Remote Sensing of Coral Bleaching Using Temperature and Light: Progress towards an Operational Algorithm

William Skirving,Peter Mumby,Sophie Dove,Gang Liu,John Hedley,Susana Enríquez,C Eakin,Ove Hoegh-Guldberg,Alan Strong,Roberto Iglesias-Prieto,Jacqueline De La Cour,Robert Mason

doi:10.3390/rs10010018

Abstract

The National Oceanic and Atmospheric Administration’s Coral Reef Watch program developed and operates several global satellite products to monitor bleaching-level heat stress. While these products have a proven ability to predict the onset of most mass coral bleaching events, they occasionally miss events; inaccurately predict the severity of some mass coral bleaching events; or report false alarms. These products are based solely on temperature and yet coral bleaching is known to result from both temperature and light stress. This study presents a novel methodology (still under development), which combines temperature and light into a single measure of stress to predict the onset and severity of mass coral bleaching. We describe here the biological basis of the Light Stress Damage (LSD) algorithm under development. Then by using empirical relationships derived in separate experiments conducted in mesocosm facilities in the Mexican Caribbean we parameterize the LSD algorithm and demonstrate that it is able to describe three past bleaching events from the Great Barrier Reef (GBR). For this limited example, the LSD algorithm was able to better predict differences in the severity of the three past GBR bleaching events, quantifying the contribution of light to reduce or exacerbate the impact of heat stress. The new Light Stress Damage algorithm we present here is potentially a significant step forward in the evolution of satellite-based bleaching products.

Highlights

Corals live in an endosymbiotic relationship with unicellular algae forming what is referred to as the “holobiont”
This paper describes a methodology that is planned to underpin a major evolution of the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch program (CRW) satellite products
Demonstrating the Light Stress Damage (LSD) algorithm required a location that had a long, continuous dataset of quality PAR measurements, reliable sea surface temperature (SST) data and a complete and thorough set of in-water surveys to ensure that all bleaching and non-bleaching events were known. No such sites were found in the Caribbean; a useful site was located in the southern Great Barrier Reef at the Keppel Islands, Australia (Figure 2)

Summary

Introduction

Corals live in an endosymbiotic relationship with unicellular algae forming what is referred to as the “holobiont”. These dinoflagellate algae (genus Symbiodinium), collect light and perform photosynthesis, transferring energy to the coral. Coral bleaching refers to the dramatic loss of the Symbiodinium population that inhabits coral tissues, leaving the coral polyps transparent and making visible the underlying white calcium carbonate skeleton. This occurs when the symbiosis breaks down under any stressful condition that pushes the symbiosis beyond its limits of stability. It is important to distinguish between coral bleaching and coral holobiont homeostatic adjustments to the environment, since bleaching involves a dramatic change in coral pigmentation but is an indication of a dysfunctional condition of the symbiotic relationship

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