4.3.7—Climate change impacts

Heat stress can bleach corals by disrupting symbiosis; acidification changes carbonate chemistry and can reduce calcification. They are distinct pressures.

Warm water stresses coral physiology and may cause algal expulsion. Dissolved CO₂ lowers pH and carbonate availability. Storms, pollution and overfishing can add further stress.

On the Great Barrier Reef, marine heatwaves can trigger coral bleaching by disrupting the coral–algal symbiosis. Ocean acidification is a separate CO₂-driven pressure that reduces carbonate availability and can slow reef calcification; repeated stress can degrade habitat and food webs used by aquatic populations.

Temperature/bleaching data for heat stress; pH/carbonate and calcification data for acidification.

Both involve climate change, but one does not explain every observed coral impact.