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The Prince Edward Islands

Les noms des biens figurent dans la langue dans laquelle les Etats parties les ont soumis.

Afrique du Sud (Afrique)

Date de soumission : 24/06/2004
Critères: (vii)(viii)(ix)(x)
Catégorie : Naturel
Soumission préparée par :
Department of Environmental Affairs and Tourism
Coordonnées
Marion Island 46°49'30"-46°58'30" S / 37°35'-37°54' E Prince Edward: 46°35'50"-46°39'55" S / 37°52'50"-38°00'45" E
Ref.: 1923

Description

Topography



Marion Island consists of a central highland area that reaches 1,249m ASL at its highest point..There is a 4 - 5. km wide coastal plain (up to 300m ASL) on the northern and. eastern sides of the island that slopes gently up to the highlands. The coastal plain on the western and southern sides of the island is only about 100m in altitude and irregular due to extensive erosion by wave action on these sides of the island. The Island Group is characterised by abundant conical cones of scoria (volcanic cinder).



Prince Edward Island rises to 872m ASL at its highest point (Van Zinderen Bakker Peak) and consists of a central highland that slopes gently to the east and drops to the western lowland in the form of a 400m high escarpment.



The coastlines of both islands consist mostly of coastal cliffs rising abruptly from the sea, interspersed by small pebble and boulder beaches in protected bays.

Geology and geomorphology



The Island Group is located near the centre of the West Indian Ocean Ridge and represents summits of a volcano of Hawaiian type rising more than 3500m from the ocean floor. The age of the oldest lava flows on Marlon Island are estimated at 450,000 years. Marion Island is regarded as a dormant volcano, since the latest (and only recorded) volcanic eruption occurred on the island's west coast in 1980. This makes Marion Island one of only two sub¬Antarctic Islands to have erupted volcanically in recorded history.



It is thought that Prince Edward Island is a remnant of a closely associated shield volcano, of which four fifths have since subsided below sea level.



Two stages of volcanic activity can easily be recognised on both islands: older grey lava and younger black lava flows. The grey basalt lavas, which are between 270,000 and 48,000 years old, occur mainly as elevated ridges with a smooth topography and bear extensive marks of glaciation in the form of deep striations, unsorted rocky material and large solitary boulders. Glaciation occurred between 12,000 and 16,000 years ago, Prince Edward Island does not show signs of glaciation, possibly because the island has never been covered by an ice sheet or because the glaciated sections have since eroded away.



With the retreat of glaciers about 16 000 years ago, Marion Island was subjected to a second wave of lava flows that formed the black basalt lavas. The black lavas form very ragged-flows between and over the grey lavas and mainly occupy intervening valleys between the ridges, As they have never been subject to glaciation, their topography is very uneven. These younger flows are associated with approximately 130 scoria cones on Marion Island. Scoria cones are distinctive features of the geomorphology of both Islands.



There is a stationary glacier or "ice plateau" in the central highlands of Marion Island the only glacier on South African territory. The glacier is static and consists mostly of hard blue ice that is partially hidden by large moraines.

Soils

Most of the rock on the island has not weathered sufficiently to form deep, well-developed soils. Many of the higher lying "fjeldmark" or wind desert areas are characterised by desolate wind-swept surfaces covered by loose stones and volcanic ash. Most of the soils consist almost entirely of slowly decomposing organic matter (peat) from plants and fine volcanic ash. Generally, the islands' soils are characterised by Immaturity, negligible influence of parent material on the soil profiles and a marked effect of slight variations in topography and wind exposure.



Deeper peat soils occur along the waterlogged coastal plain and. in valleys that are protected from wind. Peat slips are common features of these soils, especially on slopes where they have been disturbed by human trampling or by seats. Soils of low-altitude and vegetated areas are usually peat, containing volcanic ash in varying amounts.

Climate

The Island Group has a cool climate with an annual mean air temperature of 5.9°C. The absolute maximum and minimum temperatures ever recorded at the base are 23.8°C and - 6.8°C, respectively. Absolute minimum temperatures are below zero every month of the year, but even in the winter temperatures rarely fall below -4°C because of the moderating influence of the ocean.



