Coral reefs are one of the most vulnerable marine ecosystems , and more than half of the world's reefs are under medium or high risk of degradation. Mass coral bleaching and mortality, triggered by positive temperature anomalies , is the most widespread and conspicuous impact of climate change. Ocean acidification reduces biodiversity and the calcification rate of corals  while at the same time increasing the rate of dissolution of the reef framework . 'In summary, ocean warming is the primary cause of mass coral bleaching and mortality , which, together with ocean acidification, deteriorates the balance between coral reef construction and erosion .'
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report