Corals are amazing animals. They form the most biodiverse regions on the entire planet. They have a symbiotic relationship with algae. Some species can live for thousands of years and sometimes they participate in war by firing their guts and digesting each other, which is known as mesenterial filaments - these parts are not actually their guts but they are used for digestion.
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However, these singular animals are in serious danger. Rising temperatures, increasing ocean acidity, and decreasing shark populations among other threats, all endanger the very existence of coral reefs. If you would like to learn more, read on.
Around the world, there are 6000 species of coral[1]. Coral reefs cover only 0.1% of the world’s oceans but they support ¼ of its marine species. In other words, coral reefs are some of the most biodiverse regions on the planet[2].
Each individual coral is made up of sometimes thousands of individual polyps all connected together that each help grow an exoskeleton made of calcium carbonate, a form of limestone. This process of expansion is so slow that some of the coral reefs today started growing over 50 million years ago[3].
To survive, these coral polyps have a specific type of algae called zooxanthellae. Zooxanthellae live inside the tissues of the coral polyps and in return they supply 90% of the polyps’ energy from photosynthesis[3].
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Deep sea corals on the other hand rely on anything they can reach and catch with their tentacles which means they mainly eat passing plankton. Deep sea corals live up to 6000 meters (20,000 feet) below the ocean’s surface. There are more than 3,300 species of deep-sea corals which makes them about as diverse as their shallow-water relatives[4].
Deep sea corals also happen to be far more widespread than other corals because they do not depend on warm shallow water. They have been found off waters near the United Kingdom, Australia, Canada, Ecuador, and Japan, among other places[4]. The coral reefs they form, however, are completely distinct from shallow water living corals[5].
As there are far fewer nutrients in their habitat, deep sea corals can grow ten times more slowly. However, as there is less crowding in the deep these corals can grow much larger. Even so, these colonies are generally smaller than the light-dependent corals above[5].
As a result of their more extreme environment, deep-sea corals can have very long lifespans with some black corals making it over 4000 years. This longevity actually makes black corals the oldest living skeleton-creating marine organisms in the world[6]. Some deep-sea coral species can be as tall as 10 meters (35 feet)[4].
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Get notified of top trending articles like this one every week! (we won't spam you)Corals and Climate Change
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Unfortunately, these corals (both types) are under threat. Since 1950 half of the world’s coral reefs have already been lost[7]. This has mainly been because of bleaching in shallow-water living corals. As temperatures rise, bleaching events have become more and more common.
Bleaching in corals occurs when temperatures become too high. Sometimes even a rise of 2 degrees Fahrenheit is too much for them. As a result of the stress, the zooxanthellae are expelled into the water. Corals can survive for a little while without the zooxanthellae and when temperatures cool back down, they can accept the algae back in, but if temperatures are too hot for too long the coral will die[8].
Already, the number of severe bleaching events have quintupled since the early 1980s and they are now occurring worldwide on average every 6 years instead of every 25 to 30 years. Even if a coral reef does survive a bleaching event, it is an enormous strain on its resources and can still cause great damage[9]. By 2034, sever bleaching to coral reefs worldwide is expected to occur annually[10].
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From the years 2014 to 2017, there was an unprecedented global three-year long global ocean heat wave. This heat stressed out corals worldwide and caused many of them to bleach and die. In parts of the South Pacific, 98% of the corals in some reefs were killed.
The Great Barrier reef also lost huge amounts of coral. Worldwide, more than 75% of the entire Earth’s tropical reefs experienced bleaching-level heat stress between 2014 and 2017 and nearly 30% of all reefs died from it[11].
Warming temperatures are not the only threats to coral reefs though.
Another major threat to corals that climate change brings with it is ocean acidification. The entire process of ocean acidification is complex but suffice it to say that when carbon dioxide meets ocean water it can turn into an acid. The problem with that is that the chemistry of calcium carbonate (the stuff that makes up corals and also the shells of many ocean creatures) encourages it to bind with acid.
