(calcite, aragonite and magnesium-rich calcite, in order of increasing sensitivity to low pH) are used by different organisms. Therefore, to evaluate the differential sensitivities of calcium carbonate-utilizing species to ocean acidification, comparative studies should take into account the types of carbonate employed by different phytoplankton and animals. Because these two lines of investigation—mechanistic and comparative—are both necessary and, ideally, complementary, there is a need to judiciously allocate resources to both types of study and define priorities.

In the context of research scope and priorities, the committee believes that there is an imbalance in the emphasis given to different types of physiological processes and the effects that ocean acidification may have on these biological processes. As pointed out above in the context of imbalance in the literature citations, there is an overemphasis on calcifying organisms. This overemphasis reflects the past research focus on calcification, which is by now the most studied of the impacts of ocean acidification. Although calcification is a critically sensitive physiological process for many taxa, many other key physiological processes (e.g., nitrogen fixation, photosynthesis, respiration, and behavior) are affected by ocean acidification in ways that affect non-calcifiers as well as calcifiers (Gattuso and Hansson, 2011). A more balanced program that incorporates studies on the lesser known effects of ocean acidification thus is needed.

As mentioned above, it is important to evaluate the effects of ocean acidification at all levels of biological organization, and the Strategic Plan concurs with this perspective. The recommendation to study ‘other factors’ in addition to physiological processes could also be expanded to emphasize the need for information that will enable a scaling-up from single species to population and community levels. The value of measuring organisms’ responses to ocean acidification, especially when studies incorporate effects of other factors and environmental stressors, is greatly increased when they provide key parameters for population and community models. Although physiological and behavioral studies can yield insights into the state of health of individual organisms, it is critical to incorporate analyses of rates of growth, survival, and reproduction of individuals, as well as analyses of effects on predation and competition, because data from these measurements can potentially be translated to rates of biomass production and demographic status for populations. Such measures can be essential for developing ecosystem models, including models focused on fisheries-related issues of socioeconomic importance.

This Theme does a comprehensive job of outlining sets of 3- to 5-year and 10-year goals for the National Ocean Acidification Program. The discussion of goals reflects a good summary of proposals found in previous reports and papers. To be consistent with previous reports, however, some of the 10-year goals need to be addressed sooner in the Program. As

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