The soundscapes of the modern ocean are fundamentally different from those of pre-industrial times. Each and every day — for centuries — human activities have been making Earth's oceans an exponentially noisier place.
The raucous cacophony of vast global fishing fleets, tireless transoceanic shipping and subsea development has become louder and more prevalent. And this is to say nothing of climate change,overfishing, and the near constant stream of chemical pollutants and trash that find their way beneath the waves.
Now, imagine yourself a fish and the ocean your fishbowl: Humans really are the worse neighbors.
In a Review published in the February 5 issue of Science, Carlos Duarte, a researcher at King Abdullah University of Science and Technology and a multidisciplinary team of researchers show how the rapidly changing soundscape of modern oceans impacts marine life worldwide.
By evaluating more than 40 years' worth of published research, the authors found, overwhelmingly, that anthropogenic noise is negatively impacting marine animals, affecting their behavior, physiology and, in some cases, their overall survivability.
According to the authors, changing ocean soundscapes have become the neglected "elephant in the room" of global ocean change and mitigating these impacts is key to achieving a healthier and more sustainable ocean.
"Anthropogenic noise is an invisible global stressor of marine life that should be considered together with climate change, chemical pollution, overfishing and habitat loss in terms of its global reach and effects," said Duarte.
"A healthy ocean requires a healthy soundscape."
Anthrophony — The Not-So-Silent-Killer
Between the snapping chatter of tiny reef shrimp to the plangent songs of lone cetaceans — which reverberate across ocean basins — and the snapping chatter of reef communities, the boundless, deep, dark and cold oceans are full of sound.
Traveling far faster and farther than other sensory cues, sound has become incredibly important in marine environments and many marine animals have evolved a wide range of ways to use it for crucial ecological and biological tasks, such as communication, navigation, foraging and defense. What's more, many sea creatures use sound to recognize important information about their environments. For example, grinding Arctic sea-ice could signal a change in seasons and the rhythmic lashing of waves against rocks could mark a prime hunting or spawning location.
For millions of years, the ocean's natural chorus was performed largely uninterrupted by a vast ensemble of geological (geophony) and biological (biophony) sounds. However, for more than a century, sounds from human activities on the high seas have increasingly added a dissonant third section to the mix — anthrophony, the sounds made by humans and their creations — making modern oceans far noisier than ever before.
Sounds from ship traffic, sonar, military weapon testing and resource exploration and extraction have all become significant sources of sound in the oceans. Vehicles passing over bridges and airplane traffic to and from coastal airports also impart a great deal of noise into marine environments.
One of the loudest sources of sound in the ocean — the seismic air guns used in deep-sea surveying — can be heard between continents and reach noise levels approaching 250 underwater decibels. For context, this is nearly as loud as NASA's Saturn IV rocket — one of the loudest sounds ever recorded.
"Anthropogenic noise is very diverse, in frequency, intensity and patterns over time, and practically occupies the entire sonic space that animals have to share," said Duarte.
According to the authors, human noise can have a myriad of detrimental effects on marine animals and environments. Not only does it elevate stress in individual marine species, impacting crucial needs like feeding and reproduction behaviors, but it can also displace critical community members from habitats, unbalancing the structures that hold together sensitive ecosystems.
What's more, like having a conversation at a busy cocktail party, animals that vocalize to communicate, including whales, need to raise their voices to be heard across the noise. As the noise continues to grow, these animals often become silent, "unable to hear or be heard, waiting for the noise to stop, which, in some cases, may never happen," said Duarte.
But it's not just new noises added — human activities have made some areas of the ocean quieter. Deterioration of habitats like coral reefs and hunting of large marine mammals, including highly vocal whales, has led to drastic declines in the abundance and diversity of sound-producing animals. Environmental changes due to climate warming, such as increased storm activity or rapid ice loss, have also drastically altered the natural acoustics of marine ecosystems.
"New noise, together with the silencing of the soundtrack of healthy habitats, is likely to be adding significant mortality from organisms that exhaust their resources before they can hear the call of their habitats," said Duarte.
Switching Off The Sound
However, compared to other, more persistent global stressors of marine life, addressing anthropogenic noise and reversing the damage it can cause is relatively low hanging fruit. Mitigating anthropogenic noise is easily actionable and, because the effects of noise pollution cease after "switching off" their sources, would yield near immediate benefits in ocean health. What's more, making less noise in the oceans could strengthen the resilience of marine ecosystems already facing a host of other pressures, said Duarte.
"We saw how, under the human lockdowns with COVID-19, as shipping and noise in our ocean decreased by about 20%, marine animals immediately occupied their former habitats," said Duarte. This unusual expansion of animals to what were previously noisy waters bustling with human activity is a testament to the immediacy of the benefits of reducing noise.
According to Duarte, efforts such as regulating noise thresholds in vessels, changing propeller styles to quieter — and more efficient — alternatives, and employing underwater acoustic barriers, such as bubble curtains, during underwater surveying, construction and drilling are feasible ways to mitigate our acoustic impact on the ocean.