A recent Twitter campaign, #SkypeaScientistQuestions, inspired me to write down some of the most common and most creative questions that I have gotten over the last six sessions with various classrooms through Skype a Scientist. Many of these were from 5th graders, of which only two were in coastal states and had regular access to the shore:
Do all jellyfish sting?
Yes, as far as we know, all jellyfish sting! This is because all jellyfish have stinging cells (nematocytes), which are the defining character, or trait, for the group. Jellyfish are also carnivores, so it makes sense that they have to sting in order to catch prey.
What are the weakest or least venomous jellyfish?
Tough question because, for humans, most jellyfish are not dangerous at all. Many jellies are quite little, a few millimeters or less, such that their stinging cells are too small to puncture our skin. Some of the weakest stingers are likely medusivores, or jellyfish that only eat other jellyfish, such as the Egg-yolk Jellyfish. These jellies have adhesive stinging cells to grab onto other jellies, but these kinds of stinging cells typically do not inject much, if any, venom. There is actually a Jellyfish Lake where people can dive with jellyfish, which are most closely related to the Spotted Jellyfish (Mastigias papua), and survive through a symbiosis with algae that shares food with the jellyfish, so because they do not need to catch prey they have become very weak stingers.
What is the most dangerous jellyfish?
For humans, the most dangerous group would be box jellies, a group of about 50 animals of which several members are very dangerous. This includes the Australian Box Jellyfish (Chironex fleckeri), which can kill an adult human male in under two minutes from heart failure. Linked is a video from Dr. Jamie Seymour at James Cook University talking more about the sting from this animal. There is also a 2018 article in Science about the work of Dr. Yanagihara, who studies box jellyfish venom. The Portuguese Man-of-War (Physalia physlais), a member of the class Hydrozoa, is also a particularly dangerous stinger, which causes so much pain that some people actually drown in the water. There are also some instances of severe allergic reactions due to multiple encounters with Man-of-wars. Nomura’s jellies (Nemopilema nomurai) are large jellies that bloom along the coasts of China, and several deaths have occurred from encounters with these animals. There are other several other jellies that can cause harm to people, including sea nettles (Chrysaora,sp.) upside-down jellies (Cassiopea sp.) and thimble jellies (Linuche unguiculata). See Table 1 of Purcell et al 2007 for reports of major stinging events, including deaths, across the world due to various jellies. (And for those that have access to non open-source research articles, Tibballs et al 2011also reports on various health issues associated with jellyfish stings).
Do jellyfish have the venom of a snake? (Probably my favorite question)
Such a profound question! In a way, yes, they do! Almost 15% of all described species are venomous, which includes snakes, fish, cone snails, insects, scorpions, spiders, and jellies. Venoms are dynamic, meaning they are constantly changing depending on their environment, such that venom may be different between similar species, different populations of the same species, or even within the same individual at different ages. But, surprisingly, the toxins that compose venoms are derived from very similar gene families. This is an instance of convergent evolution, where similar environmental pressures have resulted in similar evolutionary solutions. In other words, venom evolved multiple times independently within different animal lineages. This similarity is what makes studying venoms so interesting, because the mechanisms of synthesis (building a toxin) or how a toxin works can be similar between a fish and scorpion, a bee and cone snail, or a snake and a jellyfish!
What is the largest jellyfish?
The Lion’s Mane jellyfish (Cyanea capillata) can reach a bell diameter of 2 meters (6 feet) and tentacle length over 40 meters (120 feet)! That makes them longer than a blue whale! Many people encounter these animals when they are much smaller, such as during the winter in the Chesapeake Bay when these animals are typically in bloom. There are also deep sea siphonophores can also be 20-30 meters long.
What do jellyfish eat?
All jellyfish are carnivores, and typically consume zooplankton and small invertebrates, but really anything they can catch jellyfish will try to eat. Some of the more toxic eat fish as well, and many also love fish eggs. Jellyfish may consume other jellyfish too, as mentioned above.
What eats jellies?
The two most well-known are sea turtles and the sunfish (Mola mola), but recent work featured in NYTimes Science showed that many different fishes and birds (including penguins) also eat jellies. Jellyfish are eaten within several coastal Asian countries, and recently a technique has been developed to turn jellies into chips. I also wrote more about what eats jellyfish in a previous post.
How long do jellyfish live for?
This one is always a little tricky for me to answer. Typically, the actual medusa lives for a few months to a few years. For hydromedusae, these stages may just be for dispersal (moving from one place to another) since polyps do not move. For true jellies (Class Scyphozoa), the medusa stage is larger and lives longer. Box jellies spend up to a few years as a medusa as well, but we know very little about the lives of polyps. The complicated part is how long do polyps live. Most jellyfish polyps are asexual – they reproduce through various mechanisms of budding. Because budding produces a clone, that animal is the same genetically. Polyps can do this over and over, giving rise to a biological species strain. Strains are really important for research, because different labs across the world use the same strain to ensure reproducibility in research and to reduce variables ins experiments. Strains can survive for decades, so technically these animals are alive for decades as well! For individual polyps, it not clear how long they might live. My conservative guess would be a few years, depending on the species. A single Hydra, a model for developmental and regeneration research, can survive for decades in proper conditions (see this great video for a short story about Hydra).
