Coral reef fish ‘make risky life decisions’ when exposed to oil


SYDNEY — Even a small amount of oil can cause coral reef fish, like the colorful damselfish, to make ill-advised and risky decisions, an Australian study has found.

“The fishes were unable to differentiate between friend and foe, stopped travelling in groups, and made poor choices regarding their habitat,” Jodie Rummer, one of the co-authors of the study, told dpa on Wednesday.

She said the oil-exposed fish were also slow to respond to danger and likened their response to being drunk or high.

“When given a choice, they chose the least suitable habitat. Instead of a healthy, fully-functioning coral, they chose open waters or the one with a pile of rubble,” Rummer said.

“Neither would provide shelter from predator or nutrition.”

The five-week-long study, based in Lizard Island in the Great Barrier Reef region, was conducted on six species of coral reef fish, including the damselfish that was made famous as Nemo’s cousin in the popular animated film “Finding Nemo.”

The study, which was published in the journal Nature Ecology and Evolution on Tuesday, said oil exposure caused “elevated mortality and stunted growth rates” and risky behaviors which made fish more likely to be eaten by predators.

The study looked at what happened to the fish when exposed to oil in the first three weeks of their life, a vulnerable period during which they would be developing their organs and immune system.

“The amount of oil we are talking about is equivalent to a few drops in an Olympic-size swimming pool, but it dramatically altered their behavior,” said Rummer, a researcher with James Cook University.

She said the idea came after the Deepwater Horizon oil spill in the Gulf of Mexico seven years ago, the largest marine spill in history, and one of 340 major spills in the past 40 years.

“High concentration of oil could wipe out an entire population, but even after they have been cleaned, many years later, or low level of oil or other toxic pollutants linked to shipping or industrial activities in the ocean would have significant effect,” Rummer said.

The study said that each year more than 6 million metric tons of petroleum products are estimated to enter global oceans from sources such as industrial discharge, urban run-off and shipping operations.

Rummer said the low oil concentration used in the study reflects levels already found in many areas near the coral reefs, including the Great Barrier Reef.

While the low concentration of oil was not killing the fish immediately, it was having long-term effects.

“The immediate effect was behavioral and the long-term effect was decrease in growth and decrease in survival rates,” Rummer said.

“Fishes are important to coral ecosystem and if they are making poor decisions, it’s not good for the whole ecosystem.”