Midnight Feast: The Secret Jellyfish Dinners of the Arctic Depths

First observation of marine invertebratesInvertebrates are animals that do not have a backbone. They make up the majority of the animal kingdom and include animals such as insects, worms, mollusks, and arachnids. Invertebrates are found in almost every habitat on Earth, from the depths of the oceans to the highest mountains. They play important roles in the ecosystem as decomposers, pollinators, and as a food source for other animals. Invertebrates have a wide range of body shapes, sizes, and behaviors, and they have evolved a variety of ways to survive and thrive in their environments.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>invertebrates eating live and dead jellyfish during Arctic winter.

In the dark and cold of the months-long polar night, food resources are limited. Some groups of marine organisms in the polar regions overcome this challenge by going into a metabolic resting state in winter, surviving on reserves accumulated during the short growth season. But others, such as several speciesA species is a group of living organisms that share a set of common characteristics and are able to breed and produce fertile offspring. The concept of a species is important in biology as it is used to classify and organize the diversity of life. There are different ways to define a species, but the most widely accepted one is the biological species concept, which defines a species as a group of organisms that can interbreed and produce viable offspring in nature. This definition is widely used in evolutionary biology and ecology to identify and classify living organisms.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>species of marine zooplankton, have evolved a different strategy: they shift from a specialized to an omnivorous diet during the polar night, profiting from a wide range of potentially less rewarding foods that are available throughout the year.

Now, scientists have shown that one key source of food for such seasonal Arctic omnivores has been overlooked until now: dead and living jellyfish. The results are published in Frontiers in Marine Science.

Pink helmet jellyfish, a hydrozoan. Credit: C. Havermans

“Here we show for the first time that jellyfish – thought to be typically poor in nutrients – are nevertheless an important food source for amphipods during the Arctic polar night,” said Annkathrin Dischereit, a doctoral student at the Alfred Wegener Institute in Germany, and the article’s first author.

“For example, we found evidence that some amphipods feast on ‘jelly-falls’, naturally sunken jellyfish carcasses. Other species may also prey on living jellyfish.”

Ctenophore or comb jelly. Credit: C. Havermans

Research Expedition and Findings

In January and February 2022, Dischereit and others from the Helmholtz Young Investigator Group ARJEL at the Alfred Wegener Institute took part in an expedition to the German-French AWIPEV research station on Svalbard.

Venturing out in a small boat from Kongsfjorden, Svalbard, the researchers found its waters to be teeming with jellyfish: not just ‘true jellyfish’ like the lion’s mane jellyfish, but also hydrozoans like the thimble-shaped pink helmet jellyfish, colonial siphonophores, and unrelated comb jellies or ctenophores.

The researchers sampled the local amphipods – crustaceans between five and 20 millimeters long – with nets and baited traps. They had chosen to focus on amphipods because they are locally abundant and important components of the fjord systems. The catch mainly consisted of four species: Orchomenella minuta and Anonyx sarsi, scavenging amphipods in the superfamily Lysianassoidea, and two distantly related Gammarus species.

DNA Metabarcoding of Ingested Prey

The researchers dissected the guts out of each amphipod, and then used DNADNA, or deoxyribonucleic acid, is a molecule composed of two long strands of nucleotides that coil around each other to form a double helix. It is the hereditary material in humans and almost all other organisms that carries genetic instructions for development, functioning, growth, and reproduction. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>DNA metabarcoding to identify the remains of prey within.

Jellyfish DNA from multiple species predominated in the guts of both Gammarus species, together with traces from algae and crustaceans. Jellyfish DNA was likewise found, but less abundant, in A. sarsi and O. minuta, proving that all four species studied routinely consume jellyfish tissue. The authors conclude that A. sarsi and O. minuta seem to opportunistically feed on jelly-falls, while both Gammarus may in addition prey on live comb jellies.

The French-German AWIPEV research station on Svalbard, where the research was done. Credit: E-Horvath (AWI)

Fish – living or dead – were likewise important food for both A. sarsi and O. minuta, together with polychaete worms, crustaceans, and mollusks.

Dischereit et al. also found that between 27% and 60% of the sampled amphipods had empty guts. This confirms that food scarcity and starvation are a challenge to marine invertebrates during the polar night, even for species that can shift to a more omnivorous diet.

Sampling marine organisms with handnets on Svalbard. Credit: E Horvath (AWI)

Paradigm Shift on Jellyfish

“There has been a recent paradigm shift in the marine biology literature that recognizes that far from being a ‘trophic dead-end’, jellyfish are in fact eaten by a wide range of organisms. Our observations corroborate this major change in how scientists view the role of jellyfish in the food web,” said Dr Charlotte Havermans, the leader of the 2022 expedition and the study’s last author.

“Because jellyfish tissue is quickly digested, they may have been overlooked as a prey item in previous studies, which unlike our study relied on visual identification of food items to determine the diet of Arctic invertebrates.”

The scientists at the AWIPEV research station on Svalbard. Credit: G. Tran

‘Atlantification’ and the New Arctic

Today, the Arctic is warming at a record rate compared to the rest of the world, and jellyfish species from the Atlantic Ocean have been observed to spread northward. This ‘Atlantification’ may make jellyfish even more important as a resource within Arctic food webs.

“To get a better idea of the role of jellyfish in the Arctic marine food web, and how this may change when their populations increase in the ‘new Arctic’, we plan to further investigate the diet of other invertebrates and fish that potentially feed on jellyfish. Questions remain, for example, whether jellyfish are a regular part of the diet of amphipods or whether they are simply a survival food during the polar night,” concluded Dischereit.

Inventorizing catch from baited traps. Credit: C. Havermans

Reference: “DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey” by Annkathrin Dischereit, Jan Beermann, Benoit Lebreton, Owen S. Wangensteen, Stefan Neuhaus and Charlotte Havermans, 9 January 2024, Frontiers in Marine Science.
DOI: 10.3389/fmars.2024.1327650