Mean bleaching was 6.8 percentage points higher with high surface heat at 61 Reef Check sites matched by depth and month in 2003–2019

We tested whether coral bleaching was greater during high accumulated surface heat at the same site, recorded depth and calendar month. We used Reef Check records in the Global Coral-Bleaching Database, BCO-DMO version 2. High heat was supplied CoRTAD TSA_DHW of at least 4 °C-weeks. Low heat was at most 1 °C-week. We matched visits from different years, averaged contrasts within sites, and gave each site equal weight. The matched set had 226 visits at 61 sites in 2003–2019. Mean bleaching was 7.45% during high heat and 0.69% during low heat. The mean difference was 6.76 percentage points. A 95% interval from 10,000 draws of 21 spatial cells was 0.67 to 17.79 points. The median site difference was zero: 21 sites had a positive difference, 29 had zero bleaching in both classes, and 11 had a negative difference. Five sites in the Gulf of Thailand and the Lesser Sunda Islands and Savu Sea supplied 84.8% of the net contrast. Removing these two regions left a mean difference of 1.12 points at 56 sites. Removing one survey year at a time gave means from 3.97 to 9.27 points, with changing site support. A screen for implausible supplied climatology values retained a positive contrast. The result supports a positive but uneven association in the matched records. Only 1.6% of eligible sites met the match rules. The spatial interval is conditional on observed years. Selection, survey timing, changes in coral communities and surface heat measurement limit inference. The result does not estimate a causal effect or a universal bleaching threshold. The package contains source data, matched records, provenance, code, results, figures and reproduction steps.

coral bleaching · heat stress · Reef Check · matched surveys · spatial bootstrap · CoRTAD · reproducibility