SOURCE: New York Times
DATE: February 4, 2021
SNIP: Although clown fish are conceived on coral reefs, they spend the first part of their lives as larvae drifting in the open ocean. The fish are not yet orange, striped or even capable of swimming. They are still plankton, a term that comes from the Greek word for “wanderer,” and wander they do, drifting at the mercy of the currents in an oceanic rumspringa.
When the baby clown fish grow big enough to swim against the tide, they high-tail it home. The fish can’t see the reef, but they can hear its snapping, grunting, gurgling, popping and croaking. These noises make up the soundscape of a healthy reef, and larval fish rely on these soundscapes to find their way back to the reefs, where they will spend the rest of their lives — that is, if they can hear them.
But humans — and their ships, seismic surveys, air guns, pile drivers, dynamite fishing, drilling platforms, speedboats and even surfing — have made the ocean an unbearably noisy place for marine life, according to a sweeping review of the prevalence and intensity of the impacts of anthropogenic ocean noise published on Thursday in the journal Science. The paper, a collaboration among 25 authors from across the globe and various fields of marine acoustics, is the largest synthesis of evidence on the effects of oceanic noise pollution.
Anthropogenic noise often drowns out the natural soundscapes, putting marine life under immense stress. In the case of baby clown fish, the noise can even doom them to wander the seas without direction, unable to find their way home.
In the ocean, visual cues disappear after tens of yards, and chemical cues dissipate after hundreds of yards. But sound can travel thousands of miles and link animals across oceanic basins and in darkness. As a result, many marine species are impeccably adapted to detect and communicate with sound. Dolphins call one another by unique names. Toadfish hum. Bearded seals trill. Whales sing.
The new study maps out how underwater noise affects countless groups of marine life, including zooplankton and jellyfish.
Marine life can adapt to noise pollution by swimming, crawling or oozing away from it, which means some animals are more successful than others. Whales can learn to skirt busy shipping lanes and fish can dodge the thrum of an approaching fishing vessel, but benthic creatures like slow-moving sea cucumbers have little recourse.
If the noise settles in more permanently, some animals simply leave for good. When acoustic harassment devices were installed to deter seals from preying on salmon farms in the Broughton Archipelago in British Columbia, killer whale populations declined significantly until the devices were removed, according to a 2002 study.
These forced evacuations reduce population sizes as more animals give up territory and compete for the same pools of resources. And certain species that are bound to limited biogeographic ranges, such as the endangered Maui dolphin, have nowhere else to go.
Even temporary sounds can cause chronic hearing damage in the sea creatures unlucky enough to be caught in the acoustic wake. Both fish and marine mammals have hair cells, sensory receptors for hearing. Fish can regrow these cells, but marine mammals probably cannot.
A healthy ocean is not a silent ocean — hail crackling into white-crested waves, glaciers thudding into water, gases burbling from hydrothermal vents, and countless creatures chittering, rasping and singing are all signs of a normal environment. One of the 20 authors on the paper is the multimedia artist Jana Winderen, who created a six-minute audio track that shifts from a healthy ocean — the calls of bearded seals, snapping crustaceans and rain — to a disturbed ocean, with motorboats and pile driving.
When warships and other anthropogenic noises cease, sea grass meadows have a soundscape entirely their own. In the daytime, the photosynthesizing meadows generate tiny bubbles of oxygen that wobble up the water column, growing until they burst. All together, the bubble blasts make a scintillating sound like many little bells, beckoning larval fish to come home.