Deep-sea mining would impact ecosystems beyond those in targeted areas – report

Mineral-laden water emerging from a hydrothermal vent on the Niua underwater volcano in the Lau Basin, southwest Pacific Ocean. (Image courtesy of the Pacific Coastal and Marine Science Center, provided by the Okinawa Institute of Science and Technology).

An international team of researchers has published a study showing that the destruction of key hydrothermal vents by deep-sea mining could have knock-on impacts on vent fields hundreds of kilometres away.

According to the paper, which was published in the journal Ecology and Evolution, hydrothermal vents are extreme deep-sea environments that exist in geologically active areas on the seafloor. These vents, which are like underwater geysers, spew hot water filled with minerals out from cracks in the seabed. And despite the intense heat and pressure, these vent systems teem with strange and unique life. The creatures around these vents, such as crabs, shrimps and worms, all rely on bacteria, which use chemical energy from the vent to make biomass.

The chemical-rich waters that sustain life also make these environments an attractive target for deep-sea mining. When the chemicals that come out of the earth’s crust meet the cold seawater, they precipitate and create chimney-like deposits on the seabed, called seafloor massive sulphides.

“These chimneys contain a high quality and quantity of gold, silver, copper and other rare earth minerals that we need to feed our technology-hungry society,” Otis Brunner, first author of the study, said in a media statement.

Brunner pointed out that, despite the abundance of minerals and metals in such deposits, resource extraction destroys the creatures living there, and severely impacts those on nearby chimneys within the same hydrothermal vent site.

“Each hydrothermal vent often hosts some endemic species, meaning they only live there. So if you remove or severely damage their ecosystem, not only have you lost those animals, but you’ve lost that species entirely,” he said.

And now, Brunner’s research shows that the damage to hydrothermal vent ecosystems is also unlikely to be limited to just one single vent site, but could impact other vent sites hundreds of kilometres away.

Although hydrothermal vents seem isolated from each other, many hydrothermal vent species can actually disperse from one vent to another while in the larval stage, assisted by ocean currents. If they reach another vent and the conditions at the new vent are similar, then the creatures can settle and mature into adulthood.

This means that if a species population is wiped out at one hydrothermal vent, then the population of the same species at another hydrothermal vent, where the larval used to disperse to, will also be threatened.

In his study, Brunner looked at vent sites within three sub-regions of the Northwest Pacific—the Okinawa Trough, the Izu-Bonin Arc and the Mariana Trough. He inferred how connected each vent site was to the others by comparing how many species the vent sites had in common.

By creating networks from the species data, the researcher and his colleagues identified which vent sites act as essential hubs within each sub-region.

Two vent sites, Sakai and North Knoll Iheya Ridge, were found to be the most important for maintaining connectivity in the Okinawa Trough sub-region and should be prioritized for conservation.

“Unfortunately, the Sakai and North Knoll Iheya vent sites are situated in the central region of the Okinawa Trough, an area of particular interest for mining,” Brunner said. “But any disturbance to these two sites would have particularly strong impacts on all the species at hydrothermal events across Japan.”

For the Izu-Bonin Arc and Mariana Trench, Nikko volcano and Alice Springs were the most important hub, respectively. There is no current interest in deep-sea mining at these sites.

The study also identified pathways of connectivity linking both the Okinawa Trough and the Mariana Trench to the Izu-Bonin Arc. However, these linkages only occurred across a few hydrothermal vents, including the Daisan-Kume Knoll in the Okinawa Trough, situated within an area of mining interest. Based on these findings, the scientists concluded that mining activity here could cause a collapse in the network across the Northwest Pacific region.