From: The Ecologist, The Ecologist, More from this Affiliate
Published December 24, 2014 01:09 PM

Carbon Dioxide Threat To Mussels' Shells

The world's mussel population could be under threat as rising CO2 levels in atmosphere and oceans makes their shells weaker and more brittle shells - making them more vulnerable to stormy seas, and predation.

In a new paper published today in the Royal Society's journal Interface, researchers from the University of Glasgow describe how mussels' shells become more brittle when they are formed in more acidic water. 

The world's oceans are becoming increasingly acidic as they absorb some of the atmospheric carbon dioxide which contributes to climate change.

The water reacts with the carbon dioxide to form carbonic acid, which is gradually lowering the pH of the oceans (indicating an increase in acidity). Scientists expect the pH of the world's oceans to have dropped from 8 today to 7.7 by the end of the 21st century.

"What we've found in the lab is that increased levels of acidification in their habitats have a negative impact on mussels' ability to create their shells", said research team leader Susan Fitzer of the University's School of Geographical and Earth Sciences.

As oceans get more acid, less bicarbonate for shell-making

Mussels' shells are composites of calcium carbonate and organic material created by the mussels through a process known as biomineralisation.

Mussels draw bicarbonate ions from seawater and use proteins in their bodies to make crystals of calcium carbonate to form their two-layer shells. In more acidic water, there are less bicarbonate ions available for the mussels to make their shells.

"This could mean that mussels growing in the wild in the future could be more vulnerable to attack from predators, as well as from the effect of ocean forces", explained Dr Fitzer.

"As blue mussels are commonly used for human consumption, it could also have an effect on the yields of mussels available for the fishing industry."

The mussels do have way to resist the more acidic water once their shells have formed. Their shells' outer later is composed of calcite, a form of calcium carbonate that is more resistant to acid decay. Only the inner layer is made of the more soluble aragonite.

But even that mechanism is under threat, says Dr Fitzer: "What we found was that the calcite outer shells of the mussels past a certain threshold of acidity was stiffer and harder, making it more brittle and prone to fracture under pressure, and the aragonite inner shell became softer."


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