The American blue crabCallinectes sapidusRathbun on the German North Sea coast: Status quo and further perspectives

Live specimens of the American blue crabCallinectes sapidus Rathbun, 1896 (Crustacea: Decapoda: Brachyura) were found in the German North Sea estuaries of Elbe and Weser in 1964, ca. 1965, ca. 1990, 1998 and 2007. Due to these infrequent records the potentially invasiveC. sapidus is considered a non established alien species in German waters until now. Climate warming might facilitate the establishment, increasing stocks and subsequent spread of blue crabs in European waters. An early detection of alien species is essential for taking rapid measures at the earliest stage of establishment or spread. ‘First finders’ such as fishermen should be integrated as key-component in an early warning system of an alien observation concept. To verify records of new alien species, proper documentation of finding, specimen identification by reliable taxonomists and depositing of confirmed voucher specimens are essential.