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 show that their balancing organs are so badly damaged by sound similar to submarine noise pollution that they become practically immobile. The consequences seem permanent.
鈥淔or the first time we are seeing the effects of noise pollution on species that apparently have no use for sound,鈥� says of the Technical University of Catalonia in Barcelona, Spain. 鈥淲e were shocked by the magnitude of the trauma,鈥� he says.
The results of the experiments, in which 础苍诲谤茅鈥檚 team exposed captive cuttlefish, octopuses and squid to low-frequency sound for 2聽hours, seem to confirm that 鈥渆ar鈥� damage in nine giant squid that unexpectedly washed up on Spanish beaches in 2001 and 2003 was caused by low-frequency sounds from nearby seismic surveys for oil and gas.
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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�
Stuck in the middle
In their recent experiments, 础苍诲谤茅 and his colleagues were astonished by extensive damage to the statocyst, a bulbous organ in the head of cephalopods that senses gravity and motion, enabling them to balance in the water and direct where and how fast they swim. Without this organ, cephalopods are practically powerless to move, are unable to hunt, and will become easy prey themselves.
Squid, octopuses and cuttlefish were exposed to sweeps of low-frequency noise ranging from 50 to 400聽hertz 鈥� an 鈥渁coustic smog鈥� similar to that created by .
Post-mortems showed that the linings of statocysts from cephalopods not exposed to sound retained the fine hairs that sway as the animals move through water, and are essential to the animals鈥� balance and orientation.
Statocysts from the exposed animals, by contrast, had lost huge patches of hair, leaving holes in the membranes of the organ鈥檚 cells. The insides of the cells had pushed their way through the holes, and mitochondria 鈥� the power plants of cells 鈥� had suffered extensive damage.
By killing and examining the animals at intervals up to four days after the single sound exposure, the team showed that the damage got worse with time, long after the sound had been turned off.
Flight and freeze
础苍诲谤茅鈥檚 team also observed the behaviour of the animals during and after exposure. Their first reaction was to try to escape, says 础苍诲谤茅, but they soon stopped moving. The cuttlefish settled on the bed of the tank and the other cephalopods simply floated at a constant depth.
The team say the unexpected results could mean that human noise affects the entire web of ocean life. They reinforce the need for regulations to limit noise pollution from marine activities, says 础苍诲谤茅.
His team is planning experiments to determine how the damage happens, and, crucially, what levels of sound would be tolerable to the animals.
Journal reference: , DOI: 10.1890/100124
