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Latest Research Finds Serious Heart Troubles When Oil and Young Tuna Mix

This story was first published on March 26, 2014. It was updated April 9, 2015 to reflect additional research.

Atlantic bluefin tuna prepares to eat a smaller fish.

Atlantic bluefin tuna are a very ecologically and economically valuable species. However, populations in the Gulf of Mexico are at historically low levels. (Copyright: Gilbert Van Ryckevorsel/TAG A Giant)

In May of 2010, when the Deepwater Horizon rig was drilling for oil in the open waters of the Gulf of Mexico, schools of tuna and other large fish would have been moving into the northern Gulf. This is where, each spring and summer, they lay delicate, transparent eggs that float and hatch near the ocean surface. After the oil well suffered a catastrophic blowout and released 3.19 million barrels of oil into the Gulf, these fish eggs may have been exposed to the huge slicks of oil floating up through the same warm waters.

An international team of researchers from NOAA, Stanford University, the University of Miami, and Australia recently published a study in the journal Proceedings of the National Academy of Sciences exploring what happens when tuna mix with oil early in life.

“What we’re interested in is how the Deepwater Horizon accident in the Gulf of Mexico would have impacted open-ocean fishes that spawn in this region, such as tunas, marlins, and swordfishes,” said Stanford University scientist Barbara Block.

This study is part of ongoing research to determine how the waters, lands, and life of the Gulf of Mexico were harmed by the Deepwater Horizon oil spill and response. It also builds on decades of research examining the impacts of crude oil on fish, which began after the 1989 Exxon Valdez oil spill in Alaska. Based on those studies, NOAA and the rest of the research team knew that crude oil—including oil from the Deepwater Horizon oil spill (Incardona et al. 2013)—was toxic to young fish and taught them to look carefully at their developing hearts.

“One of the most important findings was the discovery that the developing fish heart is very sensitive to certain chemicals derived from crude oil,” said Nat Scholz of NOAA’s Northwest Fisheries Science Center.

This is why in this latest study they examined oil’s impacts on young bluefin tuna, yellowfin tuna, and amberjack, all large fish that hunt at the top of the food chain and reproduce in the warm waters of the open ocean. The researchers exposed fertilized fish eggs to small droplets of crude oil collected from the surface and the wellhead from the Deepwater Horizon spill, using concentrations comparable to those during the spill. Next, they put the transparent eggs and young fish under the microscope to observe the oil’s impacts at different stages of development. Using a technology similar to doing ultrasounds on humans, the researchers were able create a digital record of the fishes’ beating hearts.

All three species of fish showed dramatic effects from the oil, regardless of how weathered (broken down) it was. Severely malformed and malfunctioning hearts was the most severe impact. Depending on the oil concentration, the developing fish had slow and irregular heartbeats and excess fluid around the heart. Other serious effects, including spine, eye, and jaw deformities, were a result of this heart failure. (Incardona et al. 2014 [PDF])

Top: A normal young yellowfin tuna. Bottom: A deformed yellowfin tuna exposed to oil during development.

A normal yellowfin tuna larva not long after hatching (top), and a larva exposed to Deepwater Horizon crude oil as it developed in the egg (bottom). The oil-exposed larva shows a suite of abnormalities including excess fluid building up around the heart due to heart failure and poor growth of fins and eyes. (NOAA)

“Crude oil shuts down key cellular processes in fish heart cells that regulate beat-to-beat function,” noted Block, referencing another study by this team, (Brette et al. 2014).

As the oil concentration, particularly the levels of polycyclic aromatic hydrocarbons (PAHs), went up, so did the severity of the effects on the fish. Severely affected fish with heart defects are unlikely to survive. Others looked normal on the outside but had underlying issues like irregular heartbeats. This could mean that while some fish survived directly swimming through oil, heart conditions could follow them through life, impairing their (very important) swimming ability and perhaps leading to an earlier-than-natural death.

“The heart is one of the first organs to appear, and it starts beating before it’s completely built,” said NOAA Fisheries biologist John Incardona. “Anything that alters heart rhythm during embryonic development will likely impact the final shape of the heart and the ability of the adult fish to survive in the wild.”

