Ocean Acidity Affects Fish Senses

Here's another worry for Nemo's father, the Pixar-Disney animated clownfish. Acidic ocean conditions can disrupt orange clownfish larvae's ability to distinguish and respond to olfactory cues that help them locate a suitable adult habitat in a coral reef, according to a new study (Proc. Nat. Acad. Sci. USA, DOI: 10.1073/pnas.0809996106). High levels of human-generated carbon dioxide are the main reason that oceans are acidifying. Global pH of surface-ocean waters is currently about 8.1 and is expected to drop by approximately 0.3 units in the next 50–100 years. Scientists recognize that ocean acidification threatens marine ecosystems, but few studies have examined effects on fish. Philip L. Munday of James Cook University, in Australia, and colleagues raised clownfish (Amphiprion percula) in seawater acidified with CO₂. At pH 7.8, a condition that could arise around 2100 if the oceans continue to absorb CO₂ at the current rate, the fish lost the ability to distinguish between chemical cues that might help them locate a proper habitat. At pH 7.6, the fish didn't respond to any environmental cues. If the pH drop is widespread, it could threaten the survival of a broad range of marine species, Munday says. More studies are needed to see whether the effect is reversible.