[Presence of red tides along the eastern coast of the Gulf of California]. / Presencia de mareas rojas en la costa este del Golfo de 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.

[Red tides in México: a review]. / Mareas rojas en México: una revisión.

With the purpose to make a review on the red tides occurence at mexican coasts, previous studies were analyzed. Dinoflagellates seem to be the main cause of toxic events mainly Gonyaulax polygramma, Gymnodinium catenatum, Pyrodinium bahamense var. compressum and Ptychodiscus brevis. There are other species which cause red tides but are not toxic. They are: Mesodinium rubrum, Gonyaulax triacantha, Noctiluca scintillans, Prorocentrum dentatum, Gymnodinium splendens, G. sanguineum, Ceratium tripos var. ponticum, C. furca, Scrippsiella trocoidea and Oscillatoria erythraea. The first of these is the most common cilliate of the Pacific coastlines and the last one is the most common cyanophyceae during the strong events of "El Niño". The magnitude is quite variable, from small stains of a hundred square meters to several square kilometers and its density ranges from 0.5 to 36 million cells/l. Their residence time goes from 1 or 2 days to as long as 5 months. The great densities are due to Prorocentrum dentatum and P. minimum, the latter is only observed in estuarine ponds for shrimp cultivation, they have not been related to poisoning episodes. New areas of the red tide occurrence have been recorded during the last decades, such as Acapulco Bay, Huatulco, Salinacruz and Puerto Madero. These localities and also Mazatlán, are the only regions in which paralytic shellfish poisoning (PSP) have registered fatal cases and in the Gulf of Mexico a great mortality of fishes has been noted due to ictiotoxin produced by Ptychodiscus brevis. On the other hand, at Yucatan and west coast of the Peninsula of California red tide events are little known.