Guest Post by Willis Eschenbach
I love the coral reefs of the planet. In my childhood on a dusty cattle ranch in the Western US, I decorated my mental imaginarium of the world with images of unbelievably colored reefs below white sand beaches, with impossibly shaped fish and strange, brilliant plants. But when I finally first got to dive on the reefs, some forty years ago now, I found that my wildest imagination was only a pale, sickly phantasm compared to the real reef, the real beach, and the real sea life around it. It is a marvel of rioting color and exploding life where I have spent many happy hours, mesmerized.
Figure 1. Thousands of different types of living creatures together form the coral reef environment. SOURCE
Unfortunately, coral reefs are supposed to be threatened by increasing CO2. It’s supposed to make the various animals’ carbonate skeletons and shells dissolve, by decreasing the “pH” of the ocean (pH is a measure of relative alkalinity/acidity) and thus making the seas more neutral than they are today. Careful chemical calculations based on the complex carbonate chemistry of the ocean are said to prove that, no question. Aquarium tests are said to have shown it beyond a doubt, with statistically significant results. The claim has been repeated ad nauseam … and yet the reefs are thriving where they are not impacted by true threats like pollution and coral mining and curiously, the killing of parrotfish.
I have long held that the chemistry of the ocean was not ruled by the chemical energetics of the hundreds of various reversible reactions. That is the generally held view, that the ocean is ruled by chemistry. I hold the contrasting view, that the chemistry is not the last link in the chain. I say that the chemistry of the ocean is in turn ruled by life, and not the other way around as is the common assumption.
An early piece of evidence that shaped this view was when I found out that the pH of the water over a reef is not driven by chemistry, nor by the partial pressure of CO2 in the air. It is driven by the reef itself, which is a net producer of CO2. In other words, the biological products of the reef creatures themselves cause the water over the reef to move from more to less alkaline, often on a short time span. In one study the pH of the reef water changed by one full pH unit (1000% change) in 12 hours … and yet climate researchers breathlessly forecast dire consequences from much smaller pH changes than that spread out over a century, not 12 hours. From my experience with life in the ocean, and from my research, I am much more confident in the adaptability and tenacity of life than those researchers seem to be.
Figure 2. Cross section through a coral colony showing the living polyps, along with the carbonate skeleton built by the polyp. SOURCE
So I was interested to come across a research paper (paywalled, alas) with the unwieldy name of “Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophelia pertusa.”
Ocean acidity has increased by 30% since preindustrial times due to the uptake of anthropogenic CO2 and is projected to rise by another 120% before 2100 if CO2 emissions continue at current rates. Ocean acidification is expected to have wide-ranging impacts on marine life, including reduced growth and net erosion of coral reefs. Our present understanding of the impacts of ocean acidification on marine life, however, relies heavily on results from short-term CO2 perturbation studies.
Here we present results from the first long-term CO2 perturbation study on the dominant reef-building cold-water coral Lophelia pertusa and relate them to results from a short-term study to compare the effect of exposure time on the coral’s responses. Short-term (one week) high CO2 exposure resulted in a decline of calcification by 26-29% for a pH decrease of 0.1 units and net dissolution of calcium carbonate.
In contrast, L. pertusa was capable to acclimate to acidified conditions in long-term (six months) incubations, leading to even slightly enhanced rates of calcification. Net growth is sustained even in waters sub-saturated with respect to aragonite. Acclimation to seawater acidification did not cause a measurable increase in metabolic rates. This is the first evidence of successful acclimation in a coral species to ocean acidification, emphasizing the general need for long-term incubations in ocean acidification research. To conclude on the sensitivity of cold-water coral reefs to future ocean acidification further ecophysiological studies are necessary which should also encompass the role of food availability and rising temperatures.
I don’t have the full paper yet, but let me briefly discuss the abstract. The main message I see there is, the reef abides. The plants and animals of the ocean abide. The creatures that form carbonate shells and structures are tough and tenacious, they can do things we haven’t imagined. Their lifespan is often short enough to allow for evolution in human rather than geological time. They are able to change and modify, to adapt in response to changing water conditions. In addition, a healthy reef contains not just the dominant species in any given ecological niche, but a host of competing species. If it gets a bit warmer or colder, this alters the balance of the reef’s major simbionts, emphasizing a better-adapted competitor, and the reef keeps going. Even the “bleaching” events so feted by doomsayers are only minor occurrences in the reef’s geological history. Drill down, this has happened in the past. It is the extreme end of the scale of how the reef adapts to changing conditions. It gets rid of its symbionts wholesale, and starts over again. But the reef abides.
Next, a nitpick. The correct description for their claim is that the ocean waters have become more neutral. They have not become “more acidic” as the paper claims. They have moved towards neutrality. They have to pass through neutrality before they can start getting “more acidic”, and the ocean is a long ways from that.
