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“Very low levels” of Exxon Valdez oil threaten salmon and herring survival 25 years later

“Very low levels” of crude oil from the 1989 Exxon Valdez spill in Prince William Sound, Alaska, are a threat to the survival of herring and pink salmon that spawn in the region, according to a study released today by the US National Oceanic and Atmospheric Administration.

The study shows that embryonic salmon and herring exposed to very low levels of crude oil can develop hidden heart defects that compromise their later survival.

That means that the Exxon Valdez spill on March 24, 1989 may have had much greater impacts on spawning fish than previously recognized, according to the study published in Nature’s online journal Scientific Reports Very low embyronic crude oil exposures cause lasting defects in salmon and herring.

“These juvenile fish on the outside look completely normal, but their hearts are not functioning properly and that translates directly into reduced swimming ability and reduced survival,” said John Incardona, a research toxicologist at NOAA Fisheries’ Northwest Fisheries Science Center (NWFSC) in Seattle. “In terms of impacts to shore-spawning fish, the oil spill likely had a much bigger footprint than anyone realized.”

This is a juvenile pink salmon exposed to low levels of crude oil as an embryo. While these fish appear outwardly normal, they nevertheless developed heart defects that compromised their ability to swim. Fish that are less able to forage and avoid predators are much less likely to survive to adulthood. (NOAA)

Previous research has shown that crude oil disrupts the contraction of the fish heart muscle cells. Embryonic fish exposed to trace levels of crude oil grow into juveniles with abnormal hearts and reduced cardiorespiratory function.

“With this very early impact on the heart, you end up with an animal that just can’t pump blood through its body as well, which means it can’t swim as well to capture food, form schools, or migrate,” said Mark Carls, toxicologist at the Alaska Fisheries Science Center. “Crude oil is changing basic physiology, or what makes a fish a fish.”

The research builds on earlier work by the Auke Bay Laboratories, part of NOAA Fisheries’ Alaska Fisheries Science Center, which found much reduced survival of pink salmon exposed as embryos to polycyclic aromatic hydrocarbons (PAH) from crude oil.

“Our findings are changing the picture in terms of assessing the risk and the potential impacts of oil spills,” said Nat Scholz, leader of the NWFSC’s ecotoxicology program and a coauthor of the new study. “We now know the developing fish heart is exquisitely sensitive to crude oil toxicity, and that subtle changes in heart formation can have delayed but important consequences for first-year survival, which in turn determines the long-term abundance of wild fish populations.”

The Exxon Valdez aground on Bligh Reef in Prince William Sound in May 1989. (NOAA) — The Exxon Valdez aground on Bligh Reef in Prince William Sound in March 1989. (NOAA)

The Exxon Valdez spill was the largest in U.S. history, with extensive oiling of shoreline spawning habitats for Pacific herring and pink salmon, the two most important commercial fish species in Prince William Sound.

Herring larvae sampled in proximity to oil were visibly abnormal, and mortality rates were higher for pink salmon embryos at oil spill sites than unaffected regions.

The herring fishery collapsed three to four years after the spill, when the herring spawned in oiled areas reached reproductive maturity.

The paper notes that the contribution of the spill to the herring population collapse, if any, was never determined and remains controversial.

Other studies, however, tend to confirm the findings, including heart problems for fish exposed to the Gulf of Mexico Deepwater Horizon spill and even fish exposed to naturally occurring oil seeps.

Oil spill caused unexpected lethal impact on herring, study shows

Gulf oil spill caused heart defects in fish embryos new study finds

The new findings suggest that the delayed effects of the spill may have been important contributors to the declines.

This image shows transient embryonic exposures to crude oil cause lasting reductions in the swimming speed of salmon and herring, months after additional juvenile growth in clean seawater. (NOAA)

Scientists from the Northwest Fisheries Science Center and Alaska Fisheries Science Center temporarily exposed embryonic salmon and herring to low levels of crude oil from the North Slope of Alaska and found that both absorbed chemicals at similar concentrations in their tissues. The embryos were then transferred to clean seawater and raised as juvenile fish for seven to eight months.

Few of the exposed embryos were outwardly abnormal in any way. However, closer examination of the fish revealed subtle defects that could reduce their long-term survival.

Juvenile salmon exposed to oil grew more slowly, with those exposed to the highest concentrations growing the slowest. For salmon, early survival in the ocean is strongly influenced by juvenile growth, with smaller fish suffering higher loss to predators.

