Exposure, vulnerability, and resiliency of French Polynesian coral reefs to environmental disturbances

Julie Vercelloni,Yannick Chancerelle,Mohsen Kayal,Serge Planes

doi:10.1038/s41598-018-38228-5

Abstract

Preserving coral reef resilience is a major challenge in the Anthropocene, yet recent studies demonstrate failures of reef recovery from disturbance, globally. The wide and vigorous outer-reef system of French Polynesia presents a rare opportunity to assess ecosystem resilience to disturbances at a large-scale equivalent to the size of Europe. In this purpose, we analysed long-term data on coral community dynamics and combine the mixed-effects regression framework with a set of functional response models to evaluate coral recovery trajectories. Analyses of 14 years data across 17 reefs allowed estimating impacts of a cyclone, bleaching event and crown-of-thorns starfish outbreak, which generated divergence and asynchrony in coral community trajectory. We evaluated reef resilience by quantifying levels of exposure, degrees of vulnerability, and descriptors of recovery of coral communities in the face of disturbances. Our results show an outstanding rate of coral recovery, with a systematic return to the pre-disturbance state within only 5 to 10 years. Differences in the impacts of disturbances among reefs and in the levels of vulnerability of coral taxa to these events resulted in diverse recovery patterns. The consistent recovery of coral communities, and convergence toward pre-disturbance community structures, reveals that the processes that regulate ecosystem recovery still prevail in French Polynesia.

Highlights

Within few decades, the concept of Earth’s ecological vulnerability has arisen and established as an undeniable global issue[1,2,3]
Coral reefs are emblematic examples of biodiverse non-equilibrium ecosystems where community dynamics naturally alternate between demographic expansions in a limited-resource environment, and pulse occurrences of mass-mortality events[10,13,14,15].In absence of major disturbance, occupation of habitats and community organization are mostly determined by distribution in primary resources and abiotic forcing, biotic interactions, and availability in refuges from different stresses[5,16]
By confronting long-term responses of coral communities to disturbances with functional models describing theory of non-equilibrium ecosystems, we evaluate the level of exposure and the degree of vulnerability of French Polynesian reefs to disturbances, and discuss key ecological processes that contributed to their successful and rapid recovery

Summary

Introduction

The concept of Earth’s ecological vulnerability has arisen and established as an undeniable global issue[1,2,3]. The Australian’s Great Barrier Reef has been subject to declines in water quality[27], major outbreaks of the coral predator crown-of-thorns starfish (COTS)[28] and intense cyclones[29] as well as unprecedented marine heatwaves[30,31] whose cumulative effects have come to undermine the historical resiliency of these reefs[23,32,33,34,35] This global demise of Nature is urging for investigations on the directionality and steadiness of community recovery, which can constitute a baseline for future management strategies. Long-term observations from the disturbance-driven French Polynesian outer-reefs provide a unique opportunity to evaluate coral resilience at large spatial scale[15,40]

Methods

Results

Conclusion