Throughout our oceans coral reefs including both tropical shallow water reefs and deep ocean cold water reefs are greatly affected in a negative way by our currently changing global climate change that creates bleaching events over many of our reefs and is a very current and pressing problem which needs to be addressed sooner rather than later, but why?

The reason as to why this problem needs to be addressed is due the importance of coral reefs both to the rest of our oceans and beyond into other environments as coral reefs provide refuge and nutrients for organisms that dwell within and around them but due to their photosynthetic nature they also supply oxygen to other marine ecosystems as well as providing some oxygen to the surface another benefit coral reefs can provide is strong monetary value to the local communities through ecotourism, fisheries and the aquarium industry.

There are two major players in the coral bleaching events which is ocean acidification and water temperature rise, which are both effects of global warming and anthropogenic (human) impacts.

What is Ocean Acidification?

Ocean acidification is the lowering of the pH value of the world’s oceans from absorbing carbon dioxide molecules. The heightened absorption of carbon dioxide into the ocean in the past century is mainly caused by anthropogenic impacts such as heavy industry and vehicle use.

Bleached Coral on a reef in the Maldives (Oksana 02/12/06)

Ocean acidification is currently a very highly studied area with several research programmes with large impacts on research within the field such as the European Project on Ocean Acidification (EPOCA), the U.K. Ocean Acidification Research Programme (UKOA) and the U.S Ocean Carbon and Biochemistry Programme (OCB) as well as the American organisation NOAA having its own research project titled Ocean Acidification Project (OAP) being interested in researching the levels of acidification as well as the effects it can have on both our environment and ocean communities. This lowering in pH has a particularly heavy effect on organism that utilise calcium or aragonite within their life strategies such as coral. Corals build large calcium carbonate structures or stony skeletons that grow relatively slowly and are there for vulnerable to disturbances such as acidification. The process of acidification disables the corals ability to absorb calcium from the water inhibiting its ability to grow further and dissolving the actual stony structure itself.

Temperature Change and how it affects Coral

Temperature change of the world’s oceans is another large factor causing coral bleaching events globally and due to its widespread nature can even affect the remotest of the world’s reefs. The process of how the oceans temperature is well known within science. And again, its cause is due to increased Carbon dioxide emitted into our atmosphere via anthropogenic impacts. This emitted CO2 is much greater at trapping heat than oxygen ions and the heat is then trapped within our atmosphere, raising the earth temperature by around 6 degrees Celsius, the world’s oceans have been rising temperature slower than terrestrial environments at only 1-2 degrees rise but marine environments are much more fragile than that of the land. This 1-2-degree change is intolerable to most coral species due to there usually very stable environments and causes the corals to expel their symbiotic algae known as zooxanthellae which supplies up 80% of nutrition to shallow water corals through photosynthesis, these zooxanthellae are also what give the coral their color, causing this bleaching appearance once the algae has been expelled. The algae are expelled due to their inability to cope with stress of the rising temperatures.

The Double-edged Sword

With effects of both ocean acidification and temperature rise being explained we can now move on to the issue that lurks within the background the so called double edged sword that affects the corals on a more I depth basis, although the two previously mentioned causes of bleaching events are the main cause of what’s happening it’s the secondary effects they can have on the corals that is harming them even further.

The acidification and temperature rise causes the coral to enter a ‘stressed’ state which in turn hinders there ability to cope with usually more minor stressors such as disease, or it hinders their ability to regrow after relentless storms which In the case of tropical shallow water corals are a common occurrence, not only does acidification and temperature rise hinder their ability to cope with these natural stressors it also has effect on their regrowth after human impacts such as the aquarium industry or through direct human contact.


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