Too much sound can kill squid and octopuses, according to a study to be published in a forthcoming issue of the journal Frontiers in Ecology and the Environment.
Michel André and 11 colleagues found that continued exposure to low frequency sounds in cephalopods (the group that includes cuttlefishes, octopuses and squids) resulted in massive acoustic trauma in the form of damage to their statocyst (a structure that helps to maintain balance and posture).
Previous observations have suggested that high-intensity, low-frequency sounds may kill cephalopods: increased numbers of dead Giant squids (Architeuthis dux) encountered along the west coast of Asturias, Spain in 2001 and 2003 coincided with the proximity of ships in the area using compressed airguns for geophysical prospecting.
When the squid carcasses were examined, all of them displayed lesions in the statocyst. Because these lesions could not be linked to previously known causes of death, the presence of the geophysical prospecting vessels in the area suggested that the squids were killed by exposure to excessively loud sounds.
The authors exposed 87 adult individuals of four cephalopod species: the Shortfin squid (Ilex coindetii), European squid (Loligo vulgaris), Common octopus (Octopus vulgaris), and Common cuttlefish (Sepia officinalis) to short sweeps of relatively low-intensity, low-frequency sound between 50 and 400 hertz. The statocysts were extracted for analysis at various intervals after exposure, ranging from immediately after to 12, 24, 48, 72, and 96 hours after exposure.
The authors found that all four cephalopod species exhibited identical lesions in the statocysts when exposed to the low-frequency sounds.
These lesions start out as damage to the hair cells; the associated nerve fibres underneath these cells also became swollen and showed signs of degeneration. Over time, large holes in the sensory epithelium began to appear as a result of the massive damage to the hair cells, with the appearance of these lesions becoming more pronounced after 12, 24, 48, 72, and 96 hours. The damage in the statocysts confirms that these structures are involved in sound reception and perception.
"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," said lead author Michel André, "but this is the first study indicating a severe impact on invertebrates, an extended group of marine species that are not known to rely on sound for living. It left us with several questions: Is noise pollution capable of impacting the entire web of ocean life? What other effects is noise having on marine life, beyond damage to auditory reception systems? And just how widespread and invasive is sound pollution in the marine environment?"
For more information, see the paper: André, M, M Solé, M Lenoir, M Durfort, C Quero, A Mas, A Lombarte, M van der Schaar, M López-Bejar, M Morell, S Zaugg and L Houégnigan (2011) Low-frequency sounds induce acoustic trauma in cephalopods. Frontiers in Ecology and the Environment, doi:10.1890/100124