House mice brought by seal hunters in the 1900s devastated Marion Island nature
Researchers say house mice are the most harmful of several non-native species that were introduced to Marion Island, off the coast of South Africa, over 100 years ago. They’ve written a book chapter describing what we know about these mice and other invasive species on the islands.
South Africa has in its territory a large, sub-Antarctic island called Marion, and a smaller one called Prince Edward. An island is a piece of land surrounded by water, and, because they are so isolated, are often home to unique plants and animals not found anywhere else.
When species found in one place are introduced into new environments, they often become invasive, meaning that these non-native species thrive at the expense of native species or harm the native habitats in some other way.
In a 2020 book chapter, researchers said a total of 46 species were introduced to Marion Island, of which 29 caused harm. Only 8 species were introduced into Prince Edward Island, 7 of which were problematic.
They said house mice, thought to have been brought to Marion Island by seal hunters around 1900, were the most problematic. Seals are sea animals, which were at the time hunted for their fur to make expensive clothes. The mice brought by the seal hunters ate plant seeds, damaged and even killed plants. They also ate too many insects and birds. The authors said those insects were important for breaking down plant residues to make the soil fertile.
The government was to eradicate the mice by 2021, and previously, in 1948, they had introduced domestic cats to help control the mice. However, these cats also fed on seabirds and greatly reduced their numbers, so the island management eradicated the cats in 1991 through hunting, trapping, and poisoning.
The authors also said domestic pigs, sheep, goats, chickens, domestic dogs and parrots, had been introduced to Marion but later removed.
The authors reported a total of 27 introduced species of insects, flies, butterflies and moths on both islands. They however said Marion Island had more invasive insects because it was more frequently visited. The insects had come in through fresh fruit and vegetables, dry foods, and building materials brought to the island, and it would be difficult to eradicate them.
As for plants, the authors said 17 have been introduced to both islands, mainly through building materials, fodder or birds. Out of those, 8 in Marion and 3 in Prince Edward were causing harm.
They said researchers have not studied invasive microorganisms on the islands in detail yet. Microorganisms are tiny living things that cannot be seen without special equipment, such as viruses, bacteria and certain fungi. Only 1 fungus that attacks cabbage leaves has been reported in Marion island so far.
They also said only 2 fish species were known to have been introduced to the islands, even though they were no longer there.
These findings highlight the existing and potential harm of invasive species on these two South African islands.
The authors therefore recommended that island authorities should strictly adhere to and enforce policies to manage invasive species, and they called for further research to identify other invasive species.
The authors were from universities in South Africa.
The sub-Antarctic Prince Edward Islands (PEIs) constitute South Africa’s most remote territory. Despite this, they have not been spared from biological invasions. Here, we review what is known about invasions to the PEIs for terrestrial taxa (vertebrates, invertebrates, plants and microbes), freshwater taxa and marine taxa. Currently, Marion Island is home to 46 alien species, of which 29 are known to be invasive (i.e. they are alien species that have established and spread on the island). Prince Edward Island, which has no permanent human settlement and is visited only infrequently, has significantly fewer alien species: only eight alien species are known from Prince Edward Island, of which seven are known to be invasive. The House Mouse (Mus musculus), which occurs on Marion Island, can be considered the most detrimental invader to the islands; it impacts on plants, insects and seabirds, which result in changes to ecosystem functioning. The impacts of other terrestrial invaders are less well understood. At present, no invasive freshwater or marine taxa are known from the PEIs. We conclude by discussing how invasion threats to the PEIs are changing and how the amelioration of the climate of the islands may increase invasion threats to both terrestrial and marine habitats.
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