Sunday, 21 February 2010

Paper of the week: What ocean acidification means for the plankton

It appears that we humans had taken oceans for granted for too long. A widely known fact is that most of what we discard makes its way to oceans. Oceans are sinks for all things including 1/3 of the carbon dioxide that has been released in the last 200 years. This has resulted in the acidification of the oceans. The science behind is that carbonic acid is formed when carbon dioxide dissolves in sea water. This raises the hydrogen ion concentration and bicarbonate ions, but limits carbonate ions. This interferes with the ability of many marine plankton to build shells. We are just beginning to understand how anthropogenic ocean acidification affects marine ecosystems and the long term consequences of this phenomenon. A report released from a team of over 100 European scientists during the Copenhagen Summit highlights this fact and alleged that marine species are being affected by the acidification of the oceans which according to the scientists are irreversible. According to the document, acidification is occurring at such a rapid pace increasing by 30% since industrial revolution and states that if CO2 emissions are not curtailed it will severely affect coral reefs, and algae. This prompts the question asking whether the acidification of oceans is uniform & universal? It seems not so, with oceans around the globe showing different degrees of acidification. North Atlantic, Pacific and Arctic seas are predicted to be affected by this phenomenon the most.

Is there any cause for concern? Absolutely, The effect of acidification on plankton cannot be trivialised as they are the powerhouses and form the lower echelons of the ecosystem on which the larger vertebrates subsist.

Where does the evidence for the acidification affecting plankton come from? There is convincing evidence from studies on limited species- cocolithophores and formaniferans. But there are caveats, as previous studies by different research groups on cocolithophore species had shown that not all species behave in the same way to increased carbon dioxide levels. While some species show decreased calcification , others show no change , yet another show non linear calcification and interestingly some show increased calcification. In addition, closely related organisms such as tropical and temperate sea urchins showed different responses to acidification. Even among same species, results from different laboratories showed contrasting effects. A reason for this has been attributed to different methods the labs used in mimicking acidification. Other reasons could be due to difference in experimental conditions, for example access of the species to nutrientss , temperature etc, all of which can consequently affect the way the organisms respond. Although these are valid reasons, it will be hard to convince general public of the enormity of the situation with such conflicting results. This warrants further studies.

The interests in ocean acidification has been rekindled recently by the publication of a research paper from some researchers from Princeton who have given a scientific basis explaining how acidification is deleterious to plankton. It all falls on iron which is a nutrient for phytoplankton. The chemistry of iron is extremely sensitive to pH and the acidification of the sea water will alter its availability to the planktons. Shi et al showed that acidification decreased the iron uptake of phytoplankton in the laboratory. The downside of this study is that the work was done in the laboratory and field studies are needed to corroborate this.

Ocean acidification is a crtical issue and we should act urgently. Often action requires concrete evidence. A unified protocol experimental protocol that is followed globally would address many of the discrepancies posed by lab based research as advocated by the researcher Victoria Fabry. But the proof of the pudding are evidences of field work. However one only hopes that those will not uncover problems that have progressed to such an extent that it is a impossible to be mitigated.

Shi et al, Science 327 (2010)

Fabry VJ, Science 320 (2008)

(PS- The topic of mismanagement of oceans was touched upon in a previous blog 'Ten Years Hence' By David Buss

Shi D, Xu Y, Hopkinson BM, & Morel FM (2010). Effect of ocean acidification on iron availability to marine phytoplankton. Science (New York, N.Y.), 327 (5966), 676-9 PMID: 20075213

Fabry, V. (2008). OCEAN SCIENCE: Marine Calcifiers in a High-CO2 Ocean Science, 320 (5879), 1020-1022 DOI: 10.1126/science.1157130

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