Deepwater Horizon Oil Spill Causes Development Abnormalities in Tunas: NOAA

Crude oil from the 2010 Deepwater Horizon disaster, the largest marine oil spill in the history of the Unites States, was causing developmental abnormalities in the bluefin and yellowfin tunas, NOAA said in new finding.

On the 25^th anniversary of 1the 989 Exxon Valdez oil spill disaster, NOAA highlighted how the 2010 accidental Deepwater Horizon oil spill affected the development of hearts in tunas. The marine oil spill also impacted other species spawned in the oiled offshore habitats in the northern Gulf of Mexico.

During the spring and summers, tuna species such as Atlantic bluefin tuna, yellowfin tuna and other large marine predators are known to spawn in the northern Gulf. This spawning time collided with the 2010 Deepwater horizon spill.  The embryos these fishes produce face a greater risk as they float near the ocean surface and crude oil spills form surface slicks. Exposure to this crude oil causes a significant abnormality in the heart development in the two species of tuna and an amberjacks.

Exposure to oil spill led to uncoordinated heart rhythms in tunas and it can lead to heart failure.

"The timing and location of the spill raised immediate concerns for bluefin tuna," Barbara Block, Ph.D., a study coauthor and professor of biology at Stanford University, said in a news release. "This spill occurred in prime bluefin spawning habitats, and the new evidence indicates a compromising effect of oil on the physiology and morphology of bluefin embryos and larvae. We now have a better understanding why crude oil is toxic, and it doesn't bode well for bluefin or yellowfin embryos floating in oiled habitats. At the level of a single heart muscle cell, we've found that petroleum acts like a pharmacological drug by blocking key processes that are critical for cardiac cell excitability."

Earlier researchers at Stanford-NOAA showed that Deepwater Horizon crude oil blocked the contraction and pacing of hearts in single heart muscle cells of the juvenile bluefin and yellowfin tuna.

For this study, it was difficult to have access and raise tunas in captivity. Also the researchers found it challenging to assess the developmental cardiotoxicity in samples collected near the Deepwater Horizon surface oil slicks. To overcome this challenge, researchers brought the oil to the fish.

They collected samples of crude oil from the damaged pipes as well as the surface skimmers. These oil samples were later transported to the land-based hatcheries globally that spawn tunas in captivity.  With this the researchers were able to design environmentally relevant crude oil exposure for bluefin and yellowfin tuna at different facilities in Australia and Panama.

"It is challenging to maintain bluefin in culture and we were privileged to have successfully tested the crude oil in Australian facilities, the only on-land hatchery that has bluefin tuna in culture. This gave us access to tuna embryos and allowed us to study the developmental toxicity of oil," said Gardner.

The researchers identified the developmental abnormalities in bluefin and yellowfin tunas at low concentrations (ranging from 1-15 parts per billion total PAHs). When compared to samples collected from the oil spill source, the level of PAH concentration was low. The fishes with heart failure and deformed jaws died soon after hatching.

NOAA had earlier showed that fish surviving exposure to crude oil with mild effects have irreversible changes in heart shape that drastically lower the swimming performance in later life.

This finding was documented in the Proceedings of the National Academy of Sciences.