Editorial: 鈥�Squid and octopuses need their peace and quiet鈥�
It鈥檚 not just dolphins and whales that suffer from the noise of shipping, sonar and oil prospecting. Experiments on squid, cuttlefish and octopuses strongly suggest their balancing organs are ruined by submarine noise pollution.
In the experiments, sound immobilised the cephalopods, even though it was quieter than noise near oil and gas rigs, and offshore wind farms. The results seemed permanent.
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鈥淲e were shocked by the magnitude of the trauma,鈥� says Michel Andr茅 of the Technical University of Catalonia in Barcelona, Spain.
The results of the experiments, in which Andr茅鈥檚 team exposed captive cuttlefish, octopuses and squid to low-frequency sound for 2 hours, seem to confirm that damage in nine giant squid which washed up on Spanish beaches in 2001 and 2003 was caused by low-frequency sounds from nearby seismic surveys for oil and gas. Post-mortems of the beached squid had revealed badly damaged statocysts 鈥� the bulbous organ that senses gravity and motion in cephalopods, allowing them to balance and direct where and how fast they swim. Without this organ, cephalopods are practically powerless to move, unable to hunt, and likely to become easy prey themselves.
鈥淎t the time, we couldn鈥檛 prove the cause of the damage,鈥� says Angel Gonz谩lez of the Institute of Marine Investigation in Vigo, Spain 鈥� a member of the team that reported the fate of the giant squid in 2004. 鈥淏ut this new paper confirms for the first time that low-frequency sounds induce acoustic trauma in cephalopods.鈥�
In their experiments, Andr茅 and his colleagues also found extensive damage to statocysts (Frontiers in Ecology and the Environment, ). Animals were exposed to noise ranging from 50 to 400 hertz, an 鈥渁coustic smog鈥� similar to that created by oil and gas exploration, and shipping.
Post-mortems showed that the linings of statocysts in animals not exposed to sound retained their fine hairs, which sway as the animals move through water and are essential to their sense of balance and orientation.
Exposed animals had lost huge patches of hairs, leaving holes in the cell membranes. The insides of the cells had pushed their way through the holes, and mitochondria 鈥� the power plants of cells 鈥� were greatly damaged.
The damage got worse with time, and continued long after the sound had been turned off.
Andr茅鈥檚 team also observed the behaviour of the animals during and after exposure. The first reaction was to try to escape, says Andr茅, but they soon stopped moving. The cuttlefish settled on the bed of the tank and the other cephalopods simply floated at a constant depth. It is not known how the animals would respond in the wild, says Andr茅, but it is likely that sound from drilling or offshore wind farms would prevent them from escaping.
The team say the results suggest that the sounds of human activities affect the entire web of ocean life, and reinforce the need for regulation of marine noise pollution. They now want to find out how the damage happens, and, crucially, what level of sound is tolerable to the animals.