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Dangerous Marine Critters Print E-mail

By Rosemary Jilders - catamaran Sokari

Queensland waters are cruised by a large number of boats every year as they migrate up and down the coast during the season.  The owners of many of these vessels are from southern climes so they may be unfamiliar with some of the creatures that inhabit our waterways and unaware that there are a lot that can really hurt us.  All boaties who cruise these waters should learn which ones you can touch, which ones you can’t and what first aid treatment is necessary if you are stung, stabbed or struck.  There are a number of books available and perhaps one of them should be part of your vessel’s library along with your favourite first aid book.  On Sokari, our Simpson 13.25m catamaran, we carry what we consider to be the best – Dr. Carl Edmond’s excellent publication called Dangerous Marine Creatures –  which not only has first aid treatments for numerous dangerous critters but also the treatments to be carried out by the doctor whose help should be sought as soon as possible.


Common throughout Australian waters, this jellyfish can deliver a painful sting but it is not fatal.


 The Tamoya is a large four-tentacled jellyfish from tropical waters which causes a very painful sting but while collapse may occur there are no recorded deaths. The Jelly blubber only causes minor irritation.

Jellyfish (Marine Stingers)
The waters surrounding our country are home to some harmful jellyfish which are easy to avoid but which can result in effects ranging from discomfort through intense pain and in some cases even death.

The Irukandji and Box Jellyfish which are found in tropical waters are prime examples of those whose stings can prove fatal.  The term ‘box’ jellyfish often confuses people as it is a name used to describe Cubozoan jellyfish, including Irukandji and Chironex fleckeri (more commonly referred to as Box Jellyfish).


 The Irukandji is another dangerous marine stinger that is potentially fatal. The Jimble is a small four-tentacled box jellyfish.

First aid treatment for many marine stingers is simply the application of cold packs or cold water, or alternatively hot packs or hot water, as the venom is not heat stable.  However, it should be remembered that this is not the case for the Box jellyfishes as noted below.

The best protection against all stingers is to cover up, preferably with a stinger suit or wetsuit.  Any bare piece of skin is susceptible so try to keep all sensitive areas covered, e.g. if wearing a hood, the neck area between hood and suit are at risk.  It has been discovered that tentacles will retract from the Lycra used in the manufacture of stinger suits.  This differs from the animal’s reaction to the old form of protection, nylon panty hose, in that the tentacles adhere and tear off the animal leaving the victim open to being stung when removing the pantyhose.

According to my research, all tropical jellyfish stings should be doused with vinegar.

Box Jellyfish (Chironex Fleckeri) also known as the Fire Medusa and Sea Wasp, is probably the most well known.  It was once commonly called the Sea Wasp but this name was discouraged after it was discovered that many tourists watched the sky for the creature.  The name Box Jellyfish became more commonly used because of its shape which is like a bell or cuboid with four distinct sides – up to 20cm along each side – like a box.  From each corner hang as many as 15 tentacles up to three metres in length with up to 5,000 nematocysts – stinging cells.  The animal jets itself along at speeds of up to four knots.  They are pale blue and transparent, hence very difficult to see.  Even in clean water they are virtually invisible.

Box jellyfish have very advanced eyes and research has shown that they display complex behaviours such as fast directional swimming and obstacle avoidance which are obviously visually guided.  Between the tentacles, on each side of the bell, is a sensory structure in a small cavity.  Each cavity has six eyes giving them 24 eyes in total.

Marine stingers may be present during the entire year in tropical Queensland but in general the danger season typically runs from October to April – the cyclone season.  Further south the season may run from November to March but can sometimes continue weeks beyond the close of the season.  After nearly three decades living and working in and on the water on a daily basis, my hubby John and I believe that they breed up creeks and rivers.  So in the wet season after a good fall of rain that washes out the creeks, these animals are also washed out to then follow the currents.  Dry areas with low rainfall, such as Bowen, don’t seem to get the number of box jellies that appear in some wetter areas.       

These animals don’t like rough conditions, preferring calm waters and they swim towards shore on the rising tide avoiding areas with extensive seagrass beds or other obstructions.  They feed on crustaceans and small fish and aren’t out to ‘get you’.   You aren’t part of their diet and stinging you is either an accident or reflex action when their tentacle is jerked which activates the nematocysts.

The Box Jellyfish is considered to be the most venomous marine animal known.  Death can occur within two to three minutes but this is not a foregone conclusion.  In the 1980’s every year just before the stinger season, warnings would appear on TV which had most of us convinced that if we even dared to set foot in the water during the season we would die!  I am testimony to the fact that this is not true.  Enter the water slowly as this jellyfish will often swim away from people if it has the opportunity and time. 

If stung, stay calm.  Much now depends on the victim’s reaction.  Don’t rush yelling and screaming towards shore.  Do not spin away as this tears the tentacle off the creature which causes more nematocysts to be fired.  Back away slowly.  Onlookers and would-be rescuers should also be careful that they don’t become entangled in the tentacles.  Don’t try to pick the tentacles off as you can then be stung again.  Don’t rub with sand.  Don’t scrape off with a knife.  Today, these actions would seem ludicrous but back in 1983 when I was stung the nurse at the hospital read these instructions out to me from the only notes they had on box jellyfish stings.  She was appalled that this information was still being recommended.  Although she knew that these were incorrect actions, she wasn’t really sure what should be done.  The use of vinegar was only just becoming accepted as the latest first aid treatment. 

