Population characteristics and planktonic larval stage of the New Zealand screwshell Maoricolpus roseus

Maoricolpus roseus is believed to have been introduced into Tasmania in the 1920s. Despite its wide distribution, dense populations and being considered successful in colonizing and altering several habitats, details of its reproduction and life cycle are not known. Specimens collected from the D'Entrecasteaux Channel (SE Tasmania) over 2 years showed sexual dimorphism with females relatively larger than males. A 1:1 sex ratio was observed and females were found carrying encapsulated larvae throughout consecutive austral summer seasons (September or October till February), with up to 70% of females carrying larvae. Larvae released from egg capsules were planktonic, all relatively well developed, and fed on microalgae, indicating that the species has planktotrophic development, and suggesting high potential for dispersal. This information is important for the development of management strategies to control this invasive species. © The Author 2008. Published by Oxford University Press on behalf of The Malacological Society of London, all rights reserved.