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Jellyfish - Invisible assassins with a deadly sting

While ‘invisible’ is not entirely accurate, jellyfish are extremely hard to spot when you are in the water with them. Obviously, that’s a particular nuisance given how much their stings hurt. If you are one of the fortunate people who have not been stung by a jellyfish (yet), you might be able to look at these creatures with fascination and awe. After all, they are some of the most ancient animals, inducing pain and death for over 500 million years (that’s one for the CV). Sure, they can be stunningly beautiful and often look so surreal that it is easy to assume they are spawns of Steven Spielberg’s imagination rather than a marvel of evolution, but as a toxinologist the main appeal to me lies in their highly sophisticated and optimised biochemical arsenal, as well as venom delivery mechanism. So, in this blog, I would like to explore this further and tell you about my personal encounters with two of the world’s most venomous jellyfish, the Box jellyfish and the Irukandji.

For a long time, one of my main misconceptions was that whilst you can find jellyfish nearly everywhere, you only get the bad ones in tropical regions, such as Australia, Southeast Asia, Hawaii, etc. This is true to some extent, if you classify ‘bad’ as ‘lethal’, but if you are a bit more stringent with the definition and just equate ‘bad’ to ‘super painful’, you will find these buggers closer to home.

Let me elaborate: Last summer I travelled to the south of France together with my girlfriend and some friends to enjoy the sunshine, the sea, and, of course, the exquisite food. Overall, we had a great time, but on one day the calm Mediterranean Sea transformed from a turquoise paradise into a death trap, reminiscent of the Hunger Games - there were jellyfish everywhere! But the weather was so nice and the water so gorgeous that we decided to have a swim anyway – even if we would get stung, how bad could it really be (they say you become wiser with age, but I am still waiting for that to kick in).

Illustration: Timothy Jenkins and Chandra DeDionigi

Enjoying the south of France – still blissfully ignorant about the dangers these waters hold.

Turns out that it could be pretty bad. Within a few minutes in the water my girlfriend got stung and felt sharp pain in her leg instantly. Nevertheless, I was quite hopeful that it couldn’t be too bad and that the pain would rapidly subside - little did I know. The skin where she was stung immediately turned scarlet red and started blistering within minutes. Meanwhile, the pain only got worse and extreme nausea just added to this delightful experience (Being on a boat probably also didn’t help). Eight months later and the scars are still visible. This just goes to show that you don’t need to go to particularly exotic countries to enjoy the pleasure of jellyfish venom.

Illustration: Timothy Jenkins

Pelagia noctiluca (purple-striped jellyfish) – one of the most venomous jellyfish in the Mediterranean and the bugger that stung my girlfriend (left), as well as one of the blistering stinging sites (right).

So how do these gelatinous creatures pack such a punch? Well, there are two key reasons for the success of jellyfish: (1) Their stinging apparatus and (2) their venom.

Jellyfish have specialised stinging cells called cnidocytes and organelles within them called nematocysts, which function a bit like biochemically triggered harpoons. The nematocysts consist of a sac that holds the venom and a tubule that ends in a stylet (harpoon). This firing mechanism is triggered when the sensory rod (cnidocil) of the cell is touched. The harpoon (stylet) is launched at incredible speed and pressure. In fact, the pressure under which the skin is pierced exceeds 7 billion Pascals, which is comparable to the pressure at which a bullet is fired from a gun. Now, the venom can travel via the connecting tubular structure into the victim via osmotic pressure.

Illustration: Kai-ou Tang in collaboration with Johns Hopkins SOM and the National Aquarium

Illustration of how Jellyfish stings work.

The venom that is injected varies from jellyfish to jellyfish, but one toxin that has been found in all jellyfish venoms so far is called porin. These toxins are fast-acting and not very picky when it comes to what cells they should smash holes into; they have been shown to affect blood, skin, and nerve cells.

Besides these porins, jellyfish can have myriads of other chemical warheads ready to wreak havoc, but to give you an example I think we should look at the most toxic jellyfish (and one of the most toxic creatures on earth), the box jellyfish (Chironex fleckeri).

