If carbon emissions continue at their current rate, the lives of clown fish and other coral reef denizens may not end as happily as in the popular computer-animated film Finding Nemo. Carbon dioxide (CO2) in the atmosphere eventually seeps into the ocean's surface, causing the water to become more acidic. In this new environment, young clown fish may be unable to sense chemical cues directing them away from predators and toward a suitable adult habitat. According to the new study published  online today in the Proceedings of the National Academy of Sciences, clown fish swim toward streams of water containing a predator's pheromones and venture farther away from the safety of their reef habitats. Researchers detected the abnormal behavior when the water contained as little as 700 parts per million of CO2—a concentration some scientists say may be reached by 2100. This study is the first to show that an impaired sense of smell can have behavioral consequences for wild-caught fish and reveals that damselfish as well as clown fish are vulnerable. Researchers have known for some time that high CO2 concentrations in water can affect the ability of shellfish and crustaceans to build shells and skeletons. The new work describes how other marine species may suffer as well.