Effects of 1997-1998 ENSO on coral reef communities in the Gulf of Califoria, Mexico

Sea surface temperatures in the eastern tropical Pacific increase dramatically during El Niño Southern Oscillation (ENSO) events. This increase in sea temperature negatively affects two important coralline communities in the southern Gulf of California. During the 1997-1998 ENSO event, benthic sessile communities were exposed to a thermal anomaly of up to 3 °C during the summer. About 30% of live corals in six important communities in the region during 1996 (pre-ENSO conditions), 1997, 1998 and 1999 experienced coral bleaching, accompanied by 60% mortality. Coral bleaching was more intense close to the northern part of the studied area, as the southern area is normally exposed to higher temperatures. Corals located in shallow water experienced a higher incidence of bleaching than in deeper areas. This pattern is a response to temperature stratification and not to differences in light conditions. We detected variations in the densities and size distributions of the coral-associated fauna associated with coral bleaching and mortality. Annual variations in species abundance of the algal community associated with rodolith beds during 1998-2000 should provide us baseline information to assess the effects of future ENSO events on the rodolith community.