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Why do Jellyfish sting? 

Dr. Bella Galil, Israel Oceanographic & Limnological Research

Jellyfish, like corals and sea anemones, are members of the phylum Cnidaria animals with a radial body plan, bearing stinging organoids on their tentacles that serve for defence and to capture prey. Each stinging organoid, called nematocyst, contains a tightly coiled spinulate tubule, and venom. Discharged nematocyst penetrate and paralyze or kill the prey. Certain species, like to sea wasp, not occurring in the Mediterranean Sea, produce potent toxins that may cause death.

Jellyfish sting injury
Jellyfish sting injury

Each summer since the mid 1980s huge swarms of the invading jellyfish, Rhopilema nomadica, Galil, have appeared along the Levantine coast. The species originated in the Red Sea and the East African coast, but entered the Mediterranean through the Suez Canal and have established a Levantine population. Their specific name, nomadica, recalls their track through the Canal. In 1995 the jellyfish was recorded off the southeastern coast of Turkey, and in 1998 a specimen was collected near Izmir. These swarms of voracious planktotrophs, some stretching 100 km long, must play havoc with the limited resources of this oligotrophic sea, and when the shoals draw nearer shore, they adversely affect tourism, fisheries and coastal installations. Local municipalities report a decrease in holiday makers frequenting the beaches because of the publics concern over the painful stings inflicted by the jellyfish. Coastal trawling and purse-seine fishing are disrupted for the duration of the swarming due to net clogging and inability to sort yield. Jellyfish-blocked water intake pipes pose a threat to cooling systems of port-bound vessels and coastal power plants: in the summer of 2001 Israel Electric removed tons of jellyfish from its seawater intake pipes at its two largest power plants, at estimated costs of 50,000 US$. Yet, the jellyfish shelters among its nematocyst-laden tentacles the juveniles of the Red Sea carangid fish, Alepes djeddaba, and may have precipitated the sudden population increase of this commercially important species.

Rhopilema nomadica Galil Rhopilema nomadica Galil jellyfish

Rhopilema is not the first jellyfish to pass through the Suez Canal, the upside-down jellyfish, Cassiopea andromeda, preceded it by a century. Cassiopea rests on the bottom in very shallow waters, where symbiotic algae provide it with some of its food.

These jellyfish are but a small part of the Erythrean invasion through the suez Canal that has contributed the largest number of alien species to the Mediterranean, amounting to over 80% of the records of all alien fish, decapod crustaceans and mollusks. The Erytrean aliens form thriving populations along the Levantine coasts, with some invaders extending their range as far west as Tunis, Malta and Sicily.

Jellyfish sting injury
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