'How Come No One Has Ever Seen This Before?'

Before a research expedition to Antarctica's Weddell Sea last year, the biggest icefish colony scientists had ever seen contained around 60 nests. They were amazed to discover an icefish metropolis with an estimated 60 million active nests spread out over an area bigger than Seattle. Around three-quarters of the nests observed were being guarded by an icefish, with an average of 1,735 eggs in each nest, researchers wrote in a study published in Current Biology. Others contained eggs but no fish or the rotting body of an icefish. The fish breeding colony was discovered by chance as a team of biologists collecting routine data towed a large camera device a few feet above the seafloor—more than a thousand feet below the water's surface, the Guardian reports.

Deep-sea biologist Autun Purser, the study's lead author, says the team was expecting to see ordinary Antarctic seafloor. Instead, it was "nothing but fish nests" for four hours. "We were like, is this ever going to end?" he tells the New York Times. "How come no one has ever seen this before?" Researchers believe the colony, which covers an estimated 92 square miles, plays a important role in the Weddell Sea's ecosystem, with nests providing meals for predators including the Weddell seal and fish carcasses supporting populations of numerous kinds of predators. Around 30 miles west of the colony, the team found an area of seafloor with large numbers of empty nests covered in corals that take years to grow.

The team left a camera behind at the location to learn more about icefish breeding and nesting behavior—and to observe what happens when the juvenile icefish hatch. Researchers believe there are similar colonies yet to be discovered. "The deep seas are not desert wastelands, they are really abundant in life," Purser says. "The fact that there are such large ecosystems we didn’t know about goes to show how much is probably out there to be discovered still." (More marine biology stories.)