A Very Bad Year
This year was truly catastrophic for the Great Barrier Reef. The near record-breaking El Niño that rocked the east of the Pacific helped to push global temperatures almost 1.5°C warmer than average, with lethal effect on some parts of the reef. While bleaching events had already been striking other reefs, it finally reached Australian waters, with a truly shocking 93 percent of reefs experiencing some bleaching.
The northern parts, where the waters tend to be slightly warmer anyway, were worst hit. While bleaching – in which the coral ejects the algae that supply them with food, but also their myriad of colors, due to the rising temperature – is not necessarily fatal if the water temperature drops within a few weeks, it is thought that this did not occur quick enough for many parts. In fact, it is thought that a horrific 50 percent of coral in the northern Great Barrier Reef was killed off this year alone.
Yet it is not just the temperature that the reef needs to be concerned about. As we pump more CO2 into the atmosphere, it not only warms the planet, but is also absorbed by the oceans, changing its pH. When carbon dioxide reacts with water it produces carbonic acid, which in turn increases the acidity of the oceans. With atmospheric carbon dioxide concentrations exceeding 400 parts per million, and the oceans thought to absorb about a third of all CO2 put into the air by humans, things are not looking great.
This is even more bad news for the corals, as they construct their external skeletons out of calcium carbonate. This, it turns out, is highly susceptible to increases in acidity, causing the mineral to thin and making it more difficult to form in the first place. This will not only impact the corals, however, as snails, mussels, oysters and a whole plethora of other mollusks that are both economically and ecologically important will be affected.
Coral bleaching is reversible, but can also be fatal. Matt Kieffer/Flickr CC BY-SA 2.0