Persistence of an isolated population of the temperate coral Plesiastrea versipora

Successful establishment of new populations outside present geographical ranges requires the capacity for species to both disperse to and persist in isolated patches. By definition, dispersal to such patches is typically rare or sporadic, making individual-level growth and survival and self-recruitment key to population persistence. To better understand the demographic processes that lead to the long-term establishment of species in isolated patches, I studied a genetically isolated population of the reef coral Plesiastrea versipora in Sydney Harbour. I hypothesized that persistence of the population was due to either high levels of reproduction and self-recruitment or high levels of growth and survivorship that could buffer population decline. I used a size-based adaption of the Leslie matrix model to combine field-measured demographic rates and size structure data in order to quantify intrinsic population growth rate and sensitivities to changes in demographic contributions of different size classes. The results show that persistence of P. versipora population relies mostly on yearly survival, especially in larger more fecund colonies, and is less reliant on recruitment. The ‘persistent’ demographic strategy identified in this study may be key to establishing new sub-populations outside native ranges as well as maintaining existing populations during periods of environmental change, especially when dispersal is diminished or unpredictable.