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A scientist in his laboratory is not only a technician: he is also a child placed before natural phenomena which impress him like a fairy tale.

               - Marie Curie

Coral reefs are more than a colorful underwater world that those of us in temperate regions see on the occasional vacation or in the odd Disney films. Coral reefs are the most biologically diverse marine ecosystems on the planet, what many call the “rainforests of the sea”. Millions of people in the tropical regions also depend on coral reefs every day, for shoreline protection, for food, and for income.

The dominant feature of these diverse ecosystems is a symbiosis between the corals (reef-building animals) and the microscopic algae (known as zooxanthallae or symbiodinium) which live in the coral tissue.

Corals themselves are white – the colour of the animal’s skeleton. In some species, there is pink or purplish hue due to some pigmentation in the animal. Most of the colour you actually see in corals when diving or snorkeling comes from the microalgae living in the transparent coral tissue.

The symbiosis is very sensitive to the environmental conditions. When stressed, the corals can “bleach”, either via expelling the microalgae from their tissues or from an internal breakdown of the symbiosis. My research has been found that increasing water temperatures have been found to cause mass coral bleaching events at reefs worldwide in recent decades.

I have been doing research on how climate change may increase the frequency of coral bleaching events worldwide and how the coral-algal symbiosis in different regions may have to adapt to ensure the long-term survival of coral reef ecosystems. The sensitivity of corals to increasing ocean temperatures is crucial to the conservation of coral reefs in the face of many other pressures like overfishing, sedimentation and disease. As one of the most sensitive ecosystems to temperature change, coral reefs can also be an important benchmark for climate change policy.

Want to learn more?

For some general information on the coral reef health and some interesting photos of bleached corals, check Coral Watch or Reefbase.

If you’re headed on a snorkeling or diving holiday in the tropics, take a look at Reefbase for any recent reports on the coral health at your destination. If you witness any extensive area of bleached or unhealthy corals, encourage your dive operation to submit a report.

If you’re wondering when and where coral bleaching may happen, my colleagues at NOAA's Coral Reef Watch track the occurrence of the thermal stress that can lead to bleaching in real-time using satellite observations of ocean temperatures.

 Coral reefs

Everyone's friend Nemo

Reef clean-up, Bali

Partially bleached coral 

  Reef fishing in Kiribati

 Feeding time