|Title||Caribbean massive corals not recovering from repeated thermal stress events during 2005-2013|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Neal B.P, Khen A., Treibitz T., Beijbom O., O'Connor G., Coffroth M.A, Knowlton N, Kriegman D., Mitchell B.G, Kline DI|
|Journal||Ecology and Evolution|
|Type of Article||Article|
|Keywords||bleaching event; Bocas del Toro; climate change; climate-change; Coral bleaching; coral reefs; great-barrier-reef; growth-rates; montastrea-annularis; ocean acidification; Orbicella franksi; partial mortality; resilience and recovery; Siderastrea siderea; siderastrea-siderea; Stephanocoenia michelini; us virgin-islands|
Massive coral bleaching events associated with high sea surface temperatures are forecast to become more frequent and severe in the future due to climate change. Monitoring colony recovery from bleaching disturbances over multiyear time frames is important for improving predictions of future coral community changes. However, there are currently few multiyear studies describing long-term outcomes for coral colonies following acute bleaching events. We recorded colony pigmentation and size for bleached and unbleached groups of co-located conspecifics of three major reef-building scleractinian corals (Orbicella franksi, Siderastrea siderea, and Stephanocoenia michelini; n=198 total) in Bocas del Toro, Panama, during the major 2005 bleaching event and then monitored pigmentation status and changes live tissue colony size for 8years (2005-2013). Corals that were bleached in 2005 demonstrated markedly different response trajectories compared to unbleached colony groups, with extensive live tissue loss for bleached corals of all species following bleaching, with mean live tissue losses per colony 9 months postbleaching of 26.2% (+/- 5.4 SE) for O. franksi, 35.7% (+/- 4.7 SE) for S. michelini, and 11.2% (+/- 3.9 SE) for S. siderea. Two species, O. franksi and S. michelini, later recovered to net positive growth, which continued until a second thermal stress event in 2010. Following this event, all species again lost tissue, with previously unbleached colony species groups experiencing greater declines than conspecific sample groups, which were previously bleached, indicating a possible positive acclimative response. However, despite this beneficial effect for previously bleached corals, all groups experienced substantial net tissue loss between 2005 and 2013, indicating that many important Caribbean reef-building corals will likely suffer continued tissue loss and may be unable to maintain current benthic coverage when faced with future thermal stress forecast for the region, even with potential benefits from bleaching-related acclimation.
The concept that bleaching is exceeding the inherent necessary recovery period for these corals is supported by this study as all three species (in aggregate) ended the time series having experienced net loss of live tissue, regardless of prior bleaching history. This outcome did vary by species, but the living tissue decline for all of these three critical ecosystem-structuring species when faced with repetitive thermal stress suggests that Caribbean reefs may face massive challenges in a warmer future. If thermal stress and bleaching events increase in frequency and severity, and there is no acclimative increase in colony resilience, then the future persistence of massive-type corals in the western Caribbean appears possibly uncertain.