While the majority of marine alien invasive species
have been found in the tidal and subtidal zones,at least
one—the New Zealand screwshell, Maoricolpus roseus,
introduced to Tasmania from New Zealand in the
1920s—has spread across the continental shelf at
densities of 1000 s m–2 as far north as Sydney. This 5-
cm long screwshell,changes the seabed habitat,covering
soft sediments with its hard shell,providing attachment
points for other marine fauna (including another
invasive alien marine species, Undaria pinnatifida),and
once dead,its shell provides abundant homes for a
particular hermit crab that can use its heavy tapered
shell,thus shifting the pre-invasion food web.