They're Brainless, They Terrorize Beachgoers and They May Be Able to Help Humanity

Israeli researchers dive into the murky world of jellyfish

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Jellyfish at the Israel Aquarium in Jerusalem.
Jellyfish at the Israel Aquarium in Jerusalem.Credit: Ohad Zwigenberg
Netta Ahituv
Netta Ahituv
Netta Ahituv
Netta Ahituv

The 10 brave Israelis who boarded a ship in the Mediterranean Sea one day about two weeks ago, knew what they were getting into: Most of them were likely to come back with painful burns. Actually, that was even one of their unofficial aims: to examine different methods for treating jellyfish stings. One of the leaders of the maritime excursion, Prof. Dror Angel, a marine ecologist from the University of Haifa, said he was taking aboard “liters of vinegar, in order to examine if and how vinegar helps people who are stung by different jellyfish.”

That was not the only purpose of the jellyfish-study excursion organized by EcoOcean, an organization that promotes preservation of Israel’s coastal and maritime environments. “The sea was calm and convenient, and we had the feeling that the jellyfish were cooperating with us,” says doctoral student Hila Dror, who was involved in one of five studies carried out by the researchers on board. “We brought a few of them on deck very easily, and we worked with them as if they were on a conveyor belt. First, we measured and weighed each specimen. Then we analyzed their stomach contents to understand what they eat.”

Dror herself took a tissue sample from each jellyfish (to build a genetic database), other researchers examined the creatures’ sexual organs (to understand the proportion of males and females in a swarm) and still others focused on their sensory organs (to figure out their age). For Dror, the major success of the day involved extracting jellyfish mucus – all in the name of science, of course. “Something like half a liter [a little over 2 cups] of mucus was extracted from each jellyfish, which is a lot,” she says. “I collected it all and put it into deep freeze.”

Jellyfish are of interest to anyone who goes to the beach in Israel, but research on them, whether conducted here or around the world, is meager, and compared to other denizens of the deep, very little is known about them. However, that situation has been undergoing a sea change in recent years. As a result, besides starting to realize how sophisticated and efficient these marine animals are, scientists are now also aware that they can be beneficial to human beings.

For example, jellyfish contain a great deal of collagen, a protein that can have positive effects on the skin, and experiments are examining how it can be used. Some cosmetics companies are already adding it to their antiaging products; it is also being used for medical purposes, in tissue surgery and for treating certain injuries. In Chinese medicine, powders derived from the jellyfish’s bell are used to reduce pain in the stomach and joints, and scientists are now attempting to adapt these techniques to Western medicine. Jellyfish are also eaten in China and Japan, generally after being dried; nutritionists say they are full of nutritious antioxidants. Jellyfish consume large quantities of proteins and fatty acids, which are also key constituents of human nutrition.

Israeli universities and research institutes in particular are also involved in intensive study of jellyfish these days, in terms of a range of subjects: How do jellyfish develop at the start of their life? How do they propel themselves in the water? What do they eat and where are they on the food chain? When and why do they show up by the seashore, and why do they later disappear? Are there now more jellyfish than there were in the past? How are they affected by global warming? Might they be able to help rid the oceans of plastic debris? And the most practical question of all: How do heal the stings caused by their venom?

As befits amazingly dramatic, mysterious, violent, gorgeous and weird creatures, they are also generating fierce controversies among researchers. In some cases they leave behind no less than a swarm of questions.

Dror Angel extracts a sample from a jellyfish’s stomach. Credit: Yehudit Ilani

Altering bathing habits

The great drama in the relationship between Israelis and jellyfish began in the 1970s, when noticeable swarms of the marine creatures reached the coast here. There is earlier evidence of jellyfish in the Mediterranean (they are known to have been around more than 500 million years), but it was in that decade that they became an integral part of the Israeli summer – and have forced locals to change their bathing habits every year.

