Global Warming and Coral Bleaching

Mass coral bleaching cases have increased drastically over the last 20 years. This is seen to be directly linked to the amount of emissions and pollution produced by the ever growing human race. Coral reefs have been developing for over 25 million years, yet we are seeing whole reef systems being destroyed in fewer than 10. This surely is a very important matter that we as a population must address.

Mass coral bleaching has been around for over 30 years, but it is only in the last 20 that the situation has become so serious that whole reef systems have been lost.


Diagram showing mass coral bleaching cases in severity from 1998 – 2006.

Here the diagram clearly shows that the number of coral bleaching cases has risen drastically and that the number of severe cases has spread across the globe. This is believed to be a direct result to the rising temperature of our atmosphere and is just one of the reasons on the long list of why global warming needs to be dealt with.

Even though coral reefs only take up 1% of the earth’s surface, it is home to 1.5 – 2 million different species, Marshall. P (2008). Physically being the largest biological structures known to man these habitats need to be protected and managed in a way that allows for positive repair and growth so that we don’t lose them to the timeline. But are we too late? It is debatable whether the amount of damage that has already been caused will ever be restored, but to try is the only way to prove if it can be or not.

Coral Bleaching is the process of the corals that inhabit the reef losing a special type of algae from there tissues. This alga is called Zooxanthellae, and it is what gives all of the coral species there brown or green colours. These microscopic algae live inside the tissue of the coral, they are found close to the skin as they are photosynthetic and need vast amounts of sunlight to photosynthesize. This stress causes a chain reaction meaning the coral expel there precious algae. This means that coral loses its colour, becoming a bone white colour, but even more importantly means that the coral has no source of energy and therefore cannot perform any of its daily tasks, resulting in the coral dying. This process is very quick, it can take under a month for the coral to expel all of its Zooxanthellae and shortly after the coral dying. It is possible for the coral to recover but the stressor must be removed from the coral as soon as possible for the coral to re-ingest the Zooxanthellae and for them to start there symbiotic relationship again.

reefsssCoral reefs have been proved to bleach in many different circumstances, for example if there is an increase in the amount of sediment in the water, this clogs the coral polyps and can cause them to bleach. Another example is that pollutants cause a stress reaction that also can cause bleaching, but the biggest problem is temperature and acidity.

It starts with the sea temperature rising. This rise can be no more than 1-2 ˚ C but is all that is needed to begin this process. The rise in temperature means that the Zooxanthellae, the pigmented algae, cannot photosynthesize with producing an oxygenizing agent, this is harmful to the corals tissue and damages it. One of two things then happen Zooxanthellae, the first is that it will degrade inside the tissue of the coral. The other is that coral expels the algae to prevent any further damage to its tissue. In the end the coral is left with no algae, this is what gives the white appearance in colour and means that it will slowly die.

This however is not the end of the corals life. If the temperature can be lowered in time the coral will simply absorb, by means of digestion, more Zooxanthellae from the water column and can make a full recovery. It is reducing the temperature which is the biggest problem of all. We as a population have to change the way we live our lives immediately if we are to prevent the loss of our coral reef systems. If we don’t, there is simply no other way in which the reefs will survive




Marshall, P. (2008) A Reef Managers Guide to Coral Bleaching. Great Barrier Reef Marine Park Authority.

8 years ago

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