Oil Exposure Impairs Coral Fish Behaviors, Texas Researchers Find

AUSTIN, TX — The ingesting of just a few drops of oil can impact the higher-order thinking of coral fish, causing them to make poor decisions, researchers at the University of Texas at Austin found. They liken this altered behavior to decisions made by adult humans after one too many cocktails.

In a paper published Monday in Nature Ecology & Evolution, a team of fisheries biologists led by Jacob Johansen and Andrew Esbaugh of The University of Texas Marine Science Institute have discovered that oil impacts the higher-order thinking of coral reef fish in a way that could prove dangerous for them — and for the coral reefs where they make their home.

Johansen and his team examined six different species of coral reef fish, finding that exposure to oil consistently affected behavior in ways that put the fish at risk, officials said. The coral fish were especially vulnerable during several weeks when they were undergoing the juvenile stages of development, researchers found.

Even in healthy populations of reef fish, typically less than 10 percent of embryos and larvae reach adulthood, researchers noted. Those that do survive must learn to identify friend from foe and adopt protective behaviors, such as traveling in groups, minimizing movement in open waters and swimming away quickly from danger.

But in their experiments, scientists found that juvenile fish exposed to oil struggled on all these counts.

“In several different experiments, the fish exposed to oil exhibited very risky behavior, even in the presence of a predator,” said Esbaugh, an assistant professor of marine science. The scientists also found that oil exposure negatively affected the fishes’ growth, survival and settlement behaviors (their ability to find a suitable habitat).

The findings are significant given that oil concentrations are found in oceans worldwide. Yet until now, little has been known about the impact of oil exposure on coral reef fish. Earlier research that explored how oil affects the physiology of fishes has demonstrated developmental heart deformities and associated cardiac functions, but this is the first study to demonstrate that oil exposure affects behavior in a way that increases predation and reduces settlement success, university officials noted.

The findings bode ill for reefs as well, since many coral reefs depend on fish to remove algae that can restrict their growth and development, the study found. Scientists noted that coral reef ecosystems are the oceans’ most diverse ecosystems — and the most threatened. Hundreds of millions of people depend on coral reefs and their fish for income or food, but widespread coral bleaching and over-fishing threaten this way of life, officials added.

The upshot: Limiting oil-based industrial activities near reefs may be critical for reef preservation, the study suggests.

“Over the past 35 years, almost one-fifth of the world’s coral reefs have been lost and half of what’s remaining is either expected to disappear or be under severe threat in the next few decades,” Johansen, the lead researcher, noted. “Still, many governments continue to allow industrial activities, including oil drilling and exploration, in sensitive reef habitats. If a spill were to occur, this study suggests there could be major consequences for the fish, for coral reefs and for people working in fisheries and tourism.”

Johansen noted the study centered on oil concentrations that are already present in many industrialized regions worldwide — concentrations ranging from two to five parts per billion, the equivalent of a couple of drops in a swimming pool.

Exposure to these oil concentrations caused higher rates both of immediate death and more latent death, in addition to the behavioral shifts and cognitive changes in coral reef fish, the study found. These results suggest that future studies of oil in sensitive environments, such as coral reefs, should account for behavior in addition to the toxic effects when trying to capture the overall ecological health of the system or make predictions about fish populations.

Along with Johansen and Esbaugh, researchers Bridie Allan from The Institute of Marine Research in Bergen, Norway and Jodie Rummer of the Australian Research Council Centre of Excellence for Coral Reef Studies in James Cook, Australia assisted with the findings. This research was supported by the Gulf of Mexico Research Initiative, Australian Research Council and Lizard Island Reef Research Foundation.

Read the full study by clicking here.

Photo: Damselfish, Chromis species, by Jacob Johansen