Abundance and size structure of two populations of the massive reef coral Gardineroseris planulata in non-upwelling (Uva Island reef in the Gulf of Panama) and upwelling (Pearl Island reefs in the Gulf of Chiriquí) environments affected by the 1997–98 El Niño–
Southern Oscillation (ENSO) event were measured in May 1999. A dynamic simulation model was used to predict changes in abundance and size structure of these two populations, and predictions were compared to field measures. The model is based on 25 yrs of field data of coral growth, recruitment,
predation effects by Acanthaster planci, and mortality associated with the 1982–83 ENSO event. Despite significant differences in the regional patterns of warming between the two ENSO events, the simulation model was able to predict with high accuracy coral abundances and size
structures for both populations. Intensity of the 1982–83 ENSO was greater in the Pearl Islands than at Uva Island; in 1997–98, the pattern was reversed. Coral mortality rates also reversed between these two events, with much higher mortality of colonies in the Pearl Islands in
1982–83 and at Uva Island in 1997–98. G-tests found no significant differences in population size-structure between model predictions and field measurements. This independent validation of the model suggests that the model incorporates the major ecological processes controlling
population growth and structure of this coral species. In addition, these results suggest that the rate of SST increase during an ENSO event is a key predictor of mortality for this species of coral.
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