One concern we’ve frequently voiced about ocean noise pollution is the potential for impacts across a wide range of species, up and down the food chain. A new study in Frontiers in Ecology gives yet more reason for serious worry.
A group of Spanish researchers exposed four species of squid, octopus, and cuttlefish to moderate levels of low-frequency, underwater sound for two hours. What they found in all of the animals was massive trauma “not compatible with life.”
Most of the damage occurred within the statocysts, a group of small air sacs around the animals’ head that helps them balance and orient themselves in the water. Over the course of two hours sensitive hair cells were destroyed, nerve fibers swelled and degenerated, sac linings were pocked with holes. At first the captive animals tried to escape; then they froze in their tanks. The damage is analogous to someone shredding your inner ear.
The study’s lead author said that investigators were “shocked by the magnitude of the trauma.” Particularly shocking were the levels of sound involved in their experiment: far lower than those believed to directly injure marine mammals and fish.
The new study would seem to confirm noise as the cause of two bizarre and disturbing mass stranding events from several years ago. In 2001, and again in 2003, unusual numbers of giant squid (Architeuthis dux) – a near-mythic creature that until recently had never been photographed live – washed ashore along the Bay of Biscay, in Spain. Their strandings coincided with high-powered seismic surveying for oil and gas, which produces some of the loudest sounds in the ocean. All of the dead animals showed injury in the statocysts.
Over the last hundred years, humans have radically altered the acoustic environment of the ocean, and low-frequency noise is only getting louder with increases in oil and gas exploration, naval training, shipping, and offshore construction. We’ve only tapped the surface of the impacts that ocean noise is having on marine mammals. This study makes us think again of its consequences for the broader web of ocean life.