Scientists cite heart development problem
Tuna and amberjack embryos developed abnormal hearts after being exposed to oil from the blown-out Deepwater Horizon well, even at weaker concentrations than were found in the water after the 2010 BP disaster.
“The developing fish heart is very susceptible to chemicals found in crude oil,” said Nat Scholz, director of the ecotoxicology program with the NOAA Northwest Fisheries Science Center and co-author of a new report.
The study, published in Proceedings of the National Academy of Sciences, builds on more than 20 years of studies of oil toxicity on fish that followed the 1989 Exxon Valdez oil spill. Scientists exposed Atlantic bluefin tuna, yellowfin tuna and amberjack embryos to Deepwater Horizon oil collected from the surface and oil that was taken from the riser pipe under the water.
When scientists monitored the heart development and function using digital microscopy, they found the oil exposure led to a slowing of the heartbeat or an uncoordinated rhythm of a heart beat.
“The Deepwater Horizon oil disturbed the heart rate and rhythm of every species we tested,” said John Incardona, research toxicologist with NOAA’s Northwest Fisheries Science Center and lead author of the report.
The severity of the deformities and reduced function of the heart got worse as the concentrations of the oil increased, he said.
At high concentrations, the oil exposure can cause heart problems which lead to other deformities in the developing embryo. Those deformities would mean the fish would die soon after hatching. At low concentrations, the fish would survive after hatching, but the heart defects mean the long-term health of the fish would be compromised, Incardona said.
The fish showed similar reactions to what was seen in the herring population in Alaska in the wake of the Exxon Valdez accident, he said.
“We think this is a delayed mortality,” Scholz said. “In both cases you’ll be losing those fish out of the adult spawning population.”
BP disputes the study gives any indication that there are population impacts on tuna, amberjack or other fish species in the Gulf of Mexico.
“The oil concentrations used in these lab experiments were rarely seen in the Gulf during or after the Deepwater Horizon accident,” wrote Jason Ryan, BP spokesman, in an emailed statement.
“In addition, the authors themselves note that it is nearly impossible to determine the early life impact to these species. To overcome this challenge, it would take more information than what’s presented in this paper,” he said.
Authors of the report maintain the study was drawn up to mimic what would have been found in the Gulf of Mexico during the oil spill.
This comes on the heels of a report released last month by NOAA and Stanford University which showed crude oil interferes with fish heart cells. The result of the interference is slower or irregular heartbeats that can lead to cardiac arrest.
More than 20 years of research on oil toxicity on fish also has shown similar results to what was released Monday, NOAA researchers claim.
“If there were other species spawning in the Gulf exposed to oil, they would see similar impacts,” Scholz said.
Although the impact is clear, what those effects could mean for tuna and other fish population levels in the Gulf of Mexico remains to be seen, said Barbara Block, professor of marine science at Stanford University and a co-author of the report.
Scientists are working on using satellite images and bluefin tuna tracking to come up with estimates of how much of the spawning grounds would have been impacted by the oil and how much total spawning habitat is available.
That report, which is a few months away from being released, would be another step toward seeing what the potential for impact on population could be in the future.
Tuna, Block explained, are very long-lived fish and don’t reach maturity until they are between eight and 14 years old, so there would still be years before tuna spawned during the Deepwater Horizon disaster entered into the commercial harvest.
This study is different than most of the previous work on oil toxicity on embryos because most of that work was done on small fish like zebra fish or Gulf killifish. Instead, this study focused on tuna and amberjack, which would likely have been spawning right at the time and place where the Deepwater Horizon disaster occurred, Block said
Although the oil was collected from the Deepwater Horizon, getting access to live animals wasn’t so easy.
Tuna embryos and larvae that float on the surface of the water are very delicate and can be easily damaged when collected by a net. Instead, oil samples were taken to land-based hatcheries that are capable of spawning tuna in captivity.
The report released Monday is part of the Natural Resource Damage Assessment process that uses science to quantify damage from oil spills and then come up with restoration or an monetary amount that would compensate for the oil spill damage.
The report was done by researchers from NOAA, Stanford University, the University of Miami’s Rosenstiel School of Marine and Atmospheric Sciences and the University of the Sunshine Coast in Queensland, Australia.