Chapter 02 · Nature, land & waterBiodiversity & Nature
Coral bleaching
Definition
Coral bleaching occurs when corals, stressed primarily by elevated sea temperatures, expel the symbiotic algae (zooxanthellae) living in their tissues. Because these algae supply most of the coral's energy, bleached corals turn white, stop growing and may starve; reefs can recover if conditions normalise, but recovery can take a decade or more. The Great Barrier Reef experienced six mass bleaching events between 2016 and 2025.
References
mechanism, Great Barrier Reef events, recovery timescales
Overview
What it means
Bleaching is a visible stress response and an early-warning signal of ocean warming, not necessarily immediate death — but repeated events erode recovery capacity.
How it is used
The term is used in marine science, reef monitoring (e. g. aerial and in-water surveys) and climate-impact communication, and underpins MPA management and restoration decisions.
Why it matters
Coral reefs support roughly a quarter of marine species; bleaching is among the clearest biological fingerprints of climate change.