Contribution à l’étude du phytoplancton de la côte atlantique marocaine. II. Le genre Pseudo-nitzschia (Bacillariophyceae)

A survey of the genus Pseudo-nitzschia was carried out over a two year period (1998-1999) at three localities along the North Atlantic Moroccan coastline (Moulay Bousselham, Mehdia and Témara). Light microscopy observations showed that these potentially toxic diatoms (causative organisms of the ASP syndrome) bloomed on several occasions, independently of temperature or salinity variations. Using scanning electron microscopy seven species were identifed. The dominant bloom-forming species were: P. fraudulenta, P. pungens var. cingulata, P. subpacifica and P. pseudodelicatissima, other representatives of this genus in Moroccan waters were P. multiseries, P. multistriata and P. delicatissima. Of major concern for the environment are the toxic species P. multiseries, which was only present in low numbers in Moulay Bousselham, and P. pseudodelicatissima which was abundant in Moulay Bousselham and Témara although no ASP episodes were reported during the survey period. P. multistriata, recently recognized as another domoic acid producing species, and previously observed only from the Pacific and the Mediterranean Sea, is reported for the first time in Atlantic Coastal waters.