Why did the jellyfish show up at that particular time? The best way to begin to answer that question is to turn to a veteran researcher of the colorful marine animals: Prof. Bella Galil, 70, currently a curator at the Steinhardt Museum of Natural History at Tel Aviv University. In 1990, while working at the Israel Oceanographic and Limnological Research Institution in Haifa, Galil published a breakthrough scientific article that for the first time described the most common jellyfish in Israel, the Rhopilema nomadica, or nomad jellyfish, together with two other species, the Cassiopea (upside-down jellyfish) and the Phyllorhiza punctata (floating bell jellyfish). Twenty years later, in 2010, she presented science with another new Mediterranean species, the Marivagia stellata (sea star jellyfish). And this year, a decade later, she described another new Mediterranean species of jellyfish, the Matzpenit, a name derived from the Hebrew word for “compass,” since its pattern is reminiscent of a compass. (Its scientific name is Chrysaora pseudoocellata.)

The theory put forward by Galil, whose expertise is invasive marine species, is now widely known: The nomad jellyfish entered the waters of the Mediterranean from the Red Sea following the opening of the Suez Canal in 1869. It thrives in the Mediterranean because it has few natural enemies and is opportunistic, as befits an invasive species. This theory is based, in part, on an exhibit in the Naturalis Biodiversity Center, a natural history museum in Leiden, Holland. In 1920, a Dutch scientist collected a single nomad jellyfish in the Bab al-Mandab Strait in the southern Red Sea, preserved it in formaldehyde and presented it as gift to the museum. Genetically, that specimen is identical to the vast swarms that arrive off Israel’s shores every summer, Galil and her colleagues have determined, and on the basis of that information the nomad jellyfish was classified as an invader to the Mediterranean from the Red Sea.

But that theory has lately been called into question by young researchers, one of whom works one floor below Galil in the Natural History Museum in Tel Aviv. He is Dr. Zafrir Kuplik, who is responsible for the museum’s research collection of coelenterates (aquatic invertebrates, including jellyfish).

“Theoretically,” Kuplik observes, when we meet at the museum and survey its large collection of preserved animals, “the nomad jellyfish species could have been here for hundreds of years.” His explanation is based on the fact that the species has a highly complex life cycle, one stage of which consists of microscopic polyps.

“So it’s possible that the nomad jellyfish’s polyps were always here,” he says, “and that the environmental conditions changed only in the past 40 years and enabled them to grow into mature jellyfish.”

In any event, since the jellyfish first began appearing en masse, Israeli beachgoers have seen them every summer. But not only then, it turns out. Prof. Angel and Dr. Dor Edelist, both of the University of Haifa’s Recanati Institute for Maritime Studies, have been studying the patterns of the nomad jellyfish’s appearance off the coast of Israel. One of their conclusions is that there are now more jellyfish here during the winter than previously. The reason for this is still not clear. “It may have to do with global warming,” Edelist says, “but it’s hard to say that with confidence.”

“We know for certain that temperature influences the appearance and disappearance of the jellyfish from our shores, as well as their numbers,” notes Angel, who also lectures in the departments of marine biology and maritime civilizations at the university’s Charney School of Marine Science, notes. For example, if there was a cold, very rainy winter, the jellyfish are more likely to appear later in the year. “When the sea is rough, jellyfish generally dive down,” he says. “So there might be jellyfish near the shore, but they don’t come to the surface.”

The research conducted by the two scientists is supplied with data from a website they created a decade ago. There, beachgoers and fishermen can report where, what kind and how many jellyfishes they have seen. The website also allows the general public to get updates on jellyfish sightings, so that people will know what beaches to avoid that day. Recently they turned the site into an app, under the auspices of the Israel Society for Ecology and Environmental Sciences, in cooperation with the coastal municipalities and the University of Haifa. Bathers can use the app to report about where, when and how many jellyfish they have spotted at any given moment.

“We discovered that, on average, the nomad jellyfish arrives in the third week of June and leaves at the end of July,” Angel says, although he and Edelist note that this year was different: The first wave arrived in May. “It is impossible to predict when the jellyfish will show up,” Angel says. “But if you look at the data from the past decade, we see that they are always here in July.”

