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

Bologna Bologna,Smalley Smalley,Restaino Restaino,Lourenco Lourenco,Fetske Fetske,Campanella Campanella

doi:10.3390/d11040065

Bologna Bologna, Smalley Smalley + Show 4 more

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https://doi.org/10.3390/d11040065

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Abstract

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.

Highlights

Mangrove forests represent an important coastal habitat in tropical regions globally
Was Leinster Bay and the lowest genetic diversity was found in Great Lameshur Bay (Ho = 0.129)
Mangrove forests are essential habitat for fish and invertebrates and contribute to fish biomass on nearby reefs [7]. They represent a substantial carbon sink through production of organic matter and burial within the anoxic sediments contributing to substantial carbon

Summary

Introduction

Mangrove forests represent an important coastal habitat in tropical regions globally They provide several critical ecosystem services including refuge for organisms, sediment stabilization, storm energy abatement, and carbon sequestration [1]. Diversity 2019, 11, 65 by humans to provide acreage for agriculture, housing, and aquaculture [4,5,6] When these forests are destroyed, their ecosystem services are diminished and often cause detrimental ripple effects in adjacent communities [7]. The reproductive capacity of the remaining trees may vary based on proximity to others and whether animal or wind pollination dominates, as well as the water-born dispersal phase of propagules For red mangroves, they can exhibit flowering throughout the year, but generally have an annual peak in flowering and seed production. Restoration efforts have accelerated the recovery of some forests [10]; continued anthropogenic stresses are leading to a net global loss of mangroves and the services they provide [4,5,6,11]

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