Illustration: Dr. Robert Harwick

The Box jellyfish (Chironex fleckeri) - one of the most lethal creatures on this planet.

These jellyfish can be found predominantly around the northern parts of Australia, as well as South-east Asia, and Hawaii. They are quite large and are known to grow up to 30cm in diameter and 3m in length. They also have 60 tentacles with 500,000 cnidocytes. Some more fun facts include that they sleep (unlike most jellyfish), they can actively hunt and have sophisticated strategies towards patrolling the waters for maximum coverage, and they have eyes that can detect light. They are also able to easily kill a person in under 10 min, something any venomous snake can only dream of adding to their repertoire. But why are they so toxic?

Video of my previous supervisor demonstrating how jellyfish stinging events occur in slow motion.

In this particular case the culprits are cardiotoxins that act extraordinarily rapidly and can cause loss of consciousness within seconds, followed by cardiovascular collapse which can result in fatal cardiac arrest in less than 10 minutes.

Unfortunately, there currently are no effective antivenoms against any jellyfish, so first aid and artificial resuscitation remains the only medical treatments commonly in use. Here, I should mention that when you get stung by jellyfish do NOT pee on the stinging site - somehow this still is a common misconception… Vinegar is often used, since it is thought to neutralise any stinging cells that haven’t fired yet. However, research has shown that this can also lead to the release of more venom from already fired nematocysts (usually 40% of the venom stays in the cells). So I guess that leaves the question of what you should do instead. Unfortunately, neither myself nor science have a great answer. Some studies suggest submerging the stinging site in hot water (first check the temperature with a different body part that it isn’t too hot and so you don’t boil yourself!). However, the evidence for this is also not entirely convincing. My personal advice is to first ensure that it isn’t a dangerous sting – asking a lifeguard is always a good idea. If it is, get to a hospital asap. If not, carefully rinse the sting site so that any tentacles can fall off (without touching more skin – gravity is your friend here), take some pain meds, and feel sorry for yourself.

Illustration: Paul Arps Flickr

Typical jellyfish warning signs and first aid vinegar at beaches in Australia.

The above-mentioned research on the vinegar actually stems from the university I was studying at in Australia (James Cook) and I was fortunate enough to work with some of the leading jellyfish/venom researchers worldwide. One of my supervisors was, amongst other things, particularly interested in finding ways to prevent people from getting stung while swimming. This involved exposing many different materials that could be made into stinger suits (thin wet suits) to box jellyfish tentacles. Unfortunately for him, he could not get ethics approval to make his students wear these materials, so he tested it on himself in true Aussie fashion. Needless to say that he was easily irritated on days where his experiments failed…

Another jellyfish that is related to box jellyfish and can also be found around the North-east of Australia is called Irukandji (after a local aboriginal community). This jellyfish is tiny and rarely lethal, unlike the box jellyfish. It does, however, still pack a massive punch. It can cause something dubbed the ‘Irukandji syndrome’, which in its essence is just unfathomable body-wide muscle pain. The pain is so bad that my supervisor (who regularly got stung by box jellyfish) would call it the worst pain he has ever felt and that if someone had given him a gun after he had been stung, he would have happily used it to escape the suffering caused by the Irukandji sting.

Illustration: Queensland blog (left) and Cairns Post (right)

Image of Green Island (left) and the Irukandji at the James Cook University research aquarium (right).

Here is a video of what happened when my supervisor and his PhD student got stung while conducting research on the Irukandji. I am sure the University’s health and safety department are stoked about this line of research.

