Fisheries make important contributions to global food supply, providing >2.9 billion people with ~20% of their dietary animal protein. Although the majority of global fish production will eventually come from aquaculture, supplies from capture fisheries will remain vital for food security. The distributions and abundances of many of the fish species underpinning capture fisheries are affected by climatic variability, and will be altered irreversibly by global warming. The effects of increased CO2 emissions on the distribution and quality of fish habitats and stocks in the Pacific Islands region provides a potent example of the implications for food security and public health. Fish has been a cornerstone of food security in the region but rapid human population growth is reducing access to fish – a gap is emerging between the fish needed for good nutrition and sustainable harvests from coral reefs. Changes in the distribution and quality of coral reefs due to increased sea surface temperatures and ocean acidification, and decreased catches of fish associated with coral reefs, will widen this gap. Alternative sources of fish are needed to combat increased imports of cheap, nutritionally- poor foods, which are contributing to widespread obesity and chronic non communicable diseases, e.g., diabetes. The region’s rich tuna resources provide the solution – allocating just 6% of the industrial catch for local consumption would meet demand. However, progressive eastward movement of tuna with climate change means that adaptations to increase local access to tuna will depend on flexible management arrangements, and will vary among Pacific Island countries.