What are coral reefs and why are they so important?

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If you’re an avid SEVENSEAS reader, you’ve probably dived or snorkelled beautiful coral reefs around the world; admiring their stunning colours and abundance of marine life. But how much do you actually know about coral reefs? What are they and why are they so important? We asked the team at The Reef-World Foundation to tell us more…

Coral reefs might look like colourful rocks or dazzling underwater plants but they’re actually a colony of animals all living and working together – a bit like the ants or bees of the underwater world.

One individual coral animal – called a coral polyp – is a tiny creature that looks a little like an upside-down jellyfish. It falls under the scientific classification Cnidaria, made up of animals which use special stinging cells – called cnidocytes – to capture their prey. In corals, these cnidocytes are located in their tentacles. The coral polyp can move, feed and reproduce; and it lives in a coral colony, which is a large group made up of lots of polyps, in the same way you or I might live with family members. That colony lives in a group with lots of other colonies (like a human town or neighbourhood), which is called a coral reef.

There are lots of different types of coral. Hard corals have hard skeletons and provide the building blocks of the entire reef ecosystem. Although they look like rocks, these slow-growing corals are fragile and can take a long time to recover from damage. Soft corals, which tend to look more like plants, have no skeleton – you’ve probably seen them wafting in the current.

Corals, you’ll remember, have special tentacles with stinging cells which they use to capture food. They prey on zooplankton: tiny animals that drift along in the water. At night, a coral will grab the zooplankton with their tentacles and pull them into its mouth. But this only accounts for 20% of a coral’s food source.

For the rest of its food, coral relies on a microscopic algae called zooxanthellae. These two organisms have a very special, symbiotic relationship: the zooxanthellae live inside the coral skeleton – benefitting from the shelter it receives – where it uses photosynthesis to convert sunlight into food and shares this with the coral. It’s actually the zooxanthellae which gives the coral its bright and beautiful colours. Without the zooxanthellae, the coral would not only lose its colour but also the majority of its food source.

That’s what happens when coral bleaches. These sensitive zooxanthellae can only survive at very specific temperatures. Warming waters can stress the algae and trigger them to leave the coral looking for a more suitable home. If they don’t come back, the coral won’t have enough food and will die.

Bleaching is happening in oceans around the world. If current trends continue, it’s predicted severe bleaching will occur every year on 99% of the world’s coral reefs within the next 80 years. This is not just a problem for the coral because coral reefs are the building blocks of the entire marine ecosystem – they provide food and shelter for many fish and other types of marine life. In fact, they’re often called “the rainforests of the sea” because they’re one of the most valuable ecosystems on the planet. Despite only taking up less than one quarter of 1% of the marine environment, coral reefs are home to more than 25% of all known fish species. Put simply, without them, the ocean would be in trouble.

And if the ocean is in trouble, so are we. Reefs provide many local communities with fishing grounds; providing them with food and livelihoods. As well as fishing, there are a huge number of diving, snorkelling and other tourism-related jobs that exist thanks to coral reefs. Not to mention the protection they offer from coastal storms – which themselves are becoming more frequent thanks to climate change.

Whether or not you live by the ocean, coral reefs are a hugely important part of our planet – let’s work together to protect and conserve them for future generations.

The Reef-World Foundation leads the global implementation of the UN Environment’s Green Fins initiative, which focuses on driving environmentally friendly scuba diving and snorkelling practices across the industry globally. To keep up with our latest news and developments, please follow Reef-World on Facebook, Instagram and Twitter. You can also follow the Green Fins initiative on Facebook, Instagram and Twitter to keep up to date with new materials, updates and sustainability insights from Green Fins members.