My personal encounter with these invisible assassins was within my first weeks in Australia. The university was organising a fun week for all of the new students to meet and interact and one of the events included a snorkelling trip to Green Island (an island just off the coast of Cairns). Of course, we were all super excited for it and had an awesome time there. That was until the lifeguards sounded an alarm on the beach. We had no clue what was going on but knew that it could not be too good. That feeling of impending doom only increased when we saw a lifeguard frantically paddling over to us on his ocean kayak. He told us that the couple that was swimming next to us minutes before had been stung by an Irukandji and that we needed to get out of the water (let’s just say that he didn’t have to ask twice). The 100 meters or so that we had to swim were the scariest swim I have ever had. Luckily, we got out unscathed - well physically, not emotionally.

To end this blog on a high note, things are only going to get worse with global warming and the rise of ocean temperatures. Research has already shown that you can find box jellyfish and Irukandji further south than ever anticipated and that they are spreading further each year. This is the case with most jellyfish and reports of so called ‘jellyfish blooms’ are becoming more and more frequent. So, if you don’t want to increase your chances of being stung, think about how you can play a part in reducing climate change – or just stay out of the water ;)

Timothy Jenkins holds a PhD in biomedicine and is an aspiring biotech entrepreneur. He recently completed his doctoral studies at the University of Cambridge, where he was awarded the ABCAM award for top PhD candidate at his department. Now, Tim is working as a postdoctoral fellow at the Technical University of Denmark with biotechnology-based antidotes to snake bites. Timothy Jenkins har en ph.d. i biomedicine og er biotek-entreprenør in spe. Han er uddannet ved University of Cambridge, hvor han modtog ABCAM-prisen for bedste ph.d.-kandidat i sin afdeling. Nu arbejder Tim som postdoc fellow på DTU med biotek-baserede modgifte mod slangebid.
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Tusind tak, jeg er glad for at du synes det er spaendende og nemt at laese.

This was with the help from a colleague of mine, since my Danish is still somewhat lacking ;)

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I have encounterede Pelagia noctiluca when snorkling in the Red Sea at our winter-house in Sharm el Sheikh. And I must say, that I dont find them nearly as bad, as the picture painted in the article. Its unlike a lions mane, that we know from danish waters, where the paine starts out as mildly annoying and then slowly grows to something that demands attention, ending at "aw shit, this really burns and will take hours to subsuide". I find that Pelagia noctiluca gives more of a sudden, quite powerful sharp stinging pain, that then quite fast changes into a not too bad burning pain, that goes away after 15-20 minutes. But I guess it varries from person to person. I find the initial sharp stinging feeling the most painful. The first 2-3 times you get stung on a swim, you decide, "come on, thats not too bad, how many can there really be". But then after a few more you decide enough is enough and gets out of the water. My nephew is normally a bit smarter than me and decides enough is enough already after getting stung the first time....alternatively he is a just a little sissy.

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Hi Jens, thanks for reading the blog and adding to it with your great comment! I am glad to here that P. noctiluca didn't get you that badly. All I can say is that my description of what happend last summer was not exaggerated, but as you say 'it can vary from person to person'. I should add that she got stung on several different locations and that certainly didn't help. It would also not be unheard of, if the venom composition between populations in the red sea and the western mediterranean differed...

Sounds like some nice stinger suits wouldn't be a bad idea for you trips;) They actually are pretty good, because they also provide sun protection.

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As a school kid I learned to swim i a saltwater facility built on pillars from the beach. A classmate of mine hit a large lions mane, so badly that most of his torso was hit. He made it up the ladder, then fell unconscious. He was rushed to nearest hospital and survived. He might have been oversensitive, i dont know.

But I learned that day, that even a lions mane could cause death by drowning. Never swim alone!

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Hi Peter, thanks for contributing this. He might have also had an allergic reaction. If you think about how tiny bee stings can kill people due to an allergic reaction, such a large exposure to venom is bound to have a systemic effect, even if you aren't particulalry sensitive. It's a large amount of foreign and toxic proteins entering the system. Happy to hear that he was fine in the end though!

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Hi René, thanks for reading the blog and providing some personal insights. I have personally also found that hot water is the best first aid when being exposed to any marine venom (sea urchins, anenomes, stone fish, lion fish etc.), but it is sometimes hard to come by depending where you are at the moment of the sting. Glad it helped you!

