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Ocean blooms: tracking the rise of jellyfish swarms

Ocean blooms: tracking the rise of jellyfish swarms
18 Oct
Many scientists believe that jellyfish numbers are increasing, pointing to their remarkable resilience to climate change and the increase in hugely damaging jellyfish blooms. But are jellies really taking over, and if so, what should be done to prevent the jellification of the ocean?

The winners of the 2008 Nobel Prize in Chemistry owe their success to jellyfish. Specifically, to Aequorea Victoria (or the crystal jellyfish), a delicate, translucent species whose organs emit light. It was by collecting thousands of these bioluminescent creatures, which float in the waters off the west coast of North America, that Martin Chalfie, Osamu Shimomura and Roger Y Tsien were able to extract and develop green fluorescent protein (gfp), a substance that glows intensely under ultraviolet light and which revolutionised the study of human diseases. By inserting gfp into cells, scientists around the world can now track the way cancer tumours form new blood vessels, the way Alzheimer’s disease kills brain neurons and the way HIV-infected cells produce new viruses.

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The discovery of gfp and its phenomenal usefulness is a rare anomaly in the wider jellyfish story. As the tale normally goes, jellies are a nuisance, a pest, or in some cases a deadly menace – the sting of the deadly box jellyfish can cause a human heart to stop within seconds. Most problematic of all are the huge explosions of jellyfish populations that occur in waters all around the world. Facilitated by the ability of jellyfish to reproduce asexually (‘polyps’ – the earliest stage of jellyfish life – are able to clone themselves), these ‘blooms’ can reach up to 120 tonnes of wet jelly weight. If this occurs near a fish farm, the jellies can clog nets or lodge within gills, starving valuable fish of oxygen. If it happens near a coastal power station, the swarm can block underwater cooling systems resulting in immensely costly shut-downs. Power plants in Japan, Israel, Sweden and the UK have all been affected – the Torness nuclear power station, situated 30 miles along the coast from Edinburgh, was forced to shut down for several days in 2011 due to an approaching army of jellies. What’s more, the problem might be getting worse.


It was in the 1990s and 2000s that details first began to appear in the scientific literature of increasing instances of jellyfish blooms. The studies grew more and more vociferous, pointing to the ‘jellification’ of the ocean – a future described in one study as ‘jellyfish soup’. It’s a story that’s been oft-repeated and which remains pervasive, spurred on by the discovery that some jellyfish appear to be particularly resilient to climate change, able to thrive in warm, deoxygenated waters where other fish die.

Jellyfish blooms appear to be increasing in frequency in some areasJellyfish blooms appear to be increasing in frequency in some areas

Most scientists today take a more guarded view. A damning study published in 2016 by an international group of jellyfish experts, found that the perception of a global increase in blooms was at least partly due to poor citation practices in the scientific literature. Referring to ‘time-poor scientists’ and ‘academic workloads’, the study concluded that concrete evidence for a heavy increase in blooms was weak. It led to a much more cautious approach to declaring a jellyfish apocalypse and most scientists no longer do so with such bravado.

Yet, far from heralding a decline in interest, jellyfish research is thriving and much of it still focuses on the threats. While the blanket statements of doom are gone, many scientists are still convinced that jellyfish blooms are on the rise, leading to the inevitable, but tricky questions of when and where they are likely to occur.


On a mercifully calm day in June, the RV Plymouth Quest pulls out of Plymouth harbour. Skipper Andrew Perkin steers the ship out to sea and for a while, all is calm – the crew sipping tea and eating biscuits in the hold as the Devon coast slips by. About half an hour later, everything changes. The research vessel, owned by the Plymouth Marine Laboratory, has reached the first stop of the Western Channel Observatory, a reference site in the English Channel where a series of biological, chemical and physical ocean measurements are undertaken once a week.

As the ship comes to a halt – a single buoy marks the spot – the crew and the researchers on board leap into action, turning their attention to a piece of equipment called a CTD, which measures water temperature and takes water samples. Composed of long capsules enclosed within a five-foot frame, the CTD is lowered into the ocean via a heavy-duty cable and water is sampled at various depths. Next, three conical nets are deployed. The nets are towed through the water, siphoning off the plankton that lives near the surface. This weekly collection of measurements, which includes data on light, temperature, salinity and nutrients, is one of the longest ocean time-series studies in the world, with some measurements collected since 1903. It’s a vital record for scientists studying changes to the marine environment. Bonus: it helps predict jellyfish blooms.

Every week scientists on board the Plymouth Marine Quest collect data and samples Every week scientists on board the Plymouth Marine Quest collect data and samples

Back at the lab, a short walk from Plymouth harbour, Dr Sevrine Sailley is waiting for the data to return. Her goal is to create a system that can predict when and where jellyfish blooms are likely to take place. The project is being carried out in partnership with EDF Energy, which hopes the research will lead to an early-warning system for its off-shore power plants (the Torness station which was forced to shut down in 2011 is EDF-owned). In order to create this system, Sailley is combining high-resolution satellite imagery and habitat models with environmental data, including that collected by the Quest, to identify the conditions most likely to lead to a bloom.

Sailley has been working on the project for the last two years and so far the research indicates that certain environmental factors do appear to encourage blooms, or at least those that take place in English waters (she adds that her system would be redundant in other waters where different jellyfish species are prevalent). ‘At the moment, temperature and also total primary production of phytoplankton – demonstrated by the amount of chlorophyll – are looking very promising,’ she says. In short, the jellyfish appear to respond well to warmer waters and increased phytoplankton (jellyfish food) although other factors are also relevant. ‘I’m also looking to see if the actual composition of the phytoplankton might be another factor,’ she adds. Initial findings suggest that a high prevalence of larger phytoplankton, called diatoms, could be a negative indicator of jellyfish because they appear to be popular with small crustaceans known as copepods – key jellyfish competitors.

