A study of survivors of the extinction provides unique insight into the response of deep-sea calcifiers to past episodes which resemble the potential future consequences of fossil fuel CO2 emissions. The organisms, contrary to expectations from experiments, actually increased the thickness of their shells during ocean acidification, with organisms living buried within the sediment able to survive better than forms living on the sediment surface.

The research, by scientists from the University of Bristol (UK) and Yale University (USA), is reported in this week’s early edition of the Proceedings of the National Academies of Science.

The team used Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) at the TOMCAT beamline at the Swiss Light source, Paul Scherer Institute (Switzerland) to generate high resolution (0.37 µm), 3D images of deep-sea benthic foraminifera, unicellular organisms which make fossil shells of about the size of the full-stop at the end of this sentence.

This non-destructive technique was used to understand the effects of ocean acidification on the growth of deep-sea calcifiers during the massive ocean acidification of the PETM, when an estimated 35-50 per cent of deep-sea benthic foraminifera went extinct. The team studied the most common surviving species, evaluating what might have enabled them to cope with extreme ocean acidification. The PETM has been described as one of the best analogues for anthropogenic carbon emissions, despite its rate of emission estimated at an order of magnitude slower than today’s.

Dr Laura Foster, first author of the paper, and post-doctoral researcher at the University of Bristol’s School of Earth Sciences, explained: “We use state-of-the-art techniques to virtually section foraminifera, and gain insight in their shell construction, duration of life and mode of reproduction. We have much to learn about and from single-celled organisms, which serve as monitoring organisms for deep-sea calcifiers in general, and their response to past ocean acidification. They are a crucial part of the huge deep-sea oceanic ecosystem, and understanding what happened to them during acidification in the past is critical to improving projections on the effects of future climate change.”

Dr Daniela Schmidt, a Royal Society Research Fellow at Bristol’s School of Earth Sciences, added: “Short-term experiments cannot provide information on ways in which organisms can acclimatise, adapt or evolve in the long term. We used the geological record to examine the impact of multiple stressors, such as changes in carbonate chemistry and temperature, to provide information on how organisms adapt to large CO2 releases.”

Professor Ellen Thomas from Yale University, co-author on the paper and currently a visiting Leverhulme Professor at the University of Bristol added: “The calcite shells of benthic foraminifera are widely used to measure trace elements and isotopes used to reconstruct such parameters as temperature and carbonate saturation. The methods developed at the University of Bristol to gain insight in the 3D structure of microscopic fossils are crucial in increasing understanding of such environmental proxies, as well as the organisms themselves.”

University of Bristol, 22 May 2013. Press release.

Foster L. C., Schmidt D. N., Thomas E., Arndt S. & Ridgwell A., in press. Surviving rapid climate change in the deep sea during the Paleogene hyperthermals. Proceedings of the National Academy of Sciences of USA. Article (subscription required).

Ocean acidification is damaging some marine species while others thrive, say scientists.

An international team studied the effect of ocean acidification on plankton in the North Sea over the past forty years, to see what impact future changes may have.

The study, published in PLoS One found that different species react in different ways to changes in their environment. As carbon dioxide emissions dissolve in seawater they lower the pH of the oceans making them more acidic and more corrosive to shells.

Foraminifera and Coccolithophore, which are small shelled plankton and algae, appear to be surviving remarkably well in the more acidic conditions. But numbers of pteropods and bivalves – such as mussels, clams and oysters – are falling.

‘Ecologically, some species are soaring, whilst others are crashing out of the system,’ says Professor Jason Hall-Spencer, of Plymouth University, who co-authored the paper.

The scientists are unsure whether this drop in certain species is because of changing pH levels, or whether it is due to a combination of stress factors like warming, overfishing and eutrophication -which results from a build up of excess nutrients in water.

‘We found no statistical connection between the abundance of calcifying plankton and the changes in pH. If pH is affecting calcifying plankton in the area then its effect is being masked by other climatic effects. What we do know is that laboratory experiments have shown pH changes affect pteropods adversely,’ he says.

Scientists had previously thought the reason species react so differently to ocean acidification was due to variations in the mineral composition of the shells.

‘The aragonite skeleton of pteropods dissolves more easily in corrosive waters than the low-magnesium calcite that typifies many clams and other molluscs,’ explains Hall-Spencer. ‘But now we think that it’s not as simple as that. It depends partly on how stressed organisms are by other factors, such as lack of food. It also depends on their shape and their ability to protect their skeletons.’

It is possible that the rising levels of CO₂ are boosting coccolithophore numbers by causing them to photosynthesise more and produce more energy.

The scientists used a database collected by the Sir Alaistair Hardy Foundation for Ocean Science, which has been continuously recording levels of plankton in the North Sea since 1931. But, despite being the best database available, it fails to monitor chemical changes, like acid levels, alongside ecological ones, like shifts in pteropod numbers.

Plankton sits at the bottom of the food chains, where it underpins all of our marine food sources. So if numbers drop significantly it could lead to food shortages, particularly in countries where people eat lots of seafood and fish.

Without improved monitoring , researchers say they will struggle to accurately test the consequences of ocean acidification.

‘CO₂ is driving down the pH of water, but finding evidence for that and its ecological effects is proving tricky. Most work is done in the lab, so there’s not much good long term data on changes in the water,’ says Hall-Spencer.

Coccolithophores appear to be able to cope with recent changes to their environment, the scientists don’t know how they will fare in the future.

‘We need an observing network to keep track of the effects of ocean acidification both chemically and biologically. Ecosystems are going to change, and if we want to protect fisheries, food sources and jobs we need to be forewarned,’ he concludes.

(Article corrected on 22nd May 2013 to use ‘coccolithophores’ rather than ‘coccoliths’, as coccoliths are only the outer part of the coccolitophore organism.)

Taylor J. R., Lovera C., Whaling P. J., Buck K. R., Pane E. F. & Barry J. P., 2013. Physiological compensation for environmental acidification is limited in the deep-sea urchin Strongylocentrotus fragilis. Biogeosciences Discussions 10: 8313-8341. Article.

Vargas C. A., de la Hoz M., Aguilera V., San Martín V., Manríquez P. H., Navarro J. M., Torres R., Lardies M. A. & Lagos N. A., in press. CO2-driven ocean acidification reduces larval feeding efficiency and change food selectivity in the mollusk Concholepas concholepas. Journal of Plankton Research. Article (subscription required).

Findlay H. S., Artioli Y., Moreno Navas J., Hennige S. J., Wicks L. C., Huvenne V. A. I., Woodward E. M. S. & Roberts J. M., in press. Tidal downwelling and implications for the carbon biogeochemistry of cold-water corals in relation to future ocean acidification and warming. Global Change Biology. Article (subscription required).

Calosi P., Turner L. M., Hawkins M., Bertolini C., Nightingale G., Truebano M. & Spicer J. I., in press. Multiple physiological responses to multiple environmental challenges: an individual approach. Integrative and Comparative Biology. Article (subscription required).

Wolfe K., Dworjanyn S. A. & Byrne M., in press. Effects of ocean warming and acidification on survival, growth and skeletal development in the early benthic juvenile sea urchin (Heliocidaris erythrogramma). Article (subscription required).

Porzio L. , Garrard S. L. & Buia M. C., in press. The effect of ocean acidification on early algal colonization stages at natural CO2 vents. Marine Biology. Article (subscription required).

Teichert S., Woelkerling W., Rüggeberg A., Wisshak M., Piepenburg D., Meyerhöfer M., Form A. & Freiwald A., in press. Arctic rhodolith beds and their environmental controls (Spitsbergen, Norway). Facies. Article (subscription required).