The world’s largest colony of fish nests under the ice of Antarctica

The largest known colony of fish farming in the world has been discovered off the coast of Antarctica. It stands about 500 meters (1,640 feet) under the ice that covers part of the Weddell Sea. These fish are known as ice fish. This huge community of nests extends across at least 240 square kilometers (92 square miles) of seafloor. This is a third larger area than Washington, DC

Many fish create nests, from freshwater tilapia to stomach-less puffer. But so far, researchers haven’t found many ice fish nests close to each other—perhaps only a few dozen. Even the most social species of nesting fish has been found to congregate only in the hundreds. The new one has an estimated 60 million active nests!

Autun Purser is a deep sea biologist. He works at the Alfred Wegener Institute in Bremerhaven, Germany. He was part of a team that found the huge colony in early 2021. They were aboard a German research icebreaker, Polarstern. The ship was sailing in the Weddell Sea. It is located between the Antarctic Peninsula and the main continent.

These researchers were studying the chemical bonds between surface waters and the sea floor. Part of this work involved surveying life on the sea floor. To do this, they slowly pulled out a device that records a video of it gliding over the ocean floor. They also use sound to map seafloor features.

At a site under the Filchner Ice Shelf – the floating ice in the Weddell Sea – one of his fellow Purser teammates noticed something. Circular nests kept appearing on camera. They belonged to the Yunnan Icefish (Neopagitopsis iona). These fish are found only in the Southern Ocean and Antarctic waters. The traits they have adapted to survive in extreme cold include developing clear blood filled with antifreeze compounds.

Half an hour after the nests started appearing, Purser came down to see the camera images. Surprised, “He just saw one nest after another for four hours from the first dive.” He recalls that at once it seemed “we were on our way to something extraordinary.”

Picture of many ice fish and their nests taken from above
Video and audio surveys recently revealed that a species of Antarctic fish called the Yunnan icefish congregate to breed by the millions. Adult gatherers make a range of circular nests that extend for several kilometers.Alfred Wegener Institute, PS124 Team OFOBS

Huge nursery under the ice

Purser and his colleagues conducted three other surveys in the area. Each time, kilometer after kilometer, they found more nests. Perhaps one of the closest comparisons to these ice fish is to the nesting lake fish known as blue gills (Lepomis macchirus). They can form breeding colonies numbering in the hundreds, Purser says. Researchers say the Waddell Sea colony is at least hundreds of thousands of times larger. It is based on measurements showing about one icefish nest for every four square meters (43 square feet) across hundreds of kilometers of area. Each nest, guarded by an adult, may contain about 1,700 eggs.

The Purser group described its unexpected discovery on January 13 current biology.

This colony is “an amazing find,” says Thomas Desvins. He’s an evolutionary biologist at the University of Oregon in Eugene. He was especially shocked by the intense concentration of the nests. “It got me thinking about bird nests,” Desvins says. Cormorants and other seabirds “nest like this, one next to the other,” he says. With this ice fish, “it’s almost like that.”

Scientists aboard the Polar Stern icebreaker captured these undersea photos of a huge colony of ice fish. Typically, a fish about half a meter (19.6 in) long was seen guarding eggs in a nest of roughly the same size.

It’s not clear why so many ice fish gather so closely to breed. The site appears to have good access to plankton. They serve good meals for the young fish. The team also found an area in the area with slightly warmer water. This may help ice fish at home on this breeding ground.

The researchers say that nesting fish may be having a large, previously unknown effect on Antarctic food webs. For example, they may keep Weddell seals. Many of these seals spend their days on the ice above the nesting colony. In the past, studies have reported that these seals spend much of their time diving in the waters above the nesting site.

Purser thinks there may be smaller colonies of these ice fish near shore, where there is less ice cover. However, it is possible that most of the Yunnan glaciers depend on a single huge breeding colony. If true, they would put all their eggs in one basket. This “would make the species highly vulnerable to extinction,” Desvins says.

The new discovery of the massive colony is another argument for providing environmental protection to the Weddell Sea, he says. Desvignes notes that it is something that has been done to the nearby Ross Sea.

At the moment, Purser currently has two seafloor cameras at the colony’s site. They will stay there for two years. Taking pictures four times a day, they will watch to see if the nests are being reused year after year.

“I would like to say [the massive colony] It’s almost a new type of seafloor ecosystem,” says Purser. “It’s really surprising that it’s never been seen before.”

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