Exeter, Devon UK • Jul 17, 2024 • VOL XII

Exeter, Devon UK • [date-today] • VOL XII
Home ScienceEnvironment Coral reefs: the ‘canary in a coal mine’?

Coral reefs: the ‘canary in a coal mine’?

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When you hear the words ‘coral reef’, you probably imagine a vibrant underwater community, made up of colourful fish and tangled corals. Taking up less than 0.1% of the ocean area, coral reefs are home to over a million different species – this is about 25% of all marine species. In comparison, around 70,000 land species are found in the UK.

But, sadly, this is changing. Many once colourful reefs are turning pure white. Resident fish and other animals, from turtles to sea slugs, are vacating their previous homes.

Image of coral reef and fish. Source: wikicommons

This situation is a parallel to the ‘canary in a coal mine’, where miners used to use the singing of canaries as an indicator of air quality. Much like this, coral reefs are sensitive to environmental changes that could damage other habitats in the future.

These changes are primarily down to climate change, which both warms and acidifies the oceans. When the ocean warms, corals get stressed and eject photosynthetic algae, called zooxanthellae, which they rely on in order to produce food from sunlight. These algae are responsible for the beautiful colours of the reef, and so when they aren’t present, the corals appear white due to their limestone exoskeletons. Coral in this state is weakened and more susceptible to other stresses, such as ocean acidification.

These changes are primarily down to climate change, which both warms and acidifies the oceans

Carbon dioxide (CO2) from the atmosphere often dissolves in the oceans, storing away the infamous greenhouse gas. In fact, a third of human-created CO2 has been absorbed by the oceans since the industrial revolution, without which climate change would already be much worse.

But this makes the ocean more acidic – in the past 200 years, the pH of the ocean has dropped from 8.2 to 8.1. This may not sound like a lot, but it is, as pH is measured on an exponential scale, so this 0.1 pH change is equivalent to a 30% increase in acidity.

Bleached coral reef. Source: wikicommons

This is troubling for corals as the building blocks of their exoskeletons gets locked away with acidity, hence making them even weaker. Among other things, this can make them more susceptible to diseases, and many pathogens such as Vibrio coralliilyticus (related to the bacteria that causes cholera) become more deadly in these conditions.

These effects of climate change affect the inhabitants of the reefs too. Fish get disorientated, and cannot understand the normal cues that lead them to settle on the reef. Snapping shrimps, responsible for the majority of reef noise, become silent. Clams produce thinner and weaker shells, so are more likely to be eaten.

Current fishing practices are very unsustainable, and often very destructive too. Deep sea trawling can decimate a reef, whereas artisanal fishers use methods like dynamite fishing or cyanide fishing, leading to totally unnecessary destruction.

Deep sea trawling can decimate a reef

So we need to do something about it.

In 2016, 195 countries signed the Paris Agreement. The Agreement aims to limit global warming to a maximum of 2℃, and the global average temperature was 1.38℃ than expected in 2016. Although this doesn’t oblige these nations to any specific goals, this is a huge step forward, as they are all acknowledging the existence and importance of climate change. Hopefully this will drive the development of ‘greener’ energy sources, and reducing our dependence on fossil fuels, therefore reducing carbon emissions and the impact we are having on the environment.

There is exciting research into breeding more resistant corals too. Some species, such as those from the Arabian Gulf, can tolerate higher temperatures, and so could protect vulnerable populations through interbreeding.

Image of coral reef. Source: wikicommons

Other similar research is effectively accelerating evolution by gradually exposing the vulnerable corals to greater temperatures and acidities, allowing them time to adapt and survive by themselves. In the natural reef habitat, these conditions are changing much too fast for this to happen by itself, which puts the corals at risk. By doing this research, we may be able to save the corals and therefore the iconic habitat for all marine species.

Many industries are also doing their bit. Eco-tourism is a growing area which,despite still having some negative impacts on the reef, is promoting the sustainability of the reefs on which their entire businesses depend on. Their profits are reinvested into the protection of the reefs, and with the industry estimated at receiving a $9.6 billion revenue, this has a substantial influence on conservation. They are also important in educating the public about the importance of the reefs – for example, did you know that coral reefs are a largely unresearched source of new medicines? Potential coral-derived treatments for conditions ranging from cancer to arthritis are being investigated, and there are likely to be many more undiscovered medical uses.

coral reefs are a largely unresearched source of new medicines

So what can you do to help?

One major way you can help is to reduce your carbon footprint. This is mentioned a lot, but largely ignored, and it can really make a difference. You can reduce your footprint in a variety of ways, such as using more public transport, cycling and walking instead of driving. Or you could try having a meat-free day every week (production of 1 kg of beef results in 13.3 kg of carbon dioxide being released into the atmosphere).

Another is to make sure you recycle. Recycling cardboard and metal means less deforestation and mining needs to take place, therefore reducing the associated emissions. Plus, the trees that remain standing will then absorb CO2 for photosynthesis, taking out some of the major greenhouse gas.

Recycling plastic arguably is even more important. Recently there have been a lot of pictures of ‘plastic islands’ in the Pacific Ocean in the news, alongside alarming stories about marine animals, like turtles, mistaking plastic for food, then eating or getting trapped in the rubbish. By recycling plastic, you not only reduce emission needed to produce more, you can directly save these iconic species.

Plastic island. Source: flickr

Eating sustainable seafood is simple way to stop destructive fishing. You can easily find out which species are best to eat online, and it often says whether they were sustainably caught on the label in the supermarket.

Tropical coral reefs have been described as the ‘canary in a coal mine’ for the oceans, as their health could be an indication of things to come in more robust habitats. Therefore, it is essential that we minimise the harm we cause to the coral reefs, in order to protect the rest of the seas too.


For more by Jack click below or for more on the damage caused to coral reefs, check out ‘The Decline of the Great Barrier Reef’

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