Location and General Description
Scattered throughout the Southern Ocean, these island range from the cold temperate zone (Macquarie Island) to the cool temperate zone, where the rest of the islands lie. All the islands are situated between the Antarctic and Sub-tropical Convergences. Area, location, and administrative country are listed for each island below.
The climate on all these islands is wet, cold, and windy. They lie in a belt of the Southern Ocean lashed by a relentless cycle of westerly gales and cold fronts. Mean wind speeds vary from 30 km/hr to 40 km/hr. Precipitation generally occurs on more than 300 days per year. Annual precipitation varies widely between islands, but is less than 1500 mm per year. The islands administered by New Zealand have a mean annual temperature above 5°C and support trees and woody plants. Macquarie Island, lying further to the south, has a mean annual temperature below 5°C and woody plants do not grow here.
The Auckland, Campbell, and Antipodes Island groups are all volcanic in origin. Auckland and Campbell Islands are based on old shield volcanoes, with granite, greywacke, and schist basement rock exposed in many areas. The Bounty Islands are entirely composed of granite basement rocks. Macquarie Island is geologically distinct and lies on the Indo-Australian and Pacific Plate boundary. It is the exposed crest of the oceanic plate, formed at a spreading ridge. Its geological features are the basis for its World Heritage Site listing, because it is the best preserved example of oceanic crust formed in deep water and since exposed above sea level. Volcanic rocks comprise 80 percent of the Island, with excellent examples of pillow lavas and other extrusive rocks (WCMC 1997).
Maximum altitude varies among the islands as follows: Bounty Islands (88 m); Antipodes Islands (366 m); Auckland Islands (705 m); Campbell Island (569 m); and Macquarie Island (433 m) (WCMC 1998, 1997). Topography also varies widely, but is generally hilly. Macquarie Island has a central rolling plateau covering most of the land area, with a narrow coastal strip surrounding some parts of the island. The topographies of Auckland, Antipodes, and Campbell Islands all reflect their volcanic origin. All islands in the region display a common feature with extensive coastal sections of abrupt cliffs, as a result of the constant action of storm-driven marine forces. Campbell and Auckland Islands have undergone extensive glaciation.
Soils are predominantly peaty and waterlogged and may be up to 8 meters thick on flat areas (WCMC 1998). There is no soil development on the Bounty Islands, which consist of exposed rock. Vegetation associations change across the islands with increasing latitude, which is an important defining factor of this region’s vegetation. Other key factors include climate (particularly low sunlight hours), soils (generally water-logged acidic peats), and wildlife use (through extensive trampling and burrowing). Despite modification on some islands by grazing animals, vegetation associations are relatively undisturbed. Some islands in the Auckland group (Disappointment and Adams) are essentially unmodified by human or introduced animal activity.
Vegetation on the Bounty Islands is restricted to lichens and algae. Some of the world's southernmost forests are found on Auckland Islands and sheltered parts of Campbell Island, with dominant species including southern rata (Metrosideros umbellata), Dracophyllum, Coprosma, and Myrsine spp. Shrubland, tussock, or herbfield dominate exposed or higher sites on the islands administered by New Zealand, with Chionochloa antarctica as the predominant tussock species. The vegetation of Macquarie Island consists primarily of tussock, short tussock grassland, or feldmark vegetation. Poa foliosa is dominant among tussock species. Cushion plants (Azorella and Colobanthus spp.) are common in exposed sites and bogs and mires are common throughout.
These islands have a long history of isolation from each other and from other landmasses. This isolation, combined with the harsh climate, and a relative lack of human modification, has resulted in the evolution of biota of significant scientific interest. While species richness is relatively low, reflecting the high latitude, there are several notable features of the islands’ flora. These include species at the limit of their ecological tolerance (eg. tree ferns - Cyathea smithii is the southernmost tree fern in the world) and a high number of endemics. Many plant species found at or near sea level in this region are also found in New Zealand in sub-alpine vegetation sequences. In general, the islands’ flora is transitional between the temperate New Zealand flora and the circumpolar, less diverse Subantarctic flora. The islands in this ecoregion, excluding the nearly barren Bounty Island, comprise a Centre of Plant Diversity (Given and Hnatiuk 1995). The terrestrial flora contains about 260 taxa, of which 35 are endemic to the region.
