Coral reefs are crucial, vibrant ecosystems often described as the rainforests of the ocean. Despite covering less than 1% of the ocean floor, they provide immense ecological and economic value — offering shelter and food for thousands of species, including a quarter of all known marine fish species, and generating an estimated $9.9 trillion annually.

However, coral bleaching is accelerating reef decline. Half of the world's coral reefs have already been lost, threatening biodiversity, ecosystem stability, and the livelihoods of coastal communities.

What is Coral Bleaching?

Coral bleaching is the process by which corals expel the microscopic algae (zooxanthellae) from their tissues. These algae provide corals with 90–95% of their energy and give them their vibrant colour. Without them, corals enter a starved state and appear white as their calcium carbonate skeletons become visible. Bleached corals are not dead — if conditions improve quickly they can recover. However, if not, they will die.

What Causes Coral Bleaching?

The primary trigger is elevated seawater temperatures. Other stressors include high levels of sunlight, cold seawater temperatures, sudden changes in salinity or pH, and poor water quality.

Measuring Heat Stress: Degree Heating Weeks

Degree Heating Weeks (DHW) measure how much, and for how long, seawater temperatures exceed the average warmest monthly temperature. At 4 DHW, bleaching is expected. At 8 DHW, significant mortality is likely. During the current global bleaching event, some regions have recorded DHW values exceeding 12°C-weeks.

Can Coral Reefs Recover?

Yes — if stressors are reduced and corals are given enough time to recover. But time is running out. Scientists and practitioners around the world are designing and implementing cutting-edge techniques to preserve and restore coral reef ecosystems. At Ocean Revive, we're contributing to this global effort by restoring coral resilience through science, innovation, and collaboration.

References

  • Anthony, K.R. et al., 2009. Energetics approach to predicting mortality risk from environmental stress. Functional Ecology, 23(3), pp.539–550.
  • Hughes, T.P. et al., 2018. Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science, 359(6371), pp.80–83.
  • Spalding, M.D. et al., 2001. World Atlas of Coral Reefs. UNEP-WCMC.