Ocean acidification is one of the major consequences of climate change. acidiCO₂ceans project aims at examining the effects of ocean acidification on the structure and density of the hard structures of different benthic organisms using micro-CT imaging technology. During a series of experiments, invertebrate species will be kept in different pH treatments. The acidification effects will be compared between: (a) benthic organisms that use different forms of CaCO3 (b) juvenile vs. adult life stages; (c) external vs. internal hard structures and (d) long-term vs. short-term acidification experiments.
The outcomes of this project will not be focused solely on scientific results. The videos created by the micro-CT will be used as an educational tool to visualize the acidification effects for the general public. Thus, the project will increase the public awareness of the problem, creating an additional pressure for policy-makers to make ocean acidification a top priority on their agenda.
Climate change and threats for the Oceans
Climate change currently is one of the major threats for the world's oceans and its organisms. Its consequences include changes in ocean circulation, ocean warming and sea level rise and impacts on ice cover, fresh water run-off, salinity, oxygen levels and acidification (1). The ocean is a sink of atmospheric CO2, including up to 48% of that emitted since the beginning of industrial times (2). Dissolved CO2 reacts with seawater, leading to changes in ocean carbonate chemistry and lowering seawater pH, i.e. ocean acidification. The uptake of anthropogenic carbon has led to an average decrease in ocean pH of 0.1 units so far (1). The pH might further decrease between 0.3 and 0.5 units by the end of the 21st century (3). Scientists, policy and decision-makers are concerned that ocean acidification will have significant consequences on marine organisms, which may alter species composition, disrupt marine food webs and ecosystems and damage fishing, tourism and other maritime human activities (4). Thus, the impacts of ocean acidification are global, devastating, and may drastically change marine life as we know it (1).
Most marine organisms are sensitive to changes in carbonate chemistry, and their responses to the predicted changes can lead to profound ecological shifts in marine ecosystems (5). Ocean acidification is expected to reduce biocalcification of the shells, bones and skeletons most marine organisms possess. It is expected that by 2100, around 75% of all cold-water corals will live in calcium carbonate (CaCO3) undersaturated waters which will corrode their skeletons (1). The lowering of CaCO3 saturation also affects the ionic balance of many organisms (plankton, benthic molluscs, echinoderms, corals). Recent studies suggest that the pH reduction in seawater will impair shell and skeletal production and maintenance within many calcifying marine organisms (6; 7).
In addition, calcification responses vary significantly amongst organisms using different mineral forms of CaCO3. Organisms using soluble forms usually are more resilient to ocean acidification than those whose skeletal parts depend on more stable forms of CaCO3(6; 8; 9). Highly mobile organisms such as fish, cephalopods and some crustaceans capable of controlling extracellular pH through active ion transport are predicted to be more tolerant to acidification (10). Larval and juvenile stages may be also be more vulnerable to ocean acidification than adults, as they are typically more sensitive to environmental conditions (11) and can suffer extremely high mortality (12). However, further research on different aspects of the impacts of acidification on marine benthic organisms is urgently needed.
acidiCO₂ceans objectives and dissemination of results
acidiCO₂ceans project aims at examining the effects of ocean acidification on the structure and density of the shell and other hard structures of different benthic organisms using micro-CT imaging technology. During a series of experiments, selected invertebrate species will be kept in aquaria with two different pH treatments for short periods (i.e. 2-3 months). The pH of the seawater in one treatment will be adjusted to 8.0 (current value), in the other to 7.5 (future scenario). The latter value reflects the predicted ocean acidification according to the Intergovernmental Panel on Climate Change IS92a emission scenario for the year 2100 (13; 14). An existing marine mesocosm system will be used which ensures stable and controlled conditions for the experiments. This precludes sources of variability other than the specifically manipulated variables (pH level). The acidification effects will be compared between: (a) benthic organisms that use different forms of CaCO3 (soluble mineral form vs. less soluble form); (b) juvenile vs. adult life stages; (c) external (e.g. shell) vs. internal hard structures (e.g. gastropod statoliths, sepia cuttlebone). In addition, long-term acidification experiments will be implemented using specimens from the UK Ocean Acidification Research Programme. These specimens have been subjected to reduced pH values for longer periods and the acidification effects will be compared with specimens from short-term experiments.
The effects of the acidified conditions on the organisms' calcified tissues will be assessed through an innovative approach: specimens will be imaged by micro-computed tomography (micro-CT). This technology is similar to clinical tomography and allows the creation of interactive, three-dimensional x-ray images at sub-micron resolution. Micro-CT not only can visualise structural changes but the data can be analysed quantitatively in three dimensions (e.g. density, porosity, surface area, volume measurements), providing new perspectives of acidification impacts on micro-structural tissue changes. Being non-destructive, the method also allows in-vivo scanning and assessment of changes of the same organism over time.
Our oceans provide irreplaceable goods and services, but human activities are threatening the stability of the system, inducing irreversible changes on a global scale. Predictions on the impacts of climate change, especially ocean acidification, are urgently needed and are high on the research agenda of the international community. acidiCO₂ceans project will contribute to broadening our knowledge on the acidification impacts on marine organisms, a necessary prerequisite for improving forecasting models. However, the outcomes of the project will not be focused solely on scientific results. Oceanic changes have an immediate impact on our everyday life, and ocean acidification is an especially illustrative example of human-induced impacts on these valuable resources. The videos and interactive models created by the micro-CT scanner are an impressive method to visualise the changes in affected organisms and an excellent tool for educational purposes. In addition, on the web site will be added scientific and educational material resulting from the project (e.g. raw data, but also educational videos of 3D-renderings) and a small “exhibition” on ocean acidification will be organised in the Cretaquarium. This will include short videos for the general public, interactive models of organisms and posters. Thus, the project will increase the public awareness of the problem, creating an additional pressure for policy-makers to make ocean acidification a top priority on their agenda.
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