The mean surface air temperature has increased by 0.93°C from 1951 to 1988. This Is ascribed to changing oceanic and atmospheric circulation patterns at sea level.



The Island Group experiences high precipitation (an average of 2,500 mm per annum), mainly in the form of rain, which is distributed fairly evenly throughout the year. Most of the rain falls as light showers. Heavy falls of over 25mm/day occur about twice a month on average. The Island Group experiences an average of 25 days with precipitation a month and 308 days with precipitation per annum.



Snow Is frequent in winter, particularly from July to September. Snow sometimes covers the whole of Marion Island, but in low-lying areas it usually melts within a few days. The base experiences an average of 95 days of snow and 46 days of fog per annum.



Marion Island has a high level of cloudiness (annual sunshine duration ca 30% of the maximum possible. On average, no days with more than 90% of possible sunshine are encountered. An annual average of 130 days with a cloud base below 300m above sea level are encountered. Average annual cloud cover is 79%.



The island Group is situated in the "Roaring Forties". Thus the islands are subjected to westerly to northwesterly winds approximately 60% of the time. Gate force (>55km/h) winds lasting at least one hour are experienced for an average of 107 days per annum. Gales usually exceed this speed and duration, however, and can reach speeds of up to. 200km/h. Winds exceeding 70km/h often continue unabated for more than 24 hours,

Genera! ecology



The features of the sub-Antarctic islands that have combined to produce their particular ecosystem are geographic isolation., wind exposure, temperature, high rainfall, and the strong influence of the marine ecosystem (e.g. manuring by. birds and seals).



Two factors in particular have contributed to a relatively low floral and faunal diversity on the sub-Antarctic islands in general and on the Island Group in particular. The first factor is that the Island Group is geologically very young. The second factor is the remoteness of the Islands from continents. A slow process of colonisation has established biota on small "pinpricks" of land across vast expanses of ocean.



Thus, there is a low number of species of indigenous flora. Many of these indigenous species have wide ecological amplitudes and occur over a range of habitats. Five percent of the. plant species are endemic to the Island Group and 23% of the plant species are restricted to the South Indian Ocean Biogeographlical•Province.



Indigenous species that play a major role in continental ecosystems (e.g. herbivorous and carnivorous land mammals) are absent from the natural terrestrial ecosystem of the Island Group. Combined with the very high primary production of many plant communities, this has a significant effect on ecosystem. structure and function. It means that detritivores like fungi and bacteria, rather than herbivores, control energy flow. Arthropods and other Invertebrates play very important roles as detritivores and invertebrates are by far the most dominant herbivores in the ecosystem.

Nutrient cycling

The ecosystem of the Island Group can be regarded as semi-closed systems with significant interaction between the terrestrial and oceanic systems. The ecosystem is characterised by a significant level of nutrient transfer between the terrestrial environment and the ocean. Seabirds and seals bring nutrients to the islands, mainly in the form of guano. These nutrients support the growth of specific plant communities, particularly In the vicinity of penguin and seal colonies, but also farther inland. An example is the way that tussock grasslands replace fembrake communities where burrowing petrels and prions establish their burrows, These nutrients are further spread through the soils by invertebrates.

Nutrients are returned to the oceans when they are washed off the island by rainfall. The nutrients are absorbed by plankton, and are then cycled higher up the food chain and eventually to inshore-foraging seabirds such as Gentoo penguins and cormorants and to seals,

Vegetation



The vegetation of Marion Island is relatively poor in species. This is typical of sub-Antarctic islands due the isolation from other landmasses and rigorous climate_ The Island Group has 22 indigenous vascular plant species and 21 alien plant species, either naturalised or transient. See Appendix A for a species list of vascular plants, Mosses (79 species),



liverworts (36 species) and lichens (ca 50 species) are important components of the vegetation,



Most of the island's vegetation has a very slow growth rate due to the extreme climate. This, combined with slow reproduction, makes the vegetation very sensitive to external disturbances.



Six main plant communities can be distinguished. Vegetation distribution is mainly affected by factors such as the soil-water regime, the influence of salt spray, mechanical damage (e.g. due to trampling) and enrichment by guano deposition,

Invertebrates

Some 147 species of indigenous and introduced invertebrates are known from Marion Island, This includes 19 alien species that have become naturalised and 13 introduced species that have not, as yet, established themselves. 39 Species of soil ciliates have been found on Marion Island.



