The Kerguelen Islands are one of the most remote archipelagos on Earth, sitting in the southern Indian Ocean roughly halfway between Africa and Australia, with no permanent human population. The main island, Grande Terre, is about the size of Corsica and anchors a cluster of roughly 300 smaller islands and islets at approximately 49°S latitude. Administered by France as part of its Southern and Antarctic Lands, the archipelago hosts a small rotating staff of scientists and support personnel but has never been permanently settled. What makes Kerguelen fascinating is not just its isolation but the collision of forces playing out there: ancient volcanism, subantarctic biology pushed to extremes, a wave of invasive species reshaping ecosystems, and glaciers in visible retreat.
Born from a Mantle Plume
The Kerguelen Archipelago sits atop the Kerguelen Plateau, one of the largest underwater volcanic features on the planet. The plateau, along with the connected Broken Ridge and Ninetyeast Ridge, represents roughly 119 million years of volcanic activity attributed to a single deep source in the Earth’s mantle known as the Kerguelen mantle plume.1Journal of Petrology. Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial That is an extraordinarily long-lived hotspot. The volcanic rocks making up the islands themselves are younger than the plateau beneath them, but the archipelago is still built from layer upon layer of basaltic lava flows. The landscape shows it: broad plateaus, steep-walled fjords carved by glaciers into the volcanic rock, and a mountainous interior dominated by the glacier-capped Mount Ross, which rises to about 1,850 meters.
The volcanic origin left Kerguelen with something unexpected for such a windswept, treeless place: a geological record that tells a story of dramatically different conditions in the past. The islands were once warm enough to support forests. Fossil wood from the Tertiary period is common across the archipelago and was first described by nineteenth-century naturalists. More surprisingly, wood discovered in a Pleistocene moraine showed that trees persisted on Kerguelen into the Quaternary, far more recently than anyone initially expected.2Comptes Rendus de l’Académie des Sciences. Tertiary and Quaternary fossil wood from Kerguelen (southern Indian Ocean) Today, not a single tree grows on the islands. The shift from forested to barren happened as the landmass drifted poleward and the climate cooled over millions of years, leaving behind only hardy low-growing vegetation adapted to relentless wind and cold.
Climate and the Retreat of Ice
Kerguelen’s weather is dominated by the Southern Ocean. Temperatures hover around 2°C in winter and rarely climb above 8°C in summer. Precipitation is frequent and driven by westerly storms that batter the islands almost year-round. The western side of Grande Terre, facing the prevailing winds, gets substantially more rain and snow than the sheltered eastern coast, creating a surprisingly sharp divide in landscape character over a relatively short distance. Winds regularly exceed gale force; the islands sit squarely in the belt of ocean sometimes called the “Roaring Forties” and “Furious Fifties.”
The Cook Ice Cap covers a large portion of the western highlands, and smaller glaciers extend across much of Grande Terre’s mountainous interior. But these glaciers have been shrinking fast. Satellite data, field observations, and modeling all point to an acceleration of glacier wastage driven by reduced snow accumulation and a rising snow line since the 1970s.3Journal of Geophysical Research: Earth Surface. Recent glacier decline in the Kerguelen Islands (49°S, 69°E) derived from modeling, field observations, and satellite data The Cook Ice Cap has lost a substantial fraction of its area over the past half-century. This is consistent with broader warming trends across the subantarctic, but it is especially visible on Kerguelen because the ice cap was already marginal for its latitude. As the snow line creeps higher, glaciers that once reached nearly to the coast now terminate well inland, exposing new rock and sediment.
Seabirds, Seals, and a Rich Marine Margin
Despite the harsh terrestrial conditions, the waters around Kerguelen are biologically rich, and the islands serve as critical breeding habitat for marine animals. Surveys conducted in the 1980s documented 35 bird species breeding on the archipelago, including King Penguins, Macaroni Penguins, Wandering Albatrosses, Black-browed Albatrosses, and several species of petrels and prions. Four species were identified as newly breeding on Kerguelen during that period: the Yellow-nosed Albatross, the Southern Giant Petrel, the Soft-plumaged Petrel, and the Fairy Prion.4Emu. The Avifauna of the Kerguelen Islands Population trends varied: King and Macaroni Penguins were increasing, while Wandering and Black-browed Albatrosses were declining.
