A DYNAMIC SIZE-STRUCTURED POPULATION-MODEL - DOES DISTURBANCE CONTROLSIZE STRUCTURE OF A POPULATION OF THE MASSIVE CORAL GARDINEROSERIS-PLANULATA IN THE EASTERN PACIFIC

Using a long-term data set of Gardineroseris planulata (Dana) on Uva I sland reef, Panama, we developed a simulation model that relates size- specific schedules of growth and partial mortality to predation by Aca nthaster planci (Linnaeus) and El Nino-Southern Oscillation (ENSO)-rel ated elevation of water temperature. We compared the model predictions to field observations for both the subpopulation of colonies that was used for model development and for the entire population. No statisti cally significant differences in the size-frequency distributions of t he real and modeled coral populations were found for the subpopulation during any of 9 yr or for the entire population during 4 yr. These re sults suggested that the model relationships were reflecting field con ditions. Longer-term (100 yr) simulations were conducted to assess the relative importance of predation and ENSO-related colony losses in de termining the size structure of the coral population. Predation by A. planci was of overwhelming importance due to both stronger effects of predation (larger transitions) and the frequency of predation (yearly) compared to ENSO (episodically). Even the least-frequent predation sc enario skewed the distribution toward smaller colonies, while simulati ons where populations were subjected to frequent ENSO events (greater than or equal to 3 yr) still maintained colonies in the largest size c lass. The model results suggested that sea star predators may not have been in the present abundance on this reef prior to the last 30 yr; w ith predators present, the model predicts that the distribution would be skewed toward smaller colonies.