Finally, I doubt greatly that we have anywhere near enough data to make the statement that “Ocean acidity has increased by 30% since preindustrial times”. See the second link above (repeated here http://wattsupwiththat.com/2010/06/19/the-electric-oceanic-acid-test/ ) for some of the very scarce real data.
I’ll update this if I can get a copy of the paywalled paper from my undersea connections …
[UPDATE—A denizen of the sub-aquatic world has tapped a trans-oceanic undersea fiber optic cable and sent me the paper, my thanks as always to Davey Jones. My comments follow.]
First, their statement about the so-called increase in ocean acidity is repeated in the body of the paper, but without citation … not good. They assert, without any evidence, that:
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.
As mentioned above, that’s sketchy, observations of ocean pH are very scarce. Other than that, however, it is a fascinating paper. The experiment is very well described. They went down in a submersible and picked the coral branches, to assure good specimens and avoid damaging the reef. And also because it would be an awesome trip. They grew the specimens in their lab. Care to know what coral eat? Brine shrimp babies, that’s what, and not only that, they eat them alive, the heartless monsters.
The corals were fed twice a week with live Artemia franciscana (Premium, Sanders) nauplii and once a week with defrosted Cyclops (AD068, amtra Aquaristik) or ground fish flakes (TetraMarine Flakes, Tetra).
So. They did the short-term experiment using air with different amounts of CO2 above the water. The levels they chose were 509, 605, 856, and 981 µatmospheres (approximately, ppmv). This range starts with CO2 levels at about twice the pre-industrial values, and ends at around a thousand ppmv, a level which is extremely unlikely to be reached in this century.
In the short-term experiment (a week), the coral polyps fared very poorly. They failed to thrive, and at the higher levels, the corals’ carbonate skeletons were being eaten away by the high-CO2 water.
Then they did the long-term experiment, ramping up to the higher levels over a period of a few months. In this regard, there is a very revealing comment.
At the beginning, all CRS [the "closed recirculating systems" containing the coral] were supplied with ambient air with a pCO2 level of approx. 406 µatm. After taking water samples for TA [total alkalinity], DIC [dissolved inorganic carbon], and nutrients and measurements of the physicochemical water parameters (temperature, pH, salinity), sampling, the physicochemical parameters (salinity, pH, temperature) of each reactor were monitored by inserting a multi sensor device (Multi350i, WTW) into a small opening in the lid. During incubations, pH and pCO2 [partial pressure of CO2] can change differently in each bioreactor depending on rates of respiration and calcification of the enclosed coral branches. Therefore, the carbonate system parameters (pH, pCO2, ΩAr) and growth rates were calculated separately for each bioreactor.
In other words, what I said above—chemistry is being ruled by life, and not the other way around. The pH and the pCO2 are not simply functions of the amount of CO2 in the overlying air. They are functions of the reef and the reef life itself.
There were other interesting outcomes. In the short-term experiments, there is a statistically significant correlation between increasing CO2 and decreasing calcification rates (growth rates). As CO2 went up, growth went down, and coral skeletons were actually being eroded at the highest CO2 levels. This is a great example of how a statistically significant result can be entirely wrong because the experiment itself is conceptually flawed. The results are statistically significant … but meaningless.
Because in the long-term experiment (six months), the opposite occurred. The corals, once they had time to adapt to the change in pH and CO2 levels, did very well. The study reports:
Growth rates in the long-term experiment (LTE) did not follow the negative trend with increasing pCO2 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. … Surprisingly, corals maintained in waters sub-saturated with respect to aragonite (CRS3, Tables 4 & 5) displayed the highest average Gr of 1.88 ± 1.34 × 10-2 % d-1. Positive net calcification in waters corrosive to aragonite was also confirmed by measurements of total alkalinity repeatedly performed over the course of the incubation, showing a continuous decrease during the long-term incubation in the highest CO2 treatment. There was no statistically significant relationship between average growth rates and pCO2 concentrations (Kruskal-Wallis ANOVA on ranks, H = 1.46, P = 0.482).
I want to expand on a couple of their statements. First, even when the chemistry predicted that the ocean waters would actively erode and dissolve the coral skeleton … it didn’t happen. In waters where it should have dissolved, it didn’t.
But the most important finding was the final one, which I can paraphrase as:
Coral growth rates are not related to CO2 levels.
It’s not even that CO2 doesn’t affect growth levels much. They’re not related at all. As the paper said,
There was no statistically significant relationship between average growth rates and pCO2 concentrations
Even the highest CO2 levels tested, far above anything in the coming century, couldn’t stop the corals from growing, heck, it didn’t even slow them down. In other words, life wins out once more, against all odds. Gotta love it.
PS—for those interested in the carbonate chemistry of the ocean, there’s a great calculator here.