Cochlodinium polykrikoides Margalef, an armored harmful dinoflagellate, appeared first in the Oman Sea and the Persian Gulf in August 2008, formed a huge red tide for an extremely long duration, from August 2008 to August 2009, and caused fish and shellfish mass mortalities. Since a few reports of its taxonomy and ecology in the Oman Sea and the Persian Gulf have been published, we report the molecular phylogenetic position of C. polykrikoides found in the Oman Sea and the east coast of the Persian Gulf , the harmfulness of C. polykrikoides, and the significance of its geographical distribution in the world. C. polyrkikoides occurring in the above-mentioned areas belongs to the American/Malaysian ribo-type, which is distributed worldwide. Large-scale mass-mortalities of various benthic organisms are accompanied by red tides of this species. On the basis of field observations, we concluded that this phenomenon did not occur due to oxygen radicals, but mainly due to polysaccharides.

Cochlodinium polykrikoides, HAB, fish mass mortality, Persian Gulf, Oman Sea.