northNoise pollution is one of the most serious but least recognized health threats of our time. Even moderate levels of noise, the kind that surrounds us in any urban setting, increases the risks of cardiovascular disease, cognitive decline, developmental delays, and dementia. Now, scientists are revealing that non-humans also suffer from noise pollution, and that they are much more sensitive than humans.
Perhaps nowhere is this more urgent than in the global oceans. Marine animals see and feel the world through sound, which travels faster and farther underwater than light. Whales, which use sound to find prey and navigate, communicate and mate, are a well-known example. But scientists are now revealing that a wide range of sea creatures are exquisitely sensitive to sound. The range of negative effects caused by marine noise pollution is staggering: developmental delay, hindered reproduction, stunted growth, distorted migration paths.
Extreme noise can kill outright. A single shot from a seismic survey air gun can kill zooplankton, the base of the marine food chain, up to a mile from the blast site. The noise of a motor boat has been found to affect fish embryos. like a study grimly noted: human noise may even be stirring baby fish eggs.
More remarkably, even aquatic plants are very sensitive to sound. Take, for example, the marine seagrass. Like terrestrial forests, seagrasses are a carbon sink that help stabilize our global climate. Shorelines were once abundant in seagrass meadows, which provide food and shelter for marine life, protect against erosion, allow for nutrient cycling, stabilize the seafloor, and filter pollutants. In the Pacific islands, seagrass beds are both pantry and pharmacy, hunting ground and healing space. The world’s oldest known seagrass colony (Posidoniaceae oceanicaoff the Mediterranean coast of Ibiza) is over 100,000 years old, and quite possibly closer to 200,000, which would make it the oldest living organism in the world.
In recent decades, seagrass beds the size of the Amazon have disappeared. Climate change, pollution, ship anchors and dredging, construction of levees and ports, and hypersaline water from desalination plants are likely factors. As researchers from the Polytechnic University of Catalonia have recently discovered, we can now add noise pollution to this list of threats. When scientists exposed a sample of Mediterranean seagrass to the sound of a seismic blast, the seagrasses were severely damaged, as were the symbiotic fungi that help plants absorb nutrients.
Why would plants, without any apparent means of hearing, be sensitive to sound? Marine plants have organelles called amyloplasts, which help plants sense sound vibrations and also store food, orient themselves to gravity, and thus root themselves on the ocean floor. These tiny organelles are analogous to organelles found in octopuses and shrimp, called statocysts, which can sense even tiny sound vibrations in the water. In octopuses, statocysts are grouped in lateral lines on the head and arms. This explains how, even without ears, octopuses can locate prey or predator, especially in low light conditions: they hear with their arms. Similarly, plants hear with their bodies.
Their sensitive hearing is an asset in the dark depths of the ocean, but makes aquatic organisms very vulnerable. Loud sounds underwater can damage or destroy your hearing. These effects occur at sound intensities much lower than those known to harm terrestrial animals. As an analogy: imagine a loud siren passing by. Now imagine that it makes you deaf; disrupts your digestion; and you get so dizzy you can’t walk or tell which way is up. This is the fate of marine organisms in an increasingly noisy ocean: an avalanche of noise that stunts, injures and even kills.
These findings underline the great threat that marine noise pollution poses to our oceans. As offshore operations proliferate, from seabed mining to oil and gas construction and renewable energy, little attention has been paid to noise pollution. While threshold levels of exposure have yet to be determined, it is clear that this emerging science will eventually lead to further restrictions on the permitting and operations of shipping and industrial activities.