The French islands of the Southern Ocean harbour the greatest species diversity of invertebrates and plants of all the subantarctic islands. The vertebrate wildlife represents one of the Earth’s richest biomasses. Plants and animals in the region show some very special adaptations developed over several million years of evolution in total isolation, in the middle of the ocean, thousands of kilometres from any continent.
However, on land the number of autochthonous species is restricted. Only 22 flowering plants grow on Kerguelen and 16 on Crozet (compared with 3000 species in metropolitan France). Similarly, among the Insects, there are 11 species of Diptera on Crozet Island and only 6 on Kerguelen, as against a mighty 6500 in mainland France! As for land Vertebrates, no mammal is found and only 2 bird species: Eaton’s pintail and lesser sheathbill (Chionis minor). However, these islands are frequented by many species of sea birds and 3 marine mammals: the elephant seal and 2 species of fur seal.
The terrestrial communities are relatively poor, but there is a high level of endemism: on Crozet, 90% of the invertebrates belong to the subantarctic region of the Indian Ocean and 55% occur only on that archipelago. The endemism of plant species is less marked, the majority of species spread widely over most of the subantarctic islands. The lyallia cushion (Lyallia kerguelensis), for example, is the only higher plant really specific to Kerguelen.
Faced with the forbidding nature of the soil and climate, the flora of the Southern and subantarctic islands is quite poor with low diversity. Kerguelen and Crozet Islands are carpeted at low altitude with a community made up of Acæna, Azorella and certain grasses (Poaceae). In some places, petrified wood testifies to the past presence of forests that no longer exist. On Amsterdam Island, there is a limited area that bears a Phylica arborea wood (the only tree in the TAAF), the last remnant of forests that covered the island before human-induced fires in the last Century and the introduction of allochthonous species. In Kerguelen, Kerguelen cabbage has suffered owing to the introduction of rabbits.
Typically, the birds that have adapted to the particular conditions of these regions are marine species. The most numerous of them are penguins. Four species predominate in the Southern and subantarctic islands: king, gentoo, southern rockhopper and macaroni penguins. The islands are also home to 10 species of albatross. The other sea birds are spread between petrels (25 species), cormorants, skuas, gulls, terns and the Cape petrel. The Chionis and Eaton pintails are the only non-marine birds in the TAAF.
The Crozet islands are known as the world’s largest natural bird reserve. They are indeed nicknamed the “25 million bird islands”: 36 species of birds reproduce there, including 6 species of albatross and 60 tonnes of birds are present per km²!
Amsterdam has the largest population of Atlantic yellow-nosed albatross in the world and the only population of Amsterdam albatross, a species endemic to the island whose only current reproduction site is the Plateau des Tourbières, at 600 m altitude.
The most common in Crozet and Kerguelen are elephant seals. On Amsterdam Island there are impressively strong colonies of fur seals. The subantarctic latitudes are home to many Cetaceae, which find abundant food there. Around the coasts can be seen fin whales, Commerson’s dolphins and killer whales (orca whales).