Scientists used swimming speed as a measure of cardiorespiratory performance and found that fish exposed to the highest concentrations of oil swam the slowest. Slower swimming is an indication of reduced aerobic capacity and cardiac output, and likely makes fish easier targets for predators.

Exposure to oil as embryos altered the structural development of the hearts of juvenile fish, potentially reducing their fitness and swimming ability. Poor swimming and cardiac fitness is also a factor in disease resistance.

Earlier studies on the ecosystem-scale crash of the Prince William Sound herring population several years after the Exxon Valdez spill were based on higher levels of exposure to the oil. The new study shows that that cardiac injury occurs in normal-appearing fish that survive even lower level exposures.

The scientists reviewed data on measured oil concentrations in surface water samples collected in Prince William Sound after the oil spill and during the 1989 herring spawning season. Most of the 233 samples contained less oil than was believed to be toxic to herring at the time, based on visible gross developmental abnormalities. However, nearly all of the samples contained oil at or above concentrations shown in the new study to alter heart development.

If the Exxon Valdez spill impacted heart development among a large majority of fish that were spawned in proximity to oiled shorelines, the subsequent losses of juveniles to delayed mortality would have left fewer adults to join the population. Although not direct proof, this provides a plausible explanation for the collapse of the Prince William Sound herring stock four years later, when fish spawned during the oil spill would have matured.

The study concludes that the impacts of the Exxon Valdez spill on near shore spawning populations of fish are likely to have been considerably underestimated in terms of both the geographic extent of affected habitat and the lingering toxicity of low levels of oil. The findings will likely contribute to more accurate assessments of the impacts of future oil spills, Incardona said. “Now we have a much better idea of what we should be looking for,” he said.

That means, according to the study “that the impacts of the Exxon Valdez oil spill on populations of near shore spawning fish are likely to have been considerably underestimated, in term of both the geographic extent of affected habitats and the lingering toxicity of low levels of residual oil.”

The report calls for more studies of the sensitivity of the developing fish heart since the vulnerability “also has implications for other pollution sources in marine ecosystems, including increasing maritime vessel traffic and expanding land-based urban runoff.”

In 2013, the Northern Gateway Joint Review panel said this about the Exxon Valdez oil spill.

Scientific studies after the Exxon Valdez spill indicated that the vast majority of species recovered following the spill and that functioning ecosystems, similar to those existing pre-spill, were established.

Species for which recovery is not fully apparent, such as Pacific herring, killer whales, and pigeon guillemots, appear to have been affected by other environmental factors or human influences not associated with the oil spill. Insufficient pre-spill baseline data on these species contributed to difficulties in determining the extent of spill effects.

Based on the evidence, the Panel finds that natural recovery of the aquatic environment after an oil spill is likely to be the primary recovery mechanism, particularly for marine spills. Both freshwater and marine ecosystem recovery is further mitigated where cleanup is possible, effective, and beneficial to the environment.

Natural processes that degrade oil would begin immediately following a spill. Although residual oil could remain buried in sediments for years, the Panel finds that toxicity associated with that oil would decline over time and would not cause widespread, long-term impacts.

25th anniversary of Exxon Valdez disaster looms over Northern Gateway dispute

Gulf oil spill caused heart defects in fish embryos new study finds

There is more proof that the toxic agents in crude oil are damaging to the development of fish embryos.

A study, “Deepwater Horizon Crude Oil Impacts the Developing Hearts of Large Predatory Pelagic Fish,” to be published on March 25, shows that several Gulf of Mexico fish embryos developed serious defects in heart development following exposure to crude oil from the Deepwater Horizon oil spill.

This study is the first to analyze the effects of the primary toxic agents released from crude oil on several commercially important pelagic fish species that spawn in the Gulf of Mexico.

The research team, which included five researchers from the University of Miami Rosenstiel School of Marine and Atmospheric Science, concluded that, “losses of early life stages were therefore likely for Gulf populations of tunas, amberjack, swordfish, billfish, and other large predators that spawned in oiled surface habitats.”

“This study is the first to understand the impacts of the Deepwater Horizon oil spill on the early life development of commercially important fish in the Gulf of Mexico,” said Daniel Benetti, Rosenstiel School professor of marine affairs and policy and director of the Aquaculture Program. “The findings can be applied to fisheries management questions in marine regions where crude oil extraction is prevalent.”

