Historical Observations of Algal Blooms in Mazatlan Bay, Sinaloa, Mexico (1979-2014)

A 35-year record of algal blooms in Mazatlan Bay is reviewed in order to register bloom-forming species, their seasonal presence, duration, degree of toxicity and environmental impact. 202 algal blooms have been recorded and 25 dominant species identified: 6 toxic, 5 harmful and 14 harmless species. A harmless species, Myrionecta rubra, tended to decrease in frequency, while toxic species Gymnodinium catenatum and Cochlodinium polykrikoides show a clear trend towards an increase in frequency. The discoloration days attributable to blooms are highly variable in each year, but a decadal analysis revealed a tendency to increase, except in the last half decade. The monthly distribution of algal blooms for decades show two peaks of high frequency, the larger from February to May and the smaller from September to November. The duration of blooms varies from a few days to more than three months; the ephemeral are most frequent, but in the last decade the frequency of the longer-lasting blooms has increased. An absence of blooms in 1983-4 and 1992-3 coincided with strong El Niño events, but this pattern was not consistent in subsequent El Niño years. Years with more or less discolorations days appear to be associated with cold or warm phases of the Pacific Decadal Oscillation.