Invasions often go on under water. Northern Pacific seastars (Asterius amurensis) appeared in Hobart's waters in 1986 and in Melbourne's Port Philip Bay in 1995, carried around by ships and boats.
 
They swarm over the seafloor, reaching densities of up to 9 per square metre, devouring everything dead or alive - mussels, worms, snails, fish, crabs, barnacles, sea urchins, even drowned dogs.
 
See the article on the 2004 ISC Froggatt Award