There is a tremendous amount of renewable energy off the coast of the United States in strong ocean winds, currents, and waves. Submarine power cables can transport offshore energy back to land, but scientists are just beginning to understand how they might influence marine ecosystems. This week, at the American Geophysical Union's Ocean Sciences Meeting, researchers from the University of California–Santa Barbara and the Bureau of Ocean Management presented findings from a study of marine communities around the seafloor cables. Their results are heartening for both marine ecosystems and advocates of offshore renewable energy.
Scientists have long worried about the effects of underwater power cables on marine animals. When electricity runs through the cables, they emit an electromagnetic field that many marine creatures can detect. Some marine animals use the Earth's magnetic field to guide their migratory movements; others use electromagnetic signals to detect prey.
The electromagnetic field of a buried cable would be virtually undetectable on the seafloor surface.
"The fear is that you're going to have all of these power cables running on the seafloor, and that marine organisms will somehow detect them and it'll alter their behavior," says Milton Love, a professor at UC-Santa Barbara and a co-author on the study. To find out if those fears were warranted, Love and his colleagues compared marine communities around energized and non-energized cables linking the Exxon oil rigs off the coast of Santa Barbara, California, to the shore.
First, the team set out to determine the strength and reach of the electromagnetic field emitted by the cables. The hot cables emit about 100 microteslas (a number well within the range detectable by sharks, rays, and other marine animals that pick up on electromagnetic fields). But the field dissipated quickly away from the cable itself. "Even though its relatively strong if you put the meter right on the cable," Love says, "by the time you're about three feet away its essentially undetectable."
Thus, the electromagnetic field of a buried cable would be virtually undetectable on the seafloor surface, but some cables lie directly on the ocean floor—like those leading to the Exxon rigs. To study their effects on seafloor communities, the team used scuba divers and a manned submersible to identify and count creatures living on or around the energized cable, a cold pipe, a non-energized cable, and the natural, muddy seafloor itself in water between 40 to 800 feet deep.
"We really didn't see any striking differences between what lives on a hot cable, what lives on a nearby pipe, what lives on the seafloor, and what lives on a cold cable," Love says. "The apparent effect of these energized cables is, in our case, really not detectable."
That doesn't mean an effect doesn't exist, Love notes. More research is needed, and manmade structures can have unexpected and nuanced effects on nature, as Love's work on oil platforms as giant reefs has shown. "They actually act as better spawning grounds for some species of fish," he says. "If you look at fish production, the platforms off California are the most productive habitat in the world."
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