1997-98 El Niño effects on the pelagic ecosystem of the California current off Baja California, Mexico

Abstract

We analyze the plankton response to 1997-98 El Niño in the southern region (26-32°N) of the California Current, from four IMECOCAL cruises. Integrated chlorophyll a showed a moderate increase at the end of the ENSO, but chlorophyll in Vizcaino Bay remained fairly constant. The medians were higher than 40 mg m^-2 through 1998. Zooplankton biomass showed a local decrease from Punta Baja (30°N) to Vizcaino Bay, but not in other areas. The zooplankton decrease was mainly due to the lower abundance of copepods and euphausiids at the end of El Niño. High concentration of zooplankton from Punta Eugenia (27.7°N) to San Ignacio (26.7°N), could be explained by the presence of abundant salps. A strong presence of tropical copepod species was observed during the peak of El Niño, most abundant being the oceanic Nannocalanus minor and Eucalanus subtenuis. Abundances of the transitional species Calanus pacificus, Pleuromamma borealis and Rhincalanus nasutus were low.