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By Qi-Fan Wu (Niels Bohr Institutet, University of Copenhagen)

During our journey, we saw many beautiful cloud patterns while looking outside the METEOR!  Even though people do not always pay attention to them, clouds are among the most visible elements of the sky and naturally form part of our everyday background. And when we sailed away from the coastal region of Recife to the open ocean, the sky seemed to open up, allowing clouds to reveal their full variety and structure.

In climate modelling, clouds are one of the biggest sources of uncertainty. There is a famous saying in mathematics: “Mathematics is the queen of the sciences, number theory is the crown of mathematics, and the Goldbach Conjecture is the pearl on the crown.” The same idea can be applied to the study of clouds in Earth science. There is still no general macroscopic theory of clouds. Cloud physics is an absolutely fascinating topic, as it combines turbulence, stochastic processes, chemicals in the air, multiscale interactions within the Earth–atmosphere system, and a close connection to our daily weather.

In this blog entry, we would like to share some lovely photos of cloud patterns that we took on METEOR. Instead of serious systematic investigations, we focus on the basic cloud physics behind some typical cloud phenomena shown in these photos. These examples might provide something interesting to think about during our leisure time, even after returning to land. If nature is an artist, clouds are among its finest masterpieces, shaped by physical laws and stochastic processes.

What are clouds, and what is inside them? Clouds are made of many liquid water droplets and ice crystals inside the boundaries of the cloud. They are mostly air, with the many particles dispersed widely and more or less randomly throughout the cloud interiors [a]. The individual particles that make up a cloud are very, very small and not generally visible to the human eye.

When we look up from our research vessel METEOR and observe clouds, we first see their macroscopic structure: their overall shape, height, thickness, and organization across the sky. Broad, layered clouds often form through slow, large-scale ascent, while towering clouds with visible turrets reflect rapid rising motion in smaller air parcels. These visible forms are continuously shaped by moisture supply, cooling, turbulence, mixing with drier air, and precipitation, linking the large-scale atmospheric flow to the clouds we observe [a,b].

After leaving Recife, we entered a region typically influenced by the southeast trade winds of the tropical South Atlantic, where a vertically layered atmosphere, warm ocean conditions, and wind-driven mixing often promote a turbulent marine boundary layer. In Figure 1, the sky shows a layered cloudscape ranging from thin, high cirrostratus and altocumulus clouds to low cumulus and towering cumulonimbus clouds. These different forms reflect how the atmosphere organizes moisture, cooling, and vertical motion: broad layers are associated with gradual ascent, while the rising turrets of cumulus and cumulonimbus reveal stronger localized updrafts. Together, they illustrate the visible macroscopic structure of clouds, shaped by atmospheric motion and the microphysical processes occurring within them.

Figure 1: Photograph showing different cloud types observed near 04°06.5’S, 23°18.5’W, together with a schematic summary of the major cloud types. Adapted from a photograph by Federico Scarscelli and [a].

It should be noted that, in general, atmospheric temperature in the troposphere decreases with increasing altitude. Over the subtropical oceans, however, this is not the case. A relatively thin temperature-inversion layer lies above the subtropical marine boundary layer, within which temperature increases with height and the atmosphere is highly stable (Figure 2). Cloud occurrence above the marine boundary layer is relatively low in this region. The base of the trade-wind inversion is typically located at an altitude of approximately 1–2 km, separating the moist lower layer from the dry free troposphere [c].

Figure 2: Schematic illustration of the key physical processes in the marine boundary layer. Adapted from [c].

This large-scale thermodynamic structure provides the environmental conditions under which clouds form and evolve. At the microscopic scale, however, clouds consist of particles: liquid water droplets, ice crystals, or a mixture of both. Clouds composed entirely of liquid droplets are commonly referred to as “warm clouds”, whereas clouds containing ice particles are classified as “cold clouds”. When liquid droplets and ice crystals coexist, the cloud is described as a mixed-phase cloud. However, the distinction between “warm” and “cold” clouds hinge on the phase of the particles, not on the temperature. The warm/cold distinction depends on the microphysical phase of the particles inside the cloud, which a normal naked eye observation cannot resolve.

