Responses of three coral communities to the 1997–98 El Niño–Southern Oscillation: Galápagos Islands, Ecuador
One deep (13–15 m depth) and two shallow water (1.5 and 7 m) coral communities in the Galápagos Islands, Ecuador were monitored for tissue response (bleaching, paling, morbidity) and secondary responses during and after elevated temperature stress associated with the 1997–98 El Niño–Southern Oscillation (ENSO) event. Between March and May 1998, the fungiid coral Diaseris distorta paled and bleached (up to 88.0% of all individuals bleached) at 13–15 m depth. The small branching colonial coral, Psammocora stellata, paled (79.2% of all colonies) with very little bleaching (11.1%), also at 13–15 m depth. However, by May 1998 colonies of this species in shallower water (7 m depth) suffered high mean mortality (72.4% of colony area, 85.1% decrease in numbers of live colonies). In March 1998, colonies of Pavona clavus, a massive coral species, were 100% bleached at 1.5 m depth and experienced subsequent partial mortality averaging 34.0% per colony. Both Diaseris and Psammocora in deeper water (13–15 m depth) recovered pigment by June 1999. Numbers of Diaseris individuals within permanent transect plots decreased 56.1% from March 1998 through August 2000, but this loss was most likely due to coral displacement by currents and surge rather than temperature-induced mortality. Numbers of Psammocora colonies in deep water did not change appreciably during the survey period (−16.1%). In contrast, surviving shallower water (7 m depth) Psammocora recovered pigment by June 1999, but numbers of live colonies remained low through August 2000 (−83.3% compared to March 1998). Initial recovery of pigmented tissue was evident in Pavona by June 1999, but a decline in live tissue again occurred by August 2000. Sea water temperature at the deeper site reached 28–30°C, but periods of semi-diurnal cooling may have mitigated the bleaching response. Highest temperatures occurred in shallower water (7 m), where Psammocora experienced high mortality and periodic subsurface cooling was suppressed. These data cannot be compared with those from the 1982–83 ENSO because of the lack of quantitative data from the earlier event. However, these observations provide a framework of comparison with other ENSO-affected eastern Pacific coral communities and reefs during the 1997–98 event.
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Document Type: Research Article
Publication date: July 1, 2001
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