Colony size is estimated at 240 square kilometers and includes 60 million active nests. This unprecedented colony represents a biomass of 60,000 tons. The nests have a diameter of about 60 centimeters and the density is around 0.26 nests per meter, that is, one nest every four meters, approximately. Oceanographic conditions influence habitat suitability for icefish
Ice fish or draco fish (Channichthyidae) are a family of fish of the perciform order whose distribution is in South America and the Arctic Ocean. The species studied in the article is the Jonah icefish ( Neopagetopsis ionah ), which lives at depths of 10 to 900 meters and was described by Orvar Nybelin in 1947.
“Our most important finding is the existence of a very large icefish breeding colony,” says Autun Purser of the Alfred Wegener Institute in Bremerhaven, Germany. “Dozens of nests have been observed in other parts of Antarctica, but this find is of a larger magnitude.”
Purser and his colleagues made the discoveries while surveying the Filchner-Ronne ice shelf. It is a large ice shelf in Antarctica with an area of 430,000 square kilometers on the southern slope of the Weddell Sea. It was discovered in 1912 by the German Antarctic Expedition led by Wilhelm Flichner (1877-1957). Although this German explorer suggested the name Kaiser Wilhelm , Emperor Wilhelm II refused the honor, saying that it should be named after the discoverer. The research team responsible for finding the icefish nests used the Ocean Floor Bathymetry and Observing System (OFOBS).
“It’s basically a big towing device that weighs a ton, which we tow from the RV Polastern icebreaker at speeds of one to four kilometers per hour,” explains Purser. “We towed from a height of approximately 1.5 to 2.5 m above the seabed, recording videos and acoustic bathymetry data.”
“We identified 16,160 fish nests within an area of 45,600 square meters of seabed, captured directly by the Ocean Floor Bathymetry and Observing System (OFOBS) camera,” reads the article.
The researchers were especially interested in this area of the seafloor because they knew it included upwelling water that was warmer than the surrounding bottom water, about 2 degrees Celsius warmer. Despite this, what they found was unexpected.
“We weren’t expecting any kind of fish nest ecosystems,” says Purser. This part, he adds, was a “total surprise.”
Most of the nests they found were occupied by a single adult fish guarding more than 1,700 eggs. Parental nest care and egg guarding is a behavior that has previously been observed in isolation in the icefish family. The nests were clearly differentiated from the surrounding seabed by the absence of any type of detritus inside the nests themselves. Smooth sediment and small pebble-sized rock fragments of various lithologies and colorations can be seen in the upper section of the nest. Egg deposition on gravel is a known strategy of icefish to help maintain aeration and cleanliness. To this we must add that the bowl shape prevents the eggs from being carried out of the nest by benthic currents (from the bottom of the sea).
The team was also able to observe numerous adult fish carcasses inside and outside the nesting colony, suggesting that they play an important role in the surrounding food web. In some photographs you can see starfish feeding on these dead fish, as well as octopuses and several species of fish that feed opportunistically. Although more studies are needed, they suspect that the colony may support predators such as Weddell seals ( Leptonychotes weddellii ), which were in the post-breeding phase and were fattening up for the coming winter during the COSMUS expedition. Other species of diving seals such as adult male sea lions ( Mirounga leonina ) have also been observed in the Flichner area.
“Many Weddell seals spend much of their time in the vicinity of fish nests,” says Purser. “We know this from historical tracking data and from our vessel data. The nests are exactly where the warmest water emerges. These facts could be a coincidence, so more studies are needed, but the recorded data from the seals shows that they dive to the depths of the nests, so they could be eating these fish.”
The findings reveal a unique ecosystem worldwide and provide support to the Marine Protected Area in the Antarctic Ocean, under the umbrella of the Convention for the Conservation of Antarctic Marine Living Resources.
The researchers have now deployed two camera systems to monitor the icefish nests until another research ship returns. They have pinned hopes that the photos taken several times a day will provide new insights into the workings of this newly discovered ecosystem.
This research reported in the article A vast icefish breeding colony discovered in the Antarctic, in the journal Current Biology.