Warm clouds consist of liquid water droplets spanning a range of sizes, from small haze droplets and cloud condensation nuclei to cloud droplets, drizzle drops, and raindrops (Figure 3). Cloud droplets typically form when water vapour condenses onto cloud condensation nuclei. Rainfall develops when some droplets grow much larger: larger droplets fall faster, collide with smaller droplets, and collect them. As a result, many small cloud droplets can combine to form fewer, larger drizzle drops and eventually raindrops [a]. This process approximately conserves the total liquid-water mass within the cloud, while transferring water from numerous small droplets to a much smaller number of large drops that are heavy enough to fall as rain.

Figure 3: Relative sizes of various liquid drops found in clouds. The bright spots highlighted by the green circles are circumzenithal halos produced by the refraction of sunlight through hexagonal ice crystals. Adapted from a photograph by Herbert Rafael Barbosa near 10°22.8’S 35°40.8’W and [a].

Cold clouds contain ice particles, either alone or together with supercooled liquid water droplets [a]. Unlike liquid droplets, which are nearly spherical because of surface tension, ice particles can develop a wide range of crystalline shapes, including plates, columns, needles, dendrites, and aggregates (Figure 4). Their shape depends mainly on temperature and ice supersaturation during growth by water-vapour deposition. As ice crystals become large enough to fall, they may collide and stick together to form snow aggregates, or collect supercooled droplets that freeze on contact, a process known as riming. The regular hexagonal structure of ice crystals can also produce optical phenomena such as halos, which form when sunlight is refracted or reflected by suitably oriented ice crystals in high-level clouds as shown in Figure 3. In mixed-phase clouds, uplift supports the growth of ice crystals at the expense of supercooled droplets. Once sufficiently large, the ice precipitates and may melt into rain or drizzle while falling through the melting layer (Figure 3).

Figure 4: Conceptual illustration of cold-cloud microphysical processes. Ice crystals grow in the subfreezing part of the cloud, precipitate downward, and melt into drizzle or rain as they pass through the melting layer. Localized updrafts can recirculate hydrometeors and promote further ice production. Photographs of snow crystals and a classification of snow-crystal habits by temperature and excess water-vapour density are also shown. Adapted from a photograph by Leonie Jaeger taken near 10°22.8′ S, 35°40.8′ W, and from [a, b].

When we approached the equator, we saw many cumulus clouds with remarkably flat bases, marking the lifting condensation level where warm, moist air rising from the ocean cooled to its dew point and condensed into droplets. Similar temperature/humidity across an area leads to clouds sharing flat bases. Their uneven, towering tops reflected continued turbulence and convection above this level, revealing the active vertical mixing of the tropical atmosphere (Figure 5). As moist tropical air rises toward the cold-point tropopause, it encounters extremely low temperatures. When an air mass reaches a local temperature minimum, water vapour can freeze into very thin cirrus clouds (Figure 6).

Figure 5: Flat-bottomed, fluffy-topped cumulus clouds. Adapted from a photograph by Joelle Habib taken near 00°00.0’S, 23°06.8’W.
Figure 6: Cirrus uncinus clouds. Adapted from a photograph by Joelle Habib taken near 00°00.0’S, 23°06.8’W.

After crossing the equator, we entered the Intertropical Convergence Zone (ITCZ), a band of heavy rainfall extending across the tropical Atlantic. Cloud organization within and around the ITCZ varies markedly from day to day. Extensive low-level stratocumulus clouds can also occur in the surrounding region, acting like a blanket that reduces the amount of incoming solar radiation reaching the ocean surface (Figure 7).

Figure 7: Cloud patterns in the ITCZ. Adapted from a photograph by Naomi Krauzig taken near 10°05.5′N, 23°02.5′W.

As we continued northward on our way home, we moved closer to the continent and witnessed some spectacular roll clouds, a very rare meteorological phenomenon. This type of cloud is known as “Morning Glory,” although evening land breezes can also produce roll clouds. The roll cloud is not attached to other clouds. associated with a solitary wave, a wave that has a single crest and moves without changing speed or shape.

