nutrients such as nitrogen and phosphorous, the productivity of the Southern Ocean is not as high as might be expected because of low levels of iron (an essential micronutrient) and low light levels (because of persistent cloud cover and reduced daylight hours during winter).