Ocean Acidification: Making Sense of Crabs and Skeptics

by on October 09, 2013

Tanner crabs, like this one on the floor of Monterey Canyon, are one of the bottom- dwelling marine organisms being studied by MBARI researchers, to gauge how acidification of ocean waters will impact their ability to form their calcium carbonate shells. Photo: 2002 MBARI.



Like other aspects of climate science, ocean acidification (OA) science has drawn the fire of skeptics. Some have used the findings of OA researchers to argue either that the science isn’t settled or that OA isn’t necessarily such a bad thing.

By way of background, sufficiently acidic seawater can either prevent organisms from forming their protective shells, or actually dissolve shells once they’re formed. Creatures that build their shells from calcium carbonate are the most vulnerable. But variations in shell structure—such as a matrix of carbonate and organic material, or an organic outer layer—seem to reduce the impact. With all that variability in the response of marine organisms, it isn’t hard to cherry-pick the data.

In particular, climate change deniers cite a study by Justin Ries of the University of North Carolina at Chapel Hill. Ries measured changes in shell calcification in a number of species, including mollusks (clams, oysters, scallops), echinoderms (sea urchins), and crustaceans (crabs, lobsters, shrimp). Although calcification declined in most of his test subjects, in the crustaceans it actually increased, and was greatest at the highest carbon dioxide concentration tested, 2856 parts per million—well beyond current ocean levels of about 400 ppm, and way beyond anything in even the direst forecasts. (The higher the CO2 concentration, the lower the pH and the greater the acidity.)

Researchers at the Monterey Bay Aquarium Research Institute (MBARI) have been studying the impacts of increased CO2 in the deep marine environment for over a decade. This “benthic respirometer” on the floor of Monterey Canyon has chambers in which a variety of deep sea organisms are exposed to differing levels of CO2 to see how they respond. Photo: 2012 MBARI.

Researchers at the Monterey Bay Aquarium Research Institute (MBARI) have been studying the impacts of increased CO2 in the deep marine environment for over a decade. This “benthic respirometer” on the floor of Monterey Canyon has chambers in which a variety of deep sea organisms are exposed to differing levels of CO2 to see how they respond. Photo: 2012 MBARI.

Testifying in US Senate hearings in 2010, skeptic John Everett claimed that “crustaceans build more shell when exposed to acidification… [S]ome species flourish while others diminish. With no laboratory or observational evidence of biological disruption, I see no economic disruption of the commercial or recreational fisheries…” Ries’s response: “The published variability in the responses of marine organisms to ocean acidification should not be misconstrued as evidence of their immunity to it.”

Local scientists Jim Barry of the Monterey Bay Aquarium Research Institute and Tessa Hill of UC Davis’ Bodega Marine Lab don’t question Ries’s findings. But context is important. In his testimony, Barry pointed out to the Senate committee that those anomalous lobsters may have been harmed in ways that Ries’s study wasn’t designed to detect: “[W]e do not know how ocean acidification might have affected physiological processes other than calcification in these organisms, or how lifelong immersion in acidified waters would affect their growth, survival, and successful reproduction…[W]ould they grow more slowly or produce fewer young to support high skeletal growth?” Barry’s own research shows that some deepwater crabs suffer metabolic stress when exposed to acidified seawater. He also warns that even if the crabs and lobsters got a boost in shell formation, they’d be out of luck if their molluscan prey died out. In the sea, as elsewhere, no species is an island.

Joe Eaton is a land-based writer, although he has been curious about sea creatures since early summers in the Georgia Sea Islands and on the Florida Gulf Coast. Eaton wrote the Bay Nature Magazine article, Ocean Acid Trip: The Hidden Harm of Climate Change, which appeared in the October- December issue. 

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Ocean acidification: making sense of crabs and skeptics | Ocean acidification on October 10th, 2013 at 3:52 am

[…] Joe Eaton, Bay Nature, 9 October 2013. Article. […]

Bruce Richardson on October 10th, 2013 at 7:29 pm

Mr. Eaton, I don’t presume to speak for everyone who is skeptical of destructive ocean “acidification” claims. I can only explain why I’m skeptical.

First. It is based on a false premise. Look up “acidify” in the Merriam-Webster Unabridged dictionary and you will see that it means “to make acid (as by the addition of sufficient quantity of an acid) : convert into an acid.” The oceans are alkaline and the chemistry is such that the oceans will always remain alkaline. That’s because ocean water is a complex buffer system that tends to resist changes in pH. It might be possible for the oceans to be come slightly less alkaline. But the oceans can never be “acidified.” When a buffer system is warmed, it favors a lower pH. The oceans have probably been warming since the end of the last major ice age. It’s reasonable to assume that the there has been some decrease in ocean pH on average.

The term ocean acidification is deceptive and I really think intentionally so. Suggesting that the oceans are become acidic is more likely to frighten folks than saying the oceans are becoming slightly less alkaline i.e. more like drinking water.

Second. A common claim is that since 1751 and 1994, ocean surface pH is estimated to have decreased from around 8.25 to 8.14 i.e. eleven hundredths of a pH unit. “Estimated” based on what?

The pH of ocean water is difficult to measure. In fact, it has only been since the 1970′s that presumably accurate pH measurement of ocean water has been possible. There is no way to know to two decimal places what the pH in 1751 was. I have never seen any reasonable answer to “how do we know what the pH in 1751 was?” Can you answer that?

