Warming oceans might sound like a good thing for swimmers and surfers, but they're wreaking havoc on the plants and animals that call those waters home. Australia's Great Barrier Reef has undergone two consecutive years of severe coral bleaching, from which large swathes of it might not recover. Now, research out of the University of California, Davis (UC Davis) has found some more bad news. A combination of warming and acidifying waters can cause invertebrate organisms called bryozoa (or moss animals) to start dissolving – and other sea creatures could soon face a similar fate.

The increasing amounts of carbon dioxide we pump into the atmosphere isn't just polluting the air: a huge chunk of that is being absorbed by the ocean. That in turn is increasing the acidity of the waters, which could have all sorts of unexpected consequences on the wildlife.

To investigate just what those effects might be, the UC Davis team raised tanks of bryozoans, invertebrate aquatic organisms that often grow on the surface of kelp. Each of the tanks had different levels of water temperature and acidity, as well as varying their access to food. Alarmingly, when the bryozoans were raised in warmer waters and then exposed to more acidic waters – conditions that already exist off the coast of California – large parts of the creatures dissolved completely in a matter of months.

"We thought there would be some thinning or reduced mass," says Dan Swezey, lead author of the study. "But whole features just dissolved practically before our eyes."

On closer inspection, the scientists found that the animals brought up in warmer temperatures were using more magnesium to build their skeletons, which they mostly make out of calcium carbonate, and the effect was exacerbated if food was less abundant. The researchers aren't sure why these conditions led the bryozoans to increase their magnesium intake, but unfortunately, the elevated levels of the element in their skeletons makes them dissolve more easily.

Bryozoans (seen here as the white "frosting") often grow on kelp(Credit: Jackie Sones/UC Davis)

It wasn't for lack trying, either. The researchers found that in response to increased acidity, the stressed out animals turned more of their energy towards growing, but they were dissolving faster than they could add new mass.

Bryozoans aren't the only sea creatures that grow by building calcareous skeletons, and the scientists consider them a canary in the coal mine for other species, like starfish, sea urchins, tube worms and some algae.

"Marine life is increasingly faced with many changes at once," says Eric Sanford, co-author of the study. "For bryozoans, their response to warmer temperature makes them unexpectedly vulnerable to ocean acidification. The question now is whether other marine species might respond in a similar way."

The research was published in the journal Proceedings of the Royal Society B: Biological Sciences.

Source: UC Davis

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