Lingering Impacts of Hurricane Hugo on Rhizophora Mangle (Red Mangrove) Population Genetics on St. John, USVI

Stochastic events can have catastrophic effects on island populations through a series of genetic stressors from reduced population size. We investigated five populations of red mangrove (Rhizophora mangle) from St. John, USVI, an UNESCO Biosphere Reserve, which were impacted by Hurricane Hugo in 1989. Our goal was to determine diversity and to ascertain potential population bottlenecks two decades after the event. With the lowest observed heterozygosity, highest inbreeding coefficient, and evidence of a major bottleneck, our results demonstrated that the Great Lameshur mangroves, devastated by Hurricane Hugo, were the least diverse stand of trees. The other four populations from St. John manifested diversity reflecting the vegetation patterns of fringing mangrove or developed forest characteristics. The two fringing mangrove populations (Hurricane Hole and New Found Bay) evinced low observed heterozygosity and high inbreeding coefficients, while the fully forested sites showed higher heterozygosity and lower inbreeding frequencies. As such, fringing mangroves may be at greater risk to disturbance events and especially susceptible to sea level rise since they do not have room landward to expand. Our pair-wise population analysis indicated genetic similarity between the hurricane-damaged Great Lameshur and Coral Bay population, whose propagules were used in previous restoration attempts and is the geographically closest population. While the effective population size for Great Lameshur Bay places it in risk of genetic dysfunction, future rehabilitation of the site may be possible by the introduction of propagules from other regions of the island. However, recovery will ultimately be contingent upon hydrological connectivity and environmental improvements