Third. The oceans represent around 70% of the earth’s surface. That’s a large area. The pH of ocean water can vary from place to place. And it can vary from time to time in a particular place. If varies with ocean depth. The pH deeper is lower generally. Sometimes there is upwelling where the deeper ocean moves up.

How is it possible to have a representative sample of the oceans? Even tens of thousands of simultaneous pH measurements still wouldn’t be a representative sampling. Certainly, any sampling done near the shore would not be representative because most of the ocean area is not near the shore.

Forth. If the science is truly settled, then making the case ought to be easy. Just laying out the evidence should be enough to answer the skepticism of folks like me. That’s not what happens. We are called “deniers” and worse. For what? Looking at the available empirical evidence and pointing out that the case has not been made?

Fifth. What sort of science suggests that a consensus of opinion is a substitute for hard evidence? Science isn’t a democracy where the natural laws are based on a popular vote.

Mr. Eaton, do you think that my skepticism when it comes to ocean “acidification” is unfounded?

Colorado Bob on October 13th, 2013 at 8:18 am

Pteropods, tiny marine snails that are a primary food source for salmon, are considered the “ground zero” species, Wiley said. Ocean acidification also affects coccolithophores, the main food source for copepods, another important part of a salmon’s diet, Wiley said.

A colleague of his recently found pteropods’ shells actually dissolving in the Southern Ocean. Until that discovery, the phenomenon had been observed only in a laboratory setting, and at oyster hatcheries in Oregon and Washington, he said. OARC researchers are now looking for evidence of this in the Gulf of Alaska.

Bruce Richardson on October 14th, 2013 at 10:19 am

Bob, actually I had seen the story that you provided the link to. They never once mentioned that the oceans are alkaline or that the oceans can never become acidic. They described pH as a measure of acidity. Actually it is a measure of acidity or alkalinity (basicity). They spoke of ocean “acidification” which is a misrepresentation. As I mentioned, the oceans can never be acidified. The oceans are a buffer system. The oceans could become slightly less alkaline which is not the same as becoming acidic. Talking about “acidification” may be better from a propaganda standpoint but it is a misrepresentation that has become ubiquitous among climate scientists. The fact that it is a common misrepresentation doesn’t make it less of a misrepresentation.

They said that “Some recent die-offs at oyster hatcheries in the Pacific Northwest have been attributed to high CO2 concentrations in the water.” Attributed by whom? They never mentioned ocean upwelling which can bring up less alkaline ocean water from the depths. They never mentioned a correlation between upwelling and die-offs.

The story said “Combining recent data with ice core samples stretching back 800 years, scientists have observed a growing trend of atmospheric CO2 concentration in the oceans and graphed its increase.” Ice core samples do not measure CO2 concentration in the oceans. That ice came from precipitation. They measure atmospheric CO2 concentrations. There is disagreement over how precisely the ice core samples represent atmospheric CO2 levels. Based on what assumptions they are willing to make, they can calculate a pH for the oceans based on the concentration of atmospheric CO2 but such calculations are little more than speculation based on little more than opinion.

Actually the rate of increase of CO2 would have to double to get to 800 ppm (0.08%) by 2100. At the present rate of increase, it would be more like 2200 before we would reach 800 ppm (0.08%).

Atmospheric CO2 concentrations have been rising steadily since the start of the industrial revolution and the end of the Little Ice Age. The story only mentioned the start of the industrial revolution. It has been warming on average since the end of the Little Ice Age. I don’t know to what extent the overall warming might have decreased the pH of the oceans. From just a chemistry standpoint, warming a buffer favors a lower pH. We don’t know what the pH of the oceans was at the end of the Little Ice Age or is now for reasons that I mentioned.

J on October 25th, 2013 at 3:12 pm


Arguing over the name “Acidification” is pointless. Most people don’t understand the effective difference between alkaline and acidic and most people don’t have the time to learn it. It wouldn’t make a difference if they did. The effects will still be the same no matter what it’s called.

The “Acidification” can also refer to the fact that the pH is moving toward the acidic spectrum, which is another way of saying less basic. So it’s all true.

I’ve actually spoken with a number of scientists in the field about where the name comes from and it was just coined by some higher up and it stuck because they didn’t know what else to call it. I think your theories about propaganda are rooted in your own willingness to bend truths. Most scientists are more focused on the science than policy. And if a scientist was truely bending results or fabricating conclusions, he’d never work again.

Furthermore, if you hate the name acidification so much come up with a better name and stop complaining.

I could be wrong but your “slightly” less basic seems to be referring to units on the pH scale. If that’s the case you’re forgetting that the pH scale is logorithmic, so those “slight” decreases are actually significant.

The oysters problems are caused from upwellings. But those upwellings are more acidic than they previously were which means the oysters can’t handle them anymore.

The oceans are massive and the pH does vary in location and depth and from creature to creature. That makes it extraordinarily hard to confidently say that X will be the outcome of all of this. Which is probably why you haven’t found your example of the science being “settled”. What people are refering to when they say the science is settled is one pH levels effects on one creature with Y number of other observed influences, in a lab setting.

Lastly, with regards to the vastness of the oceans and pH levels your right where scientists where a decade ago. “It’s too big, there’s no way CO2 could ever significantly affect the pH level.” Turns out they were wrong. The difference between you and them is they admit it and move on to find the truth.

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