The alien invasive land snail <i>Theba pisana </i>in the West Coast National Park: Is there cause for concern?

Abstract

The distribution, abundance, size distribution and diurnal activity patterns of invasive land snails, Theba pisana, in the West Coast National Park (WCNP), South Africa, were investigated. The park was divided into 1 km 2 grids, within each of which five 1 m 2 quadrat counts of live snails were recorded. Of 106 grids sampled, 19% contained live snails. The average density of snails was 4.04 m -2 ± 24.9, significantly lower than in disturbed habitats adjacent to the park (57 m -2 ± 96.25), but very high densities were recorded at two sites. Snails were most abundant along roadsides and densities decreased dramatically with distance from roads. T. pisana in the WCNP appear to have an annual lifecycle, breeding in autumn to winter and growing to adult size of about 14 mm diameter by the end of the following summer. Snails were observed on a wide variety of endemic and introduced plant species and appeared to have a catholic diet. They are active mostly at night and especially during periods of high humidity, irrespective of temperature. Given the very high densities that T. pisana can attain at some sites, plus their apparently catholic feeding habits, their potential impact on the vegetation of the park is cause for concern and should be further investigated. Control of the main colonies should also be considered.

Plant selection and grazing activity of the invasive snail Theba pisana in coastal Algoa Bay, South Africa

“…This confirms the generalist diet of T. pisana reported elsewhere (e.g. Odendaal et al 2008). The plant species identified here are common along much of the south-western South African coast (Lubke and de Moor 1998), and T. pisana is found throughout the region (Herbert 2010), therefore the preferences observed here may also be applicable throughout the region.…”

“…These snails appear to have a generalist diet with significantly higher preference and feeding rate for Tetragonia decumbens over the other plant species occurring in the area. The average density ± SE of snails was 68 ± 23 individuals m −2 , which is an order of magnitude higher than the 4 individuals m −2 reported by Odendaal et al (2008) in the West Coast National Park, and closer to the 57 individuals m −2 reported in disturbed habitats adjacent to the park. It is even comparable with densities of 39-202 individuals m −2 reported in Wales, where T. pisana has been established since the 1700s (Cowie 1984).…”

“…While some studies have reported that T. pisana has a generalist diet (e.g. Cowie 1984;Odendaal et al 2008), there is a lack of knowledge regarding which plant species are preferentially targeted by these snails. One particular study by Odendaal et al (2008) investigated the distribution and abundance of T. pisana in the West Coast National Park and concluded that these snails were a cause for concern in the park, but did not identify any plant species that may be at risk.…”

“…Cowie 1984;Odendaal et al 2008), there is a lack of knowledge regarding which plant species are preferentially targeted by these snails. One particular study by Odendaal et al (2008) investigated the distribution and abundance of T. pisana in the West Coast National Park and concluded that these snails were a cause for concern in the park, but did not identify any plant species that may be at risk. Similarly, semi-arid coastal regions of South Africa have been successfully colonised by T. pisana (McQuaid et al 1979), but a review of the literature reveals no studies concerning its diet in coastal dune vegetation, and therefore there is no insight into whether endemic coastal plant species are threatened by T. pisana.…”

Global metabolite analysis of the land snail Theba pisana hemolymph during active and aestivated states

“…T. pisana is native to the Mediterranean region, yet has become an invasive species in other parts of the world, often resulting in agricultural damage (Odendaal et al, 2008) and is thus of great agricultural and economic importance. We hypothesize that there are clear aestivation-associated differences in the hemolymph metabolome compared with active states, including an abundance of certain amino acids and phospholipid classes found predominantly during aestivation.…”