A biogeochemist sees the value of diversity in a changing ocean

Ocean acidification in response to excess carbon dioxide in the atmosphere could become a problem for marine organisms, especially those that make skeletons or shells out of calcium carbonate. Corals and clams are at risk, as are the coccolithophorids — microscopic algae that are, by volume, the most important shell producers.

These algae have been the guinea pigs in a series of lab studies measuring their response to acidified seawater. But I worry about whether these studies give us an accurate picture of the future. They typically start with clones — descendants of a single cell — grown in acidified conditions for only a few weeks. This set-up precludes the kind of natural selection and adaptation that might occur over decades and centuries in the ocean.

To cloud the waters further, different labs often obtain conflicting results on the same species, a situation some attribute to subtle differences in methods. Fortunately, a recent study by Gerald Langer of the Autonomous University of Barcelona in Spain and his colleagues provides a more satisfying and ultimately more optimistic explanation (G. Langer et al. Biogeosci. Discuss. 6, 4361–4383; 2009). These reserachers grew four different strains of a calcifying algae, Emiliania huxleyi, at different seawater pH levels, and showed that the response to acidification varies significantly among the strains. They argue convincingly that these diverse responses have a genetic basis.

Identifying diverse responses among strains of a species puts us one step closer to capturing the true potential of adaptation in this group of organisms. It would be naive to assume that this puts coccolithophorids out of harm’s way. However, diversity is good insurance in a changing ocean. Moreover, I am hopeful that scientific experiments are starting to take that into account.

Stoll H., 2009. Journal Club: A biogeochemist sees the value of diversity in a changing ocean. Nature 460: 935. Article (subscription required).

Discuss this paper at http://blogs.nature.com.gate1.inist.fr/nature/journalclub

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