The Great Barrier Reef

One of the most beautiful natural wonders on our planet is suffering at the hands of climate change…

Written by: Iona Jenkins

Art by: Sotiria Kal

It’s hard to convey just how breathtaking the Great Barrier Reef is in words; you simply cannot capture the magnificent colours, the unusual sea creatures, the luminescent fronds of the soft corals and anemones that wave gently with the ocean tides. It’s hard to imagine what it must have looked like before the onset of the sharp climate change caused by humans as a result of the Industrial Revolution: it must have been surreal.

In many ways, it makes a visit to the Reef actually rather sad. No matter how amazing it may seem now, the wildlife is suffering, the corals are bleaching and species are struggling to adapt to change.

Corals are formed from myriads of individual polyps that colonise together to form clusters. They are home to an estimated 1-9 million species of aquatic organisms including plants and algae, but their bleaching has become a serious problem. Corals ‘bleach’ when they are exposed to physically stressful environments, such as a sudden change in temperature; this causes them to expel the microalgae that reside in their cells. This microalgae, mainly a species named zooxanthellae, is their primary source of food and nutrients.Together the algae and coral form a mutualistic relationship: one cannot survive without the other. Whilst the algae provides the coral with some products of photosynthesis such as glucose,  the coral provides the algae with a protective environment in which to thrive. Thrive they cannot when suddenly expelled from their polyp home. As well as losing their source of food and energy, stony or hard corals also lose their colour, making the reef look white and devoid of life.

Nevertheless, a coral can survive bleaching if the water returns to lower temperatures for a prolonged period of time, provided there are no other physical stresses to the coral. However, climate change projections don’t suggest that this is likely to happen any time soon, meaning that it is highly unlikely that the corals in the Great Barrier Reef will experience the changes required to recuperate in cooler waters.

The output of carbon dioxide into our atmosphere has dramatically increased over the past 100 years, with the sharpest increases in the last 30-40 years. The ocean is the world’s biggest ‘carbon sink’, as it sequesters carbon in the form of dissolved carbon dioxide. When carbon dioxide dissolves in water it becomes carbonic acid (H2CO3), releasing H+ ions that decrease the pH of the ocean water. This affects the capacity of hard corals to build their tough skeletons, as this acidification interferes with the formation of calcium carbonate, the material from which the corals’ exoskeletons are formed. It does this in two ways: firstly, it can cause corals to build their skeletons more slowly, leaving them to grow at a slower rate and thus be more liable to damage in the ocean;  secondly, exoskeletons can actually weaken and dissolve due to this acidification. Evidence suggests that the pH of oceans has decreased in correlation with the increase of carbon dioxide in the atmosphere over the last 100 years.

Coral reefs are known to be one of the most diverse and complex environments on the Earth. Moreover, their disappearance will not only cause untold damage to aquatic life, but also to the disintegration of another prize ecosystem: the Queensland Rainforest. The Reef and the rainforest survive on a feedback mechanism between each other, each affecting  water distribution, chemical and nutrient cycling, and food and nutrient exchange. Thus, the impacts of declines in the Reef environment are not isolated: it will also affect many land species and other environments.

Will the Reef survive climate change? It has been argued that the damage done is beyond repair, but work can be done to protect the Reef, and all the valuable aquatic life it harbours. It has long been known that reduction of greenhouse gas emission is required, but if this is the Reef’s only lifeline, then it’s easy to fear that it is too little, too late, unless drastic action in terms of environmental management is taken… immediately.

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