The deep seas are truly Earth’s last frontier, faraway worlds of alien beauty of which only an infinitesimal fraction have been explored—and it’s time to start thinking about how to restore them.

Just a few decades after their exploration began in earnest, deep-sea ecosystems are subject to ever-increasing impacts from human activity. Heavy metals will soon be mined from abyssal plains and submerged mountaintops and hydrothermal vents; declines in shallow-water trawl fisheries have sent vessels scouring deep-sea canyons and cold-water coral reefs. Seabed oil and gas exploration is yet another threat.