**2. Results**

Six coral reef sites were monitored in the Alifu Alifu and Baa Atolls in the Republic of Maldives (Figure 1) to assess post-bleaching coral mortality. The percentage of live coral cover at each coral reef site (*n* = 6) and depth was variable and ranged between 3% and 26% of substrate cover in December 2016, following the peak of the heating event that occurred in May of the same year (Figure 2). Of all the sites, live coral cover was lowest at Hurasdhoo, with an average of 3 ± 4% (mean ± standard error, *n* = 51) at deep sites (Figure 2). No records were available for this site at shallow depths. All other sites had similar live coral cover at shallow depths, ranging from 13 ± 8% (*n* = 34) at Rasdhoo to 26 ± 13% (*n* = 51) at Dhonfanu (Figure 2). Live coral cover at depth had a similar range, from 13 ± 14% (*n* = 51) at Nika Point to 27 ± 12% (*n* = 51) at Dhonfanu (Figures 2 and 3).

**Figure 1.** Reef site locations within the northern atolls (Baa and Alifu Alifu Atolls) of the Republic of Maldives. Sampling locations are marked with a black dot on the map.

Recently dead coral, classified as coral skeletons covered with turf algae but with the skeleton still intact, was also abundant at each of the sites surveyed (Figure 2). At shallow depths, this was as high as 54 ± 19% (*n* = 52) of the substrate cover at Digga Thila (Figure 2). The percentage of recently dead coral at shallow transects at all other sites ranged from 12 ± 8% (*n* = 50) at Nika Point to 40 ± 14% (*n* = 51) at Dhonfanu (Figure 2). Of the deep transects, the percentage of recently dead coral was highest at Hurasdhoo, averaging 41 ± 25% (*n* = 51), although this was highly variable between transects and replicates (Figure 2).

Very few coral colonies were still bleached, with translucent live tissue covering the skeleton, at the time of data collection seven months after peak heat stress. The total substrate covered by bleached corals ranged from 0.1 ± 0.7% (*n* = 54) to 2.9 ± 7.6% (*n* = 54) across all reef sites and depths.

Modelling of variables influencing the percentage cover of live coral suggested that the best model fit was obtained when including additive effects of reef site, depth, and morphology (Table 1). When accounting for these variables, live coral cover was estimated to be considerably lower at Hurasdhoo (3% live cover, with confidence intervals (CI) of 2–5%), compared with all other reef sites, over which coral cover ranged from 18% (15–22% CI) to 29% (25–34% CI) (Figure 4a). Mean live coral cover was found to be higher at deep rather than shallow sites, estimated to be 23% (19–27% CI) and 16% (13–19% CI), respectively (Figure 4b). In addition, mean live coral cover was found to be greater in massive corals than branching corals, estimated to be 33% (27–39% CI) in massive corals and 6% (5–7% CI) in branching corals (Figure 4c).

**Figure 2.** Box and whisper plot showing the percentage of substrate cover of live corals and recently dead corals at both shallow and deep transects at each of the six reef sites surveyed.

**Figure 3.** Extensive stands of dead corals (*Acropora* spp.) in the Maldives, where reefs exhibited high levels of coral mortality in December 2016 following the 2015–2016 El Niño mass coral bleaching event ((**a**) and (**b**)).


**Table 1.** Generalised linear mixed effect model (GLMM) fit statistics investigating the most important variables influencing both (**a**) live coral and (**b**) recently dead coral. Shown are the number of parameters (*n*), Akaike information criteria (AICc), δ AICc, and AICc weight (ωi). The best fitting model is highlighted in bold.

**Figure 4.** Predicted percentage of substrate cover of both live coral and recently dead coral by (**a**) reef, (**b**) depth, and (**c**) morphology, with 95% confidence intervals.

Modelling the cover of recently dead coral also suggested the best fitting model included additive effects of reef site, depth, and morphology (Table 1b). The percentage of dead coral cover at each reef site varied. The highest percentage was found at Hurasdhoo, with 56% (±45–69%) recently dead coral cover, whereas the remainder of the reef sites ranged from 19% (±15–23%) to 29% (±24–36%) (Figure 4a). Overall, there were more recently dead corals at shallow depths, with estimates of 35% (±28–43%) compared to 24% (±20–29%) at deep sites (Figure 4b). Estimates of recently dead massive corals were also lower than those for branching corals, with massive estimates of 17% (±14–21%) and branching estimates of 42% (±34–52%) (Figure 4c). The percentage of cover of recently dead corals was inverse to the trends observed for live coral cover (Figure 4).
