Non-indigenous species may have substantial impact on the marine ecosystems, especially in coastal regions. They may change the original habitat, oust the native species and consequently alter the ecosystem structure and functioning. They hence are of particular managerial concern and therefore addressed by the EU Marine Strategy Framework Directive. To monitor new arrivals, MARECO searches for (new) non-indigenous species on various man-made hard substrates in the Belgian marine waters like those in offshore wind farms, groins, buoys and harbor walls. An inventory of the number of non-indigenous species newly introduced by human activity is reported once every six years.