Response to coral bleaching for 7368 coral colonies exposed to similar levels of temperature stress at a similar depth of occurrence and similar subsequent mortality. Collected in situ following  moderate thermal bleaching events in the GBR in 2002 and the Maldives in 2016. Data gives species, site, depth of occurence and bleaching response which was scored by tissue colour.   

For the GBR in 2002 and the MA in 2016, sea surface temperatures (SSTs) exceeded bleaching thresholds over wide areas for several weeks (NOAA, 2021), resulting in mortalities at some sites to 68% and 86% respectively (Cowburn et al., 2019; Done et al. 2003). We restricted our analyses to sites with a DHW of between 4 and 7, which is currently considered moderate bleaching stress (NOAA 2021, Skirving et al., 2019). Ten locations (30 sites) from the Maldives were included, all within the large (~2000 km²) Ari Lagoon complex on high coral-cover reef slopes adjacent to small islands with little or no human populations (Figure 1a). Sites were protected from most ocean swells and extended to a sandy base at 20-30 m depth. Included sites for the GBR (14 locations, 22 sites) were also situated on high coral-cover reef slopes within the large GBR lagoon complex (Figure 1b). These sites were either adjacent to small islands or on the back, lagoon or southern slopes of mid or outer shelf platform reefs.

At each site, timed surveys using SCUBA or snorkel dives of 45-80 minutes duration were conducted, recording bleaching responses and recent mortality of individuals according to standard methods. Species identifications were mostly made in situ, with high-resolution macro photographs or small samples taken from problematic morphotypes (under permit) for later analysis by comparison with material available in the Queensland Museum, consultation with relevant experts and reference to standard texts (see Supporting Information for details). Both datasets were converted to current valid species (Hoeksema & Cairns, 2019). For certain genera (e.g. Montipora, Porites, Goniopora and Cycloseris) it was not possible to accurately assign a species or morphotype in situ, so these were assessed as grouped species and only considered in a supplementary analysis.

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