Invasives killed the biodiversity star

george the snail
George, a Hawaiian tree snail and the last known member of the species Achatinella apexfulva. Photo: Aaron K. Yoshino, Honolulu Magazine.

The start of 2019 brought sad news when George, the last tree snail of his kind (Achatinella apexfulva) died on New Years Day. His death highlights the plight of Hawaiian snails and epitomises the rapid decline of biodiversity on the Hawaiian Islands.

George had become somewhat of a local celebrity in Hawaii, a mascot for endangered Hawaiian snails, which are revered in native Hawaiian legend as the ‘voice of the forest’. George was born in a lab as part of efforts to save his species, and over his 14-year lifetime was visited by hundreds, if not thousands, of schoolchildren.

As well as climate change, invasive species have taken a huge toll on native animals and insects in Hawaii; snails like George were once ubiquitous throughout the islands. It is thought that the snails likely arrived on the islands by hitchhiking on sea birds millions of years ago, where they thrived and developed into a multitude of difference species.

In the late 19th century over 750 land snails had been recorded, including a little over 200 in the tree snail family. It was even claimed at the time that 10,000 or more shells could be collected in just one day. “Anything that is abundant in the forest is an integral part of it,” said Michael Hadfield, an invertebrate biologist, to National Geographic.

However, in 1955, a new snail was intentionally introduced to the island – Euglandina rosea, known as the rosy wolfsnail. The hope was that it would control the population of the accidentally introduced giant African snail (Achatina fulica). The rosy wolfsnail is a predator of other snails and slugs, tracking their slime and attacking with brutal efficiency. The giant African snails were intended to be its prey but unfortunately, the rosy wolfsnail found native snails much more palatable. Had the intentional introduction of the rosy wolfsnail been preceded by rigorous research identifying this huge risk of predation on indigenous snails, this would not have happened.

Euglandina rosea.jpg
The rosy wolfsnail is native to south-eastern North America but where it is invasive, it has been responsible for the dramatic decline or eradication of many endemic species

Ever since, the rosy wolfsnail has been spreading, even into higher altitudes, the Hawaiian snails’ last refuges. Scientists suspect that this is due to climate change where increased rainfall and higher temperatures have allowed the predator to venture higher. “We’ve had [native] populations that have been monitored for over a decade, and they seemed stable… then, within the past two years they’ve completely disappeared,” reports David Sischo a wildlife biologist with the Hawaii Department of Land and Natural Resources and coordinator of the Snail Extinction Prevention Program.

Hawaiian snails eat decomposing leaves or the fungus which grows on trees, and in doing so they reduce the abundance of fungi on leaves while also increasing fungal diversity. This is a vital part of forest ecology and some biologists believe that healthy snail populations could have prevented the current outbreak of Rapid ʻŌhiʻa Death, a new fungal pathogen killing native trees.

achatinellinae-subfamily-snail-collage
By the early 1900s, many of the species were “collected” to extinction for their attractive shells. Photo: David Sischo/Hawaii Department of Land and Natural Resources

Due to the rapid decline of these native mollusks, the early 1980s saw scientists start to bring snails into the lab in order to preserve them. Today, a lab in Oahu has thousands of native snails in residence and some have even been reintroduced into remote forests, though the exact locations are well under wraps.

Although scientists have said no funeral will be held for George, his shell and body are being preserved, and back in 2017 a tiny piece of George’s foot was sent to San Diego’s Frozen Zoo where it might one day be cloned. However, without forest restoration and the removal of invasive species, there may not be anywhere safe to reintroduce any future Georges.

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