Jellyfish on the South Coast
Jellyfish tend to float or move with the tides, currents and winds. Most are not good swimmers – even the best can move only in a limited way. The South Coast is visited in summer months by a number of jelly fish. Jellyfish comprise gelatinous mesogloea, which is 98% water, though the mesogloea can form fibrous material appropriate to the structure of the species.
In broad terms the true jellyfish have two principal life phases, first as the readily identified floating medusa disc or bell, which is the stage of sexual reproduction, shedding larvae, and second as a small polyp attached to the seabed, able to clone replicas or to bud off small medusae. Those seen in the marine reserve vary enormously in size and shape, two are quite common and two much less so. The most common are the moon jellyfish and the Portuguese Man of War (which is not a real jellyfish). Much less common are the very small Box jellyfish and a relative newcomer, the very large Lion Mane jellyfish.
Moon Jellyfish Aurelia aurita
Moon jelly are probably the most common and widely recognized type of jellyfish. They can be found in the Atlantic, Arctic and Pacific Oceans near the coasts, and is widely distributed in New Zealand waters. The animal ranges in size from 5cm to 40cm across. The moon jelly is easily recognizable by its four blue/violet (male) or pink (female) crescent shaped gonads on the underside and at the centre of its translucent medusa bell or umbrella. Also, its bell is thicker towards the middle, thinning towards the edge. The name is obvious from its shape, with the gonads to some extent giving the medusa an uneven, crescent moon appearance.Like many other species of jellyfish, the moon jelly’s ability to move by itself is limited, so it is subjected to the water currents of the ocean. It is the jellyfish which turns up on shores as a gelatinous and often smelly blob, or may be seen from boats, wharves and in marinas when winds push the medusa into sheltered areas. Beach cast specimens generally dehydrate rapidly, though they can be a nuisance to fishing nets and in clogging the nets of fish farms (sometimes clogging the gills and killing the farmed fish). Moon jellyfish seem to be comfortable in harbours and estuaries, even in waters of very low salinity. They can swim with a pulse of water as a jet which pushes the medusa up through the water column, but movement downwards is passive.
Moon jelly feed on plankton that includes organisms such as molluscs, crustaceans, tunicate larvae, rotifers, diatoms, eggs, fish eggs, and other small organisms, collecting small organisms on mucus layers. Both the adult medusae and larvae have stinging nematocysts – like minute harpoons fired by springs – to capture prey and also to protect themselves from predators. The stingers are generally not powerful enough to penetrate human skin, though small children with sensitive skin may be stung.
Portuguese Man of War Physalia physalis
So called, apparently, because of a similarity in float and sail to a centuries-old Portuguese battleship (or to a Portuguese soldiers helmet!). These are not true jellyfish. Not only is it not a jellyfish, it’s not even an “it,” but a “they.” The Portuguese man-of-war is a siphonophore, an animal made up of a colony of organisms working together.
The man-of-war comprises four separate polyps. The first is the float or pneumatophore. Man-of-wars are also known as ‘bluebottles’ for the purple-blue colour of their pneumatophores, good camouflage in sea water. The tentacles are the man-of-war’s second organism and can extend 10 to 20 meters below the surface. They are covered in venom-filled nematocysts used to paralyze and kill fish and other small creatures, which are then drawn up to be digested in the third polyp organism. A fourth polyp comprises the sex organs.
Bluebottles are incapable of swimming but float with the tides, currents and wind. The floats interestingly hold the organism at 45 degrees to the left or right of the wind, which may influence the dispersal of the species around the oceans of the world. As we know, these ‘jellyfish’ are washed up on coasts and beaches after strong and prolonged onshore winds.
Detached tentacles and dead specimens (including those that wash up on shore) can sting just as painfully as the live creature in the water and may remain potent for hours or even days after the death of the creature or the detachment of the tentacle. For humans, a man-of-war sting is excruciatingly painful, but rarely deadly. Stings usually leave whip-like, red welts on the skin that normally last 2 or 3 days after the initial sting, though the pain should subside after about an hour. However, the venom can travel to the lymph nodes and may cause, depending on the amount of venom, a more intense pain. A sting may lead to an allergic reaction.
Box Jellyfish Carybdea (or Copula) sivickisi
More of a warmer water organism than the Moon jelly, and vastly smaller in size, the box jellyfish has been found in a few rock pools at Island Bay. It is only about 6 mm in size and is related to sea wasps which, in Australian waters are known to deliver a sharp sting sometimes with fatal consequences. The NZ specimens are fast swimmers and may sometimes be seen as a fast swirl or track of water across a rock pool. They probably have subtropical origins as they appear in the warmest waters in Cook Strait on the D’Urville current at the height of summer.
The photos and diagrams of this box jellyfish give an almost clown like, or even a space landing craft appearance. There are 4 tentacles at each corner under the box-shaped ‘bell’, and these can extend up to 60 mm. They are armed with nematocysts that can deliver ‘amour piercing’ projectiles into their victims, followed by a syringed toxin. They can adhere upside down by sticky pads to seaweeds and therefore, amongst jellyfish, are almost unique in being able to fix in position at all life stages, rather than just drift with the currents in the adult phase.
Another unique feature of box jellyfish is an intricate mating dance, which sees individuals pairs forming and coupling for sexual reproduction; other true jellyfish have a more dispersed reproduction akin to many marine organisms.
Lion’s Mane Jellyfish Cyanea sp.
These colder water jellyfish appear to be comparative newcomers, being much more common in northern hemisphere waters. They have not been much studied but are known as amongst the largest jellyfish with bell discs of up to 2 metres in width and up to 800 tentacles 8 to 10 m long or more in NZ waters. Some northern species stretch up to 30 m and compete with blue whales as the longest marine organisms!http://www.flickr.com/photos/hershman
They form oases of life to small pelagic fish and shrimps, apparently impervious to the nematocysts, preying on the jellyfish catch. People can be painfully stung, though the stings are apparently not known to be serious or fatal to humans. Lion’s Mane jellyfish venom was apparently a feature of one of Conan Doyle’s Sherlock Holmes stories, no doubt carefully handled!
Treatment for Stings
It is important to remove any traces of tentacles or jellyfish matter from the skin as soon as possible, preferable with gloves so as not to add further welts to bare hands. Rinse any material off with hot, salty water – as hot as one can stand. Use of a stick, shell, credit card or similar piece of plastic to scrape off material is suggested. Australians appear to swear by the use of vinegar to neutralise the toxins from any remaining ‘unfired’ nematocysts. Vinegar is often held at northern Australian beaches for this use, especially for the venomous box jellyfish.
New Zealanders will generally most likely be stung by bluebottles as the other common jellyfish are not especially venomous or common enough for painful encounters. Vinegar is not recommended for Portuguese Man of War stings. Both vinegar and fresh water appear to worsen the effect of the venom. If eyes have been affected, irrigate the eyes with lots of water. Ibuprofen will reduce the pain. Urine is not considered useful for treating stings!
Be vigilant for symptoms of fever or anaphylactic shock, as with an allergic reaction, and, as they say, if the pain persists, see a doctor!
For comprehensive advice, go to: http://www.health.govt.nz/yourhealth-topics/bites-and-stings/jellyfish-stings
Alan Hoverd, VUW, from ‘The Taputeranga Marine Reserve’ Second Edition, edited by J. Gardner and J. Bell, published by First Edition, 2008
Wikipedia and associated resources
NZ Department of Health