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A fisherman shows a female blue crab with eggs in the lagoon of Scardovari, south of Venice, Italy, on Aug. 11. The blue crab is a particularly aggressive species threatening local shellfish and fishPIERO CRUCIATTI/AFP/Getty Images

Invasive species pose a growing and costly threat to global biodiversity as varieties of animals, plants, fungi and micro-organisms increasingly turn up in places where they don’t belong, a United Nations-sponsored report has warned.

According to the report, more than 37,000 invasive species have now been established around the world on every continent, including Antarctica – a figure that is growing by about 200 species per year.

Experts estimate that the cost of the invasions exceeds US$423-billion annually, mainly through effects on food supply and human health as well as lost benefits when native plant and animal populations are negatively affected or supplanted by alien interlopers.

And while awareness of the issue has reduced deliberate introduction of new species compared with decades ago, the increase in global trade and travel since then has provided ample opportunity for invaders to migrate and spread unintentionally.

“Humans are right at the core of this problem,” said Helen Roy, a researcher with the UK Centre for Ecology and Hydrology and co-chair of the report. “We are accelerating the movement of species around the world through our activities.”

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Speaking with reporters, Dr. Roy and her colleagues called for a more robust and co-ordinated effort to manage the problem – a goal they said is achievable through border controls, scientific monitoring and other measures.

The report was released on Monday by IPBES, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. The organization, which is based in Bonn, Germany, was established in 2012 with the goal of monitoring the global state of nature in order to inform international negotiations.

In 2019, IPBES produced a global assessment of the planet’s biodiversity, which found that one million species faced the threat of extinction because of a combination of drivers that include habitat destruction, overharvesting, pollution and climate change. Invasive species were also identified as a driver, and they are at the focus of the new report, which examines the problem in detail.

The result, assembled by 86 experts over a four-year period, offers a comprehensive look at the causes and effects of invasive species on a global scale.

Among the report’s key findings:

• More than 3,500 invasive species found worldwide are harmful to nature or to human well-being.

• Invasive species have contributed to 60 per cent of global plant and animal extinctions and been the sole cause of 16 per cent.

• Forty-five per cent of countries currently do not invest any resources in the management of invasive species.

The report contains numerous examples of invasive species that have caused biological havoc and economic woe after their introduction. Among them are the European green crab, which threatens commercially important shellfish beds in New England and Atlantic Canada.

A more localized but devastating example is the brown tree snake, which wiped out most of Guam’s 25 native bird species after it became established there.

Looking more broadly, the report says the world is undergoing a process of “biotic homogenization” as native species that have evolved to fill highly specific ecological niches are displaced by more generalist invaders.

If left unchecked, the problem will worsen because of the interaction of invasive species with other drivers of biodiversity loss, particularly climate change.

Dr. Roy noted that global warming has opened the door for some tropical species that were previously not a problem to become established when they are transported to temperate areas. A case in point is the red imported fire ant, a native species of South America that has now become a persistent pest in much of North America, Australia and East Asia.

Overall, the report found that North America has the largest number of reported invasive species with 37 per cent of the global total.

Hugh MacIsaac, a professor at the University of Windsor who holds a Canada Research Chair in Aquatic Invasive Species, said that number may not reflect the full extent of the problem worldwide.

“In the case of Africa, with the exception of South Africa, they really don’t have a lot of money for these types of programs. So I think we’re still looking at a serious underestimate,” said Dr. MacIssac, who was not involved in the report.

He said that while the report laid out specific remedies that could be implemented to curb the problem, wealthy countries, including Canada, should be playing a leadership role in supporting the adoption of those solutions.

Anthony Ricciardi, an invasive-species specialist and professor at McGill University in Montreal who co-wrote the chapter in the report that deals with the causes of the problem, said that policy makers worldwide need to adopt a more serious approach.

“Invasive species should be regarded as biological pollution,” Dr. Riccardi said. “We should treat biological spills – for example, from ship ballast tanks – with at least the same concern as we treat oil spills.”

He added that unlike chemical waste, biological pollution does not become diluted over time and space. Instead, “It adapts, proliferates and spreads.”

To assess the economic impact of the problem, the report’s authors drew on a database developed by the Paris-based consortium InvaCost. In a 2021 study published in the journal Nature, experts with the project estimated that the cost totalled a minimum of US$1.288- trillion between 1970 and 2017.

“The cost estimates are, we believe, extremely conservative,” said Peter Stoett, a specialist in global environmental policy based at Ontario Tech University in Oshawa and another of the report’s co-chairs.

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