Normal, The Blob, and El Nino conditions: Effects on macroalgal blooms in a subtropical zone of the Gulf of California

The different oceanographic conditions influence marine ecosystems, particularly on macroalgae communities. For this reason, this study explored the effect of oceanographic events such as Normal Conditions, The Blob, and El Nino in the Southwest Gulf of California, in terms of species richness and biomass of macroalgal blooms. Temperatures in 2013 (Normal condition) were lower than in 2014-2015. The high temperatures recorded in 2014 (22.8 degrees C-32 degrees C) are associated with a warming phenomenon known as The Blob, whereas 2015 was an El Nino year. The anomalies in these two years ranged from 0.1 to 2.8 and from 0.3 to 1.7, respectively, relative to the average for 2002-2021. It was evident that the co-occurrence of The Blob and El Nino modified the patterns of species richness and abundance in the macroalgal blooms recorded in Bahia de La Paz, compared to a year under the Normal condition. The lowest species richness was observed in 2014. Regarding seasonal variability, in 2014 the highest species richness was recorded in spring and the maximum biomass in summer, contrary to what is generally the case in the bay. Species of tropical affinity such as Spyridia filamentosa, Padina durvillei, and Caulerpa sertularioides significantly increased their biomass in the El Nino year.