Chrysaora fuscescens. Credit: Dan90266/Wikimedia Commons CC BY-SA 2.0
The jellyfish one sees on the beaches in Greece are probably the least dangerous of any anywhere, with their size being much smaller than those found in the worlds oceans.
Jellyfish, also called jellies, or medusas because of their tentacles are a large group of zooplankton organisms that exist in all seas of the world and live at all depths.
They typically eat small sea plants, shrimp, or fish. They use their poisonous tentacles to stun prey before eating it.
Jellyfish have significant active motion but their movement depends on sea currents. Large populations of jellyfish appear in the Greek seas with a periodicity of 10-12 years, similar to that observed in other Mediterranean countries.
In Greek seas, jellyfish typically remain for two to three years, and the period of their stay varies depending on the region and the environmental conditions of each marine area.
It is a misconception that the presence of jellyfish in our seas is because of pollution.
The most common jellyfish in Greek seas is the Pelagia noctiluca, which lives on the high seas and its population growth has been proven to have nothing to do with pollution.
Population fluctuations of Mediterranean jellyfish are more closely linked to sea temperature fluctuations and other environmental factors affected by climate change, such as periods of drought or even just heavy rainfall in the Spring months.
All jellyfish bite because they need to eat. They cannot see, but they can detect motion. They have urticaria cells that secrete toxic substances to stun their prey. With few exceptions, the sting of most jellies is not annoying to humans.
The jellyfish species found in the Greek seas are the least dangerous of all jellies.
A huge increase in the jellyfish population on the beaches in northern Greece has generated concern this year among scientists and beachgoers alike.
Biology professor at the Aristotle University of Thessaloniki, Chariton Chintoroglou, spoke to interviewers from Agency 104.9 radio explaining the phenomenon.
The jellyfish species seen on the beaches in Greece is the most common of all, called moon jellyfish, the professor explained.
Sampling was done in Thermaikos Gulf and we realized that the number of jellyfish, Aurelia Aurita, is increasing dramatically, which shows a periodicity in its reproductive behavior.
We are in a period of successful reproductive behavior, with many offspring. It is a phenomenon that we will be able to overcome, Chintoroglou stated.
We can only speculate on such population outbursts. It has been found that there is a periodicity in increasing their population limit, the professor added.
This species of jellyfish is not toxic, he stressed. The system receives such pressures of population outbursts, which will balance after a period of time.
Chintoroglou further explained that after August 15 the big blue medusas (Rhizostoma pulmo) will appear in the waters of northern Greece.
Due to climate change and the prolonged increase in the average annual temperatures, we have phenomena that are becoming more and more frequent. Phytoplankton is growing at a rapid rate, providing plenty of food for zooplankton, the professor added.
Pelagia noctiluca. Credit: Hans Hillewaert/Wikipedia CC BY-SA 4.0
The color is purple of the Pelagia noctiluca or reddish and its average diameter is just 6 cm (2.3 inches). To us it is known simply as the purple jellyfish, the only jellyfish with this delicate hue in Greece.
A true bioluminescent organism, as its name implies, it even glows at night, offering a rather spectacular sight, but its sting is painful and annoying.
If you see it where you are swimming, it is best to get out of the water.
Aurelia aurita, or moon jellyfish. Credit: Alexander Vasenin/Wikipedia CC BY-SA 3.0
Also known as glass, the Aurelia aurita jellyfish is the most common in all the seas in Greece. Its umbrella is relatively flat and is transparent with a slightly white shade and four characteristic circles on its outer part.
Its sting is not annoying to most people; hard to spot when you look down from above, it is also known as the moon jellyfish.
Cotylorhiza tuberculata. Credit: Fredski20139/Wikipedia CC BY-SA 3.0
Very large in size and with a brown-yellow color, Greeks also call theCotylorhiza tuberculata the fried egg jellyfish because of its shape and color. It is sometimes referred to as the Mediterranean jellyfish.
In addition to looking like a fried egg from above, it also resembles a bouquet of flowers as seen from the side. It is widespread in the Aegean and its diameter can reach 40 cm (15.7 inches). Its sting is not dangerous.
Rhizostoma Pulmo. Credit: Ales Kladnik/Wikipedia CC BY 2.0
Also known as blue jellyfish, the Rhizostoma pulmo is large in size and its umbrella has a bluish color with purple shades or a purple band on the outside. It closely resembles a mushroom in form.
The sting of the rhizostoma pulmo is not annoying or painful.
The Cotylorhiza tuberculata, also called the brown medusa or saloufa, as Greeks term it, is very common in Greek seas; it is also harmless.
This particular jellyfish is being found everywhere in the Greek seas this year. It is harmless, so you can even hold it without fear, as seen below.
Several ecological groups advise not to take out of the water and throw these harmless medusas in the sand or the trash.
