Gastropods alien to South Africa cause severe environmental harm in their global alien ranges across habitats

Abstract

Alien gastropods have caused extensive harm to biodiversity and socioeconomic systems like agriculture and horticulture worldwide. For conservation and managementpurposes, information on impacts needs to be easily interpretable and comparable,and the factors that determine impacts understood. This study aimed to assess gastropods alien to South Africa to compare impact severity between species and understand how they vary between habitats and mechanisms. Furthermore, we explore therelationship between environmental and socioeconomic impacts, and both impactmeasures with life-history traits. We used the Environmental Impact Classification forAlien Taxa (EICAT) and Socio-Economic Impact Classification for Alien Taxa (SEICAT)to assess impacts of 34 gastropods alien to South Africa including evidence of impactfrom their entire alien range. We tested for correlations between environmental andsocioeconomic impacts per species, and with fecundity and native latitude rangeusing Kendall's tau tests. Kruskal-Wallis tests were used to compare impact magnitude among mechanisms and habitats, respectively. This study presents the first application of EICAT and SEICAT for invertebrates. There was no correlation betweenenvironmental impacts and socioeconomic impacts. Habitats did not differ regardingthe severity of impacts recorded, but impacts via disease transmission were lowerthan other mechanisms. Neither fecundity nor native range latitude was correlatedwith impact magnitude. Despite gastropods being agricultural and horticultural pestsglobally, resilience of socioeconomic systems makes high impacts uncommon.Environmental systems may be vulnerable to gastropod impacts across habitats, having experienced multiple local extinctions of wetland island snail fauna. South Africastands out as the only continental country that follows this trend. The knowledgegained on severity and nature of gastropod impacts is useful in risk assessment, whichcan aid conservation management. To make impact assessments more realistic, wesuggest alternative ways of reporting impacts classified under EICAT and SEICAT.