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But I learned that day, that even a lions mane could cause death by drowning. Never swim alone!

I have also had one of my friends take a major hit from a big lions mane, right it the face. He litrally had to lift it off his head, and he also had to take a little trip to the hospital. So they definitely shouldn't be underestimated.

Interrestingly, on the decostop after a dive, when dodging the lions manes, you may sometimes see a really big one, with 10-20 small 5-10 cm long juvenile fish swimming right under the lion manes body right in between the stinging threads. The juveniles of some fish species are some how imune to the sting and live within the threads for protection against predators, and I guees probabbly also to take advantage of left overs from the meals of the lions mane. How they do it I have no idea.

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Hi Jens, I just realised I forgot to reply to your comment - apologies. It sounds like your friend really got a close up view of that lion's mane...

This kind of mutalism is quite common actually, e.g. clown fish and anenomes. In that case a layer of mucus on the clownfish's skin makes it immune to the fish-eating anemone's lethal sting.

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@Jens: Det er hvilling, hvis yngel man ofte ser i den røde brandmand - er lige kommet op fra et dyk på Väderöarna 😀

@Timothy: it’s the juvenile Merlangius merlangus (cod family) you ofte see in the lion’s mane - just experienced it a few hours ago

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Hi Flemming, thanks for following the blog! It is indeed Merlangius merlangus. Jealous of you having seen this yesterday ;) Was it in Denmark?

The lion's mane actually has a bunch of other cool symbiotic realtioships:

One mutual relationship the Cyanea capillata has is with the small crab megalops larva that lives on the outside of its bell and helps keep it clean.

Practicially all tropical jellyfish have a mutual relationship with a Dinoflagellate, and Cyanea capillata is no exception. Zooxanthellae is a Dinoflagellate that lives inside the jellyfish. This tiny protist creates energy from sunlight and also organic molecules that the jellyfish can then use. In return, the jellyfish excretes ammonium molecules for the Zooxanthellae to use. However, this relationship is primarily in the tropical regions and are therefore only found in the smaller Lion's Mane jellyfish.

Another important mutual relationship the Lion's Mane jellyfish has is with shrimp. Cyanea capillata helps protect and provide food for the shrimp while the shrimp plays a similar role as the crab larva.

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@Jens: Det er hvilling, hvis yngel man ofte ser i den røde brandmand - er lige kommet op fra et dyk på Väderöarna 😀

Det er også hvad jeg tidligere har fået af vide. Jeg har dog aldrig fundet nogen gode kilder til at bekræfte det. Har også andre steder fået at vide, at flere fiskearter kan dette trick som unger.

Hvad er din kilde til at det er hvilling?

Ellers hyggeligt med dyk ved Väderöarna da. Er det hos Dyk-Leif med thaimad til middag?

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Hej Jens

Vi har lejet en “Sjöbod” heroppe i en uge og har vores egen RIB med, så vi er ret autonome 😀

I dag skal vi dog ud med Dyk-Leif, han må dykke også på fredede skær, hvor private er udelukket om sommeren, så vi tager altid en dag eller to med ham, når vi er her - får også fyldt tanke der.

Mht hvilling tror jeg, det er fra min “bibel”, men jeg har den ikke med, så jeg må lige vende tilbage, når jeg kommer hjem - men jeg kan ikke helt udelukke, at det også blot er noget, “jeg har hørt” 😉

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Hi Jens,

I have found some things here:

The association between scyphomedusae such as C. capillata and Rhizostoma octopus (Linnaeus) and juveniles of whiting Merlangius merlangus (Linnaeus) may be an example of mutualism, cleaning of parasites on the medusae by the whiting and medusan protection due to their toxins for the whiting (Arai 1988). However, there are controversial observations between them, probably depending on differences in individuals and the age of the fish. https://www.jstage.jst.go.jp/article/pbr/4...

And here (page 214 etc.): https://link.springer.com/content/pdf/10.1...

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