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A recent paper published in the journal Current Biology reports a decrease in marine animals both in and around the area where Japan performed the first successful test extracting cobalt crusts from the top of deep-sea mountains to mine cobalt.
According to the study, not only do directly mined areas become less habitable for ocean animals, but deep-sea mining also creates a plume of sediment that can spread through the surrounding water.
“These data are really important to get out,” Travis Washburn, a benthic ecologist who works with the Geological Survey of Japan and led the article, said in a media statement. “A set of regulations is supposed to be finalized soon, so a lot of these decisions are happening now.”
Washburn and his colleagues analyzed data from three of Japan’s visits to the Takuyo-Daigo seamount: one month before the mining test, one month after, and one year later. After taking a seven-day boat trip from port, a remotely operated vehicle went to the seafloor and collected video of the impacted areas.
One year after the mining test, researchers observed a 43% drop in fish and shrimp density in the areas directly affected by sediment pollution. However, they also noted a 56% drop in the fish and shrimp density in surrounding areas. While there are several possible explanations for this decrease in fish populations, the team thinks it may be due to the mining test contaminating fish food sources.
The study did not observe a major change in less mobile ocean animals, like coral and sponges. However, the researchers noted that these observations are the result of a two-hour test, and coral or sponges could still be impacted by long-term mining operations.
“I had assumed we wouldn’t see any changes because the mining test was so small. They drove the machine for two hours, and the sediment plume only traveled a few hundred meters,” Washburn said. “But it was actually enough to shift things.”
The scientists pointed out that they will need to repeat this study several times to gain a more accurate understanding of how deep-sea mining impacts the sea floor. Ideally, multiple years of data should be collected before a mining test occurs to account for any natural variation in ocean animal communities.
“We’re going to need more data regardless, but this study highlights one area that needs more focus,” the researcher said. “We’ll have to look at this issue on a wider scale because these results suggest the impact of deep-sea mining could be even bigger than we think.”
