The world beneath the waves is a surprisingly loud place. Wind and waves, earthquakes, volcanic eruptions, and the rumbling, grinding and crashing of ice all combine to create something of an underwater cacophony. Numerous species use sound to communicate and navigate across distances from centimeters to hundreds of kilometers.
But over the last several decades, those natural sounds have in many places become overwhelmed by noises from human activities, some of them loud enough to be heard halfway across the ocean. By lowering a hydrophone into the water, says Dr. Christopher Clark of Cornell University, “I can hear seismic activity off the north coast of Brazil; I can hear it 2,000 miles away in the middle of the Atlantic Ocean.”
The seismic activity to which he is referring is the search for oil and gas deposits in the seabed: seismic vessels tow an array of air guns, which release a volume of air under high pressure, creating a sound wave from the expansion and contraction of the released air bubble. I’ve been in a ship in the vicinity of a seismic vessel, and it was a discomfiting experience. Each blast from the air guns resonated off our ship’s hull as if Thor were clanging his hammer against the side.
There has long been concern about the impact of such seismic blasts on wildlife such as marine mammals; indeed, the United States Marine Mammal Protection Act requires the presence of observers on board seismic vessels to ensure no seals or whales are in the region before blasting begins. But a new study in the journal Scientific Reports has shown that they can also cause physiological deformations in shellfish – specifically the larvae of New Zealand scallops.
In the study, four flasks of scallop larvae were exposed to playbacks of seismic pulses, while four flasks of scallops were set aside as controls. Within 24 hours, some of the larvae that were being subjected to noise had begun to show physical malformations. After 66 hours, all the larvae in the control group were developing normally, but 46 percent of the noise-exposed larvae showed abnormal growth, with localized bulges in their soft bodies.
The strong impacts observed in the experiment suggest that abnormalities and growth delays could also occur at lower noise levels in the wild, suggesting routine underwater sounds from oil exploration and construction could affect the survival of wild scallops.
In a press release announcing the study, team leader, Dr Aguilar de Soto of the University of St Andrews and the University of La Laguna said that, “Nobody knew that noise exposure could affect the growth of animals so dramatically so it was a real surprise to discover malformations in these microscopic larvae. What is actually going wrong inside the cells is still a mystery that we need to investigate. Shellfish larvae go through radical body changes as they grow and noise seems to disrupt this natural process.
“Fishermen worldwide complain about reductions in captures following seismic surveys used for oil explorations. Our results suggest that noise could be one factor explaining delayed effects on stocks.”
IMAGE: Close up of the brightly colored mantle and rows of minute eyes of the Coral-boring Scallop (Pedum spondyloideum) in Malaysia. (Corbis)