Distribution of toxic dinoflagellates along the leaves of seagrass Posidonia oceanica and Cymodocea nodosa from the Gulf of Tunis

This study examined the first results about the occurrence of epiphytic dinoflagellate species in the Gulf of Tunis. Three potentially harmful marine species were found: Prorocentrum lima (Ehrenberg) Dodge 1975, Ostreopsis siamensis Schmidt, 1901 and Coolia monotis Meunier 1919. From June 2001 to May 2002, the annual distribution of these species was studied on the seagrass Posidonia oceanica (Linnaeus) Delile. In the area where P. lima was the most abundant species, two peaks were recorded in fall and spring. The maximum density of O. siamensis was recorded in August until September whereas the maximum density of C. monotis was recorded in September and May. The abundance of epiphytic dinoflagellates was higher from August to October. These species displayed host Substratum preference on Cymodocea nodosa (Ucria) Ascherson where the cell abundance was higher than on P. oceanica, particularly for P. lima.