Southern Indian Ocean islands tundra

• Category: Grassland, Tundra, and Human Biomes.
• Geographic Location: Indian Ocean.
• Summary: These islands are home to flourishing Antarctic and sub-Antarctic populations of seabirds and seals, but are vulnerable to introduced species and climatic changes.

The Southern Indian Ocean Tundra biome occurs on islands in the sub-Antarctic region of the Indian Ocean. These islands belong to different countries, but have similar climates and species. They include Prince Edward Islands (PEI), a territory of South Africa; the Crozet and Kerguelen archipelagos, which belong to France; and the Heard and McDonald islands, property of Australia. Few people live here; those who do are mostly scientists or monitors. The islands have unique environments and some have conservation designations or environmental restrictions for visitors. The climate here is extreme, with the strong, cold winds of Antarctica bringing rain, snow, and rough seas.

PEI is the westernmost island group in the Southern Indian Ocean Tundra biome. Its two components, Marion Island and Prince Edward Island, are 112 square miles (290 square kilometers) and 17 square miles (45 square kilometers), respectively. These islands are the remains of a shield volcano from the center of the West Indian Ocean Ridge, and are the youngest of all these islands.

The PEI and Crozet groups are relatively close to each other. The Crozet archipelago comprises 193 square miles (500 square kilometers) on five main volcanic islands: the western group of Île aux Cochons, Îles des Pingouins, and Îlots des Apotres; and the eastern group of Île de la Possession and Île de l’Est. The two eastern islands are the oldest of the Crozets, at 8 million years. Among the western islands, Île aux Cochons is 400,000 years old, Îles des Pingouins is 1.1 million years old, and Îles des Apotres is 5.5 million years old. Île de la Possession is the largest island in this archipelago, at 50 square miles (130 square kilometers) and with a maximum height of 3,064 feet (934 meters). Île de l’Est is the second-largest island, at 46 square miles (120 square kilometers).

The Kerguelen Islands are located 932 miles (1,500 kilometers) east of the Crozet Islands; they range as high as 6,070 feet (1,850 meters). The entire land area is 2,703 square miles (7,000 square kilometers). The group is basically one large island—Grand Terre, of 2,548 square miles (6,600 square kilometers)—and about 300 other islets. There is a permanent ice cap, and the archipelago is approximately 39 million years old.

Heard Island is 147 square miles (380 square kilometers) in area and includes two active volcanoes. The McDonald Islands are 25 miles (40 kilometers) west of the Heard Islands; they are composed of McDonald Island, Flat Island, and Meyer Rock. McDonald is the body here, at about 1 square mile (2.6 square kilometers), formed of two parts joined by a narrow isthmus.

Biodiversity

The Southern Indian Ocean Tundra islands are characterized by low biodiversity. All ecological niches may not be filled, due to the geographical isolation here, or in some cases due to their geologically recent formation. Some species may not be fully adapted in the best ways to their ecosystems, leaving them vulnerable to competition from aggressive introduced species. Additionally, there may be short food webs with fewer species at each level, and individual species can be absolutely essential. A marine example is caridean shrimp off the coast of PEI, which are consumed by the top predators on the food chain: penguins. Similarly, the Marion flightless moth aids in the release of nutrients from plants. Removal or depletion of either one of these species could lead to rapid devastation of the entire biota.

All these islands are rocky but support plants such as grasses, lichens, liverworts, and mosses. Tussock grasses, in particular, are well-adapted to snow and cold. In past times, sailors visiting these islands consumed Kerguelen cabbage, an important source of vitamin C.

Marine vegetation flourishes in this area, and it has become a vital aspect of supporting the terrestrial ecosystems. Giant brown kelp forms underwater forests at up to 164 feet (50 meters) in hard-bottom subtidal areas, and hosts many colorful invertebrates, while the cochayuyo bull kelp attaches to rocky coasts. Storms tear off large quantities of the giant algae, which then rots on the beaches and stones; it provides vital nutrients to plants, animals, birds, and insects.

The islands attract wildlife such as penguins, seals, and seabirds. The largest bird colonies of the biome are on PEI, followed by the Crozet Islands, which have breeding colonies of all six species of albatross and a very large portion of the world’s population of king penguins.

All six Antarctic seal types can be found here on the islands. The fur seals and southern elephant seals breed in the region, and they are increasing in numbers now that seal hunting has mainly stopped. Large numbers of leopard seals winter on the rocks of Heard Island. The colony of southern elephant seals on Heard Island and the Kerguelen Islands is one of the three largest such colonies in the world.

Related Antarctic and sub-Antarctic species and subspecies coexist, living alongside one another but rarely breeding with one another. The sooty albatrosses and light-mantled albatross, the northern giant petrel and southern giant petrel, and the Antarctic fur seal and sub-Antarctic fur seal live together on the islands.

Environmental Threats

These Southern Indian islands are nearly pristine, but their species are not varied or perfectly adapted, so they are quite vulnerable to human activity and to introduced plant and animal species. Invasive grasses have become dominant in parts of the islands, while introduced mice and cats prey on breeding seabird colonies. Climate change, particularly warmer temperatures and seasons, could encourage these nonnative species and adversely affect seabirds and their reproduction. Diving seabirds are already under stress, often caught by long line fishing for the Patagonian toothfish, also known as Chilean sea bass, that occurs around the islands. The gray-headed albatross and white-chinned petrel may be especially damaged as they habitually follow fishing boats. Sea-level rise and greater storm surges, too, hold the potential to disrupt the intertidal and shoreline habitats here.

Bibliography

"Australia Moves to Expand Antarctic Marine Park." Phys.org, 8 Oct. 2024, phys.org/news/2024-10-australia-antarctic-marine.html. Accessed 2 Jan. 2025.

Bester, M. N., et al. “A Review of the Successful Eradication of Feral Cats From Sub-Antarctic Marion Island, Southern Indian Ocean.” South African Journal of Wildlife Research 32, no. 1 (2002).

Chandra, Satish, V. Suryanarayan, and B. Arunachalam, eds. The Indian Ocean and Its Islands: Strategic, Scientific and Historical Perspectives. Thousand Oaks, CA: Sage, 1993.

Sinclair, Ian and Olivier Landgrand. Birds of the Indian Ocean Islands. London: New Holland Publishing, 2008.