[Presence of red tides along the eastern coast of the Gulf of California].

Records of the occurrence of red tides during the last 24 years in Guaymas and for the last 16 years in Mazatlán, on the coast of the Gulf of California, Mexico are presented here. The results indicate the presence of 4 dominant species in 34 red tides in Guaymas and 9 dominant species in 60 red tides in Mazatlán. The most common species is Mesodinium rubrum, while the toxic one is Gymnodinium catenatum. Noctiluca scintillans and Gonyaulax sp. were also present in Guaymas. In Mazatlán Scrippsiella trocoidea, Prorocentrum dentatum, Ceratium tripos var. ponticum, C. furca, Gymnodinium splendens and Gonyaulax triacantha were also present. Red tides occur frequently during winter in Guaymas and during the late winter and early spring in Mazatlán. Both periods coincide with the upwelling season in the region. The absence of the red tides is related to the "El Niño" phenomenon, which is significant in the Mazatlán area. Ciliates decrease 11.4%, while dinoflagellates increase from 1.6 to 3.8%. The duration period of red tides increase (5.6%) from 3 to 6 days, as compared with the records between 1979 and 1990.