The hearts of bluefin tuna, some of the largest fish in the ocean, are vulnerable to spilled crude oil. | Science/AAAS
CHICAGO -- New research on tuna shows why the toxic compounds from an oil spill such as the 2010 Deepwater Horizon disaster are damaging to fish hearts.
The study, published in the 14 February issue of the journal Science, reveals the susceptibility of bluefin and yellowfin tuna hearts -- and possibly the hearts of other vertebrates -- to polyaromatic hydrocarbons, or PAHs, released in crude oil spills.
Tracking studies and fisheries catch data have shown that bluefin tuna spawn near the site of the Deepwater Horizon disaster, and other research suggests that this population is down by as much as 80 percent. "Having an oil spill at the peak time of spawning could interrupt the successful recovery of this population," said study author Barbara Block, a professor of marine sciences at Stanford University, at a news briefing at the AAAS Annual Meeting. "The question is, how were the larvae and the embryos impacted by a spawning habitat that was oiled?"
Scientists have known that PAHs are harmful to the hearts of embryonic and developing fish, causing heart failure and arrhythmias, but they haven't known just why. Most work to date has been done on model fish species, not those exposed to large environmental spills. Now, Block's team has shown that PAHs disrupt the electrical signaling cycle that controls the heartbeat.
The researchers evaluated two tuna species known to have spawned in the Gulf of Mexico during the Deepwater Horizon spill. At a specialized Monterey Bay Aquarium facility devoted to housing and studying live tuna, they studied the physiological effects of four crude oil samples on heart muscle cells from juvenile fish.
They found that crude oil from the Deepwater Horizon spill suppressed the electrical activity of isolated heart muscle cells in two ways, both involving the pores or "channels" in the cell membrane through which potassium and calcium ions flow to create a signal called an action potential. First, the oil blocks potassium channels, which leads to a slowdown of the heartbeat. It also interferes with the release of calcium ions, which weakens heart muscle contraction.
"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," said study co-author Nat Scholz, leader of the Ecotoxicology Program at the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center in Seattle.
Block speculated that these findings might be relevant other species, including humans.
"The potassium channels being impacted by oil in this vertebrate are similar -- 'homologues' -- to channels in humans of the same type, which are already known to be very sensitive to drugs. In fact, every pharmalogical agent put on the market has to be tested in humans in order for us to know that it's safe for us to utilize. If oil was in that lineup, it would not pass the test," she said.