Marion Island: Against the odds

Antarctica is among the final nice wildernesses on Earth, however a lot of the continent is a frozen desert. By comparability, the oceans surrounding Antarctica teem with life. The Southern Hemisphere accommodates way more ocean than the Northern Hemisphere, and nowhere is that this extra obvious than at mid-to-high latitudes. Between 40˚ South and 60˚ South, 98 per cent of the Southern Hemisphere is ocean, which makes its few islands significantly necessary for seabirds and seals that must return to land to breed. These warm-blooded predators outcompete predatory fish on this planet’s colder oceans, leading to a number of the biggest concentrations of wildlife on these lonely outposts of land.

There are solely a handful of islands within the African sector of the Southern Ocean. These closest to Africa are the sub- Antarctic Prince Edward Islands, 2,000 kilometres south-east of its southern tip. Antarctica lies 2,300 kilometres south, and the closest neighbours are within the Crozet Archipelago, 950 kilometres to the east. The Prince Edward group contains two principal islands 20 kilometres aside: the 300-square kilometre Marion Island and 65-square kilometre Prince Edward Island. Each are of latest volcanic origin, with small eruptions sometimes recorded on Marion Island.

The terrestrial biota is considerably missing in selection, having needed to disperse throughout hundreds of kilometres of ocean. There are solely 15 native species of flowering crops, a few of which have been carried to the islands by birds (for instance the crops Acaena magellanica and Uncinia compacta). By comparability, there are greater than 200 ferns, mosses, liverworts and lichens – crops with light-weight spores which might be readily blown by the wind. Azorella cushion crops and grasses are the tallest crops on the windswept coastal plains, and there are few vascular crops in any respect within the polar desert above 400 metres of elevation.

The variety of terrestrial invertebrates is equally modest, with solely 20 native species of bugs, two spiders, 52 mites, 11 springtails and one snail. Apparently, most bugs are flightless, together with each moths, all 10 beetles and several other flies. These species misplaced the power to fly after reaching the islands and are discovered nowhere else on Earth.

The caterpillars of the 2 flightless moths, which dwell for round 5 years, play a key position in recycling vitamins from useless vegetation. They’re significantly frequent within the nests of Wandering Albatrosses, the place they develop sooner because of the hotter microclimate created by the albatrosses’ physique warmth.

Biodiversity Bonanza

In comparison with the terrestrial wildlife, the abundance and variety of seabirds is staggering. The islands are house to actually thousands and thousands of seabirds from 29 species: 4 penguins, 5 albatrosses, two big petrels, seven petrels, two prions, two diving-petrels, no less than two storm-petrels, two terns and Brown Skua, Kelp Gull and Crozet Shag. A number of different non-breeding seabirds additionally happen offshore. Three species of seal additionally breed on the islands: Southern Elephant Seal and two species of fur seal. The islands’ waters entice a range of cetaceans, together with a number of pods of Orcas, and Pygmy Blue Whales are common guests.

Though the islands have been first sighted in 1663, the primary touchdown was solely round 1800, when sealers went ashore to use the islands’ massive populations of seals and penguins. Small groups of males have been left ashore for months and even years at time, dwelling off the land whereas accumulating fur seal skins and barrels of oil rendered from seal and penguin carcasses. By the point sealing led to 1930, seal populations have been vastly decreased. There have been just a few Subantarctic Fur Seals on Marion Island within the Nineteen Fifties, however their numbers have since recovered to greater than 100,000 people, and a few 6,000 Antarctic Fur Seals additionally breed on the island.

By comparability, numbers of Southern Elephant Seals continued to lower all through the twentieth century. The variety of pups born annually on Marion Island fell from greater than 3,000 within the Nineteen Fifties to barely 300 within the Nineteen Nineties. The final 20 years have seen a restoration to 800 pups per yr.

In the case of spectacle, it’s arduous to beat penguin colonies, and a few 800,000 pairs breed on the islands. King and Macaroni Penguins nest in massive, dense, noisy colonies. Each are confined to websites the place there are gently sloping touchdown seashores, however as soon as ashore, Macaronis are extra agile, generally scrambling just a few hundred metres up the coastal cliffs. Trampling and manuring are so intense that colonies of each species are devoid of vegetation. Rockhoppers are in a position to come ashore at extra uncovered websites, and are dispersed round a lot of the shoreline.

All three species feed offshore on prey out within the open ocean. By comparability, the small resident inhabitants of Gentoo Penguins feeds inshore on fish and crustaceans close to the ocean mattress – a distinct segment they share with the localised Crozet Shag.

Albatross Central

Virtually half of the world’s Wandering Albatrosses breed on the islands, in free colonies on stage coastal plains. Their numbers have elevated for the reason that Nineteen Eighties, and at the moment are secure at round 1,800 pairs on every island. The opposite 4 albatross species all breed on cliffs and steep slopes: some 11,000 pairs of Grey-headed Albatross, 7,500 pairs of Indian Yellow-nosed Albatross, 2,800 pairs of Sooty Albatross and 400 pairs of Light-mantled Albatross. Once more, most populations seem like secure, because of decreased ‘bycatch’ by fisheries, however chicks of all species are attacked by mice on Marion Island, including impetus to the calls to eradicate these non-native rodents.

Essentially the most ample birds on the islands are burrow-nesting petrels, that are seldom seen through the day. They arrive ashore primarily at evening to keep away from predation by Brown Skuas and big petrels, utilizing their acute sense of scent to find their burrows. Numbers of burrowing petrels have been vastly decreased by cats that roamed Marion Island from 1948 to 1991. The density of burrows on Marion Island is an order of magnitude lower than on Prince Edward Island, the place there aren’t any launched mammals, however Marion Island nonetheless nonetheless helps greater than 300,000 pairs of petrels, dominated by Blue Petrels and Salvin’s Prions.

The eradication of cats led to some restoration in petrel numbers, however this has been slower than anticipated resulting from predation by mice. Thankfully, we now have the means to eradicate mice from Marion Island – a one-off intervention that may permit the island’s seabird populations to get well to their unique glory.