In early July at Kerteminde, most of the individuals I observed were longer than 10 cm, including one close to 15 cm. Their size, and their timing, deserve immediate attention.
One out of many large speciments I got from Kerteminde (Javidpour, July 2026)
It does not matter whether you call it ribbegople in Danish, Rippenqualle in German or comb jelly in English. The species is the same: Mnemiopsis leidyi. And what I have observed in Kerteminde this summer should concern us. During our current summer field course at the Marine Research Centre, I have repeatedly seen unusually large individuals of M. leidyi around the pier. Most of the animals I observed were longer than 10 cm, even bigger than the one I photographed.
Yes, yes, a pier observation is not a formal population survey….I know. We still need systematic sampling to determine the abundance, distribution and size structure of the population. Nevertheless, the observation is striking because both the size of the animals and the timing of their appearance are unusual, said by someone who is studying this species for the last 20 years.
This is happening earlier than expected
In previous years, the maximum population size of M. leidyi generally occurred several weeks later, mainly during August and early September. Our previous research, including work based on daily sampling, showed a clear seasonal development of the population. The timing varies among years and is influenced by environmental conditions, including winter temperature. Temperature is particularly important because it strongly affects the metabolism of M. leidyi. At warmer temperatures, individuals use their carbon reserves much faster and therefore require more food to maintain themselves and grow. This year, however, the pattern appears to be different. We are seeing very large individuals already in early July. We do not yet know whether this is a local aggregation, an unusually early bloom, transport from another area, particularly favourable feeding conditions or a combination of these factors. But it is a signal that deserves attention.
What does it take to grow by one centimetre?
It is tempting to ask how much energy an individual needs to add one centimetre to its body. The answer is not straightforward because one centimetre of length is not a fixed amount of biomass. Growing from 5 to 6 cm is not the same as growing from 14 to 15 cm…OK? However, we can make a rough carbon-budget calculation using a published relationship between the length and body-carbon content of M. leidyi:
Body carbon in milligrams = 0.0017 × body length in millimetres²·⁰¹³⁸
According to this relationship, an individual measuring 10 cm contains approximately 18.1 mg of carbon. At 11 cm, it contains about 21.9 mg. Adding this single centimetre therefore represents an increase of approximately 3.8 mg of body carbon. If we assume that the animal assimilates approximately 40% of the carbon it consumes, it would need to ingest at least ~10 mg of prey carbon to produce this additional tissue. Using an approximate value of 1 micrograms of carbon for a small copepod, this would correspond to more than 10,000 copepods.
For an already large individual growing from 14 to 15 cm, the estimated increase is approximately 5.3 mg of body carbon. At the same assimilation efficiency, that would require at least 13.3 mg of prey carbon: the equivalent of roughly 15,000 small copepods.
These calculations are only rough, conservative estimates. They are not complete energy budgets. They do not include the food needed for respiration, movement, reproduction, mucus production, excretion or unsuccessful feeding. The real prey requirement would therefore be considerably higher. The important point is that an individual measuring 15 cm represents a substantial transfer of material from the surrounding planktonic food web into gelatinous biomass. One additional centimetre is not “just” one centimetre.
Our students are tracing the food web
The timing of these observations coincides with our summer field course. The students are now collecting M. leidyi, fish, other gelatinous organisms and potential prey for stable-isotope analysis. By comparing carbon and nitrogen isotope values, we hope to obtain a rough picture of the relationships within the local food web. Carbon isotopes can help us trace the original sources of the material entering the food web, while nitrogen isotopes can provide information about relative trophic position.
This will not give us a direct photograph of one organism eating another. Stable-isotope values represent assimilated food over time, and their interpretation depends on appropriate baselines and turnover rates. Nevertheless, combined with information about size, abundance, prey availability and experimental feeding, they can help us understand where M. leidyi is obtaining its biomass and which organisms may be affected. …In simple terms, we are trying to determine who might be eating whom, and where this unusually large population fits into the food web.
