(Inside Science) -- When marine oil spills devastate an ecosystem, images of oil-drenched seabirds and dead fish fill the news. But creatures also suffer out of the public eye, such as the sharks and rays that sink to the seafloor after dying.
"It’s kind of out of sight, out of mind," said Stephen Kajiura, a biologist at Florida Atlantic University in Boca Raton and one of the two co-authors of a new study published recently in the journal Zoology that looks at how oil affects the ability of stingrays to hunt.
Sharks and rays have unique abilities to detect the electric fields generated by their prey’s underwater movements. Previous research by Kajiura and first author Eloise Cave revealed that Atlantic stingrays exposed to crude oil lost their ability to smell prey underwater. Now follow-up research shows that the oil can also dull the rays’ electrosensory abilities. Both senses are critical for the animals, since they often hunt in murky waters and their eyes aren’t on the same side of their bodies as their mouths.
The researchers captured wild stingrays and put them in water tanks in a lab. They first tested the animals’ ability to detect prey in clean water using devices that created weak electric fields similar to what would be created by the movement of prey like small crabs or shrimp.
Once they understood how accurately the rays could find the simulated prey, they did another experiment where they added crude oil to the tanks, exposed the animals for five hours and ran the same tests. The oil they added was similar to the type and concentration spilled during the 2010 Deepwater Horizon disaster in the Gulf of Mexico, which was the largest accidental oil spill in history.
The rays still tried to feed after exposure, but they simply didn’t detect the prey signals until they were much closer, Kajiura said.
He speculates that the change could have something to do with the chemicals in the oil binding to the gel in the stingrays’ electrosensory organs.
Kajiura said he was surprised that only five hours of exposure was enough to see such an effect. The Deepwater Horizon rig spilled oil for much longer, and even after the surface slick was cleared away, some of the oil settled onto the seafloor of the Gulf of Mexico where stingrays spend much of their time.
"Their face is in it, their nose is in it," Kajiura said. "The animals could be impacted at low levels for a long time."