Researchers have discovered an icefish colony of “globally unprecedented” size in the Antarctic Ocean.

A team of biologists stumbled across an estimated 60 million fish nests while collecting data on the floor of the Weddell Sea last February. The researchers published their findings this week in the journal Current Biology.

The colony probably covers roughly 93 square miles, the scientists found — about the size of the island of Malta. It is “the most spatially expansive continuous fish breeding colony discovered to date globally at any depth,” the researchers wrote — a finding that highlights the magnitude of biological mysteries and astonishments that remain undiscovered, even with so much of the planet thoroughly explored.

“I was immediately quite shocked because I’ve seen hardly any nesting fish, let alone nests and nests and nests,” said Autun Purser, a deep-sea biologist at the Alfred Wegener Institute in Germany and lead author of the article on the discovery.

Blue and partly transparent, icefish have proved adept at surviving in the frigid, deep-sea waters of Antarctica. Their blood is copper-based — rather than iron-based like human blood — which allows their bodies to transport oxygen in such an extreme environment.

Purser’s research team was diving and photographing the seabed from a German research vessel one night in the south of the Antarctic Weddell Sea when a seemingly endless field of icefish nests came into view. Images transmitted from a towed camera system about 1,370 to 1,760 feet below the ship revealed circular nest after circular nest, each about 2.5 feet in diameter.

The team sent photographs of the nests to icefish experts around the world, who told them that no breeding ground of the kind had been observed before, Purser said.

The researchers spent 30 hours filming the nests and calculated that they numbered around 60 million. Each “active” nest contains between 1,500 and 2,500 eggs, guarded in most cases by an adult icefish.

Researchers have discovered an ice fish colony of “globally unprecedented” size in the Antarctic sea which likely covers roughly 93 square miles. (Courtesy of: Alfred Wegener Institute / PS124 OFOBS Team)

Previously, the largest observed grouping of icefish — found farther south in the same sea — consisted of fewer than 100 nests, Purser said.

The discovery has shed new light on the marine ecosystem in the Weddell Sea. The colony was found in an area with warmer water than its surroundings, and researchers think the icefish probably migrate to the area to breed. This may explain why so many seals also hang out there, Purser said.

“So if you lost these fish, you may also have an impact on the seals,” he added.

German Federal Research Minister Bettina Stark-Watzinger congratulated the researchers on their “fascinating discovery,” according to a news release from the Alfred Wegener Institute on Wednesday.

“This discovery can make an important contribution towards protecting the Antarctic environment,” she said.

Researchers are calling for the establishment of a marine protected area to shield the icefish colony from fishing and other disruptive practices. European Union member states and a number of other countries support the proposal, but it has yet to be adopted by the international body charged with conserving Antarctic marine life.

Purser said that icefish are not a very desirable fish to eat and that people have little commercial interest in the area, so he’s optimistic about gaining this international protection.

The bigger threat, he said, is climate change. Ice completely covers the area, but if it begins to melt, that would affect algae growing on the bottom of the ice field. Icefish migrate to surface waters to feed on zooplankton there, so changes to global warming patterns could affect this vital food source and produce ripple effects up the food chain, Purser said.

The team left behind two cameras to photograph the sea floor four times per day over the next two years. The next striking images they hope to capture: what happens when the eggs hatch.