Marine science technician, Oban Jones, extracts water samplesMarine science technician, Oban Jones, extracts water samples

Though Sailley’s project is in partnership with the energy industry, as a scientist she believes her research could have wider applications. Not least, it contributes to the fundamental question of whether these blooms really are increasing and if so, why. Like most people in the field, Sailley says that existing data does point to a rise in jellyfish blooms and that climate change does appear to be enabling them, though like most experts she is cautious of declaring this as an undying truth. ‘In any kind of time series or longer record, there’s a trend towards more blooms,’ she says, adding that, ‘warmer water will boost the growing speed.’ But, she says, there are other reasons for this apparent rise: ‘It is happening, but at the same time I think there are a lot more people paying attention.’

The rise in jellies might also have less to do with the jellyfish themselves, and more to do with other fish doing badly. This is the view of Nicole Aberle-Malzahn, associate professor in biological oceanography at the Norwegian University for Science and Technology. She is working on a separate project to predict jellyfish blooms in a number of regions, including the Mediterranean and Norwegian Seas. ‘I think that the combination of warming waters and overfishing are the major factors which are driving the jellification of the ocean,’ she says. ‘In many areas the predators of jellyfish have been reduced, and also jellyfish and fish compete for the same food sources.’

Aberle-Malzahn’s research into blooms is still in its early stages. Her team is busy collecting vast amounts of environmental data in order to create prediction models. But while the research is not yet as advanced as that being done in Plymouth, it feeds into a project that asks a much wider question. Namely: if there are too many jellyfish in the water, what should we do with them?


With its natty name and cute logo, it might be tempting not to take the GoJelly project seriously. But with funding from the European Union’s Horizon 2020 Research and Innovation programme and a global team of marine scientists on-board, that would be a mistake. The goal of the project is to control blooms by creating a commercial market for jellyfish, thereby encouraging their capture and removal from the ocean. In doing so, the project leads claim they can also tackle another pervasive environmental problem.

Cotylorhiza tuberculata, also known at the fried egg jellyfish, is used in GoJelly experimentsCotylorhiza tuberculata, also known at the fried egg jellyfish, is used in GoJelly experiments [Image: GoJelly]

‘The idea was to look at jellyfish not as a pest or a plague, but as something we could make use of,’ says Carlos Andrade, a GoJelly project scientist from the Madeira Agency for the Development of Research Technology and Innovation. This encompasses a number of strands – project scientists are working on promoting jellyfish as a food source (they are already a popular delicacy in some Asian countries, but rarely eaten in the West), as a cosmetic ingredient (jellyfish contain collagen), as a fertiliser, as fish feed for aquaculture and, perhaps the piece de resistance, as a microplastic catcher. For the latter, Andrade explains that if ‘one could extract the mucus from the jellyfish then we could use it, because the mucus tends to aggregate particles around it. You could use it in sewage treatment stations to trap microplastics.’

Before any of this can really take off there is a great deal more research to do. For his part, Andrade is working on developing effective harvesting methods for jellyfish, which are notoriously difficult to catch because their soft bodies are easily damaged and can clog nets with slime. Nevertheless, he insists that the final product is viable, adding that project scientists at the University of Haifa, Israel have already created a working prototype of the mucusy microplastic filter. Their goal now is to turn this invention into a commercial product.


Taking a pest and using it to reduce pollution sounds perfectly sensible, but our increased interest in jellies, and their commercialisation, raises a crucial question – are we seeking to tackle a man-made problem with yet more potentially harmful tinkering?

It’s a crucial issue, not least because recent research has indicated that jellyfish play a much more important role in the ecosystem than previously understood. ‘It used to be assumed that jellyfish were a trophic dead end,’ says Kylie Pitt, discipline head of marine science at Griffith University and an author of the seminal 2016 study which placed doubt on the jellyfish explosion narrative. ‘That’s completely over now. We now know that there’s a whole lot of animals that feed on jellyfish and things such as the giant leatherback turtle will only eat jellyfish.’ In addition, jellyfish have also been shown to play a vital role as shelter for fish. Described in a 2019 study by researchers at Queen’s University Belfast as being a ‘gingerbread house’ for fish, they offer both food and shelter for the larvae and juveniles of certain fish species, more than two-thirds of which are of commercial value.

Once considered a trophic dead-end, jellyfish are a key food group for other marine animalsOnce considered a trophic dead-end, jellyfish are a key food group for other marine animals

It’s also not necessarily true that all jellyfish are on the up. While some are certainly thriving (Pitt points to the prolific moon jellyfish in particular) it might not be the case for other species. The fact remains that jellyfish remain vastly understudied. ‘We’ve been focusing all of our research on the species that are easy to study, and those are the same species that thrive in degraded conditions,’ says Pitt. ‘What we’re not studying is a whole lot of species that are probably rare and endangered and actually might be disappearing.’

Those involved with the GoJelly project insist that it has the sustainable harvest of jellies firmly in mind. ‘By doing studies, we know how to reproduce the jellyfish and produce juveniles,’ says Andrade. The thinking is that if ever ocean jelly stocks need to be replenished, those Andrade has reared in captivity will be able to be released safely. Aberle-Malzahn adds that research done to predict blooms will help ensure that only those populations which are thriving will be harvested.

But while these assurances demonstrate that GoJelly is taking a responsible approach to the commercialisation of jellyfish, the very nature of the project means that the burden of responsibility may not always rest with well-meaning scientists. The jellyfish story so far has been dominated by their threat to us, but as projects such as GoJelly take-off, and as our ability to locate and catch jellies increases, the key for those at the forefront of this research is to ensure that the threat does not become the threatened.

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