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The Absolute Resilience of French Polynesian Reefs to Environmental Disturbances

Paper Reviewed
Vercelloni, J., Kayal, M., Chancerelle, Y. and Planes, S. 2019. Exposure, vulnerability, and resiliency of French Polynesian coral reefs to environmental disturbances. Scientific Reports 9: 1027, doi:10.1038/s41598-018-38228-5.

Increasing efforts have been expended to assess both the vulnerability and resilience of natural ecosystems to disturbances resulting from climate change. The latest work to dive into this topic -- at least for coral reefs -- comes from the research team of Vercelloni et al. (2019), who evaluated coral recovery trajectories by analyzing long-term data on coral community dynamics with a set of functional non-equilibrium ecosystem response models.

The setting for the authors' work was French Polynesia, where detailed coral observations have routinely been made (approximately every 2 years) at 17 reefs located on 13 different islands within a geographic spread of over 15° of longitude and 10° of latitude since 1994. Using coral community dynamics data collected from the outer-reef slopes between the 14-year period 1994-2008, Vercelloni et al. quantified "levels of exposure, degrees of vulnerability, and descriptors of recovery" in the reef communities in the face of three major types of disturbances, namely, tropical cyclones, temperature-induced bleaching events and crown-of-thorns starfish outbreaks. And what did their study reveal?

First off, at least one major episode of each type of severe reef disturbance occurred during the analysis period. And although such disturbances varied in terms of the magnitude and spatial extent, approximately 42% of the surveyed reefs were affected in at least some manner during the analysis period, with the most severely-affected reefs suffering an average 76% decline in coral cover.

With regard to their recovery and resilience, Vercelloni et al. report that "despite undergoing a sustained regime of intense disturbances of multiple types, the French Polynesian outer-reef system shows a particularly high resilience capacity, with full recovery in coral cover repeatedly observed within 5-10 years following mass mortality events." They also note that "no major decline without subsequent recovery was observed on any reef, confirming that the coral communities systematically bounce back following mortality events and thus the reefs possess a high resiliency," which resiliency, they add, was "driven by the elevated ability of coral larvae to repopulate reefs shortly after the impacts of disturbance, which implies a sustained connectivity among populations on spatial scales that extend beyond the range of disturbance."

The above findings are very encouraging and attest to the ability of coral reefs to successfully respond and cope with severe environmental disturbances, including temperature-induced coral bleaching events. And that is a major ray of light among the darkened projections of imminent reef collapse from global warming that climate alarmists say will cause an increase in the frequency and severity of coral bleaching events.

Posted 19 April 2019