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upstart writes:

The largest group of nesting fish ever found lives beneath Antarctic ice:

Five hundred meters below the ice covering Antarctica's Weddell Sea sits the world's largest known colony of breeding fish, a new study finds.

An estimated 60 million active nests of a type of icefish stretch across at least 240 square kilometers, nearly the size of Orlando, Fla. Many fish create nests, from freshwater cichlids to artistically inclined pufferfish (SN: 10/13/20). But until now, researchers have encountered only a handful of icefish nests at a time, or perhaps several dozen. Even the most gregarious nest-building fish species were previously known to gather only in the hundreds.

The icefish probably have a substantial and previously unknown influence on Antarctic food webs, researchers report January 13 in Current Biology.

Deep sea biologist Autun Purser of the Alfred Wegener Institute in Bremerhaven, Germany, and colleagues stumbled across the massive colony in early 2021 while on a research cruise in the Weddell Sea, which is located between the Antarctic Peninsula and the main continent.

[...] The researchers were studying chemical connections between surface waters and the seafloor. Part of the research involved surveying seafloor life by slowly towing a device behind the scientists' icebreaking research vessel. That device recorded video as it glides just above the bottom of the ocean and used sound to map seafloor features.

At one location on the Filchner ice shelf in the Weddell Sea, one of Purser's colleagues was operating the camera tow and noticed that it kept encountering circular Jonah's icefish (Neopagetopsis ionah)[*] nests down below. Icefish, of the family Channichthyidae, are only found in the Southern Ocean and Antarctic waters and have strange adaptations to the extreme cold such as clear blood full of antifreeze compounds (SN: 9/19/98).

"When I came down half an hour later and just saw nest after nest the whole four hours of the first dive, I thought we were onto something unusual," Purser recounts.

[*] Jonah's icefish entry on Wikipedia.

Journal Reference:
Autun Purser, Laura Hehemann, Lilian Boehringer, et al A vast icefish breeding colony discovered in the Antarctic, (DOI: 10.1016/j.cub.2021.12.022)

Original Submission