Powelliphanta
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Powelliphanta gilliesi |
The shell of a species of land snail.
Powelliphanta is a genus of giant, carnivorous land snails from New Zealand. They live mostly in tiny pockets of moist native bush in small areas of the North and South Islands, with the greatest diversity of species in the mountains of North West Nelson. They are sometimes known as amber snails.
There are 21 species and 51 subspecies. The relationship between the species is complex, and it has been suggested that the group Powelliphanta gilliesi-traversi-hochstetteri-rossiana-lignaria-superba forms a ring species. In November 2003 a subspecies, thought to be extinct, was rediscovered alive on the West Coast; it had last been documented on the basis of shell fragments in 1934.
These snails are real giants, with shells up to 9 cm across (Powelliphanta superba prouseorum).
Their striking delicately-patterned shells come in an array of shades, from brown or red to yellow or black. The structure of these shells is very delicate, with a very thin layer of calcium carbonate, covered by a thicker chitinous outer layer. That is why these snails need moist surroundings. Otherwise the outer layer (periostracum) dries up, shrinks and cracks.
They are carnivorous and eat mostly earthworms or slugs. They are nocturnal. They need moist surroundings and live buried under leaf mold and logs. They can live for 20 years or more and are slow to mature, reaching sexual maturity around 5 years of age. They are hermaphrodites, having both male and female characteristics. They lay 5 to 10 large eggs a year.
Their origin goes back 200 million years to the continent Gondwana. Through their isolation on New Zealand, they have evolved into a unique set of characteristics. They are a testimony for New Zealand’s unique biodiversity.
An unspecified species of Powelliphanta recently appeared on a New Zealand 40-cent postage stamp.
[edit] Conservation status
The IUCN Red List states for Powelliphanta marchantii a lower risk, near threatened. But most of these snails are under serious threat or even in danger of extinction. They have no defense against introduced predators, such as Common Brushtail Possums (Trichosurus velpecula) and rats. Many recovery plans are being launched by the Department of Conservation of New Zealand. The subspecies Powelliphanta gilliesi brunnea and Powelliphanta traversi atakia are the most threatened.
Since 2004, plans by Solid Energy to destroy the main habitat of Powelliphanta "augustus" while mining for coal caused controversy (see Save Happy Valley Campaign). Solid Energy, whose past mining activities had already significantly reduced the species' habitat, plan to mine the skyline ridge including Mt Augustus. In May 2005, they sought a permit from the Department of Conservation to translocate some Powelliphanta "Augustus" but intended to begin mining regardless of whether the permit was granted or not. The Royal Forest and Bird Protection Society obtained a declaration in December 2005 from the High Court requiring Solid Energy to get permission from the Minister of Conservation and the Ministers of Energy for this translocation, as well as any transfer by heavy machinery, and any impact on habitat. Permission was granted in April 2006 for this translocation plan.[1] This was condemned by Forest and Bird, by the Save Happy Valley Coalition [1] and by the Green Party,[2] in part because of significant doubts as to whether the translocation would succeed, and the lack of guarantee that this measure would protect the species from extinction. Powelliphanta "augustus" numbers are estimated to be less than 500, and their existing habitat covers 3-4 ha. The Wildlife Permit grants Solid Energy permission to mine 96% of this area. There is also concern over the destruction of Powelliphanta habitat by the mining company OMYA on Mount Burnett, in Golden Bay.
On 4 December 2006 twenty snails removed from Solid Energy's planned opencast mine expansion at Stockton were released back into the wild.
A further 20 snails collected from the ridgeline of the mine site were also released about 800 m from where they were found.
The giant carnivorous snails, Powelliphanta augustus, were released into an area of the Stockton Plateau that will not be mined.
[edit] Notes
- ^ Permits approved to move Mt Augustus snails. NZ Government press release, 12 April 2006
- ^ Snails sold out by State to Solid Energy. Green Party press release, 12 April 2006.
