A study published last month shows that jellyfish may be a far more important source of food than previously thought. A discovery that could well call into question some of our knowledge of the Arctic food chain.
Jellyfish are organisms with watery, fragile and often transparent bodies. Their gelatinous appearance and ability to defend themselves by inflicting particularly painful wounds make them a less-than-popular animal to the general public. Yet jellyfish play an important role in the marine ecosystem, particularly as food for predators such as fish.
In the Arctic seas, jellyfish, along with the whole range of gelatinous zooplankton that also includes siphonophores, ctenaria and pelagic tunicates, constitute a source of food that was previously thought to be rather marginal. However, a study published on 14 August in the journal Royal Society Open Science seems to prove otherwise.
Conducted by scientists from the prestigious Alfred Wegener Institute (AWI) and Thünen Institute, the study found that fish feed extensively on these invertebrates. At least, that’s the conclusion of the researchers, who analyzed the stomach contents of seven species of Arctic fish caught in Greenlandic waters. “We detected up to 59 species of gelatinous invertebrates in the stomachs of the fish. This clearly shows that they play a significant but previously overlooked role in the subarctic food web.”, says Annkathrin Dischereit, PhD student at AWI and lead author of the study, in a press release published on 14 August on the AWI website.
For a long time, it was thought that fish disdained jellyfish and other gelatinous organisms, feeding on them only in emergency situations. However, this is not the case. In the seven species of fish studied, jellyfish and gelatinous zooplankton were found in varying quantities in the stomachs. Or rather, their DNA.
Thanks to the DNA metabarcoding technique, the research team was able to trace these invertebrates in the digestive system: “Their watery nature and delicate tissues are quickly digested in predators’ stomachs, which is why their contribution to predators’ diets is frequently overlooked using conventional (microscopy) stomach analyses.”, the authors state in their study.
More rapidly digestible, easy to hunt, available in large numbers and energetically interesting, gelatinous zooplankton have the potential to feed predators at lower cost. A discovery that could well call into question the role of these organisms in the Arctic food chain and the impact of the presence of these invertebrates, currently on the increase due to global warming.
With its jellyfish-rich waters, Greenland’s invertebrate populations are not only growing but also moving northwards, increasing the abundance of jellyfish in Arctic waters.
Jellyfish are one of the species on which climate change is having a rather positive impact. They proliferate in marine environments that are becoming warmer, softer and more acidic. But in addition to their numbers, it is their importance in the diet of other species that should make us reconsider our knowledge: “The results of our current study raise doubts about how well we understand subpolar ecosystems and how the recently observed increase in gelatinous zooplankton might affect them.”, notes Charlotte Haverman, head of the ARJEL junior research group at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), in the AWI press release.
An ubiquitous animal in the world’s waters, jellyfish are found in all the world’s oceans and at all depths, from the epipelagic zone to the deep sea. Their proliferation in many marine ecosystems has given rise to the term “ocean jellification”, a phenomenon that can cause problems: fishing, tourism or even human infrastructures obstructed by gelatinous masses, these profusions of invertebrates are rarely viewed positively.
Similarly, their increasing numbers can lead to competition with other fish for the same food. A real problem when species are already under stress from heavy fishing in certain regions.
Mirjana Binggeli, Polar Journal AG
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