Science 20.02.2018

In recent years, there is an increase in jellyfish blooms in the Mediterranean and Black Sea due to the changes in climate and food chains. Furthermore, new alien jellyfishes, like "Lessepsian species" that entered the eastern Mediterranean via the Suez Canal, cause serious problems in the Eastern Mediterranean Basin. This jellyfishes and gelatinous organisms clog fishing nets and damage mainly coastal fisheries. On the other hand, some venomous species may cause nuisance to bathers and especially they may become a real health hazard for babies and elderly individuals. Consequently, this has a negative impact on tourism and diving industry. It is known that thousands of people in Europe  are hospitalized due to jellyfish sting in recent years. Therefore, we have just started a new programme to learn and understand abnormal jellyfish blooms, outbreaks and their negative impacts on the Eastern Mediterranean coasts on a scientific platform and to guide the decisions makers to elaborate prevention/adaptation measures.

A poster was prepared by CMAS, TSSF and Turkish Marine Research Foundation (TUDAV) to highlight the dangerous gelatinous organisms for human health. In this poster 13 gelatinous species are defined as alien/invasive and stingers. Among them, six species are defined as very harmful (shown by red arrow) while seven species are mildly harmful (shown by orange arrow) for the eastern Mediterranean region. By sending your information on these jellyfishes to TUDAV, you will be able to contribute to this programme and to the knowledge of marine species in the Easterm Mediterranean and the understanding of the effects of alien species. You can also learn about these species by checking the project website ( or the poster of jellyfish. This is a citizen science programme and we need your help. For this, you can send your photos and descriptions to our e-mail (; or fill the form in our website

The Phylum Cnidaria consists of about 10,000 species. Common jellyfish, anemones, corals, sea pens, cube shaped jellyfish are all cnidaria with diverse morphology. Cnidaria is characterized by cells called nematocytes (cnidocyte). These cells secrete a very special organelle called nematocyst (cnidocyst). Cnidocyst, sine qua non of cnidarian, is used for defense and prey. Inside the cnidocyst, there is an inverted tubule, venom and a huge osmotic pressure.

Poster in PDF


13 Harmful Gelatinous Species Presented in the Poster


  • Carybdea marsupialis : Mediterranean box jellyfish are much less dangerous than its Australian counterpart whose sting can be lethal to humans. However, the Mediterranean box jellyfish is still a stinging jellyfish which can inflict a painful, albeit non-lethal sting. Although it is not a species common to the Mediterranean Sea, over recent decades it has been detected at some points.
  • Chrysaora hysoscella : Compass jellyfish can be distinguished from other jellyfish by its brown-violet lines on bell surface. Its sting may cause pruritus, erythema, edema and burning. These complaints spontaneously disappear in a few hours. In some cases, pruritus, erythema, and edema may occur after 48 hours of the contact.
  • Rhopilema nomadica : This species has negative consequences on human health, tourism and fishing activities. Many people swimming on the beaches have been stung and sought for a medical treatment. Local fishermen claim a decrease in catch from their stationary nets (e.g. gill net) as they clog the nets and make them heavy.
  • Pelagia noctiluca : This species is considered as the most venomous jellyfish in the Mediterranean. The tentacles, oral arms, exumbrella, and gastric pouches are covered in nematocysts, which means that all the body parts can string. It is a severe stinging jellyfish causing local symptoms, such as erythema, edema and vesicles as well as persisting pain in the stung skin. It takes 1-2 weeks for the pain to completely disappear. Hyper pigmentation may occur on skin. Systemic symptoms are bronchospasm, pruritus, dyspnoea, numbness, nausea, vomiting, low blood pressure, diarrhea, and shock.
  • Macrorhynchia philippina : This species is highly stinger, distinctive, black-stemmed, branching colony, up to about 17 cm. Shallow reefs are their habitats and they distribute in temperate regions.
  • Olindias phosphorica:  Cigar jellyfish is a species of jellyfish from the Central and East Atlantic, and the Mediterranean Sea. It is a serious stinger and its length can reach up to 6 cm.
  • Cassiopea andromeda : It is called "Upside-down jellyfish" because it usually lies mouth upward on the sea bottom. This interesting behavior is caused by the symbiotic relationship with photosynthetic dinoflagellate algae. Jellyfish protects algae by its nematocyst from fish, in turn, algae provides food produced by photosynthesis. Its sting may result in pain, rash and swelling on contact area. Vomiting and muscle pains may occur depending on victim’s sensitivity to the toxin of nematocysts.
  • Aequorea globosa : This is a mildly stinger jellyfish originally from the Indo-Pacific and can reach up to 10 cm. Presence of this species in the eastern Mediterranean is possibly due to ship-mediated transport.
  • Discomedusa lobata : Its length can reach up to 15 cm and it is a disk-shaped jellyfish. Not a very common species in the Mediterranean, although it has been spotted since 2013.
  • Rhizostoma pulmo : This species has blue and white hemispherical umbrella with a rugged fringe. Commonly known as barrel jellyfish. It is found in the northeast Atlantic, and in the Adriatic, Mediterranean Sea, Black Sea and Sea of Azov.  It typically is up to 40 cm (16 in) in diameter, but can exceptionally reach 90 cm. It is a favorite food of the leatherback turtle.
  • Cotylorhiza tuberculata : This is an endemic species to the Mediterranean Sea (found only in the Mediterranean), including the Turkish waters and lives at the sea surface and it is often accompanied by juvenile fish such as horse mackerel.
  • Aequrea vitrina : Crystal jellyfish is mildly stinger and its length is between 5-15 cm.  This is the jellyfish from which the luminescent protein aequorin and the associated fluorescent molecule Green Fluorescent Protein (GFP) were extracted and purified.
  • Phyllorhiza punctata : It may cause slight burning sensation and complaints like itching and tingling. It has only a mild venom and not considered a threat to humans.

The first aid against cnidaria envenomations consists of preventing further nematocyst discharges, alleviating the local effects and controlling systemic reactions. In case of contact with jellyfish, the tentacles generally stay attached to the skin and a significant amount of nematocysts are not activated. The nematocysts are sensitive to osmotic changes (like freshwater application) or tactile stimuli (like rubbing). Therefore, it is important to avoid further nematocyst discharge and to remove all the unfired nematocysts as soon as possible.

The safest way to get rid of unfired nematocysts is to rinse away the sting area by sea water. Remaining tentacles could also be removed by scrubbing the skin by a credit card or dull edge of a knife or detaching by tweezers. Pressure (rubbing, scratching, itching etc.) or rinsing by freshwater, alcohol, methylated spirits should be avoided.

Some chemicals have been shown to stabilize unfired nematocysts so they cannot inject venom. Among them, 5% acetic acid (vinegar) can effectively neutralize the nematocysts of Chironex fleckeri. So, in the first aid of box jellyfish (class Cubozoa) stings, vinegar application is recommended as a part of the standard treatment.

Most jellyfish envenomations are mild. They cause slight discomfort or a painful, itchy rash. Although rare, some systemic reactions may be seen, such ase hypotension, hypertension, shock, anaphylaxis, blurred vision, acute renal failure, fulminant hepatitis, autonomous nervous system disturbances, Guillain Barre syndrome, stroke, peripheric neuropathy, etc. The patient should be followed for a probable systemic reaction. The most effective and safe first aid to control the pain is hot sea water immersion. Immersion of the affected area in the sea water heated as 43–45°C for 20-40 minutes will ease the pain in most cases. If no thermometer is available, hot water immersion can be applied as hot as can be tolerated.

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