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Impacts of snails and slugs as alien species

The African giant land snail (Achatina fulica)

The African giant land snail (Achatina fulica) is one of the most devastating snails globally as it has decimated native snails on islands. It has not been reported as alien in South Africa to this date, but it is common in the pet trade. (Photo credit: By Thomas Brown [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons)

Even though snails and slugs (gastropods) are some well-known agricultural pests, environmental systems are more vulnerable to alien gastropod impacts. A recent study by C·I·B Hons student, David Kesner and C·I·B Core Team Member, Dr Sabrina Kumschick, at Stellenbosch University on this topic was published in the journal Ecology and Evolution.

Besides their impacts on horticulture and agriculture through the feeding on plants, some alien gastropods have devastated populations of native species. For example, various gastropods have been implicated in the declines of native snail species on several islands. For conservation of biodiversity and management in socio-economic systems, information on impacts needs to be easily interpretable and comparable. This can be achieved using the Environmental Impact Classification of Alien Taxa (EICAT) and the SocioEconomic Impact Classification of Alien Taxa (SEICAT).

Applying these schemes to gastropods that are alien to South Africa, the study found that environmental impacts were equally high in all habitats. The severity of their impacts, however, differed between mechanisms with the predation, grazing/herbivory and competition causing more damage than disease transmission. The relatively low impact found on the socio-economy can be explained by a general resilience of these systems to arthropod pests. Contrary to the authors’ expectations, species with higher numbers of offspring and a larger native range did not have higher impact magnitudes. This leaves the question open to whether any inherent traits of the species could predict their impacts in new ranges.

“Having experienced several local extinctions of wetland snail fauna, environmental systems may be vulnerable to the impacts of alien snails and slugs across habitats”, Dr Kumschick states. She adds that “the knowledge gained on the severity and nature of impacts in studies like ours can directly feed risk assessments and is therefore useful for conservation management.”




Read the paper:

Kesner, D. & Kumschick, S. (2018). Gastropods alien to South Africa cause severe environmental harm in their global alien ranges across habitats. Ecology and Evolution https://doi.org/10.1002/ece3.4385

For more information, contact Sabrina Kumschick at sabrinakumschick@sun.ac.za