Seattle scientists show how Deepwater Horizon spill caused heart damage in young tuna
Formed after the Exxon Valdez spill, a NOAA team continues to document the harmful effects of oil spills around the world.
Seattle Times science reporter
On the 25th anniversary of the Exxon Valdez disaster, Seattle scientists are adding to the evidence that oil spills exact a toll far beyond soiled beaches and seabirds drenched in crude.
The latest findings, published Monday, document toxic effects on the hearts of young tuna and other top predator fish from the Gulf of Mexico — where the 2010 explosion of BP’s Deepwater Horizon rig killed 11 people and unleashed the biggest marine spill in U.S. history.
The study is part of ongoing federal efforts to assess environmental damage from the estimated 4 million barrels of crude that gushed into the Gulf from the damaged well on the seafloor.
The new results also build on more than two decades of research by the Seattle-based team, which was organized shortly after the Exxon tanker ran aground in Alaska’s Prince William Sound in 1989.
“Basically, we focus on the microscopic effects of oil spills,” said John Incardona, lead author of the study and a member of the National Oceanic and Atmospheric Administration’s (NOAA) ecotoxicology program, based at the Northwest Fisheries Science Center in Seattle.
The Deepwater Horizon spill gushed for months and coincided with the spawning season for tuna, marlin, swordfish and some of the other top sport and commercial species in the Gulf.
But it’s nearly impossible to study oil’s effects on floating fish eggs and embryos in the sea, because being scooped up in nets is fatal for the fragile spawn, Incardona explained. And very few laboratories in the world have succeeded in rearing tuna and other open-ocean species in captivity.
So the NOAA team packed up its experimental gear and traveled to two of those labs, in Panama and Australia. Working with researchers from Florida, California and Australia, the team exposed embryos and larvae of bluefin tuna, yellowfin tuna and a species called amberjack to oil from the Deepwater Horizon well at levels comparable to those measured in the Gulf during the spill.
The larvae are transparent, so the scientists were able to monitor how well their hearts functioned simply by looking through a microscope.
“You can watch their heart form, watch it start beating and watch it take shape, all in real time,” Incardona said.
What the scientists saw mirrored effects already documented in salmon, herring and other cold-water species — and helped put to rest arguments that warm-water fish might not be as vulnerable.
The hearts of larvae exposed to higher concentrations of oil — up to about 15 parts per billion — were deformed and beat more slowly and erratically than those of control larvae. Poor circulation also led to secondary effects, like deformed jaws and fins and tiny eyes. Most of those larvae died.
Milder effects were present at concentrations as low as one part per billion. At those levels, larvae mostly survived, but persistent heart damage left them weak, slow and probably destined for a short life.
“They’re more likely to end up as prey instead of being a predator,” Incardona said.
In earlier studies, the researchers showed that the heart damage is mainly caused by compounds in oil called polycyclic aromatic hydrocarbons, or PAHs. The chemicals disrupt the molecular process responsible for regular heart rhythms, said Barbara Block, a marine scientist at Stanford University and co-author of the new study published in the Proceedings of the National Academy of Science.
The mechanism is common to all fish species and other vertebrates — including humans, she pointed out. That might help explain the fact that high levels of air pollution, which also contains PAHs, can trigger heart problems in people.
Bluefin tuna can grow to 1,400 pounds and take eight to 12 years to mature. That makes it hard to evaluate the effect of the spill on overall populations, even though it’s now clear that huge numbers of larvae must have perished, Block said.
In a statement, BP spokesman Jason Ryan stressed the lack of evidence for population effects, and questioned whether the oil concentrations used in the experiments really reflect what larvae were exposed to during the spill.
BP pleaded guilty to criminal charges in the case, including manslaughter and negligence, and agreed to pay $4.5 billion. But a legal battle is still under way over how much the company will pay for damage to the ecosystem.
Sandi Doughton at: 206-464-2491 or email@example.com