Coral Bleaching

BY Cecilia GIMENO VEIRA, EEB4, S6FRD

What is coral bleaching ? 

Many types of corals need a tiny marine algae called zooxanthellae in order to survive. These algae live in the corals’ tissue and provides 90 % of the energy that corals need to grow and reproduce. They also give coral much of their color.

Coral bleaching occurs when the relationship between the algae and the coral breaks down. Without these algae the tissue of the coral appears transparent and the white skeleton of the coral is revealed. Once they start to bleach, corals begin to starve. A small percentage of the corals are able to nourish themselves, while the majority will struggle to survive without the zooxanthellae.

In order to survive and regain their natural colour, the conditions must return to normal and corals need to regain the zooxanthellae. Corals live under stress because they do not have the algae to survive; this causes a decrease in the growth of corals and reproduction, as well as an increase in diseases. Bleached corals often die if the stress persists. Coral reefs that have high rates of coral death followed by bleaching can take many years or even decades to recover.

Why is coral bleaching happening?

Warmer or cooler water temperatures can cause coral bleaching. When the oceans are too warm or too cold due to climate change, corals will expel the algae that live in their tissue. The rise of sea levels due to melting ice because of climate change, also disturb the algae from their natural habitat. They go live somewhere else where there is a presence of corals and also where the environmental conditions are favorable to their development.  If conditions return like they used to be, the chances that the algae restore themselves back to their original state are very high .

Can coral survive after they bleached?

If the stress that the corals endure is not severe, corals would know how to recover. If the loss of the algae and the stress are prolonged, corals eventually die. When corals bleach,  they can survive but are under more stress and eventually die if the zooxanthellae do not return. Cold-stress, which is the stress that corals are under when the water temperatures are cooler, often cause more diseases than coral bleaching.

In 2002 there was a global mass bleaching and 60%  of reefs were affected. This was the largest coral bleaching event recorded. The hot weather led to an increase in the temperature of the sea surface a few degrees higher than the summer maximum that coral can support. About 5% of the Great Barrier Reef in Australia was damaged. 27% of the world coral reef has been lost and 32% is at risk in the next few decades.  In 2016, 51% of the world’s corals were in a stressed situation.

How can you help?

It is pretty easy to help: you only have to change small everyday habits. There are things you might be doing on a regular basis without realizing they are damaging the ecosystem.                                                     

First of all, try to reduce your plastic consumption. Buy a reusable water bottle and not a plastic water bottle that will end up in the ocean and damage marine life and corals. Secondly, recycle and dispose of your trash effectively. If you throw your waste on the ground it will eventually end up in the oceans. Do not litter on the beaches!

Third, save energy at home. When you ventilate your rooms, be careful and check if the heater is on. If yes turn it off.  Use low energy bulbs. Try to buy solid shampoo and hair conditioner. Turn off or unplug electronic devises when you do not use them as they continue to consume energy. Saving energy is important because wasteful energy use makes the temperatures increase.                                                                                                         

Fourth, boycott damaging fish methods. Try to buy fish that was not caught in a way that damaged coral reefs. Fish that are sold in bulk or large quantities are usually fished in a way that harms coral reefs. Sometimes coral reefs are blown up with explosives so they can easily catch the fish that cluster them.

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