How does a widespread reef coral maintain a population in an isolated environment?

Abstract

In a changing global environment, previously suboptimal habitats may become climate refuges for species. For instance, the ranges of some tropical reef corals are already expanding poleward. Understanding the demographic strategies by which isolated or marginal populations persist is therefore important, especially since such populations are often both vulnerable to local extinction and sources of evolutionary novelty. This study builds an integral projection model from individual-level demographic rates for a genetically isolated population of a reef coral, Plesiastrea versipora, in Sydney Harbour, Australia, in order to understand the population-level demographic characteristics allowing its persistence. We show that this population is thriving, with the potential to rapidly increase in benthic cover, due to high adult survivorship and at least sporadic high recruitment. Medium-sized colonies are the most important for long-term population viability due to their reproductive potential. Nonetheless, the population's persistence is sensitive to recruitment and growth rates, and protecting it from factors that affect these processes is likely to be crucial for its longer-term survival.