The Mediterranean Sea is one of the most affected areas by alien invasions, which are continuously increasing due to the intense human activities and environmental changes that favor the introduction of species previously unable to colonize the basin. This is the case of the copepods of the genus Pseudodiaptomus, first described in the Indian Ocean and considered as one of the most resistant to unfavorable conditions but never recorded in the Mediterranean until 2011, though present in adjacent seas.
Pseudodiaptomus marinus, in particular, is common in shallow marine-brackish waters and is one of the species often found in ballast waters and in aquaculture plants. Native of Japan, it has started spreading since 1950s, and its populations have established in several harbors, eutrophic inlets, and lagoons along the coasts of the Pacific and Indian Oceans. In the last few years, P. marinus has been increasingly reported in European Seas (Mediterranean Sea and North Sea).
