While tracing the footsteps of polar explorer Sir Ernest Shackleton and his ill-fated Endurance ship, researchers discovered hundreds of fish nests arranged in particular patterns.
A remotely operated vehicle (ROV) investigating the seafloor in Antarctica’s Western Weddell Sea found over 1,000 circular nests making up a large geometric neighborhood. The discovery sheds light onto the unique ecosystems thriving in Earth’s most extreme environments and carries significant implications for conservation efforts.
A dynamic fish community
The nests (the divots in the sand pictured in the image below) belong to a species of rockcod known as the yellowfin notie and were located in an area previously covered by a 656-foot-thick (200-meter) ice shelf. Some were arranged individually, while others were in curves or clusters. It even turns out yellowfin notie are orderly homekeepers—while the surrounding seafloor was covered in plankton detritus, each nest was clean.
The yellowfin notie nests. © Weddell Sea Expedition 2019
The researchers describe the fish community as a mix of cooperation and self-interest in a study published today in Frontiers in Marine Science. A parent fish would have guarded each nest, but the arrangement of the nests themselves also played a defensive role. The nest clusters represent the “selfish herd” theory, which suggests that individuals in the center of a group are safer than those on the margins. According to the researchers, the isolated nests likely housed larger and stronger fish who were better suited to protecting their nests.
Following the footsteps of Endurance
Researchers found the fish neighborhood during the Weddell Sea Expedition 2019, which aimed to conduct research near the Larsen Ice Shelf and find the wreck of Sir Ernest Shackleton’s ship. Endurance was crushed by pack ice in 1915 before it got swallowed by the sea. Miraculously, the entire crew survived the misadventure.
Endurance sinking in the ice. © Frank Hurley, Public domain, via Wikimedia Commons
The same perilous conditions that upended Shackleton’s undertaking over 100 years ago prevented the 2019 expedition aboard South African polar research vessel SA Agulhas II from locating his ship—that happened in 2022. Nonetheless, the team found a peculiar habitat associated with ice shelves, a crucial formation involved in ice flow and sea level rise.
In the wake of A68 iceberg
Antarctica’s borders are laced with floating ice shelves that hold back the flow of glaciers. When ice shelves are lost, glaciers flow freely into the ocean, raising sea levels. The Larsen Ice Shelf is in West Antarctica, and it’s so long that researchers refer to its various sections as Larsen A, B, C, and D. In 2017, a giant chunk of Larsen C broke off and turned into one of the world’s largest icebergs. Called the A68 iceberg, it measured 2,240 square miles (5,800 square kilometers) at its peak.
The team was able to explore previously inaccessible areas of the seabed with an ROV and autonomous underwater vehicles (AUVs) in the wake of the ice shelf’s splitting. Their subsequent discovery of the fish nests indicates that the area hosts an unusual and vulnerable habitat vital to biodiversity with important ramifications for conservation, given that their study joins a host of other research supporting the proposal to formally designate the Weddell Sea as a Marine Protected Area.
More broadly, the paper represents further evidence that life finds a way even in the most inhospitable of regions.
