In honour of World Jellyfish day, we’d like to share with you a collection of interesting facts and mesmerising imagery on these remarkable ancient creatures.
One of the oldest and most mysterious life forms in the ocean, medusae have long held a fascination with scientists and beachgoers alike. We’ve all seen them along the shorelines, their movement like a mesmerising dance, flowing with the waves. But what exactly are these ancient creatures and why are they important for marine life?
Jellyfish are not fish, but plankton (from the Greek word planktos, meaning to wander or drift) and are not strong swimmers, so they are mostly at the mercy of the ocean currents.
Jellyfish have roamed Earth's oceans for more 500 million years, and up to 4,000 species of them have been discovered, according to the Smithsonian Ocean.
Their bodies may look complex at first sight due to their bell shape and intricate tentacles but they are in fact quite simple. Jellyfish have a smooth, gelatinous body containing mostly water, complete with tentacles that contain tiny stinging cells that are used for catching prey or defending themselves. They have no bones, brains, heart. Most species don't even have eyes. Their mouths can be found at the centre of their bodies.
Free-swimming jellyfish can be seen in every ocean in the world, from warm tropical waters to the cold Arctic Ocean. They include the well known disk-shaped invertebrates that are often seen drifting along the shorelines. Most have a lifespan of only a few weeks, but some are known to survive for longer than a year. According to Encyclopedia Britannica: “The coronate jellyfish are the most primitive of the present-day free-swimming jellies and are thought to be descended directly from the fossil form Conulata, which flourished between about 180 and 600 million years ago.“
Though they are not usually aggressive, jellies are famous for their ability to sting in order to catch prey or defend themselves from potential predators . Their stings can cause local pain and irritation and can sometimes require immediate medical attention. Some stings can even be life-threatening. The most dangerous sting comes from Australian Box Jellyfish, which is the most deadly jellyfish in the world for humans.
Jellyfish are primarily carnivores. When there is an abundance of food in their environment, they grow exponentially in size and breed in large numbers, with swarms of jellies containing up to 500,000 jellyfish. They mainly eat zooplankton, krill, shrimp, and in some cases, small fish and other types of medusae. Jellies digest their prey extremely fast.
ART & ILLUSTRATIONS
The German marine biologist and artist Ernst Haeckel was fascinated by medusae, the bell-shaped invertebrate that we now call jellyfish. Haeckel grew up in the romantic victorian era, and for him the jellyfish expressed the mysterious yet fragile beauty of nature.
He published a two-part monograph dedicated to jellyfish full of wonderful imagery: System of Medusae published in 1879 and Reports of the British Challenger expedition (1873–76), published in 1881. Later on, in 1904, Adolf Giltsch captured these absorbing illustrations into wondrous lithographs and had them published in the remarkably popular Art Forms of Nature, that can still be purchased today.
Heckel even named a few jellyfish species after his wife, Anna Sethe, who died suddenly of an “undetermined fever”, after the couple was only married for less than two years: the Desmonema annasethe and the Mitrocoma annae. This is what he wrote about the medusae whose name paid homage to his late wife:
"Mitrocoma annae belong to the most charming of all the Medusae. It was first observed by me in April 1864 in the Bay of Villafranca near Nice. Its tentacles hung like blonde hair ornaments of a princess. I named this species as a memorial to my unforgettable true wife, Anna Sethe. If I have succeeded, during my earthly pilgrimage in accomplishing something for natural science and humanity, I owe the greatest part to the ennobling influence of this gifted wife."
IMPACT & ROLE IN MARINE ECOSYSTEM
As seawater temperature rises due to climate change and predators of jellies are being actively removed by fishing, some types of jellyfish are finding it easier to thrive. Huge explosions in jelly numbers - what is called a jelly bloom- can affect fisheries, make for unpleasant or dangerous swimming, or even disrupt the works of power plants that use seawater for cooling.
Jellies can invade and disrupt ecosystems, one notable example being the Black Sea in 2010. According to NASA: “The Mnemiopsis Leidyi (nee-mee-OP-sis LEEdee-eye), had turned the once fertile fisheries of the Black Sea into an unhealthy gelatinous food web. Once in the Black Sea, the ravenous population quickly increased and spread, feasting on plankton, fish eggs, and fish larvae. Without a natural predator to halt its expansion, the ctenophore’s population grew rapidly, depleting commercial fish stocks in the Black Sea and ravaging the ecosystem, eating up the fish larvae as well as the plankton that the fish feed on. The Black Sea fisheries have only recently started to recover, thanks to the introduction of another ctenophore species that eats Mnemiopsis.”
The good news comes from a more recent study conducted by the scientists at Queen’s University, Belfast. They have discovered that some types of jellyfish can create important symbiotic relationships with developing larval and juvenile fish. Their findings indicate that a huge range of fish partner up with jellyfish to survive: whether this is to protect themselves from predators, to gain sustenance, or sometimes for both. They call this association phenomenon "the gingerbread house". This has beneficial implications not only for the marine food chain but also for the global fishing industry.
Moreover, European scientists think that they have found a way to use jellyfish against microplastics in the ocean. The Go-Jelly project is a EU-financed project that aims to harvest the mucus that medusae produce to create filters which in turn will act like net and catch plastic particles from wastewater before it even reaches the ocean.
Another key aspect to know is that jellyfish are also a major source of food worldwide for the marine ecosystem, as creatures the likes of whale sharks, turtles, tuna, penguins, sea birds and others eat jellyfish naturally. However, their main predators are surprisingly: other species of jellyfish.
SURPRISING JELLYFISH FACTS
They are edible. In some parts of the world are considered a delicacy, and the Go-Jelly project team even worked with chefs to produce a jellyfish cookbook. It is worth mentioning that the book cautions against eating just any jellyfish: "Several species of jellyfish are safe to eat, but you have to be very careful, to reduce the risk of poisoning or foodborne diseases, it is important to eat only jellyfish species that are well-known and tested as food and, above all, jellyfish products that have been cleaned and processed according to a recognized and validated food process."
They have a high nutritional value. They are a good source of protein, antioxidants, and other important minerals.
Box Jellyfish have 24 eyes. Although most species of jellies don’t have eyes, the most deadly one has been blessed with an abundance of them.
They travelled to space. Nasa sent around 2,000 polyps of jellyfish to space, to study how the lack of gravity will affect their development. They Jellies reproduced but their offspring had a difficult time adapting to the conditions back on Earth.
Some jellyfish have bioluminescent organs. Essentially, they can glow in the dark. Furthermore, they are more visible in the deep ocean, and you may spot them in colours such as red, yellow, violet, and blue.
They’ve only recently started to be called “jellyfish”. The word has been in use since 1976, and it’s usually used for medusae, comb jellies and other similar animals.
Lastly, we will leave you with one very important fact. If you ever get stung by a jellyfish, vinegar and salt may help lessen the severity of the symptoms. Nevertheless, if you are swimming in a new environment, seek medical assistance immediately, however minor the sting may appear.