With atmospheric CO2 levels and global temperatures continually on the rise, our oceans are more critically under threat than ever before. To see the problem more clearly, we’re going to have to take a little dive…
Welcome to the ocean. With all its incredible colours and marine life of all shapes and sizes, it’s hard to imagine that all of this is at risk of disappearing. After all, the ocean is so big, what could we have possibly done?
First and foremost, the additional heat that the oceans are absorbing due to global warming is causing the ice caps at the poles to melt. Each year, we are seeing less and less sea ice coverage, which is causing sea level rise. As a result, coastal communities and low-lying areas are at a greater risk of flooding. Additionally, sea ice has a very high albedo, meaning that it reflects large amounts of light. This is important because the ice acts as a big shield, protecting the Earth from the Sun’s rays by reflecting them back out into space, which helps to keep our planet cool. But with sea ice declining every year, less sunlight is being reflected, causing more global warming, which causes the oceans to heat up even more, causing more sea ice to melt. This repeats over and over again in a cycle known as a positive feedback loop; unfortunately, it’s not as good as its name sounds. You can find out more about feedback loops here.
While the water itself may not show any visible problems, its chemical composition shows worrying changes. When carbon dioxide reacts with seawater, it dissolves to form carbonic acid, a weak acid; this increases the ocean’s acidity. Since pre-industrial times, the oceans have become around 25% more acidic; this may not seem like a massive change, but it has already led to devastating impacts.
Less than 60m underwater in equatorial coasts lie colourful sanctuaries teeming with life: coral reefs. Despite covering less than 1% of the Earth’s surface, coral reefs have a biodiversity that rivals that of tropical rainforests, housing almost a quarter of all marine species. Coral is actually an animal, or rather a colony of tiny carnivorous animals known as polyps. They build a limestone casing around themselves using calcium carbonate found in seawater. The beautiful colours that we see come from various species of algae that live on the coral, providing the polyps with food in exchange for shelter. Because they are living creatures, coral reefs are extremely sensitive to even the tiniest changes in their environment. They require very specific conditions to grow, which is why they are only found in some areas around the world. And these areas that are suitable for coral are becoming scarcer as climate change causes the world’s oceans to change. Rising temperatures can cause the coral to become stressed, resulting in a phenomenon known as coral bleaching. The coral will expel all of its algae, exposing its white skeleton and depriving the polyps of food. If conditions improve, the coral can recover, but in extreme cases, the coral will starve to death. Ocean acidification is also threatening coral reefs by literally causing them to disintegrate - limestone is a type of rock that is easily dissolved in acid. Since coral reefs are made of limestone, the increased levels of acid in the water are causing the reefs’ structure to dissolve.
And it’s not just the coral reefs, it’s also every sea creature that has a limestone shell: crabs, lobsters and oysters are all threatened by ocean acidification in a similar way. Shellfish cannot survive without their shells. It is possible, at this rate of global warming, that some parts of the ocean will become so acidic that shellfish shells will completely dissolve by the end of the century. And that’s not just bad news for seafood lovers…
Coral reefs are an incredibly important ecosystem. All the species that rely on coral reefs for food, shelter and nursing grounds are directly affected if the reefs are damaged. This is a serious threat to marine biodiversity as a loss of coral reefs can also lead to the loss of countless sea creatures. Biodiversity ensures a healthy and functioning ecosystem, so a loss of biodiversity could hinder the ocean’s ability to help regulate the world’s climate. Coral reefs can also impact the global seafood supply. For example, the bigfin reef squids are a type of squid that live in coral reefs. They are eaten by tuna which are in turn eaten by humans. If there are fewer coral reefs, there will be fewer reef squid, so there will be less food for the tuna, and less tuna available to us.
While this article was quite heavily focused on coral reefs, there are many other important ocean ecosystems, such as mangroves and salt marshes, that are also threatened by climate change and just as worth saving as the reefs for similar reasons. In our next article, we’ll be exploring another threat lurking in the ocean…
Credits:
Image - USDOS
Information - UN, USEPA, NOAA, Sail-World
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