Seven endemic invertebrate species have been identifed. The endemic species include two springtails (Isotoma marionensis and Katianna n, sp.), three beetles (Bothrometopus elongatus, Ectemnorfrinus marioni and E. similis) and two moths (Pringleophage marioni and P. kerguelensis).



The distribution and density of many invertebrates is strongly Influenced by manuring by birds and seals. High densities and biomass of invertebrates accompany high plant densities, soil nutrient content and plant nutrient content in heavily manured areas.

Mammals



There are three seal species on the Island Group. Their numbers are indicated in parentheses: the southern elephant seal Mirounga leonine (2,000), Antarctic fur seal Arctocephalus gazelle (330), and sub-Antarctic fur seal A. tropicalis (44,800). Leopard seals Hydrurga leptonyx and Weddell seals Leptonychotes weddelui are occasional non-breeding vagrants.



There are no indigenous land mammals an the Island Group. Introduced house .mice are present on Marion Island but do not occur on Prince Edward Island. The. introduced feral cat was exterminated in the early 1990s.

Birds

The Island Group supports 29 species of breeding birds as well as 22 species of vagrant seabirds and 28 species of non-marine vagrant species (see Appendix D for a complete list of. species). Although the breeding bird species Include only one endemic taxon (the Lesser Sheathbill Chionis minor marionenis) most species have a very limited breeding area that is restricted to a handful of sub-Antarctic islands. Furthermore, the large distances between breeding sites and the high philopatry (natal site fidelity) characteristic of these species have led to limited genetic interchange and hence considerable geographical variation within species.



Most of these species are wholly or predominantly dependant on the marine environment for their energy needs and are capable of foraging great distances away from the Island Group; they only use the Island Group as a platform for breeding and moulting (in the case of penguins). Outside their breeding seasons they disperse away from the islands to more productive foraging areas. The large numbers of seabirds that breed on the Island Group are an important vehicle for importing nutrients from the marine environment to the terrestrial island environment, primarily in the form of guano. The seabirds on the Island Group are generally long lived. They only breed after a prolonged juvenile stage and breed very slowly. Almost all species breed only once a year and only lay one or two eggs. The chick-rearing



period is prolonged with moderate breeding success. Some albatross species only lay one egg every second year. Just over half the eggs successfully fledge a chick in a given season. This means that populations are extremely sensitive to adult mortality, and will take a long time to recover from a perturbation to the population demographics (e.g. a decrease in adult survival).



Four orders of seabirds are present on the Island Group: Sphenisciformes (penguins), Procel[ariiformes (albatrosses and petrels), Charadriiformes (skuas, gulls and terns) and Pelecaniformes (cormorant).

Freshwater systems



Marion Island has three perennial streams, but it is not known whether Prince Edward Island has any perennial watercourses due to the infrequent visitation of this island. Apart from the flowing water types, there is a range of lentic waters on the Island Group, Including shallow takes, lava-lakelets (primarily on black lava flows), crater lakes (in the craters of scoria cones) and wallows formed by the activity of animals.



There are no indigenous fish in the freshwater environments (the introduced brown and rainbow trout are now extinct), and zoopiankton, therefore, represent the highest level in the freshwater food chain. Two species of copepods Pseudoboeckella vofucris and Daphniopsus studeri dominate fresh waters and there are also a number of species of mites and a common freshwater midge Umnophyes minimus.

Marine environment



The Island Group is in the path of one of the world's widest current systems, the Antarctic Circumpolar Current (ACC), which flows clockwise around' the Antarctic continent at a surface speed of 0.5-2km/h. As a result the Island Group effectively has an upstream (westerly) and a downstream (easterly) side. This is important because all the Island Group's land-based vertebrate predators depend on the sea for food. The availability of food is controlled by oceanographic conditions. The ACC .carries food, in the form of plankton, to the island Group from the west. The Island Group also lies close to two major oceanic frontal systems. These fronts separate major water bodies with different chemical and physical properties and act as strong biogeographical boundaries with different suites of marine species to the north Sand south of each front. In addition, the fronts are areas of enhanced biological activity. They consequently form important feeding grounds for land-based predators.