Most islands have a large number of rare plants, including an estimated 15 percent of all vascular species on the Auckland Islands alone. Auckland Island also harbors all three species of Pleurophyllum, a genus endemic to this ecoregion. Corybas dienemus is endemic to Macquarie Island and is the only known orchid in the Subantarctic region. Even the tiny Antipodes Island has three endemic taxa. Plants on these islands also have a greater diversity of flower color compared to related species in New Zealand. Megaherbs are well represented in this ecoregion, found on all islands except for the Bounty Islands, including some species with circumpolar distributions and some endemics. Megaherbs tend to have larger leaves and flowers than similar vegetation in temperate areas to the north, and this characteristic form is thought to be an adaptation to cool temperatures and cloudy, humid conditions. All three Pleurophyllum spp. are confined to the region, as is Stilbocarpa polaris and a number of endemic Anisotome spp. (Given and Hnatiuk 1995).
Avian fauna also has strong themes of both endemism and rarity, with 30 species listed on the IUCN Redlist as Endangered, Vulnerable or Lower Risk. There are over 55 seabird and 80 landbird species breeding, with endemism particularly high among landbirds (O’Connor 1999). Seabirds are also found in massive populations, with over 1.5 million endemic royal penguins (Eudyptes schelegli) found on Macquarie Island. Species include penguins, albatross, petrels, ducks, passerines, rail, gull, skua, tern, shags, and snipes.
Taxonomy revision of albatross species was carried out by Robertson and Nunn (1998), identifying 24 species (from 10 previously). Of these, 10 species or subspecies breed in the islands in the region, and five of them breed nowhere else: the Antipodean albatross (Diomedea exulans antipodensis), southern royal albatross (Diomedea epomophora epomophora), Campbell albatross (Thalassarche impavida), white capped albatross (Thalassarche steadi), and Salvin’s albatross (Thalassarche salvini) (O’Connor 1999). Seven of the world’s 17 species of penguins breed in the region. There are four species of shag, each endemic to its own island, namely Bounty Island shag (Phalacrocorax ranfurlyi VU), Campbell Island shag (P. campbelli VU), Macquarie Island shag (Phalacrocorax atriceps), and Auckland Island shag (P. colensoi VU) (Hilton-Taylor 2000). The Bounty Island shag is considered one of the world's rarest shags. Three species and 11 subspecies of landbird are endemic to specific island groups, including snipes, teals, tomtits, pipits, and dotterels. The Campbell Island teal, (Anas aucklandica nesiotis) is considered the world’s rarest duck. A subspecies of the brown teal (A. aucklandica VU), the Campbell Island teal is restricted to 50 to 100 individuals (Heather and Robertson 1997).
Two endemic parakeets, the Antipodes Island parakeet (Cyanoramphus unicolor VU) and Reischek's parakeet (C. novaezelandiae hochstetteri) have evolved on Antipodes Island. A number of species have gone extinct, including the only two indigenous landbirds on Macquarie Island: an endemic rail subspecies, Rallus phillippensis macquariensis, and a red-fronted parakeet subspecies, Cyanoramphus novaezelandiae erythrolis. The latter may have been preyed upon by the weka (Gallirallus australis), a rail introduced for food by sealers in the 1880's (Taylor 1979). The Auckland Island merganser (Mergus australis) is considered extinct, and has not been sighted since 1902. Its decline was likely caused by European settlement and hastened by overzealous museum collecting (Heather and Robertson 1997).
