But I like it sparkling: why we don’t want acidic oceans

Science and Technology

Oceans make up nearly three quarters of our planet’s surface and are home to over 300,000 currently described species, with an estimated 95% of the total number yet to be discovered. But just how important are these species and why should we care to protect them?

Life underwater is so fundamentally important to our existence that we would struggle to breath without it: seven out of every ten breaths we take are using oxygen produced by phytoplankton in the oceans. In addition, the contents of the oceans constitute a large part of our diet, with 15.7% of animal protein we eat coming from seafood. A less anthropocentric argument for protecting the oceans is that life under the sea is so wonderfully biodiverse and has been for so long, containing thousands of ancient species, that we should want it kept that way. It’s possible that the greatest threat to many species in the oceans is rather indirect, in the form of ocean acidification.

“The effects of acidification can be likened to trying to building a ten-metre-high wall whilst a stranger keeps taking your bricks and burying them…”

Ocean acidification is the process by which, as the name suggests, the oceans are losing their alkalinity. It may come as no surprise to you that the main cause of this is humans. We have increased the concentration of carbon dioxide in the atmosphere to such an extent that the exchange of carbon between the atmosphere and hydrosphere has become unbalanced, with a net flow of carbon dioxide into the oceans. This carbon dioxide consequently reacts with ocean water to form carbonic acid, H2CO3, impacting coral species as it affects their ability to grow and maintain their shells, or exoskeleton.

This higher level of carbonic acid is worrying since it essentially eats away carbonate ions, the fundamental building blocks of coral shells formed by a process known as calcification. The lower the concentration of carbonate ions, the greater the energy required to build organisms’ shells by calcification. This is achievable for the organism down to a certain carbonate concentration, beyond which they are spending energy on calcification that would otherwise be used for basic biological process such as metabolism, enzyme activity and protein function. This is what causes the death of the organism and, when whole populations are affected, ultimately leads to species extinction.

The effects of acidification can be likened to trying to building a ten-metre-high wall whilst a stranger keeps taking your bricks and burying them ten metres into the ground, making it take longer and requiring more energy to build that wall. Examples of calcifying organisms that are likely to be affected worst by ocean acidification include starfish and sea urchins (echinoderms), clams and oysters (mollusks) as well as brachiopods, coccolithophores and many types of pteropods. Behind these long latin names are species that are often at the bottom of many food chains (such as coralline algae), important in creating habitats and niches for other, more dynamic, organisms to live and feed.

Scientists have used past and current data to predict the future of biodiversity of coral reefs given the expected rates of acidification. Under what’s known as ‘business as usual’, up to 90% of coral reefs in the world could be lost by 2050, with ocean acidification playing a big factor. For the reasons explored in this article, you can start to see why we need to protect our oceans. We need to come up with ways of drastically reducing the amount of carbon dioxide that is absorbed by the ocean, and that starts with us as individuals, and our responsibility to greatly reduce our emissions.

Image Credit: Michal, Wojtek Strzelecki and Jerzy Strzelecki (CC BY 3.0)