The Atlantic shores of Morocco extend about 3000 Km from the Straits of Gibraltar to Cap Blanc (210 N), and are bathed by the Canary Current. This is one of the major coastal upwelling regions of the world. Upwelling occurs throughout the year and is most intense in spring and summer. Algal blooms often affect the area from Cape Juby to Gibraltar (28 0 N to 36 0 N) where upwelling is more active in summer.

The first records of red tides in Atlantic Moroccan waters date from 1966. Since then, red tides have been recorded regularly during late summer and early autumn. The years 1971, 1975 and 1982 were marked by shellfish contamination with PSP levels exceeding the public health safety threshold and their consumption was forbidden. The species responsible were not identified. In October-November 1994, an exceptional bloom of Gymnodinium catenatum appeared on the coast between 31° N and 35° N and caused a human poisoning near Casablanca (33° 39‚ N). In August 1998 extensive red tides occured in coastal waters between 28° N and 33° N. Alexandrium minutum, Prorocentrum micans, Scrippsiella sp and Lingulodinium polyedrum were the main species. In July and August 1999 a progressive monospecific bloom of Lingulodinium polyedrum occured in the same area progressing from North to South, and caused DSP contamination in shellfish tested by mouse bioassay. The seasonal variability of upwelling on the Moroccan coast between 1994 and 1999 has been investigated and compared with the occurrence and timing of harmful algae blooms. The results of this study for the continental shelf from Casablanca (33° 30\' N) to Cape Blanc (21°N) will be discussed.