Competition with fish is only part of the problem
The concern is not limited to competition for zooplankton. Mnemiopsis leidyi consumes copepods and other small planktonic animals that are also important food for pelagic fish. When the ctenophores are abundant, they can therefore compete directly with fish for prey. Our experiments have also demonstrated that M. leidyi can potentially feed directly on the early life stages of fish. In the study by my previous PhD student, the ctenophores captured and digested Baltic herring yolk-sac larvae. Predation was related to ctenophore size and was not simply eliminated when alternative copepod prey were available. This means that M. leidyi may/can affect fish populations in two ways: by consuming the food needed by fish and by consuming fish eggs or larvae directly.
A recent study by Lucila Sobrero and colleagues in Argentina, within the native range of M. leidyi, found a similar pattern. Their experiments showed size-dependent predation on fish eggs and larvae. Larger ctenophores consumed more eggs. Some eggs were later regurgitated, but many were no longer viable, while fish larvae were retained and digested. These findings are particularly relevant to what we are observing in Kerteminde. The size of an individual is not merely an interesting measurement. It can influence what that individual is capable of capturing and how strongly it affects the surrounding ecosystem. A population consisting of fewer but much larger individuals may still exert substantial pressure on zooplankton, fish eggs and fish larvae.
We need to investigate use, not only control
For several years, I have tried to obtain funding to investigate innovative approaches to this invasive species.
Once M. leidyi is well established, we may not be able to control its regional spread or completely prevent its blooms. But that does not mean that we have no options. We should investigate whether at least part of this recurring biomass can be collected and converted into something useful.
This is not a proposal for a miracle solution. Any utilisation strategy would have to be tested carefully. It must not encourage the further spread of the species, create damaging bycatch or provide an economic incentive to maintain an invasive population. We also need to understand the environmental costs of collection, transport and processing.
But these are exactly the questions that research funding should allow us to answer.
So far, my attempts to secure support for this work have been unsuccessful. Funding agencies do not seem to sense the urgency of studying approaches whose benefits may not be immediate or easily visible. and EPAs do not have any resource to invest in this part. The contrast with events on land is striking. This week, the oak processionary moth, the so-called “larva from hell”, has attracted considerable attention in Odense. Its microscopic hairs can cause rashes and allergic reactions, residents have reported serious discomfort, and a kindergarten has reportedly had to close temporarily. Those concerns are real and deserve a response.
But the case also illustrates how differently we react to environmental threats.
When the impact appears visibly on human skin, the urgency is immediately understood. When ecological damage develops below the surface of the sea, in the form of disappearing zooplankton, altered food webs, consumed fish eggs or reduced larval survival, it is much easier to overlook.
Marine ecosystem changes are often gradual, underwater and largely invisible to the public. By the time their consequences become obvious, the opportunity for early and relatively inexpensive action may already have passed.
Concern does not mean panic
One photograph and a series of observations from one pier do not prove that an ecological crisis is underway. I am not suggesting that they do. But science should not have to wait for undeniable damage before investigation becomes urgent.
The unusually large M. leidyi appearing in Kerteminde this July give us an opportunity to act early. We need systematic monitoring of their abundance and size distribution. We need to measure the available prey field. We need to determine their trophic position and investigate possible consequences for fish recruitment. And we need to explore whether biomass that we may be unable to prevent could be collected and used responsibly.
Whatever language we use and whatever name we give it, the message is the same:
We should measure early, investigate early and support innovative solutions while the warning is still only a warning, not after it has become a crisis.
Relevant publications
Javidpour, J. et al. (2009). “Seasonal changes and population dynamics of the ctenophore Mnemiopsis leidyi after its first year of invasion in the Kiel Fjord, Western Baltic Sea.” Biological Invasions.
