Oh, how I wish fine dining led to carbon storage.

Rebecca Horridge asked a really good question over on the “Contact Us” page, and I wanted to give it the in-depth explanation it deserved:

My Dad is a professor of physiology and a marine scientist. He reckons that if everyone ate oysters this would help global warming through shell sequestration. Do you know of anyone who works on this idea? ie could we use oysters, corals or possibly (excuse me if this is blasphemy) genetically engineered organisms to make calcium carbonate which we could then bury in the soil.? I am having trouble finding info about this.

I hereby dub this proposal “Oyster World,” and I sure do wish it were feasible. I LOVE to eat oysters (not to mention mussels, clams, and shelled critters of all kind. I am a bad, bad Jew.) However, Oyster World would not work, for the reasons I’ve listed below in order of least to most scary.

1) Oysters and corals are animals that respire. That is, they breathe in oxygen and breathe out CO2. So growing lots and lots of oysters would actually add some CO2 to the water. I don’t know how this balances with the amount of carbon stored in the shell matrix, but it would definitely lessen the carbon storage impact of Oyster World.

2) Oyster World would also be thwarted by the balance of carbon ions in the ocean. In order to form calcium carbonate shells, critters need both calcium ions and carbonate ions. Here’s the chemical equation:

Ca+ + CO3 –> CaCO3

There’s a lot of calcium ions in the ocean, so that’s usually not a problem. But carbonate ions are a little harder to come by. That’s because most of the carbon ions in the ocean exist in the form of bicarbonate (HCO3), which organisms cannot use. Here’s the equation:

CO2 + CO32- + H2O <-> 2 HCO3

This is an oversimplification of a complicated set of reactions, but essentially it means that CO2 and CO32- are inversely related. If you’ve got a lot of CO2, you’re only going to have a little CO32-, and vice versa.

In Oyster World, we would make a lot of CaCO3 shells,  and then remove them from the ocean. This would remove an important source of  CO32- ions, which would increase the proportion of CO2 ions. Unfortunately, increasing CO2 in the ocean has a very nasty side effect…

3) Ocean Acidification (Or, the Terrifying Other Effect of Carbon Emission.)

So remember how increasing CO2 decreases the CO32- that our heroic oysters need to make shells? That’s what is happening right now. As more and more CO2 is absorbed into the ocean, less and less CO32- is available to anything that make a shell. This isn’t just oysters, but also corals, sea urchins, snails, lobsters, tiny shelled phytoplankton (foraminifera) – a vast swath of ocean life. Various studies have shown that critters have a hard time make shells when there isn’t enough carbonate around. And here’s the really scary part – in 2099, nothing that needs a shell may be able to live in huge areas of the ocean.

To illustrate this, here’s a map from Woods Hole Oceanographic Institute. (This map also appeared in “An Inconvenient Truth,” as some of you might recall.) The purple, red, and orange is enough carbonate to make shells for oysters & friends, yellow is tough but possible, green and blue means not enough carbonate to live.

Not only is Oyster World an unlikely solution to global warming, but the oysters themselves could be in future trouble.

Here are some resources to get you started. I am not sure how much science training you have, so I’ve included a selection of different sources.


7 Responses to Oh, how I wish fine dining led to carbon storage.

  1. anna says:

    aaaaaaaaaahhh! chemical equations! flashbacks. misery.

    (and sadness. i too like eating trafe shell things and having a semi-functioning planet.)

  2. But equations are fun! They explain things! (says the hypocrite who barely passed organic chemistry).

    Also, some bivalves, like blue mussels, are a good happy-earth seafood choice. They just don’t sequester carbon. So trayf away!

  3. Ken says:

    Check out “http://portlincoln.yourguide.com.au/news/local/news/general/oysters-role-in-cutting-carbon/1329567.aspx”

  4. Hi Ken,

    Thanks for posting the link. I can’t comment on the feasibility of Mr Hickey’s plan without further details. I am somewhat dubious because as the ocean becomes saturated with carbon dioxide, it will become more acidic, which will reduce the saturation of carbonate. This means that it will become increasingly difficult for oysters and other calcium carbonate-shelled organisms to form their shells.

  5. Freddo says:

    Calcium Carbonate CaCO3 contains 44% CO2 by weight.
    One dozen British oysters weigh 840 gms. Let us be generous and assume that all of that weight is CO2, no flesh and no organic matter. In order to sequestrate a reasonable 11 Tons of CO2 per person per year (that just begins to loosely relates in magnitude to the scale / amount of CO2 we are responsible for the emission of – see “withouthotair” via google), we EACH would have to consume 81.5 dozen oysters EACH AND EVERY DAY.

    For one long-haul return flight per person, that would be c. 102,000 Oysters you’d be eating to offset the CO2 resulting from the 2 tonnes of fuel the plane burned just for you (your share of the total).

    Actually one would not actually HAVE to eat them, one can feed them to animals or even throw them away. Simply growing them is the important bit.

    Unlike growing trees there is no wood to bury or to shoot off into space. Shells can simply be dropped into the sea.

    However the numbers involved do perhaps show the improbability of oyster propagation as a form of carbon sequestration on a scale that could make any difference at all!!!

  6. Freddo says:

    I forgot to convert again in the flight calculation from CaCO3 to CO2, but it makes little difference – 100,000 oysters per person per long haul flight (wrong result, conversion factor inadvertantly omitted), 230,000 oysters person per long haul flight, either way it’s a totally infeasibly big number ! Maybe from the probability of food poisoning per oyster, someone can figure out how many times you’d fall ill per 5,000 or so oysters consumed…..

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