Thousands of Humboldt squid died off the coast of Oregon in 2004 and hundreds again in 2008. The culprit was originally considered a shift in deep-sea currents, but a new study pinpoints the physical trauma noise pollution can inflict on cephalopods and raises new concerns over the incidents of squid strandings.
Dolphins and whales and other marine mammals aren't the only sea life vulnerable to noise pollution from human activities.
Earlier indications that squid might be susceptible to noise occurred in 2001 and again in 2003, when giant squid washed up along the shore of Asturias, Spain. After struggling to identify the reason, biologists eventually concluded that the deaths were most likely related to the presence of vessels using seismic air guns for geophysical prospecting of the seabed.
A new study, published in the journal Frontiers in Ecology and the Environment, has found that even low intensity noise can leave cephalopods damaged and likely to wash ashore.
In the study, led by Michel André of the Technical University of Catalonia in Barcelona, biologists exposed 87 individual cephalopods of four species- Loligo vulgaris, Sepia officinalis, Octopus vulgaris and Illex coindeti-to short sweeps of relatively low intensity, low frequency sound between 50 and 400 Hertz (Hz). Then they examined the animals' statocysts – fluid-filled, balloon-like structures that help these invertebrates maintain balance and position in the water. André and his colleagues found that, immediately following exposure to low frequency sound, the cephalopods showed hair cell damage within the statocysts. Over time, nerve fibers became swollen and, eventually, large holes appeared.
"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 could be considerable," said André in a press release to announce the findings.
Noise underwater travels far and fast and the ocean is full of natural sounds, such as snapping shrimp. Consequently, many underwater species have adept hearing that are extremely sensitive to the cocaphanie of noise, from boat engines to sonar, that humans are contributing to this marine symphony.
"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; in other words, this would not be compatible with life," André said.
The discovery raises questions, he continued about just how widespread the impact of noise pollution on marine life might be:
"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?"
IMAGE 1: A cuttlefish, Sepia officinalis, one of four species studied for their response to noise pollution. (Image credit: Corbis)
IMAGE 2: Researchers found that noise pollution could literally blow a hole in structures the cephalopods need to determine their orientation. Photos courtesy Laboratori d'Aplicacions Bioacústiques, Universitat Politènica de Catalunya.