Diversity and distribution of the dinoflagellates Brachidinium, Asterodinium and Microceratium (Brachidiniales, Dinophyceae) in the open Mediterranean Sea

Brachidiniacean dinoflagellates have been investigated in the open waters of the Mediterranean Sea, along a transect from the south of France to the south of Cyprus (20 June–18 July 2008). Brachidinium and Karenia papilionacea often co-occurred, B. capitatum predominating in the surface waters. The highest abundance of Brachidinium were found in the upper 25m in the westernMediterranean with a maximum (24 cells L–1) at a depth of 5 m in the Balearic Sea. Asterodinium (up to 4 cells L–1) was recorded below of deep chlorophyll maxima. The genus Microceratium, only known from the tropical Indo-Pacific region, is reported for the first time in theMediterranean Sea.Microceratium was found below 100m in the easternMediterranean Sea, with the highest abundance of 8 cells L–1 at 125 m depth, in the Levantine Basin. This study also illustrates for the first time specimens under the division of Brachidinium andMicroceratium. This first occurrence ofMicroceratium in theMediterranean Sea should be considered an indicator of climate warming. However, it should not be considered a non-indigenous taxon. Microceratium is the 'tropical morphotype', the adaptation of a local species (a life stage of Karenia – Brachidinium – Asterodinium) to the tropical environmental conditions that prevail in summer in the open Mediterranean Sea.