They have been living in a small area west of the Antarctic Peninsula for 780,000 years and were only recently discovered by researchers – Antarctic dragonfish of the previously unknown species Akarotaxis gouldae. However, the very slow-reproducing fish could be endangered by krill fishing in the region.
When the researchers discovered the new species, which they named Akarotaxis gouldae (Banded dragonfish), it was not in the wet lab of a research vessel as they examined a fresh catch, but rather in the comfort of their home lab, while describing specimens of the only previously known species of the genus Akarotaxis – Akarotaxis nudiceps – that had been collected years earlier. These larval-stage specimens originated from expeditions conducted between 2007 and 2018 and are housed in collections at the Virginia Institute of Marine Science (VIMS), the Oregon State University Ichthyology Collection, Yale University and the Muséum national d’Histoire naturelle in Paris.
It was only through genetic analyses and more detailed morphological examinations that the researchers realized they were not only looking at A. nudiceps, but also a second, previously unknown species, which is described in detail in a recent study published in the journal Zootaxa on August 30, 2024.
“There are two distinct bands on the sides of adult Akarotaxis gouldae that are not present on Akarotaxis nudiceps, so we were surprised that the species already existed in collections but had been previously overlooked,” says Andrew Corso, PhD student at VIMS and lead author of the study, describing the discovery in an institute press release. “In the world of fish taxonomy, it’s becoming common to distinguish species with genetics alone. Genetic testing is an extremely valuable tool, but our discovery highlights the importance of early life stage morphology and natural history collections like those at VIMS and other institutions.”
Enigmatic “dragons”
Although Antarctic dragonfish are important prey for penguins and other Antarctic species, they are poorly researched, and consequently, little is known about them. However, the capture locations of the museum specimens provide some insight into their distribution.
The species A. nudiceps, known since 1916, has been caught in the Bellingshausen Sea, the Weddell Sea, the Lazarev Sea, and the Ross Sea, indicating a circumpolar distribution over the Antarctic continental shelf. In contrast, the distribution of the newly described A. gouldae appears to be much more limited: both larvae and adult specimens have so far only been found in a roughly 400-kilometer-long strip along the western Antarctic Peninsula.
Both species live at similar depths: Adult individuals of A. gouldae were caught between 600 and 705 meters depth, the larvae are somewhat more widespread in the water column at depths between 215 and 964 meters. Adult A. nudiceps have been found at depths between 103 and 1191 meters.
According to estimates by the research team, the evolution of A. gouldae as a distinct species began around 780,000 years ago, at a time when the Antarctic Ice Sheet covered the Southern Ocean.
“This process [time-calibrated phylogeny, editor’s note] essentially looks at the rate of genetic mutations as a guide for a species’ evolutionary history,” explains Corso. “We hypothesize that a population of dragonfishes may have become isolated within deep trenches under glaciers, surviving on food pushed in by the moving ice. Once the glaciers retreated, this subpopulation had become distinct enough to be reproductively incompatible with Akarotaxis nudiceps.”
Just discovered and already threatened?
The research team also analyzed the ovaries of the fish and found that the fertility of A. gouldae is relatively low, meaning the species produces few offspring. Furthermore, its known range overlaps with a prime fishing area for krill, raising concerns that larvae and juvenile fish could end up as bycatch in krill nets—an unfortunate outlook for a species that has only just been discovered and may be endemic to the region.
“Acarotaxis gouldae appear to have one of the smallest ranges of any fish endemic to the Southern Ocean,” says Corso. “This limited range combined with their low reproductive capacity and the presence of early life stages in shallower waters suggest that this is a vulnerable species that could be impacted by the krill fishery.”
The authors therefore suggest, especially in light of the increasing threat of climate change, “that the exceptionally high prevalence of larval A. gouldae sp. nov. and other notothenioid larvae during the austral summer near the coastal wAP region be considered as CCAMLR [Convention on the Conservation of Antarctic Marine Living Resources, editor’s note] continues to develop seasonal and regional closures for the krill fishery”.
“Since we know so little about the biodiversity of this area, we feel caution should be taken in extracting resources until we have a better understanding of the impact to the greater ecosystem,” Corso says.
Julia Hager, Polar Journal AG
More about this topic:
