A new study has found that five hundred meters below the ice covering the Weddell Sea in Antarctica lies the largest known colony of fish farming in the world.
An estimated 60 million active nests of a species of ice fish span at least 240 square kilometers, roughly the size of Orlando, Florida. Many fish create nests, from freshwater crustaceans to artistically slanted pufferfish (SN: 10/13/20). But so far, researchers have only encountered a few ice fish nests at any one time, or perhaps several dozen. Even the most gregarious of nest-building fish was previously known to congregate only in the hundreds.
13 Jan 13, researchers report that ice fish may be having a major and previously unknown effect on Antarctic food webs. current biology.
Deep-sea biologist Otton Perser of the Alfred Wegener Institute in Bremerhaven, Germany, and colleagues found the huge colony in early 2021 during a research expedition in the Weddell Sea, which lies between the Antarctic Peninsula and the main continent.
Researchers have been studying the chemical bonds between surface waters and the sea floor. Part of the research involved surveying life on the sea floor by slowly pulling a device behind the scientists’ icebreaking research vessel. This device recorded a video of it sliding over the ocean floor and used sound to map the sea floor’s features.
At a location on the Filchner Ice Shelf in the Weddell Sea, one of Purser’s colleagues was running a camera pull and noticed that he was keeping track of the Jonah icefish (Neopagitopsis iona) Nests at the bottom. Icefish, of the family Channichthyidae, are found only in Southern Ocean and Antarctic waters and have peculiar adaptations to extreme cold such as clear blood full of antifreeze compounds (SN: 9/19/98).
“When I got off half an hour later and saw nest after nest for a full four hours of our first dive, I thought we were into something out of the ordinary,” Purser recounts.
Piercer and his colleagues conducted three other surveys in the area and continued to find nests of similar densities, kilometer after kilometer. Perhaps one of the closest comparisons to icefish among nest-spawning fish is the blue gills (Lepomis macchirus), which form breeding colonies that can house hundreds of individuals, Purser says. But based on measurements showing about one icefish nest per four square meters across hundreds of kilometers of area, the Weddell Sea colony is several times larger by size, the researchers say.
The colony is an “amazing discovery,” says evolutionary biologist Thomas Desvins of the University of Oregon in Eugene, who was not involved in the research. He was especially shocked by the intense concentration of the nests.
“It got me thinking about bird nests,” Desvins says. “When we see cormorants and other seabirds nesting like that, one next to the other – it’s almost like that.”
It is not clear why so many ice fish congregate in one place to breed. There appears to be good access to plankton at this site, which will be an important food source for newly hatched fish. The team also found an area with slightly warmer water in the area, which may help the ice fish locate a breeding site.
Researchers say ice fish could conserve Weddell seals. Previous studies have shown that seals spend a lot of time diving in the waters above the colony area.
Purser thinks there may be smaller colonies of Yunnan ice fish near shore where there is less ice cover. However, it is possible for the Yunnan icefish to depend disproportionately on the huge breeding colony, laying all their eggs in one basket. If so, that “would make the species highly vulnerable to extinction,” Desvins says. The discovery of the massive colony is another argument for providing environmental protection to the Weddell Sea as it did to the nearby Ross Sea, he says.
Currently, Purser has two cameras on the sea floor at the colony’s site, where they will stay for two years, taking pictures four times a day to see if the nests are reused over time.
“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.”