21 May 2013, by Harriet Jarlett – Planet Earth Online
Ocean acidification is damaging some marine species while others thrive, say scientists.
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 coccoliths, 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.
‘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 coccolith 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.
A new study, published in PLOS ONE thie month investigates how a strain of the coccolithophore Emiliania huxleyi might respond if all fossil fuels are burned by the year 2100 – predicted to drive up atmospheric CO2 levels to over four times the present day. Specimens grown under this high CO2 scenario were compared with specimens grown under present day CO2 levels.
Below, the press release published at the NOCS website.
Press Release: Marine algae show resilience to carbon dioxide emissions
A type of marine algae could become bigger as increasing carbon dioxide emissions are absorbed by the oceans, according to research led by scientists based at the National Oceanography Centre, Southampton (NOCS).
Coccolithophores are microscopic algae that form the base of marine food chains. They secrete calcite shells which eventually sink to the seafloor and form sediments, drawing down and locking away carbon in rocks. Because of their calcitic shells, some species have been shown to be sensitive to ocean acidification, which occurs when increasing amounts of atmospheric CO2 are absorbed by the ocean, increasing seawater acidity.
But these findings suggest that not all coccolithophore species respond to ocean acidification in the same way.
“Contrary to many studies, we see that this species of coccolithophore gets bigger and possesses more calcite under worst-case scenario CO2 levels for the year 2100,” says Dr Bethan Jones, lead author and former researcher at University of Southampton Ocean and Earth Science, which is based at NOCS. “They do not simply dissolve away under high CO2 and elevated acidity.”
However, the researchers also observed that cells grew more slowly under the high CO2 scenario, which could be a sign of stress.
The researchers also tested for changes in protein abundance – using a technique developed by the collaborating institutes – as well as other biochemical characteristics. They detected very few differences between the two scenarios, indicating that apart from growth, this strain of coccolithophore does not seem to be particularly affected by ocean acidification.
Co-author Professor Iglesias-Rodriguez, formerly at University of Southampton Ocean and Earth Science, says: “This study suggests that this strain of Emiliania huxleyi possesses some resilience to tolerate future CO2 scenarios, although the observed decline in growth rate may be an overriding factor affecting the success of this ecotype in future oceans. This is because if other species are able to grow faster under high CO2, they may ‘outgrow’ this type of coccolithophore.
“Given that chalk production by calcifiers is the largest carbon reservoir on Earth – locking away atmospheric CO2 in ocean sediments – understanding how coccolithophores respond to climate change is a first step in developing models to predict their fate under climate pressure such as ocean acidification.”
The team used a technique called ‘shotgun proteomics’, optimised for marine microbiological research at the University of Southampton’s Centre for Proteomic Research, to detect changes in proteins under the different CO2 scenarios.
The collaborative study involved researchers at University of Southampton Ocean and Earth Science (which is based at NOCS), University of Southampton Institute for Life Sciences, University of Southampton Centre for Proteomic Research, University of Cambridge, University College London and Xi’an Jiaotong-Liverpool University, China.
Microscopic ocean algae called coccolithophores are providing clues about the impact of climate change both now and many millions of years ago. The study found that their response to environmental change varies between species, in terms of how quickly they grow.
Coccolithophores, a type of plankton, are not only widespread in the modern ocean but they are also prolific in the fossil record because their tiny calcium carbonate shells are preserved on the seafloor after death – the vast chalk cliffs of Dover, for example, are almost entirely made of fossilised coccolithophores.
The fate of coccolithophores under changing environmental conditions is of interest because of their important role in the marine ecosystem and carbon cycle. Because of their calcite shells, these organisms are potentially sensitive to ocean acidification, which occurs when rising atmospheric carbon dioxide (CO2) is absorbed by the ocean, increasing its acidity.
There are many different species of coccolithophore and in an article, published in Nature Geoscience this week, the scientists report that they responded in different ways to a rapid climate warming event that occurred 56 million years ago, the Palaeocene-Eocene Thermal Maximum (PETM).
The study, involving researchers from the University of Southampton, the National Oceanography Centre and University College London, found that the species Toweius pertusus continued to reproduce relatively quickly despite rapidly changing environmental conditions. This would have provided a competitive advantage and is perhaps why closely-related modern-day species considered to be its descendants, (such as Emiliana huxleyi) still thrive today.
In contrast, the species Coccolithus pelagicus grew more slowly during the period of greatest warmth and this inability to maintain high growth rates may explain why its descendants are less abundant and less widespread in the modern ocean.
“This work provides us with a whole new way of looking at living and fossil coccolithophores,” said lead author Dr Samantha Gibbs, Senior Research Fellow at University of Southampton Ocean and Earth Science.
By comparing immaculately preserved and complete fossil cells with modern coccolithophore cells, the researchers could interpret how different species responded to the sudden increase in environmental change at the PETM, when atmospheric CO2 levels increased rapidly and the oceans became more acidic.
“We use knowledge of how coccolithophores build their calcite skeletons in the modern ocean to interpret how climate change 56 million years ago affected the growth of these microscopic plankton,” said co-author Dr Alex Poulton, a Research Fellow at the National Oceanography Centre.
“This is a significant step forward and allows us to view fossils as cells rather than dead ‘rocks’. Through this we can begin to understand the environmental controls on oceanic calcification, as well as the potential effects of climate change and ocean acidification.”
Reference: Gibbs S.J., Poulton A.J., Bown P.R., Daniels C.J., Hopkins J. Young J.R., Jones H.L., Thiemann G.J., O’Dea S.A., Newsam C. (2013) Species-specific growth response of coccolithophores to Palaeocene–Eocene environmental change. Nature Geoscience doi: 10.1038/NGEO1719
The study was primarily supported by the UK Ocean Acidification Research Programme, which is jointly funded by the Natural Environment Research Council (NERC), the Department of Environment, Food and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC).
The Ocean Acidification talk that Paul Bown and Samantha Gibbs presented in the Third Symposium on The Ocean in a High-CO2 World, held on 24-27 September in Monterey, provoked interest from the journalists, and Nature have run a short piece on their News page .
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