An individual-based model for population viability analysis of the brooding coral Seriatopora hystrix

Species of brooding corals are declining and disappeared from some reefs near southwestern Japan. We therefore developed an individual-based model of the threatened species Seriatopora hystrix to assess local population viability. Life history parameters of the individual colonies represented in the model were estimated from field observations made on a 5m×5m quadrat at Urunosachi, Kerama Islands, during 2009 and 2010. When assuming that recruitment was restricted to local self-recruitment, we found that the modelled Urunosachi population was maintained if the survival rate was equal to the upper limit of the 95% confidence interval, but gradually declined close to extinction after 10 years if the survival rate was the estimated means value. If larvae were supplied from outside the population, the population could persist over time even if the expected survival rate was considered, but the immigrating rate of larvae required for persistence was very high. Further research is necessary to locate other S. hystrix populations near the Urunosachi population and to evaluate the connectivity among populations to determine whether the Urunosachi population is viable. We also examined how many recruits from other populations were needed to initiate the recovery of the population if it was severely affected by certain disturbances. Constant recruitment or occasional high-level recruitment could promote the recovery of the S. hystrix population.