That means that high levels of carbon dioxide in the air increases levels of acid in the oceans which ties up the materials needed for animals to build their shells or, in the case of coral, their skeletons. In extreme cases ocean acidification may even start shrinking the very shells that make up organisms[12].
If emissions continue unabated, carbon dioxide levels are predicted to reach 560 parts per million in the atmosphere and those extreme cases of ocean acidification will be reached. At this point all coral reefs worldwide would stop growing entirely and then they will start to shrink in size instead. Coral growth in the Great Barrier Reef has already decreased by 14% since 1990[13].
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Corals and Sharks
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Another threat to coral reefs is the hunting of sharks. Sharks balance and support the entire coral reef ecosystem by eating large predatory fish such as groupers. This allows smaller fish species to live in abundance which increases the variety and biodiversity on a coral reef. Some of the smaller fish species that are preyed upon by groupers are parrotfish which eat the algae that grows on coral reefs (not the zooxanthellae, another unhelpful kind).
If shark populations crash in a coral reef ecosystem that means that there are more groupers which directly results in fewer smaller fish species such as parrotfish. As there are fewer parrotfish eating the harmful algae, it starts growing out of control all over the reef, literally burying the coral and killing everything[14].
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What if Coral Reefs Disappeared?
By now this question may have entered your mind. What would happen if the world lost all of its coral reefs? First of all, a habitat that supports 25% of all marine life in the world’s oceans would be gone.
That would be the greatest blow to the world[15]. The oceans are home to 240,000 known species and it is estimated that 91% of species living in the ocean still await discovery[16],[17]. A quarter of those species would suddenly have no place to live for at least part of their lives. Many migratory species such as sharks and sea turtles also rely on coral reefs so the damage would not be limited to the coral reefs themselves.
However, the damage caused by the loss of coral reefs would also not be limited to just the oceans. Coral reefs support the livelihoods of 1 billion people worldwide. 200 million of those people depend on coral reefs for protection from storm surges and waves[18]. In fact, coral reefs buffer shorelines against 97% of the wave energy coming in. Without the corals, many coastlines would start to suffer huge amounts of erosion and damage[19].
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This is especially bad news for countries such as Tuvalu, the Maldives, Kiribati, and the Marshall Islands that are all almost entirely made up of coral atolls, islands that are supported by coral reefs. Large parts of Kiribati have lost 90% of their coral and as a result are already facing erosion[20],[21]. 90% of the islands in the Maldives also have severe erosion and 97% of the country no longer has fresh groundwater.
As a result, almost 80% of the Maldives could become uninhabitable by 2050 by the combined threats of sea level rise and the loss of its corals[22]. Without corals, all four of these countries could very well disappear almost entirely as the ocean erodes the ground from beneath them.
In total worldwide, the services that coral reefs provide to humanity are estimated to be worth $9.9 trillion dollars annually[23]. For comparison, the entire world GDP is estimated to be $106 trillion[24].
What Can Be Done To Help Corals
So now, the question is what can you do to help save the coral reefs? The answer to that, unfortunately, is nothing. If global temperatures rise by 2 degrees Celsius compared to pre-industrial levels, there will be a predicted 99% decline of the entire world’s coral population by 2100 at the latest.
In other words, corals will effectively become extinct[25]. The world is basically certain to rise in temperature by at least that much[26]. There has been so much inaction when it comes to climate change that now the fate of these amazing animals is sealed.
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However, just because the corals are doomed does not mean that you cannot still act against climate change. If the world waits any longer to stop the ravages of climate change, the consequences will only get worse and worse, and more ecosystems will be lost. You must act now to ensure that this scenario does not come to pass. Yes, the situation is dire and it may seem hopeless, but any environmental action today will greatly decrease the damage done to the environment and the world in general in the future.
Even though 2°C temperature rise is still fatal to coral reefs, there is a real chance that global emissions have already peaked which is the first step in avoiding any more serious impacts of climate change. However, if the world is truly going to stay at 2°C, then you must act now. At no point in all of human history has there been more awareness about the environment and today we have by far the greatest chance of effectively fighting back against climate change.
However, it also happens to be our last chance so that means you really must act now. There is no time to lose[27].
