Biogeography

Scotia Sea Islands tundra

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South Georgia Island, United Kingdom. © Eco-Expeditions

The Scotia Sea Islands ecoregion is a terrestrial area comprising several groups of islands in the Southern Atlantic Ocean, some continental and some of volcanic origin. Generally associated with Antarctica in terms of flora and fauna, these islands are partially or fully covered in permanent ice sheets and snow. The dominant vegetation is a tundra of mosses, lichens, and algae. While there are no native land mammals and only a handful of land-birds, the Scotia Sea Islands support very significant seal, seabird, and penguin rookeries. The cold, harsh climate of the region has deterred permanent human settlement of the islands, though the region’s seal populations were drastically reduced during an era of intense hunting in the 17th and 18th centuries. The current commercial fishing industry in the Scotia Sea now poses threats to seal and seabird populations.

Location and General Description

The Scotia Sea Islands tundra ecoregion includes South Georgia, South Sandwich, South Orkney, and South Shetland Islands, all of which are UK territories, and also Bouvet Island, belonging to Norway. South Georgia Island (54º48' S 36º90' W) is the second largest of the sub-Antarctic islands, with an area of 3755 square kilometers. Bird, Willis, Cooper, and Annekov Islands and Clerke and Shag rocks lie offshore. The landscape of the island is rugged and mountainous, rising to over 2934 meters at Mt. Paget. The mountains are surrounded by ice fields and glaciers, and 50% of the island is permanently covered by ice and snow. Though there is no permanent human settlement, the British Antarctic Survey has a base on Bird Island, and a new fisheries laboratory replaced the former military garrison at King Edward Point in March 2001. In April 1982, Argentina and Great Britain battled at South Georgia Island, in a dispute over scrap metal left from abandoned whaling stations.

caption WWF

 

 

 

 

 

 

 

 

 

 

 

 

The South Sandwich Islands (57º S 27º W) are twelve main volcanic islands and several islets located 470 km south of South Georgia and 1300 km north of the Antarctic coast. This is the only volcanic arc in the Antarctic region, with a deep sea trench (8265 meters) at the eastern boundary. The larger islands of Bristol, Cook, Saunders, Thule, Visikoi, and Montagu are mostly ice-covered, while the smaller islands are virtually free of ice during the summer. Volcanic activity is recent on these islands, and many have active fumaroles.

caption South Orkney Islands, Antarctica. Source: Galen R. Frysinger

Four main islands and several minor islands, islets and rocks make up the South Orkney Island group (60º40' S 45º15' W), which are about 600 km northeast of the tip of the Antarctic Peninsula. About 85% glacierized, Coronation is the largest and highest of the group, with a high point at Mount Nivea (1,265 m). Signey Island is the most biologically significant, as almost half of the island is snow- and ice-free for 3 months during the summer. Several small freshwater lakes are located on the coast. The South Shetland Islands (62º S 58º W) form a chain of 11 main islands 539 km long about 480 km to the west of the South Orkney Islands. The most widely known of the South Shetlands chain is Deception Island, a horseshoe-shaped flooded caldera. The central harbor, Port Foster, is warmer than the outside sea due to activity of many sea-level fumaroles. Interestingly, the harbor is mostly devoid of birdlife, while many penguin rookeries are found on the outside coast of the island.

Bouvet (54°43' S 3°40' E) is a small volcanic island having the distinction of being the most isolated island in the sub-Antarctic. It is located about 2,500 km southwest of Cape Town, on the southern extremity of the Mid-Atlantic Ridge. Covered by a thick, permanent sheet of ice, Bouvet has no vascular vegetation. Sheer ice cliffs drop vertically to black beaches formed of volcanic sand. The inactive volcano at the center of the island contains an ice-filled crater named Wilhelm II Plateau. Since sealing and whaling have ceased in the Southern Ocean, Bouvet is only rarely visited. An automatic weather station operates on the island, and occasional scientific expeditions are made to the island. Other islands were once reported in the vicinity, and an island dubbed Thompson is now believed to have been destroyed by a volcanic eruption in 1895.

