Is underwater construction noise leaving scallops defenseless?
Sea scallops expend a lot of energy reacting to noisy pile drivers
Estimated reading time: 4 minutes
Sea scallops are relatively simple animals, at least when you consider their basic morphological blueprint. There’s an upper and lower shell, or “valve,” connected by a small hinge, with an adductor muscle inside acting as the open-and-close mechanism.
Researchers have long understood that a scallop’s valve angle, or the degree to which its shell opens and closes, directly affects its biological functions. It modulates how much water flows in and out of the body cavity, which is tied to feeding and respiration. It also controls what a scallop can see with its 200 or so beady blue eyes.
What hasn’t been well understood, however, is the amount of energy scallops use when they close their valves in response to underwater noise. And that may be important. According to research conducted at the Sensor Ecology and Bioacoustics Lab at WHOI, sea scallops do a lot of clamming up when subjected to the loud underwater banging of pile drivers, machinery that offshore wind developers use to hammer turbine support tubes into the seabed. If the animals expend a lot of their energy doing that, the researchers suggest, they may not have enough left in the tank to respond to real marine threats.
“Scallops need as much energy as possible to avoid predators,” said WHOI associate scientist Aran Mooney, who studies the impacts of underwater noise on marine life. “If reacting to underwater sound cuts into their overall energy budget, their ability to defend themselves may be compromised.”
Sea stars are one of the more common predators sea scallops need to worry about. The brainless and bloodless invertebrates prey on scallops by prying open their shells using rows of suction disks on their underside, and then injecting their stomachs (through their mouths, no less) into the shell opening to devour them. It’s not a particularly pretty sight, nor is it an uncommon one given that sea stars outnumber scallops by a ratio of two-to-one, according to estimates.
The above video shows how sea scallops react to the sound of piledriving underwater. (Video courtesy of Seth Cones, © Woods Hole Oceanographic Institution)
Scallops can, and do, escape from predators; they’re one of the few bivalves that swim. But, like snails, oysters, and other close relatives, their physical fitness level is akin to a Wi-Fi signal in an elevator—it’s barely there. In fact, just a few seconds of swimming leaves them metabolically compromised for tens of minutes, said Seth Cones, an MIT-WHOI Joint Program PhD student in the Mooney Lab.
“To swim away from predators, a scallop needs to apply enough adductor muscle force to pressurize the water inside its body cavity and jet propel through the water column,” said Cones. “At the same time, it has to work against the opposing force of a ligament attached to the shell’s hinge.”
Opening and closing its shell repetitively over time, Cones and his colleagues speculate, could zap a scallop’s energy and leave it more defenseless. Other species like squid, which are also affected by pile driving noise, tend to get used to the clanging after a while and stop reacting. Sea scallops, however, don’t seem to tune the equipment out.
Former WHOI postdoctoral investigator Youenn Jezequel transports a handful of sea scallops down to a submerged experimental cage in Woods Hole, Mass. (Photo courtesy of Seth Cones, © Woods Hole Oceanographic Institution)
Cones, along with Youenn Jezequel, a former postdoctoral investigator in the Mooney lab, discovered this during field experiments in 2021 in Woods Hole, Mass. where they submerged cages of dozens of sea scallops near an underwater construction site. They mounted magnetometers to the top shells of the scallops and glued magnets onto the bottoms, allowing them to measure valve angles via changes in the magnetic field during pile driving activity. From this, they determined that the scallops clenched their valves with each hammer strike—in human jaw-clenching-like fashion—and continued to do so until piledriving activity stopped.
Now, Cones and his team are working on a new study aimed at quantifying the energetic output associated with scallop shell closures to better understand how much fatigue underwater piledriving noise actually causes, and what the potential energy costs mean for predator-prey interactions. Ultimately, the researchers hope that the data will help inform potential sound mitigation strategies that the offshore wind industry can consider during construction.
“So far, we’ve been able to show in our studies that the scallops had fewer reactions to vibratory hammering techniques than they had to impact hammers,” said Cones. “So that could be one way to try to reduce impacts.”
And if developers must use impact hammering, perhaps there is a way for them to ease into it, so it is not such a novel and startling stimulus right from the start. “Given the economic importance of scallops to the region,” Cones said. “it would seem important to consider different approaches.”
MEET THE AUTHOR Evan Lubofsky
Evan Lubofsky is a science writer and editor at Woods Hole Oceanographic Institution. Read more
