Marine ecosystems, and the services they provide, are predicted to alter considerably as a result of climate change. This paper outlines important expected alterations in these ecosystems, considers their economic consequences, and examines economic policies that may be adopted in response to these changes. In doing so, it focuses on two main cases, namely findings about the impact of ocean acidification (and climate change generally) on the Norwegian fisheries and predictions about alterations in coral reef systems. A number of theoretical issues are raised. These include the possibility that if economic impact analysis is used to measure economic value, the global economic value of coral reefs could rise as their area is reduced. This, however, is not necessarily an appropriate measure of economic value, even though it is often used for this purpose. Also the importance of taking into account the opportunity costs involved in conserving marine ecosystems is stressed. Furthermore, several dynamic aspects of variations in marine ecosystems are shown to be important for valuation purposes as well as for economic policy. Both the economics of mitigation and adjustment policies are discussed. Optimal economic policies for responding to climate change are shown to be sensitive to the dynamics of ecosystem change and are likely to vary regionally.