Some four or five million barrels of oil released during the Deepwater Horizon disaster reached the open water of the Gulf of Mexico in April of 2010. Researchers now show that the spill may have caused fatal heart defects fish.
Several species of large predatory fish, such as tuna, spawn in the northern Gulf during the spring and summer months. They produce delicate embryos that float near the surface of the water, mixing with plankton. When crude oil from the damaged wellhead rose from the seafloor, it formed large slicks on the surface... putting the buoyant embryos in harm’s way.
In particular, the oil exposed developing embryos and larvae to toxic polycyclic aromatic hydrocarbons (PAHs), which can also be found in coal tar, air pollution, and storm water runoff. In previous lab experiments using muscles cells that have been isolated from the hearts of two tuna species, scientists found that crude oil disrupts “excitation-contraction coupling,” vital processes for normal beat-to-beat contraction and pacing of the heart. Atlantic bluefin tuna, which can grow up to 12 feet long and weigh 1,400 pounds, are already some of the most threatened fish. And petroleum seems to act like a pharmaceutical drug to block their key cardiac processes.
In this new work, the researchers extend the findings to the whole organism. A team led by John Incardona of the National Oceanic and Atmospheric Administration (NOAA) exposed live embryos of bluefin tuna, yellowfin tuna, and amberjack to oil samples collected from the damaged riser pipe and surface skimmers.
They found that each species developed consistent cardiac defects including: slow and irregular heartbeats, uncoordinated rhythm, circulatory disruption, and fluid accumulation around the heart. Other morphological abnormalities include deformed jaws and poor growth of fins and eyes. “Larvae exposed to high levels were dead within a week,” Incardona explains.
In the wild, they likely died soon after hatching, and those suffering only mild effects couldn’t swim as well. And unfortunately, “swimming is everything for these species,” Incardona adds. But they can’t say much about their survival in the wild for sure because tuna take eight years to mature -- the point at which they can be commercially caught. Since only four years have passed since the spill, the fish that were embryos, larvae or juveniles at the time of the spill haven’t reached adulthood and can’t be caught.
Additionally, these physiological defects occurred at low PAH concentrations (about one to 15 parts per billion total PAHs). In fact, these levels were much lower than in many of the surface water samples collected during the spill -- suggesting that the loss of pelagic fish larvae due to cardiac defects was pretty widespread as a consequence of the spill. The northern gulf is also a critical spawning area for swordfish, marlin, sailfish, mahi-mahi, and mackerel.
The new work adds to a growing list of fish that are affected by crude oil. “This fits the pattern,” Incardona says in a press release. “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.” The Environmental Protection Agency recently lifted a ban on the BP.
The work was published in Proceedings of the National Academy of Sciences this week.
Image courtesy of John Incardona