March 29, 2012

Acclimation to Ocean Acidification: Give It Some Time

Filed under: Adaptation, Animals

Rising atmospheric carbon dioxide levels lead to an increasing amount of CO2 being dissolved in the oceans which drives down the oceans’ pH level. This is often referred to as “ocean acidification” and included among the list of ills that energy production from fossil fuels imparts to the environment. Type “ocean acidification” into your Google search and you’ll quickly be confronted with a litany of potential impacts—all bad. The Center for Biological Diversity refers to it as global warming’s “evil twin.”

“We mean it this time” our greener friends are saying about this current apocalypse. But is ocean acidification any different than the population bomb, global starvation, acid rain, ozone depletion, global cooling, and global warming—all forecast to cause the end of the world as we know it, and all falling a bit short?
It’s beginning to look like the same old same old. In what will come as no surprise to World Climate Report regulars, alarmists are overdoing things just a little. Their biggest mistake comes in assuming that the oceans’ denizens cannot deal either with the pace or the magnitude of the projected changes to the oceans’ chemistry.

The more researchers look into this, the more they report findings to the contrary.

A large and continually updated annotated and summarized collection of findings which report acclimation and adaptation to “ocean acidification” is maintained at the Center for the Study of Carbon Dioxide and Global Change. Spend a little time there and you will come away with a completely different view of the subject than was returned to you in your Google search above. The Center also maintains a digital archive of citations to the relevant primary scientific literature, so you can see for yourself.

A new paper just published in the journal Global Change Biology titled “Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophelia pertusa “ is surely soon to be an inductee in the Center for the Study of Carbon Dioxide and Global Change database.

The authors, Armin U. Form (no relation to the conservative blogger Charles U. Farley) and Ulf Riebesell, are from the Leibniz Institute of Marine Sciences in Kiel
Germany. They introduce the problem:

Ocean acidification, often termed ‘the evil twin of global warming’, is caused when the CO2 emitted by human activity dissolves into the oceans. Presently, the ocean takes up about 25% of man-made CO2, which has led to a decrease in seawater pH of 0.1 units since 1800. By 2100, surface ocean pH values can easily drop by another 0.3–0.4 units. Although there is reasonable certainty about the chemical changes related to ocean acidification, the impacts it may have on marine organisms and ecosystems are still poorly understood. A major gap in our understanding of the impacts of ocean acidification on life in the sea is the potential of marine organisms to acclimate and adapt to increasing seawater acidity. Most of our present understanding on the biological impacts of ocean acidification is based on short-term perturbation studies.

The last sentence nicely sums up the problem underlying the proclamations of impending catastrophe from “ocean acidification”—that is, there are very few long-term studies of the response of organisms to changing conditions, instead, the vast majority of results come from studies which scoop things up out of the ocean, plop them into an aquarium, jack up the acidity of the water, and watch what for a few days to see what happens. That’s about as far from the real world as you can get, and it’s little wonder that the organisms don’t tend to fare particularly well.

Basically, Form and Riebesell follow this same procedure, but in addition to watching what happens over a few days, they maintain vigilance, and follow the response for about 6 months. The organism they are studying is a cold-water coral species, Lophelia pertusa, which they describe as “the most common reef framework-forming and ecosystem engineering cold-water coral with a cosmopolitan distribution.” One reason they chose to look at a cold-water coral is that “cold-water coral reefs are considered the ecosystem most vulnerable to ocean acidification.”

What they found was that in an experiment that lasted only 8 days, that the growth rate of the coral was slowed down by the dissolution of extra CO2 into the aquarium water—the more the researchers added CO2 (increasing the acidity and lowering the pH) the worse the corals fared (Figure 1).


Figure 1. The growth rate (G) of the coral Lophelia pertusa, in relation to the pH level of the aquarium water after 8 days of exposure (source: Form and Riebesell).

In a second experiment in which the coral specimens were exposed to lower pH levels for 178 days, the growth rate did not decline, and in fact, even appeared to increase under the lower pH (more acid) conditions (Figure 2).


Figure 2. The growth rate (G) of the coral Lophelia pertusa, in relation to the pH level of the aquarium water after 178 days of exposure (source: Form and Riebesell).

Form and Riebesell describe their findings:

Growth rates in the long-term experiment (LTE) did not follow the negative trend with increasing pCO2 [decreasing pH] observed in the short-term incubation. Instead, growth rate, which was comparable to that of the control treatment in the short-term experiment, stayed high at elevated CO2 levels… Although not statistically significant, a linear regression analysis reveals an increasing trend of coral growth with rising pCO2 concentration [decreasing pH].*

They comment on the importance of longer-term experiments:

It is surprising that the ability to tolerate sub-saturated conditions in terms of maintaining calcification rates is not manifested in short-term high CO2 experiments. This could indicate (i) that it takes several days to weeks for Lophelia to activate the metabolic pathways needed to calcify when subjected to sub-saturated waters, or (ii) that triggering the activation of these pathways requires longer-term high CO2/low pH exposure. …The differences in observed responses between short- and long-term exposure experiments highlight the importance of long-term incubation studies allowing for complete acclimation of the test organisms.

And they have this to say as to the significance of their findings:

This is the first study showing a positive response in calcification to increasing pCO2 for the predominant reef-forming cold-water coral L. pertusa and, to our knowledge, for scleractinian corals in general.**

Now, Form and Riebesell are quick to point out that laboratory conditions do not necessarily mimic the real world environment and that therefore their results are only the first steps in an extended series of observations and experiments that would be required to establish the in situ response of the corals in their ocean environment and its changing conditions. And we are sure that they are right about this.

But the larger lesson is this: Don’t jump to conclusions based on an inadequate analysis of complex systems.

If everyone followed this advice, our future would certainly appear much less “alarming.”

Reference:

Form, A. U., and U. Riebesell, 2012. Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophela pertusa. Global Change Biology, 18, 843-853, doi:10.1111/j.1365-2486-2011.02583.x, http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02583.x/abstract

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* What has happened to rigorous peer-review? A “trend” that is not statistically significant means it cannot be statistically discriminated from zero, i.e. no trend. This sentence should have said “A linear regression reveals no significant relationship between coral growth and rising pCO2 concentration.”

** Same here; should simply read, “This study shows no negative relationship between coral growth and ocean acidity.”




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