Science Interviews


Sun, 25th Mar 2007

How increased carbon dioxide levels affect shellfish

Frederic Gazeau from the Netherlands Institute of Technology

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Chris Now were going to start off with something a little bit different this week, and thats with two emails. The first is from Simon in Burwell who says, Im a great believer in trying to alleviate climate change and I even have solar water heating fitted to my house. Ive recently watched a programme called the Great Global Warming Swindle. The main thrust of the programme was that although scientific studies have shown that there is a close relationship between rising CO2 in the atmosphere and an increase in planetary temperature. The relationship is that the planet warms first and then the CO2 rises. This could be accounted for by the increase in plants and animals. The programme therefore alleges that the CO2 man creates is not only insignificant compared to volcanic emissions, animal emissions and sea emissions, but CO2 doesnt appear to cause any increases in planetary temperature anyway. They blame it on the activity of the sun. Now I dont really know what to think.Diatoms - a key Phytoplankton group

Ive also got an email here from Steven who writes about Al Gore. Hes had a documentary called An Inconvenient Truth. Steven says for the past few years Ive taken for granted that global warming is happening. After doing a lot more reading recently and talking to someone whos interested in this and done a lot of research, Im now unsure. I feel that humanity pumping CO2 and other greenhouse gases into the atmosphere must be doing damage, but is it as bad as is feared? The important thing here is that both of these emails focus on one aspect of CO2, which is the impact we think it might have on global temperatures. But thats not the whole story necessarily because CO2 could also be having dire consequences for our oceans. Someone whos got evidence of that and is about to publish an important paper on it in the near future is Frederic Gazeau. Tell us about your research.  

Frederic What we did was to try to estimate the impact of increase in CO2 in the ocean on the calcification of shellfish and molluscs. The calcification of molluscs is the growth of a shell.

Chris So in other words things like mussels, oysters or anything that has a shell.

Frederic Exactly. We did our experiments on mussels and oysters, which are the most important in terms of aquaculture so it has an economical impact. So thats why we chose these species.

Chris So why should CO2 in the atmosphere have anything to do with the sea?

Frederic What you have to know is that the CO2 that is released by human activities such as the consumption of petrol, gas and coal, one third of this CO2 is pumped by the ocean. If you pump CO2 in the ocean, you will decrease its pH.

Chris So in other words the sea is soaking up carbon dioxide that weve put into the air.

Frederic Exactly. One third is taken by the ocean. Thats what we estimated. So if you have more CO2 in the ocean you will have a stronger acidity of the ocean. The problem is that this acidity can damage organisms that grow skeletons or shells made of calcium carbonate.

Chris This is the same stuff that builds up as limescale in the kettle and we add acid to remove it.

Frederic Yeah exactly. The thing is that CO2 in the ocean has three different species: the CO2 by itself, bicarbonate and carbonate. If you decrease the pH, you will shift the equilibrium between these three species towards more CO2 and less carbonate ions.

Chris The thing is that its all very well saying that Frederic, but how much CO2 does it take to make a big difference in the ocean? Have we got any evidence that the CO2 that we make does make a difference to the ocean and how are you proving that it actually makes a difference in the long run to animals in the ocean?

Frederic We first have evidence that in some places on Earth in the ocean we had a decrease in the oceanic pH in the last decade. Thats a fact.

Chris So the sea genuinely has got more acidic in recent years. Frederic They are more acidic, they are not acid of course. They are still basic but the pH is lower, so they are more acidic, yes.

Chris And how do you know that this has an impact on animals?

Frederic The thing is, its just a chemical reaction. If you want to build a calcium carbonate shell or skeleton, you need carbonate ions. If you decrease the pH, you will decrease the concentration of carbonate ions, so thats a chemical fact. The thing is, now were thinking that some organisms are able to adapt and acclimatise to the new environment and thats now what Im going to do in the next month. Im going to try and see if the organisms are able to adapt themselves.

Chris What experiment did you do to prove that there is a problem in the first place?

Frederic We incubated in a chambers in an aquarium two populations of the mussels and oysters. One population of mussels was incubated with a CO2 concentration which is what we have now. Another population was incubated with increased CO2 concentrations in the water. What I did was to measure the rate of production of their shells and I saw that if you increase the CO2, you decrease the rate of shell formation.

Chris Now when you said you incubated them with increased CO2, how much increase? Is it within the realms of what we expect to see in the atmosphere within, say, the next fifty or one hundred years?

Frederic Yes. I went further than these limits but I covered the range that is expected in the next one hundred years.

Chris Now obviously the problem wont just be confined to shellfish, so what other animals might be affected?

Frederic A lot of different animals. For instance the most famous ones are the coral reefs as they are made from calcium carbonate. Also we have small planktonic organisms that we call pteropods. You also have small planktonic algae, and you have species like sea urchins for instance. We have evidence for several of these species that if we increase the CO2 of the ocean then we will threaten and decrease their ability to produce their skeletons or their shells.

Chris So irrespective of what CO2 does to the weather or to the temperature of the earth, it will definitely have this effect on the oceans and therefore there could be quite serious repercussions.

Frederic Thats what we think and thats what the first experiments have shown already. But now what we have to do is to see whether these different organisms are able to acclimatise first or also genetically adapt to an increase in CO2, and thats something that will be done in the next years, but we cant really answer this question now.

Chris Sobering words there from Frederic Gazeau whos at the Netherlands Institute of Technology.


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