Explore how rising ocean acidity is affecting animals in this video from NOVA: Lethal Seas. In laboratory experiments, researchers found changes to the brain chemistry and behavior of fish that were exposed to high levels of carbon dioxide (and, therefore, higher acidity). They repeated their experiments at a coral reef in Papua New Guinea where CO₂ levels are extreme. They found that fish that grew up in areas of higher CO₂ and, consequently, higher acidity do not avoid the smell of predators. The CO₂ seems to have affected their cognitive ability so that they do not avoid the smell of a predator, even though they can still identify a predator's odor.