Javidpour, J. et al. (2020). “Cannibalism makes invasive comb jelly, Mnemiopsis leidyi, resilient to unfavourable conditions.” Communications Biology.
Stoltenberg, I. et al. (2024). “Predation on Baltic Sea yolk-sac herring larvae (Clupea harengus) by the invasive ctenophore Mnemiopsis leidyi.” Fisheries Research.
Sobrero, L. et al. (2025). “Predatory impact on ichthyoplankton by Mnemiopsis leidyi is size-dependent: an experimental approach.” Marine Ecology Progress Series.
Ribbegople, Rippenqualle or Comb Jelly: Whatever You Call Mnemiopsis leidyi, You Should Be Concerned
What do you think about when you hear the words “microplastic pollution?” Your mind may immediately go to imagery of colorful fragmented plastics broken off from bottles, buckets and other items we use in our everyday lives. Or, perhaps, you imagine a pile of microplastic fibers—the tiny, squiggly, spaghetti-shaped plastics that shed from our synthetic clothing. You may be surprised to hear there is another major source of microplastic pollution that’s hiding in plain sight, quite literally under our feet, that might change how you think about microplastics: tire particles.
We all know tires wear down over time—that’s why we have to replace them on our cars roughly every 60,000 miles or so. Every time a vehicle accelerates, brakes or simply drives down the road, the friction between its tires and the pavement creates tiny fragments of rubber, known as tire wear particles.
Driving a car or even riding in a bus is a bit like dragging an eraser across the planet, except the crumbs are microplastics. Toxic microplastics.
Tires are made from a complex mix of natural and synthetic rubber along with a range of additives, fillers and chemical compounds—some of which, like the preservative 6PPD, have been shown to be highly toxic to coho salmon when they break down into derivative product 6PPD-Q in the environment—even in tiny concentrations.
Some studies have shown that a single vehicle’s tires can emit more than two trillion particles per mile driven—and that the average person generates nearly two pounds of tire particles per year! Once these particles are shed from tires, they don’t just disappear. Some are small and light enough to become airborne, drifting away from roadways as dust. Others settle on road surfaces, where they accumulate until the next heavy rain washes them into storm drains and from there, into streams, rivers and eventually the ocean.
That’s why tire wear particles are now considered one of the top sources of microplastics to the environment. In fact, until recent developments in analytical methods, scientists weren’t reliably able to detect tire wear particles in microplastic counts—thus, these pesky microplastics may have been evading our detection for years.
Why green infrastructure may be one of our best near-term solutions
Unlike some sources of plastic pollution, we can’t simply stop driving overnight. Reformulating tire rubber to be less toxic or shed less material, while promising, will take time to develop, test and scale across the global vehicle fleet. So, what can we do about tire wear particle pollution right now?
This is where green infrastructure comes in. Green infrastructure refers to engineered natural systems (things like bioswales, rain gardens, roadside buffers and permeable pavement) that are designed to slow down, filter and treat stormwater before it reaches rivers, lakes and coastlines. Instead of routing runoff directly into storm drains and out to sea, green infrastructure gives contaminated water a chance to percolate through soil, plants and other natural filtration media, which helps trap microplastics, including tire wear particles, preventing them moving further downstream.
Early research on green infrastructure has been promising, showing that these systems are quite effective at capturing microplastics and other contaminants carried in road runoff. But there’s a critical piece we still don’t fully understand: What would it take to scale up green infrastructure across an entire city, and how much of a dent would that actually make in long-term tire wear particle pollution?
Our research on green infrastructure capture of tire wear particles
Funded by the Tire Industry Project, our plastics science and policy teams at Ocean Conservancy have partnered with the University of Toronto on a new study evaluating the costs and benefits of scaling up green infrastructure at the city level specifically to capture tire wear particles.
If you happen to be driving on the roadways of Portland, Oregon, you may spot our scientists crouched over, precariously scooping dirt with spoons from a sample area on the roadside. Don’t be alarmed—that’s just us doing science! Feel free to give us a wave.
