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UBC Theses and Dissertations

Assessing the extent of global mass coral bleaching with an updated database Virgen Urcelay, Alejandra


The recurrence of mass coral bleaching events and associated coral mortality driven by climate change in the past few decades has raised numerous questions about the future of coral reef ecosystems. Although these phenomena have been widely studied, our understanding of the geographical extent of these events has been limited. In this study, I present an updated version of the global mass coral bleaching database. The updated database provides the most comprehensive collection of global bleaching reports from 1963 to 2017, which were used to spatially model the probability of bleaching occurrence for 1985 through 2017 across the world’s warm-water coral reefs at a 0.05° x 0.05° resolution using indicator kriging. With this new spatially-explicit data, I provide a more accurate and up-to-date global and regional assessment of the extent of bleaching through the 1985-2017 period with a focus on the three global mass coral bleaching events that occurred in 1997-1998, 2009-2010, and 2014-2016. Results indicate that between 56% and 71% of the world’s coral reefs have experienced bleaching at least once during the assessed time period, with the greatest extents observed in the Southeast Asia, Australia, and Caribbean regions. High bleaching probabilities were more common towards the last decade of the period, and the most recent global bleaching event was assessed as up to 2.6 times more extensive than each of the first two. Results also show a positive relationship between the annual maximum Degree Heating Week, a measure of thermal stress, and high bleaching probability values. The updated database will help make global-scale analyses more robust, enhance real-time predictions, calibrate models for future projections, test for evidence of adaptive responses from corals and gain insights into the spatial-temporal trends of coral bleaching over time.

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