USC study finds urchins work overtime to cope with rising ocean acidity

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Marine scientists at the University of Southern California have found sea urchins work overtime to cope with the effects of climate change. An article published Monday in the Proceedings of the National Academy of Sciences offers glimpse into how living organisms can evolve to handle environmental stress, particularly from oceans made more acidic by carbon dioxide and higher temperatures.

The USC team was led by Donal Manahan, a professor of biological sciences in the USC Dornsife College of Letters, Arts and Sciences.

As humans pump more carbon dioxide into the atmosphere, the world’s oceans are absorbing much of it, making seawater more acidic. 

Marine scientists study urchins to understand how life responds to the changing chemistry of the ocean. In a special lab on Catalina Island, USC researchers grew sea urchins and subjected some of them to ocean acidity levels predicted by the end of the century. A second group grew in regular seawater. 

They found urchins living in acidic waters need to work harder at a basic life function – growing and rebuilding cells by processing protein. Manahan and his team found that urchins are working a little more than twice as hard – leaving less energy to fight other environmental stressors like disease and pollution. 

Manahan says that the researchers learned new things about how sea urchins synthesize and process the protein ATP -- adenosine triphosphate -- which is a basic building block for life.

“If you have a lot of stress to deal with you do it very quickly. And if you don’t, you do it more slowly,” Manahan says.

The discovery came as Manahan and his team studied the metabolic budget for urchins raised in tanks whose chemistry mimics what the oceans could look like at the end of this century.

He says to imagine a metabolic budget like a household budget, and protein turnover, a basic expenditure of energy necessary to life, is like your rent.

Essentially, added stresses from climate change are raising the rent for sea urchins. Urchins he studied were able to keep paying the rent – that is, regulating ions in cells and synthesizing protein – even as the amount of energy it took for those processes more than doubled from 40% to 84% of the creature’s metabolic budget.

But Manahan says that leaves little energy for dealing with other potential stresses.

“If you keep spending your available energy to fix this problem, oh, and here there’s a new problem, and ooh, we need twenty percent over here - I’m sorry, I don’t have twenty percent. And then, boom!” he says. “In comes a microbial contaminant and maybe kills you because you can’t mount a response to it.”

Manahan maintains the findings aren’t all bad news.

“The reason we’re optimistic is it may be that this set of organisms has figured out how to handle the stress now,” Manahan says. “Some of them will handle it well, and some of them will handle it not so well, mostly set by their genetics. That’s totally Darwinian evolution.”

His team, including study co-authors Francis Pan and Scott Applebaum, is now interested in identifying which sea urchins cope well with ocean acidification, and why.

“There’s always a small set of winners versus losers,” he says. “You’re always trying to find the winners.” 

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