It was never quiet in the oceans – but humans turned the regulator in a fatal manner: A comprehensive study now shows how intensely the marine background noise has changed and how surprisingly many animal species are threatened by the anthropogenic underwater noise. The researchers are now calling on decision-makers to take steps to counter the increasing cacophony in the oceans. As they show, practicable concepts are already available.
Normally, no noises from the underwater world reach our ears – it therefore appears rather quiet to us. But the opposite is the case: It’s quite loud there, because there are many sources of noise and the water ensures that the sound spreads over a wide area. Water movements, the crunch of ice and other sources of noise form the component of what is known as geophony. In addition, there is biophony: many marine animals produce sounds and also have the appropriate hearing abilities. But a third factor mixes more and more into this natural soundscape: anthrophony. Ship traffic, construction projects and many other man-made sources of noise cause a din underwater in many places.
Experts have long warned that the communication of life in the sea is more and more disrupted by the spreading noise floor. But so far the information seems vague. “The different behaviors that animals exhibit in noise have made it difficult to draw conclusions about the big picture from individual observations and to assess the dangers of noise comprehensively,” says Ilse van Opzeeland from the Alfred Wegener Institute, Helmholtz Center for Polar and marine research in Bremerhaven. She is one of the 25 international scientists who have now provided more clarity in this research area: They have evaluated hundreds of studies relating to underwater noise in order to better assess how humans have changed the marine sound sphere and how bad the noise pollution actually is and which marine animals are particularly affected.
Louder, but also quieter
It is becoming apparent how intensely the noise pollution from human activities in the sea has increased. However, we have not only ensured more, but in some cases also less noise: the decimation of whale populations and the destruction of habitats such as coral reefs have led to a drastic decline in the number of noise-producing animals. It is important to note: “The sound of the ocean is one of the most important sources of information for marine animals,” says co-author Andy Radford of the University of Bristol. The researchers emphasize that the loss of sea ice in the wake of climate change has also drastically changed the natural acoustics of the Arctic marine environment.
However, their focus was primarily on the effects of anthropogenic noise sources. Many thousands of cargo ships and other watercraft are making themselves heard. In addition, there are blasting or pile driving for construction work and the extraction of raw materials, which roar for many kilometers and meanwhile no longer only affect the coastal area. The researchers’ evaluations clearly show how strongly these stresses can influence marine animals in their behavior: They are driven away, their foraging is disturbed or they even lose their hearing. Not only marine mammals such as seals, whales and dolphins are affected by this, because fish, crabs and other invertebrates also communicate or orient themselves using sounds, the researchers emphasize.
Pay more attention to the invisible pollution!
They were also able to make it clear that the pitch of the sea noise lies to a large extent precisely in the areas that are important for these animals. Some sources of interference also make noise over very wide pitch ranges – from very low to very high frequencies. These include, above all, small and large ships, the rattling fishing gear of trawlers, and work on oil and gas platforms, the researchers report. “We have known for a long time that harbor porpoises in the North Sea, for example, flee to wind farms during pile driving,” says van Opzeeland. “The studies we evaluated make it clear, however, that completely different animal species also react to noise – such as cnidarians, which include jellyfish, and even mussels,” says the researcher.
According to the team, marine noise has received little attention in international maritime policy compared to aspects such as warming, ocean acidification or plastic pollution. “Although Europe and individual states have the issue of marine noise on their agenda, there have not yet been any extensive international protection efforts,” says van Opzeeland. With their overview study, the scientists now want to stimulate stronger international cooperation, which should enable effective measures to regulate noise pollution. “Of course, not all sources of noise in the sea, such as the expansion of wind power and merchant shipping, can be completely switched off,” says van Opzeeland. “Nevertheless, the sea noise can be reduced very well through various measures.”
Some of them are already being used successfully and should now be used more widely: In the North and Baltic Seas, for example, bubble veils have been placed around the wind turbine construction sites for some time, which dampen the sound of the pile driving. In the eastern Mediterranean, on the other hand, a speed limit for ships of around two knots reduced noise by around 50 percent. And according to the scientists, the explosions and shots of the air guns when searching for raw materials can be replaced by devices that send their vibrations down from the sea floor. “We also want to give hope with our study. Our study shows how serious the problem is. But also that you can fight the noise primarily through international cooperation, ”concludes van Opzeeland.
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, specialist article: Science, doi: 10.1126 / science.aba4658
Audio: A composition of underwater recordings of fish, mammals,
Articulated animals, ice, water, and man-made noises. (Credit: Jana Winderen 2020, Touch Music / Fairwood Music UK Ltd)