El Niño related coral bleaching in Palau, Western Caroline Islands

Abstract

Mass coral bleaching is currently viewed as a major threat to the long-term health of coral reef communities. Here we quantify coral bleaching in Palau coincident with the 1997/1998 El Niño Southern Oscillation event and with local sea surface temperatures of 31 °C, which were 1.0–1.25 °C higher than long-term, satellite-derived climatological maximum monthly means for the region. We sampled nine sites, including protected lagoon and fringing reefs, vertical reef walls, and exposed barrier reefs. The percentage of living scleractinian coral tissue that was bleached was 53.4±6.2 (range: 32.3–79.3, n=8 sites) at 3–5 m depth and 68.9±6.2 (45.7–91.7, n=6 sites) at 10–12 m and did not differ significantly between depths. The overall mean percent cover of bleached scleractinians was 18.9±1.5 (mean±1 SE, n=9 sites), while the cover of healthy corals was only 15.6±2.0. Nearly half (48%) of 946 surveyed colonies belonging to 20 scleractinian taxa were totally bleached, while 15% were partially bleached. Overall, the results indicate that the 1998 coral bleaching episode in Palau was relatively severe and widespread across depths, sites, habitats, and coral taxa.