Back-to-back coral bleaching events on isolated atolls in the Coral Sea
Severe bleaching events caused by marine heat waves over the past four decades have now affected almost every coral reef ecosystem in the world. These recurring events have led to major losses of coral cover, with adverse consequences for tropical reef ecosystems and the people who depend on them. Here, we document two consecutive and widespread coral bleaching events on remote atolls in the Coral Sea in 2016 and 2017. In each year, the proportion of colonies that bleached was strongly related to heat exposure (measured as degree heating weeks, DHW, °C-weeks), depth and coral assemblage structure. Bleaching was more severe at higher DHW exposure and at sites with a higher proportion of susceptible taxa. Bleaching was also lower at 6 m than at 2 m depth. Despite the severe bleaching in 2016 on reefs in the central section of the Coral Sea Marine Park, total coral cover was not significantly reduced by 2017, suggesting that most bleached corals survived. Moreover, bleaching was less severe in 2017 despite a higher exposure to heat stress. These results indicate that while the isolation of these oceanic reefs provides no refuge from bleaching, low nutrient levels, high wave energy and proximity to cooler deeper waters may make coral on these reefs more resistant to bleaching-induced mortality.
KeywordsBleaching Coral reefs Marine heat wave Coral Sea Coral Sea Marine Park
This research was jointly funded by the Director of National Parks, Australia, an ACR Discovery Early Career Research Award to HBH (DE160101141) and the ARC Centre of Excellence for Coral Reef Studies. This research was conducted in the Coral Sea Marine Park under Permit No. CMR-16-000394 and CMR-16-000443. The authors wish to thank the relevant staff at Parks Australia, with particular mention given to Andy Warmbrunn, Jennifer Hoy, Bianca Priest, Samantha Fox and Jason Mundy. We thank Cpt Peter Sayre, Glenn Percy and the crew of the MV Phoenix for their assistance in the field. We are grateful to Thomas DeCarlo for producing Fig. 1b, c and two anonymous reviewers for their thoughtful comments. The findings and views expressed are those of the authors and do not necessarily represent the views of Parks Australia, the Director of National Parks or the Australian Government. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect the views of NOAA or the US Department of Commerce.
M.A.-N., A.H.B., H.B.H. and C.MacD. collected the field observations and S.F.H. collated the NOAA temperature data; A.H.B. and H.B.H. planned the study, and all authors analysed the data and wrote the paper.
Funding was provided by the Director of National Parks, Parks Australia, an ACR Discovery Early Career Research Award to H.B.H. (DE160101141) and the ARC Centre of Excellence for Coral Reef Studies.
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
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