Summary
Heat stress causes corals to expel their symbiotic algae, turning white and risking death.
In depth
Zooxanthellae are expelled when water is 1 to 2 °C above summer maxima for weeks. Corals can recover if stress subsides. Mass bleaching has occurred in 1998, 2010, 2016, 2017 and 2020s. Degree heating weeks measure stress.
Bleached corals starve if stress persists. Recovery takes a decade or more. Local stressors reduce resilience. Assisted evolution and shading are experimental.
Remember: bleaching is not death but a stress response.
Bleaching happens when stressed corals expel their symbiotic algae (zooxanthellae), exposing the white skeleton through transparent tissue. The main trigger is sea temperature 1 to 2 °C above the normal summer maximum for several weeks; other causes include pollution, low salinity and strong light.
Bleached corals are starved but alive and can recover if conditions improve within weeks; prolonged stress causes death, followed by algal overgrowth. Mass bleaching events have become more frequent, with global events in 1998, 2010, 2016 and 2023 to 2024. Degree heating weeks (DHW) from satellites predict risk.
Example: the Great Barrier Reef suffered consecutive bleaching in 2016 and 2017.
Key idea: some corals host heat-tolerant algae, offering hope for adaptation.
Frequently asked questions
What is Coral Bleaching?
Heat stress causes corals to expel their symbiotic algae, turning white and risking death.
Which area of biology covers Coral Bleaching, and how advanced is it?
Coral Bleaching is one of the 54 topics in Marine & Environmental Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Marine Genomics, Global Warming, Coral Reefs.
Can you give an example of Coral Bleaching?
Some corals associate with heat-tolerant symbionts.
What should I learn before Coral Bleaching?
Work through the Beginner topics in Marine & Environmental Biology first, such as Oceans, Ocean Zones, Plankton, then return to Coral Bleaching. Intermediate topics assume the Beginner vocabulary.
What topics are related to Coral Bleaching?
The closest topics to Coral Bleaching are Marine Genomics, Global Warming, Coral Reefs, Marine Symbiosis. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Coral Bleaching?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Coral Bleaching. To practise the whole of Marine & Environmental Biology, use the Marine & Environmental Biology quiz.
How is Coral Bleaching different from Marine Genomics?
Coral Bleaching: Heat stress causes corals to expel their symbiotic algae, turning white and risking death. Marine Genomics: Genome sequencing reveals adaptation to salinity, pressure and temperature in marine species. Read both side by side and note what each one explains.
How should I study Coral Bleaching step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Marine Genomics and explain the difference aloud. Finally, take the Marine & Environmental Biology quiz and come back to this page for any question you miss.