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It’s an often repeated fact that we know less about the ocean floor than we do about the surface of the Moon, but that doesn’t make it any less surprising when ocean scientists stumble across unprecedented scenes under the sea. Once such wonder emerged beneath the Filchner Ice Shelf in the south of the Antarctic Weddell Sea recently, where a research team discovered the world's largest fish breeding area known to date.
Announced in the journal Cell, the discovery was facilitated by a towed camera system led by the German research vessel Polarstern, which papped the Glastonbury of nesting grounds belonging to the icefish species Neopagetopsis ionah. Stretching across a section of the seabed roughly the size of Malta, the nesting ground had on average one breeding site per 3 square meters (32.3 square feet). That's one hell of a crèche.
Icefish are pretty spicy as ocean critters go, evolving to have a protein-based antifreeze in their blood (which is white and near-see-through, by the way). It’s the only known vertebrate that lacks red blood cells containing hemoglobin, which is what makes our life juice so richly red.
Estimates from the Polarstern's observations put the population of the nesting ground at around 60 million, demonstrating that the area is a vital one for the species and a marine environment worthy of protection. A proposal to establish a Marine Protected Area here has been under consideration since 2016 by the European Union and the international Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) but has not yet come to fruition.
"The idea that such a huge breeding area of icefish in the Weddell Sea was previously undiscovered is totally fascinating," said lead author Autun Purser, deep-sea biologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), in a statement.
Purser’s sentiments are easy to comprehend when you realize that the AWI has been scanning this particular stretch of the Weddell Sea for the past 40 years, in which time only small clusters of icefish breeding sites were found. So, why here? Using oceanographic and biological data, the team behind the discovery was able to establish that the breeding site bonanza coincided with an inflow of warmer deep water from the Weddell Sea that swoops up onto the nesting ground shelf.
With each active nest containing between 1,000-2,000 eggs and many adults hanging around to protect them, it’s estimated the biomass of the colony equates to around 60 thousand tons. This would explain why the resource-rich area is also such a hotspot for hungry Weddell seals (which make really cool spaceship sounds).
The impressive nesting site, therefore, tops the charts for significant breeding sites, being perhaps the most spatially extensive contiguous fish breeding colony ever recorded on Earth. As such, it constitutes a pretty solid argument for the establishment of a Marine Protected Area (MPA).
The non-invasive technology that facilitated the discovery was developed by a team including AWI Director and deep-sea biologist Professor Antje Boetius — who was not directly involved in the nesting ground discovery — and enabled the Polarstern crew to observe the ecosystem without disturbing it.
“Considering how little known the Antarctic Weddell Sea is, this underlines all the more the need of international efforts to establish a Marine Protected Area (MPA),” said Boetius. “Unfortunately, the Weddell Sea MPA has still not yet been adopted unanimously by CCAMLR. But now that the location of this extraordinary breeding colony is known, Germany and other CCAMLR members should ensure that no fishing and only non-invasive research takes place there in future.”
