ticular, understanding the effects of ocean acidification requires research on the changes in the chemical composition of seawater; the direct and indirect influences of ocean acidification on chemical, biological, and ecological processes; socioeconomic impacts; and the capacities of biological systems and human societies to adapt to the challenges arising from ocean acidification. This requires a multi-focused yet coordinated program that integrates knowledge about ocean acidification across the natural, social and economic sciences to provide a foundation for predicting the future consequences of acidification and for development of effective strategies to address these consequences.

Decreasing seawater pH has already been shown in laboratory experiments to have widespread influences on biological processes and numerous types of additional effects likely remain to be discovered. Many—and perhaps most—of these effects of acidification will have negative impacts on individual species and the ecosystems in which they are enmeshed. For example, ocean acidification decreases the availability of carbonate ions at calcification sites, making it increasingly difficult for many calcifying organisms such as corals, oysters, and calcifying phytoplankton to build their calcium carbonate skeletons and shells. However, calcifiers differ in their responses to ocean acidification, notably in the case of different species of reef-building corals. In contrast, some processes or certain species (e.g., photosynthetic carbon fixation in some plants), may benefit from rising CO2 and bicarbonate levels. Disparity among species in responses to ocean acidification remains a critical unknown for efforts to predict what ocean acidification portends for marine life. In addition, many metabolic and cellular processes besides calcification and photosynthesis are affected by ocean acidification due to decreases in the pH of blood and cellular fluids. Falling pH can impede oxygen uptake by certain marine animals and directly or indirectly reduce metabolic rates.

The full suite of biological processes and structures perturbed by ocean acidification is difficult to predict. Some recently discovered effects of ocean acidification were wholly unanticipated. For example, laboratory studies of coral reef fish have revealed that neurological and behavioral processes can be affected by a decrease of seawater pH. These behavioral abnormalities may translate into changes in predator-prey interactions and capacities for locating suitable sites for settlement and recruitment.

Most of our knowledge of the effects of decreasing pH on marine organisms is from controlled laboratory and field mesocosm studies; we know much less about ocean acidification’s effects on natural (or wild) communities and ecosystems. Thus, efforts are under way to extrapolate from controlled laboratory experiments and limited in situ observations to impacts at the community and ecosystem level. However, predicting the future consequences of ocean acidification for the marine environment



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