Distribution and abundance of the alien helicid Otala punctata (Müller, 1774) (Mollusca Helicidae) at Baħrija, Malta, a site of agricultural and conservation importance

Abstract

The alien helicid Otala punctata has to date been recorded from two localities on the island of Malta. Based on field surveys, this study assesses the distribution and abundance of the species in one of these localities, Baћrija valley, an agriculturally important area and a site of conservation interest. O. punctata was found to have colonised three areas along the valley system, with the highest densities where there was low, virescent vegetation. Juveniles had a high abundance at the peripheries of the area of distribution, suggesting active dispersal outwards from the centres of the population, possibly in response to intraspecific competition for resources. Spread of the snail appeared to be slowed or halted by physical barriers, but anthropogenic transport through carriage of agricultural produce from Baћrija to markets elsewhere, and discarded agricultural material, has overcome natural barriers. The occurrence of O. punctata in the study area does not appear to have affected the population density of the closely-related indigenous helicid Eobania vermiculata thus far. Given the alien species’ potential to become an agricultural pest, and the conservation importance of Baћrija valley, close monitoring is recommended.