The invasive ctenophore Mnemiopsis leidyi A. Agassiz, 1865 along the English Channel and the North Sea French coasts: another introduction pathway in northern European waters?

The presence of Mnemiopsis leidyi A. Agassiz, 1865 along the French coasts of the Eastern English Channel and the North Sea (EEC-NS) was established via morphological observation and molecular evidence. The earliest records were from surveys carried out in autumn 2005 in Le Havre harbour (Bay of Seine, EEC) and coincided with the historical introduction of the species in other Northern European waters. Since 2009, the species has also been frequently observed along the French coast of the North Sea. Results indicate M. leidyi has established a selfsustaining population in the Bay of Seine, which may act as a source population for northern European harbours via commercial shipping.