The Great Reef of Toliara, on the southwestern coast of Madagascar, has been documented as harbouring flourishing reef communities in the 1960s, but has since been affected by various threats, causing a coral decline last reported in 2008. In 2017, we examined the spatial heterogeneity in coral community structure in the region of Toliara. Coral assemblages were characterized by a marked spatial variability, with significant variation for most of the descriptors among the three major habitats and also among stations within habitats. We recorded high coral cover, with values >40% at six of the 10 stations, which was associated with high abundance of coral colonies. We also documented the return to an Acropora-dominated coral assemblage. While these positive results suggest a recent return to healthier coral assemblages, they must be tempered, as the diversity that we recorded was lower than in the 1960s. Moreover, we found a high cover of algae at several stations, suggesting that the ecosystem is likely close to the tipping point toward a phase shift. Finally, the population size-structure of major coral taxa was positively skewed, with few large colonies to ensure the replenishment of local populations. The marked spatial variation suggests that marine protected areas should integrate a sufficiently large area to capture the scale of this spatial heterogeneity.

Madagascar is a major hotspot of biodiversity in the Western Indian Ocean, but, as in many other regions, coral reefs surrounding the island confront large-scale disturbances and human-induced local stressors. Conservation actions have been implemented with encouraging results for fisheries, though their benefit on coral assemblages has never been rigorously addressed. In this context, we analyzed the multiscale spatial variation of the composition, generic richness, abundance, life history strategies, and cover of coral assemblages among 18 stations placed at three regions around the island. The potential influences of marine protected areas (MPAs), algal cover, substrate rugosity, herbivorous fish biomass, and geographic location were also analyzed. Our results highlight the marked spatial variability, with variation at either or both regional and local scales for all coral descriptors. The northeast coastal region of Masoala was characterized by the high abundance of coral colonies, most notably of the competitive Acropora and Pocillopora genera and stress-tolerant taxa at several stations. The southwest station of Salary Nord was distinguished by lower abundances, with depauperate populations of competitive taxa. On the northwest coast, Nosy-Be was characterized by higher diversity and abundance as well as by high coral cover (~42–70%) recorded at unfished stations. Results clearly underline the positive effects of MPAs on all but one of the coral descriptors, particularly at Nosy-Be where the highest contrast between fished and unfished stations was observed. Biomass of herbivorous fishes, crustose coralline algae cover, and substrate rugosity were also positively related to several coral descriptors. The occurrence of reefs with high diversity, abundance, and cover of corals, including the competitive Acropora, is a major finding of this study. Our results strongly support the implementation of locally managed marine areas with strong involvement by primary users, particularly to assist in management in countries with reduced logistic and human resources such as Madagascar.