Wildlife of Antarctica

The wildlife of Antarctica are extremophiles, having to adapt to the dryness, low temperatures, and high exposure common in Antartica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.

There is relatively little diversity in Antarctica compared to much of the rest of the world. Flying birds nest on the milder shores of the Peninsula and the subantarctic islands. Eight species of penguins inhabit Antartica and its offshore islands. They share these areas with seven pinniped species. The Southern Ocean around Antarctica is home to 10 cetaceans, many of them migratory. There are very few terrestrial invertebrates on the mainland, although the species that do live there have high population densities. High densities of invertebrates also live in the ocean, with Antarctic krill forming dense and widespread swarms during the summer. Benthic animal communities also exist around the continent.

Over 1000 fungi species have been found on and around Antarctica. Larger species are restricted to the subantarctic islands, and the majority of species discovered have been terrestrial. Plants are similarly restricted mostly to the subantarctic islands, and the western edge of the Peninsula. Some mosses and lichens however can be found even in the dry interior. Many algae are found around Antarctica, especially phytoplankton, which form the basis of many of Antarctica's food webs.

Human activity has caused introduced species to gain a foothold in the area, threatening the native wildlife. A history of overfishing and hunting has left many species with greatly reduced numbers. Pollution, habitat destruction, and climate change pose great risks to the environment. The Antarctic Treaty System is a global treaty designed to preserve Antarctica as a place of research, and measures from this system are used to regulate human activity in Antarctica.

Environmental conditions

Around 98% of continental Antartica is covered in ice up to 4.7 kilometres (2.9 mi) thick.^[1] Antarctica's icy deserts have extremely low temperatures, high solar radiation, and extreme dryness.^[2] Any precipitation that does fall usually falls as snow, and is restricted to a band around 300 kilometres (186 mi) from the coast. Some areas receive as little as 50mm of precipitation annually. The coldest temperature recorded on Earth was −89.4 °C (−128.9 °F) at Vostok Station on the Antarctic Plateau.^[1] Organisms that survive in Antarctica are often extremophiles.^[2]

The dry interior of the continent is climatically different from the western Antarctic Peninsula and the subantarctic islands. The Peninsula and the islands are far more habitable, some areas of the peninsula can receive 900mm of precipitation a year, including rain, and the northern Peninsula is the only area on the mainland where temperatures are expected to go above 0 °C (32 °F) in summer.^[1] The subantarctic islands have a milder temperature and more water, and so are more favourable for life.^[3]

The surface temperature of the Southern Ocean varies very little, ranging from 1 °C (33.8 °F) to 1.8 °C (35.2 °F).^[4] During the summer sea ice covers 4,000,000 square kilometres (1,500,000 sq mi) of ocean.^[5] The continental shelf surrounding the mainland is 60 kilometres (37 mi) - 240 kilometres (149 mi) wide. The depth of the seafloor in this area ranges from 50 metres (164 ft) - 800 metres (2,625 ft), with an average of 500 metres (1,640 ft). After the shelf the continental slope descends to abyssal plains at 3,500 metres (11,483 ft) - 5,000 metres (16,404 ft) deep. In all these areas 90% of the seafloor is made up of soft sediments, such as sand, mud, and gravel.^[6]

Animals

At least 235 marine species are found in both Antarctica and the Arctic, ranging in size from whales and birds to small marine snails, sea cucumbers, and mud-dwelling worms. The large animals often migrate between the two, and smaller animals are expected to be able to spread via underwater currents.^[7] Antarctic animals have adapted to reduce heat loss, often developing warm windproof coats and layers of blubber.^[8]

Antarctica's cold deserts have some of the least diverse fauna in the world. Terrestrial vertebrates are limited to sub-antarctic islands, and even then they are limited in number.^[9] Antarctica, including the subantarctic islands, has no natural fully terrestrial mammals, reptiles, or amphibians. Human activity has however led to the introduction in some areas of foreign species, such as rats, mice, chickens, rabbits, cats, pigs, sheep, cattle, reindeer, and various fish.^[9] Invertebrates, such as beetle species, have also been introduced.^[10]

The benthic communities of the seafloor are diverse and dense, with up to 155,000 animals found in 1 square metre (10.8 sq ft). As the seafloor environment is very similar all around the Antarctic, hundreds of species can be found all the way around the mainland, which is a uniquely wide distribution for such a large community. Deep-sea gigantism is common among these animals.^[6]

Birds

The rocky shores of mainland Antarctica and its offshore islands provide nesting space for over 100 million birds every spring. These nesters include species of albatrosses, petrels, skuas, gulls and terns.^[11] The insectivorous South Georgia Pipit is endemic to South Georgia and some smaller surrounding islands. Freshwater ducks inhabit South Georgia and Kerguelen.^[9]

