Scientists Find a Hidden 'Fish City' Beneath Antarctica's Ice

In 2017, a gigantic iceberg designated A-68 split from the Larsen C ice shelf, giving scientists a unique opportunity: access to an extensive region of the seabed that had previously been hidden away under the ice. Researchers from institutions in the UK seized that opportunity and discovered something that's never been seen before, which they have reported in a study published in Frontiers in Marine Science. Via a remote submersible camera, the researchers found more than a thousand fish nests – carefully cleared patches in the plankton detritus at the bottom of the ocean. It wasn't just the discovery of the nests that was remarkable – it was how they were arranged. This structured ecosystem is being presented as further evidence in the case for making this part of the Weddell Sea a Marine Protected Area. "This study documents a large and widely dispersed nesting aggregation of the yellowfin notothenioid, Lindbergichthys nudifrons, in the western Weddell Sea, an area made accessible by the recent calving of the Larsen C Ice Shelf," write the researchers in their published paper. "The most significant finding is the discovery of six distinct, geometric nesting patterns, which we propose are primarily driven by biotic interactions, namely predation pressure, rather than the abiotic factors observed in other large Antarctic fish breeding colonies." The icefish L. nudifrons, also known as the yellowfin notie, can grow up to 19.5 cm (7.7 inches), and was first identified as a species in 1905. Several thousand eggs can be laid in each of the fish's nests, which are then guarded by the males for up to four months. Besides studying underwater ecosystems, the Antarctica mission described in this study was also tasked with finding the wreck of Sir Ernest Shackleton's ship, Endurance, which sank in 1915 in the same region. While the wreck wasn't found this time (it was finally discovered in 2022), the fish nests were everywhere. "Nesting sites were found at all locations surveyed during the Weddell Sea Expedition 2019 onboard the SA Agulhas II using the remotely operated vehicle," write the researchers. The researchers identified six distinct patterns that the nests were arranged in on the seafloor, with the most common – accounting for 42 percent of all nests found – being the type designated as a cluster. In this pattern, the nests are tightly packed together, even touching and overlapping in some instances. Unlike many fish colony nests, these nests hadn't been put in warmer waters, suggesting temperature wasn't the reason for the clusters. The researchers think the nest groupings are related to protection. There's safety in numbers with multiple male fish patrolling the borders of the clusters, while the high concentration of nests might mask the smell of the fish eggs from certain predators by bunching together, creating a more confusing scent trail. "This would offer a significantly reduced risk to the nests in the center of the cluster," write the researchers. "Such defensive patterning, while novel for this species, is a well-documented phenomenon in fish nesting colonies in shallow tropical reef scenarios, where it is also attributed to increased predation protection." The place that the yellowfin notie has in the food chain means that the fish and its nest clusters are an integral part of the ecosystem in the Antarctic. Although the Weddell Sea region has proved a challenge to explore, as Shackleton and others have discovered, marine life is still thriving in the depths, making the need to have the area marked as a protected zone – for the fish and organisms that live under the waves as well as the more visible penguins and seals. Related: Antarctic Iceberg Breaks Away to Reveal a Never-Before-Seen Ecosystem "These findings provide critical evidence of unique, structured breeding habitats, fulfilling key criteria for the designation of Vulnerable Marine Ecosystems and strengthening the case for the proposed Weddell Sea Marine Protected Area," write the researchers. The research has been published in Frontiers in Marine Science. This article was fact-checked by Rachel Garner and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.