Exeter, Devon UK • May 21, 2024 • VOL XII

Exeter, Devon UK • [date-today] • VOL XII
Home Science The decline of the Great Barrier Reef

The decline of the Great Barrier Reef

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The Great Barrier Reef is the largest coral reef on the planet. Spanning 2,300km down the eastern coast of Australia, it is more than twice the size of the next largest coral reef, and covers an area similar to the size of Italy. For many, when we think of the Great Barrier Reef we think of a vast expanse of bright colour, teeming with fish of all shapes and sizes. Ancient structures that curl around one another to create a seemingly never ending tangle of prehistoric ancestry. Those with the opportunity to visit a coral reef will not easily forget the experience. However, those who haven’t been may well be running out of time. If we don’t lower our carbon dioxide (CO2) emissions now, we could be responsible for the decimation of our planet’s most biodiverse ecosystem: from an array of magnificent structures that house a multitude of marine life, to a possible future of white skeletons in a barren wasteland.

Great Star Coral polyps by Nick Hobgood. source: wikimedia.commons

Great Star Coral polyps by Nick Hobgood. source: wikimedia.commons

Coral reefs are formed from individual invertebrates called coral polyps. The polyps create the reefs we see by secreting hard outer skeletons and anchoring themselves to rocks or other neighbouring corals. Within the tissue of the coral lives brown algae, known as zooxanthellae, which photosynthesise to generate the coral’s main source of food. There is a vital partnership that exists, as the coral obtains a constant food source, whilst the zooxanthellae have a place to settle and thrive. It is this partnership that we are putting under strain.

The oceans are a heat sink, absorbing over 90% of the excess heat we generate from greenhouse gases. As the temperatures of the oceans rise, the algae within the coral tissues produce toxic compounds. This leads to the coral polyps expelling the zooxanthellae from their tissues. Without zooxanthellae the corals

Bleached coral by Oksana. source: wikimedia.commons

Bleached coral by Oksana. source: wikimedia.commons

lose their main source of food, and as such turn white. This process is known as coral bleaching and results in the corals being more vulnerable to disease and storm damage. The delicate symbiosis that is easily disrupted by climate change is one of the reasons why coral reefs have earned the name of ‘canary in the coalmine’ – they act as a warning for the consequences we could see as a result of our careless use of finite resources.

If we let the Great Barrier Reef become a ghostly memory of one of the most complex ecosystems on the planet, the impacts will be extensive. The reef acts as a natural barrier, protecting nearby coastal communities from the action of strong waves. It allows juvenile fish to grow and develop in a safer environment before they migrate to open waters. Pharmaceutical ingredients can be harvested and used for medicine. And in terms of the economy, Australia gain a contribution of AUS$5.7 billion thanks to the reef; with over 90% of the contribution coming from tourism alone. Add to this an estimated 64,000 people who are employed full time in the Great Barrier Reef catchment area and you can clearly see the possible repercussions.

Great Barrier Reef by Sarah Ackerman. source: wikimedia.commons

Great Barrier Reef by Sarah Ackerman. source: wikimedia.commons

The good news is that corals can recover – all they need is the time to do so. In the absence of storms, coral bleaching, and a voracious coral predator, the crown-of-thorns starfish; the Great Barrier Reef will be able to grow at a rate of 2.85% a year. It has become the focus of the Great Barrier Reef Marine Park Authority to improve the conditions before it is too late. All we can do is hope that their mission succeeds so that the next generation doesn’t only have Finding Nemo as a reference when they are told about one of the Seven Natural Wonders of the World.

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