JELLYWATCH

Introduction:

Jellyfish are soft-bodied invertebrates, belonging to the phylum Cnidaria, which also includes coral and sea anemones. Jellyfish are present in all Earth’s oceans and live at a wide range of depths and water conditions; they range greatly in colour and size with some species larger than man, while others may be as small as a pin head.

Most jellyfish are not able to control their horizontal movements; they drift with the ocean currents and surface winds. However, they are able to propel themselves through the water column; this occurs when water is taken into the bell cavity and forced out behind them, this movement has been likened to a simple form of jet propulsion.

The main sources of food for jellyfish are zooplankton, small fish as well as eggs and larvae of other marine organisms. Larger jellyfish also consume crustaceans and other jellyfish. Jellyfish catch their prey using their long tentacles that contain stinging cells called Nematocysts, which are fired when the tentacles come into contact with something. The venom either paralyses or kills the prey and it is then ingested. Predators of Jellyfish themselves include other jellyfish, sharks, tuna, swordfish and sea turtles.

Despite their reputation and untoward appearance, jellyfish do not actively seek out their prey or sting humans deliberately. Jellyfish are unable to control their own movements, and may therefore come into contact with humans unintentionally via ocean currents.

Interesting Jellyfish facts:

• Jellyfish have existed on Earth for over 650 million years

• The body of a jellyfish is perfectly symmetrical

• Jellyfish are made up of more than 95% water

• Over 2000 species of jellyfish have been discovered

• Jellyfish don’t have a brain, blood or nervous system

• Waste is discharged through a jellyfish’s mouth

• The largest jellyfish is the Lion’s Mane jellyfish, which can grow to over 120 feet long

• The most poisonous species of jellyfish is the Irukandji jellyfish, largely found in Australian waters; stings from this jellyfish cause Irukandji Syndrome which results in an array of systemic symptoms including severe headaches, nausea, anxiety and can, without treatment result in death.  

• A group of jellyfish is called a smack.

• Jellyfish are able to reproduce both sexually and asexually during different parts of their lifecycles

Commonly seen Jellyfish species:

Portuguese Man-of-war (Physalia physalis):

This is infact not a true jellyfish but instead a jelly invertebrate known as a Siphonophore and comprised of a colony of different polyps. It is usually found in the surface waters and is easily recognised by a transparent blue and purple coloured float, which is filled with gas. The tentacles of this species can be up to 50m long, causing painful stings, if seen Portuguese Men-of-war should be avoided.

Mauve Stinger/Purple-Striped Jellyfish (Pelagia noctiluca):

It is pink to purple in colour, with tentacles up to 10m in length, they may have a striped appearance. These jellyfish are also known to have a painful sting.

Compass Jellyfish (Chrysaora hysoscella) :

This jellyfish is semi-transparent and often has small white dots and reddish-brown stripes on its bell. A painful rash will appear if stung.

Upside-down Jellyfish (Cassiopeia xamachana) :

This jellyfish has short tentacles hanging over its head, which may sting. Cassiopeia xamachana are largely transparent but may have slight colouration ranging from browns, blues, and greens to white.

Mushroom Jellyfish (Rhopilema nomadica) :

This species has a clear, translucent or white bell. Rhopilema nomadica does not have tentacles, but has long finger-like appendages protruding from the bell that may sting.

Pink meanie Jellyfish (Drymonema dalmatinum):

The bell is pale pink in colour, with very long tentacles beneath it that can cause a painful sting.

Flower hat Jellyfish (Olindias Formosa):

This genus of jellyfish has lustrous tentacles that coil up when not in use; the bell is translucent and pinstriped with opaque bands. 

Box Jellyfish (Carybdea marsupialis):

The Box Jellyfish has a square shaped bell, which is usually transparent. Each corner of the bell has a tentacle, so there are only 4 in total, but they are still able to sting.

By-the-wind Sailor/Purple Sailor Jellyfish (Velella velella):

This species has a float which keeps them on the oceans surface, they are transported by the wind and are usually blue (or shades of) in colour.

Moon Jelly/Figure-eight Jellyfish (Aurelia aurita):

The bell is usually clear or with a white tint, there is a pink or orange cloverleaf pattern in the centre (the cloverleaf normally has 4 lobes, but may have more). This species has very short tentacles around the bell margin.

Spotted Jellyfish (Phyllorhiza punctata)

May also be known as the spotted jelly, due to the white spots found on its white, transparent or semi-opaque bell. Frilly oral arms extend from the large bell.

Mediterranean jelly /fried egg jellyfish (Cotylorhiza tuberculata):

It has an elevated dome surrounded by a gutter-like ring, beneath which there are many appendages that vary in size.

