As soon as the remotely operated camera glimpsed the bottom of the Weddell Sea, a student researcher at the Alfred Wegener Institute in Germany saw the icefish nest. The sandy craters were the size of a hula hoop and less than a foot apart. Each crater held a single stolid icefish, dark pectoral fins outspreading like bat wings over a clutch of eggs.
Icefishes thrive in waters just above freezing with huge hearts and blood. Their blood is transparent because they don't have red blood cells or hemoglobin. Icefishes have been able to absorb oxygen-rich waters through their skin because of their loss of hemoglobin genes.
The polarstern, a research ship that had come to the Weddell Sea to study other things, spotted the icefish in the camera room in February of 2021. The sun was out but most of the ship were asleep. The camera kept sending pictures as it moved with the ship, showing an icefish nest every 20 seconds.
Ms. Boehringer said that it didn't stop. They were everywhere.
Autun Purser, a deep-sea Biologist at the same institute, joined Ms. Boehringer. There was nothing on the camera feed.
Is this ever going to end? Dr. Purser said so. How come no one has seen this before?
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Some nests were guarded by a single fish, others had eggs but no fish, and a fish carcass was white withbacteria.
A total of 16,160 were recorded on camera during the four-hour dive. The scientists estimated the colony of Neopagetopsis ionah icefish stretched across 92 square miles of the sereneAntarctic sea, with 60 million active nests. The researchers described the site in a paper published in the journal Current Biology.
C.-H. Christina Cheng, an evolutionary biologist at the University of Illinois-Urbana-Champaign, was not involved with the research. She said this was really unprecedented. It is very dense. It is a big discovery.
Mario La Mesa, a Biologist at the Institute of Polar Sciences in Bologna, Italy, was not involved with the research. Dr. La Mesa said he would not be surprised to find other massive colonies of breeding fishes elsewhere.
The average number of large, yolky eggs held by each of the newly discovered nests was 1,735. Dr. Cheng said that an easy snack would be starfish, polychaete worms and sea spiders. The males stand sentry to ensure their offspring are not eaten, at least not before they have the chance to hatch, according to a researcher at the Bernardino Rivadavia Museum of Natural Science in Argentina.
A single fish guarded about three-quarters of the colony. The others had eggs, but no fish, and the carcass was white withbacteria. There are many unused or abandoned nest near the edges of the colony that hold icefish carcasses, many with starfishes and octopuses eating their eyes and soft parts.
If you die in the fish nest area, you will rot there. If you die at the edges, everyone grabs you and starts eating you.
The colony was found in a patch of water that was warm enough to warm up to about 35 degrees.
The discovery of the nest raises more questions than it answers. How often are the nest built? Do the fish die after the eggs hatch? It's obvious: Why there? Dr. Cheng asked.
The authors don't have any answers. The warm deep currents may lead the fish to the grounds. Maybe there is a lot of zooplankton for the fry to eat. Maybe it is something else.
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The icefish nest is home to a Weddell seal.
There must be something special about the location of the colony. The researchers found a patch of the ocean with no birds. The sponges and corals took over the nest and took years to grow.
The icefishes have a large settlement above the water. The seals dive primarily to the icefish nest when the researchers collected satellite tracking data from them during the expedition. Dr. Purser said that they were having a nice dinner.
The researchers deployed a camera before the end of the cruise to take pictures of the site twice a day for two years. Dr. Novillo is looking forward to seeing what the camera captures. He wrote in an email that it might be the first field observation of nest preparation.
New insights into how icefish reproduce and contribute to the polar food webs could help manage and conserve populations. The new paper provides enough evidence to protect the Weddell Sea, according to the authors.
Dr. Purser said that the seafloor is not boring. Even in the 21st century, there are still huge discoveries to be made.
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