Noise pollution in the ocean is increasingly recognized as harmful to marine mammals, affecting their ability to communicate, find mates, and hunt for food. But what impact does noise have on invertebrates -- a critical segment of the food web? Very few studies have attempted to answer that question. The harder question to answer might be 'How do you measure hearing in ocean invertebrates'? A new study by researchers at Woods Hole Oceanographic Institution and their colleagues examined behavioral responses to sound by cuttlefish, a type of shell-less mollusk related to squid and octopi. The study is the first to identify the acoustic range and minimum sound sensitivity in these animals. Their findings, published in the Journal of Experimental Biology, can help decision makers and environmental managers better understand the impacts of noise in the ocean.

Noise pollution in the ocean is increasingly recognized as harmful to marine mammals, affecting their ability to communicate, find mates, and hunt for food. But what impact does noise have on invertebrates -- a critical segment of the food web?

Very few studies have attempted to answer that question. The harder question to answer might be 'How do you measure hearing in ocean invertebrates'?

A new study by researchers at Woods Hole Oceanographic Institution and their colleagues examined behavioral responses to sound by cuttlefish, a type of shell-less mollusk related to squid and octopi. The study is the first to identify the acoustic range and minimum sound sensitivity in these animals. Their findings, published in the Journal of Experimental Biology, can help decision makers and environmental managers better understand the impacts of noise in the ocean.

'It's hard to study loudness, or the perception of sound, with animals,' said WHOI biologist Aran Mooney. 'Generally, you need to train an animal, such as a chimp or a dolphin, to tell you its perception.'

Some studies have inferred loudness by measuring how fast an animal responds to sound. But, says Mooney, that requires a leap in logic to conclude the animal perceives a sound as louder by measuring how fast the animals runs or swims away. He was interested in a well-designed, controlled study that measured all the right variables to truly map what a cuttlefish hears and its sensitivity to sound.

Mooney and lead author Julia Samson, then a student in Mooney's lab, set about to design a study to test hearing in cuttlefish, one animal at a time.

Their plan relied on previous studies by co-author Roger Hanlon of the Marine Biological Laboratory (MBL) in Woods Hole, who had observed and defined a series of behavioral responses in cuttlefish, such as inking and jetting, mild color change, and twitching. Each response is associated with a perceived level of threat to the animal. For example, inking and jetting is done when cuttlefish predator is close by or they perceive some other threat; mild color change and fin movements demonstrates a reduced level of aversion such as when the animal is startled but not in fear for its life. Twitching is another behavior indicating a very mild response to a stimulus, from which the scientists can determine the sound is perceived but that it requires little response.

Continue reading at Woods Hole Oceanographic Institution.

Cuttlefish image via Shutterstock.