With temperatures hovering around minus 30 degrees, icy winds and the darkness of the polar night: winter is not the most pleasant time to navigate around the coast of Spitsbergen in a small vessel. But that is exactly what a team headed up by Prof. Charlotte Havermans and Dr. Ayla Murray from the Alfred Wegener Institute undertook in the winter of 2022. In Kongsfjord, in the west of the archipelago, the researchers took water and sediment samples and then assigned the DNA they contained to various marine organisms. This enabled them – for the first time - to gain an overview of what goes on in these Arctic waters during the polar night. And that is an astonishing amount, as the team reports in a new study in the journal Marine Environmental Research.
"It used to be a common belief that the polar night was a kind of resting phase for marine life, during which not much was going on," says Charlotte Havermans, biologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and professor at the University of Bremen. For about ten years, however, there have been growing indications that a rich and hitherto little-studied community is also active during the dark months. During the AWI-led MOSAiC expedition in 2019 and 2020, for example, video cameras captured numerous images of jellyfish wandering under the Arctic ice.
This is particularly exciting for Charlotte Havermans, given that, as head of the "Arctic Jellyfish" (ARJEL) junior research group, she studies so-called gelatinous plankton – jellyfish, comb jellies and tunicates, whose striking common feature is their jelly-like bodies. These sea creatures clearly do not take any winter breaks: far more, the large number of young animals in the water suggests that many species reproduce at this time of year – regardless of the darkness and cold. "So there is still a lot to discover about the ecology of the polar night," as the researcher comments. Reason enough for her to plan an expedition to Spitsbergen in the winter of 2022 and, for the first time, to examine the biological diversity of Kongsfjord using molecular methods at this time of year.
A conventional inventory using nets or other fishing gear, however, is extremely difficult to handle during the polar night given its harsh conditions. That is why the researchers have also opted for a relatively new method that is gaining increasing popularity in marine research. It is based on the fact that ocean dwellers leave genetic traces in the water or sediment. Their excrements and shed cells, their eggs and sperm, their mucous membranes and their dead bodies contain genetic material that can be isolated from corresponding samples. Experts can subsequently assign this environmental DNA, also known as eDNA for short, to the various species. In order to accomplish this, they use genes that have a slightly different sequence of DNA building blocks for each species of interest. Similar to the barcode on goods in the supermarket, this short, commonly used, sequence rapidly reveals which species is involved.
Such DNA barcoding is often much less time-consuming than identifying animals and plants based on their external characteristics. "What's more, we have to interfere far less with the ecosystem, as no animals are caught," emphasises Ayla Murray. "This is particularly significant when dealing with endangered or very sensitive species."
The latter include, for example, many jellyfish, which are often damaged in nets and then become almost impossible to distinguish visually. At the same time, eDNA analysis provides another advantage: while different nets are sometimes required to catch different species of jellyfish, their genetic traces can all be found in the same samples. All that is needed is to bottle six litres of water at different locations and use small gripping instruments to collect ten grams of sediment from the seabed. "It's really amazing what we've found in these samples," as Ayla Murray enthuses.
The scientists identified the individual species using a gene called cytochrome c oxidase subunit 1 (COI), which serves as a barcode for many different marine organisms. With its help, the team was able to detect a total of 225 species in their samples – from tiny plankton organisms to the giant sperm whale. Many of these species were not even known to exist off Spitsbergen to date. This applies, for example, to the brown algae Dictyosiphon ekmanii and Saundersella doloresiae, the red algae Ahnfeltia borealis and Boreolithothamnion lemoineae, as well as the amphipod Lembos websteri and the krill Hansarsia megalops.
The 16 fish species whose DNA the researchers found were already known to inhabit the waters around the archipelago. The fact that halibut, Arctic char and small sand eels also swim in Kongsfjord during the polar night, however, is a decidedly new discovery. "We found an astonishing number of traces of vertebrates in our samples," says Charlotte Havermans. Seabirds such as the black guillemot have left their genetic fingerprints in the water, as have sperm whales, walruses and harbour seals.
The researchers are also more than satisfied with their new findings concerning the gelatinous plankton in Kongsfjorden in winter. They discovered a total of 19 species in their samples, plus three genera whose representatives could not be identified more precisely. In fact, this is a richer community than previous studies have shown, even in summer. Apparently, many species can be detected much more easily with the help of eDNA than with the methods commonly applied to date. This is also confirmed by the classic net catches that the team conducted in parallel with its genetic search: each of the two approaches captured a different part of the biological diversity, with only five species and genera being detected by both. "That's why we still need traditional investigations," as Charlotte Havermans emphasises - especially given that eDNA analyses do not yet reveal much about the abundance of individual species.
"By combining both methods, we have learned a lot of new things about the polar night in one of the most researched fjords in the Arctic," the researcher relates happily. "And there is still much more to discover!" To this end, she and her team are planning additional research trips to Spitsbergen in 2026. They advocate conducting more winter studies of this kind to shed even more light on the subject. The current findings could then serve as a foundation for comparisons tracking future changes in the species communities.
Like the rest of the far north, Kongsfjorden is also likely to undergo drastic changes as a result of rising temperatures. After all, the Arctic is warming around four times faster than the global average – and fjords are particularly sensitive to such changes. There are already indications that fish and other animals from the North Atlantic are increasingly migrating there. In addition, more and more species from other marine regions are being introduced in the ballast water of ships. And as warming advances, the easier it is for these new arrivals to establish themselves. Meanwhile, many native polar inhabitants are likely to lose their habitats due to climate change. "eDNA analysis is very well suited as an early warning system for such worrying shifts and changes in the Arctic," says Ayla Murray. "We urgently need to find out more about this sensitive ecosystem so that we can protect it better."
Original publication:
Ayla Murray, Adria Antich, Annkathrin Dischereit, Luisa Düsedau, Clara J.M. Hoppe, Charlotte Havermans: Surveying marine biodiversity using eDNA metabarcoding of seawater and sediment in a high Arctic fjord during the polar night (Kongsfjorden, Svalbard), Marine Environmental Research (2025). DOI: https://doi.org/10.1016/j.marenvres.2025.107443