When do they disappear with certainty?

Angel: “My sister always says to me, jokingly, ‘You remember that the jellyfish leave on Tisha B’Av, right?’” – referring to the Jewish fast day commemorating the destruction of the two temples in antiquity, which this year fell this week – “and the truth is that she’s partly right.”

There are a great many jellyfish in the seas and a great deal of plastic there. So it’s at least worth exploiting it for human benefit.

Hila Dror

The researchers know that the jellyfish swarms are swept northward with the currents along the Mediterranean coastline, so that at the start of the season there will be more jellyfish in the south and at the end more along the country’s northern coasts.

“From observations by colleagues, we know that from here they move north toward Syria, Turkey and also westward, in the direction of Cyprus and Greece,” Angel notes.

Sting-free beach

There is one beach in Israel that has deservedly gained a reputation for being free of jellyfish, Angel and Edelist confirm: Bat Galim beach, in Haifa. There are two reasons for this. First, because it’s a relatively closed area thanks to its breakwaters; second, because it is located at the tip of Carmel Bay, at the end of the only isthmus on Israel’s coast, where currents are unusually strong and sweep the jellyfish away.

Hila Dror in her lab at the Mevo’ot Yam School. “We are trying to find a solution to the microplastics problem in sewage treatment facilities using jellyfish mucus.”Credit: Tomer Appelbaum

It is widely thought that the number of jellyfish along Israel’s beaches increases every year, but the researchers are divided on this point.

“There are no more jellyfish now than there were in the past,” Edelist asserts. “There is tremendous change from one year to the next, but in the decade during which we have been tracking them, there has been no upward trend.”

In contrast, Dr. Tamar Guy-Haim maintains that “locally, we are seeing more jellyfish swarms.” According to Guy-Haim, head of the zooplankton ecology lab at the Israel Oceanographic and Limnological Research Institute, one of the reasons for this is accelerated warming. At the same time, she qualifies this by saying that “there is no agreement that there are actually more jellyfish globally, but there is natural fluctuation that is affected by marine currents and temperatures.”

If so, will we one day be swimming in a steamy jellyfish soup? That gruesome scenario is played down by Dr. Tamar Lotan, head of the University of Haifa’s Charney School of Marine Biology.

“It’s true that there was general concern that the sea would turn into a gelatinous mush, which is why a great deal of money has been invested in the study of the subject over the past two decades. As a result of the studies, fewer people now believe in these predictions,” she explains. “The general conclusion from the various research studies is that it is impossible to say with certainty that there are more jellyfish swarms today than there were in the past, or that the swarms are larger. What we can say without doubt is that because of globalization there are more species of jellyfish today in places where they did not previously exist.” (Some jellyfish relocate by attaching themselves to cargo ships, others by traversing the world’s manmade canals.)

It still sounds threatening.

Lotan: “Jellyfish ‘clean up’ the sea. Think of a creature of one millimeter that grows to 40 centimeters within three months. That is a rapid development, stemming from the fact that they eat a great deal.”

And what is the normal diet of a Mediterranean nomad jellyfish? That, too, is a focus of debate. Galil, the veteran scientist, maintains that they consume small fish and fish eggs. Lotan, though, is convinced that the nomad is low on the food chain and does not eat fish. Kuplik agrees with Lotan, arguing that it is not possible that nomad jellyfish eat fish. His explanation is somewhat startling, in more than one sense: Scientists know about it, but it may come as a surprise to the general public that the nomad jellyfish doesn’t have one central mouth – so there is little likelihood that it lives on small fish.

Aurelia aurita, the common jellyfish, at the Israel Aquarium in Jerusalem.

Kuplik: “They have many small mouths on their tentacles, which are incapable of swallowing fish. I have also examined the contents of the stomachs of jellyfish and found no trace of fish. Most of the food of the jellyfish is micron-size.”