As we were relatively close to the shoreline of West Africa, these roll clouds may have been produced by internal gravity waves propagating along a stable marine boundary layer [d]. The collision or sudden advance of a sea breeze or cold front can disturb the stable air layer near the surface, generating an atmospheric bore (a train of internal gravity waves). Such waves consist of alternating regions of upward and downward motion. Along the crest of the wave, moist air is lifted and cools to saturation, forming clouds, while behind the crest the air descends and warms, causing the cloud to evaporate. Because this cycle of ascent and descent extends along a long line of low-level convergence, cloud is continuously generated at the leading edge and dissipated at the trailing edge, maintaining a long, coherent band (Figure 8).

Figure 8: Roll cloud observed from METEOR, shown with a satellite image from approximately the same time. Adapted from a photograph by Naomi Krauzig taken near 28°01.265′N, 17°27.985′W, and [d].

I think observing and thinking about clouds can be a nice hobby for enjoying the beauty of nature. Cloud processes are stochastic because nucleation and droplet collection do not occur at exactly the same time for every particle, even under the same environmental conditions [a]. Instead, freezing, condensation, and coalescence depend on chance microscopic events, so only some droplets become “lucky” and grow or freeze earlier than others. Perhaps cloud viewing could also give us good food for thought. After all, many cloud-related problems in climate modeling remain among the most beautiful mysteries in climate science.

Figure 9: Adapted from a photograph by Leonie Jaeger taken near 11°30.0’S, 34°13.0’W.

Enjoy ~

References:

[a] Lamb D, Verlinde J. Physics and Chemistry of Clouds. Cambridge University Press; 2011.

[b] Levizzani, V., Kidd, C. (2025). Cloud Physics. In: Precipitation. Geophysics and Environmental Physics. Springer, Cham. https://doi.org/10.1007/978-3-031-97096-2_3

[c] Shang-Ping Xie. Subtropical climate: Trade winds and low clouds. In: Coupled Atmosphere-Ocean Dynamics. Elsevier; 2024. p. 139–163. doi:10.1016/B978-0-323-95490-7.00006-0.

[d] The Morning Glory and related phenomena. https://www.meteo.physik.uni-muenchen.de/~roger/AustralianProjects/TheMorningGlory/TheMorningGlory.html

Cloud: The Pearl on the Crown

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Ocean Acidification

Team Madeira – At least one of us is thinking

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It all started with a bang – several million years ago. Beneath the Atlantic, successive eruptions raised an enormous volcanic mountain from the ocean floor, and its very tip now forms rugged cliffsides, deep red canyons and fertile ground for hotel chains. How land was formed here, in the middle of the ocean, is still plainly evident in the red and black banded mountainsides of Madeira, in pools of volcanic rock frozen mid-flow and in cliffs sculpted by magma, wind and water. Life clings to this volcanic ground with stubbornness: Cacti climb sheer ridges, while sage-green, brown and vibrant yellow shrubs crouch against the rugged terrain.

Today, Madeira is known as the Island of Flowers, an image that echoes across postcards, signs and souvenirs. Indeed, many of the winding mountain roads are lined by eucalyptus trees from Australia, tall white and lilac lilies from South Africa, and hydrangeas from Asia. Fitting for an island that lives from tourism, while also beginning to buckle under its strain.

Panaroma from the eastern most tip of Madeira, a few kilometers from the experimental site in the marina of Quinta do Lorde (Photo: Jana Firus)

Our own project looks, at least partly, at another, less visible invader: human-made sound. Beneath the ocean’s surface, boat engines add to the island’s natural underwater soundscape, and during the six months we spend here we want to find out whether sound changes where the larvae of marine sessile animals, such as bryozoans, tunicates or polychaetes, choose to settle. Those animals are sessile in their adult life, but as larvae they are free floating. In this stadium, they are influenced by a wide variety of environmental factors—including noise—while they seek out a suitable habitat in which they could settle and survive.

