Salinity and temperature tolerance of the invasive freshwater gastropod Tarebia granifera
Invasive aquatic species, such as the gastropod Tarebia granifera, can cause ecological isturbances and potentially reduce biodiversity by displacing indigenous invertebrates. In South Africa, T. granifera was first recorded in an estuarine environment in the St Lucia Estuary. Its tolerance to salinity and temperature was investigated through the experimental manipulation of these factors. T. granifera can tolerate temperatures between 0 ÂºC and 47.5 ÂºC, allowing it to survive high temperature extremes. The species may also survive cold snaps and invade higher altitude areas. More remarkably, this snail survives high salinity for a relatively long time, as LS50 (lethal salinity for 50% of the population) was reached at 30 psu over 65 - 75 days. However, higher salinity adversely affected the T. granifera population. Snails acclimated to freshwater conditions and suddenly transferred to 30 psu experienced 100% mortality within 48 h. Snail activity also declined with increasing salinity. T. granifera's environmental tolerance and parthenogenetic characteristics are the keys to successful introduction and establishment. Therefore, the management of T. granifera may prove diffcult in the short to medium term. The present findings constitute a contribution to the knowledge of biological invasions in Africa and to the understanding of estuarine invasions by T. granifera.
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