Not only can squids and octopuses sense sound, but as it turns out, these and other so-called cephalopods might be harmed by growing noise pollution in our oceans—from sources such as offshore drilling, ship motors, sonar use and pile driving.
"We know that noise pollution in the oceans has a significant impact on dolphins and whales because of the vital use of acoustic information of these species," Michel André, of the Technical University of Catalonia's Laboratory of Applied Bioacoustics and one of the authors on the new study, said in a prepared statement. But research had yet to probe the extent to which human-made noise might be affecting other pelagic species.
Cephalopods, prevalent invertebrates in Earth's seas, might actually be suffering life-threatening injury from loud intrusions into their marine habitats.
For instance, mass strandings of giant squid (Architeuthis dux) in 2001 and 2003 off the coast of Spain occurred while ships were in the area prospecting with compressed air guns, André and his colleagues noted in their paper, published online April 11 in Frontiers in Ecology and the Environment.
"This is the first study indicating a severe impact on invertebrates, an extended group of marine species," André said.
To examine the issue more closely in the lab, André and his team exposed common octopuses (Octopus vulgaris), European squid (Loligo vulgaris), common cuttlefish (Sepia officinalis) and squid in the genius Illex to low-intensity, low-range sound (50 to 400 hertz) in short sweeps over two hours. After a period of 12 hours to four days, the researchers killed some of the subjects and examined them under light microscopes, scanning electron microscopes and transmission electron microscopes.
They found some rather striking damage. In the statocyst, the compartment responsible for spatial orientation and hearing, the researchers found large lesions, missing or damaged hairs and ruptured plasma membranes.
"If the relatively low intensity, short exposure used in our study can cause such severe acoustic trauma, then the impact of continuous, high intensity noise pollution in the oceans would be considerable," André said. "For example, we can predict that, since the statocyst is responsible for balance and spatial orientation, noise-induced damage to this structure would likely affect the cephalopod's ability to hunt, evade predators and even reproduce."
Even in fish and marine mammals that have been studied more closely, low- and mid-intensity noise has not been shown to cause such severe damage.
The findings "indicate that the deleterious effects of marine noise pollution go well beyond those observed in whales and dolphins," the researchers noted. And for cephalopods, the injury might "not be compatible with life," André noted.
If increased low-frequency noise pollution has the same impact on octopuses and their brethren in the open ocean, the resulting changes in cephalopod health and populations could have a substantial impact on entire ocean food webs—not just calamari supplies.
Image of common squid courtesy of Wikimedia Commons/Hans Hillewaert