And with that “Óla” from Team Madeira. We are Elin and Jana, two German students who have come to Madeira for half a year to take part in this year’s GAME (Global Approach in Marine Ecology) project.

Jana studies biology at the Ruhr-University in Bochum. “I was always interested in marine biology and had already worked in this field for my bachelor’s thesis. When I decided that I didn’t want to move away from Bochum for my Masters, I was a little bit sad, deep down, thinking that I couldn’t continue to pursue marine biology. So, I was thrilled to return to the ocean and to fieldwork when I got accepted for GAME”.

Jana and Elin exploring the island on one of their first days in Madeira in April. (Photo: Niklas Firus)

Elin studies biological oceanography in Kiel “This year’s GAME topic of The influence of soundscapes on hard bottom community colonization seemed made for me, since I had already written my bachelors thesis about the colonization of hard substrates and if I could’ve picked any field, sound would have been it.”

This year is the first time that GAMIEs are working with sound, which made the planning phase in Kiel in March extra exciting for us. We tested underwater microphones, so called hydrophones, tried out speakers and had many, many, many discussions about scientific literature and the experimental setup. In the end all teams agreed on one basic concept: One student in each country would analyze the effects of boat noise and the other the influence of natural soundscapes on the formation of invertebrate communities. Natural soundscapes will be captured by deploying thydrophones in underwater habitats that are typical for the marine region a team is working in. In Madeira, the underwater world is strongly shaped by the past volcanic activity, and features steeply sloping rock faces and rocky areas that are overgrown with algae and sessile animals. These form the most typical habitat of the region. Furthermore, here and there they give way to sandy bottoms at greater depths.

We are investigating the settlement under the influence of natural sounds, because more and more marine habitats have been destroyed by human activity. In the past, several studies have been conducted on marine mammals, fish, shellfish and coral species, which found that when sound was used to simulate healthy habitats in otherwise disturbed environments, it led to the successful re-establishment of populations. A concept that is known as acoustic restoration.

In our experiments, both, the natural sounds and the boat noise, will be played back from speakers and will be directed onto plastic plates hanging in the water, to which the larvae of sessile animals can attach.

So much for the theory.

After arriving on Madeira in early April, we got to work and realized quickly that reality is lots of planning, glue, trips to the hardware store and starting over. Luckily, we have kind and helpful supervisors at MARE, the research institute here in Madeira, many of which are former GAMIEs. They contributed their experience, advice and occasional emotional first aid. But most of the time we’re trying to do as much as we can on our own – with special support from Jana’s electronics-technician-husband, Niklas, who also came along to Madeira and is of great help with all the equipment. Even though we had many long and a few frustrating days, it was nice to plan and build everything on our own. Actually, it’s incredibly rewarding to see the finished results of our work running smoothly while the experiments are going on.

One of our four frames inside and outside of the water. These are the structures that hold the plates on which the communities we study grow on. Our experimental site is the the marina of Quinta do Lorde. (Photos: Elin Disse)

Our workplace here in Madeira is the marina in Quinta do Lorde, which is almost on the eastern tip of the island. It’s a beautiful workplace, because most days the water is calm and clear and we get to see sepias, triggerfishes and a school of barracudas swimming in the shallow waters. This makes it all the more frustrating that it is forbidden to go in, due to the ship traffic – you can imagine how hard it is for two marine scientists to follow this rule, and how often we stare into the water longingly.

Two sepias spotted in the marina on a working day (Photo: Elin Disse)

The ideal way for us to run the two experiments was conducting them both at the same time. But of course, the playbacks of the natural soundscape and the boat noise shouldn’t mask or overlay each other. And they should not reach those panels that we have to study invertebrate settlement in the absence of any playbacks. This prerequisite is called acoustic isolation: whatever happens near one speaker shouldn’t affect the other settlement plates. Since sound can travel far under water, we choose the two opposite ends of the marina and two jetties in between for the deployment of the settlement panels.

Unfortunately, our workplace is in a busy marina and to check if the play-backed boat noise doesn’t affect the other locations where we placed settlement plates, we need silence throughout the entire area. So, we had to stop and redo the measurements many, many times, because of incoming and departing boats, loud wind, cracking noise from the jetties or technical difficulties with our hydrophones.

