How did things get so bad? What is it that is threatening the reefs?
 
Next to unsustainable local activities that I will discuss in a future post, there is one big global factor undermining the health of the reefs: Global warming.
 
How is global warming affecting coral reefs?
 
Coral Bleaching
Corals have but a narrow temperature tolerance. When the water becomes too warm for them, they get stressed and start to eject the algae (zooxanthallae) that live inside their bodies. But, corals depend on their symbiotic relationship with these algae. The zooxanthallae provide the coral with nutrients and the compounds that they need to build their hard skeleton. (A little more about corals and zooxanthallae in an earlier post: https://mspsteem.com/nature/@mirjamsvideos/corals-are-animals-join-me-on-my-journey-to-go-restore-coral-reefs)
Because the algae give the coral their beautiful colors, when they are gone the coral turns white. That´s why they call this: coral bleaching.
When stressed out and not well fed, the corals are more susceptible to disease. So bleaching events often are followed by breakout of diseases (and a lot of death).
 
In this video you can see coral bleaching happening:
 
https://www.youtube.com/watch?v=bFdPmiwZzVE
 
Sea level rise
With the ocean warming sea glaciers melt, resulting in higher sea levels. The Intergovernmental Panel on Climate Change (IPCC) informs that the sea level is rising at a rate of 0.12 inches per year. This means that corals will end up deeper underwater and will therefore receive less sunlight. The zooxanthallae need sunlight for photosynthesis, to be able to produce all those nutrients that also the coral needs. Receiving less sunlight will mean that the corals will grow slower.
 
Extreme weather
Another predicted consequence of global warming is more frequent and more intense tropical storms. Hurricanes, cyclones and typhoons feed on global warming, they gain more speed and strength from warmer ocean temperatures. These storms can generate great water movement of greater power than reefs can handle and can break coral branches and overturn complete colonies.
Also heavy rain from storms can create runoff from land leading to increased nutrients and sediment in the water. Like this, a fragile balance is taken away. Too much sediment can then again prevent the corals from getting the light that they (the zooxanthallae) need.
 
Ocean acidification
Since the start of the industrial revolution the amount of carbon dioxide (CO2) in the air has increased by one third.
About 30% of all emitted CO2 is absorbed by the oceans, another 25% by plants and trees and the remaining +/- 50% stays in the atmosphere.
When the ocean absorbs CO2 a series of chemical reactions result in an increased amount of hydrogen ions in the water which causes the oceans to become more acidic and for carbonate ions to be less abundant.
Carbonate ions are an important building block for corals and other marine animals to grow their shells and skeletons. So when more CO2 is absorbed into the water, it will become more difficult for corals, oysters, clams, sea urchins and others to grow their shells and other protective structures.
With weaker skeletons corals are more susceptible to disease and breakage from more fierce weather.
 
Another short video that explains a little more:
https://www.youtube.com/watch?v=6SMWGV-DBnk
 
Ozone depletion
The ozone layer, a layer of gas naturally occurring 15 to 30 kilometers above the Earth is a protective shield from the harmful ultraviolet B radiation from the sun.
Several chemicals released into the atmosphere destroy this protective shield. Among the ozone´s greatest enemies are chlorofluorocarbons (CFC) found in many spray aerosols. When they reach the upper atmosphere and are exposed to ultraviolet rays they break down in among other compounds: chlorine. This again reacts with the oxygen atoms in ozone and basically rips apart the ozone molecule.
The deterioration of this protective shield allows more harmful ultraviolet B to reach earth which increases the risk of skin cancer and cataracts in humans and harms other animals as well.
It also inhibits the reproductive cycle of phytoplankton, single-celled organisms such as algae that make up the foundation of the food chain.
Corals have a natural sunscreen, but of course, at increased level, ultraviolet radiation can harm corals as well.
 
If you want to know why it is so important to protect the coral reefs, please check a previous post: https://mspsteem.com/nature/@mirjamsvideos/why-are-corals-so-important-join-me-on-my-journey-to-go-restore-coral-reefs
 
Of course not only because of the corals should we make an effort to stop global warming. In the end our own survival is depending on it. There are many small actions that you can do. For some inspiration, you can go here: https://globalwarming-facts.info/50-tips/2/

I am doing my best to follow some of this advice and next to that, for some magical reason, coral reef restoration has caught my interest. At the moment I am learning diving, taking an online course in Oceanography and I am comparing the organisations that work in restoring the reefs. Like this, in some time, I will be qualified to follow a course in coral reef restoration at the organisation of my choice.

Sources:
https://coral.org/coral-reefs-101/reef-threats/
http://wwf.panda.org/our_work/oceans/coasts/coral_reefs/coral_threats/
https://www.nationalgeographic.com/environment/global-warming/ozone-depletion/
https://oceanservice.noaa.gov/facts/acidification.html