An invasive crustacean in Tasmania, Australia : a study on the introduced porcelain crab Petrolisthes elongatus

Petrolisthes elongatus (Family: Porcellanidae) was introduced into Tasmania over a century ago from New Zealand, most probably via the dry and semi-dry ballast vector as well as associated with the live oyster trade. Since its initial introduction, P. elongatus has invaded new intertidal zones across the north, east, and southern coastlines of Tasmania and attains densities of over 200 individuals per m¬¨‚â§. There is a lack of literature that documents the impacts associated with the invasion of P. elongatus and the interactions occurring in the occupied intertidal ecosystems. This project examined the distribution and densities of P. elongatus around Tasmania's coastline and examined how these metrics related to native grapsid crabs distribution and density (biotic) and environmental stress (abiotic) to determine if these factors influenced the range and densities of P. elongatus. Furthermore, P. elongatus carapace length between sites and coastlines was examined to determine if there were differences in morphology across the introduced range, while also examining ovigerous females and sex ratios between sites and coastlines. A monthly quadrat study from February 2012 to January 2013 was conducted at one site, Low Head in the north of Tasmania, to determine seasonal changes in morphology, ovigerous females, and sex ratios within the population. The introduced range of P. elongatus in Tasmania extends from the northwest, down along the east coast and into the southeast , with more individuals found along the north and south coast then the east coast, no individuals were observed on the west coast. Densities were found to be higher in populations along the southern coast of Tasmania when compared to northern and eastern sites. P. elongatus were observed colonising small to medium sized rocks on coastlines with low to moderate wave energy. No direct interaction was found between densities of P. elongatus and two native grapsid crabs Paragrapsus quadridentatus and Paragrapsus laevis at either the site or quadrat scales. Morphology between coastlines of Tasmania revealed larger carapace lengths at northern sites (U [1] = -7.57, p<0.001); furthermore sex ratios were found to be equal at all sites except for Dunalley and Dover (south Tasmania). Northern sites produced a higher proportion of ovigerous females compared to southern sites (˜ìv°2 [10] = 42.4; p<0.001). Potential seasonal changes wereevident within the Low Head (north Tasmania) population with larger carapace lengths in the warmer months (F[1,10] = 26.394; p<0.001). Rapid declines in ovigerous females were observed during winter with large increases into warmer months. Sex ratios become more female dominated into spring and summer. This study begins our understanding of the demography of this introduced crustacean, revealing its ability to successfully invade and produce high densities of individuals in recipient ecosystems. The need for continued research is important to further develop our understanding on the possible impacts and future spread of Petrolisthes elongatus in Tasmania and mainland Australia.