Do Noises affect Life on the sea floor?

Countless marine animals rely on noise to survive, for e.g: to detect predators, for echolocation, and as a means of communication with the co-species. In recent decades, the sounds caused by human activities are affecting marine species, especially the sounds emitted by cargo ships, loud explosions, and seismic surveys.

A study by the Alfred-Wegener institute showcases that the sounds may impact the functioning of the ocean floor. Invertebrates such as mussels, crustaceans, and worms(referred to as ecosystem engineers) frequently sediment the area they live in by burrowing, feeding, aerating, and fertilizing with their excreta. These activities play a vital role in the nutrient cycle in the ocean, allowing more carbon from the dead organic material to be stored on the sea floor and nutrients to be recycled. 

Sound can travel long distances underwater, sometimes hundreds and even thousands of kilometers whereas light can travel only tens of meters. 

A research team from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven has now shown in a study published in the journal Environmental Pollution that these sounds stress not only marine mammals but also invertebrates.

"We investigated how crustaceans, mussels, and worms on the seafloor respond to low-frequency noise and how frequently and intensively they are able to transform and break down sediment during noise exposure," says Sheng V. Wang from the Department of Biosciences. Low-frequency noise is sound with frequencies between 10 and 500 hertz and in water, these sounds can be transmitted over many kilometers.

Despite the constant rise in noise pollution caused by human activities, little is known about how noise affects invertebrates on the seafloor. To help fill this research gap, AWI scientists studied in the laboratory how amphipods, lugworms, and Baltic clams are affected by sound waves with frequencies between 100 and 200 hertz using so-called "noise eggs."

"After six days, we could clearly see that all three species responded to the noise even though they belong to very different groups of animals that lack actual organs for hearing," says AWI ecologist Dr. Jan Beermann.

For example, the amphipods burrowed significantly less and not as deep into the sediment. No clear response has been observed for the lugworms but they seemed to behave more inconsistently. Potential stress responses were noted for the Baltic clams which need to be further investigated. The researchers stress the urgent need for field research, however, as experimental setups under laboratory conditions do not encompass the full complexity of nature.

That additional man-made noise could inhibit seafloor invertebrates from cultivating and restructuring sediments and may affect important functions of marine ecosystems, from nutrient supply to food availability for those higher up in the food web such as fish. "Things could get even 'noisier' on the seafloor due to human activities," Beermann says.

"We are just beginning to understand how exactly noise processes work here. Understanding this, however, is crucial for the sustainable use of our oceans," which is why the team plans to conduct further research in this area.