Researchers in Antarctica have discovered a strange collection of icefish nests.
The scientists were on expedition in the Weddell Sea looking for Sir Ernest Shackleton's lost ship, the Endurance – which sank in 1915 and was discovered in 2022 – when they found the nesting grounds in a remote area which had, until recently, been underneath a large ice shelf.
When the 5,800-square-kilometre A68 iceberg calved from the Larsen C Ice Shelf, scientists were finally able to access the seabed beneath.
It wasn’t easy. “As with a lot of Antarctic research we battled the cold, sieving freezing cold mud on the back deck for hours,” says Dr Michelle Taylor, head of science at Ocean Census.
“The sea ice in particular was a challenge as, at the time, there was a bottleneck and a build of sea ice around that area – we were heading directly towards this, playing chicken with icebergs as we went.”
But the challenge was worth it as they found something spectacular. Using an underwater robot called 'Lassie’ to explore the seafloor, they discovered more than 1,000 dimples arranged in neat patterns in the sand.
At first, they didn’t know what they were looking at. “There was fervent discussion on board about what the dimples in the sand may be as they were so clear, and clean, in obvious contrast to the surrounding carpet of green phytoplankton,” says Taylor.
Putting together the clues – the size, shape, and the fact that there were fish nearby – they realised that these were the nests of icefish called the yellowfin notie (Lindbergichthys nudifrons).
“Icefish are a remarkable and uniquely adapted group of fish that survive in water temperatures below zero Celsius and thrive in the extreme environments within Antarctica,” says study author Russell Connelly, a marine biologist at the University of Essex.
Most of the 1,036 nests were inactive but 72 of them had larvae in the nest or nearby. The discovery has been published in the journal Frontiers in Marine Science.
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“These fish live deep on the dark, cold Antarctic seabed,” says study author Connelly. “They build small, circular nests in the fine sediment, and then the males guard the eggs for around four months. Their main threat comes from predators on the seafloor, like brittle stars and predatory worms, which try to eat the eggs.”
The geometric patterns might be a way the fish protect themselves from predators. By arranging their nests in these tight groups, the fish in the centre are protected by the neighbours surrounding them. Larger, stronger fish usually live in the outer nests as these are more likely to be able to defend themselves from predators.
These large nesting areas are also important for the ecosystem around them. “These fish are habitat builders, creating vast nesting aggregations which will support the wider biodiversity of the Antarctic,” says Connelly.
The team from the Weddell Sea Expedition 2019 say the discovery of this unique habitat shows how important it is for the area to be designated as a Marine Protected Area.
Image and video credits: Weddell Sea Expedition 2019
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