These islands lie south of the Antarctic convergence, a biological barrier encircling Antarctica's waters. Temperatures, especially of the ocean, vary dramatically on either side of this barrier. The climate is cold, windy, and cloudy with little variation between seasons. Some of the islands experience extremely heavy cloud cover, such that daily sunshine only average one and one-half hours per day on the South Orkney Islands.

The existing vegetation of the sub-Antarctic botanic zone is primarily tundra dominated by mosses, lichens, liverworts and algae. Its make-up is quite similar to the feldmark vegetation found on islands farther north in the Atlantic, such as Tristan da Cunha and Gough Islands. Other vegetation types are tussock grassland, bogs, and feldmark. Small stands of Antarctic hair grass (Deschampsia antarctica) occur on most of the Scotia Sea Islands, though Bouvet Island is lacking any higher plants, and may be considered as part of the Antarctic botanic zone. South Georgia's flora is more diverse. Here, unglaciated parts of the island are covered by tundra meadows dominated by fescue grass (Festuca erecta), peat bogs of rush (Rostkovia sp.) and Sphagnum moss, and feldmark composed of mosses and lichens. Tussock grasslands (Paradiochloa (Poa) flabellata) occur along the coastlines. In full, recorded flora for South Georgia includes 26 native vascular plants with two endemic species, Uncinia smithii (a sedge) and Acaena magellanica georgiaeaustralis (Rosaceae). On some islands, such as the Sandwich Islands group, rich bryophyte and liverwort communities occur around fumaroles.

Biodiversity Features

caption Gray-headed albotross (Diomedea chrysostoma) on South Georgia Island. © Peter Harrison/Eco-Expeditions

Though land animals are almost non-existent, the Scotia Sea Islands have very important seabird, penguin and seal rookeries. Southern elephant seal (Mirounga leonina), Antarctic fur seal (Arctocephalus gazella), sub-Antarctic fur seal (A. tropicalis), Weddell seal (Leptonychotes weddellii), leopard seal (Hydrurga leptonyx), and crabeater seal (Lobodon carcinophagus) are all found in this ecoregion. Over 95% of the species Arctocephalus gazella breeds on South Georgia Island. Resident and breeding penguins include king penguin (Aptenodytes patagonicus), macaroni penguin (Eudyptes chrysolophus), rockhoppper penguin (Eudyptes chrysomoe), adelie penguin (Pygoscelis adeliae), chinstrap penguin (Pygoscelis antarctica), and gentoo penguin (Pygoscelis papua). While high rocky cliffs and glaciers make many of the islands inhospitable to penguins, other areas are made available by volcanic activity, where rocks are kept warm and free of ice.

The albatrosses, largest of the seabirds, have very long life spans, with some individuals living to over 60 years of age. They also have one of the lowest reproductive rates of any bird, with all species laying a single egg, and many breeding only every other year. Four species of albatross breed on South Georgia Island: black-browed albatross (Diomedea melanophry), gray-headed albatross (Thalassarche chrysostoma), light-mantled sooty albatross (Phoebetria palpebrata), and wandering albatross (Diomedea exulan). A few of the other seabirds breeding on the islands are cape pigeon (Daption capense), black-bellied storm petrel (Fregetta tropica), Antarctic prion (Pachyptila desolata), fairy prion (Pachyptila turtur), snow petrel (Pagodroma nivea), South Georgia diving petrel (Pelecaniodes georgicus), blue-eyed shag (Phalacrocorax atriceps), and Antarctic Tern (Sterna vittata). In some cases, more than half of the world population of a species is represented on South Georgia Island alone.

caption Royal albotross (Diomedea epomophora) on Enderby Island. (Photograph by © Eco-Expeditions)

