Maoricolpus roseus

New Zealand screw shell
Maoricolpus roseus
Maoricolpus roseus, Tasmania, Australia, Photo: Graham Edgar


Temperate Australasia


Large brown screw shell with a pointed tip. It was introduced from NZ to Tasmania about 80 years ago with live shipments of oysters and now occurs in massive aggregations. The species now poses a threat to local species, because living and dead shells have carpeted the seabed in places such the D’Entrecasteaux Channel, greatly altering the habitat. The numbers of the native screw shell Gazameda gunnii seem to decline following the arrival of Maoricolpus roseus in an area. Gazameda gunnii is smaller, with a more mottled appearance, and has fine beads forming ridges around the shell.


Max Size: 9 cm

Sea Temperature Range: 9.6-19.6°C

Depth: 3-150m

Habitat Generalization Index: N/A

Also referred to as the SGI (Species Generalisation Index), this describes the habitat niche breadth of the species. Species with values less than 15 are found in a relatively narrow range of reef habitat types (specialists), while those over 25 may be found on most hard substrates within their range (generalists). Learn more here.

Conservation and Rarity

IUCN Status: Not Evaluated

Occurrence: Frequent (11.8% of sites)

Occurrence describes how often the species is found on surveys within its distribution. It is calculated as the % of reef sites surveyed by RLS divers across all the ecoregions in which the species has been observed

Abundance: Many (51 per transect)

Abundance is calculated as the average number of individuals recorded per RLS transect, where present.

Edit by: GJ Edgar. 2008. Australian Marine Life. New Holland, Sydney