Deeper Reef Check surveys averaged 0.29 percentage points less bleaching at 986 paired sites, 1–20 m, 1998–2020

We tested whether deeper Reef Check surveys recorded less population bleaching at the same site and date. We used BCO-DMO Global Coral-Bleaching Database version 2. We removed repeated sample rows and compared the shallowest and deepest recorded depths at each site-date. The primary set had 1,692 pairs at 986 sites in 49 country labels, from 1998 to 2020. Depths were 1–20 m, with a gap of at least 3 m. Median depths were 5 and 10 m. We first averaged paired differences within each site. Deeper surveys then averaged 0.289 percentage points less bleaching. The 95% interval from 10,000 spatial block draws was −0.604 to +0.019 points. Two stricter depth subsets showed small decreases. However, 998 pairs had zero bleaching at both depths. Only 96 pairs met a supplied surface heat-stress cutoff at both endpoints. Their mean difference was +0.362 points, with an interval of −3.323 to +4.142. The overall average contrast was small across these sampled dates. These data do not establish depth protection during severe heat stress. The package includes the matched table, raw data, source record, code, figures, and reproduction steps. This is an observational result within one survey programme. It does not measure survival or protection below 20 m.

coral bleaching · Reef Check · depth · paired surveys · spatial bootstrap · open data · reproducibility