Effects of El Niño on beds of Ulva lactuca along the northwest coast of the Gulf of California, Mexico

The effect of El Niño 1997-1998 on the biomass and size of beds of the green alga Ulva lactuca L., along the northwest coast of the Gulf of California across the Canal de Ballenas, was evaluated in May 1998 and compared with May 1995, 1996 and 2000. The El Niño event (97-98) had a significant negative effect on size and biomass. The percent cover area was reduced by 70%, and biomass by 80%, with respect to previous years. A complete recovery was observed in 2000. Growth of the algae was studied under controlled conditions in the laboratory. No significant effect of irradiance was detected, but temperature did have a significant effect on growth. Optimum growth was found at 18°C. Temperatures of 14°, 22° and 26°C caused reduced growth. A temperature of 30°C was lethal to U. lactuca.