The native land animals of this group of islands are restricted to five land birds on South Georgia, including two endemic species: South Georgia pintail (Anas georgica) and South Georgia pipit (Anthus antarcticus). Occasional vagrant birds appear, which are far off course and have not become established. There are no native mammals, reptiles or amphibians, though several species have been introduced deliberately or unintentionally (that is, reindeer, dogs, mice, cats, sheep, horses, and rabbits). Only the rat and reindeer have thrived. Reindeer (Rangifer tarandus) were introduced to South Georgia Island in 1911, and there is now a population of about 2000. The invertebrate population of the islands, while not diverse, often has high population densities. Included are arthropods (primarily springtails and mites), earthworms, mollusks, spiders, beetles and flies, as well as micro-invertebrate groups (nematodes, tardigrades, rotifers). The waters of the Scotia Sea have abundant whale populations as well.

South Georgia and South Sandwich Islands are protected under the 1975 Falklands Islands Dependencies Conservation Ordinance. Bouvet Island became a Nature Reserve in 1971. Recent tourism is mostly confined to King Edward Point and the Bay of Isles on South Georgia, with all other parts of the island closed to access without a permit.

Current Status

Due to the inhospitable climate of the Sub-Antarctic region, the Scotia Sea Islands ecoregion has not been subject to degradation associated with any wide-spread human settlement. The greatest impact by far on the islands' biodiversity was suffered during the time that intense whaling and sealing occurred in the region. These islands became the center of British and American sealing in the late 18th century, and the human population at South Georgia's whaling stations had reached almost 500 by 1,964. Antarctic fur seals were hunted almost to extinction for their fur, while the elephant seal was killed for its blubber, as a source of oil. The seals are now protected by the Convention for the Conservation of Antarctic Seals (CCAS), the Antarctic Treaty, and various other national legislations.

Types and Severity of Threats

Since protection, Antarctic fur seal populations have been growing steadily, with a population growth now close to 10% per annum. The southern elephant seal, however, after an initial recovery, has only maintained a steady population at South Georgia Island. On the other side of Antarctica, such as on Marion Island and Macquarie Island, populations have been decreasing over the past forty years. A possible explanation is that the elephant seal had reached its natural limit in terms of food competition. Seals are in competition for food with commercial fisheries as well as with such other marine predators as whales, that are recovering from previous exploitation. Another threat to seals is from entanglement in debris from marine traffic; fishing net caught around the neck can result in drowning or starvation. A 1988-89 study at Bird Island, South Georgia, reported 208 sightings of entanglement, extrapolated to an average of 5000 to 10,000 fur seals entangled for the whole of the South Georgia population.

While most Antarctic penguins have abundant populations, rockhopper and macaroni penguin populations have decreased substantially without explanation in recent years. Albatross populations at South Georgia have been decreasing mainly due to longlining for various fish, particularly the Chilean sea bass. Commercial fisheries in the Scotia Sea are currently focused on Chilean sea bass (or Patagonian toothfish) (Dissostichus eleginoides), which has replaced a longtime interest in harvesting krill. The fishing industry is subject to several measures attempting to reduce casualties to wildlife, however, illegal fishing is responsible for thousands of deaths each year.

Introduced plants, invertebrates and mammals are a problem especially on South Georgia Island. Many seabirds avoid predators on the coastal grasslands by breeding on such offshore islands as Bird Island.

Justification of Ecoregion Delineation

The Scotia Sea Islands are generally associated with Antarctica in terms of flora and fauna, as they lie south of the Antarctic convergence, a biological barrier encircling Antarctica's waters. However, they share a close sub-Antarctic affinity only with the extreme northern tip of the Antarctic peninsula, and are not included in Udvardy’s biogeographic division with Marielandia, or West Antarctica. Vegetation types also occur on these islands that are similar to the feldmark vegetation found on islands farther north in the Atlantic, such as Tristan da Cunha and Gough Islands. Hence, species assemblages are a unique blend.

Additional Information on this Ecoregion

See Also

Further Reading

 

Disclaimer: This article contains information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

 

 

 

Glossary

Citation

Fund, W. (2014). Scotia Sea Islands tundra. Retrieved from http://www.eoearth.org/view/article/51cbeed57896bb431f69a9b7

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