Study shows how ocean acidification will affect algae

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Ocean acidification may have far-reaching effects on algae.

‘Subtle changes in calcification can cause dramatic changes in skeletal performance …’

Staff Report

LINZ — Scientists working at an underwater volcano near Sicily say they have new evidence that ocean acidification could change fundamental parts of marine ecosystems.

Their research shows that acidification weakens algal skeletons. Even a small loss of skeletal calcification caused by exposure to corrosive waters can have a significant impact and leave algae at risk of losing access to light and nutrients, the researchers concluded in a new paper published in the Royal Society’s Biology Letters.“Based upon current forecasts, many calcified organisms will be corroded by acidified waters by the end of the century,” said Professor Jason Hall-Spencer, with Plymouth’s School of Marine Science and Engineering, and its Marine Institute.”What this study shows is that a dramatic weakening of algal skeletal strength can have implications for performance, which in turn could transform an entire ecosystem.”

The surveys showed that the algae ranged in appearance from those with bright white cups at the low CO2 site to green cups at the high site, and no calcified algae were present in the region nearest the volcanic seeps.

Microscopic study showed that algae from low CO2 areas had an intact sheath of aragonite that supported the stem, while those in acidic waters were eroded and pitted and were up to 32 percent less calcified.

The lack of calcification led to “droopier” stems, which raised important questions about the impact upon their performance. And the scientists say the relationship between calcification and material stiffness was exponential, not linear, so even relatively small reductions in calcification led to a disproportionate drop in the ability of the material to resist a load.

“Although calcifying organisms can tolerate high CO2 conditions, even subtle changes in calcification can cause dramatic changes in skeletal performance, which may in turn affect key biotic and abiotic interactions,” said Professor Hall Spencer.

“A less rigid stem droops towards the seafloor likely reducing the distance spores can travel away from the cup. The cup is also photosynthetic, so bending may reorient it away from light and increase shading by neighbors, thereby reducing the scope for growth,” he said.

“But there are also potential benefits to being less stiff. A more flexible stem allows the algae to reorient in flow, reducing drag and the likelihood of dislodgement, and may aid in gas exchange as the stem moves back and forth like a pendulum.”

“This study underscores the fact that some organisms may survive ongoing ocean acidification despite reduced calcification; this facultative calcification may explain why certain calcified organisms reappear in the fossil record after mass extinctions associated with periods of high atmospheric CO2,” said Professor Laura Newcomb, of the University of Washington.

“Many ocean acidification studies show reduced calcification at high CO2, but do not examine the consequences for organismal performance. Our ecomaterial approach establishes these linkages between calcification and performance (and ultimately fitness) which are vital for long-term predictions of how organisms will fare in a high CO2 world,” Newcomb said.

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