A regional model to predict coral population dynamics in response to El Nino-Southern Oscillation

The objective of this paper was to modify an existing size-structured popul ation model for the coral Gardineroseris planulata developed from field mea surements at the Uva Island reef, Panama, for use at the regional scale (Tr opical Eastern Pacific). The modified model can be used to aid in predictio n of changes in coral population dynamics in response to ENSO events of dif ferent frequency and magnitude. The earlier model incorporates coral growth , predation by the sea star Acanthaster planci, and mortality associated wi th EI Nino-Southern Oscillation (ENSO) events. The regional model was modif ied from the earlier local version by extending the coral growth-temperatur e relationship to include the lower temperatures observed in areas of stron g seasonal upwelling. In addition, ENSO-associated mortality was modified b y incorporating a dynamic function that relates partial mortality of corals in different size classes to the rate of temperature change during an ENSO event. This function is based on data from three reef areas (Uva Island an d the Pearl Islands, Panama, and the Galapagos Islands, Ecuador), which rep resent a regional gradient from an area characterized by relatively high an nual temperature with low variability to areas with lower annual temperatur e subject to seasonal upwelling. Model predictions of coral population size structure in different areas agreed with field observations. Predictions f or coral recovery after an ENSO event were most accurate for the Uva Island population and least accurate for the Galapagos Islands population. We als o tested the effect of various ENSO frequencies on the size structure of th e coral population. Increasing ENSO frequency in the upwelling area resulte d in an increase in the proportion of small colonies, while the same increa se in ENSO frequency in the thermally stable reef area had little effect on the population, Sensitivity analysis suggested that more accurate estimate s of growth of the smallest and largest colonies in upwelling areas as well as predation on intermediate-size colonies are important to improve predic tive capability.