(CNN) — A breeding colony of 60 million fish was discovered in the Weddell Sea, in Antarctica, a unique and previously unknown ecosystem that occupies an area the size of Malta.
The fascinating find shows how little is known about the depths of the ocean.
The vast colony, believed to be the largest in the world, is home to the extraordinary icefish or drake (Neopagetopsis ionah), which has a transparent skull and blood. The icefish is the only vertebrate that does not have red blood cells.
The discovery of the nests of the icefish, Neopagetopsis ionah, was a surprise.
To survive such low temperatures, he developed an antifreeze protein in his transparent blood that prevents the growth of ice crystals.
The breeding colony was discovered in February 2021 by the German polar research vessel Polarstern, which was surveying the seabed half a kilometer below the ship using a car-sized camera system attached to the stern of the ship that transmits the images to the cover.
The nests are evenly spaced across the seafloor.
The expedition was focused on the ocean currents, so the discovery of the nests, differentiated from the seabed by a circle of stones, was a surprise.
“We saw one fish nest after another for four hours, and in that time we covered about four miles of the seabed,” explains Autun Purser, a postdoctoral researcher at the Alfred Wegener Institute in Bremerhaven, Germany. He is the lead author of a study on the icefish colony that was published this Thursday in the Scientific journal Current Biology.
“I’ve never seen anything like it in the 15 years I’ve been an ocean scientist,” Purser said. “After that dive, we emailed the shoreline experts who know about fish like this. They said yes, it was unique.”
The seals that live in the area probably feed on the ice fish.
Spectacular extension
Four more camera dives revealed the spectacular expanse of the colony, and its surprisingly uniform nature.
“This is a surprising discovery,” says John Postlethwait, a biology professor at the University of Oregon, who studies these fish and was not involved in the research.
“It is also significant. The magnitude of the biomass is, at least to me, unexpected. And the extent to which the fish change the structure of the bottom of the sediments creates (a) habitat for a community that moves up the food web to maintain a huge variety of species, “he added.
The colony covers more than 240 square kilometers, the researchers said. With an average of one nest for every three square meters, they calculated that the colony includes about 60 million active nests.
Each of the evenly spaced nests was about 15 centimeters deep and 75 centimeters in diameter, and contained an average of 1,735 eggs. Most were guarded by an adult fish. Some nests contained only eggs and others were unused.
The nests are guarded by an adult.
“Nest spacing is kind of like bird spacing on a phone line,” Postlethwait added by email.
“Some animals like to be social, but there is a limit. Congregating can give them advantages in finding a mate, but it provides a fertile focal point for predation.”
The fish appear to be attracted to warmer water, which is about 2 degrees Celsius warmer than the surrounding seafloor, which is a cold 0 degrees Celsius, Purser said. (Sea water freezes at a temperature lower than fresh water).
Researchers have deployed two camera systems to monitor icefish nests until a research vessel returns. The hope is that the photos capture more details about the fish nest ecosystem.
One of the questions the researchers want to answer is how long adult fish monitor their eggs, experts suspect it could be months, and whether it is the male or the female who watches.
“It appears that the reproductive behavior of most, if not all, ice fish revolves around the courtship of females by males by building a good nest,” says the fish expert by email. Icemaker H. William Detrich, Emeritus Professor of Biochemistry and Marine Biology at Northeastern University. Detrich was not part of the investigation.
The findings reveal an ecosystem unique in the world, according to the researchers, and they say it should be designated as a protected area.
“The implications for the conservation of this species are clear: a marine protected area should be established in the Weddell Sea to prevent exploitation of this species of icefish,” Detrich added.
The discovery was made by a team aboard the German polar research ship Die Polarstern vor A74.
Seal food?
Although the Weddell Sea is covered in sea ice year-round, the ice is relatively thin, one meter thick, which means photosynthesis is still possible and life can thrive. According to Purser, the bottom of the Weddell Sea is far from sterile, as there are sea sponges, corals, octopuses and starfish on the seafloor.
There are also about 2,000 seals living in the area, likely to dive in the nursery area and feed on the ice fish, he said, although there is no definitive evidence.
Purser said that while there are species of freshwater fish that make similar types of nests, scientists “have never seen a colony like this in the deep sea.”
“I guess we’ve only recorded maybe 1% of the Weddell Sea floor, and who knows what else is hiding out there. I’m convinced there are a lot of gaps in our understanding of the deep sea.”