Coral and coral reef responses to the 1997–98 El Niño event on the Pacific coast of Colombia

Several coral reef localities on the Colombian Pacific were surveyed between May 1997 and August 1998 to assess the nature and effects of the 1997–98 El Niño sea warming event. A characteristic feature of this episode was the presence of two elevated sea surface temperature (SST) peaks (August 1997 and April–May 1998). COADS and NCEP SSTs for the Pacific coast of Colombia indicated that thermal anomalies above +1°C lasted for approximately 15 mo, with the highest thermal anomalies reaching +3.3°C. Spatial and temporal differences in the duration and intensity of the warming were evident, hence a possible reason for the differences in coral bleaching and mortality found among sites. By May–June 1998, coral bleaching at Gorgona Island was as high as 21 and 24%, mainly at shallow and intermediate depths at La Azufrada and Playa Blanca reefs, respectively. Nearly 92% of the bleached corals were Pocillopora damicornis, whereas Pocillopora eydouxi was the least affected species. Massive coral species bleached severely and suffered the highest mortality rates. The extent of coral bleaching was variable and low (ca 1%) at other sites, including the coastal Utría and Tebada sites, and Malpelo Island in an open ocean setting. Linear extension rates of P. damicornis at Gorgona Island and Utría were significantly higher during the warming event compared with normal (non-ENSO) years. This result suggests that non-lethal elevated thermal anomalies may have a positive effect on coral metabolism. A comparison between the 1982–83 and 1997–98 El Niños indicated that while the patterns of duration and intensity were similar, relatively fewer corals bleached and died during the more recent disturbance. Community recovery following both disturbances also varied greatly, probably due to differences in the extent of coral mortality between the 1983 and 1998 events. Evidence suggests that spatial and temporal patterns of ENSO-related coral bleaching and mortality are an important determinant of coral population density, size structure and community composition on Colombian Pacific reefs.