Ocean acidification, the ugly twin of climate change

Ocean acidification (OA) is a current and future challenge not just for coastal communities that depend on shellfish such as oysters, and clams for their livelihood, but for the entire planet. It has the potential to disrupt the entire marine food web which would of course not only alter marine food chains, but food supply to humans. OA is not climate change per se, yet another consequence of increased levels of carbon dioxide (CO2) in the atmosphere.

OA is mainly caused by CO2 in the atmosphere dissolving into the ocean; approximately 25% of the man-made carbon dioxide emissions are absorbed by the oceans. The increased concentration of CO2 in the atmosphere has resulted in increased ocean absorption rates and in turn, this has resulted in a lowering of seawater’s pH, making it more acidic. According to the Smithsonian Institute, the ocean water has become 30% more acidic in the past 200 years – faster than any known change in ocean chemistry in the past 50 million years. This rate of change is turning out to be a surmountable problem, as many species that have evolved over millions of years simply cannot adapt.

A healthy coral colony in Australia's Great Barrier Reef. A new study was the first ocean acidification experiment of a natural coral reef community.

It was previously thought the oceans’ increased rate of absorption of CO2 would not be a concern as the constant inflow of water from rivers was thought to be enough to keep the oceans’ pH stable. However, this is not the case; since the industrial revolution the mean ocean pH has dropped from 8.2 to 8.1 and is expected by fall another 0.3 units by the end of the century. This may not seem like a large drop; however, many essential chemical reactions are sensitive to small changes in pH. For example, a drop in blood pH of 0.2-0.3 in humans can cause seizures, comas and even death. Similarly, a small change in the pH of seawater is found to have very harmful effects on certain marine species, particularly corals and certain species of shellfish.

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