We had one truly frustrating Friday afternoon when we wanted to test acoustic isolation but couldn’t get even five minutes of silence without a boat engine in the background for hours! And then, shortly before we had to catch the last bus home, we finally managed to do the test- and it was perfect. We had recordings without any disturbances and we had acoustic isolation- which meant we could run both experiments in parallel.

Then the wind blew the hydrophone from the jetty into the water, while we were packing up. Jana was over it and ready to give up, but Elin declared it the best thing that had happened that day. She had in the morning naively predicted a short workday with plenty of time to go snorkeling. Instead, she got special permission to go into the marina just this once – and gleefully fished out the hydrophone. Everything was done just in time before the last bus came and we decided never to test acoustic isolation on a Friday afternoon again.

Fishing out the hydrophone after it fell into the water, from Elin’s and from Jana’s point of view. (Photo: Elin Disse; Jana Firus)

Since Jana studies the effects of natural soundscapes on larvae settlement, she needs to record the marine ecosystems of Madeira. The team at MARE helped her to choose a few promising locations, which best reflect Madeira’s rocky underwater landscape. They are in protected areas and have little boat traffic.We built six hydrophone stands, of which one was placed at each location with the help of a technical diver. The stands were constructed in a way that the hydrophone could be attached and detached by freediving from the surface, and this allows us to work independently of the diver. And, of course, to have the opportunity to go snorkeling for work :). For the first month it was just Elin who could hold her breath long enough to reach the hydrophone stand, which was in 5 to 8 meters water depth, because she had years of experience. But after training freediving while snorkeling in beautiful locations all over the island, first Niklas and then Jana figured it out and now we can divide this very popular task among the three of us.

Hydrophone stand ready for recording and Elin testing if she can reach it while freediving. (Photos: Susanne Schäfer)

Even when the project is running smoothly, there are always a million little things to think of, to plan and to organize. Our motto became ‘at least one of us is thinking’ – because of how often one of us forgot something or didn’t think ahead and the other one caught it just in time. And there is something to it. Even though we will write separate Master theses, we share the work and the responsibility, and it is amazing to work in a team in which you can truly rely on the fact that the other person cares just as much and is right there with you.

Elin and Jana working on the colonization panels and their first sampling event. (Photos: Niklas Firus)

When we’re not in the workshop building our frames or glued to the binocular during long sampling days, we love to be in the water for snorkeling trips or go hiking in the beautiful mountains. The island’s nature is fascinatingly versatile, and after almost 5 months have passed now, we’re sure that we’ll never grow tired of the amazing views. There are so many Levada trails with waterfalls, hidden paths through the mountains and small towns to visit. Levadas are man-made irrigation channels on Madeira. They carry the water from the mountains from the north to the south. The network, which spans a total of 2,000 to 3,000 kilometers, is used today not only for agriculture but primarily as a world-famous hiking trail. We make a point to go exploring new places, but the joy of staying for half a year is that you get to find your favorites and come back to them.

Elin and Jana on different hiking trips around the island. We both frequently get visits from friends or family members, and it is possible this to integrate into our work life. Since the experiments are running, it’s much easier to take a day off or even show the workplace our loved ones. (Photos: Niklas Firus)

We are really happy to have worked and lived here on Madeira, and we can’t believe that half a year has almost come to an end; we’d do it all over again in a heartbeat.

Team Madeira – At least one of us is thinking

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Ocean Acidification

Do Sea Turtles Get Lost?

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Did you know some female sea turtles can travel hundreds—or even thousands—of miles through open ocean before returning to nest on or near the very beaches where they hatched? In fact, Leatherback sea turtles take this long-distance travel to an extraordinary level. Pacific leatherbacks nesting in Indonesia have been documented migrating more than 10,000 kilometers to the West Coast of the United States. That’s the longest migration of any air-breathing marine vertebrate. So how do they accomplish this without Google Maps?

