Phase III – Preparing for climate change by identifying practical coral reef fisheries and protected area management options in the Western Indian Ocean

The research presented in this report develops a synoptic view of the biodiversity and resilience of coral reefs to climate change in the western Indian Ocean. Studying reefs over a gradient of environmental variability, we tested for differences in corals’ acclimatization and adaptation response to climatic fluctuations and changes expected with global warming. The study had three major foci: one on the ecology of coral reefs, a second on the ecology of algal symbionts in corals, and finally, an evaluation of the types of management restrictions that coral reef stakeholders in the region prefer and are likely to support. The combination of the ecological and management preference studies identified priority areas and conservation actions. Studies were undertaken throughout the western Indian Ocean and compared with all available published and unpublished data to develop the broadest view provided by the current science. 

Ecological studies focused on assessing benthic cover (of corals and other functional groups), coral community structure, and bleaching response, and relating these to management type (fished reefs vs. fisheries closures), and physical environmental conditions (exposed vs. sheltered) and before, immediately after, and 7 to 10 years after the 1998 mass coral bleaching mortality). Coral cover was lowest in the period immediately after 1998 and decreased with latitude going northward. Fishery closures had lower coral cover than fished reefs during this period. Analysis of late post-1998 data indicated that sheltered reefs (behind reefs and islands) had higher cover than exposed reefs. Acroporid and pocilloporid corals showed changes in cover that were opposite to those in Poritiids and were more abundant on exposed reefs in the south, reflecting weaker patterns in bleaching in the south and, therefore, higher coral community susceptibility in the south. Coral taxonomic richness was higher in closures, particularly sheltered closures, and richness and diversity increased northward. Fleshy algae dominated on fished reefs in high-energy areas in the south. Patterns of coral and benthic composition in the region reflected the strong impact of the 1998-bleaching disturbance in the central northwestern Indian Ocean. The study suggests a strong positive relationship between total coral cover and cover of bleaching susceptible taxa, such Acropora and Montipora. Exposed reefs suffered the highest declines in cover in 1998, which is contrary to assumptions that exposure mitigates the impact of coral bleaching. The highest priority areas for securing corals against the future impacts of climate change and fishing are sheltered reefs, such as reefs behind islands, in enclosed bays, and back reefs. 

Studies of the algal symbionts (Symbiodinium spp.) in these corals were undertaken to evaluate their ecology and potential value in promoting adaptation to climate change. Large-scale regional studies of algal symbiont distribution indicate that Symbiodinium in clade C is the most common and is a broad tropical generalist. Clade D is less common and found in more specific environments where temperatures are high and often variable, including dominance in some shallow fringing reefs of Kenya and high abundance in northwest Madagascar. Changes in the relative frequency of clades C and D at different sites in Kenya depended on coral taxon and interacted strongly with location (driven by variation in temperatures at different sites) and weakly with time. 

Some coral taxa, such as Pavona and Pocillipora, frequently hosted clade D and are increasing on Kenyan reefs. Branching Porites and Acropora have stronger associations with clade C, and their populations are declining. There was some evidence that strong thermal anomalies can promote changes in symbionts from C to D in some coral taxa, but this change may not persist beyond five years after the disturbance unless background temperature anomalies, or continued warming, continue to promote clade D. Given that sheltered reefs are the most likely to persist under climate change due to associations with acclimatization and community changes in the symbionts, these reefs are high priority sites for increasing management restrictions. 

The regional evaluation of management preferences indicated that there is generally broad-scale support for management restrictions, particularly gear and minimum size restrictions. There was support for restrictions on space, such as no-fishing closures, species, and temporal closures, but there were also several communities (in all countries) that did not support these restrictions. Communities with a long history of marine protected areas tend to support closures, especially those that are less reliant on marine resources, supporting the need for diversified and profitable alternative livelihoods. Consequently, we recommend the introduction and enforcement of broad-scale gear and size restrictions at the national and regional levels, and the immediate implementation of more site-specific closures and species restrictions in supportive communities. Greater interaction and communication between communities with positive views on restrictions and those with negative views is expected to increase support for the implementation and evaluation of these restrictions at the regional scale. There is an immediate need to increase the successful co-management of sheltered coral reefs to ensure they persist as refuges from climate change.