However esoteric it may sound, the diet of the jellyfish is important. The prevailing theory is that the large summertime swarms have a large impact on the marine food chain, and cause immense damage.

While Kuplik agrees with this, he notes that this damage is secondary, because the jellyfish consumes the food eaten by other fish and is not directly nourished by large sea animals. The principal damage jellyfish cause is not environmental, Lotan says, it is economic – mainly because they frighten away bathers and stop up infrastructure pipes that have been laid in the ocean.

Galil, too, agrees. In an article she published a few years ago, she reports that the jellyfish swarms cause annual economic damage ranging from 7 million shekels to 24 million shekels ($2.1 million to $7.1 million).

But perhaps the damage issue does the jellyfish wrong. As it happens, a European Union project is now examining whether jellyfish can be of benefit to humanity – by ridding the sea of plastic. The GoJelly project, which brings together a number of research groups, bears a decidedly catchy subtitle: “A gelatinous solution to plastic pollution.”

“That project takes as its point of departure that there are a great many jellyfish in the seas and a great deal of plastic there,” says Dror, the doctoral student. “So it’s at least worth exploiting it for human benefit.”

We are visiting her jellyfish laboratory at the Mevo’ot Yam School in Mikhmoret, located north of Netanya on the coast. Dror, who is a member of the GoJelly project’s Israeli research group, explains that each group is studying a different subject in this connection.

“We are trying to find a solution to the microplastics problem in sewage treatment facilities using jellyfish mucus,” she notes.

Australian box jellyfish.Credit: gautsch.

“Together with a research team from the Braude College of Engineering in Carmiel, led by Prof. Issam Sabbah and Dr. Arik Ben David, we found that jellyfish mucus binds to the microplastics efficiently,” add Prof. Angel. “We don’t yet fully understand the mechanism, but based on our observations we are now building a model of a filter that will exploit the mucus to help reduce the pollution of the sea and of the environment.”

For those wondering how mucus is extracted from jellyfish: The pressure they experience when pulled from the sea makes them drip a large amount of mucus.

Says Dror: “In the first stage, scientists drew up a profile of which jellyfish species bind to the microplastics best. There are two: Aurelia aurita [the common jellyfish], which are found mainly in the western Mediterranean, and the nomad, which is more common on Israeli shores.”

Microscopic missile

There is one thing that everyone involved in research in this area has in common: They are all amazed at the abilities evidenced by jellyfish even though they do not have a brain. What they do have are central sensory points around the bell (the upper rounded part from whose base the tentacles dangle), a simple nervous system and a digestive system – and that’s all. And yet there’s a feeling that they could take over the world, a notion that is common both among scientists who study them and a general public that has a deep fear of jellyfish.

They are also are aided by their stinging mechanisms, which are not managed by a central nerve network but by means of a small sensor in each sting cell. The cell contains a microscopic stinger containing a coiled needle. When the sensor feels contact with food that is worth stinging, the needle bursts out at tremendous speed like a microscopic missile that can penetrate almost any organic material, while emitting venom. That’s the burning sensation that has made the jellyfish the terror of ocean bathers (and which can be felt even if there is just venom left behind in the water), and it, too, is at the heart of the research into jellyfish.

About a month ago, Rambam Medical Center in Haifa launched a study to identify patterns in jellyfish stings, one aim being what can be used to treat them. This constitutes the continuation of research that Galil conducted three years ago, in which she examined 41 cases of children who were taken to hospital after being stung by jellyfish. Of them, 95 percent were stung in the legs, 88 percent developed a rash and 20 percent required hospitalization.

Vinegar is said to be effective for the stings. Is it?

The maritime excursion, earlier this month.Credit: Yehudit Ilani

Edelist: “Vinegar does not anesthetize the pain of the sting, but it can neutralize jellyfish venom. So it’s effective in cases of lethal jellyfish like the Australian box jellyfish. In the case of the nomad jellyfish, it’s not yet clear if it works. We hope that after the survey we’re conducting we will know in greater detail. If a different substance turns out to be effective, we will promote its use.”

