Antarctic Researchers Discover Largest Nesting Ground of ‘White Blooded’ Icefish in the World 500m Below Weddell Sea

Antarctic Researchers Discover Largest Nesting Ground of ‘White Blooded’ Icefish in the World 500m Below Weddell Sea
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team
Michael Wing
Updated:
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Researchers aboard German research icebreaker Polarstern in February 2021 made an unexpected discovery: the world’s largest icefish nesting ground, located 500 meters (1,650 feet) under the Weddell Sea off the coast of Antarctica.

While imaging ocean floor topography using the vessel’s towed video camera sled system, graduate student Lilian Böhringer upon sighting the vast, incredible icefish nesting “metropole” contacted the bridge where Autun Purser, of the Alfred Wegener Institute, was stationed.

This Antarctic region, known as the Filchner Trough, was of particular interest to the team because of its enigmatic inflow of slightly warmer, topographically guided bottom waters, up to two degrees Celsius warmer than surrounding bottom waters. Such underwater troughs often act as conduits for upflows to the Weddell Shelf, and this one flowed directly over a vast breeding colony unlike anything that had been seen before.

Filchner Trough in the Weddell Sea, Antarctica. (The Epoch Times)
Filchner Trough in the Weddell Sea, Antarctica. The Epoch Times
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team

It was here that they found the ocean pockmarked with thousands of circular, crater-like nests, most of which contained a single, ghostly icefish (or Neopagetopsis ionah)—specially adapted to cold water, with transparent blood (or “white blood” lacking hemoglobin) containing antifreeze compounds.

“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 told ScienceNews.

“I would say [the massive colony] is almost a new seafloor ecosystem type,” he added. “It’s really surprising that it has never been seen before.”

The Polarstern’s 20 hours of footage and several thousand images directly sighted a total of 16,160 icefish nests, of which 12,020 (79 percent) were under active use, usually inhabited either by one (and no more than two) living adult icefish, eggs alone, or both fish and eggs together, the researchers reported in a study. But the researchers concluded that some 60 million active nests were located here, over at least 240 square kilometers (92 square miles) of the eastern flank of the Filchner Trough—with an associated fish biomass of over 60,000 metric tons.
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team

The nests were dispersed at a density of 0.26 per square meter, the researchers said, each measuring just over a half meter (1.6 feet) in diameter—the same length as the fish itself. The occupying icefish guarded 1,735 eggs on average. These bowl-shaped excavated nests offer the eggs protection from water currents, while the coarse, rocky detritus found at the bottom of each nest provides aeration and cleanliness for eggs laid over top.

Degraded icefish carcasses were also spotted throughout, in and around the nesting colony, which would provide input for local food webs, amphipod scavengers, and overall biogeochemical processing. The water column above the nesting ground exhibited higher concentrations of such biological matter than elsewhere in the Weddell Sea.

Meanwhile, inside abandoned nests, with their exposed gravel and protection, were found colonization of fauna such as tube dwelling polychaetes, bryozoan colonies, and sponges, thusly enhancing local biomass and diversity. Elevated concentrations of phytodetritus were discovered in many of these abandoned nests, presenting food for anemones, sponges, other suspension feeders, and the like.

(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / PS124 AWI OFOBS Team)
Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team
(Courtesy of <a href="https://www.awi.de/en/">Alfred Wegener Institute</a> / Mia Wege)
Courtesy of Alfred Wegener Institute / Mia Wege

Furthermore, adolescent icefish which would spawn from these eggs would frequent shallower depths in the water column, making easy meals for apex predators such as Weddell seals on the shelf above. The researchers observed these Antarctic mammals diving in greater numbers in the vicinity of the Filchner Trough than in other areas.

The incredible discovery of such a colossal nesting ground raises many questions about how this ecosystem behaves over time. To address the matter, Purser positioned two camera systems at depths of 3 meters (10 feet) above the seafloor to monitor the benthos and lower water column for two more years.

The vast icefish breeding colony is, in fact, believed to be the largest fish nesting area on earth, the authors wrote. Further research to determine the spatial extent, reason for, and significance of this concentration is needed; but researchers say the discovery supports making the Filchner Trough a regional marine protected area under the Convention on the Conservation of Antarctic Marine Living Resources umbrella.
(Courtesy of Alfred Wegener Institute / PS124 AWI OFOBS Team)
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Michael Wing
Michael Wing
Editor and Writer
Michael Wing is a writer and editor based in Calgary, Canada, where he was born and educated in the arts. He writes mainly on culture, human interest, and trending news.
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