Many may wonder how global warming could impact our lives daily as well as long-term, but people have not taken a keen interest in the effects of global climate change on Earth’s most undiscovered territory: the ocean. Although we may not know much about our vast oceans, we have discovered large, vibrant coral reefs, which are home to thousands of marine species across the globe and are considered to be immensely diverse ecosystems. Unfortunately, human activity is causing a continuous rise in global temperature and CO2 levels, which is responsible for the destruction and/or bleaching of vital ecosystems including coral reefs.
During the last fifty years, not only are global temperatures rising, but along with it is proof of CO2 concentration rising simultaneously. CO2 is not the only culprit in the growing issue of rising temperature because other greenhouse gases such as methane (CH4) and nitrate (N2O) are just as much to blame. The greenhouse effect is when these gases are released into the atmosphere to keep the Earth’s temperature above 25oC, but without the presence of these greenhouse gases Earth’s temperature would be at, or below 25oC.
Chlorofluorocarbons (CFCs), which have been banned as part of the Montreal Protocol in 1987, are the main reason for the depletion of the ozone layer of our atmosphere. This layer is responsible for absorption of ultraviolet radiation expelled from the Sun; so when there are tears or holes present in the ozone layer, there is a higher concentration of ultraviolet light hitting Earth’s surface. These high levels of ultraviolet radiation can be a large cause of eye damage or skin cancers, as well as other health problems. Prior to the Montreal Protocol and enforcement of CFC emission, the main source of this chemical compound came from its use in refrigerators and air conditioners as well as its ubiquitous use in aerosol cans. When this compound is emitted into the atmosphere, its elements split and recombine in ways that thin the stratospheric ozone layer and the chemicals stay in the atmosphere for long periods of time. With the high levels of ultraviolet radiation, free molecules of chlorine cause ozone molecules to break up, thus breaking up the ozone layer, and allowing radiation to pass through and hit the Earth’s surface.
Although humans do not acknowledge the extent of our responsibility in the deterioration of the Earth’s climate, we are largely to blame. Depletion of ozone through CFC diffusion and emissions of CO2 are unfortunately not the only human-influenced causes of climate change. Along with point-source and diffuse pollution, acid rain and habitat loss play a major role in adjusting global climate and weather patterns.
Coral reefs may be considered “cities of the sea”, according to Smithsonian NMNH, meaning that they function as whole ecosystems housing hundreds of species. Particularly, coral itself is made of calcium carbonate, which forms their mineral skeleton called a calicle are polyps. Reefs form when these corals attach to rock, or the sea floor and continue to reproduce one on top of the other. Some may be porous, which makes corals a perfect home for animals such as sea anemones, jellyfish, as well as crustaceans. Along with these organisms, corals are known to have a mutually-beneficial relationship with zooxanthella, a dinoflagellate and type of algae.
Coral reefs are known for their vibrant colors, but it’s little-known that their color actually comes from the algae residing on them. Once various conditions cause the loss of zooxanthellae from the surface of coral polyps, a condition called “coral bleaching” takes place, as seen in Figure 1. Ultraviolet radiation and additional heat, which pass through the hole in the ozone layer cause the temperature of oceans to rise accordingly. This fluctuation in temperature produces a strain on the coral, which causes the loss of its symbiotic algae.
The vastest coral reef that is known to us is called “The Great Barrier Reef”, which spans for approximately 2,300 km and has six hundred types of coral near northeastern Australia. Regrettably, even the Great Barrier Reef has been subject to bleaching due to global warming. According to the article in nature.com, there were three times in recent history where major signs of bleaching in the Reef, which occurred in 1998, 2002, and 2016, with the latest bleaching event being the worst of the damage in recorded history. It has been noted that 61-63% of the reef had experienced upwards of four weeks a year of heating, proving the phenomenon of global warming has had a significant impact on the coral reefs.
The longest continuous section of the Great Barrier Reef, which is 1,000 km long and located towards the north. This is the site where the most heating was observed in 2016, but when compared to measurements from 1998 and 2002, the heat stress found to cause coral bleaching was further south. Since global temperatures rise each year as a cause of global warming, this means that the heat of water will consequently rise, specifically at latitudes further up north. Provided this, it is clear evidence that as climate change is taking place, so is coral bleaching.
There is also the possibility of the coral reefs to have been bleached more than once with only 9% never have been bleached, located in a southern region of the Great Barrier Reef.