Saturday, April 11, 2026

Unexpected predator: Jellyfish shown to hunt polychaete worms

University of Southern Denmark

fig 1b — image:
The researchers found one and sometimes two polychaete inside a jellyfish. This *aurelia aurita* jellyfish has two worms in its gut. Photo: Hannah Yeo/SDU.
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Credit: Hannah Yeo/SDU

Most polychaete species spend their lives in burrows in the seabed. However, adult individuals of two species, Alitta succinea and Platynereis dumerilii, leave their burrows to spawn during warm summer nights around full moon.

The worms swarm with thousands of individuals swimming simultaneously in the open water. During this journey their bodies rupture while releasing eggs and sperm before they die. They are a luxury diet for many carnivores and are snapped up by trout and other predatory fish. And now University of Southern Denmark (SDU) biologists have shown that certain jellyfish also capture and eat the swarming polychaetes.

“Although jellyfish are known to be omnivorous and generally consume whatever they encounter, it is the first time, this behaviour is documented,” says one of the researchers behind the discovery, biologist and postdoc Hannah Yeo from SDU’s Marine Biology Research Centre in Kerteminde, Denmark.

The team behind the discovery also includes biologists Laura Ferreira (SDU and University of Copenhagen), Erik Kristensen (SDU), Anders Garm (UCPH) and Jamileh Javidpour (SDU). Their findings have been published in the scientific journal Hydrobiologia.

Over the course of a year, the researchers recorded 56 cases where a jellyfish contained at least one polychaetes in their gut. The worms were found in two jellyfish species: the common moon jelly Aurelia aurita and the invasive comb jelly Mnemiopsis leidyi. The most common polychaete species recorded was Platynereis dumerilii.

All observations were made in Kerteminde Fjord and the nearby Kertinge Nor in Denmark. Among the 166 collected Aurelia aurita, 45 individuals contained at least one polychaete. Among the 71 Mnemiopsis leidyi, three contained at least one Polychaete.

Digested in a few hours

The actual number is likely higher, the researchers say.

“It takes only a couple of hours for the jellyfish to digest these worms, so there were probably more cases than the ones we observed,” says co-author, Professor Erik Kristensen from Department of Biology, University of Southern Denmark.

To confirm that the worms served as actual nutrition – and weren’t ingested by accident – the researchers performed isotope analyses on the jellyfish tissue. These showed that nutrients from the worms were absorbed by the jellyfish rather than simply passing through.

In the bigger picture, polychaetes are probably not a major food source for jellyfish, but they do represent a concentrated seasonal burst of energy in summer that may help jellyfish thrive.

For the invasive Mnemiopsis leidyi, this is more concerning, the researchers note – precisely because its invasive nature makes any newly documented feeding behaviour a potential ecological concern.

“We suspect that Mnemiopsis consumed more worms than we could detect. They also hunt at night, which is exactly when the worms swarm. By the time we sampled them in daylight, the worms would have been fully digested and impossible for us to see,” says co-author Jamileh Javidpour, associate professor at Department of Biology, SDU, “Mnemiopsis are invasive and unwanted in Danish waters because they can outcompete native species. They are highly opportunistic feeders, and this appears to be yet another food source they are able to exploit.”

The discovery not only sheds new light on jellyfish feeding behaviour but also reveals a previously overlooked exchange of energy between the seafloor and the water column. Typically, this flow is seen as one‑way: organic material sinks down to bottom‑dwelling animals – such as dead polychaetes after spawning.

“But here we see energy moving upward instead: bottom‑dwelling animals rising into the water column and being hunted there. While several predator species are known to exploit these spawning events, it has not been documented before in jellyfish or Mnemiopsis. This means gelatinous zooplankton are tapping into a benthic energy source that has been largely overlooked”, said Jamileh Javidpour, concluding:

“We need to consider this upward transfer when modelling the resilience of coastal ecosystems. Even sporadic access to benthic resources may influence how both native and invasive gelatinous species compete and persist.”

Journal

Hydrobiologia

Method of Research

Observational study

Subject of Research

Animals

Article Title

Polychaete capture by native jellyfish and invasive ctenophore reveals a novel benthic–pelagic trophic link

This species of polychaete, Alitta succinea, was one of two species found in the gut of jellyfish. Photo: Erik Kristensen/SDU.

Credit

Erik Kristensen/SDU

A bacterium from bumblebees can produce vitamin B2 in soya drinks

Researchers at DTU have developed a new method that can reduce the time needed to find new bacteria for fermentation. They have now identified a bacterium that can be used both for acidification and to increase the vitamin B2 content of soya drinks.

