Phytoplankton biomasses and hydrographic conditions during El Ni o 1997-1998 in Bahía Concepción, Gulf of California, Mexico

The biomass of phytoplankton groups, particularly dinoflagellates as indicated by their signature pigment peridinin, and the physicochemical conditions in Bahía Concepción, Gulf of California are analyzed for the years 1997-1999, in order to observe the changes in phytoplankton and hydrographic structure linked to El Ni o 1997-98. Three significant changes occurred in 1998 compared to 1997 and 1999: higher temperatures in the water column, lower nutrient and peridinin concentrations, and a 2 to 3 month delay of the stratification period. These data suggest the influence of Equatorial Surface Water (low nutrients, high temperatures) and a negative effect on the proliferation of dinoflagellate groups during El Ni o 1997-98. Possible causes of the low dinoflagellate biomass are discussed.