Oil exposure negatively affects reef fish behavior

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It’s no secret that big oil spills can decimate ocean life, but a recent study published in Nature Ecology & Evolution by UT Marine Science Institute researchers shows just how pervasive the after-effects of oil spills can be.

The study examined the effect of exposure to small amounts of oil on the behavior of coral reef fish. The fish, exposed to the oil for 24 hours during their larval stages, demonstrated risky behavior.

“They’re doing something that’s bad for their self interest,” said Andrew Esbaugh, one of the team’s lead researchers. “We make (the analogy) in the lab all the time: It’s like these fish are a little drunk.” 

The researchers found that the young fish were less likely to swim in groups or choose safe spots in the reef to live, significantly increasing the rate of death by predation. Normally, the coral reef species studied by Esbaugh’s team settle inside strong coral habitats because they provide hiding places and food. However, oil exposure negatively affected the fishes’ decision-making when first choosing a home.

“The animals are essentially making bad decisions,” Esbaugh said. 

In the experiment, the young fish are put into a simulated arena with strong coral reefs, damaged coral reefs and exposed sand and are allowed to choose where to settle. When the fish are exposed to oil, they don’t choose to settle in the strong coral reefs.

Their study also found that the surviving fish experienced early death even when there were no predators around and plenty of food was available. More research is required to find out exactly what is causing this loss of longevity, but a possible hypothesis involves heart failure, Esbaugh said.

“There’s a lot of work that shows that oil can interfere with the cardiorespiratory system … essentially the ability of the heart to pump blood,” Esbaugh said. “(However) there are many different ways that oil can (affect) mortality.”

Coral reefs are some of the most biodiverse ecosystems on the planet, like underwater rainforests, according to a 2013 article in Nature Education Knowledge. Jay Banner, a UT geological sciences professor, said protecting coral reef fish is important. 

“The health of ecosystems depends on (the diversity of their species), and if ecosystems start to fail … then they’re no longer going to provide us … services,” Banner said. 

In addition to their important ecological role and ability to provide seafood, coral reefs also protect coastal communities against powerful waves, which may break against reefs instead of inhabited land. 

The corals that we often think of as plants are actually skeletons formed from calcium and carbonate ions pulled from the water by small, fleshy animals called coral polyps. 

“The polyp always sits at the top, secreting its skeleton, growing upward,” Banner said. 

The skeletons used to elevate the polyps also become handy homes for the diverse array of marine life that inhabits coral reefs. However, erosion caused by coastal land development leads to extra silt in the water, which along with oil spills, warming ocean temperatures and overfishing, is disrupting these important ecological reservoirs, Banner said.

“(The coral reefs) have adapted over … tens of millions of years so they could occupy that special ecological niche,” he said. “And now the conditions of that niche are changing.”

Even years after an oil spill is cleaned up, coral reef fish may still be in danger from the small amounts of oil left in the water. 

“Oil and most petroleum products are a heterogeneous mixture of a whole bunch of different chemicals,” Esbaugh said. 

These chemicals include a class of molecules called petrogenic polycyclic aromatic hydrocarbons (PAHs), which degrades very slowly in the open ocean and can stick around for a long time. 

The fish in Esbaugh’s study were shown to have abnormally developed brains. A transcriptomic analysis showed that the PAHs were affecting the fishes’ gene expression and disrupting their brain development. 

“Just because an animal is alive doesn’t mean it’s going to live for its normal (lifespan),” Esbaugh said. 

Banner said the average person can consider their contribution of carbon dioxide into the atmosphere and reduce their carbon footprint if they want to help the coral reefs. Carbon dioxide in the atmosphere can dissolve into ocean waters and increase their acidity, damaging coral reefs. 

Esbaugh said stopping oil exploration near at-risk habitats can reduce the impact of oil spills on the coral reefs.

“While no one wants to plan for an oil spill, and no one wants to think it’s going to happen, it’s going to happen,” Esbaugh said. “(Oil) is a major driver of our economy, (but) we do have to be cognizant of some of the downsides.”