Taxonomic and Conservation Status of a Newly Discovered Giant Landsnail from Mount Augustus, New Zealand
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Conserv Genet DOI 10.1007/s10592-007-9495-8 RESEARCH ARTICLE Taxonomic and conservation status of a newly discovered giant landsnail from Mount Augustus, New Zealand Steven A. Trewick Æ Kath J. Walker Æ Corina J. Jordan Received: 25 July 2007 / Accepted: 11 December 2007 Ó Springer Science+Business Media B.V. 2008 Abstract The Rhytidae (Mollusca; Gastropoda; Pulmo- Powelliphanta patrickensis. Powelliphanta ‘‘Augustus’’ nata) are a group of large carnivorous land snails appears to be a specialised local endemic species. Despite a distributed in the southern hemisphere, with a particularly growing international awareness of the importance of rich fauna in New Zealand. The endemic genus Powelli- biodiversity conservation, the demand for foreign earnings phanta consists of at least 10 species and many more continues to take priority over the protection of our biota. recognised subspecies, most of which are restricted to the western margin of South Island, New Zealand. Powelli- Keywords mtDNA Coal mining Extinction phanta taxa tend to have restricted ecological and spatial Mollusc BiodiversityÁ Gastropod Á Á Á Á ranges among the mountains of this region, with some species being limited to lowland forest and others to hab- itats at or above the treeline. Among recent discoveries is a Introduction population of snails occupying habitat on and around a peak called Mt Augustus, which is situated at the edge of The Rhytidae (Mollusca; Gastropoda; Pulmonata) are a a large and economically important coalfield. Since rec- group of large carnivorous land snails distributed in the ognition of the potential biological significance of the Mt southern hemisphere (South Africa, New Guinea, Austra- Augustus snails in 2004, almost all of their habitat has been lia, New Zealand and islands in the south west Pacific), destroyed by opencast mining revealing a direct conflict with a particularly rich fauna in New Zealand (Spencer between economic and biodiversity prioritisation. Our et al. 2004). Powelliphanta O’Connor 1945 is an endemic analysis of mtDNA sequence data indicate Powelliphanta genus that is almost entirely restricted to the region west ‘‘Augustus’’ is a distinctive evolutionary lineage, more of the major mountain chain that dissects South Island, closely related to a nearby lowland species Powelliphanta New Zealand. Tectonic activity has yielded a mountainous lignaria than the spatial and ecological neighbour landscape in the west, with a high rainfall due to oro- graphic lift of moist air arriving from the Tasman Sea. The genus includes the largest New Zealand rhytidid, Powelliphanta superba prouseorum (shell diameter up to S. A. Trewick (&) C. J. Jordan Á 90 mm), and the glossy, intricately patterned and coloured Allan Wilson Centre for Molecular Ecology and Evolution, shells of all Powelliphanta are attractive. The larger Massey University, Private Bag 11-222, Palmerston North, New Zealand species living in relatively accessible native forests came to e-mail: [email protected] the attention of Western science soon after European C. J. Jordan settlement of the country in the 1860s (e.g. Pfeiffer 1862), and e-mail: [email protected] many were described by the 1930s and 1940s, culminating in a taxonomy consisting of 10 species and 27 subspecies K. J. Walker (Powell 1979). However, smaller Powelliphanta living in Research, Development and Improvement Division, Department of Conservation, Private Bag 5, Nelson 7042, New Zealand remote alpine areas were more easily overlooked and a few e-mail: [email protected] new species are still being discovered today. 123 Conserv Genet The conservation status of many species of Powelli- The Stockton Plateau, a high (600–1,100 m asl) uplifted phanta and other rhytidids in New Zealand is of concern as plain that slopes gently to the east from a precipitously a result of habitat loss and predation by introduced pre- steep western scarp, has been the site of coal extraction dators (Walker 2003). Habitat loss and modification since the 1870s. The Eocene coal deposits here are gen- previously had its most pronounced impact on the species erally in the form of a single seam (Mangatini) 4–15 m in occupying relatively low altitude forest habitats, but now depth (Nathan 1996; Barry et al. 1994). Extraction was taxa at higher altitudes are equally threatened; the most originally by underground shafts, but later by opencast recently discovered alpine Powelliphanta became critically mining by the state-owned coal company, Solid Energy endangered as a result of opencast coal mining almost as New Zealand Ltd. (SENZ). This involves stripping of the soon as it was found. In this paper we describe the rec- overburden, which at Mt Augustus includes snail habitat, to ognition of Powelliphanta ‘‘Augustus’ in 2004 and the access the coal. The overburden (Fig. 1) consists primarily destruction of almost all its remaining habitat by 2007 to of quartz