Jellyfish are usually poisonous fish that come in all different shapes, colours and sizes. They are usually transparent which means you can see through them and they can hurt you if they sting you. They are called jellyfish because their bodies are wobbly like jelly! Once caught these curious creatures of the sea appear like jelly-like shapeless blobs on land.

Hereunder are some answers to your most frequently asked questions.

How do jellyfish swarms come about?

Jellyfish swarms or blooms consist of large numbers of jellyfish, which aggregate occasionally, mainly as a result of the direction of prevailing water currents. Why do such increases occur? Several theories have been proposed by different scientists, including the fact that nutrient concentrations in the sea have increased, that the jellyfish predators, such as turtles, have decreased over recent years and that the Mediterranean Sea is warming up due to climate change. It may well be that the recent observed increases in jellyfish numbers are simply part of natural life cycles.

Can jellyfish swim?

Jellyfish are members of the plankton family – that is they cannot oppose the existing water currents but rather sway along with them.

Some jellyfish species are capable of making pulsating movements, which allow them to control their vertical position in the water column.

Is the presence of jellyfish a sign of a polluted sea?

Jellyfish populations are normally highest in overfished seas and the Mediterranean Sea is a case in point, where large increases in jellyfish populations have been observed recently, at the same time that the fishing intensity in the same basin has been increasing in recent years.

Researches are still in the process of establishing if an increase in pollution levels will lead to more jellyfish infested waters.

Are there any jellyfish species that live only in the Mediterranean Sea?

There are no jellyfish which are restricted (that is, endemic) to the Mediterranean but there are jellyfish species, which are very common in the Mediterranean Sea. These include the mauve stinger (Pelagia noctiluca) and the fried egg jellyfish (Cotylorhiza

tuberculata).

The Mediterranean is additionally being colonised by alien jellyfish species coming in through the Suez Canal, mostly from the warmer waters of the Indian and the Pacific Ocean. Examples include the upside-down jellyfish (Cassiopea andromeda), the nomadic jellyfish (Rhopilema nomadica) and the Australian spotted jellyfish (Phyllorhiza punctata).

Do all jellyfish sting?

No. In fact, many species are harmless. Those jellyfish which do sting (known as stingers) only make up a small proportion of the 200 known jellyfish species.

The jellyfish sting is actually a mild venom/poison contained in stinging cells called nematocysts, arranged in rows on jellyfish tentacles.

Who eats jellyfish?

A number of jellyfish-eating fish exist in our seas, including the ocean sunfish Mola mola, besides marine turtles, like the common loggerhead turtle, which are known to consume jellyfish as well.

Numerous seabird species are known to scavenge on dead jellyfish once these are stranded on the beach. Jellyfish are also consumed by humans in a number of countries, namely in countries like Japan, China and Indonesia, after being soaked overnight in water to desalt them.

Which are the most dangerous and largest jellyfish?

The largest ever-recorded jellyfish specimen belonged to the lion’s mane jellyfish species washed up on an American beach in 1870, having tentacles which were almost 40m long (longer than a blue whale). Don’t worry – such a species is confined to the cold waters of the Arctic and northern Atlantic Oceans!

The most toxic jellyfish venoms belong to a group of jellyfish known as the box jellyfish (Cubozoa), most notably the Irukandji jellyfish and Chironex fleckeri.

Which are the most common jellyfish in the Maltese islands?

The mauve stinger (Pelagia noctiluca) is by far the most common jellyfish species throughout the year, with swarms in local waters being recorded as far back as the 1950s.

The fried egg jellyfish is seen more at the end of summer (September-October) and for this reason this species is known by the monicker of “tal-lampuki” (dolphin fish jellyfish) since this period coincides with the lampuki fishing season

The above article was sent to us by IOI-Kids, University of Malta. IOI-KIDS, www.ioikids.net is a dedicated website on the sea for school children and youngsters. If you love the sea and would like to become a member, go ahead and add your name on their Guestbook and become a member of this fantastic website.

On the other hand, if you encounter a jellyfish while swimming you may report it on www.ioikids.net/jellyfish

Did you know?

• Jellyfish have existed for more than 650 million years and happen to be the oldest living creatures on the planet. They have existed before the dinosaurs and have survived longer than the dinosaurs.

• One of the interesting jellyfish facts is that they have no blood, brain and nervous system. They are also capable of sensing light from dark.

• Jellyfish population has increased drastically and is causing scores of problems to human beings living on the coastal front. The number of people stung by jellyfish has risen dramatically. Most jellyfish do not cause any substantial harm. However, some can spearhead extreme reactions. Some jellyfish are as big as 40 metres long, as long as a train, with lots of stinging cells in their tails.