Technical University of Denmark

Droplet Cultivation — image:
Each tiny droplet (the round grey circles) contains a single bacterial cell, which grows and develops its own distinctive appearance over time (the small dots inside the droplets). By forming thousands of these microscopic droplets, researchers can cultivate and study many microorganisms in parallel at the single-cell level, revealing hidden microbial diversity and helping to discover rare bacterial strains. Photo: Hang Xiao
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Credit: Photo: Hang Xiao

A new method developed by researchers at the DTU National Food Institute can speed up the process of identifying bacteria that can be used both for fermentation and to increase the vitamin B2 content in soya drinks. In the study, the microbiome (the complete bacterial community) from bumblebees was examined and tested in microscopic droplets for its ability to produce vitamin B2.

“Our research shows that it is possible to screen entire microbial communities directly and rapidly, and that promising bacteria can be identified from environmental samples without prior isolation and analysis of individual bacteria. This can make the development of new starter cultures faster and more targeted,” says Associate Professor Claus Heiner Bang-Berthelsen from the DTU National Food Institute.

The research has been published in the scientific journal LWT – Food Science and Technology.

Researchers have discovered promising bacteria in bumblebees

The study addresses a problem common to many plant-based dairy alternatives: they contain fewer vitamins and minerals than cow’s milk. One of the nutrients typically lacking is vitamin B2 (riboflavin).

The researchers therefore set out to quickly identify bacteria that could both thrive in soya drinks and produce vitamin B2 themselves during fermentation. They used bacteria from bumblebee guts as a starting point for screening potential vitamin B2-producing strains.

“Bumblebees live close to plants, and their guts contain many microorganisms that are already adapted to plant-based environments. That is why it was interesting for us to test whether we could find bacteria in bumblebees capable of producing vitamin B2 in soya drinks,” says Postdoc Hang Xiao from the DTU National Food Institute.

Tested the bacteria in microscopic droplets

In the study, the researchers applied an existing technology known as ‘droplet screening’ in a new way.

“Unlike conventional agar plate-based methods for microbial cultivation and screening, we encapsulated the bee gut bacteria in microscopic droplets so that each droplet contained only one bacterium and acted as an enclosed culture chamber. In this way, the individual bacterium could be analyzed at ultra-high speed by using our microfluidics screening platform, enabling us to screen millions of bacterial cells within just a few hours,” says Hang Xiao.

Ordinary soya drinks are often cloudy and full of particles, which can interfere with measurements. To make droplet screening compatible with soy-based drinks, the researchers developed a highly transparent soy medium.

“By making the soya liquid transparent, we were able to both screen the bacteria in an environment resembling their future application and, at the same time, obtain more stable droplets and more precise measurements,” says Claus Heiner Bang-Berthelsen.

The bacteria were first exposed to roseoflavin, a substance structurally like riboflavin that can promote the growth of the bacteria best suited to producing vitamin B2. The researchers then selected the droplets that glowed the brightest, as high fluorescence indicates high vitamin B2 production.

“This droplet-based microbial screening approach saved months of work and significantly reduced the resource use compared with conventional screening methods,” says Claus Heiner Bang-Berthelsen.

A particular Lactococcus lactis strain stood out

Among the bacteria identified, one lactic acid bacterium proved particularly interesting. When the researchers tested the bacterium in real plant-based products, it proved especially effective in soya drinks:

“The results suggest that the bacterium works not only under laboratory conditions, but also in actual foods containing a significant amount of protein,” says Hang Xiao.

It turned out that the bacterium continued to produce vitamin B2 in soya drinks even at high levels of added (fortified) vitamin B2, demonstrating robust and stable production.

The bacterium was also found to be capable of utilizing many different types of sugar. This makes it an interesting candidate for use as a starter culture in plant-based fermentation processes, as it is not restricted to a single, very narrow substrate.

It generally performed less well in rice and oat drinks, as well as in some almond drinks, which the researchers attribute to their low protein content. Their interpretation is that the bacterium requires a certain level of fermentable protein to grow well and produce vitamin B2 effectively.

“The exciting thing about the method is that it can not only identify vitamin B2-producing bacteria in soya drinks. It can also be adapted to identify other interesting substances, provided they can be detected using fluorescence. However, the method only works if the medium is transparent and has a low fluorescence background,” says Hang Xiao.

Facts

New method for identifying bacteria capable of producing vitamin B2 in plant-based products
The bacteria were sourced from the guts of wild bumblebees
The researchers screened them in microscopic droplets, one cell at a time
A special transparent soy medium made the screening possible
The most promising bacterium was Lactococcus lactis NFICC2835
The bacterium produces up to 1.23 mg/L riboflavin in soy drinks
The results were best in soy-based plant drinks
The results were obtained using the MALDI-TOF Biotyper, which is part of the FOODHAY research infrastructure at the DTU National Food Institute.

The scientific article 'Droplet microfluidics-based isolation, adaptation, and screening of riboflavin-producing lactic acid bacteria for fermenting plant-based dairy alternatives' has been published in the scientific journal LWT – Food Science and Technology.

The research was supported by, among others, Novonesis and the Innomission research project REPLANTED. Additional support was provided by DTU and FoodHay