Coral Reefs: What are they and what’s happening to them?

Their bright, vivid colours can be seen in tropical ocean waters around the globe. Beyond their appearance lies a hidden significance.


Corals are animals. Though they look like plants, corals are in fact made up of tiny animals called polyps. Their size can range from the size of a pinhead to a slightly larger than a basketball.


Corals are mega builders. Polyp calicles connected to one another, creating a colony that acts as a single organism. As colonies grow over thousands of years, they join other colonies and become reefs that can grow to hundreds of miles long. The largest coral reef is Australia’s Great Barrier Reef which began growing about 20,000 years ago.


Coral reefs are some of the most diverse ecosystems on Earth. They are homes to 25% of all marine creatures even though they only cover 1% of the ocean floor. It has been estimated that up to 2 million species inhabit coral reefs rivaling the biodiversity of the rainforest. Fishes keep algae that grow on coral in check, allowing corals to breathe and access sunlight.


Corals are translucent. They get the rainbow colours from algae that live in their tissue. While corals get most of their nutrients from the algae’s photosynthesis, they also have barbed, venomous tentacles that stick out usually at night to grab zooplankton and small fishes.


Unfortunately, coral reef ecosystems are severely threatened. Some threats are natural; diseases, storms and predators while others are caused by Us, mankind. Pollution, sedimentation, unsustainable fishing practices, and climate change which raise the ocean temperature and cause ocean acidification are some of the threats faced by the reefs. These unfortunate events can cause stress to corals, leading to coral bleaching, physical damage, and possible deaths to these delicate ecosystems. Warming waters result in prolonged coral bleaching that kills coral reefs or leaves them vulnerable to other threats. The incident in 2014-2017 which partially associated with the El Nino phenomenon has affected 70% of the coral reef ecosystem worldwide. The Great Barrier Reef was hit particularly hard where hundreds of miles of corals were bleached.


PHOTOGRAPH BY GREG LECOEUR, NAT GEO IMAGE COLLECTION

What happened during coral bleaching?

When corals experienced stress from intense hot temperatures, they will end their symbiotic relationship with the algae, expelling them and turning white (their original color). A recent study also indicates that some corals turn to bright neon colour. Although they are still alive when they bleach, many will starve and die, eventually turning to a dark brown colour.


Corals are able to recover from bleaching events if conditions improve before they die though it takes many years for the ecosystem to heal itself. Scientists are also testing new methods to help the ecosystem; growing coral in a nursery and transplant it to the damaged areas.


A world without corals not only affects the diversity and the ocean’s beauty but also leads to economic disaster predominantly in developing countries. Reefs attract millions of tourists every year and offer natural coastal protection, especially in areas where hurricanes and tropical storms frequently hit. Something has to be done because, without significant action on climate change, our oceans could lose many of their colourful reefs by the end of the century.