Population abundance and size-structure of an eastern tropical Pacific reef coral after the 1997-98 ENSO: A simulation model predicts field measures

Abundance and size structure of two populations of the massive reef coral G ardineroseris planulata in non-upwelling (Uva Island reef in the Gulf of Pa nama) and up-welling (Pearl Island reefs in the Gulf of Chiriqui) environme nts affected by the 1997-98 El Nino-Southern Oscillation (ENSO) event were measured in May 1999. A dynamic simulation model was used to predict change s 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 dat a of coral growth, recruitment, predation effects by Acanthaster planci, an d mortality associated with the 1982-83 ENSO event. Despite significant dif ferences in the regional patterns of warming between the two ENSO events, t he simulation model was able to predict with high accuracy coral abundances and size structures for both populations. Intensity of the 1982-83 ENSO wa s 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 popu lation size-structure between model predictions and field measurements. Thi s 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.