After the massive 2010 Deepwater Horizon oil spill, concerns mounted about the quality of oysters, shrimp, and other seafood exposed to the slick in the Gulf of Mexico, but scientists say they've observed some of the worst effects in the tiniest victims: fish eggs.
In an experiment re-creating oil-deluged waters, a new study found exposure to oil caused severe and consistent heart defects in the embryos of some of the Gulf of Mexico’s most valuable species, including Western Atlantic bluefin, yellowfin, and amberjack.
The study prompts worries of reduced fish populations over the next few years as those surviving embryos mature—especially in the case of Western Atlantic bluefin, whose spawning season coincided with the spill and whose numbers hover at historically low levels. There are currently about 40,000 adult Western Atlantic bluefin, according to the most recent estimate available from 2009.
The study was published yesterday, on the 25-year anniversary of the Exxon Valdez oil spill, in the Proceedings of the National Academy of Sciences.
Crude oil “disturbed the heart rate and rhythm of each species we tested in a concentration-dependent manner,” said Dr. John Incardona, National Oceanic and Atmospheric Administration research toxicologist and the study’s lead author. “That means problems increased as oil concentration increased.”
“They have transparent eggs and embryos, which allows us to see the heart when it first starts beating,” said Incardona of the lab-based experiment. “By using digital video microscopy, we can get a lot of early information. It’s comparable to using ultrasound in people.”
BP responded to the study by saying it lacks evidence of population effects on tuna, amberjack, or other species.
“The oil concentrations used in these lab experiments were rarely seen in the Gulf during or after the Deepwater Horizon accident,” spokesperson Jason Ryan said. “In addition, the authors themselves note that it is nearly impossible to determine the early-life impact to these species.”
Scientists were able to monitor heart rate, rhythm, the size of the chamber walls, as well as the body shape and eyes of developing fish embryos. Barbara Block, Ph.D., a study coauthor and professor of biology at Stanford University, says they now have a better understanding of why crude oil is toxic.
“It doesn’t bode well for bluefin or yellowfin embryos floating in oiled habitats,” says Block.
Researchers maintain that severely affected fish with heart failure or deformed jaws, two known defects, likely died after hatching. Surviving fish that suffered only mild effects showed permanent changes in their heart shape that would reduce swimming performance later in life—which can be a major deficit for a fish dodging a harpoon or a bigger fish predator.
“Swimming is everything for these species,” said Incardona.
Shana Miller, a science adviser with The Pew Charitable Trusts, says the study is especially important given the timing of the BP oil spill, which coincided with peak spawning season for Western Atlantic bluefin.
“They only spawn in the Gulf of Mexico and only in the springtime. It’s a spawning hot spot. The oil spill hit at the worst time for that species,” says Miller. “We knew oil was harmful to fish, but we weren’t sure why and how. This study confirmed it and showed exactly why it was harmful to fish: It’s damaging to their hearts.”
A related study published in Science last month found similar effects on the heart development of fish exposed to polycyclic aromatic hydrocarbons—a component of crude oil.
Earlier this month, the Environmental Protection Agency lifted the ban on BP, allowing it to bid on new oil and gas leases, but Miller says the wrangling over funding for restoration projects continues.
“They haven’t done the offshore restoration projects yet,” Miller said. “This study confirming the oil spill had an impact on the species should move that process along. Clearly there was an impact, and BP therefore should be required to be responsible in trying to reverse the impact of the damages of that spill.”