Whales and dolphins aren’t the only marine creatures bothered by the increasing amount of undersea noise. The first study to detail the physical toll of low-frequency noise on cephalopods has revealed a surprising amount of trauma, according to a study published today in the journal Frontiers in Ecology and Environment.
In four separate species, noise exposure resulted in significant permanent damage in the statocyst, the fluid-filled structure in a cephalopod’s head responsible for helping the animal determine its position and maintain balance. Hair cells and nerve fibres in the statocyst were missing or damaged within 12 hours of noise exposure. And, in the worst cases, large holes were present immediately in the sensory epithelium of the statocyst—and became more pronounced 96 hours after noise exposure. The noise impact was acute and immediate, yet worsened over time.
“We expected some lesions after noise exposure but not the level of trauma that we found,” says Michel André, a bioacoustics specialist at the Technical University of Catalonia in Barcelona, Spain. “What we found was typical of what you might find in mammals after violent, high intensity sound exposure,” he adds.
Low frequencies, perceived as tones with a low pitch, can be more intense at higher volume. But the surprise is that low-frequency, low-volume noises—administered to the cephalopods as a pitch sweep from 50 to 400 Hz at the volume equivalent of a balloon pop (157 decibels)—could cause such extensive damage. By comparison, the 88 keys on a piano span the frequency range from 27.5 Hz to 4186 Hz; Middle C, for music aficionados, is roughly 262 Hz.
In the ocean, such low-frequency sounds are in the same range as those produced by shipping, oil prospecting and extraction operations, and windmills—all ongoing uses of the ocean, explains André.
And, according to a US Marine Mammal Commission’s 2007 report these types of underwater noises will only increase over time.
André and colleagues don’t yet know why such extensive damage occurred in cephalopods. Going forward, they plan to determine the threshold for damage and test whether cephalopods are more sensitive to particle motion, acoustic pressure, or both.
This study adds to accumulating evidence that suggests that cephalopods are sensitive to low-frequency sounds. In fact, the findings may help explain strandings of giant squid (Architeuthis dux) with damaged statocysts in the fall of both 2001 and 2003—time periods that coincided with the nearby vessels using compressed airguns, which produce high intensity, low-frequency (~100 Hz) sound waves, for geophysical prospecting.
Until now, most studies of noise on marine organisms have focused on species that rely on sound to navigate, communicate and hunt such as dolphins and whales. “To see that low frequency noise exposure affects animals not specifically using sound to survive means that noise may be affecting the entire food chain,” says Andre.
Posted on behalf of Virginia Gewin
Photo: Sepia officinalis, one of the cephalopods used in the study.
Credit: Laboratori d’Aplicacions Bioacústiques, Universitat Politènica de Catalunya