Scientists have found that sea turtles can sense magnetic information and use it as a navigational cue. Because the strength and angle of Earth’s magnetic field vary across the planet, these subtle differences can provide turtles with information about where they are and help guide their movements across the ocean. For turtles that return to their birthplace to nest (a behavior known as natal homing), these magnetic cues may be especially important. It’s an extraordinary system, but even the best navigation can take a turtle only so far.

Despite their great sense of direction, sea turtles don’t always make it where they’re going.

A sea turtle may be capable of navigating thousands of miles, but reaching the right destination is that much more of a challenge when human-caused obstacles lie in the way.

Artificial light is one example. Artificial lighting not only discourages nesting females from coming ashore but also has a harmful impact on hatchlings, which historically emerge from their nests at night and orient toward the brightest horizon. On a natural, undeveloped beach, that is generally the open ocean. But artificial light from coastal development can overwhelm the natural cue, drawing hatchlings inland away from the water and causing them to get lost on day one.

Coastal development not only brings more artificial light and human activity to the shoreline, but it also changes turtle habitats themselves. Buildings, roads and other development can alter or reduce areas sea turtles need for nesting. Shoreline armoring, such as seawalls, can eliminate the dry sand turtles need to successfully nest, while beach driving and other activities can further disrupt nesting habitats. And these challenges extend beyond the beach.

The ocean is getting noisier, too. Sea turtles have internal ears and can hear underwater sounds. Vessel traffic, oil and gas surveys, underwater construction and sonar all add noise to the marine environment. Human-generated sound can cause stress, disrupt normal behaviors or even force marine animals to move from preferred habitats or divert from migratory paths.

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Evolution never saw the plastic grocery bag coming.

Then there’s a threat sea turtles encounter almost everywhere they travel: plastic pollution. Sea turtles evolved over millions of years to spot drifting prey, like jellyfish. But plastic rapidly started to be used only around 60+ years ago.

Our plastic trash entered the ocean so quickly that animals haven’t had time to adapt. To a hungry sea turtle, a floating plastic bag still looks enough like dinner to trick even an experienced turtle. Plastic bags, balloons, soft plastic packaging and other plastics, once swallowed, can block a turtle’s digestive tract or puncture internal organs. And it doesn’t necessarily take much.

A recent Ocean Conservancy study of more than 10,000 marine animal autopsies found that nearly half of the sea turtles studied had ingested plastic. Even more alarming, researchers found that for adult loggerhead turtles, swallowing just one and a half times the plastic in a golf ball was enough to kill 50% of these creatures.

It’s a heartbreaking reminder that something we use for minutes can threaten an animal that’s been roaming Earth’s ocean for more than 100 million years.

A Hawaiian Green Sea Turtle captured from above as it glides over the reef.

Ancient animals still face very modern threats.

Sea turtles survived the extinction event that wiped out dinosaurs. They’ve outlasted shifting continents and dramatic changes to our planet. But surviving millions of years doesn’t make them invincible. Today, they’re facing threats that appeared in the blink of an evolutionary eye: plastic pollution, habitat loss, vessel strikes, fishing gear entanglement and climate change. The remarkable thing is that many of these challenges aren’t inevitable. They’re problems we can all help solve.

Together, we can reduce the amount of plastic that reaches the ocean. We can protect and restore nesting beaches. And we can support policies that protect healthy ocean ecosystems. Every action helps make our waters a safer place for animals that depend on it.

So, do sea turtles get lost? When left to their own devices, not often. Sea turtles have an extraordinary ability to navigate across vast stretches of open oceans. But there’s a bigger question worth asking: Can we help make the ocean a safe place while they make these incredible journeys? Navigation is only part of the challenge for sea turtles trying to find their way home. Sea turtles may know where they’re going, but it’s our job to ensure the ocean and coastlines they depend on are safe when they get there. That’s why Ocean Conservancy is committed to protecting our entire ocean—and all the creatures that dwell there.

We’re fortunate to share the planet with these amazing creatures. Their journeys are a remarkable feat of science and survival. To all the turtles out there: Here’s to finding your way—wherever you’re going!

