The Arctic is changing rapidly due to climate change. It is not only affected by increasing surface temperatures, but also by warm water from the Atlantic, which is flowing in more and more – changing the structures and functions of the ecosystem as it also leads to species from warmer regions, like jellyfish, arriving in the Arctic. Using DNA metabarcoding, researchers from the Alfred Wegener Institute have now been able to prove for the first time that these jellyfish serve as food for amphipods on Svalbard during the polar night and thus play a greater role in Arctic food webs than previously assumed. They present their findings in a recent article in the journal Frontiers in Marine Science (doi: 10.3389/fmars.2024.1327650).
In recent years, warm, salty water from the Atlantic has increasingly found its way into the European Arctic. The Norwegian archipelago of Svalbard is also under the influence of this "Atlantification": the Kongsfjorden on the west coast has switched to an Atlantic regime; the water temperature during the polar night (November to February) is increasing by around 2 degrees Celsius per decade. These changes also lead to biotic shifts, as species from warmer waters also flow into the Arctic along with the warm Atlantic water. "Some jellyfish species in particular tend to spread poleward and into the Arctic," says Charlotte Havermans, head of the ARJEL junior research group at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI). " When we were in Kongsfjorden in the Polar Night in 2022, we were very surprised to see the fjord teeming with jellyfish life, consisting of many different species and life stages, and they seemed to be the dominant zooplankton in winter time."
In the past, jellyfish were considered a trophic dead end in marine food webs, but recent studies suggest that they are an important prey for marine invertebrates and fish. "Therefore, we wondered whether the 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 Havermans. To answer this question, one of the team’s PhD students, Annkathrin Dischereit, analysed the stomach contents of various amphipod species. For a month, they regularly collected samples from four different amphipod species (Gammarus oceanicus, G. setosus, Orchomenella minuta and Anonyx sarsi) during the polar night, using baited traps and hand nets.
Jellyfish are an integral part of the diet of amphipods during the polar night
The AWI researchers used DNA-metabarcoding to determine the food spectrum of the small crustaceans. This cutting-edge method can detect short gene fragments in the stomach, which are then 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 tiny hydrozoans," explains Charlotte Havermans. Using DNA metabarcoding, the AWI team was able to identify and categorise the soft parts of jellyfish and other organisms that had been consumed, even if they were already heavily digested. "We were able to prove for the first time that amphipod scavengers feed on the remains of jellyfish. This had previously only been shown in experimental environments." All the species studied fed 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 species such as the polar cod or snailfish played an important role for other species. Whether the amphipods fed on eggs, larvae, carrion or feces of fish remains to be clarified. What also remains to be determined, is whether jellyfish act as a survival food in winter, or are part of the regular prey of these organisms in all seasons. “We have always assumed that the nutritional value of jellyfish is low, but this has only been investigated for less than a handful of species, and also depends on the tissues that are utilized.”
Original publication
Dischereit A, Beermann J, Lebreton B, Wangensteen OS, Neuhaus S and Havermans C (2024) DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey. Frontiers in Marine Science. doi: 10.3389/fmars.2024.1327650
