**3. Results**

There were significant differences in coral cover among study sites (one-way ANOVA, *p* < 0.05) (Figures 2 and 3). The highest percentages of live coral cover were found at Ko Ngam Noi (77.3 ± 9.3) and Ko Kula (57.7 ± 6.9) in Mu Ko Chumphon and at Ko Losin (West) (47.0 ± 18.0), Ko Losin (East) (45.7 ± 20.5) and Ko Losin (South) (26.7 ± 10.2), while the lowest coverage was observed at Ko Ngam Yai (5.4 ± 0.6). All study sites except Ko Ngam Yai had a higher percentage of live coral cover compared to dead coral cover.

**Figure 2.** Average percentage cover of live corals, dead corals and other benthic components at the study sites. Error bars indicate standard deviation.

**Figure 3.** Live coral cover at the study sites (one-way ANOVA, *p* < 0.05). Error bars indicate standard deviation. Different letters above bars indicate statistical differences (*p* < 0.05), as determined by Tukey's HSD.

All reef sites except Ko Kula harbored relatively high coral diversity. The highest resilience potential site was Ko Ngam Noi, which was dominated by *Acropora* spp. The high potential sites included Ko Kula, Ko Losin (West) and Ko Losin (East), while the low resilience-potential sites were Ko Ngam Yai and Ko Losin (South), which were dominated by *Porites lutea* (Figure 4). Overall, only Ko Ngam Yai had low resilience potential in terms of survival after bleaching and anthropogenic disturbances. The Shannon–Wiener index of diversity (H') was significantly different among the six study sites (one-way ANOVA, F = 25.27, *p* = 0.001). Tukey HSD tests showed that Ko Losin (East) was more diverse (H' = 1.7 ± 0.2) than Ko Kula (H' = 0.5 ± 0.1) (Figure 5).

**Figure 4.** Species composition of corals at the study sites. Error bars indicate standard deviation.

**Figure 5.** Shannon–Wiener index of diversity (mean ± SD) of coral species for each study site (one-way ANOVA, *p* < 0.05). Different letters above indicate statistical differences (*p* < 0.05), as determined by Tukey's HSD.

ANOSIM indicated significant differences in the taxonomic composition of corals between Ko Losin and Mu Ko Chumphon (R = 0.52, *p* < 0.001, Figure 6). The average similarity in the composition of coral species between Ko Losin and Mu Ko Chumphon ranged from about 41.64% to 69.62%, whereas dissimilarity between Ko Losin and Mu Ko Chumphon was 59.74% (SIMPER analysis), Table 2.

**Figure 6.** Two-dimensional non-metric multidimensional scaling (NMDS) plot of the taxonomic composition of corals at the study sites.


**Table 2.** Similarity percentage (SIMPER) analysis of benthic communities in two regions in the Gulf of Thailand.

The two-dimensional non-metric multidimensional scaling (NMDS) plot of the study sites based on the live corals, dead corals and other benthic components revealed that there were three groups of study sites, i.e., all three study sites of Ko Losin, Ko Kula and Ko Ngam Noi study sites, and Ko Ngam Yai study site (Figure 7).

**Figure 7.** Two-dimensional NMDS plot of the study sites.

Underwater photographs of the six study sites are shown in Figure 8. All study sites at Ko Losin and Ko Ngam Noi still displayed high live coral cover of *Acropora* spp., indicating that these reef sites were highly resilient to the coral bleaching events in 1998, 2010 and 2016.

**Figure 8.** Underwater photographs showing the dominant coral species at the study sites.

The total densities of juvenile corals, i.e., those less than 5 cm in diameter, at the study sites were in the range of 0.89–3.73 colonies/m2. The highest average density of juvenile corals was found at Ko Ngam Yai (3.73 colonies/m2), while the lowest average density was found at Ko Losin (West) (0.89 colonies/m2). The total density of juvenile corals at Ko Ngam Yai was significantly higher than that at Ko Ngam Noi, Ko Kula and all study sites of Ko Losin (one-way ANOVA; Tukey's HSD test; *p* < 0.05) (Figure 9). A total of 19 genera of juvenile corals were commonly observed, namely, *Pocillopora*, *Tubastrea*, *Montipora*, *Galaxea*, *Pavona*, *Pachyseris*, *Fungia*, *Lithophyllon*, *Hydnophora*, *Turbinaria*, *Lobophyllia*, *Favia*, *Favites*, *Oulastrea*, *Leptastrea*, *Cyphastrea*, *Porites*, *Goniopora* and *Plerogyra*. The juvenile corals of *Pocillopora* were dominant at all study sites except Ko Kula. The most dominant juvenile corals at the study sites of Ko Losin were *Pocillopora*, *Porites* and *Tubastrea*, while the dominant juvenile corals at the study sites of Mu Ko Chumphon were *Pocillopora*, *Porites*, *Fungia*, *Pachyseris*, *Pavona*, *Favites* and *Leptastrea* (Figure 10).

**Figure 9.** Densities of juvenile corals (mean ± SD) on available substrate at the study sites (one-way ANOVA, *p* < 0.05). Di fferent letters above bars indicate statistical di fferences (*p* < 0.05), as determined by Tukey's HSD.

**Figure 10.** Composition of the juvenile corals on available substrate at the study sites. Error bars indicate standard deviation.

ANOSIM indicated significant differences in the composition of juvenile corals between Ko Losin and Mu Ko Chumphon (R = 0.63, *p* < 0.001, Figure 11). The average similarity in the composition of juvenile corals between Ko Losin and Mu Ko Chumphon ranged from about 43.17% to 73.68%, whereas dissimilarity between Ko Losin and Mu Ko Chumphon was 63.81% (SIMPER analysis), Table 3.

**Figure 11.** Two-dimensional NMDS plot of the composition of juvenile corals at the study sites.



The juvenile coral densities of the brooder *Pocillopora* were relatively high at Ko Ngam Noi (0.37 ± 0.15 colonies/m2), Ko Losin Pinnacle (South) (0.66 ± 0.08 colonies/m2) and Ko Losin (West) (0.44 ± 0.05 colonies/m2). The juvenile coral densities of broadcast spawners at the study sites of Mu Ko Chumphon were much higher compared to those at the study sites of Ko Losin (Figure 12). Underwater photographs of the dominant juvenile corals, *Pocillopora*, *Porites* and *Tubastraea*, at the six study sites are shown in Figure 13. The juvenile corals were in healthy conditions without any signs of partial mortality or stress from competitors, diseases and bleaching.

**Figure 12.** Densities of juvenile corals on available substrate for broadcast spawners and brooders at the study sites. Error bars indicate standard deviation.

*Pocillopora Porites Tubastraea* 

**Figure 13.** Dominant juvenile corals on available substrate at the study sites.