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The post Do Sea Turtles Get Lost? appeared first on Ocean Conservancy.

https://oceanconservancy.org/blog/2026/08/27/do-sea-turtles-get-lost/

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Ocean Acidification

First Spotted, or Simply First Recorded? Velella and Our Ecological Blind Spots

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A remarkable strandline discovery deserves attention, but not exaggeration. The arrival of Velella velella on Sylt is probably Germany’s first documented record. It is not the first occurrence in the North Sea, nor is one stranding sufficient proof of a climate-driven invasion.

The discovery of Velella velella on Sylt on 23–24 August 2026 has been announced as the first German record of this oceanic hydrozoan (Listen to the News here). It is an exciting observation, but the word “first” needs careful interpretation. A first documented record is not necessarily the species’ first arrival. It may instead be the first time somebody recognized, photographed and reported it through the right channels. Fragile marine organisms such as Velella decompose rapidly, and their transparent floats are easily overlooked among material on the strandline.

A photographed Velella found on the west coast of Jutland in 2018 was considered the country’s first documented record. However, earlier reports exist (see here). Velella velella, known as the by-the-wind sailor or Segelqualle, is often described in the German media as a “Mediterranean jellyfish.” This is misleading. The species is a widely distributed oceanic hydrozoan found in tropical and warm-temperate waters, including the Mediterranean and the Northeast Atlantic. The familiar blue object is not a single conventional jellyfish but a floating colony of specialized polyps. Its diagonal sail allows wind to push the colony across the sea surface. Velella cannot swim effectively against this transport, so large strandings are principally the outcome of population size, surface currents and persistent onshore winds. The Sylt animals should therefore be understood as oceanic visitors transported into German waters, not automatically as an invasive species or an established North Sea population.

The North Sea has seen Velella before

In February 1988, thousands of colourless Velella floats washed ashore along the Belgian coast after strong westerly storms. The event was described as the first published North Sea record (See the article) Denmark also has a documented history. A photographed colony was found at Grønhøj on the west coast of Jutland on 26 July 2018. It was considered Denmark’s first documented record, although unverified reports exist from 1947, 1976 and 1997. Naturbasen

In Scotland, strandings have been recorded since at least the 1950s, with another mass event in the Clyde in 2002. Scottish Marine Atlas

The Sylt discovery is therefore regionally unusual, but it is part of a longer history of intermittent Velella transport into northern European waters.

Is this climate change?

Ocean warming may increase the probability that warm-water organisms survive and occur farther north, while winds and currents determine whether they reach Sylt in a particular year. Calling this one observation definitive proof of climate-driven range expansion would be premature. Equally, dismissing it as an irrelevant accident would ignore the wider pattern of warming seas and increasing biological movement into the North Sea.

This is exactly why systematic observations matter.

Historical absence from a database is not proof of ecological absence. It may reflect limited monitoring, failed identification or observations that were never preserved. The public can help close this gap. Photograph unusual strandline organisms, record the date and exact location, include a size reference, estimate their number and submit the observation to us (GoJelly/JellySpotter APP) or another biodiversity platform like the iNaturalist. Today’s carefully documented beach find may become tomorrow’s essential evidence of how marine distributions are changing.

Recommened for reading:

  1. Pires RFT, Cordeiro N, Dubert J, Marraccini A, Relvas P, dos Santos A (2018) Untangling Velella velella (Cnidaria: Anthoathecatae) transport: a citizen science and oceanographic approach. Mar Ecol Prog Ser 591:241-251 https://doi.org/10.3354/meps12266
  2. Betti, F., Bo, M., … Enrichetti, F. (2019). Massive strandings of Velella velella (Hydrozoa: Anthoathecata: Porpitidae) in the Ligurian Sea (North-western Mediterranean Sea). The European Zoological Journal86(1), 343–353. https://doi.org/10.1080/24750263.2019.1671506

Picture courtesy to https://commons.wikimedia.org/wiki/File:20160518_170717_Velella_velella_1.jpg

First Spotted, or Simply First Recorded? Velella and Our Ecological Blind Spots

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