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Far out at sea between South Africa and Antarctica, and buffeted almost incessantly by the ‘roaring forty’ winds, the desolately beautiful seas of Marion and Prince Edward Islands are home to an enormous wealth of seabirds and marine mammals. But in this remote and hostile environment, it is a small introduced predator that needs major conservation action to restore nature’s balance.
Antarctica is one of the last beautiful forests on Earth, but most of the continent is a frozen desert. In comparison, the oceans surrounding Antarctica are teeming with life. The Southern Hemisphere contains more ocean than the Northern Hemisphere, and nowhere is it brighter than in the mid to high latitudes. Between 40˚ South and 60˚ South, 98 percent of the Southern Hemisphere is ocean, making some of its islands particularly important for seabirds and seals that must return to land to breed. These warm-blooded predators compete with predatory fish in the world’s colder oceans, resulting in some of the greatest concentrations of wildlife in these lonely outposts of land.
There are only a few islands in the African sector of the Southern Ocean. The closest to Africa are the sub-Antarctic Prince Edward Islands, 2,000 kilometers southeast of its southern tip. Antarctica is 2,300 kilometers to the south, and the nearest neighbor is in the Crozet Archipelago, 950 kilometers to the east. The Prince Edward group consists of two main islands 20 kilometers apart: the 300 square kilometer Marion Island and the 65 square kilometer Prince Edward Island. Both are of recent volcanic origin, with small eruptions occasionally recorded on Marion Island.
Light-mantled Sooty Albatross, copyright Matt Jones, from surfbirds galleries
Terrestrial biota are relatively lacking in variety, having to be dispersed over thousands of kilometers of ocean. There are only 15 native species of flowering plants, some of which were brought to the islands by birds (for example the Acaena magellanica and Compact hooks). In comparison, there are more than 200 ferns, mosses, liverworts and lichens – plants with light spores that are easily blown by the wind. Azorella cushion plants and grasses are the tallest plants on the coastal plain, and few vascular plants in polar deserts are more than 400 meters tall.
The diversity of terrestrial invertebrates is equally modest, with only 20 native species of insects, two spiders, 52 mites, 11 springtails and one snail. Interestingly, most insects are flightless, including both moths, all 10 beetles and some flies. These species lost their ability to fly after reaching the islands and are no longer found anywhere else on Earth.
The caterpillars of the two flightless moths, which live for about five years, play an important role in recycling nutrients from dead plants. They are particularly common in nests of Wandering Albatrosseswhere they grow faster due to the warmer microclimate created by the albatrosses’ body heat.
Biodiversity Bonanza
Compared to terrestrial wildlife, the abundance and diversity of seabirds is staggering. The islands are home to literally millions of seabirds from 29 species: four penguins, five albatross, two giant petrels, seven petrels, two prions, two diving-petrels, at least two storm-petrels, two terns and Brown Skua, Kelp Gold and Crozet Shag. Several other non-breeding seabirds also occur offshore. Three species of seals also breed on the islands: Southern Elephant Seals and two species of fur seals. The islands’ waters attract a diversity of cetaceans, including several pods of Orcas, and Pygmy Blue Whales are regular visitors.
Although the islands were first sighted in 1663, the first landing was only around 1800, when sealers came ashore to exploit the islands’ large populations of seals and penguins. Small groups of men were left ashore for months or even years, living off the land while collecting fur seal skins and barrels of oil made from the carcasses of seals and penguins. By the time the sealing ended in the 1930s, seal populations had greatly declined. There were only a few Subantarctic Fur Seals on Marion Island in the 1950s, but their numbers have since recovered to over 100,000 individuals, and about 6,000 Antarctic Fur Seals also breed on the island.
In comparison, the number of Southern Elephant Seals continued to decline throughout the 20th century. The number of pups born each year on Marion Island dropped from over 3,000 in the 1950s to about 300 in the 1990s. The last two decades have seen a recovery of 800 pups per year.
When it comes to spectacle, penguin colonies are hard to beat, and some 800,000 pairs breed on the islands. king and Macaroni Penguin nest in large, dense, noisy colonies. Both are confined to sites where there are gentle landing beaches, but once on the coast, the Macaronis are more agile, sometimes scrambling several hundred meters up the coastal cliffs. Crushing and fertilization are so severe that colonies of both species are devoid of vegetation. Rockhoppers come ashore in more exposed areas, and are scattered along most of the coast.
All three species feed offshore on prey in the open ocean. In comparison, the small resident population of Gentoo Penguins feeding inshore on fish and crustaceans near the sea bed – a niche they share with the local Crozet Shag.
Albatross Central
About half of the world’s Wandering Albatrosses breed on islands, in loose colonies on flat coastal plains. Their numbers have increased since the 1980s, and are now stable at around 1,800 pairs on each island. The other four species of albatross all breed on cliffs and steep slopes: about 11,000 pairs of Albatross with a gray head7,500 pairs of Indian Yellow-nosed Albatross2,800 pairs of Sooty Albatross and 400 pairs of Light-mantled Albatross. Again, most populations appear stable, thanks to reduced ‘bycatch’ by fisheries, but chicks of all species are being attacked by rats on Marion Island, adding strength to calls to exterminate these non-native rodents.
The most numerous birds on the islands are burrow-nesting petrels, rarely seen during the day. They come ashore mainly at night to avoid predators Brown Shakes and giant petrels, using their keen sense of smell to find their burrows. The number of burrowing petrels was greatly reduced by cats that roamed Marion Island from 1948 to 1991. The density of burrows on Marion Island was an order of magnitude lower than on Prince Edward Island, where no introduced mammals, but Marion Island nevertheless still supports more than 300,000 pairs of petrels, dominated by Blue Petrels and Salvin’s Prions.
The extermination of cats led to some recovery in petrel numbers, but this was slower than expected due to predation by rats. Fortunately, we now have a way to eradicate rats from Marion Island – a one-off intervention that will allow the island’s seabird populations to return to their original glory.
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