Even at low levels, oil can have severe effects on young fish, not only in the short-term but throughout the course of their lives. This is why the research team, composed of scientists from NOAA, Stanford University, and the University of Miami, is studying fish exposed to low levels of crude oil as embryos that subsequently grow into juveniles and adults in clean water. Initial research has shown that subtle disruptions of the embryonic heartbeat can produce permanent changes in heart shape that negatively affect swimming performance and other behaviors critical for fish survival. The team has shown similar underlying effects on juvenile mahi mahi (Mager et al. 2014), and studies are ongoing using zebrafish.

These subtle but serious impacts are a lesson still obvious in the recovery of marine animals and habitats still happening 25 years after the Exxon Valdez oil spill.

Find the most up-to-date summary of NOAA-funded research on crude oil’s potential effects on fish in the Gulf Mexico.


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How Do You Picture Science?

Explaining the environmental ramifications of the Deepwater Horizon/BP oil spill [leaves this blog] in the Gulf of Mexico is no easy task. Visualizing those impacts in an easy-to-understand way? Maybe even harder.

Last year NOAA scientists Mary Baker and Debbie Payton needed to figure out how to do just that, and as a communications coordinator for NOAA’s Office of Response and Restoration (OR&R), it was my job to make it happen. Although I had yet to work with her, I thought of Kate Sweeney, a medical and scientific illustrator for UWCreative [leaves this blog], out of the University of Washington (Seattle), whose specialty is creating accessible and understandable illustrations that depict complex scientific processes.

After the initial spill in the Gulf, oil moved through the water column in a variety of ways, and the potential for it to move into the sediments at the bottom included several possible scenarios. The challenge for this graphic was to clearly describe the different ways the oil could move into the sediment layer at the ocean floor. Using mapping data provided by OR&R and discussing the concepts with NOAA scientists and myself, Kate developed a single, striking graphic illustration that clearly encompassed all the possibilities. As a result, we were able to use the illustration extensively to inform the public about the spill.

Potential Pathways of Oil

Illustration showing the potential pathways of spilled oil following the 2010 Deepwater Horizon/BP incident in the Gulf of Mexico. Click to view larger image. Credit: NOAA/Kate Sweeney.

Kate compares the process of creating complex scientific images to telling a story, and she has seen demand for her illustrations grow as the expectation for high-quality visuals has increased.

According to Kate, a key component to this process is working collaboratively with the scientists. When we first sat down with her at our office, she created a rough sketch in the first hour that we were able to comment on. With that initial feedback, she returned to her office and developed the first electronic draft. She didn’t hesitate to do several rounds of drafts back and forth, using discussion along with trial and error to get it right.

Kate recently completed another marine illustration for OR&R, “Conceptual Model of Arctic Oil Exposure and Injuries,” that shows natural resources at risk and the potential impacts of an oil spill in the Arctic.

Oil impacts on Arctic food webs

The illustration shows potential oil spill impacts to wildlife and habitats in the Arctic sea. Click for larger view. Credit: NOAA/Kate Sweeney, Illustration.

As sea ice recedes in the Arctic, shipping routes will open, increasing vessel traffic and increasing the likelihood of spills. Increasing pressure for more oil exploration in the region also highlights the need to be prepared in the event of a spill during offshore drilling. This diagram in particular is useful in discussions with the public, industry, and other trustee agencies to reach a common understanding of which resources are most at risk, and what information on those resources is needed now as baseline data we can use for comparison and for planning how to respond in case of a spill.

Kate says that her biggest challenge as a scientific illustrator is gaining enough of a fundamental understanding of the subject matter. Meeting that challenge, however, and executing the drawing successfully is what she enjoys most about her job.

Contact Kate Sweeney at kateswe@u.washington.edu.

Example illustration of repair of a herniated diaphragm

Example of the artist’s recent work for the University of Washington: Repair of Herniated Diaphragm, prepared for JD Godwin, MD, Department of Radiology. A: Front cutaway view of herniated diaphragm B: Plication sutures are placed in the diaphragm C: Top view of sutures before they are drawn tight D: Sutures are drawn tight to reduce the bulge in the diaphragm. Credit: Kate Sweeney.

“To create the images for this surgical procedure, I met with both the radiologist and the surgeon who performs this repair, and we discussed the anatomy and subsequent repair. Over a series of sketches, we developed and refined the views and details of the narrative.”–Kate Sweeney