Overall invertebrate species richness is low, but this is consistent with the ecoregion’s high latitude, isolation, and small land area. As with birds and plants, invertebrates show a high level of endemism, and 36 of the 78 species of Lepidoptera represented are endemic. Many species are restricted to individual islands. There are endemic genera of wetas (Orthoptera) and all seven stonefly species found in this region are endemic. Insect faunas for each islands follow: Antipodes (50 spp., 25 percent of which are endemic); Auckland Islands (280 spp., 30 percent endemic); Campbell Island (275 spp., 40 percent endemic); and Macquarie Island (100 spp., 10 percent endemic) (WCMC 1998). Invertebrates on the islands tend toward flightlessness in response to the windy, isolated environment. Most beetles and 70 percent of moths are either flightless or have reduced wings. There are 32 species of endemic freshwater invertebrates (O’Connor 1999)
Five species of pinnipeds breed on the islands, including the world's rarest, the New Zealand or Hookers sea lion (Phocarctos hookeri VU). Of the estimated total population of 12,000 to 14,000 animals, 95 percent breed on the Auckland Islands (WCMC 1998). Macquarie Island has one of the main worldwide populations of southern elephant seal (Mirounga leonina). Fur seals breeding on the islands include New Zealand fur seal (Arctocephalus forsteri), Subantarctic fur seal (also known as Amsterdam Island fur seal) (A. tropicalis), and Antarctic fur seal (A. gazella). On Macquarie Island most New Zealand fur seals are non-breeding males, there are small breeding populations of Subantarctic and Antarctic fur seals, with hybridization common. Leopard seals (Hydrurga leptonyx) are regular visitors but do not breed here. Other Antarctic seal species are occasional vagrants, including the crabeater seal (Lobodon carcinophagus) and Weddell seals (Leptonychotes weddelli). Baleen and toothed whale species are common in Sub-Antarctic waters, with Southern right whales (Balaena glacialis) breeding in the waters around Campbell and Auckland Islands.
No amphibians or reptiles have been recorded on the islands, and there are no native land mammals.
All island groups in the region are classified as Nature Reserves under the legislation of New Zealand and Australia, and are listed as World Heritage Sites. Permits are required to land on any island, and visitor numbers are restricted. The New Zealand Department of Conservation manages the Antipodes, Bounty, Auckland, and Campbell Islands, while Macquarie Island is managed by the Tasmanian Parks and Wildlife Service. Marine Protected Zones of various types exist around the coastlines of some of the islands, and all World Heritage Sites extend into surrounding waters for 12 nautical miles, or approximately 22 km.
Portions of this ecoregion remain some of the least modified natural environments in the world. While settlements and habitat modification have occurred over the past 200 years, the overall impact is relatively limited. Introduced animals have had a lasting impact on both flora and fauna, although Bounty Islands and most offshore islands in other groups are free of introduced mammals. Management of introduced animals has eradicated sheep and cattle from Campbell Island, mice, rabbits, and cattle from Enderby Island (in the Auckland group), weka (a rail introduced from New Zealand) and cats from Macquarie Island, and goats from Auckland Island. A Norway rat (Rattus norvegicus) eradication project on Campbell Island was undertaken in the austral winter of 2001.
A number of birds and animals have suffered significant population decline in recent years, although exact reasons are unclear. New Zealand sea lions were struck by an unidentified illness in January 1998, resulting in the deaths of over 53 percent of pups and 20 percent of adults in that summer breeding season (O’Connor 1999). The Macquarie Island population of southern elephant seals is intensively studied by the Antarctic Wildlife Research Unit at the University of Tasmania, and is known to be declining at about 2 percent per annum. Numbers of rockhopper penguins (Eudyptes chrysocome) on Campbell Island have decreased by about 90 percent within the last 50 years, and an estimated 20 percent decline has occurred in erect-crested penguins on the Antipodes Islands since the mid 1990's (O’Connor 1999). It is possible that these population decreases are related to changing sea temperatures, which may isolate these species from food species, because food species would move further south to colder waters and the increased distance to travel would reduce breeding success.
Types and Severity of Threats
While all habitat types are well represented and protected, threats to the biota exist from a wide range of sources. The potential for the accidental introduction of new species is high, and introduced diseases could also adversely affect existing species. Already established mammalian predators such as rats and cats are of ongoing concern. Preventing the establishment of new species is the highest priority for island conservation, and both New Zealand and Australian managing agencies have quarantine procedures aimed at averting new introductions. Direct human disturbance is a low level threat on the New Zealand islands, as they have no permanent population, but potential disturbance of breeding birdlife is possible on Macquarie Island, where a permanent base is operated by the Australian Antarctic Division.
