Coral Mortality Outside of the Eastern Pacific During 1982-1983: Relationship to El Niño

Abstract

1982-83 witnessed the most widespread coral bleaching and mortality in recorded history. In early 1982 coral bleaching and subsequent mortality was reported from the Great Barrier Reef (GBR). These reports were followed in early 1983 with observations of coral bleaching and mortality in the Java Sea, Tokelau Islands, French Polynesia, Galapagos Islands, and on the Pacific coast of Panama and in mid-1983 with bleaching in the southwestern Indian Ocean, southern Japan and the Caribbean. This world-wide coral bleaching and mortality coincided with one of the strongest El Niños on record. Many ecological anomalies that occurred during 1982-83 have been related to this strong El Niño/Southern Oscillation (ENSO) event and we have sought to ascertain if the observed coral bleaching and mortality outside of the eastern Pacific can also be attributed to ENSO-related effects, such as shifts in wind patterns, water mass movements and solar insolation. In the central Pacific the relationship is clear. ENSO-related anomalies included an increase in the frequency of cyclones and a lowering of sea level that were directly responsible for the extensive coral mortality observed there. In other regions, where the signal of ENSO is less well defined, a causal relationship between ENSO and coral death is more difficult to establish. On the Great Barrier Reef, high temperatures and high light may have played a role in the bleaching. However, the proximal cause of bleaching is not known, and ENSO-related anomalies that were observed in the area during 1982-83 did not coincide with the bleaching event. Therefore, a causal relation cannot be established. On the Caribbean coast of Panama (San Bias Islands), elevated water temperatures are thought to have led to the observed bleaching. Analyses of available meteorological and oceanographic data failed to reveal a mechanism for the onshore warming nor is there a clear link between the bleaching and the ENSO. The lack of knowledge on the mechanisms and global interactions of ENSO, as well as the lack of appropriate meteorological and oceanographic data at the sites of bleaching/mortality, have hindered our ability to establish a connection between the 1982-83 ENSO event and coral mortality.