First bloom event of the small dinoflagellate Prorocentrum shikokuense in the Mediteranean Sea: cryptogenic or introduced?

A bloom of putatively non-indigenous species (NIS) Prorocentrum shikokuense was detected for the first time in the Mediterranean Sea at the Brindisi harbor (Southern Adriatic Sea) on September 2016, in the context of EU Marine Strategy Framework Directive monitoring in the ports. This species is usually observed in the East China Sea and Japanese and Korean waters. In the Brindisi harbor this dinoflagellate reached the concentration 105 cell/L and represented from 30 to 50 % of the total phytoplankton population. Besides this event, Prorocentrum shikokuense has not been found blooming until today in Mediterranean waters. This study suggests the necessity to improve the monitoring surveys in areas that are known vulnerable systems to alien and invasive species, such as ports.