Species composition and seasonal changes in macroalgal blooms in lagoons along the southeastern Gulf of California

Species composition and seasonal changes in macroalgal blooms in six coastal lagoons highly impacted by human activities were tracked for the three seasons between May 2004 and April 2005. Though temperatures were lower during the cold season than during the dry and rainy seasons and some locations showed variations in salinity during the rainy season, nutrient concentrations showed no defined pattern and varied according to season and location. A total of 10 seaweed species and the cyanobacterium Microcoleus lyngbyaceus had biomasses > 1 g m(-2) dry weight, but only four species represented > 1% of the annual biomass. During the dry season, Spyridia filamentosa had the highest biomass (57.5 g m(-2)). During the rainy season, Gracilaria vermiculophylla was the most conspicuous and abundant species (64.0-291.0 g m(-2)) and during the cold season, Caulerpa sertularioides had the highest biomass (180.1 g m(-2)). Abundances of these species were higher than previously reported for this region. Correlation analyses showed a positive correlation between total phosphorus and the biomass of G. vermiculophylla, suggesting that this nutrient might be limiting its growth. C. sertularioides abundance had a positive correlation with N:P ratios, suggesting that high concentrations of nitrogen relative to low phosphorus levels favor its growth. These analyses revealed that nutrient concentrations are most likely to affect macroalgal growth, but temperature and salinity also play a role. This information may be useful for monitoring future blooms and determining changes overtime.