The flightless penguins are all located in the Southern Hemisphere, with the greatest concentration located on and around Antartica. Four of the 18 penguin species live and breed on the mainland and its close offshore islands. Another four species live on the subantarctic islands.^[12] Emperor penguins have four overlapping layers of feathers, keeping them warm. They are the only Antarctic animal to breed during the winter.^[8]

Fish

There are very few species of fish in the Southern Ocean. The Channichthyidae family, also known as white-blooded fish, are only found in the Southern Ocean. They lack haemoglobin in their blood, resulting in their blood being colourless. One Channichthyidae species, the mackerel icefish (Champsocephalus gunnari), was once the most common fish in coastal waters less than 400 metres (1,312 ft) deep, but was overfished in the 1970s and 1980s. Schools of icefish spend the day at the seafloor and the night higher in the water column eating plankton and smaller fish.^[13]

There are two species from the Dissostichus genus, the Antarctic toothfish (Dissostichus mawsoni) and the Patagonian toothfish (Dissostichus eleginoides). These two species live on the seafloor 100 metres (328 ft) - 3,000 metres (9,843 ft) deep, and can grow to around 2 metres (7 ft) long weighing up to 100 kilograms (220 lb), living up to 45 years. The Antarctic toothfish lives close to the Antarctic mainland, whereas the Patagonian toothfish lives in the relatively warmer subantarctic waters. Due to the low water temperatures around the mainland, the Antarctic toothfish has antifreeze proteins in its blood and tissues. Toothfish are commercially fished, and illegal overfishing has reduced toothfish populations.^[13]

Another abundant fish group is the Notothenia genus, which like the Antarctic toothfish have antifreeze in their bodies.^[13]

Mammals

Seven pinniped species inhabitat Antartica. The largest, the elephant seal (Mirounga leonina), can reach up to 4,000 kilograms (8,818 lb), while females of the smallest, the Antarctic fur seal (Arctocephalus gazella), reach only 150 kilograms (331 lb). These two species live north of the sea ice, and breed in harems on beaches. The other four species can live on the sea ice. Crabeater seals (Lobodon carcinophagus) and Weddell seals (Leptonychotes weddellii) form breeding colonies, whereas leopard seals (Hydrurga leptonyx) and Ross seals (Ommatophoca rossii) live solitary lives. Although these species hunt underwater, they breed on land or ice and spend a great deal of time there, as they have no terrestrial predators.^[4]

The four species that inhabit sea ice are thought to make up 50% of the total biomass of the world's seals.^[14] Crabeater seals have a population of around 15 million, making them one of the most numerous large animals on the planet.^[15] The New Zealand sea lion (Phocarctos hookeri), one of the rarest and most localised pinnipeds, breeds almost exclusively on the subantarctic Auckland Islands, although historically it had a wider range.^[16] Out of all permanent mammalian residents, the Weddell seals live the furthest south.^[17]

There are 10 cetacean species found in the Southern Ocean; six baleen whales, and four toothed whales. The largest of these, the blue whale (Balaenoptera musculus), grows to 24 metres (79 ft) long weighing 84 tonnes. Many of these species are migratory, and travel to tropical waters during the Antarctic winter.^[18]

Invertebrates

Most terrestrial invertebrates are restricted to the sub-Antarctic islands. Although there are very few species, those that do inhabit Antarctica have high population densities. In the more extreme areas of the mainland, such as the cold deserts, food webs are sometimes restricted to three nematode species, only one of which is a predator.^[9] Many invertebrates on the subantarctic islands can live in subzero temperatures without freezing, whereas those on the mainland can survive being frozen.^[10]

Arthropods

Mites and springtails make up most terrestrial arthropod species, although various spiders, beetles, and flies can be found.^[9] Several thousand individuals from various mite and springtail species can be found in 1 square metre (10.8 sq ft). Beetles and flies are the most species rich insect groups on the islands. Insects play an important role in recycling dead plant material.^[10]

The mainland of Antarctica has no macro-arthropods. Micro-arthropods are restricted to areas with vegetation and nutrients provided by the presence of vertebrates,^[9] and where liquid water can be found.^[10] Belgica antarctica, a wingless midge, is the only true insect found on the mainland. With sizes ranging from 2-6mm, it is the mainland's largest terrestrial animal.^[19]

Five species of krill, small free-swimming crustaceans, are found in the Southern Ocean.^[20] The Antarctic krill (Euphausia superba) is one of the most abundant animal species on earth, with a biomass of around 500 million tonnes. Each individual is 6 centimetres (2.4 in) long and weighs over 1 gram (0.035 oz).^[21] The swarms that form can stretch for kilometres, with up to 30,000 individuals per 1 cubic metre (35 cu ft), turning the water red.^[20] Swarms usually remain in deep water during the day, ascending during the night to feed on plankton. Many larger animals depend on krill for their own survival.^[21] During the winter when food is scarce, adult Antarctic krill can revert to a smaller juvenile stage, using their own body as nutrition.^[20]

