Ocean Acidification Found To Dissolve Sea Snail Shells

Heat-map shows where differences are most likely to occur in shell shape among gastropods exposed to raised CO2 levels. Red indicates a greater degree of change. Ben Harvey

An international team of researchers turned to one of the ocean’s smallest creatures in order to understand how climate change will affect the world’s marine ecosystems.

As atmospheric carbon dioxide (CO2) contributes to climate change, oceans around the world are increasingly acidifying, disproportionately impacting particularly vulnerable marine organisms, such as the “Triton shell” sea snail. Shells collected near volcanic seeps with CO2 levels similar to predicted levels in the future were found to be smaller, damaged, and lacking pigment when compared to their larger, intact, better-camouflaged cousins found in regions with healthier levels of CO2.

"Ocean acidification is a clear threat to marine life, acting as a stressor for many marine animals,” said study author Ben Harvey, from the University of Tsukuba, in a statement. “Here we found that the ability of the triton shells to produce and maintain their shells was hindered by ocean acidification, with the corrosive seawater making them smoother, thinner, and less dense.”

Like many other shelled marine organisms, the predatory Charonia lampas makes its namesake calcium carbonate shell by combining calcium with carbonate from the surrounding seawater, releasing carbon dioxide (CO2) and water in the process. But in waters with increased CO2 – and thus a lower, more acidic pH level – calcium carbonate species are not able to effectively control how they calcify their shells, making them especially vulnerable and an indicative species of how ecosystems will respond to future climate predictions.   

“As calcifying organisms are a fundamental component of coastal marine communities, the effects of ocean acidification are expected to lead to profound ecological shifts,” wrote the authors in their work published in Frontiers in Marine Science.

The team conducted their research at a marine volcanic seep off the coast of Japan. Here, CO2 bubbles out of volcanic vents and through the seabed, lowering seawater pH from present-day levels to those predicted in the future. Though it’s a naturally acidic area, it becomes an ideal “laboratory” to study the effects of carbon dioxide.

Using computed tomography (CT) scanning, scientists measured the thickness, density, and structure of the shells. They found that those near the volcanic seeps had half the shell thickness of those further away and their lengths were reduced from 178 millimeters to 112 millimeters, exposing body tissue and causing the shell to dissolve in some cases. 

“The extensive dissolution of their shells has profound consequences for calcified animals into the future as it is not something they can biologically control, suggesting that some calcified species might be unable to adapt to the acidified seawater if carbon dioxide emissions continue to rise unchecked,” said Harvey.

A comparison of shells assessed during the research, with the top shell taken from waters with present-day CO2 levels and the bottom one from waters with future predicted levels. Ben Harvey/University of Tsukuba

 

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