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George the snail died on the first day of 2019. Image: The Department of Land and Natural Resources, Hawaii.

Death of George the tree snail marked the first extinction of 2019

A 14-year-old Hawaiian tree snail called George died on New Year's Day. He was the last known member of his species, meaning his demise signalled one of the first extinctions of the year.

George was born in a captive breeding facility at the University of Hawaii, and was the last of the species Achatinella apexfulva. He had been dubbed the loneliest snail in the world, as researchers had searched for a mate for George for more than a decade without success.

The rest of his species was largely eaten by a carnivorous animal known as the rosy wolfsnail (Euglandina rosea). These were introduced to Hawaii in 1955, with catastrophic consequences.

Land snails were once common in Hawaii, with more than 750 species living there, but their numbers have since been decimated, partly because they became dinner for the rosy wolfsnails.

It is estimated that over 90% of the snail diversity in Hawaii has been lost - although many species thought to be extinct have since be found living in remote places. 

A rosy wolfnsail (Euglandina rosea) pictured in Hawaii. Image via Wikimedia Commons.

A rosy wolfnsail (Euglandina rosea) pictured in Hawaii. The species has been eating its way through many other Hawaiian snails, causing some to go extinct. Image by Dylan Parker via Wikimedia Commons.

 

Dr Tom White, a senior curator of invertebrates at the Museum, says, 'This is a very sad story. George's species had been functionally extinct for years.

'The Hawaiian land snail story has become a cautionary tale about the potential unwitting impacts of intentionally introducing a species. Many other Hawaiian species have also been reduced to populations living in labs and zoos due to the introduction of the carnivorous species, the rosy wolfsnail.'

Although George's story is tragic in itself, an even bigger natural catastrophe is happening across the globe.

Dr White says, 'The real issue is the massive scale of extinction. Land snails around the world are facing a similar fate.

'This story should highlight to us all that literally hundreds of invertebrate species have gone extinct in just a few decades. We don't even know that some of them existed. The pressure on some species, especially invertebrates, is acute, and it is getting worse as habitats are being lost to human impacts and climate change.'

Rosy wolfsnails

Rosy wolfsnails were deliberately introduced to Hawaii to control another population of introduced giant African snails, which had become a crop pest.

But they are ravenous eaters, and instead set their sights on the archipelago's native snails.

They hunt their prey by tracking the slime trails of slugs and snails, and can swallow smaller ones whole. Native to Florida, they are happy living in hardwood forests and urban gardens.

It is generally agreed that the introduction of the carnivorous species to Hawaii was a mistake, as it has eaten its way through a wide variety of endemic species. Since its introduction, at least 50 Hawaiian species are now extinct.

This is also the case on other Pacific island groups. 

An o'ahu tree snail on a branch

O'ahu tree snails are colorful, tropical, tree snails that are endemic to Hawaii. All species in the genus are now endangered, like so many other snail species in the Pacific islands. Image: Mikeledray/Shutterstock.com.

 

According to the International Union for Conservation of Nature (IUCNInvasive Species Specialist Group, 'the Pacific region has a wide diversity of mollusc species, most of them unique to the region, and the majority endemic to single islands or archipelagos.

'More and more, these unique species are becoming replaced with a homogenous group of tropical tramp snail and slug species that are increasingly widespread.

'Of the 400 extinct species we listed from oceanic islands, 234 lived on islands to which Euglandina rosea had been introduced, and it is highly probable that of these 234 extinctions, 134  of them were ultimately caused by the introduction of E. rosea.'

According to the 2007 IUCN Red List, molluscs are the group most affected by extinction.

The future looks bleak for the remaining mollusc species in Hawaii, which are battling habitat loss, climate change and other introduced animals such as rats.

Plate 19 from Studies on the Genus Partula by Henry Edward Crampton

Plate 19 from Studies on the Genus Partula by Henry Edward Crampton (1916). Found only in French Polynesia, this entire genus is on the brink of extinction due to predation from the introduced rosy wolfsnail.

 

The last of a species

The University of Hawaii began its captive breeding programme at Mānoa, Honolulu, in the early 2000s in an effort to save some of the species.

Michael Hadfield, an emeritus professor of biology at the University of Hawaii, began the programme after he noticed that various populations were facing dire threats.

George hatched there 14 years ago, after his parents were collected from the last known wild population. Some additional offspring were produced but all the A. apexfulva eventually died, except for George.

There are currently about 2,000 snails in the facility, representing 30 species that are either extinct in the wild or very rare. The facility is now run by the Snail Extinction Prevention Program (SEP).

George's remains and shell will be preserved for future study. A two-millimetre snippet of his foot was also collected in 2017 for research purposes, and the living tissue remains alive in a deep freezer at San Diego's Frozen Zoo.

The plight of invertebrates

Rapid declines are being recorded in land snail populations all over the world. Dozens of papers are published about endangered snails each year, and more and more conservation initiatives are being set up in an attempt to preserve them.

Dr White has researched invertebrates like George from countries including Vietnam and Sri Lanka, and has seen snails suffer a similar fate. It doesn't help that many of them have very restricted ranges, making them susceptible to habitat loss.

He says, 'A whole species can live on a single limestone outcrop in a forest. If 90% of that forest gets taken away, you also potentially take away 90% of an area's biodiversity.

'Invertebrates often get overlooked in favour of charismatic animals like elephants or polar bears, but we need to pay attention to what is happening to them.'

But there is some cause for hope for snails.

The carnivorous snails on some Pacific island groups have eaten so many of their peers that their own populations are now declining. This may allow for future reintroductions of some native snail species, which currently survive in captivity thanks to the hard work of conservation groups.

Museum collections can also provide an important baseline of data, particularly about species diversity before human impacts such as deforestation took their toll on habitats.

Many land snail specimens collected in the nineteenth century are the only record of a species, and it is not known if these are still living in remote areas or long extinct.

We can only hope that these turn up in future and are not part of the broader pattern of invertebrate extinctions continuing around the world.

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