How increased carbon dioxide levels affect shellfish

25 March 2007

Interview with

Frederic Gazeau from the Netherlands Institute of Technology

Chris - Now we're going to start off with something a little bit different this week, and that's with two emails. The first is from Simon in Burwell who says, 'I'm a great believer in trying to alleviate climate change and I even have solar water heating fitted to my house. I've 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 doesn't appear to cause any increases in planetary temperature anyway. They blame it on the activity of the sun. Now I don't really know what to think.'Diatoms - a key Phytoplankton group

I've also got an email here from Steven who writes about Al Gore. He's had a documentary called An Inconvenient Truth. Steven says 'for the past few years I've taken for granted that global warming is happening. After doing a lot more reading recently and talking to someone who's interested in this and done a lot of research, I'm 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 that's not the whole story necessarily because CO2 could also be having dire consequences for our oceans. Someone who's 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 that's 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 we've put into the air.

Frederic - Exactly. One third is taken by the ocean. That's 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 it's 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. That's 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, it's 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 that's a chemical fact. The thing is, now we're thinking that some organisms are able to adapt and acclimatise to the new environment and that's now what I'm going to do in the next month. I'm 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 won't 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 - That's what we think and that's 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 that's something that will be done in the next years, but we can't really answer this question now.

Chris - Sobering words there from Frederic Gazeau who's at the Netherlands Institute of Technology.

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