Rising Ocean Acidification Makes Even Fish Anxious: Fisheries May be Impacted

Ocean acidification isn't just making environmentalists anxious; it's also worrying the fish. Scientists have discovered that increased carbon dioxide in the world's oceans is causing fish to be more anxious, which could impact fisheries across the globe.

The oceans are currently acidifying as more and more carbon dioxide is absorbed from human activities. The water's pH is slowly declining which, in turn, increases acidity. This can disrupt the growth of shells and skeletons of certain marine mammals. Yet behavioral impacts have largely remained unknown--until now.

The new study examined how rising acidity might impact juvenile rockfish, an important commercial species in California. The scientists used a camera-based tracking software system in order to compare a control group of rockfish kept in normal seawater to another group in waters with elevated acidity levels that matched those projected for the end of this century. The scientists measured each group's preference to swim in light or dark areas, which is known to test anxiety in fish; normal fish will swim between light and dark areas continuously while those administered an anxiety-inducing drug seldom venture into the light.

So what did they find? It turns out that the rockfish in the acidified environment preferred dark areas far more than their counterparts. This seemed to indicate that the rockfish were far more stressed and anxious.

"These results are novel and thought-provoking, because they reveal a potential negative effect of ocean acidification on fish behavior that can possibly affect normal population dynamics and maybe even affect fisheries," said Martin Tresguerres, one of the researchers, in a news release.  "If the behavior that we observed in the lab applies to the wild during ocean acidification conditions, it could mean that juvenile rockfish may spend more time in the shaded areas instead of exploring around. This would have negative implications due to reduced time foraging for food, or alterations in dispersal behavior, among others."

The findings reveal how ocean acidity may have more impacts than we even realize. If it can alter fish behavior, then fisheries are liable to be in danger of collapsing in the future if certain precautions aren't taken. That said, the lab conditions cannot fully model the steady progression of ocean acidity in the wild. The findings show the importance of future studies that aim to understand how rising sea levels will impact the oceanic ecosystems.

The findings are published in the journal Proceedings of the Royal Society B: Biological Sciences.