SD4: Improved Understanding of Population, Community and Ecosystems Impacts of Ocean Acidification

Predicting the impacts of ocean acidification (OA) upon fisheries is a rapidly evolving sphere of interest. This project, conducted between the Centre of Sustainable Aquaculture Research (Swansea), Exeter and Strathclyde Universities, and Plymouth Marine Laboratory, will address these challenges using a holistic multi-disciplinary approach. We will examine the physiological and life history responses of commercially important examples of bivalves, crustacea and finfish, using the large (750 m2 floor, 150 m3 water) state-of-the-art Centre for Sustainable Aquaculture Research at Swansea in which these organisms, together with their live food items, can be grown under the same conditions. We will compare the physiology and growth of the selected organisms at different water acidity and temperatures (increased acidity being associated with elevated CO2 and global warming). The output from these experiments will be scaled-up to identify effects at population and community levels. The consequences of these changes for the fishing industry will then be explored. OA, however, will not only affect commercially important species, and so the wider impacts for society of changes in marine ecosystems will also be examined. OA is expected to affect reproduction and early life stages in particular; our research will focus on egg fertilization and growth over the first 2-4 months. These stages can be acid-critical (e.g. sperm swimming is sensitive to acid levels) and are the most susceptible to the external environment due to their high surface-area: volume ratio and poor ability to compensate for changes in internal acidity. Early formation of shell and skeletal structures are also vulnerable to acid changes. OA will also provide direct and indirect effects through changes to food organisms. While it is not possible to change feed species composition, we will grow phytoplankton, zooplankton and other target animals to consider food chain impacts at different acidity levels and temperatures during their most sensitive period. This will enable us to consider the potentially synergistic effects of changes to food quantity and quality, the efficiency of food conversion into growth and energy, and the support of the food chain. Continuing these studies into juvenile stages will provide data for the impact of OA upon the most sensitive stages of cell growth. The results obtained during the studies of early life stages will be complemented by more detailed studies to identify the biological mechanisms that result in an organism's vulnerability to acidity and temperature change. Data from experiments will be used to develop models of organism growth which will provide a sound base for the future development of our understanding of OA upon other species. Supported with data collected from other OA projects, these models will then be developed to link with models that can explore the social and economic consequences to the fishing industry resulting from changes in fish populations. Existing models for such estimates are in their infancy but this project will integrate new developments that relate fisheries production to whole ecosystem ecology to improve upon classic, but simplistic, fisheries models. This is especially important when considering the impacts of global climate change and OA because of the varied interactions between organisms and their environment. Using the findings generated by this study and those arising from other OA projects, the wider impacts of OA on marine ecosystems will be explored. These will be used to examine how the benefits we obtain from the marine environment change (e.g. the availability of clean water for aquaculture and recreational activities, health benefits, and the regulation of gases and climate) and how the value of these benefits change. What these changes mean for industry and society will be explored.

"The results indicate the primacy of fishing as the most important process affecting total fish biomass, together with varying responses to environmental factors which may be relevant in the context of climate change. The non-linear responses and parameter interactions identified by the analysis also highlight the necessity to use global rather than local methods for the sensitivity analysis of ecosystem models.

The results indicate that ocean acidification may potentially induce cascading effects throughout marine ecosystems even when the direct effects are small. In particular our results indicate the efficiency with which food is converted to new consumer biomass - something which is known to be affected by acidification through changes in gut chemistry - has the biggest effect in the ecosystem model. We found that demersal fish (fish such as cod and haddock) are most sensitive to direct and indirect impacts. Moreover, indirect impacts can be simultaneously positive and negative. In fact changes of as little as 2% in functional group mortality can be magnified to 10% drop in landings."