(The following is a reformatted version of a press release
issued by NOAA and received via electronic mail. The release was
confirmed by the sender.) 
MARCH 24 2014 
Contact: Ben Sherman, NOAA 301-713-3066 (office), 202-253-5256
Crude oil causes developmental abnormalities in large marine
Study shows Deepwater Horizon oil disrupts heart development in
Crude oil from the 2010 Deepwater Horizon disaster causes severe
defects in the developing hearts of bluefin and yellowfin tunas,
according to a new study by a team of NOAA and academic
The findings, published in the Proceedings of the National
Academy of Sciences on the 25th anniversary of the Exxon Valdez
oil spill, show how the largest marine oil spill in United
States history may have affected tunas and other species that
spawned in oiled offshore habitats in the northern Gulf of
Atlantic bluefin tuna, yellowfin tuna, and other large predatory
fish spawn in the northern Gulf during the spring and summer
months, a time that coincided with the Deepwater Horizon spill
in 2010. These fish produce buoyant embryos that float near the
ocean surface, potentially in harm’s way as crude oil from the
damaged wellhead rose from the seafloor to form large surface
The new study shows that crude oil exposures adversely affect
heart development in the two species of tuna and an amberjack
species by slowing the heartbeat or causing an uncoordinated
rhythm, which can ultimately lead to heart failure. 
“We know from the 1989 Exxon Valdez spill in Prince William
Sound that recently spawned fish are especially vulnerable to
crude oil toxicity,” said Nat Scholz, Ph.D., leader of the
ecotoxicology program at NOAA’s Northwest Fisheries Science
Center in Seattle. “That spill taught us to pay close attention
to the formation and function of the heart.” 
“The timing and location of the spill raised immediate concerns
for bluefin tuna,” said Barbara Block, Ph.D., a study coauthor
and professor of biology at Stanford University. “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.” 
Recent studies are increasingly painting a more detailed picture
of how oil-derived polycyclic aromatic hydrocarbons (PAHs) act
on the heart. Earlier this year, the Stanford-NOAA team showed
in a related paper published in Science (Brette et al. 343: 772)
that Deepwater Horizon crude oil samples block excitation-contraction coupling--vital processes for normal beat-to-beat
contraction and pacing of the heart--in individual heart muscle
cells isolated from juvenile bluefin and yellowfin tuna. 
“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.” said Block. “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.” 
This mechanism explains why the team observed a range of cardiac
effects in the developing hearts of intact embryos in the
present study. “We directly monitored the beating hearts of
living fish embryos exposed to crude oil,” said Dr. John
Incardona, NOAA research toxicologist and the study’s lead
author. “The tiny offspring of tunas and other Gulf species are
translucent, and we can use digital microscopy to watch the
heart develop.” 
The major difficulty facing the researchers was access to live
animals. Tunas are difficult to raise in captivity and few
facilities exist worldwide with spawning fish. In the open
ocean, fragile fish embryos and larvae are mixed with many other
types of plankton, and they usually don’t survive the rough
conditions in a net towed near the surface. This made it close
to impossible to assess developmental cardiotoxicity in samples
collected near the Deepwater Horizon surface oil slicks. 
To work around this challenge, the international team brought
the oil to the fish. Samples of crude oil were collected from
the damaged riser pipe and surface skimmers. The samples were
then transported to the only land-based hatcheries in the world
capable of spawning tunas in captivity. 
This approach allowed the scientists to design environmentally
relevant crude oil exposures for bluefin tuna and yellowfin tuna
at marine research facilities in Australia and Panama,
respectively. Luke Gardner, an Australian native post-doctoral
associate from Stanford University and co-author on the PNAS
paper, was vital in helping the team investigate the bluefin. 
“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 pioneering effort to develop new testing methods
was also led by Martin Grosell, Ph.D., at the University of
The new research adds to a growing list of fish that are
affected by crude oil. “This fits the pattern,” said Incardona.
“The tunas and the amberjack exposed to Deepwater Horizon crude
oil were impacted in much the same way that herring were
deformed by the Alaska North Slope crude oil spilled in Prince
William Sound during the Exxon Valdez accident.” 
Crude oil is a complex mixture of chemicals, some of which are
known to be toxic to marine animals. Past research has focused
in particular on PAHs, which can also be found in coal tar,
creosote, air pollution and stormwater runoff from land. In the
aftermath of an oil spill, PAHs can persist for many years in
marine habitats and cause a variety of adverse environmental
Developmental abnormalities were evident in bluefin and
yellowfin tunas at very low concentrations, in the range of
approximately one to 15 parts per billion total PAHs. These
levels are below the measured PAH concentrations in many samples
collected from the upper water column of the northern Gulf
during the active Deepwater Horizon spill phase. 
Severely affected fish with heart failure and deformed jaws are
likely to have died soon after hatching. However, the NOAA team
has shown in previous work that fish surviving transient crude
oil exposures with only mild effects on the still-forming heart
have permanent changes in heart shape that reduce swimming
performance later in life. 
“This creates a potential for delayed mortality,” said
Incardona. “Swimming is everything for these species.” 
The nature of the injury was very similar for all three pelagic
predators, and similar also to the response of other marine fish
previously exposed to crude oil from other geologic sources.
Given this consistency, the authors suggest there may have been
cardiac-related impacts on swordfish, marlin, mackerel, and
other Gulf species. “If they spawned in proximity to oil, we’d
expect these types of effects,” said Incardona. 
The research was funded by NOAA as part of the on-going Natural
Resource Damage Assessment for the Gulf ecosystem following the
April 20, 2010 Deepwater Horizon oil spill. Contributing to the
findings in addition to NOAA and Stanford University were
researchers from the University of Miami’s Rosenstiel School of
Marine and Atmospheric Sciences and the University of the
Sunshine Coast in Queensland, Australia. 
(bjh) NY 
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