Lotan, who examined the vinegar question in the lab, is more unequivocal. With Mediterranean jellyfish, she says, vinegar does not help and can even be harmful.

“In an experiment in the lab we found that in the case of the nomad jellyfish, vinegar actually causes the opposite effect and activates burn cells,” she explains. “So it makes no sense to use vinegar for nomad jellyfish sting burns. The site of the sting should be washed with seawater, and if a systemic reaction sets in, go immediately to the ER.”

Another study in which Lotan is involved aims to understand how the jellyfish swims. That sounds odd, because ostensibly we know how it moves (in part it is carried along with the current), but in fact not everything is understood. In experiments carried out in seawater channels, scientists discovered that jellyfish are able to swim against the current. Now they are trying to understand how they progress: Is the movement of the jellyfish swarm passive, or do they actively determine their place in the sea?

To determine a swarm’s swimming patterns, local researchers are making use of no less than drones, an underwater robot, divers, observers, boats and a light plane. Some jellyfish were even marked by a GPS device for prolonged monitoring. And we haven’t yet mentioned their multistage, efficient life cycle, whose early stages no one has yet managed to see in nature.

“During the summer, adult jellyfish secrete their sexual cells, sperm or an egg, into the water, and external fertilization takes place,” Lotan says. “The fertilization produces a small larva, less than a millimeter in size. After a week to 10 days, the larva undergoes a metamorphosis, like the larva of a butterfly, and becomes a polyp similar to a coral or a sea anemone. And then, for the first time, the mouths open and the hunting tentacles start to work. Now the polyp starts to eat.

“Then it starts to multiply the way grass does, by means of asexual reproduction. The polyps divide by sending out more and more buds, which produce more and more polyps, all of which carry the same genetic cargo. The warming of the waters during Israel’s spring is the environmental signal that causes them to elongate and divide into horizontal grooves. They will be released from the stalk and grow into jellyfish within three months. When we see their sophisticated and efficient reproductive mechanism, we understand why there are so many jellyfish in the world.”

The early stages of the cycle have only been seen in laboratory conditions, as a microscope is needed to see them. “The polyp stage in the sea is the question of questions in jellyfish research,” Dror explains. “Researchers want to come up with an answer to it by many different means.”

The nomad jellyfish, specifically, presents researchers with an additional challenge: It is difficult to grow it to full adulthood in the lab. In contrast to their natural setting, where they grow to 40-50 centimeters in length, in the lab they have been grown to only 8 centimeters, and never has the life cycle of a nomad jellyfish taken its full course in captivity.

On the other hand, in natural conditions, researchers are unable to say how old the jellyfish are, or how long they can live. In contrast to other creatures, there is no substantial difference between jellyfish of different ages. Thus, one of the aims of Israeli scientists is to try to determine their age according to the sensory organs. Time will tell whether this is an effective method.

No deadly ones

About a month ago, the close relationship between Israelis and jellyfish received a timely reinforcement: a mention in the pantheon of Hebrew language. Following a lengthy process, which involved jellyfish researchers, linguists and philologists, the Academy of the Hebrew Language granted names to 28 types of jellyfish. Among them are eight famous jellyfish from elsewhere in the world – they are not present in Israel but well known enough to be given a Hebrew name – among them a Japanese giant jellyfish and a deadly Australian variety, which belongs to the family of box jellyfish and is one of the most toxic marine animals in the world.

“Sometimes we need to say thanks for what there isn’t, not only for what there is,” Angel sums up. “And we don’t have [deadly] box jellyfish,” on our Mediterranean coast. Yet.

That feeling was certainly bolstered further in last week’s maritime excursion. “I was stung like crazy,” he says, and adds that he sprayed plenty of vinegar on himself and on the others in the research boat, to test its effect. “It helps,” he says unhesitatingly. “I definitely felt less pain.”

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