GCRMN_COI_2017-Western Indian Ocean Reef Status

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Coral reef status report for the Western Indian Ocean (2017) Global Coral Reef Monitoring Network Fish community structure has also shown an important change. Presumably before the 1998 bleaching (and certainly before the advent of heavy fishing pressure in earlier decades), functional group structure would have been diverse, representing a balanced food web. It has now shifted to strong dominance by herbivores and detritivores (about 80% of fish biomass), and increasingly, by smaller-bodied individuals of these functional groups. Coral bleaching - 2016. The second largest bleaching event in the WIO occurred in 2016, with just over one third of reported sites affected by severe bleaching at its peak in April-May 2016. Seychelles was the most affected by bleaching with over 50% of reported sites showing high or extreme bleaching, closely followed by Tanzania and Mauritius. Fortunately, the high and extreme levels of bleaching did not translate into the same level of coral mortality, with less than 10% of sites reporting severe mortality. However, the region did not survive completely un-scathed with over 70% of reports recording some level of mortality. The future? Western Indian Ocean coral reefs seem to have shifted from a pre-1998 state to a post-1998 state with 25% lower coral cover and 2.5 times algae abundance. For almost 2 decades, coral and algal cover have been equivalent, which may be an early indicator that at the regional scale, reefs are approaching a threshold past which they may become dominated by algae, or by other non-hard coral invertebrates. This may be exacerbated by the fish communities also shifting from more complex to simpler trophic webs in which herbivory and detritivory by small-sized fish are dominant processes. EXECUTIVE SUMMARY Exactly what the implications of these regional trends in coral and algal cover and fish community structure are likely to be is difficult to predict. Coral cover experienced another step decline due to the bleaching event of 2016, but fortunately the decline in the order of 10%, is less than the 25% decline documented in 1998. Fishing pressure on reefs continues to increase with human population growth and migration to the coastal zones. The latter will also drive up pollution and eutrophication on coral reefs, providing bottomup fuel to the increasing role of algae and herbivory/detritivory as dominant processes. Ongoing climate change is already inducing more frequent major coral bleaching and disease events, and acidification will increasingly undermine the ability of corals to resist other threats. In coming years, will algal cover continue to increase above the level of hard coral cover? And if this happens, as more and more individual reefs decline, will it become harder and harder to return coral reefs to a coral-dominated state from local to national and regional levels? The results of coral reef monitoring from 1992 to 2016 paint a clear picture for coral reefs in the Western Indian Ocean. While the current state is reasonably good in terms of coral cover, the high algal cover may be a sign of vulnerability to future changes. To have any hope of coral reefs resisting and recovering from major threats, climate change must be addressed globally with greenhouse gas emissions reduced sharply to meet the Paris Agreement levels. On the other hand, local drivers of decline must also be reduced as far as possible to limit the number of and interactions between threats. Increasing ‘effective management’ to all coral reef areas is a goal that should be attractive to key reef stakeholders such as local and national government, fishers and tourism operators, as this will be the only way to sustainably derive benefits from coral reefs in a warming and increasingly populated world. xiv
Coral reef status report for the Western Indian Ocean (2017) Global Coral Reef Monitoring Network Recommendations Regional reef health – in relation to the overall health of coral reefs in the Western Indian Ocean: • Countries, reef managers and resource users across the region should recognize that the health of the region’s reefs has undergone a step-decline after the 1998 mass coral bleaching event • Similarly, the bleaching event in 2016 likely means a second step-decline in reef health regionally • An institutional anchorage of the national reef network to the national network of protected areas in association with the University of Comoros and active NGOs would be desirable Conclusion - to maximize coral reef health, it is imperative to implement even stronger management measures than those in place from 1999-2015,. Recognizing this through regional and continental mechanisms, and in national coral reef, coastal management and development policies, will be essential to motivate for and enforce the broader actions needed to cope with the likely reduced health of reefs in the future. Scaling up of efforts needs to be sufficient to meet the 10% coverage of well-managed areas envisaged in SDG 14 Target 2 and Aichi Target 11 by 2020, with a clear long term goal that this should increase to the broadly accepted 30% target by 2030. Actions and interventions – should focus on building the resilience and recovery ability of coral reefs, as well as of management systems to protect coral reefs: • Improve the management of protected areas, fishery grounds and other use-areas to minimize and even eliminate impacts to critical habitats. Local, national and regional connectivity and integration of protected areas and management principles should be a priority. • Improve the scope and coverage of area-based management tools, including monitoring, habitat maps, economic valuations, and others. • Promote the full range of management models (regimes), including government-run, co-managed and privately-managed areas. Ensure staffing is at appropriate levels, with training programmes to build capacity and cope with staff turnover. • Manage fisheries to maintain taxon and functional group diversity, and limit selective impacts to key trophic groups (secondary consumers/predators as well as herbivores). No-take areas are necessary to maintain fish community structure in key areas, but effective fisheries management may be sufficient in broader areas to maintain the ecological functions of fish. • Manage and reduce bottom-up factors that promote algal growth, including sewage from coastal towns and tourism areas, river discharge of sediments and nutrients, and surface runoff. Land-use change and waste management on land are the primary mechanisms for effecting these changes, so reef management should be fully integrated with land-based management measures. EXECUTIVE SUMMARY xv
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GCRMN_COI_2017-Western Indian Ocean Reef Status

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