Barrel Jellyfish/Football Jellyfish (Rhizostoma pulmo):

This genus has a large bell (at least 20cm), which is white in colour, with a dark rim. It has no tentacles but instead has appendages beneath the bell.

Comb Jellyfish (Mnemiopsis leyidi):

The Comb Jelly has a highly transparent elongated body with semi-transparent rows running the length of the organism.

Crystal Jellyfish (Aequorea victoria):

This species has an almost transparent bell with long delicate tentacles. Aequorea Victoria is a bioluminescent jellyfish, giving off a blue-green glow when disturbed.

Salpa:

Has a transparent body with a visible gut nucleus which is orange in colour. These can be found as either solitary free floating tunicates or as a part of a long chain of Salps. 

Jellyfish, like any other marine animal, are fundamental to the balance of marine ecosystems and food webs, and in this way their abundance and distribution worldwide is key to keeping this natural equilibrium. A large scale increase in jellyfish numbers can have extensive detrimental impacts, not only in terms of environmental imbalance but also with regard to socio economic disruption, directly impacting fisheries practices and tourism. Likewise invasive species of jellyfish which have been introduced either naturally or through anthropogenic sources can cause large scale disruption, dominating regions and in some cases wiping out native species completely.

What is a Jellyfish bloom?

A population bloom is when jellyfish reproduce in mass numbers in a small area, outbreaks of tens to hundreds of medusa can occur per cubic metre usually as a result of prey abundance, temperature and light availability. By the pulsed nature of their life cycles, jellyfish come and go seasonally meaning that even the most undisturbed circumstances can lead to summer blooms. Even species like ctenophores increase in number in the spring or summer when planktonic food is available in greater abundance. Beyond the basic lifecycle-driven seasonal change in numbers, several other kinds of events appear to be increasing the numbers of jellies present in some ecosystems. Over recent decades, man’s expanding influence on the oceans has begun to cause real change and there is reason to think that in some regions, new blooms of jellyfish are occurring in response to some of the cumulative effects of these impacts. The issue is not simple and in most cases there are few data to support our perceptions. Some blooms appear to be long-term increases in native jellyfish populations. A different phenomenon is demonstrated by jellyfish whose populations regularly fluctuate, apparently with climate, causing periodic blooms. Perhaps the most damaging type of jellyfish increase in recent decades has been caused by populations of new, invasive species gradually building-up to ‘bloom’ levels in some regions.

As mentioned there are two types of ‘Jellyfish’, Cnidaria and Ctenophora.  Apart from being in different phylum’s, the other major difference between the two groups is that Cnidaria have stinging cells (Cnidocytes and Nematocytes), whereas Ctenophora do not. Stings from pelagic cnidarians cause discomfort and sometimes medical emergencies for swimmers and waders primarily in warm marine waters worldwide, a description notably accurate to the Mediterranean. During jellyfish blooms, when pelagic cnidarians occur in great abundance, stinging can occur at epidemic levels, thereby leading to both amplified health risk and economic downturn in areas reliant on coastal tourism. Blooms have been documented to have high negative impacts on fisheries in numerous parts of the world, where their high cumulative biomass physically affects the ability of fishermen to carry out their practice.

Invasive Jellyfish species:

The introduction of non-native species into an area can occur in many different ways, both naturally and due to human influence. In recent years it has becoming increasingly apparent that anthropogenic activity has become a sizeable factor in the movement of species to new environments. The significant increase in commercial shipping around the world has meant that organisms are easily transported both on the vessels themselves as well as part of ballast water. Some commercially important marine species have been introduced into areas in order to try and create new natural resources without taking into account the impact these may eventually have on the native ecosystem.

When a new species is introduced into an area it either out-competes or is out-competed. The competition that is created as a result of their introduction means that at times the biodiversity of the area can be greatly reduced.  One such example of an invasive species of Jellyfish is that of the White spotted jellyfish Phyllorhiza punctata a species native to Australia that was introduced to Californian waters in 1981. The species is thought to have entered through the Panama Canal attached to the hulls of ships and its impacts have been extensive. Phyllorhiza punctata preys on native Californian jellyfish species and has shown to negatively impact the shrimp fishery industry by clogging the nets and damaging fishing equipment.

Report your Sighting:

Jellyfish exhibit great diversity in their size, shape and colour. Archipelagos is working in collaboration with CIESM, the Mediterranean Science Commission who have established a Jelly watch program in the Mediterranean in order to gather baseline data and gain a clearer view of jellyfish abundance and distribution. The contribution of the public is fundamental in facilitating a better picture of their numbers, size and range. More information on the work of CIESM can be found here.

To report your Jellyfish sighting please complete the electronic form below, alternatively email the relevant details listed on the CIESM poster to medousa@archipelago.gr or jellywatch@ciesm.org