Main Findings

• In 1998, coral reefs in the Western Indian Ocean crossed a threshold, due to impact of the 1st global bleaching event in that year.
  • On average, coral cover declined by 25% – from 40% before 1998 to 30% after 1998.
  • Algal cover increased by 2.5 times after 1998, from 15% before to about 35% after.
  • Fish community structure is now dominated (about 80% of biomass) by small-bodied herbivores and detritivores.
• In 2016, the 3rd global bleaching event impacted the WIO, with 30% of reefs showing evidence of high or severe bleaching, but only 10% showing high or severe mortality.
• The threat from all major drivers of reef decline has increased and is projected to continue to increase in the coming decades – ocean warming and acidi cation, shing pressure, human population growth and development in the coastal zone, expanding global trade.

• The future

• While resistance of corals to the 2016 bleaching event was signi cant (2 of affected corals recovered) and the decline in coral cover resulting from the bleaching event was less than in 1998, the recovery potential of reefs is likely to be less than in 1998 due to the lower coral cover, higher algal cover, and increasing role of algal-herbivory dynamics.
• The broad-based coral reef monitoring community in the Western Indian Ocean is active, but would bene t from increased investment and stability, and more secure data management and sharing practices.
• Management of local threats and increasing the coverage of effective management to
  meet 2020 and 2030 targets will be needed to buy time for coral reefs, while countries increase their commitments to achieve the Paris Agreement.