In one of the most remote and frozen places on Earth, scientists have made a surprising discovery deep under the icy surface of Antarctica's Weddell Sea. Using a robotic explorer called“Lassie,” they found thousands of carefully arranged fish nests spread across the ocean floor, a secret world of life thriving where people had never thought it could exist.

A View Hidden Beneath the Ice

This discovery was made possible by a major event in 2017, when a massive iceberg named A68 broke off from the Larsen C Ice Shelf. The iceberg was the size of a small country and covered an area of more than 5,800 square kilometres. When it moved away, it revealed a part of the seabed that had been buried under 200 metres of ice for centuries. This offered scientists a rare opportunity to explore a part of the planet that had never been seen before.

In 2019, researchers started the Weddell Sea Expedition to study this newfound area. Their goal was to examine the ocean environment and, if possible, find the wreck of Sir Ernest Shackleton's famous ship Endurance, which disappeared in the ice in 1915.

Lassie's Deep-Sea Find

On the South African research ship SA Agulhas II, the team used autonomous and remotely operated underwater vehicles, robotic explorers built to survive in harsh, freezing conditions. One of these robots, known as“Lassie,” sent back astonishing images from the dark ocean floor.

The scientists saw thousands of circular depressions in the seabed. Each one was clear of the plankton and debris that covered the area around it. These were fish nests, perfectly shaped and arranged in patterns that stretched far into the distance. Some nests were in neat lines, others in clusters, forming what looked like an organized underwater city.

The fish responsible were identified as a type of Antarctic rockcod called the yellowfin notie. Each nest was home to a devoted parent protecting a group of eggs.

A Complex Community Under the Sea

The researchers think the fish colony's setup is not random. The nests grouped together form a protective“herd,” with individuals in the centre shielded from predators by those on the edges. The fish on the outer edges are usually larger and stronger. This balance between cooperation and competition increases the colony's ability to survive, a remarkable example of how life adapts in extreme conditions.

A Legacy Connected to Shackleton

Although the team didn't find Shackleton's Endurance during the 2019 expedition, their experience working in the difficult sea ice proved valuable. It later helped guide the Endurance22 mission, which successfully located the well-preserved wreck in 2022, resting more than 3,000 metres below the surface.

But Lassie's discovery of the vast nesting area was equally significant. It revealed not just new animal behaviour but an entire hidden ecosystem beneath the Antarctic ice.

Preserving a Fragile Destination

The discovery shows how little we understand about life in polar oceans and how delicate these ecosystems are. Scientists now believe this area qualifies as a Vulnerable Marine Ecosystem, meaning it is both ecologically important and at risk from damage.

Protecting such areas is essential because they support Antarctic wildlife, including penguins, seals, and microscopic plankton that form the base of the food chain. Along with earlier findings that found one of the world's largest fish-breeding colonies in the Weddell Sea, Lassie's discovery supports calls to officially protect the region as a Marine Protected Area.

As climate change and human activity continue to change polar regions, these discoveries go beyond scientific achievements, they serve as warnings. Protecting Antarctica's icy ecosystems is crucial, not only for the wildlife that relies on them but for the health of the entire planet.

Source: Frontiers. "Antarctic robot 'Lassie' uncovers thousands of icefish nests beneath Antarctic ice." ScienceDaily. ScienceDaily, 29 October 2025.

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