Both islands in the Island Group have relatively unstable and hostile littoral environments, which results in a generally low biodiversity and low density of littoral organisms, All the shores around the islands are exposed (those with a westerly aspect severely so) due to the predominantly westerly winds. Large swells and unstable substrates (e.g. boulders) that result in abrasion also contribute to unfavourable conditions.



The Island Group forms the highest point of a shallow plateau, approximately 200 to 500 m deep, that drops off very rapidly Into much deeper waters (ca, 3 000 m). This plateau supports a rich seabed community of approximately 550 species, dominated by filter feeders, These are largely supported by local phytoplankton production_ The swimming prawn Nauficaris marfonis links this community to the seabirds. Adult prawns feed on the seabed community and are important in the diets of birds with short foraging ranges, especially the Gentoo, Macaroni and Rockhopper penguins and the Imperial cormorant.



33 Species of fish from 13 families are known from the oceans around the Island Group. This Is more than has been recorded at the lies Crozet (25 species) but Inferior to the number at the lies Kerguelen (59 species).



History and development



The Island Group was probably first sighted in March 1663, when a vessel of the Dutch East India Company, the Maerseveen, under command of Barent Barentzoon Ham, went off course en route to Batavia. Commander Ham named the northerly island "Dina" and the southerly island "Maerseveen".



The French naval officer Marion du Fresne, who was in command of the vessels Le Mascarin and Marquis du Castries, rediscovered, the Island Group more than 100 years later in January 1772 in ignorance of the first discovery..



The next person to sight the Island Group was Captain James Cook. He reached the Island Group on 12 December 1775. Having a chart that did not indicate du Fresne's earlier names for the islands, Cook renamed the Island Group "Prince Edward's Islands' after the fourth son of King George III.



It was only by the middle of the 19o century that the larger of the two islands became known as Marion island, presumably due to the notorious vagueness with which sealers named the islands they visited.



'None of the above-mentioned voyagers landed on either of the islands. Although mention is made of sealers having been established on the islands by 1802, the first recorded landing was in December 1803 or January 1804 from the vessel the Catherine. The Commander of the Catherine, John Fanning, however, made no claim to have made the first landing, and the name of the first vessel to have landed at the Island Group remains a mystery.



The Island Group was heavily exploited by the sealing industry in this early part of the 1 P century - so much so that by 1810 the fur seal population had been virtually decimated.



Exploitation of elephant seals for blubber and oil continued, but by 1860 this activity had also become uneconomical as elephant seal numbers were declining. Sealing continued until the early 20th century, but had ceased by the 1930s when the industry became uneconomic due to dwindling seal numbers.



There have been several shipwrecks on both Prince Edward island and Marion Island. Few have been well documented, however. Artefacts from sealers and castaways are present at several sites on Marion Island and Prince Edward Island. Some remains of a village of 17 huts constructed by shipwrecked sailors from the Solgiimt (dating from 1908) can still be seen at Ship's Cove close to the Marion Island base.



Following in the wake of World War II, the South African government realised the strategic value of the Island Group for navigation and defence. Lieutenant-Commander John Fairbaim, in command of the frigate MHSAS Transvaal, annexed Marion Island and Prince Edward Island on 29 December 1947 and 4 January 1948, respectively, The South African Parliament subsequently passed the Prince Edward Islands Act (Act 43 of 1948) to formalise the annexation of the Island Group. Transvaal Cove, where the Marion Island base is situated, was named after the naval frigate 7ransvaal.



The first meteorological party started work on the island in February 1948, Since then, an unbroken record of meteorological data has been kept, Research teams were relieved twice a year until 1956, and once a year since then.



Research teams are relieved by ship. No fixed wing aircraft has been used on the Island Group apart from emergency aerial drops such as after the burning down of the accommodation and communications building In 1966 and an emergency crash landing of a light aircraft during 2002 on Marion Island.



Formal biological research started in 1965 with the first biological and geological expedition led by Prof. Eduard van Zinderen Bakker Sr. of the University of the Orange Free State, Since then ongoing research has yielded a wealth of findings, and has given rise to more than 800 scientific publications and items of popular literature.