sandstone, and soils developed on this tend to be provide direct material benefit to humans. shallow and infertile supporting subalpine heaths rather In 1996 a handful of Powelliphanta shells were found on than forests (Wardle 1991). Soil pH is low, and there is a Mount Augustus on the Stockton Plateau north of Westport very high rainfall ([6,000 mm/annum), which leaches South Island, New Zealand. Initially, these were thought to what little nutrients the thin soils contain. The Mangatini be Powelliphanta patrickensis, whose type locality is also coal measure extends beneath the entire western escarp- the Stockton Plateau. However, in 2003, during a detailed ment, including Mt Augustus, so mining this seam involves survey of the range of Powelliphanta patrickensis, the Mt permanently lowering the ridgeline by 30–50 m. High Augustus shells were critically examined and found to quality coking coal in the Stockton mine is nearly differ substantially from these in terms of shell morphol- exhausted, so the coal under the ridgeline is the last ogy. Shell shape, colour and size indicated that the taxon available, but unfortunately also particularly valuable. As was either a highly distinctive new subspecies of Pow- the snails are restricted to one of the highest and wettest elliphanta lignaria, or a separate new species. peaks along the ridgeline, coal extraction will result in the Stockton Plateau is the site of a large opencast coal destruction of almost all of their available habitat. mine (*2,300 ha) and by 2004 the original collection site Following the discovery of the snails, about 60% of the for the Powelliphanta from Mt Augustus had been individuals were salvaged and taken into captivity and destroyed. A small population remained on about 5 ha of mining of the Augustus ridgeline continued. The vegeta- the Mt Augustus ridgeline, though this too was in the tion, soils and substrate of almost all of the snail habitat has process of being mined. Exhaustive searches elsewhere now been removed, and the cliffs are being ‘‘deconstruct- failed to find any further colonies of the Mt Augustus ed’’; this lowering of altitude may in turn impact on snail, and thus the snail’s taxonomic distinctiveness orographic rainfall and drainage in the sliver of snail became a prime importance in decisions as to whether habitat that remains on the western escarpment below the mining should continue. coal seam. The long-term survival of the snail population Fig. 1 Cross-section schematic of coal deposits at Mt Augustus extent of mining impact on the Stockton Plateau, South stripped by March 2007 Island, New Zealand (based on stripped by 2005 ‘‘Stockton Opencast Mine Ridgeline Mining: Augustus ridge crest Environmental Impact Assessment’’ by Solid Energy 975 l e New Zealand, July 2005). v Sandstone & g rit (ov Overburden (dark grey) 950 erburden) indicates rock strata overlying e sea le San coal measure (black) that are v dstones & Conglomer ate being removed to gain access to 925 coal. The east–west extent of snail distribution on Mt metres abo 900 Augustus is indicated by pale ault grey line, although snail density ugustus F was highest at the higher Basement Granite A elevations West East 123 Conserv Genet salvaged before mining is uncertain, thus it remains taxon P. lignaria to which they are morphologically more important to determine whether the Mt Augustus snail is a similar. distinct evolutionary lineage and therefore a unique part of New Zealand’s endemic biodiversity, or a genetically undifferentiated but isolated population of a more wide- Methods spread taxon. This study used mitochondrial DNA sequence data to Biological material place the Mt Augustus snails in a phylogenetic context. As no previous phylogenetic analysis of Powelliphanta has Powelliphanta snails were collected in the field, and been undertaken with DNA sequence data, we used a broad common species were killed by freezing. Soft parts were sampling of the wider taxonomic and spatial range of the removed and held at -80°C for genetic analysis, and shells genus, in addition to extensive sampling in the vicinity of stored dry at ambient temperatures. Most material was Mt Augustus (Fig. 2). This provided the best opportunity to collected in 1987–1990 for use in an allozyme analysis of assess the relative diversity within the group as a whole and the genus (Walker 2003). Rare species were not collected identify the closest genealogical relations of the Mt until 2004, when tissue biopsies were taken before the live Augustus snails. In particular, it allowed us to test whether snails were returned to the wild. Snails from the Mt Mt Augustus snails are phylogenetically closest to the Augustus population were initially sampled in 2004 and alpine species Powelliphanta patrickensis, as initially 2005 as two whole animals found freshly dead. Soft parts supposed on the basis of their close proximity on the coal were stored in ethanol and shells dried. In order to obtain a measures of the Stockton Plateau, or nearer the lowland more extensive sample without further impact on an Fig.