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Increasing Ocean Acidity Harming More Than Just Corals

By Tim Radford, Climate News Network

LONDON – The chemistry of the oceans is changing. And it isn’t just the corals and the baby oysters that are unhappy. It makes juvenile rockfish really anxious, and it upsets the digestion of sea urchins.

The pH (a measure of acidity – the lower the pH, the more acid the water) of the planet’s oceans is dropping rapidly, largely because the carbon dioxide levels in the atmosphere are increasing. Since carbon dioxide dissolves in water to form carbonic acid, the seas are responding to global change.

A water melon sea urchin.
Credit: Marco Busdraghi via Wikimedia Commons

The first and clearest victims are likely to be the corals, which are adapted to a specific value of pH in the oceans, but there have also been problems reported by oyster farmers.

Now Martin Tresguerres of the University of California, San Diego reports in the Proceedings of the Royal Society B that at least one species of juvenile fish responds badly to the changes in ocean chemistry.

There is a natural aspect to ocean acidification — submarine volcanoes discharge carbon dioxide and turn the deep seas around them to a kind of fizzing champagne, and upwelling ocean currents can occasionally deliver a stressful level of lower pH sea water to blight fishing waters.

But Tresguerres reports that he and colleagues subjected young Californian rockfish to the kind of water chemistry predicted as atmospheric carbon levels rise, and then measured their behavior in response to changes of light in the aquarium, and to an unfamiliar object in the tank.

Stomach Problems

What the researchers found was that the lower pH had a pronounced effect on one of the fish neuroreceptors linked to anxiety, and this effect lasted for at least seven days after the little creatures were returned to normal sea water. The change was not permanent: normal responses seemed to return after 12 days.

Meanwhile, across the Atlantic, Meike Stumpp of the University of Gothenburg in Sweden has been looking at how sea urchin larvae respond to altered pH in the seas. She and colleagues report in Nature Climate Change that they too tweaked the seawater chemistry, to discover that digestion took longer and was less effective, a bit of a problem for any young creature — especially one hardly a fifth of a millimeter in length — in the competitive world of the oceans.

“My measurements demonstrated a very strong pH dependency”, she said. “The enzymes in the sea urchins’ stomachs are optimised to function at very high pH — which is different from the situation in mammals, where stomach pH is acidic and enzymes work best at low pH.”

The implications are that as pH levels fall, life will become a great deal more problematic for at least some key marine species. And the likelihood of change is increasing. Scientists of the International Geosphere-Biosphere Program recently allotted a “very high” confidence level to a set of simple findings.

One was that humans were indeed making the seas more acidic, another was that the capacity of the oceans to absorb carbon dioxide would fall with increasing acidity, and a third was that the impact of this change in water chemistry would be felt for centuries. They also had “high confidence” that cold water corals and mollusk communities would be affected.

Tim Radford is a reporter for Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.


By Philip Haddad (Alvin, TX 77511)
on December 25th, 2013

How does anyone know whether the acidification of the oceans is due to CO2 or to SO2 from the burning of coal. At a pH of 8.2 a drop to 8.0 would be an increase of 0.00000003 milliequivalants per liter. This is an insignificant amount when compared to the sulfate ion of 56 m.e./liter and nearly impossible to measure the necessary change with accuracy.

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By Dave (Basking Ridge, NJ 07920)
on December 26th, 2013

It is my understanding that some scientists (at least) have related measurements of the decrease in the carbonate ion concentration in seawater directly to the 25% or so of anthropogenic CO2 emissions that enters the oceans. By that means, that specific correspondence is then understood to identify the primary source of the protons that produced the measured change in carbonate saturation / concentration.

I found this, perhaps unusual source, interesting. It is a page to do with reef aquarium chemistry and the impact of different atmospheric CO2 levels:

This is not my area and others may correct me, but I have read that the reduction in the availability of carbonate ion to biological marine systems such as reef-building corals is thought – by some at least - to be a significant fraction of the threshold value required for the maintenance of corals, especially those organisms lacking internal mechanisms to regulate pH. I don’t know if this is a generally accepted fact or not. But overall, increased acidity together with ocean warming are clearly generally considered to be serious concerns for coral reefs, especially in view of other major stresses on them resulting from declining water quality due to land based pollution, particularly agricultural runoff; for example hypoxic zones and the increase in local nutrient levels that has fueled increases in the coral eating, crown-of-thorns starfish in the Great Barrier Reef.

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