High-resolution modeling of thermal thresholds and environmental influences on coral bleaching for local and regional reef management

PeerJ. 2018;6:e4382 DOI 10.7717/peerj.4382


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Journal Title: PeerJ

ISSN: 2167-8359 (Online)

Publisher: PeerJ Inc.

LCC Subject Category: Medicine

Country of publisher: United States

Language of fulltext: English

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Naoki H. Kumagai
Hiroya Yamano
Committee Sango-Map-Project


Blind peer review

Editorial Board

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Time From Submission to Publication: 10 weeks


Abstract | Full Text | Full Text

Coral reefs are one of the world’s most threatened ecosystems, with global and local stressors contributing to their decline. Excessive sea-surface temperatures (SSTs) can cause coral bleaching, resulting in coral death and decreases in coral cover. A SST threshold of 1 °C over the climatological maximum is widely used to predict coral bleaching. In this study, we refined thermal indices predicting coral bleaching at high-spatial resolution (1 km) by statistically optimizing thermal thresholds, as well as considering other environmental influences on bleaching such as ultraviolet (UV) radiation, water turbidity, and cooling effects. We used a coral bleaching dataset derived from the web-based monitoring system Sango Map Project, at scales appropriate for the local and regional conservation of Japanese coral reefs. We recorded coral bleaching events in the years 2004–2016 in Japan. We revealed the influence of multiple factors on the ability to predict coral bleaching, including selection of thermal indices, statistical optimization of thermal thresholds, quantification of multiple environmental influences, and use of multiple modeling methods (generalized linear models and random forests). After optimization, differences in predictive ability among thermal indices were negligible. Thermal index, UV radiation, water turbidity, and cooling effects were important predictors of the occurrence of coral bleaching. Predictions based on the best model revealed that coral reefs in Japan have experienced recent and widespread bleaching. A practical method to reduce bleaching frequency by screening UV radiation was also demonstrated in this paper.