Many benthic crustaceans have a non-seasonal breeding cycle, and some raise their young in a brood pouch. Glyptonotus antarcticus is an unusually large benthic isopod, reaching 20 centimetres (8 in) in length weighing 70 grams (2.47 oz). Amphipods are abundant in soft sediments, eating a range of items, from algae to other animals.^[6]

Slow moving sea spiders are common, sometimes growing as large as a human hand. They feed on the corals, sponges, and bryozoans that litter the seabed.^[6]

Other invertebrates

Many terrestrial earthworms and molluscs, along with micro-invertebrates, such as nematodes, tardigrades, and rotifers, are also found.^[9] Earthworms, along with insects, are important decomposers.^[10]

Many aquatic molluscs are present in Antarctica. Bivalves such as Adamussium colbecki move around on the seafloor, while others such as Laternula elliptica live in burrows filtering the water above.^[6] There are around 70 cephalopod species in the Southern Ocean, the largest of which is the giant squid (Architeuthis sp.), which at 15 metres (49 ft) is the largest invertebrate in the world. Squid makes up the entire diet of some animals, such as grey-headed albatrosses and sperm whales, and the warty squid (Moroteuthis ingens) is one of the subantarctic's most preyed upon species by vertebrates.^[22]

The sea urchin genus Abatus burrow through the sediment eating the nutrients they find in it.^[6] Two species of salps are common in Antarctic waters, Salpa thompsoni and Ihlea racovitzai. Salpa thompsoni is found in ice-free areas, whereas Ihlea racovitzai is found in the high latitude areas near ice. Due to their low nutritional value, they are normally only eaten by fish, with larger animals such as birds and marine mammals only eating them when other food is scarce.^[23]

Antarctic sponges are long lived, and sensitive to environmental changes due to the specificity of the symbiotic microbial communities within them. As a result, they function as indicators of environmental health.^[24]

Fungi

Fungal diversity in Antarctica is lower than in the rest of the world. Individual niches, determined by environmental factors, are filled by very few species.^[25] Roughly 1150 fungi species have been identified. Lichens account for 400 of these,^[3] while 750 are non-lichenised.^[25] Only around 20 species of fungi are macroscopic.^[3]

The non-lichenised species come from 416 different genera, representing all major fungi phyla. The first fungi identified from the sub-antarctic islands was Peziza kerguelensis, which was described in 1847. In 1898 the first species from the mainland, Sclerotium antarcticum, was sampled. Far more terrestrial species have been identified than marine species. Larger species are restricted to the sub-antarctic islands and the Antarctic Peninsula. Parasitic species have been found in ecological situations different from the one they are associated with elsewhere, such as infecting a different type of host. Less than 2-3% of species are thought to be endemic. Many species are shared with areas of the Arctic. Most fungi are thought to have arrived in Antarctica via airborne currents or birds.^[25] The Thelebolus genus for example, arrived on birds some times ago, but have since evolved local strains.^[26] Of the non-lichenised species of fungi and closer relatives of fungi discovered, 63% are ascomycota, 23% are basidiomycota, 5% are zygomycota, and 3% are chytridiomycota. The myxomycota and oomycota make up 1% each, although they are not true fungi.^[25]

The desert surface is hostile to microscopic fungi due to large fluctuations in temperature on the surface of rocks, which range from 2°C below the air temperature in the winter to 20°C above air temperature in the summer. However, the more stable nanoenvironments inside the rocks allow microbial populations to develop. Most communities consist of only a few species. The most studied community occurs in sandstone, and different species arrange themselves in bands at different depths from the rock surface. Microscopic fungi, especially yeasts, have been found in all antarctic environments.^[2]

Antarctica has around 400 lichen species, plants and fungi living symbiotically.^[3] They are highly adapted, and can be divided into three main types; crustose lichens, forming thin crusts on the surface, foliose lichens, forming leaf-like lobes, and fructicose lichens, which grow like shrubs. Species are generally divided between those found on the subantarctic islands, those found on the Peninsula, those found elsewhere on the mainland, and those with disjointed distribution. The furthest south a lichen has been identified is 86°30'. Growth rates range from 1 centimetre (0.4 in) every 100 years in the more favourable areas to 1 centimetre (0.4 in) every 1000 years in the more inhospitable areas, and usually occurs when the lichen are protected from the elements with a thin layer of snow, which they can often absorb water vapour from.^[27]

Plants

The greatest plant diversity is found on the western edge of the Antarctic Peninsula. Well-adapted moss and lichen can be found in rocks throughout the continent. The subantarctic islands are a more favourable environment for plant growth than the mainland. Human activities, especially whaling and sealing, have caused many introduced species to gain a foothold on the islands, some quite successfully.^[3]

