The Medusae of our oceans

Photo shows a beached Portuguese man o’ war jellyfish.

WHETHER visiting beaches in tropical or temperate waters, at certain times of the year do heed the warning sign posted: ‘Beware of Jellyfish!’

Nearby, there is usually a first aid post containing a spray-on bottle of household vinegar labelled, ‘For jellyfish stings’. Yes, household vinegar will help nullify the pain of a jellyfish sting, but it only brings temporary relief and does not rid our bodies of the venom injected into our skins. Much depends upon the type of jellyfish which brushed past us when we were swimming in the sea.

The word ‘jellyfish’ entered the English language as late as the 19th century and prior to then, this creature was named ‘medusa’ after the mythological Greek goddess who had serpents showing their fangs in her hair.

With seasonal rises in sea temperatures, blooms of phytoplankton appear and are fed upon by zooplankton containing copepods (minute crustaceans) on which jellyfish feed. Some species of jellyfish are completely harmless whilst others can plague bathing beaches, painfully stinging unwary swimmers, or they may be found stranded and rotting at low tide. These glutinous-like umbrellas can even be dangerous when beached, for their drying tentacles can still deliver a sting if in contact with a wet hand or foot.

As a youth, swimming off the beautiful sandy beaches of West Cornwall, in the far South West of England, I received many a small sting – more like a wasp sting – from jellyfish but never entered the summer seas when the Portuguese man o’ war jellyfish were around.

At the Tanjung Aru beach in Kota Kinabalu, I have felt the tingle of a jellyfish sting and witnessed other Europeans screeching aloud with pain.

The worst jellyfish victim I saw there was a man who was overcome by stings as he emerged from the sea with huge weals over his back. Given immediate first aid, he recovered in Queen Elizabeth Hospital. Nowadays, when thinking of swimming off the Santubong/Damai beaches and at Lundu, I do observe the jellyfish warning signs. Once bitten, twice shy!

How they sting

Jellyfish have been likened to “floating, highly organised bunches of sticky fly traps, where their prey is plankton rather than flies”.

Many species are umbrella or bell-shaped when seen floating on the surface of the sea with flanges of lacy plumes extending downwards. These are but extensions of their mouths with coverings of lethal harpoon-like cells or ‘nematocysts’. Beneath the body trail long dangling tentacles, also covered in hundreds of nematocysts.

These cells contain venom in a tightly coiled harpoon with a hair-like trigger which, when in contact with any protein bearing creature – or human skin – uncoils and fires its darts, entering its unsuspecting stabbed prey almost like a hypodermic syringe. Hundreds, if not thousands of nematocysts can fire at once, thus attacking the blood cells and nervous systems of an unfortunate victim.

The bell of a jellyfish constantly pulsates rhythmically through the sea (almost like a front crawl swimmer) in pulling and forcing a constant stream of plankton-rich water over its mouth frills and upwards past the ends of the tentacles, which immobilise its prey. In plankton rich hunting grounds, the tentacles act as a dragline or anchor in slowing down the movement of jellyfish, to allow a jellyfish to devour its prey. Jellyfish are powerful hunters, so swimmers be aware of the following three species.

Lion’s mane jellyfish is the largest species of jellyfish.

Cyanea capillata

Lion’s mane jellyfish, sometimes called the hair jellyfish, is the largest species of jellyfish, weighing up to a tonne with more than a metre diameter across its bell and thin silvery tentacles of up to 50 metres in length. These tentacles may sometimes be intertwined like a vast stinging fish net in which to trap other jellyfish and fish.

This species is found in northern colder waters and south of Australia and New Zealand. As a pelagic species living in the top 20 metres of our oceans, it relies upon ocean currents for its movements but can be swept ashore in late summer and early autumn. The larger species vary in colour from crimson to dark purple. A swimmer’s sting can cause temporary pain and localised redness.

Physalia physalis

The Portuguese man o’ war or bluebottle jellyfish is so named because of its sail-like upper body and one sub species (Physalia urtriculus) is found throughout the Indo-Pacific Ocean.

Whilst it resembles and is related to the jellyfish family, it is a siphonophore comprising a colony of organisms working together. With its balloon-like filled float (a gas filled bladder), it is mostly located in tropical and subtropical waters but may be propelled by warm ocean currents and prevailing winds to temperate latitudes.

It is easily recognised by its translucent colouring tinged with bluish purple or pink and its 10-metre long venomous and paralysing tentacles. As many as 10,000 humans each summer are stung whilst swimming off the east coast of Australia. Even when detached, these jellyfish tentacles can deliver a nasty sting creating whip-like weals on human skin, which may lead to anaphylactic shock. If stung, always carefully rinse the affected areas with seawater but avoid washing the nematocysts downwards to the feet or hands. Certainly, the use of vinegar may relieve the stings but medical treatment is always advised. This species of jellyfish is not without its predators in the form of loggerhead turtles and the blue sea slug.

Jellyfish have been likened to floating, highly organised bunches of sticky fly traps that prey on plankton.

Chironex fleckeri

Various species of the box jellyfish or seawasp are found in the Indo-Pacific Ocean, Mediterranean Sea, and in the waters off South Africa and New Zealand. In Sabah they are referred to, and most appropriately, as ‘balung api’, literally meaning ‘shooting fire pains in the body’. Certainly there is a burning sensation of one’s skin.

The largest species measures up to 30 centimetres along each side with three-metre long tentacles. With 24 primitive eyes on its transparent, almost invisible body, it carefully navigates around objects. However, 20 to 40 people in the Philippines are annually killed by these creatures.

A smaller sub-species, commonly known as ‘the invisible demon of the sea’ or the Irukandji jellyfish (Carukia barnesi), is only two centimetres across its bell with four small tentacles. It is one of the very few species that does not rely on sea drifting as its main form of propulsion for it actually hunts its prey at a speed of two metres per second.

During the South West Monsoon period, this species is driven closer to the shore. Whilst crayfish swim with impunity around its tentacles without triggering the nematocysts, its main predator is also the loggerhead turtle, which possesses a thick tongue preventing the penetration of these harpoon-like cells.

A fascinating study of Malaysian jellyfish was published last year in ‘Zoological Studies’ Vol 55 (2016) – a joint paper by marine biologists at the University of Malaya’s Institute of Ocean and Earth Sciences, and Institute of Biological Sciences. Its general conclusion was that “Malaysia may harbour many more jellyfish species that have yet to be recorded.” In their two-year study, they identified a total of 12 putative species encompassing 12 genera.

Wise advice to bathers:

1.            Heed the warning signs on beaches for there is really not a jellyfish season.

2.            Always swim in pairs, keeping an eye out for marauding ‘jellies’.

3.            Wear protective swim wear – a T-shirt, long shorts, jeans or pantyhose.

4. Never touch or prod a ‘beached’ jellyfish with your hands or feet – they can still sting.

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