deep sea

Deep sea daycare: largest fish nursery discovered in the Weddell Sea

In February of 2021, a research vessel in the Weddell Sea of the Antarctic came across  a new discovery. Autun Purser, a deep sea biologist, and his colleagues from the Alfred Wegener Institute in Germany were aboard the vessel intending to study seafloor life using cameras towed below their ship the Polarstern. As they passed through an area under a shelf of ice called the Filchner Trough, one researcher noticed something interesting captured on camera: small, circular nests scattered on the ground. After hours of surveying with more nests appearing, they realized they had stumbled across something unexpected. The researchers completed three more surveys and each time found more nests, making it the largest colony of fish ever recorded. It belongs to a species called Jonah’s icefish (Neopagetopsis ionah), found in the Antarctic and Southern Ocean and adapted to survive in the extreme cold. Researchers are buzzing about the implications of what this discovery may mean for the future of the area and this species.

Hidden Nursery

Closeup of a nest on the seafloor guarded by Jonah’s icefish and multiple nests at a distance. Photographer: PS124 OFOBS TEAM

Many fish species are known to build elaborate nests for their eggs. The Corkwing Wrasse (Symphodus melops) uses seaweed, and Garibaldis (Hypsyops rubicundus) build their nests in red algae for years before brooding. The Jonah’s icefish constructs circular divots in the ground by moving sediment and fills them with carefully selected pebbles to lay their eggs on. Fish nest colonies are groups of fish nests made in the same area, usually for breeding and protection purposes. The Weddell Sea icefish colony is thousands of times larger than any previously recorded, stretching across the seafloor over 240 square kilometers (92 square miles). That means roughly 60 million nests are present, with around 16,000 of them being actively used when surveyed. These are guarded by adult icefish, vigilantly protecting eggs laid in quantities of over 1,700 per nest. The area seems to be a perfectly suitable environment for this nursery; water temperatures were found to be warmer than its surroundings and plankton is easily accessible as a food source for hatchlings.

Deep Discoveries

This amount of organic matter or biological activity in the Weddell Sea greatly impacts the surrounding food web and ecosystem. The sedimentary formation of the Filchner Trough itself is affected as roughly 1.2 million cubic meters of it was carefully excavated by the fish during their nest construction. The exposed gravelly layer provides a secure habitat for many sessile or immobile organisms like sponges or tube dwelling worms to exist. Fish and eggs from the nests provide a large food source for several organisms in the area including octopuses, brittle stars, bacteria, other fish, and the Wedell seal. 

Antarctic Treasure

Tabular iceberg in the Weddell Sea. Photographer: 66 North

Researchers speculate that most of the icefish population may come from this nursery, making it a vital part of the species survival. This important nursery also makes them much more vulnerable to extinction. If anything negatively impacts the area, like ocean warming or seafloor disturbances, the entirety of this species could be at risk. The discovery of these fish nest colonies provides more support for the efforts to establish the location as a Marine Protected Area under the Convention on the Conservation of Antarctic Marine Living Resources. This act seeks to conserve unique and vital ecosystems, like this one, that are essential for the ocean’s stability and the existence of vulnerable species. Researchers still have many questions about the implications of this breeding ground and the life of the Jonah’s icefish. Purser and his team placed a few cameras on the seafloor to monitor activity and see if the nests are reused in the following years. It is likely this hotspot will reveal valuable new information about the importance of life on the seafloor and the health of the Antarctic ecosystem. For now, this surprise discovery brings a sense of excitement and wonder for the deep-sea research community and ocean enthusiasts everywhere.


Purser, A., Hehemann, L., Boehringer, L., Tippenhauer, S., Wege, M., Bornemann, H., … & Wenzhoefer, F. (2022). A vast icefish breeding colony discovered in the Antarctic. Current Biology.

Quignard, J.-P. and A. Pras, 1986. Labridae. p. 919-942. In P.J.P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen and E. Tortonese (eds.) Fishes of the north-eastern Atlantic and the Mediterranean. UNESCO, Paris. Vol. 2. (Ref. 4742)

Froese, R. and D. Pauly. Editors. 2022.FishBase. World Wide Web electronic publication., ( 02/2022 )

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