Macroalgaeblooms, composition, abundance, andtheir relationshipwithenvironmental variablesat asubtropical bayof theGulf of California

Background: In La Paz Bay macroalgae blooms have an important presence. Goal: Analyze the relationship of the most abundant macroalgae in algal blooms with environmental variability in a subtropical bay over two years. Methods: Temperature, salinity, nutrients (DIN, NT, PO₄^-3 and PT) and macroalgae samples were taken every three months, during 2010 and 2011, at four sites with conspicuous growth of macroalgae. Total and mean biomass (wet weight) of important species was estimated by placing three transects perpendicular to the coast, divided into five equidistant points each. At each point four quadrants (0.25 m²) were placed randomly and macroalgae were manually collected. Statistical analyzes were performed to estimate significant differences between years, months and sites of the environmental variables, nutrients, and biomass. A principal component analysis was performed, to observe the relationship between biomass and environmental variables and nutrients. Results: Nine macroalgae species, plus one cyanoprokaryonte showed a biomass greater than 1 g m^-2. Acanthophora spicifera, Caulerpa verticillata and Spyridia filamentosa were the most abundant species. A. spicifera and G. vermiculophylla were related with nutrient concentrations, and salinity. While Ulva ohnoi showed that it was not related either to environmental or nutrient concentrations. Conclusion: The bloom forming macroalgae A. spicifera, C. verticillata and S. filamentosa are consistent with genera previously reported as bloom-formers in nutrient-rich coastal waters.