Are fish getting ‘anxious’ about global warming?

New study shows behavioral impacts of ocean acidification


Is ocean acidification making Pacific rockfish more anxious? Photo courtesy NOAA.

By Summit Voice

FRISCO — If you think you’re worried about climate change, just imagine how some ocean critters must be feeling as the seas become ever-warmer and more acidic. Numerous studies already show the physiological impacts of ocean acidification, and new research suggests there may also be behavioral ramifications.

The study, combining marine physiology, neuroscience, pharmacology, and behavioral psychology, revealed a surprising outcome from increases of carbon dioxide uptake in the oceans: Anxious fish.

To track the impacts, scientists with Scripps Institution of Oceanography at UC San Diego and MacEwan University in Edmonton, Canada used a camera-based tracking software system to compare the behavior of two groups of rockfish. The control group was kept in normal seawater, while the test group was exposed to water with elevated acidity levels matching those projected for the end of the century.

They measured each group’s preference to swim in light or dark areas of a testing tank, which is a known test for anxiety in fish. The researchers found out that normal juvenile rockfish continuously moved between the light and dark areas of the tank. However, experiments have shown that fish administered with an anxiety-inducing drug prefer the darker area and seldom venture into the light. Hence, dark-preference is indicative of increased anxiety in juvenile rockfish.

Next, the researchers found that rockfish exposed to acidified ocean conditions for one week also preferred the dark area of the tank, indicating they were significantly more anxious than their normal seawater counterparts. Rockfish exposed to acidified ocean conditions remained anxious even one week after being placed in seawater with normal carbon dioxide levels. Only after the twelfth day in normal seawater did the anxious fish behave like the control group and resumed normal behavior.

The researchers say the anxiety is traced to the fish’s sensory systems. Exposure to acidified water leads to changes in neuronal activity that is reflected in the altered behavioral responses described in this study.

“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 Martín Tresguerres, a Scripps marine biologist and study coauthor.

Tresguerres said anxious behavior is a concern for juvenile rockfish because they live in highly dynamic environments such as kelp forests and drifting kelp paddies that offer variable lighting and shading conditions.

“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,” said Tresguerres. “This would have negative implications due to reduced time foraging for food, or alterations in dispersal behavior, among others.”

Similar results have been reported by other researchers who found that ocean acidification impaired olfaction in tropical clown fish. The new study adds anxiety behavior to the list of biological functions that are susceptible to future ocean acidification, and it is the first to describe effects of ocean acidification on the physiology and behavior of Californian fish.

“Behavioral neuroscience in fish is a relatively unexplored field, but we do know that fish are capable of many complicated cognitive tasks of learning and memory. Increased anxiety in rockfish could have a detrimental impact on many aspects of their daily functioning,” said Trevor James Hamilton, a neurobiologist at MacEwan University and coauthor of the study.

Tresguerres said laboratory tests cannot fully model the steady progression of acidity levels that will be seen in the wild over years and decades.

“Nonetheless, our results suggest that ocean acidification may affect an important aspect of fish behavior,” he said.

The National Science Foundation, UC San Diego Academic Senate, Scripps Institution of Oceanography, The Alfred P. Sloan Foundation, MacEwan Research Office, Arts and Science, and Student Enrichment Fund supported the research.

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