First detection of Prorocentrum cf. shikokuense bloom in the Mediterranean Sea.

Increasing intensity and spreading of toxic and non-toxic blooms, as well as global transport of non-indigenous marine species, have expanded worldwide during the last decades (Hallegraeff, 1993; McGeoch et al. 2010; Py?ek et al. 2012; Simberloff et al. 2013). HABs and NIS introduction will undoubtedly constitute a growing threat to human activities related to the sea, including fishery, aquaculture, recreational activities and tourism representing a serious ecological and economical menace (Zingone et al., 2017; Occhipinti-Ambrogi and Savini, 2003). A bloom of non-indigenous species (NIS) Prorocentrum cf. shikokuense was detected for the first time in the Mediterranean Sea at the Brindisi port (Southern Adriatic Sea) on September 2016, during a plankton survey aimed to detect and monitor non-indigenous species in the ports (Marine Strategy Framework Directive MSFD, 2008/56/EC). Morphological detailed observations by light and electron scanning microscopy and cell density were reported. In the Brindisi port this dinoflagellate reached the exceptionally high concentration 105 cell/L and represented from 30 to 50 % of the total phytoplankton population. Prorocentrum shikokuense Hada (1975) is globally scarcely studied and its toxicity is unknown. However, is usually monitored in the East China Sea and Japanese and Korean waters since it causes huge red tide (Su-Myat and Koike, 2013). Although the bloom of Prorocentrum cf. shikokuense from Brindisi port did not seem to cause any toxic event (e.g. fish kills), the presence of this species, suggests the need for improving risk assessment to manage and prevent the occurrence of harmful blooms, especially those caused by non-indigenous species, in such a sensitive area.