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Are dying coral reefs an indication of a dying planet?

BySophie Zweifel

Apr 5, 2017

Coral reefs might just be the most important biological structure on the planet. Not only do they house 25 per cent of marine life and provide coastline protection, they also may hold the key to curing cancer, arthritis and a myriad of other afflictions. Yet our voracious appetite for fossil fuels might just shatter the coral reef’s delicate balance. In fact, it is happening already.

The Student spoke to Dr Mark Spalding, a marine scientist currently working for the Nature Conservancy and a research associate at the University of Cambridge. An expert in global biodiversity, his recent focus has been on pressures and management of marine ecosystems, specifically coral reefs.

When asked what their future might look like if carbon emissions were not reined in, Dr Spalding said: “I fear we could be heading, in the next 20-30 years, towards something pretty bleak. Corals hanging on in ecosystems that are somewhat changed and might not even fit a technical definition of a coral reef.” (sic)

An estimated 2.5 billion tonnes of carbon dioxide have been absorbed by the oceans every year between 2002-2011. This correlates to 26 per cent of emissions from human activity. The absorption of carbon dioxide into the ocean causes an equilibrium reaction whereby a product named carbonic acid is created. As more carbon dioxide is absorbed into the oceans, more carbonic acid is formed. Once a critical amount of carbonic acid is reached, the equilibrium will shift, meaning the oceans will absorb less carbon dioxide in the future. This is worrying as the ocean is a valuable carbon sink.

There is, however, an even more dire consequence of this uptake of carbon dioxide: ocean acidfication.

Carbonic acid, once formed, undergoes another reaction. Namely, it breaks down into bicarbonate and hydrogen ions. Higher hydrogen ion concentration results in lower ocean pH levels. Since the mid-18th century, average pH levels of the ocean have dropped from 8.2 to 8.1. Although this may not seem significant, it actually represents a 25 per cent rise in hydrogen ion concentration. This increase, coupled with a decrease in another molecule called carbonate ions, leads to an effect, collectively referred to as ocean acidification.

Carbon dioxide reacts with carbonate ions to form bicarbonate. This has detrimental consequences for calcifying species, including: oysters, clams, several species of plankton and, most notably, shallow and deep-sea corals. Corals are not only debilitated by a lack of carbonate ions, but the higher ocean acidity has been shown to interfere with their reproduction and ability to recover from stressors.

All this gives a rather bleak picture. With a forecasted increase in carbon dioxide concentrations in 2017, is there any hope for coral reefs at all?

Dr Spalding thinks there may be, as he wrote: “Look at the Caribbean. There, most reefs have already utterly changed thanks to a host of human impacts. It might be argued that many of these are no longer true reefs, but they are still vibrant ecosystems. Very changed, but not a lifeless void.”

We may convince ourselves that we control nature, that we understand it; however, it is difficult to predict just what will be left of our coral reefs in a decade, two decades – or a century. Dr Spalding says a possible outcome could be that: “The world enters a non-reef building phase”. Or, perhaps, the reefs will adapt to the acidified oceans. Only time will tell – something we are quickly running out of.

Image: Daviddarom

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