Fishing activity is a significant threat to many seabird and seal species. The longline tuna fishing industry is a major cause of global decline of albatross and some petrel species. Squid trawling around the Auckland Islands was estimated to kill over 100 New Zealand sea lions each year. The trawlers now use a number of techniques to reduce sea lion bycatch, and the season is now closed when a predetermined number of sea lions have been killed (O’Connor 1999).
Introduced mammals still have a major impact on both flora and fauna. House mice (Mus musculus) remain on Antipodes Island; pigs (Sus scrofa), cats, and mice on Auckland; and mice, ship rats, and rabbits on Macquarie Island. However, as technology and techniques improve, the introduced mammals should be totally removed. Only Auckland and Campbell Islands have high numbers of introduced plant species, but in general, introduced plants are not major threats to indigenous vegetation.
Cats on Macquarie Island were estimated to be killing 60,000 seabirds each year (Jones 1977). Since the last known cat was killed in June 2000, numbers of Antarctic prions (Pachyptila desolata), grey petrels (Procellaria cinerea), blue petrels (Halobaena caerulea), and shearwaters have all shown steady increases (pers. obs). However, rats still prey on eggs of burrowing petrels and prions, and rabbits are still causing significant modification of vegetation patterns. Despite a huge reduction in rabbit numbers since myxomatosis control commenced in 1978, rabbits still kill large areas of tussock and megaherb vegetation, with deleterious effects on bird nesting habitat. Pigs on the Auckland Islands also cause significant damage to vegetation and soils. Predatory mammals are the biggest threat to invertebrates, with several species on the brink of extinction (O’Connor 1999).
Global climate change is also a potential threat. Changes in average temperature could spell disaster for marine and terrestrial species that utilize these islands, and terrestrial species are especially endangered. With such limited habitat available, they have little potential for migration to more suitable habitat.
Justification of Ecoregion Delineation
The Antipodes Subantarctic Islands Tundra ecoregion includes the Bounty Islands, Auckland Islands, Antipodes Islands, Campbell Island, and Macquarie Island. The islands share a long period of isolation, harsh climate, and importance for seabirds and marine mammals. These five island groups comprise the ‘Subantarctic Islands’ Centre of Plant Diversity (Given and Hnatiuk 1995). The Auckland Islands are an Endemic Bird Area and the Antipodes are a Secondary Area (Stattersfield et al. 1998).
Heather, B. D. and H. A. Robertson. 1997. The Field Guide to the Birds of New Zealand. Oxford University Press, Oxford, United Kingdom.
Hilton-Taylor, C. 2000. The IUCN 2000 Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.
Given, D. R. and R. Hnatiuk. 1995. Subantarctic Islands: Australia and New Zealand. Pages 516 – 518 in S. D. Davis, V. H. Heywood and A. C. Hamilton. editors. Centres of Plant Diversity. Volume 2. Asia, Australasia, and the Pacific. WWF/IUCN, IUCN Publications Unit, Cambridge, UK.
Jones, E. 1977. Ecology of the Feral cat Felis catus (L.), (Carnivorus Felidae) on Macquarie Island. Ausralian Wildife Resources. 4(4): 249-262.
O'Connor, T. editor. 1999. New Zealand's Sub-Antarctic Islands. Department of Conservation. Reeds, New Zealand.
Robertson, C.J.R and Nunn, G.B. 1998. Towards a new taxonomy for albatrosses. Pages 13-19 in Albatross Biology and Conservation, editors G. Robertson and R. Gales. Surrey Beatty and Sons, Chipping Norton, Australia.
Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wedge. 1998. Endemic Bird Areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom.
Taylor, R.H. 1979. How the Macquarie Island Parakeet became extinct. New Zealand Journal of Ecology 2: 42-45
WCMC. 1997. Macquarie Island. WCMC Database of Protected Areas. http://www.wcmc.org.uk/protected_areas/data/wh/macquari.html
WCMC. 1998. New Zealand Subantarctic Islands. WCMC Database of Protected Areas. http://www.wcmc.org.uk/protected_areas/data/wh/subantar.html
Prepared by: Keith Springer