The unanticipated find dwarfs any previous known collection of fish nests.
According to a recent research, the world’s largest known breeding fish colony is located 500 meters beneath the ice covering Antarctica’s Weddell Sea.
An estimated 60 million active icefish nests cover at least 240 square kilometers, an area about the size of Orlando, Florida. From freshwater cichlids to aesthetically minded pufferfish (SN: 10/13/20), many fish build nests. However, until now, researchers had only come across a few dozen or so icefish nests at a time. Previously, even the most social nest-building fish species were known to congregate in the hundreds.
Researchers reveal in Current Biology on January 13 that icefish have a significant and hitherto unknown impact on Antarctic food webs.
Deep water scientist Autun Purser of the Alfred Wegener Institute in Bremerhaven, Germany, and colleagues discovered the large colony in the Weddell Sea, which lies between the Antarctic Peninsula and the main continent, in early 2021 while on a research voyage.
The researchers were looking at the chemical links between the bottom and surface waters. A part of the investigation involves carefully pulling a gadget behind the scientists’ icebreaking research vessel to observe seabed life. As it glided just over the ocean’s surface, the gadget captured video and utilized sound to map seabed structures.
One of Purser’s colleagues was running the camera tow at one site on the Filchner ice shelf in the Weddell Sea when he saw circular Jonah’s icefish (Neopagetopsis ionah) eggs down below. Icefish, belonging to the Channichthyidae family, can only be found in the Southern Ocean and Antarctic seas, and they have unusual adaptations to the severe cold, such as clear blood full of antifreeze components (SN: 9/19/98).
“I knew we were onto something remarkable when I came down half an hour later and basically saw nest after nest for the entire four hours of the first dive,” Purser recalls.
Purser and colleagues conducted three further surveys in the region, finding comparable densities of nests kilometer after kilometer. Bluegills (Lepomis macrochirus), which create breeding colonies with hundreds of individuals, are perhaps the most similar to icefish among nest-spawning fish, according to Purser. The Weddell Sea colony, however, is many orders of magnitude larger, according to measurements that reveal around one icefish nest every four square meters spanning hundreds of kilometers of area.
According to evolutionary scientist Thomas Desvignes of the University of Oregon in Eugene, who was not involved in the study, the colony is a “extraordinary discovery.” He was particularly taken aback by the dense number of nests.
Desvignes said it reminded him of bird nests. “It’s practically like that when we see cormorants and other maritime birds that nest close to one other.”
It’s unclear why so many icefish are congregating in one place to reproduce. This area looks to have adequate availability to plankton, which would be an important food source for newly hatched fish. The scientists also discovered a zone in the area with slightly warmer water, which might aid the icefish in locating the mating habitat.
According to the experts, the icefish may be feeding the Weddell seals. According to previous research, the seals spend a lot of time diving in the seas above the colony.
Purser believes that closer to the beach, where there is less ice, there may be smaller Jonah’s icefish populations. However, it’s likely that the Jonah’s icefish rely too heavily on the enormous reproductive colony, placing all their eggs in one basket. If that’s the case, Desvignes believes the species is “very susceptible” to extinction. According to him, the finding of the large colony is another another reason to provide environmental safeguards for the Weddell Sea, as has already been done for the neighboring Ross Sea.
Purser has two seabed cameras at the colony location for the time being, where they will stay for a few years, capturing photographs four times a day to observe if the nests are reused.
Purser claims that “[the huge colony] is almost a new seabed ecosystem type.” “It’s unbelievable that it’s never been seen before.”