Most years, Spaniards encounter just one giant squid as long as a city bus along their northern shores—a fisherman might haul one up from the depths accidentally, or beachgoers might stumble across a carcass stranded on a beach. So it was surprising in 2001 when five squid littered the beaches over a 2-month period and in 2003 when four washed up or were found floating at sea near death in a single month.
At the time of the strandings, ships offshore were exploring for oil and gas with air guns, which produce high-intensity, low-frequency sounds. Some researchers suspected that the loud noises were harming the squid, just as they are known to harm marine mammals. A new study supports that hunch, reporting massive damage to the sound-detecting structures of squid and other cephalopods that were exposed to loud noises.
In recent years, scientists have gathered evidence that sonar and other humanmade noises may hurt everything from whales to crustaceans. But they didn't know whether this audio pollution could perturb cephalopods—the animal group that includes cuttlefish, squid, and octopuses—because researchers have only recently demonstrated their ability to hear.
To find out, a team led by marine bioacoustician Michel André of the Technical University of Catalonia in Spain brought 87 wild cephalopods back to laboratory aquariums. For 2 hours, the researchers blared low-frequency sounds that were between 157 and 175 decibels at the animals. For comparison, a supertanker's engine noise might hit 190 decibels in the water 1 meter away from the ship. At intervals up to 96 hours after the sound barrage, the researchers killed the animals and preserved their statocysts—the sound-detecting structures behind their eyes—for microscopic analysis. For controls, the researchers killed and collected the statocysts of 100 wild cephalopods immediately after they were captured.
All of the animals exposed to noise, but none of the controls, had seriously damaged statocysts, with crumpled or displaced sensory hair cells, swollen nerves, and in the worst cases, large lesions, the researchers report online today in Frontiers in Ecology and the Environment. And more damage had developed in animals that were killed long after the noise exposure. "We were expecting that these [noise] levels could produce some lesions but not this massive acoustic trauma," André says. Animals exposed to such sounds at sea, he says, would lose their capacity to orient themselves in the water and would probably stop feeding and swimming, ultimately dying or succumbing to predators.
"If they are correct, it's a paradigm shift. It means that we have a much bigger impact on squid than we thought we had," says Peter Madsen, a sensory physiologist at Aarhus University in Denmark who was co-author of a 2010 study confirming that squid can detect sound. That said, Madsen expresses skepticism about the results on several fronts. For one, the paper presents little quantitative data to support its assertions. For another, the control animals weren't held in an aquarium before they were killed, like the experimental animals were. That leaves open the possibility that captivity, not noise, somehow injured the experimental animals, or that capture injured all of them, with the damage developing too slowly to be detected in the controls, Madsen says.
The new paper is "a good first step" in determining whether humanmade ocean noise harms cephalopods, adds T. Aran Mooney, a marine biologist at Woods Hole Oceanographic Institution in Massachusetts who led Madsen's 2010 study. But he questions how the researchers measured the animals' exposure to noise. "If the National Marine Fisheries Service wanted to make a regulation based on this paper, they wouldn't be able to do it," he says. Still, Mooney says, that doesn't detract from the clear damage that André and colleagues demonstrated. "If that holds true, then that's a pretty astounding thing," he says, because it means that the ocean's teeming millions of cephalopods are likely to be susceptible to humanmade noise in the ocean.