Which ocean species will outlast the rising acidity of seawater?

Many of the projected effects of climate change on the world’s oceans are already visible, such as melting polar ice caps and rising sea levels. But invisible changes may be the most threatening to human food sources, beginning with the tiny species like plankton that inhabit the bottom of the oceans’ food chain.

As emissions from human activities increase atmospheric carbon dioxide, they, in turn, are modifying the chemical structure of global waters, making them more acidic.

Many researchers have speculated that most aquatic species won’t be able to adapt in time to survive the acidification that has already begun, but there are some who are more optimistic. One of them is Jennifer Sunday, a postdoctoral ecologist and evolutionary biologist at Canada’s Simon Fraser University.

“You hear people say species aren’t going to adapt in time,” she explained in an interview, “but I just knew that we don’t really know that. This really motivated me to start thinking about a study to test this. We can and did put some science and data to this question.”

Sunday and her team published a review earlier this year in Trends in Ecology and Evolution, aiming to help researchers improve their chances of finding potential survivors. It suggests that more studies should focus on identifying species with enough genetic variety to produce a mutant that can adapt.

Sunday feels that the better researchers get at searching for adapters, the more will be found.

The process that creates this risk is swift and globe-spanning. Oceans absorb roughly a quarter of the rising CO2 emissions from the atmosphere, so as that concentration increases, the oceans absorb more of the gas. In the past 150 years, human-induced climate change has changed the ocean acidity from roughly pH 8.3 to pH 8. (In the pH scale, 1 is most acidic, 7 is neutral and 14 is basic, or least acidic).

“It’s anywhere from 10 to 100 times faster than anything we’ve seen over the last million years,” said Richard Feely, a chemical oceanographer and senior researcher with the National Oceanic and Atmospheric Administration. “That’s just according to our good records.” And acidity is only expected to rise.

“By the end of this century,” Feely said, “projections are an increase by another 100 to 130 percent.”

Which tiny sea creatures can win the lottery?
Changes in pH levels can have massive effects on marine life, a fact that has led many scientists to believe that most species can’t withstand large increases in acidification. When CO2 mixes with ocean waters, it binds calcium molecules that are usually free for marine creatures to build shells. The more acidic waters can also corrode existing shells.

Sunday isn’t the first to try and isolate survivor species. Several teams worldwide have already been exploring the potential of marine life species to adapt to predicted climate changes.

In 2009, a European team published their research on the tiny circular plankton Emiliania huxleyi, made up of light-reflecting mineralized calcium ovals. These tiny plankton sometimes float in populations so large, they’ve been spotted from outer space.

Looking at strains of the plankton under varying CO2 levels, researchers found that while some plankton had difficulties forming their shells when the water was more acidic, others did not, causing researchers to speculate that the plankton might be able to use another form of calcium to substitute in shell making. Other studies have shown that certain species thought incapable of evolving quickly can, in fact, rapidly adapt.

Evolution is like a lottery. The faster a species reproduces, the greater the number of unique ticket combinations it creates in the genes of its offspring. For species that produce the right genetic mutation, their number is drawn and the prize is survival.

“This is particularly important when you want to look at a species’ ability to cope with change,” said Jennifer Pistevos, a master of research student at the Marine Biological Association, who studied clone populations of Celleporella hyalina, a tiny organism she found to have an amazing ability to reproduce in both more acidic and warmer water conditions.

“Faster reproduction rates give us a chance to see how vulnerable a species is,” Pistevos said.

In 2012, Sunday and colleagues spanning three continents reviewed past studies, and based on this work, propose future research dedicated to efforts to locate adapters by incorporating more experimental evolution into the studies.

Experimental evolution identifies members of a species born with the winning genetic ticket instead of those who can come up with the correct number during their lifetime. Being born with the winning ticket means these individuals may be able to ride the acidifying tides in the kind of time frame needed—which is immediately.

Questions that can’t be answered in the lab
Sunday and her team also suggest more work should consider a species’ response to multiple environmental changes, such as increased temperature and oxidation levels, as well as multiple stages of life. Currently, many studies only follow a species at a specific point in its members’ lives, such as infancy. Without tracking an organism over its life span and in a complicated and changing environment, it’s hard to say whether observed changes will translate into overall survival.

Although Sunday sees her work as laying the groundwork for less pessimistic predictions of the future fate of marine life, not everyone agrees that the approach is realistic. Aran Mooney, a biologist at the Woods Hole Oceanographic Institute who studies the effects of ocean acidification on Atlantic long-fin squid larvae, said some methods Sunday recommends are not practical for studying all species.

“Overall, the review is very good for us,” he said. “The authors point out some great goals and the limitations we face.” But for species like squid, Mooney said, Sunday’s suggestions are unlikely to be used.

“Measuring squid evolution in the lab might be doable to some extent,” Mooney said, “but it isn’t really possible to raise multiple generations or even young to adult—[they] don’t do all that well in captivity.”

Though Sunday agreed that predicting exactly how oceans will look in the future remains hard, researchers are starting to look in the right places. “The question just seemed too difficult before,” she said. “We wanted to put our advice out there so people could see it’s not impossible for species to adapt in time.”

“I do predict some species will adapt,” concluded Sunday, “but not all. Ultimately, it’s pretty shocking to think we’ll be losing species and it will be because of us.”

Jennifer Huizen & ClimateWire, Scientific American, 6 August 2014. Article.

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