Ocean Conservancy is currently working to:
- Quantify the scale of pollution: Collect road dust samples from 30 cities globally to measure both total microplastic and tire wear particle concentrations and determine how different variables (population density, road size, rainfall) might influence those values.
- Assess feasibility: Determine what it would take realistically—logistically, financially and spatially—to scale up green infrastructure across an entire city.
- Model positive impacts: Estimate how much city-scale green infrastructure could reduce tire wear particle pollution entering aquatic ecosystems.
- Compare across cities: Understand how well these solutions might translate across different urban contexts, focusing on Portland, Oregon; Toronto, Canada; and London, England as case-study cities.
- Make our findings accessible: Produce a public-facing toolkit to help city planners, engineers and advocates guide real-world implementation of infrastructure that captures tire-wire particles.
By pairing rigorous science with practical guidance, we hope to help cities move from asking “Could this work?” to confidently building solutions that we know can be effective.
Give today and make a difference!
How can I help?
Tire wear particle pollution can feel like an overwhelming problem. After all, it’s tied to transportation, which most of us rely on every day. But that’s exactly why research like this matters: It gives us a real, near-term path forward that doesn’t require waiting for the entire global transportation system to change first.
You can help by staying engaged with Ocean Conservancy as we continue to dig into solutions for the plastic pollution crisis—one roadway, one storm drain and one city at a time. Together, we can keep working toward a world and ocean free of plastic pollution, forever and for everyone.
The post What are Tire Wear Particles? appeared first on Ocean Conservancy.
A small jellyfish-like animal recently reported from Vejle Fjord has attracted attention. Clear photographs suggest that it belongs to the genus Gonionemus and may possibly be the clinging jellyfish, Gonionemus vertens (Picture courtesy to Jonas Bøgelund Poulsen)
Unlike the large jellyfish commonly encountered along Danish coasts, Gonionemus vertens is a small hydromedusa, usually only around 1.5–2.5 centimetres across. Its transparent bell reveals four coloured reproductive structures arranged like a cross. Numerous fine tentacles surround the bell, often appearing bent or angled. Small adhesive pads near the ends of the tentacles allow the animal to attach itself to eelgrass, seaweed and other submerged vegetation.
This unusual behaviour explains its English name: the clinging jellyfish. During the day, it often remains attached to vegetation rather than drifting freely with the current. At night, it becomes more active and swims into the water column to feed on zooplankton and small crustaceans. Consequently, it can easily remain unnoticed even in places where it is already established. Another reason the species can be difficult to detect is its life cycle. The visible medusa is only one stage. For much of its life, the animal may persist as a minute polyp attached to a hard surface, shell or vegetation. These inconspicuous polyps can reproduce asexually and later release new medusae when environmental conditions become favourable.
Gonionemus vertens is generally considered native to the northern Pacific but has been introduced into several parts of Europe and the Atlantic. Transport on ship hulls, in ballast water or with movements of oysters and other marine organisms has been suggested as possible pathways, although the pathway responsible for any particular occurrence is rarely known with certainty.
Despite its delicate appearance, the animal should not be touched. Some populations possess powerful stinging cells and have caused intense pain, swelling, muscle cramps and, in rare cases, serious allergic reactions. Sting severity differs considerably among regions, which is one reason researchers suspect that animals currently grouped under the name G. vertens may represent a complex of closely related forms.
The Vejle Fjord observation is therefore scientifically interesting, but it should not yet be presented as a confirmed record of G. vertens. Anyone encountering a similar animal should photograph it without handling it and record the date, exact location, approximate size, number observed and surrounding habitat. Observations can be submitted to Denmark’s national species portal, Arter, where they can be evaluated and contribute to tracking changes in Danish marine biodiversity. Please use either my App: GoJelly JellySpotter or reprot to the Arter.dk: Gonionemus taxon page and Danish species-reporting portal.
