 In some places in the Netherlands it covers 95% of the seabed and there is a marked decrease in populations of the sea urchin "Psammechinus miliaris" and the brittle star "Ophiothrix fragilis".On the Georges Bank, Massachusetts, the seabed community is also changed, with some invertebrates decreasing but others, such as two species of polychaete worm, increasing in abundance.Here, "D. vexillum" restricts the potential settling sites for larvae of the bay scallop ("Argopecten irradians") and the sea scallop ("Placopecten magellenaicus").