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The Arctic is changing rapidly due to climate change. It’s affected not only by rising surface temperatures, but also by warmer Atlantic water, which is flowing more and more — changing the structure and function of ecosystems as it moves from warmer areas. Also leads to future generations, such as sea jellies (also known as jellyfish) arriving in the Arctic. Using DNA meta-barcoding, researchers at the Alfred Wagner Institute have now been able to demonstrate for the first time that these jellyfish serve as food for amphipods on Svalbard during the polar night and thus They play a more important role in Arctic food webs than previously thought. They presented their findings in a recent article in the scientific journal Frontiers in Marine Science.

In recent years, warm, salty water from the Atlantic Ocean has increasingly found its way into the European Arctic. The Norwegian peninsula of Svalbard is also under the influence of this “Atlantification”: Kongsjordan on the west coast has changed the regime of the Atlantic Ocean. During the polar night (November to February) the water temperature rises by about 2 degrees Celsius per decade. These changes also lead to biological changes, as species from warmer waters also flow into the Arctic with warmer Atlantic waters. “Certain jellyfish species are particularly prone to polar and arctic expansion,” says Charlotte Heuermans, head of the ARJEL Junior Research Group at the Alfred Wagner Institute, Helmholtz Center for Polar and Marine Research (AWI). “When we were in Kongs Fjord on Polar Night in 2022, we were amazed to see the fjord teeming with jellyfish life, including many different species and life stages, and it looked like they were wintering. are dominant zooplankton in the season.”

In the past, jellyfish were considered a trophic dead end in marine food webs, but recent studies have shown that they are important prey for marine invertebrates and fish. “So, we wondered if jellyfish in Kongsfjorden also serve as food for other organisms, especially during the dark season of the polar night when other food sources are limited,” says Heuermans. To answer this question, Annkathrin Dischereit, one of the team’s PhD students, analyzed the stomach contents of different amphipod species. For a month, they regularly collected samples from four different amphipod species (Gammarus oceanicus, G. Cytosis, Arcominella minta. And Anonymous Cersei) during the polar night, using traps and hand nets

Jellyfish are an essential part of the diet of amphipods during the polar night.

AWI researchers used DNA-metabarcoding to determine the food spectrum of small crustaceans. This innovative method can detect small gene fragments in the stomach, which are compared with genetic reference databases to identify the prey species to which the fragments belong. “We found a large number of jellyfish in the stomachs of the amphipods, from the largest jellyfish in the fjord to the smallest hydrozoans,” explains Charlotte Heuermans. Using DNA metabarcoding, the AWI team was able to identify and classify the soft parts of jellyfish and other organisms, even if they had already been heavily digested. “We were able to demonstrate for the first time that amphipod scavengers feed on jellyfish remains. This had previously only been shown in an experimental environment.”

All species studied feed on both plant and animal matter. In addition to jellyfish, crustaceans and macroalgae were other important components of the diet of some species, while fish such as polar cod or snailfish played an important role for other species. Whether amphipods feed on eggs, larvae, carrion or fish faeces remains to be elucidated. It also remains to be determined whether jellyfish serve as winter survival food, or are part of the regular prey of these organisms in all seasons. “We’ve always assumed that the nutritional value of jellyfish is low, but this has only been researched for less than a handful of species, and it also depends on the tissues that are used.”

This study provides entirely new insights into the Arctic food web during the polar night and is the first natural, non-experimental evidence of the role of jellyfish in these webs. “The flourishing, diverse jellyfish community found in Kongsfjorden in winter is clearly used as a food source,” said Charlotte Heuermans, summarizing the findings. “Until now, we knew nothing about the role of jellyfish predation in this region. It was not even known that the genus Gammaridea, for example, ate jellyfish at all, not in the Arctic, but Nowhere else.” Now the question arises, does this only apply to the polar night, when the food supply is limited? The ARJEL Junior Research Group at AWI wants to continue researching this question. Because: “Jellyfish may be among the winners of climate change that will continue to spread during global warming. We also predict that jellyfish will become more common in the Arctic as temperatures rise,” Heuermans said. say As a result, their role in the food web may become increasingly important. However, until now, our understanding of it has been limited, particularly in the polar regions. “With this study, we reveal important links in the Arctic food web that were not yet known. This is fundamental because we need to understand how jellyfish fit into food webs and spread in the Arctic. is changing rapidly. This also applies to the neighboring shelf seas, because ten percent of the world’s fisheries are in these areas.”

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