The study in the March 25 issue in the journal of the Proceedings of the National Academy of Sciences (PNAS), assessed the impacts of polycyclic aromatic hydrocarbons (PAHs), a toxic agent released from crude oil, from Deepwater Horizon oil samples on embryos of bluefin tuna, yellowfin tuna, and amberjack. Embryos were exposed to two different oil samples, one collected from surface skimming operations in the Gulf of Mexico and another from the source pipe attached to the damaged Deepwater Horizon wellhead.

A vast number of the water samples collected at the Deepwater Horizon oil spill site had PAH concentrations exceeding the toxicity thresholds observed in the study, therefore researchers demonstrated the potential for losses of pelagic fish larvae during the 2010 Deepwater Horizon disaster.

“Having access to the aquaculture facility and expertise at The Rosenstiel School positioned our team of UM scientists to address questions regarding the impacts of the 2010 Deep Water Horizon oil spill on these important pelagic top predators.” said Martin Grosell, Maytag professor of ichthyology at The UM Rosenstiel School. “The present study is the first of several on the topic to emerge from efforts by scientists and graduate students at The UM Rosenstiel School.”

The embryos used in the study were collected from research broodstock located at land-based fish hatcheries in Australia and Panama. Test methods were developed and designed by Dr. Grosell and Dr. Benetti’s team at The UM Rosenstiel School’s experimental hatchery facility.

Exposure to each oil type produced virtually identical defects in embryos of all three tested species. For each species, oil exposures caused serious defects in heart development, and abnormalities in cardiac function, indicating crude oil cardiotoxicity. Bluefin tuna showed the highest percentage of larvae with the entire suite of defects, and their populations are currently listed by the IUCN as endangered due to historically low levels.

The Deepwater Horizon oil spill in the northern Gulf of Mexico released more than four million barrels of crude oil into the surrounding waters during the seasonal spawning window for bluefin and yellowfin tunas, mahi mahi, king and Spanish mackerels, greater and lesser amberjack, sailfish, blue marlin, and cobia, all commercially and ecologically important open-ocean fish species.

“Vulnerability assessments in other ocean habitats, including the Arctic, should focus on the developing heart of resident fish species as an exceptionally sensitive and consistent indicator of crude oil impacts,” said the paper’s authors.

Another recent study of the Deepwater Horizon spill found that oil spills can trigger cardiac arrest in fish affected by the spill.

A study of an oil spill in San Francisco Bay in 2007 found “unexpected lethal impact on embryonic fish,” according to scientists from the University of California at Davis and the US National Oceanic and Atmospheric Administration who spent two years on follow-up research after the spill.

The long term impact of the Exxon Valdez spill on the developing fish embryo is still being hotly debated.

How oil spills kill fish: new study points to cardiac arrest; possible implications for humans

Oil spills kill fish. That’s well known. Now scientists say they have found out why oil spills kill adult fish. The chemicals in the oil often trigger an irregular heartbeat and cardiac arrest.

A joint study by Stanford University and the US National Atmospheric and Oceanic Administration have discovered that crude oil interferes with fish heart cells. The toxic consequence is a slowed heart rate, reduced cardiac contractility and irregular heartbeats that can lead to cardiac arrest and sudden cardiac death.

The study was published Feb. 14, 2014 in the prestigious international journal Science and unveiled at the convention of the American Association for the Advancement of Science in Chicago.

The study is part of the ongoing Natural Resource Damage Assessment of the April 2010 Deepwater Horizon oil spill in the Gulf of Mexico.

Scientists have known for some time that crude oil is known to be “cardiotoxic” to developing fish. Until now, the mechanisms underlying the harmful effects were unclear.

Exxon Valdez

Studies going back to the Exxon Valdez oil spill in Alaska in 1989 have shown that exposure to crude oil-derived chemicals disrupt cardiac function and impairs development in larval fishes. The studies have described a syndrome of embryonic heart failure, bradycardia (slow heart beat), arrhythmias (irregular heartbeats) and edema in exposed fish embryos.

After the Gulf of Mexico spill, studies began on young fish in the aftermath of the Deepwater Horizon spill. The two science teams wanted to find out how oil specifically impacts heart cells.

Crude oil is a complex mixture of chemicals, some of which are known to be toxic to marine animals.

Past research focused on “polycyclic aromatic hydrocarbons” (PAHs), which can also be found in coal tar, creosote, air pollution and stormwater runoff from land. In the aftermath of an oil spill, the studies show PAHs can persist for many years in marine habitats and cause a variety of adverse environmental effects.