Some plant communities exist around fumaroles, vents emitting steam and gas that can reach 60 °C (140 °F) at around 10 centimetres (3.9 in) below the surface. This produces a warmer environment with liquid water due to melting snow and ice. The active volcano Mount Erebus and the dormant Mount Melbourne, both in the continent's interior, each host a fumarole. Two fumaroles also exist on the subantarctic islands, one caused by a dormant volcano on Deception Island in the South Shetland Islands and one on the South Sandwich Islands. The fumarole on Deception Island also supports moss species found nowhere else in Antarctica.^[1]

The bryophytes of Antarctica consist of 100 species of mosses, and about 25 species of liverworts.^[3] While not being as widespread as lichens, they remain ubiquitous wherever plants can grow, with Ceratodon purpureus being found as far south as 84°30' on Mount Kyffin. Unlike most bryophytes, a majority of Antarctic bryophytes do not enter a diploid sporophyte stage, instead they reproduce asexually or have sex organs on their gametophyte stage. Only 30% of bryophytes on the Peninsular and subantarctic islands have a sporophyte stage, and only 25% of those on the rest of the mainland produce sporophytes.^[28] The Mount Melbourne fumarole supports the only Antarctic population of Campylopus pyriformis, which is otherwise found in Europe and South Africa.^[1]

Subantarctic flora is dominated by the coastal tussock grass, that can grow up to 2 metres (7 ft). Only two flowering plants inhabit continental Antartica, the Antarctic hair grass (Deschampsia antarctica) and the Antarctic pearlwort (Colobanthus quitensis). Both are found only on the western edge of the Antarctic Peninsula and on two nearby island groups, the South Orkney Islands and the South Shetland Islands.^[3]

Others

Bacteria have been revived from Antarctic snow hundreds of years old.^[29] They have also been found deep under the ice, in Lake Whillans, part of a network of subglacial lakes that sunlight does not reach.^[30]

A wide variety of algae are found in Antarctica, often forming the base of food webs.^[31] About 400 species of single-celled phytoplankton that float in the water column of the Southern Ocean have been identified. These plankton bloom annually in the spring and summer as day length increases and sea ice retreats, before lowering in number during the winter.^[29]

Other algae live in or on the sea ice, often on its underside, or on the seabed in shallow areas. Over 700 seaweed species have been identified, of which 35% are endemic. Outside of the ocean many algae are found in freshwater both on the continent and on the subantarctic islands. Terrestrial algae, such as snow algae, have been found living in soil as far south as 86° 29'. Most are single-celled. In summer algal blooms can cause snow and ice to appear red, green, orange, or grey.^[31] These blooms can reach about 10⁶ cells per mL. The dominant group of snow algae is chlamydomonads, a type of green algae.^[32]

The largest marine algae are kelp species, which include bull kelp (Durvillaea antarctica), which can reach over 20 metres (66 ft) long and is thought to be the strongest kelp in the world. As many as 47 individual plants can live on 1 square metre (10.8 sq ft), and they can grow at 60 centimetres (24 in) a day. Kelp that is broken off its anchor provides a valuable food source for many animals, as well as providing a method of oceanic dispersal for animals such as invertebrates to travel across the Southern Ocean by riding floating kelp.^[33]

Conservation

Human activity poses significant risk for Antarctic wildlife, causing problems such as pollution, habitat destruction, and wildlife disturbance. These problems are especially acute around research stations.^[34] Climate change and its associated effects pose significant risk to the future of Antarctica's natural environment.^[35]

Due to the historical isolation of Antarctic wildlife, they are easily outcompeted and threatened by introduced species, also brought by human activity.^[36] Many introduced species have already established themselves,^[9] with rats a particular threat, especially to nesting seabirds whose eggs they eat.^[36] Illegal fishing remains an issue,^[13] as overfishing poses a great threat to krill and toothfish populations. Toothfish, slow-growing, long-lived fish that have previously suffered from overfishing, are particularly at risk. Illegal fishing also brings further risks through the use of techniques banned in regulated fishing, such as gillnetting^[37] and longline fishing. These methods increase the bycatch of animals such as albatrosses.^[36]

Subantarctic islands fall under the jurisdiction of national governments, with environmental regulation following the laws of those countries. Some islands are in addition protected through obtaining the status of a UNESCO World Heritage Site.^[34] The Antarctic Treaty System regulates all activity in latitudes south of 60°S, and designates Antarctica as a natural reserve for science.^[38] Under this system all activity must be assessed for its environmental impact. Part of this system, the Convention for the Conservation of Antarctic Marine Living Resources, regulates fishing and protects marine areas.^[34]

References

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