Southern elephant seals breed on the beaches in large numbers and use the surrounding ocean as a vast foraging ground. Tracking studies using satellite-linked devices that record location, diving behavior, and water temperature and salinity have shown that Kerguelen’s elephant seals travel enormous distances to feed. Two main foraging zones stand out: one near the Antarctic continent and another along the Polar Front, where upwelling brings nutrients close to the surface. Within these zones, seals target areas with specific temperature signatures, and both their foraging activity and body condition improve markedly when they reach productive water.5PubMed Central. Successful foraging zones of southern elephant seals from the Kerguelen Islands in relation to oceanographic conditions
The richness of the marine environment around Kerguelen is not accidental. The southern Kerguelen Plateau interacts with the Antarctic Circumpolar Current in ways that push iron-rich subsurface water upward. Iron is the limiting nutrient for phytoplankton growth in much of the Southern Ocean, and dissolved iron concentrations in the subsurface waters around the plateau vary enough to explain why large, seasonally persistent phytoplankton blooms form in some areas and not others.6Journal of Geophysical Research: Oceans. Sustained Upwelling of Subsurface Iron Supplies Seasonally Persistent Phytoplankton Blooms Around the Southern Kerguelen Plateau, Southern Ocean These blooms feed the base of a food chain that supports everything from krill to the penguins and seals on shore. The sustained upwelling of iron around the southern plateau distinguishes these blooms from those downstream of the northern plateau, where the iron supply is more ephemeral.
The Kerguelen Cabbage
Among the most distinctive plants on the islands is the Kerguelen cabbage, Pringlea antiscorbutica, a member of the mustard family found naturally only on a handful of subantarctic island groups. The species name, “antiscorbutica,” reflects the fact that early sailors ate it to stave off scurvy, since its leaves are rich in vitamin C. But the plant’s real interest lies in how it has adapted to conditions that would shut down most temperate plants.
The Kerguelen cabbage keeps photosynthesizing year-round, even on cold days when temperatures stay near 0°C. Its photosynthetic rate tracks light levels more than temperature, which makes sense for a plant living in a place where cold is constant but daylight varies dramatically with the seasons. Over the course of a year, glucose accumulates in the leaves in step with irradiance, while starch builds up in the stems and roots in proportion to air temperature. The plant shows no period of dormancy, an unusual strategy for a species living at such high latitudes.7Plant, Cell & Environment. Carbon metabolism in the subantarctic Kerguelen cabbage Pringlea antiscorbutica R. Br.: environmental controls over carbohydrates and proline contents and relation to phenology Proline, an amino acid that accumulates in response to salt stress, is a major solute in all parts of the plant, while the arrangement of fatty acids in its membranes includes a high proportion of saturated phosphatidylglycerol, a trait associated with resistance to chilling.8Canadian Journal of Botany. Lipid metabolism of a Tertiary relic species, Kerguelen cabbage (Pringlea antiscorbutica)
Botanists have called the Kerguelen cabbage a “Tertiary relic,” meaning it is a surviving lineage from a much older and warmer era. It is one of the few remaining links to the vegetation that once covered the islands when they still supported forests. Its continued presence on Kerguelen, adapted to conditions utterly unlike those its ancestors evolved in, makes it a living case study in how plants can shift their physiology over deep time.
Why So Many Kerguelen Insects Cannot Fly
One of the more striking biological patterns on Kerguelen and neighboring subantarctic islands is the high proportion of flightless insects. Across the Southern Ocean Islands, nearly half of indigenous insect species are flightless, a rate dramatically higher than on Arctic islands (under 8%) or among alien insect species that have been introduced to the same subantarctic islands (about 17%).9Proceedings of the Royal Society B: Biological Sciences. Wind plays a major but not exclusive role in the prevalence of insect flight loss on remote islands The difference is stark and has puzzled biologists for over a century.
The long-standing hypothesis, often attributed to Darwin, is that wind selects against flight on exposed, storm-battered islands: insects that fly risk being blown out to sea, so flightless individuals survive and reproduce at higher rates. Research supports the idea that wind plays a major role, but it is not the whole story. Flightlessness is more common on subantarctic islands than on temperate southern islands at similar latitudes, a pattern sometimes called the “sub-Antarctic effect.” Cold temperatures, small island size, and the energetic cost of maintaining flight muscles when resources are scarce all likely contribute. The contrast with introduced insect species is telling: aliens that arrive on Kerguelen tend to be flighted, because the ability to fly is what got them there in the first place. Over evolutionary time, though, native lineages shed their wings.
