A summary of alien marine benthic invertebrates in Danish waters

There are 18 established alien marine benthic invertebrates in Danish waters. In addition, there are nine species that have been recorded one or more times in these waters, but which do not form reproducing populations in this area. The most important recipient localities in Danish waters are the Limfjord (n=4) and the Wadden Sea (n=3). The species found in these areas are mostly marine species that have spread through secondary dispersal from their original location of introduction. Data on distribution, dispersal, vectors, and donor regions are presented, and the adequacy of Danish monitoring programs is discussed.