Researchers announced the discovery of a massive population of icefish (notothenioid) in the Weddell Sea south of Antarctica in the journal Current Biology on January 13.
The research team estimates that the icefish population spans at least 240 km2 and includes approximately 60 million active nests. This unprecedented large population has a biomass exceeding 60,000 tons.
Icefish guarding eggs in their nests. (Photo: Autun Purser).
“The most significant finding is the existence of such a large breeding population of icefish,” said researcher Autun Purser from the Alfred Wegener Institute in Bremerhaven, Germany. “We have observed dozens of nests in other parts of Antarctica, but this discovery is on a scale many times larger.”
Purser and colleagues discovered the icefish population while surveying the Filchner Ice Shelf using the Ocean Floor Observation and Bathymetric System (OFOBS). Essentially, this is a large device weighing one ton. The research team towed the device behind the RV Polarstern icebreaker at a speed of 4 km/h, at a height of 1.5 – 2.5 m above the seafloor to film and collect bathymetric data using sonar.
Scientists are particularly interested in the seafloor in this region because they know there is a warm upwelling current that is over 2 degrees Celsius warmer than the surrounding water. However, the new discovery is beyond their expectations. Purser’s team did not think there was any fish nesting ecosystem in the area.
The majority of nests they found had one adult fish guarding more than 1,700 eggs. They also observed many dead fish within and near the nesting population, indicating that this species plays a significant role in the larger food web. While further research is needed, Purser and colleagues speculate that the icefish population serves as a food source for predators like Weddell seals.
“Many Weddell seals spend a significant amount of time near the fish nests. We know this from old and new tracking data from our ship. The nests are located precisely in the warm upwelling waters. It could be a coincidence and requires further study, but the seal data indicates they dive to the depth of the fish nests and prey on icefish,” Purser noted.
This discovery reveals a unique ecosystem, providing additional data to establish a marine protected area in the Southern Ocean. The research team is deploying two camera systems to monitor the icefish nests until the research vessel returns. They hope to capture images multiple times a day, further understanding the mechanisms of the newly discovered ecosystem. Purser shared that he plans to return in April 2022 to survey the seafloor in areas north of the Weddell Sea.