One species I love to talk about is the Immortal Jellyfish (Turritopsis nutricula). This hydrozoan has the incredible ability to go from polyp to medusa and then back to a polyp! When they return to the polyp stage, all of their cells go through a process called transdifferentiation. Essentially, the cells return to stem cells, which give rise to all other cell types. That means what was once a muscle cell or a neuron goes back to a stem-cell like state and can change into a different cell type. Through this process, individuals of this species are effectively immortal, able to go back and forth continuously. Many species in this group are actually able to do this, though this species is one of the most well known and best studied. The ecological reality is these tiny animals are often eaten, so it’s hard to say what the longest living individual may have been. If you want to learn more about the Immortal Jellyfish, check out this Youtube video from SciShow and stories from the American Museum of Natural History and Discover.
Do they lay eggs? How often and how big are they?
Some do lay eggs, including my little Hydractinia. When these animals are undergoing sexual reproduction, where you need male and female gametes to form an embyro, jellies and sea anemones do produce eggs! Many are broadcast spawners and release their eggs into the water column to be fertilized, but some jellies brood their eggs until they hatch, like the upside-down jellyfish and moon jellies (Aurelia sp.).
Can jellyfish be pets?
For sure! Many salt water tanks have sea anemones, which are in the same group as jellies. Specialty tanks to keep moon jellies, like Jellyfish Art and JellyTank, are also becoming more popular. Jellyfish need special tanks called krisels that have no corners and special filtering systems that do not suck up the delicate jellies. I have a Jellyfish Art Nano that I used to raise my first moon jellies. Now, I have a salt water tank with three different anemones as well as a smaller tank for an upside-down jellyfish. Since these animals sit on the bottom of the tank, they actually prefer gravel tanks and plenty of light for their algal symbionts. I also have different polyps at home that live in glass dishes; moon jellies (Aurelia aurita), fried egg jellies (Cotylorhiza tuberculata), and purple-people eaters (Sanderia malaynesis) (common names are way more fun). I plan on getting more jellies over time, but maintaining jellyfish, and really any marine tank, is time intensive and expensive. That being said, Jellyfish Art was a great starter tank for anyone that would like jellies of their own.
Have you ever been stung by a jellyfish?
Probably every day I work with them, but they don’t get through my skin. I have been stung twice by sea nettles on the east coast and by upside-down jellyfish when I have worked with them at the National Museum of Natural History (NMNH) in Washington D.C. The sea nettle stings were the worst in terms of pain, but it went away after a few hours. The upside-down jelly stings had some minor tingling that went away after a few minutes.
Do dead jellyfish sting?
Yes they do, so do not pick them up at the beach!
Should you pee on a jellyfish sting?
No, no, no, no, no, no, and no. Peeing on a jellyfish sting is a dangerous myth that has persisted much too long popularized by an episode of Friends. Peeing on a sting will not only probably cause an infection, but will make any leftover stinging cells fire into your skin. This is because urine is mostly fresh water, and fresh water will fire any leftover stinging cells due to an osmotic imbalance. The best thing to try and scrap off any stinging cells and leftover tentacle with a credit card or razor using saltwater. Saltwater will keep stinging cells from discharging. Then add vinegar to denature any toxins. Here is a video that does a great job of explaining what to do (and what not to do). Usually pain from jellyfish stings will go away after a few hours, but depending on which beach you at, be cautious about jellyfish season. And if you spot a jellyfish, be sure to report it at JellyWatch!
Is there real jelly inside? Do jellies like peanut butter? (Close second for favorite question)
So unlike the jellyfish in Spongebob, jellies do not contain any jam. However, a majority of the inside of a medusa is a jelly-like substance called mesoglea, which looks and feels a lot like jello. Do jellies like peanut butter? Hilariously, yes! Jellyfish were fed peanut butter at the Children’s Aquariumin Dallas, Texas, because of the high protein content. Initially it was suggested as a joke by aquarists testing more sustainable types of food. To their surprise, jellies ate the peanut butter and grew! Here are a few more articles about this find from Deep Sea News , National Geographic, and i09.
What is your favorite type of jellyfish?
I do love my main research animal, Hydractinia symbiolongicarpus, also called snail fur. My favorite to look at are Blue Blubbers (Catostylus mosaicus) and my favorite to talk about are the box jellies and the Portuguese Man-of-War, for their venoms (of course).
What sparked your interest in jellies?
When I was very young, maybe fifth or sixth grade, I was determined to be a scientist. I took to heart my dad’s advice that I should go into a small field, and I had settled on marine science pretty early. So, looking to narrow down my interests, I started reading more was about deep sea biology and bioluminescence, and the jellies were the most fascinating animals. In high school I saw a video about the Immortal Jellyfish on YouTube, and I was officially hooked. The more I learned about jellies, the more fascinated I became. I was also one of those kids that loved chemistry, and wanting to combine my interests I started to read more about natural products and venoms. When I entered my undergrad at William and Mary, I emailed the only marine invertebrate lab on campus that I wanted to research “cnidarians with implications for human health.” Dr. Jon Allen, the head of that lab, would be my undergraduate researcher advisor for four years, but on flatworms instead of jellies. I had the opportunity to work in a cnidarian lab at the NMNH during my junior year, and through that experience I ended up where I am today. Now I am in graduate school working in a jellyfish lab on venom evolution, and I could not be happier!