Dr. Lennart de Nooijer

Biologist Lennart de Nooijer studies the formation of calcium carbonate in relation to CO2, and does this in various organisms that live in the ocean. ‘Shellfish, corals and certain species of algae are a vital part of the global CO2 bookkeeping and consequently our climate. Generally speaking, animals like these find it harder to form calcium carbonate as more CO2 is dissolved in the oceans. That is because, just like a fizzy drink, the water becomes more acidic and calcium carbonate dissolves more easily. Nevertheless, the actual marine situation is more complex still. Naturally, more CO2 also means more carbon, which is one of the primary building blocks of calcium carbonate. Certain organisms may well benefit from this and produce more calcium carbonate when a modest increase in the quantity of CO2 in the water occurs. We study that by adding different CO2 concentrations to water tanks and examining what this does to their calcium carbonate formation.’

Destructive sponges

‘Besides calcium carbonate producers, the oceans also contain “calcium carbonate degraders”. In the Caribbean Sea, for example, we study certain sponges that produce some acid to dissolve the inside of coral skeletons and then live in the cavities they create. When seawater becomes slightly more acidic due to the rising amount of CO2, these “bio-eroding sponges” benefit and are able to dissolve more of the coral’s skeleton. For example, we have already found locations around Curaçao and Sint Eustatius where these sponges have caused considerable damage to the coral colonies.’

Inhibiting CO₂

‘A good understanding of the relationship between CO2 and calcium carbonate producers in the seas and oceans is important for several reasons. Firstly, all of those calcium-carbonate-producing organisms actually inhibit the amount of CO2 that can dissolve in the seawater from the atmosphere. That is because during the formation of calcium carbonate, additional CO2 dissolves in the water, which makes the transfer of that greenhouse gas from the atmosphere to the oceans slightly harder. If all the algae, shellfish and corals were to stop producing calcium carbonate today, then its concentration in the atmosphere would decrease. That is exactly why it is so important to investigate whether calcium carbonate producers do better or worse in a changing climate. At the same time, the acidification of the oceans can significantly harm the biodiversity around coral reefs, for example. However, we can only gain a more precise understanding of how that works if we better comprehend the complex relationship between calcium carbonate, CO2 and calcium-carbonate- producing organisms.’