The Bleaching Year: Q3 2010 and Jamaica’s Coral Under Thermal Stress

Briefing

• Sea surface temperatures exceeded bleaching thresholds for extended periods from July 2010.
• Scientists documented bleaching events at reefs island-wide including previously healthy sites.
• Partial mortality followed bleaching at some shallow reef sites by September.
• Event linked by scientists to La Niña conditions and underlying long-term warming trend.
• Tourism operators reported diver complaints about deteriorating reef appearance.

The 2010 bleaching event came after a period in which some of Jamaica’s reefs had been showing early signs of recovery from the mass bleaching and disease events of the late 1990s and early 2000s. The recovery had been tentative and unevenly distributed — some reefs were doing meaningfully better than they had been at the nadir of their post-die-off condition, others had remained in a state of persistent algal dominance with minimal coral cover — but the trajectory at the better-performing sites had been positive. The 2010 event interrupted that trajectory. Reefs that had been building coral cover over several years of relatively favourable conditions experienced bleaching that, where it was followed by mortality, set back the recovery process by a period that scientists estimated at several years.

The event was associated with La Niña conditions in the Pacific that were influencing Caribbean sea surface temperatures, layered on top of the underlying long-term warming trend that had been raising baseline Caribbean ocean temperatures for decades. The combination had produced a summer in which the number of degree heating weeks — the metric that coral scientists use to assess thermal stress on reef systems — had exceeded the threshold for mass bleaching across the entire island. The event was not the worst that Jamaican reefs had ever experienced; the Caribbean-wide event of 2005 had been more severe. But it was severe enough, and it came after a period of partial recovery in which the reefs had become more vulnerable to thermal stress than they would have been had they maintained more robust pre-bleaching coral cover.

The Climate Science Context

The scientists who published their assessments of the 2010 bleaching event were explicit about its relationship to climate change projections. The frequency of bleaching events severe enough to cause significant mortality was projected to increase as ocean temperatures rose; events that had been once-in-a-decade occurrences would, under most warming scenarios, become once-in-a-few-years occurrences by mid-century. The implication for reef management was stark: the conservation interventions that might allow Jamaican reefs to persist in a warmer world — reducing local stressors like overfishing and water quality degradation, which increased reef stress and reduced bleaching resistance — were necessary but not sufficient. Without action on the global emissions trajectory that was driving ocean warming, the local conservation gains were buying time rather than ensuring survival.

Tourism’s Interest

Dive tourism operators who were reporting diver complaints about reef appearance in 2010 were experiencing, in commercial terms, a consequence of the reef’s ecological condition that connected the environmental and economic arguments for reef conservation in a direct way. The reefs that Jamaica’s dive tourism market depended on were the same reefs that were bleaching. The tourism industry’s interest in reef health was not merely rhetorical, and the 2010 event focused some part of that industry on the climate dimension of reef conservation in a way that the abstractions of climate science had not previously achieved. Whether that focused interest would translate into industry advocacy for the emissions policy changes that reef survival ultimately required was, in 2010, an open question.

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