Small marine animals too may depend on sound for communication

While travelling up and down from the depths of the ocean to the water's surface to feed, the community of fish, shrimp, jellies and squid make a distinct sound which could be serving as a "dinner bell" for these deep-water organisms, new research has found.

It is well-known that dolphins, whales and other marine mammals use sound to communicate underwater, but acoustic communication among smaller animals is more difficult to hear and has not been well studied by scientists.

The new research supports the idea that many ocean-dwelling animals could be communicating by listening to and responding to environmental sounds, said one of the researchers Simone Baumann-Pickering, assistant research biologist at University of California in San Diego, US.

Learning more about how marine animals communicate could shed light on these mysterious environments, she said.

"I think a large array of (marine) animals will show in the next 10 to 20 years that they are capable of producing and receiving sounds," Baumann-Pickering said.

A vast number of animals, including fish, shrimp and squid, live in the ocean's mesopelagic zone -- the waters 660 to 3300 feet below the surface.

Now, Baumann-Pickering and her colleagues have found that there is a distinct sound associated with these daily journeys upwards and downwards.

The team used sensitive acoustic instruments to record the low-frequency hum the animals emit as they move up to the surface to feed at dusk, and back down to deeper waters at dawn.

The communal sound is three to six decibels louder than the background noise of the ocean, making it difficult for the human ear to distinguish, but it could provide scientists with a new way to study these organisms and give them new insights into this ecosystem, she said.

"It is not that loud, it sounds like a buzzing or humming, and that goes on for an hour to two hours, depending on the day," Baumann-Pickering said.

The sound could be a signal for the mesopelagic zone organisms to start migrating up to the surface or back down to the darker depths of the ocean, Baumann-Pickering said.

The findings will be presented on Monday at the 2016 Ocean Sciences Meeting to be held in New Orleans, US from February 21-26.