Introduced species: a major threat to biodiversity in the sub-Antarctic islands | Polarjournal
The return of cats to the wild after their introduction to the sub-Antarctic islands poses a threat to seabirds, which form colonies on land naturally devoid of terrestrial predators. Photo: Camille Lin

The International Panel on Biodiversity and Ecosystems warns of the threat posed by biological invasions to biodiversity, health and the economy – a major problem for biodiversity conservation in the sub-Antarctic islands.

A dandelion, a rabbit and a reindeer in the middle of the Southern Ocean – it’s possible, but not exactly desirable. Introduced and invasive species are considered a threat. They contribute to 60% of global extinctions of plant and animal species. And 22% of the areas concerned are islands, where they cause the majority of extinctions, i.e. 90% of global species extinctions. Added to this are local extinctions, caused by 33 invasive species in 240 cases worldwide.

These are the findings of the latest report published on September 4 by IPBES, the Intergovernmental Panel on Biodiversity and Ecosystem Services (the climate equivalent of the IPCC). The report compiles the results of over 13,000 scientific publications.

The islands are isolated and frequently host endemic species, i.e. species that are strictly confined to one of them. The ecosystems most affected are terrestrial: for example, a quarter of the islands have more introduced plants than native ones. A quarter of impacts are reported in aquatic ecosystems.

Trout inhabit the rivers of Kerguelen, and their introduced population is one of the few in the world to be gaining habitat rather than losing it. Photo: Camille Lin

The polar regions are particularly affected. Not because human activity is intense there, but because these territories are scattered with islands featuring a sometimes unique biodiversity. “The island of Amsterdam was one of the 10 highest priority islands in the world according to the Birdlife International conservation programme. This ranking was justified by the island’s ideal environment for rare birds such as the Cook’s petrel and the Amsterdam albatross,” explains Cédric Marteau, a founding member and former director of the French Southern Territories Nature Reserve, who is currently head of department at the French League for Bird Protection.

The first recorded problematic introductions date back to the age of exploration and colonialism, i.e. the movement of people and goods in the 16th century. With the onset of industrialization and globalization, introductions increased sharply, with 37% of introduced species inventoried by 1970.

Containing biological invasions

Scientists recommend strengthening prevention policies, which are the least costly in the long term, particularly on islands. They are also important where the eradication of invasive species is a real challenge. Border surveillance is essential. “This was one of the priorities of our first management plan,” explains Cédric Marteau. “We set up a biosafety lock between Réunion, Crozet, Kerguelen and Amsterdam, with the support of Australian and New Zealand specialists who were ahead of the game.”

The IPBES report states that the key is to be well prepared, i.e. to put in place programmes that take the legislative framework into account, provide sustainable funding and bring together the right players. This is what South Georgia has managed to put in place for rodents.

“As soon as the reserve discovers a new species of plant, it is pulled out. That’s why we need to keep a close watch, set up permanent passive traps at the bases and reinforce biosecurity,” adds Cédric Marteau. “For species already established, there is very little room for manoeuvre. Grasses have strong dynamics that are impossible to correct.”

Dandelions are invasive in the Kerguelen archipelago. This image was taken on Ile longue in the Golfe du Morbihan. Photo: Camille Lin

According to IPBES, eradication campaigns are often successful when populations are small or have a low rate of spread. Over the last century, on 998 islands, 88% of the 1,550 documented examples of eradication have been successful. South Georgia, for example, became rat-free in 2018. These actions are less costly than long-term permanent controls or inaction.

There have been successful rat eradication campaigns in Saint-Paul, Château, Moules and Australia,” he recalls. But on the main island of Kerguelen, it’s not possible with the current resources, as there are too many cats, mice and rabbits. The worst thing would be to ruin the effort. The cats could, in a recolonisation phase, increase their litter of kittens and the gain would be punished in subsequent years.”

In 2017, images taken by camera traps provided evidence of the cat’s involvement in the decline in albatross reproductive success on Kerguelen. Photo: Benoit Gineste / Camille Lin / TAAF / IPEV / CEBC

According to the report, any solution must be implemented on a species-by-species and site-by-site basis, wherever possible. Some albatross colonies on the main island of Kerguelen have been cat-free for less than 10 years, and the effects are already visible. Albatross reproductive success has been restored, but this effort must be maintained.

The report also mentions the ecosystems of the continental shelf, reefs and seabed. In some cases, introduced species also represent an economic hindrance and threaten food safety and human health. In Kerguelen, mussels and trout have been introduced. Research is underway into the functioning of these populations and their impact on the environment. This is why the report specifies, for example, that it is very important not to discharge the ballast water of ships approaching these islands so that they can be preserved from biological invasions.

Camille Lin, PolarJournal

Link to study: Roy, H.E., Pauchard, A., Stoett, P., Renard Truong, T., Bacher, S., Galil, B.S., Hulme, P.E., Ikeda, T., Sankaran, K.V., McGeoch, M.A., Meyerson, L.A., Nuñez, M.A., Ordonez, A., Rahlao, S.J., Schwindt, E., Seebens, H., Sheppard, A.W., Vandvik, V., 2023. IPBES Invasive Alien Species Assessment: Summary for Policymakers. Zenodo. https://doi.org/10.5281/zenodo.8314303.

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