In recent times, heat, salty water from the Atlantic has more and more discovered its method into the European Arctic. The Norwegian archipelago of Svalbard can also be below the affect of this “Atlantification”: the Kongsfjorden on the west coast has switched to an Atlantic regime; the water temperature in the course of the polar evening (November to February) is growing by round 2 levels Celsius per decade. These adjustments additionally result in biotic shifts, as species from hotter waters additionally move into the Arctic together with the nice and cozy Atlantic water. “Some jellyfish species specifically are likely to unfold poleward and into the Arctic,” says Charlotte Havermans, head of the ARJEL junior analysis group on the Alfred Wegener Institute, Helmholtz Heart for Polar and Marine Analysis (AWI). ” Once we have been in Kongsfjorden within the Polar Night time in 2022, we have been very stunned to see the fjord teeming with jellyfish life, consisting of many alternative species and life phases, and so they gave the impression to be the dominant zooplankton in winter time.”

Prior to now, jellyfish have been thought of a trophic useless finish in marine meals webs, however current research counsel that they’re an necessary prey for marine invertebrates and fish. “Due to this fact, we puzzled whether or not the jellyfish in Kongsfjorden additionally function meals for different organisms, particularly in the course of the darkish season of the polar evening when different meals sources are restricted,” says Havermans. To reply this query, one of many staff’s PhD college students, Annkathrin Dischereit, analysed the abdomen contents of varied amphipod species. For a month, they recurrently collected samples from 4 completely different amphipod species (Gammarus oceanicus, G. setosus, Orchomenella minuta and Anonyx sarsi) in the course of the polar evening, utilizing baited traps and hand nets.

Jellyfish are an integral a part of the food plan of amphipods in the course of the polar evening

The AWI researchers used DNA-metabarcoding to find out the meals spectrum of the small crustaceans. This cutting-edge technique can detect brief gene fragments within the abdomen, that are then in contrast with genetic reference databases to establish the prey species to which the fragments belong. “We discovered numerous jellyfish within the stomachs of the amphipods, from the biggest jellyfish within the fjord to tiny hydrozoans,” explains Charlotte Havermans. Utilizing DNA metabarcoding, the AWI staff was in a position to establish and categorise the tender elements of jellyfish and different organisms that had been consumed, even when they have been already closely digested. “We have been in a position to show for the primary time that amphipod scavengers feed on the stays of jellyfish. This had beforehand solely been proven in experimental environments.”

All of the species studied consumed each plant and animal matter. Along with jellyfish, crustaceans and macroalgae have been different necessary parts of the food plan of some species, whereas fish species such because the polar cod or snailfish performed an necessary function for different species. Whether or not the amphipods consumed eggs, larvae, carrion or feces of fish stays to be clarified. What additionally stays to be decided, is whether or not jellyfish act as a survival meals in winter, or are a part of the common prey of those organisms in all seasons. “We have now all the time assumed that the dietary worth of jellyfish is low, however this has solely been investigated for lower than a handful of species, and likewise depends upon the tissues which might be utilized.”

The research offers utterly new insights into the Arctic meals net in the course of the polar evening and are the primary pure, non-experimental proof for the function of jellyfish in these webs. “The thriving, numerous jellyfish group that happens in Kongsfjorden in winter is clearly used as a meals supply,” Charlotte Havermans summarises the outcomes. “Till now, we knew nothing in regards to the function of jellyfish as prey on this space. It was additionally not recognized that the species Gammaridea, for instance, feeds on jellyfish in any respect, not within the Arctic, but in addition not elsewhere.” The query now arises as as to whether this solely applies to the polar evening, when the meals provide is restricted. The ARJEL junior analysis group at AWI needs to proceed researching this query. As a result of: “Jellyfish may very well be among the many winners of local weather change that may proceed to unfold in the course of the international warming. We have now additionally predicted that jellyfish will turn out to be extra frequent within the Arctic as temperatures proceed to rise,” says Havermans. Because of this, their function within the meals net might turn out to be more and more necessary. Till now, nonetheless, our understanding of this has been restricted, notably within the polar areas. “With this research, we reveal essential hyperlinks within the Arctic meals net that have been up to now not recognized. That is basic as a result of we have to perceive how jellyfish match into meals webs and unfold in an Arctic that’s altering quickly. This additionally applies to the neighboring shelf seas, as ten p.c of the world’s fisheries happen in these areas.”