Ocean acidification is already happening today, and will become a growing problem unless the world reduces CO2 emissions. What are the effects of this process on key organisms in food chains? And what will be the combined impacts of rising CO2 levels, higher temperatures and an expansion of oil and gas activities?
A rise in the atmospheric concentration of CO2 results in greater uptake of CO2 by the oceans. This changes environmental conditions by lowering the pH of seawater. A lower pH makes it more difficult for marine organisms to form calcareous shells and skeletons, and also affects many other physiological processes.
Scenario for 2100
Researchers at the International Research Institute of Stavanger (IRIS) are studying the combined effects of ocean acidification, climate change and pollution from the oil and gas industry on the larval development and physiology of important species in Norwegian waters.
The extent to which seawater pH is expected to change varies between the emission scenarios presented by the Intergovernmental Panel on Climate Change (IPCC). However, if CO2 emissions continue at the current rate, the pH of the oceans is expected to reach a minimum in 2300.
“In our experiments, we are testing the effects of the pH level expected in Norwegian waters towards the end of this century,” explains Senior Research Scientist Renée Bechmann at IRIS. She is project manager for the project “Combined effects of ocean acidification, climate change and oil-related discharges”.
Larval stages are sensitive
Larval stages are more sensitive than adults to changes in environmental conditions. If larval survival is poor, this will clearly affect marine ecosystems. Ocean acidification is not a short-term problem – it will persist for hundreds of thousands of years. In addition to climate change and acidification, marine organisms are exposed to natural variation, for example in food supplies, and to other stress factors such as pollution from the oil and gas industry.
“This is why we think it is so important to carry out research on the combined impacts of different factors,” says Renée Bechmann. “One of the questions we are looking at is whether lower pH make echinoderms such as starfish, sea urchins and brittlestars more sensitive to oil pollution. We are cooperating with Sam Dupont on this. He already has years of experience of research on the effects of ocean acidification on echinoderms.”
In addition to Sam Dupont of the Sven Lovén Centre for Marine Sciences at the University of Gothenburg , cooperation partners include Dan Mayor of the University of Aberdeen and Dag Hjermann of the Centre for Ecological and Evolutionary Synthesis (CEES) at the University of Oslo.
Testing the effects of warmer and more acidic water
IRIS has developed a laboratory system for the exposure of marine organisms to controlled pH levels. The pH of seawater is lowered by bubbling CO2 gas through it, and experimental animals are kept in aquaria with a constant supply of clean seawater with a stable pH. Earlier experiments have shown that acidification slows the development of shrimp larvae.
“We have now started experiments using adult shrimps carrying eggs, so that we can follow larval development for several weeks after hatching,” explains Renée Bechmann. “We are trying to find out whether shrimp eggs hatch as successfully as in ordinary seawater and whether the larvae develop normally in water with a pH of 7.6. One of our main aims is to look at the combined effects of higher water temperature and lower pH. According to the literature, ocean acidification could affect marine life in many ways, not only by affecting calcification. Impacts on various physiological processes can affect growth, the rate of development, respiration and the uptake of food. For instance, shrimps moult frequently in the first weeks after hatching. We have been looking both at survival and at the intervals between moults.”
Will coral reefs dissolve?
Coral reefs have a number of vital functions as spawning grounds, nursery areas, habitats and feeding grounds for fish, shellfish and other organisms.
“Coral skeletons contain calcium carbonate, which dissolves more readily at lower pH, so that the whole framework of coral reefs may disintegrate with ocean acidification,” Renée Bechmann tells us. “The living coral polyps may be able to compensate by speeding up the rate at which they build new skeletons, but we need to study this more closely. Because oil production may be started in new areas, we also need to look at the combined effects of ocean acidification and drilling mud on cold-water corals. IRIS researchers are already investigating the effects of drilling mud on the cold-water coral Lophelia pertusa. The next step is to investigate how corals that have been affected by ocean acidification respond to exposure to drilling mud, using earlier results as a basis for selecting the best methods to use in their experiments.”
Impacts on ecosystems
The sensitivity of marine organisms to environmental change varies widely between species and between different life cycle stages in the same species.
“To improve modelling of effects at ecosystem level, we need to run experiments with key species in the ecosystem, as we are doing in this project,” explains Ms Bechmann.
Some species are very sensitive even to small changes in pH. Sam Dupont found that all the larvae of one species of brittlestar died a few days after only a small change in pH. On the other hand, some species survive better than expected, even species with calcareous skeletons. IRIS researchers experimented on mussel larvae last year, and found that they were able to build shells and grow even in water undersaturated with respect to aragonite, the type of calcium carbonate they use. However, larvae kept under these conditions were considerably smaller than controls after two months’ exposure. Changes in growth and development in early life stages can have serious consequences, but more research is needed on a wider range of species before predictions of impacts at ecosystem level can be made. In the longer term, the question is whether marine animals will be able to compensate for the effects of continuing ocean acidification, or whether this will require so much energy that they are weakened or die. “We need more experimental biological research on the costs of compensating for environmental change and on which species can cope with it,” concludes Renée Bechmann.
Jorunn Gran, CICERO web news, 25 August 2010. Article.