The scientists found that oil interferes with cardiac cell excitability, contraction and relaxation – vital processes for normal beat-to-beat contraction and pacing of the heart.

Low concentrations of crude

The study shows that very low concentrations of crude oil disrupt the specialized ion channel pores – where molecules flow in and out of the heart cells – that control heart rate and contraction in the cardiac muscle cell. This cyclical signalling pathway in cells throughout the heart is what propels blood out of the pump on every beat. The protein components of the signalling pathway are highly conserved in the hearts of most animals, including humans.

The researchers found that oil blocks the potassium channels distributed in heart cell membranes, increasing the time to restart the heart on every beat. This prolongs the normal cardiac action potential, and ultimately slows the heartbeat. The potassium ion channel impacted in the tuna is responsible for restarting the heart muscle cell contraction cycle after every beat, and is highly conserved throughout vertebrates, raising the possibility that animals as diverse as tuna, turtles and dolphins might be affected similarly by crude oil exposure. Oil also resulted in arrhythmias in some ventricular cells.

“The ability of a heart cell to beat depends on its capacity to move essential ions like potassium and calcium into and out of the cells quickly.” said Barbara Block, a professor of marine sciences at Stanford. She said, “We have discovered that crude oil interferes with this vital signalling process essential for our heart cells to function properly.”

Nat Scholz, leader of the Ecotoxicology Program at NOAA’s Northwest Fisheries Science Center in Seattle said.”We’ve known from NOAA research over the past two decades that crude oil is toxic to the developing hearts of fish embryos and larvae, but haven’t understood precisely why.”

Long term problems in fish hearts

He added: “These new findings more clearly define petroleum-derived chemical threats to fish and other species in coastal and ocean habitats, with implications that extend beyond oil spills to other sources of pollution such as land-based urban stormwater runoff.”

The new study also calls attention to a previously under appreciated risk to wildlife and humans, particularly from exposure to cardioactive PAHs that can also exist when there are high levels of air pollution.

“When we see these kinds of acute effects at the cardiac cell level,” Block said, “it is not surprising that chronic exposure to oil from spills such as the Deepwater Horizon can lead to long-term problems in fish hearts.”

The study used captive populations of bluefin and yellowfin tuna at the Tuna Research and Conservation Center, a collaborative facility operated by Stanford and the Monterey Bay Aquarium. That meant the research team was able to directly observe the effects of crude oil samples collected from the Gulf of Mexico on living fish heart cells.

“The protein ion channels we observe in the tuna heart cells are similar to what we would find in any vertebrate heart and provide evidence as to how petroleum products may be negatively impacting cardiac function in a wide variety of animals,” she said. “This raises the possibility that exposure to environmental PAHs in many animals – including humans – could lead to cardiac arrhythmias and bradycardia, or slowing of the heart.”

Tuna spawning

The Deepwater Horizon disaster released over 4 million barrels of crude oil during the peak spawning time for the Atlantic bluefin tuna in the spring of 2010. Electronic tagging and fisheries catch data indicate that Atlantic bluefin spawn in the area where the Deepwater Horizon drilling rig collapsed, raising the possibility that eggs and larvae, which float near the surface waters, were exposed to oil.

The spill occurred in the major spawning ground of the western Atlantic population of bluefin tuna in the Gulf of Mexico. The most recent stock assessment, conducted in 2012, estimated the spawning population of the bluefin tuna to be at only 36 percent of the 1970 baseline population. Additionally, many other pelagic fishes were also likely to have spawned in oiled habitats, including yellowfin tuna, blue marlin and swordfish.

Block and her team bathed isolated cardiac cells from the tuna in low dose crude oil concentrations similar to what fish in early life stages may have encountered in the surface waters where they were spawned after the April 2010 oil spill in the Gulf of Mexico.

They measured the heart cells’ response to record how ions flowed into and out of the heart cells to identify the specific proteins in the excitation-contraction pathway that were affected by crude oil chemical components.

Fabien Brette, a research associate in Block’s lab and lead author on the study said the scientists looked at the function of healthy heart cells in a laboratory dish and then used a microscope to measure how the cells responded when crude oil was introduced.

“The normal sequence and synchronous contraction of the heart requires rapid activation in a coordinated way of the heart cells,” Block said. “Like detectives, we dissected this process using laboratory physiological techniques to ask where oil was impacting this vital mechanism.”