Effects of temperature on locomotion rate of the introduced slug Deroceras panormitanum (Gastropoda: Limacidae) on Marion Island: Impacts of global climate change

Many of the Southern Ocean Islands are experiencing rapid climate change. These islands have been invaded by a wide variety of species, which are having substantial effects on ecosystem functioning. Temperatures have increased by c. 1.2°C and rainfall has declined by 500 mm in the past half century on Marion Island. The slug, Deroceras panormitanum is an important invasive on Marion Island. Its distribution is largely restricted to moist, lowland areas below 200 m a. s. l. What the influence of temperature is on other aspects of performance that might be significant in determining the range limits of this species, such as locomotion ability, is not known. The primary aim of this study was to determine the effects of temperature on locomotion performance by investigating three aspects of performance curves: optimum temperature (Topt), performance breadth (Tbr) and maximum velocity (Umax). The responses of optimum temperature and performance breadth showed reverse acclimation. Individuals acclimated to the colder temperature (0°C) showed a higher optimum temperature and a wider performance breadth over all the groups. Field fresh individuals performed poorly overall. There were no significant acclimation effects on maximum velocity (Umax). The slugs seem to prefer temperatures between 5°C and 10°C, even though they perform poorly at these temperatures. If temperatures increase as predicted for the Southern Ocean Islands, slugs are likely to have increasing impacts on ecosystem functioning.