Greek woman holding a brown medusa (Cotylorhiza tuberculata) in her hands. Credit: ROSA/Facebook
1. Jellies are the oldest multi-organ animal in the world
Jellyfish have been around the planet for at least 600 million years. They were here before dinosaurs or bony fish, before animals or trees, even before flowers or fungi.
Jellyfish have survived five mass extinctions, including the Permian-Triassic extinction event which wiped out up to 70 percent of life on Earth.
2. Jellyfish dont have brains
Not only that, they also have no blood, no bones, and no heart. They have an elementary nervous system with receptors that detect light, vibrations, and chemicals in the water.
Jellyfish also have a sense of gravity. With these abilities, they can orient and navigate in the water.
3. Some jellyfish are immortal
There is a death-defying species of jelly called the immortal jellyfish (or Turritopsis dohrnii) found in the Mediterranean Sea and in the waters of Japan thats biologically immortal.
When the medusa Turritopsis dohrniidies, it sinks to the ocean floor and begins to decay. Amazingly, its cells then reaggregate not into a new medusa, but into polyps, and from these polyps emerge new jellyfish.
4. Jellyfish are in every sea of the world
Jellyfish are found in every ocean in every part of the planet, from the coldest freezing waters of the Arctic oceans, to the warm, temperate waters of the tropical oceans.
They exist in different water conditions and at all depths, from the ocean floor to the surface. Theyre even found in some freshwater lakes and ponds!
The moon jellyfish tha glows in the dark. Credit: Andreas Augstein/Wikipedia Andreas AugsteinOwn work selbst fotografiert; Ort: Aquarium Berlin. This image shows two moon jelly fish (Aurelia aurita).CC BY 3.0
5. Some jellyfish can glow in the dark
Many jellyfish have bioluminescent organs which emit blue or green light.
The light emission is typically activated by touch, which serves to startle predators. This light may also help jellyfish in a number of other ways, like attracting prey or warning other organisms that a particular area is occupied.
6. Not all jellyfish have tentacles
What are jellyfish known for? Some may say their trailing tentacles, but actually not all jellyfish species have tentacles. The Deepstaria, for example, is a genus of jellyfish known for their thin, sheet-like bodies and their lack of tentacles.
7. Theres a giant jellyfish called the hair jelly
The lions mane jellyfish (Cyanea capillata) also known as the giant jellyfish or the hair jelly is the largest known species of jellyfish.
The largest recorded specimen was found washed up on the shore of Massachusetts Bay in 1870. It had a bell with a diameter of 7 feet 6 inches and tentacles 121.4 feet long longer than a blue whale and it is considered one of the longest animals in the world.
8. 150 million people are stung by jellyfish each year
That means that in the few minutes or so its taken you to read this far, more than 1,000 people have been stung by jellies.
9. Jellyfish poison can be deadly
The Australian box jellyfish (Chironex fleckeri) is considered the most venomous marine animal on earth. Its sting can cause paralysis, cardiac arrest, and death within a few minutes barely enough time for a victim to swim to shore!
10. Fish eat jellyfish, too
Despite their venomous defenses, jellyfish are not without predators. Tuna, sharks, swordfish, sea turtles, and even some species of salmon are the jellyfishs natural enemies.
11. Some jellyfish are edible
Some jellyfish can be a delicacy and there are over 25 edible types. They are typically found in salads or pickled; some people say they have salty taste and a similar consistency to noodles.
12. Some jellyfish went to space
In 1991, over 2,000 jellyfish polyps were blasted into space in an experiment to test their reaction to the lack of gravity.
The guinea pig jellyfish reproduced in space, creating over 60,000 progeny. However, the space-bred jellies were not able to function properly when they returned to Earth.
The killer Chironex fleckeri (Australian box jellyfish). Credit: Guido Gautsch/Wikipedia CC BY-SA 2.0
In March this year, a 17-year-old Australian teen was lethally stung by an Australian box jellyfish, a species that is considered the most venomous marine animal.
The Australian box jellyfish is so named after its shape. It has long barbed tentacles which are covered in pockets of venom.
When the venom is injected into people or animals, it can lead to paralysis, cardiac arrest and death.
However, not all box jellyfish species can kill. There are at least 51 species of the box-shaped creature but only Chironex fleckeri, Carukia barnesi, Malo kingi, and a few others deliver a sting that can be lethal.
The lethal varieties of box jellyfish are mainly found in tropical waters off northern Australia.
The Greek beach jellyfish are not really dangerous. Their sting can be annoying and uncomfortable for a little while but this is the extent of it.
However, if you get stung by any of the jellyfish often found in Greece, you can do the following:
Rinse the affected area with sea-water. Avoid fresh water, vinegar, alcohol; or urine, as some older people wrongly suggest.
If any tentacles are still attached to the skin remove them with a gloved hand, a stick, or a towel.
Do not rub the affected area as this may result in further release of the venom.
If the sting is strong, place a dry cold pack (ice in a plastic bag wrapped in a towel or t-shirt) on the affected area.
If you are allergic and feel more than a topical sting and itch, you must seek medical attention.
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