Coral Bleaching And Climate Change

 

Coral is a marine organism found beneath the sea on the floor. It is found near coastal areas and is popularly known as coral reefs. Coral reefs are the abundance of skeletons of this marine organisms, who living in colonies, have been built up into formidable amounts over time.

Coral is found in the first hundred meters of the sea and spreads over a region of about 284,000 square kilometers globally. Coral does not do very well (except deep sea coral) in extremely cold waters and so the large majority is found in the warm waters of tropical seas.

Examples of coral reefs include the Watamu, Mombasa, Malindi, Wasini coral reefs that line up the entire Kenyan Coast off the Indian Ocean, .

A part of Watamu coral reef - source (AmboseliParkKenya.com)

Coral reefs are made up of two distinct creatures. The coral polyps and the algae. Polyps are the main invertebrate ‘animals’ whose formidable build up is visible while the algae are tiny microscopic creatures that give the coral its vibrant and lively colors. The two live in a symbiotic relationship with one another, which means they are dependent on each other for survival.

Coral polyps depend on the photosynthetic algae known as zooxanthellae for food. The algae produce and give amino acids and sugars to the host, while the hosts provide a home and anchor as well as some minerals like phosphorus and ammonia to the algae.

For many thousands of years, these coral reef systems have thrived and bloomed, providing a home to one of the most diverse and prosperous ecosystems under water. Coral reefs host about a quarter (25%) of all known ocean life.  They are vital systems of biodiversity and genetic diversity. They are breeding grounds for thousands of fish species. They are a part of the nutrient exchange of the ocean. They are tourism attractions and they protect the coast against heavy storm surge and wave action. They do this by slowing the impact of storms.

But they are under threat.

With climate change, there are two main things that affect corals. The first is temperature change or global warming. As the air gets hotter, the ocean, which regulates heat level in the planet absorbs 90% of it, causing the sea waters to warm up. This rise in ocean temperature is bad for coral, because they react by expelling the zooxanthellae from their structures.

This exposes the coral itself as its color is drained because of the removal of algae. This ‘draining of colorful algae’ is what is known as coral bleaching, as the coral is left looking white and bare. The coral can also die because of lack of food as its main producer has been removed.

Therefore coral bloom in a specified and determined balance of water temperature. Not too hot, and not too cold.

The second effect is ocean acidification. As human activities, primarily burning of fossil fuels, releases more and more carbon dioxide into the air, the ocean dissolves this extra carbon dioxide, which changes the pH of the sea from being naturally alkaline to gradually acidic. Most if not all life needs an alkaline pH to thrive.

The carbon dioxide dissolved in water forms weak carbonic acid, which precipitate a reaction whereby free hydrogen ions react with carbonate ions found in the water. The shells of most marine organisms especially the invertebrates like coral and others are made from calcium carbonate, and release of hydrogen ions takes this mineral from their bodies and skeletons causing them to die. The chemical reactions remove the carbonates.

The coral skeletons begin to dissolve and die which means that the reef is gradually destroyed.

Coral also suffers from light inhibition which means that too much light affects the working of the photosynthetic zooxanthellae. They reach a maximum of light absorption beyond which the dark part of photosynthesis is stopped by too much light.

That is, even though light is necessary, too much light flooding the upper part of the sea stops the algae from working properly.

Another important environmental thing, is that coral reefs also suffer from sedimentation. Sediment is usually carried by rivers and emptied into the ocean at river mouths, which is why coral reefs are not found next to rivers. The soil and sand particles washed and carried from the drainage system of the river literally cover the corals and so prevent light from reaching the algae.

They choke the corals.

With the rise of modern agriculture, more and more effluent containing pesticides and fertilizers is emptied into the sea and these chemicals impede the proper functioning of coral. They are poisonous.

Additionally, for obvious reasons, untreated wastewater discharged directly into the ocean kills off corals.

And hot water released from factories has the same effect as global warming and marine heat waves: they alter water chemistry and lead to coral death.

Coral polyps that have expelled their algae are predisposed to marine diseases and hotter water increases the chances of this happening.

Do coral reefs absorb carbon dioxide? Yes. They take up dissolved carbon from the water to be used by zooxanthellae in photosynthesis. They also use carbon to make calcium carbonate which is part of their skeletons. This means that with time, the bodies of these marine organisms accumulate fixed carbon and reach high.

But coral also releases carbon by respiration (the biological process of burning glucose to produce energy). When the skeletons are disturbed by other organisms they release the locked up carbon.

Coral reefs in the world are already damaged to a considerable extent, and need remedial measures.

First and most importantly, is to cut down on fossil fuel use. Increase ambition to cut down on carbon emissions. This has a twofold benefit. This is because the effect of carbon dioxide as a greenhouse gas that warms climate and the ocean is reduced, and the second is that ocean acidification goes down because carbon dioxide is the principal gas in action.

The second is to look for ways to repopulate damaged coral reefs. This includes coral gardening which is the growing of coral in laboratories and elsewhere and reintroducing these to the reefs under the sea. Care has to however be taken so that the diversity of the species that used to inhabit the reef is maintained.

Another way is gene editing, where zooxanthellae are engineered by marine scientists to adapt to higher temperature levels while still performing the same functions.

There have been efforts geared towards providing physical shading to reefs in order to protect them from excess sunlight and warmth.

As an ecosystem, coral reefs are thoroughly interlinked with other marine ecosystems like sea grasses and mangrove forests. These two are intensely carbon rich systems that continue to sequester carbon dioxide at high levels. But they can be destroyed by wave action and heavy storms, and this is where coral reefs come in to protect them from such.

The protection of coral reefs is covered by the sustainable development goal number 14, which is life under water. In this context it is also a part of goal 13 which is climate action. Coral reefs are worth over 2 trillion US dollars in the planetary scale. This is because of such key economic industries such as water transport and trade (90% of goods are transported over water), fisheries and tourism all of which are worth billions.

By this, they reduce poverty levels and so contribute to goal 1 which is no poverty. Their industrial enterprises are a part of goal 8, which is decent work contributing to economic growth and also form part of industry (goal 9).

These reefs are part of the wellbeing of communities, where they also hold spiritual and cultural value.

Recorded mass bleaching events started being observed in the eighties. The first and second worldwide events were in 1998 and 2010 respectively. The third major event was from 2014 to 2017. This last one impacted three quarters of tropical reefs worldwide.

The first two took place at the same time as the El Nino, which is precipitated by high sea surface temperatures and brings heavy rain onto neighboring dry land. The high SSTs kill off coral.

According to scientists from the University of Hawaii Manoa, business as usual emissions of carbon dioxide will continue to kill off reefs, by 2100, these reefs that are so important might vanish completely.

Others from the Global Coral Reef Monitoring Network noted that 14% of coral was lost to climate change from 2009 and 2018.

A bright spot is that temporary temperature changes do not affect coral completely. That is, when coral eject their algae because it’s too hot, they will take up this algae when the water degrees drop. Thus bleaching can be temporary.

However, when the coral is under sustained heat levels, it will die off and this will be permanent bleaching.

It is worth noting that the five warmest years on record are from 2015 onwards with 2016 and 2019 being the first and second hottest ever recorded.

This is why we must act on climate as a matter of urgency; it is not just for us, it is for the natural world as well.