New Zealand immigrants of a different kind are making their mark in Australia There is concern at the spread of the New Zealand screw shell, Maoricolpus roseus which was introduced to Tasmania about 70 years ago. The filter-feeding mollusc has established itself in vast beds in northern Bass Strait and off the coasts of eastern Tasmania, Victoria and New South Wales. It is estimated the species now covers an area of sea floor about the size of Tasmania. Scientists are concerned about the screw shellâs impact on other mollusc species, including scallops and the native Australia screw shell. Researchers are working with fishers to build a profile of the screw shellâs spread.