NEW ORLEANS—The Gulf killifish, a hardy little minnow, is a common sight all along the Gulf of Mexico coast. The males, which turn vibrantly yellow and sprout a black beard and speckles this time of year, dart in and out of marsh grass alongside the more drab females. In Louisiana, fishers call the fish by its Cajun name, cocahoe minnow, and rely on it as a feisty baitfish that helps them reel in redfish, flounder, speckled trout, and other game fish.
Since the Deepwater Horizon oil rig explosion five years ago today, biologists have worked to determine the spill’s long-term impact on dolphins, pelicans, sea turtles, and other marine life.
For scientists, the little-known killifish has become an ecological sentinel of sorts, foreshadowing the long-term damage to marine life. “We are using it as our canary in the coal mine,” said Fernando Galvez, a researcher with Louisiana State University’s Department of Biological Sciences. He has examined the fish at the cellular level and found that the toxins left behind by the spill are likely to impact fish growth, reproduction, and health.
These days, it’s hard not to cringe when a killifish dives and roots around in mucky sediment, looking for a meal of tiny mollusks. Five years ago, on April 20, 2010, the Deepwater Horizon oil rig exploded 41 miles off the Louisiana coast. During the 87-day spill, BP’s Macondo well spewed more than 200 million gallons of Louisiana sweet crude oil into the Gulf.
Scientists believe that coastal and seafloor sediment still hold high concentrations of toxins left behind by the oil and the chemicals sprayed to dissolve it.
That’s not good news for the killifish, which doesn’t do well when exposed to the marshy sediment from Louisiana’s Barataria Bay, which was badly polluted by the spill. The fish’s heart rate becomes markedly slower, said Galvez, and he commonly sees hemorrhaging around the tail. The killifish’s skeleton also doesn’t develop normally and has cranial and facial deformities. The angle at which the head and spinal cord meet isn’t right.
“These effects would make it difficult for the fish to survive in a natural environment,” Galvez said. He, like a good number of oil-spill researchers, keeps tanks of killifish in various stages of development in his lab. “Increasingly, it’s an important model fish,” he said.
Even in 2011, the trends seemed obvious to Galvez, who may have been the first person to testify about the Gulf killifish before a congressional committee.
“What our data describe are the early-warning signs that have shown in the past to correlate well with population-level declines as seen with Pacific herring, pink salmon, and the sea otter, in the years that followed the Exxon Valdez oil spill,” he said, noting that population-level effects weren’t seen until several years after the Valdez spill.
A growing number of studies indicate that the impact of the Deepwater Horizon disaster may linger for decades. Recently, researchers examining the seafloor have linked the oil spill to deadened deepwater coral reefs. Waves along the coast also regularly heave tar balls on shore from what scientists are calling a 1,200- square-mile “bathtub ring” of oil particles that the spill left on the sea bottom. Marine biologists assessing Barataria Bay dolphins found them to be in poor health. Studies of a variety of fish have also found problems with heart development, reproduction, and swimming.
LSU researcher Christopher Lee has measured less yolk in killifish eggs after mothers are exposed to low levels of oil. He and other researchers are trying to determine the billion-dollar question: what their findings mean for multiple generations of killifish and for larger populations of creatures affected by the spill.
Rep. John Fleming Jr., R-La., wasn’t buying it. “Cellular-level changes, I don’t know—that all seems a bit of a stretch to most of us in Louisiana,” he said, calling the state’s big issue “a perception problem.”
Yet thanks to DNA sequencing that’s been done for a sister species, killifish researchers are able to be precise, down to genomic-level effects.
It’s tempting to see the resilient killifish as an avatar for coastal residents who choose to stay put despite the spill, a disappearing coastline, and regular hurricanes. “Killifish are really tough fish, and they have to be—they’re living in an estuarine environment that’s extremely unfriendly and unstable,” said Lee.
Louisianans even develop their own minnow-trap recipes, said James Carr, a killifish researcher at Texas Tech University. “The people we worked with would put a hole in cat-food containers, add Vienna sausage, and gumbo crab,” he said. “That’s apparently the magic elixir that is attractive to killifish.”
None of the studies can be completely certain that oil from the BP’s Macondo well caused these effects. BP’s spokespeople inevitably respond to every study by asking whether the results could come from naturally occurring oil leaks from the seabed or whether there were variables that haven’t been considered.
Carr noted that he and his Texas Tech collaborators have carefully examined every single killifish tissue—gonads, thyroid glands, livers, hearts, and gills—and found consistent effects from the spill. “Nothing is 100 percent certain in science,” he said. “And we’re still getting data out. But there’s no question if you look at the genetic evidence that there are effects.”
When Galvez has his eye to the microscope, he can look through to the other side of the egg sac and monitor the embryo's heart, well before it's hatched. There, as he watches, he can see what he believes are likely consequences of the 2010 oil spill, as reflected in the tiny heart of the Gulf Coast's favorite minnow. "I can actually see that the heart is beating much slower," he said. "It's obvious.”
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