Антарктидын далайн ёроолоос шар сэлүүрт загасны үүр бүхий геометрийн дүрсүүд илрүүлжээ

In January 2019, a remotely operated vehicle named Lassie descended into the Weddell Sea on five separate dives, collecting 27 hours of video while an expedition above searched in vain for the wreck of Ernest Shackleton’s Endurance. The ship wasn’t there.

What the cameras found instead, scattered across the seafloor at depths between 290 and 411 meters, were hundreds of small circular depressions, each conspicuously clear of the phytoplankton debris coating almost everything around them.

Researchers who later analyzed the footage have now published their findings in Frontiers in Marine Science. The depressions were fish nests, actively maintained by a small Antarctic species called the yellowfin notie (Lindbergichthys nudifrons).

Across the five survey sites, the team counted 1,036 active nests arranged in 277 groups, plus 93 abandoned ones. Stranger than the sheer number was the way they were laid out: the nests fell into six distinct geometric patterns, none previously documented for this species.

What the Sediment Revealed

Scientifically, the phytoplankton bloom that came before the dives proved useful. It had settled over the seafloor as a layer of flocculent material, covering inactive nests but missing from the active ones.

Adult fish were keeping their depressions clean.

That upkeep gave the researchers a dependable way to tell occupied sites from abandoned ones, even though the expedition happened after the species’ known hatching period in the Austral spring. No eggs were visible, and fish larvae appeared in or around 72 of the nests.

Throughout the footage, only L. nudifrons was seen occupying or tending the depressions, matching earlier published research on the species’ nesting habits. The nests averaged 12.3 centimeters across, slightly larger than the fish’s known maturation size of 9.1 to 9.5 centimeters. Sediment was usually piled along the sides of each depression. The fish, which reach a maximum adult length of about 19.5 centimeters, guard nests through a long incubation period that can run beyond 100 days.

Six geometric configurations emerged from the footage: clusters, meaning dense and shapeless groupings; crescents; lines; ovals; sharp U-shapes; and isolated singular nests.

Clusters dominated, accounting for about 42 percent of all active nests. Singular nests ranked second and were also the largest on average, a pattern the researchers suggest may reflect larger, older individuals capable of defending nests without neighbors.

Group Geometry as Defense

Rather than a preference for particular water temperatures or sediment chemistry, the authors favor predation pressure as the explanation for why these fish arrange their nests in geometric groups. Across four of the five sites, temperatures at nesting locations did not differ significantly from the surrounding seafloor.

Ambient water across the survey area ranged from roughly -2.09°C to -1.1°C. One site did show a slight local temperature difference of about 0.2°C at nesting spots, but the authors say the overlap across sites is too large to treat temperature as a meaningful driver of where nests appear.

The cluster pattern fits especially well with what biologists call the selfish herd principle: individuals reduce their exposure to predators by putting others between themselves and an approaching threat. Nests buried inside a cluster, the researchers propose, gain protection from neighbors on every side.

The same logic may explain why lines were relatively scarce, since nests at either end are less protected than those in the middle. Singular nests point toward another strategy altogether: larger individuals able to defend territory alone.

Two plausible predators appear near the nesting sites. Brittle stars were perched on nest rims in 35 percent of cases, consistent with scavenging behavior documented elsewhere in Antarctica. The predatory ribbon worm Parborlasia corrugatus was also present, and because it hunts using chemical detection, the authors suggest that densely grouped nests may blur the odor signals from individual egg batches.

A Seafloor That Was Off-Limits Until 2017

Reaching the survey area had been difficult or impossible until the A68 iceberg, covering roughly 5,800 square kilometers, broke away from the Larsen C Ice Shelf in 2017.

The calving exposed seafloor that had spent very different lengths of time beneath the ice: one site had been clear for five to ten years, another for fifteen to eighteen years, and a third for around fifty years. A fourth site had apparently remained free of ice cover across geological history. Yet the researchers found no relationship between the length of ice-free exposure and any measurable feature of the nests.

Nests, however, appeared at all five surveyed locations rather than bunching into one patch of favorable habitat.

The densest single location, designated Site E, held 461 individual active nests. Site D, the other high-count location, contained 151 nesting groups with a mean of 2.3 nests per group.

Conservation Stakes

The discovery bears directly on an ongoing policy discussion. The Commission for the Conservation of Antarctic Marine Living Resources has long been working toward a Weddell Sea Marine Protected Area, a designation proposed but still not finalized.

At its 43rd meeting, the Antarctic and Southern Ocean Coalition specified that clear video evidence of fish nesting sites is a prerequisite for establishing a conservation measure. Footage from the 2019 expedition supplies that evidence for a breeding habitat that, before the Larsen C calving, was largely inaccessible.

According to the paper, the nesting aggregations meet published criteria for designation as a Vulnerable Marine Ecosystem, a classification used under FAO guidelines to flag sensitive deep-sea habitats vulnerable to damage from bottom fisheries. The authors describe the findings as direct support for the proposed protection area, noting that spawning and nesting grounds are also recognized as ecologically significant under the Convention on Biological Diversity.

One uncertainty remains.

Because no fish was present at every nest during filming, the team cannot rule out a small number having been built by other Antarctic fish species in the same evolutionary group. Visual species identification from ROV footage has inherent limits, and recent genetic work has found that species-level distinctions within this fish group can be difficult to confirm from appearance alone.

The nesting sites documented here lie between 290 and 411 meters deep, far above the 3,008-meter depth where Endurance was ultimately located by a later expedition in March 2022.

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