Invasive Species and Cascading Damage
The ecological story of Kerguelen cannot be told without reckoning with the damage done by introduced animals. Rabbits were brought to the islands in 1874, and their effect on vegetation was catastrophic. The Kerguelen cabbage and the cushion plant Azorella selago, both keystone species of the native coastal plant communities, were devastated by grazing. In their place, Acaena magellanica, a low-growing burr plant less palatable to rabbits, spread to form near-monocultures across large stretches of the coastline. Soil erosion accelerated as the plant cover thinned.10Biological Conservation. Recovery of native plant communities after eradication of rabbits from the subantarctic Kerguelen Islands, and influence of climate change
Feral cats, introduced to control mice and rats around early sealing and whaling stations, turned to native birds as prey. By the late 1990s, however, the diet of feral cats on Grande Terre had shifted heavily toward rabbits, which had become so abundant that they made up over 84% of cat scat contents at surveyed sites. In the 1970s, by contrast, birds had appeared in about two-thirds of cat stomach samples and rabbits in roughly a third. The reversal strongly suggests that bird populations had already declined sharply, likely under pressure from the cats themselves. The implication is bleak: in fewer than 50 years, cats had eaten through enough of the local bird population to fundamentally change their own diet.11Polar Biology. The diet of feral cats Felis catus L. at five sites on the Grande Terre, Kerguelen archipelago Most burrowing petrels on the main island are now threatened by the combination of cat predation and habitat degradation from rabbits.12Emu. The Avifauna of the Kerguelen Islands
Brown trout, introduced for sport fishing by early expeditions, have colonized the islands’ freshwater systems with remarkable efficiency. After being stocked in a handful of rivers, the species spread naturally to dozens of additional waterways. Once natural reproduction was established in a river, no local extinction was ever recorded afterward.13PLOS ONE. Invasion Dynamics of a Fish-Free Landscape by Brown Trout (Salmo trutta) Kerguelen’s rivers and lakes had no native freshwater fish at all, so the trout entered an ecosystem with no evolutionary experience of fish predation. The downstream effects on native invertebrate communities are still being studied, but the pattern of rapid, irreversible colonization is familiar from trout introductions on other isolated island systems.
Alien Plants and the Research Station Effect
Animals are not the only invaders. Floristic surveys have documented at least 68 alien vascular plant species on Kerguelen, slightly more than on the other French subantarctic islands of Amsterdam and Crozet. Nearly all of these aliens are common species from the temperate regions of the Northern Hemisphere, belonging broadly to the European flora, and a striking 72% of them are found on or near the research station and its surroundings.14Biological Conservation. Human activities, ecosystem disturbance and plant invasions in subantarctic Crozet, Kerguelen and Amsterdam Islands The pattern is clear: ships supplying the station are the primary vector, and the disturbed ground around buildings and waste deposits provides a foothold.
What happens once alien plants establish themselves is more nuanced than a simple takeover narrative. Research on Kerguelen’s plant communities has found that native and alien species occupy overlapping trait spaces. Alien species tend to be more variable in their growth strategies than natives, but on average they pursue similar approaches to dealing with the environment. Along environmental gradients, the two groups shift in parallel rather than aliens simply outcompeting natives everywhere.15PubMed Central. Living together in a context of plant invasion: the example of the plant communities at the Iles Kerguelen That greater variability among alien species is concerning, though, because it suggests invaders can fill multiple niches rather than being confined to one. Studies of how invasive plants cope with Kerguelen’s punishing winds have found contrasting growth strategies among different alien species, reinforcing the idea that there is no single invader profile and that future community impacts could come from multiple directions.16Oikos. Huff and puff and blow down: invasive plants traits response to strong winds at the Southern Oceanic Islands
Climate change adds another layer. As temperatures warm and glaciers recede, new ground opens up. Some of that ground may be colonized by recovering native species, but warming conditions also favor alien plants adapted to milder climates. On parts of the archipelago where rabbits have been removed, native plant communities have shown signs of recovery, but the trajectory depends heavily on whether the climate continues shifting toward conditions that benefit the invaders. The interaction between warming, grazing pressure, and plant invasion makes Kerguelen a kind of open-air experiment in how isolated ecosystems respond to multiple simultaneous stresses.
The Archipelago’s 300 Islands as a Conservation Buffer
One detail about Kerguelen that matters enormously for conservation is the sheer number of smaller islands and islets surrounding Grande Terre. Roughly 300 of them ring the main island, and most remain free of cats, rabbits, and other introduced mammals. These offshore refuges have preserved populations of burrowing petrels and other seabirds that have been wiped out or severely reduced on the mainland. The safety of much of Kerguelen’s native avifauna depends on keeping these islands unmodified.17Emu. The Avifauna of the Kerguelen Islands
Protecting these islands from accidental introductions is not straightforward. Every resupply ship that visits the main station is a potential source of stowaways, whether seeds in boot treads, invertebrates in cargo, or rodents in shipping containers. Biosecurity protocols exist but are imperfect, and the warming climate may make the islands progressively more hospitable to species that previously could not establish. For now, the remoteness that defines Kerguelen works in both directions: it limits access for conservation managers, but it also limits the flow of new invaders. How long that balance holds is one of the open questions hanging over this strange, wind-battered archipelago in the middle of the Southern Ocean.