Did previous ocean acidification studies underestimate impacts on coastal species?

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A new study with scientists from PML says that in order to better understand the impacts of Ocean Acidification (OA) on marine ecosystems, future studies should use more realistic scenarios in experiments.

Ocean acidification is the ongoing decrease in ocean pH caused by human CO2 emissions, such as the burning of fossil fuels. This alteration in basic ocean chemistry is likely to have wide implications for ocean life, especially for those organisms that require calcium carbonate to build shells or skeletons. Scientists have conducted many OA studies over the last 15 years, usually altering the pH (or CO2 concentration) of seawater to simulate future ocean conditions and thereby determine what the impacts on marine organisms might be.

However a study published today in Nature Ecology and Evolution, led by the Universidad de Concepción, Chile, now suggests that many previous OA experiments of this kind did not wholly take into account species’ own natural resilience to changes in their environment; particularly in the highly variable environment of coastal areas where pH/pCO2 levels fluctuate far more dramatically than in the open ocean.

Past studies have used average open ocean projections of future pH/pCO2, which may fall within the natural variation in coastal areas experienced at present, and have not considered the true changes that are likely to ensue in addition to the existing natural patchiness in the chemistry of coastal seas. It is likely therefore that the impact of OA on the different physiological traits of coastal organisms has been underestimated. The team focused their study on the highly variable conditions found along the Chilean coast, an area noted for its changeable in its seawater carbonate chemistry and so an ideal home for organisms resilient to stress and changes in climate.

​Professor Stephen Widdicombe, Head of Marine ecology and biodiversity​ and co-author on the study commented:

“There is still much to be understood about ocean acidification as one of the major global stressors associated with climate change, as well as organisms’ resistance or susceptibility to its effects. This new study explains why some previous results may have appeared to contradict each other when in reality differences between experiments may have been more due to the experimental methods employed rather than due to real differences between the responses of organisms to OA. This work highlights that the extent of possible resilience to OA demonstrated by some organisms in previous studies may have been overestimated. Both coastal and ocean ecosystems are facing changes but they are starting from different baselines, we need to include this in future experiments.”

The team of scientists in this study now recommend a step change in how OA experiments are designed, to simulate situations that better represent both present and future pH/pCO2 conditions, including the extreme scenarios posed by progressive OA. From this they aim to improve understanding of how flexibility changes across organismal traits, populations and species, and how obtained results can be interpreted, communicated and utilized elsewhere.

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