References:
Edwards, C. (1977). A study in erratic distribution: The occurrence of the medusa Gonionemus in relation to the distribution of oysters. Advances in Marine Biology, 14, 251–284. DOI: 10.1016/S0065-2881(08)60448-4.
Govindarajan, A. F., Källström, B., Selander, E., Östman, C., & Dahlgren, T. G. (2019). The highly toxic and cryptogenic clinging jellyfish Gonionemus sp. (Hydrozoa, Limnomedusae) on the Swedish west coast. PeerJ, 7, e6883. DOI: 10.7717/peerj.6883.
The JOIDES Resolution (JR) was a renowned, international, scientific research ship. It was home to over 190 expeditions, each sailing for 60 days at a time without docking. Scientists and crew members from all over the world met to discover Earth’s secrets through studying ocean cores. Every two months the JR would get a new crew, sailing to an entirely new place. This once in a lifetime experience forms special and unforgettable social connections.
Since working on the JR I’ve kept those connections strong with snail mail. I have always been an avid penpal, so meeting new friends means new addresses to send my letters and postcards to. Experiences like sailing on the JOIDES Resolution or participating in programs like OCEAN CORE Academy is one of the ways I’ve met people from all over the world.
Now that the JR is retired, there is no more scientific research drilling being done through the International Ocean Discovery Program (IODP). But, there is still plenty to learn from ocean cores, and plenty of people to meet through programs like OCEAN CORE Academy (OCA). OCA is an annual summer opportunity from the U.S. Scientific Support Program (USSSP) that hosts undergraduates interested in geoscience related careers. Students can apply to this program for a chance to research and study data recovered from cores originally brought up by the JR, now located at the Gulf Coast Repository (GCR) in College Station, Texas. Students also practice forms of science communication with the guide of mentors. As a science communicator and fan of snail mail, I ran a craft night teaching students how to make and send science-themed postcards.
Fig. 1) students using watercolor to paint onto 4 by 6 inch board paper, a photo of a thin section slide is in the background. Photo by Dr. Leah Joseph.
For this project, we based the cover image of the postcards off of rock thin section slides. These slides are a slice of a hard rock or mineral that’s been glued to a microscope slide, sanded to 0.03 millimeter thickness, and polished. Thin section slides are used to identify grain size, shape, color, and other physical properties. This helps scientists understand the textural relationships between the rocks and determine the origin or evolution of the parent rock. Thin sections can also be helpful for identifying minerals using cross polarized light (XPL). XPL reduces light reflection and glare, commonly used for sunglasses and professional photography, but in a polarizing microscope, XPL is used to create a dark field causing certain minerals to appear brighter and more visible. Different colors are associated with different minerals, and as the stage of the microscope rotates, light passes through the slide in unique ways aiding scientists with identification. Identifying minerals can help scientists in understanding more about where the rocks came from and how old they are. These thin sections are not only informative, but are incredibly beautiful, making unique and stunning postcard covers.
Fig. 2) Examples of thin section slides under a XPL microscope, bronzitite (left) and gabbro (right). Sourced from here.
After the OCA students finished their paintings, my home-made “post card” stamps go on the back, a stamp gets added, and they’re ready to be mailed out. Although most OCA participants this year were U.S. based, they came from all over, ranging from Staten Island to San Francisco to Arizona to Connecticut. In addition to one mentor from New Zealand! For many of these students this was their first time traveling on their own, and their first time forming long-distance connections. With these scientific postcards, OCA students can stay connected by reminding each other of the science they learned together. My experience on the JR taught me great things about geological research, but it also gave me life long connections that I cherish. Although the JR is gone, its legacy lives on in our memories and the ways we stay connected with friends. I’m grateful to know that even without an international ship, I’m still able to add friends to my address book.
Fig. 3) Examples of participant made postcards
Written by Kellan Moss
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