Current thinking is still the same.  Douse the area of the sting with vinegar leaving any tentacles in place, then with a vinegar soaked compression bandage wrap the area starting below and ending above the sting.  Most beaches these days have a bottle of vinegar in a stand for use in an emergency however when cruising in remote areas this may not be available so make sure that you have a good supply of vinegar onboard.  Hospitals in North Queensland should have the antivenene on hand but believe me the cure isn’t all that nice either.  It is a big needle.

Box jellyfish stings are very painful and can be fatal. The tentacles from the box jellyfish leave a raised welt, sometimes as if someone has taken a whip to the victim.

Irukandji (Carukia Barnese) is a small jellyfish with a bell diameter of approximately two centimetres and is believed to be responsible for an increasing number of stings in North Queensland.  While only small, this animal is considered to have also been responsible for some deaths.

In contrast to the Box Jellyfish, the Irukandji are usually found in deeper waters near the reef, although currents may force them inshore.  Divers and snorkellers are at particular risk so ensuring that the body is well protected is imperative.

Working in the water every day of the year in the early 1980s my husband and I ran the risk of being stung constantly.  One day when John was spearfishing – out of the stinger season – he took the basic precaution of wearing a T-shirt.  As he chased a fish the neck of the T-shirt billowed out and jellyfish poured inside the shirt stinging him on the chest.  He kept swimming as he didn’t want to lose the fish but when his breathing became laboured he quickly turned for shore.  John’s breathing became harder and harder and his chest had many red welts.  At the time we believed the Box was the only lethal marine stinger so we assumed it was just a less dangerous jellyfish and weren’t particularly concerned.  In hindsight, considering the size and shape of the jellyfish we now believe it was an Irukandji.  We drove to our home which wasn’t far away and he jumped under a hot shower.  He kept it as hot as he could stand and while under the water the pain subsided, but returned as soon as he stepped out.  Obviously, the venom was not heat stable.  The pain eventually subsided and he had no other adverse side effects.

No definitive treatment is available at this time for what is known as the Irukandji syndrome.  Analgesia is usually required – perhaps intravenously with severe pain but it is not known whether vinegar will deactivate the nematocysts as for stings by Chironex Fleckeri (Box Jellyfish).  The Australian Venom Research Unit at Melbourne University is researching an antivenom to treat Irukandji stings.

Symptoms of an Irukandji sting can take anywhere up to 40 minutes to appear so it is very important that the victim be monitored for 45 minutes out of the water and in a safe location. 

(Portuguese man-o’-war, Pacific man-o’-war)

The Bluebottle belongs to the same family as corals and sea anemones.

This jellyfish is a common sight on beaches Australia-wide and in most warm oceans anywhere in the world.  It is also prevalent at the reef, with the author having been stung at Vlassof Cay, off Cairns a few years ago.


Bluebottles are washed up on the beaches after onshore winds but even when dead the tentacles can still give a nasty sting. Bluebottles are blown through the water with their sac acting like a sail.

The animal is blown through the water by its blue air-filled sac which acts as a sail.  This sac which can grow up to eight centimetres in length usually has a single, long, blue main fishing tentacle hanging down underneath.  This tentacle can contract to just a few centimetres or extend to over a metre.  Some species have numerous main fishing tentacles and can cause severe stings with symptoms similar to the Irukandji.  Tentacles cause a sharp, painful sting which is aggravated if the area is rubbed.  Severe pain can be experienced from a few minutes to hours and may develop into a dull ache spreading to surrounding joints.  The sting causes a red line with small white lesions which look like a string of beads.  In severe cases blisters and weals can appear.  Victims may show signs of shock.  Respiratory distress may occur in children, asthmatics and people with allergies.

The victim should leave the water and any part of the animal still on the skin should be removed gently with tweezers or a gloved hand.  If left on, more capsules may be fired.  Do not rub or wash with alcohol as this will make matters worse.  Pour seawater NOT fresh water over the sting.  Milder stings can be treated with ice packs or local anaesthetic sprays.

Unattached tentacles that are floating around in the water can still inflict stings that are just as potent as those from attached tentacles.  Dead animals that have become stranded on the beach can also inflict stings.  Do not touch these animals with your bare skin, don’t enter the water if they are present and be careful even when walking on the beach.  Bluebottles are rarely found in sheltered waters and are more commonly present on exposed ocean beaches after strong onshore winds.

For tropical stings seek medical assistance immediately and provide emergency care if necessary.  Douse the area liberally with vinegar but if vinegar is not available (remember you should have this on your vessel) remove the remaining tentacles and pour seawater over the sting area ensuring that there are no broken tentacles in the water to cause further injury.

Other jellyfish
There are many more jellyfish inhabiting our waters.  Not all of them are as dangerous as the above, but many can cause discomfort.  First aid for non-tropical jellyfish is to remove any tentacles that are adhering to the victim, wash with sea water (not fresh water) and apply cold packs for 10 minutes, re-applying if necessary and if pain persists seek medical attention.

The Jelly Blubber is a mushroom shaped bell with a diameter from five to 30cms.  It has no tentacles but there are eight ‘fronds’ or ‘frills’ hanging below.  The sting causes only minor skin irritation.


The nematocysts will inflict a painful itchy rash.  A cold pack will relieve the symptoms.

The Jimble is a transparent bell with a diameter of one and a half to three centimetres, with one tentacle about five to 15cms long attached to each corner.  This marine stinger is commonly found in southern waters but significant systemic effects have recently been reported from tropical waters.   The sting is painful and leaves an angry red mark but it is not dangerous. 

The Lions Mane is found worldwide and can grow to be one of the largest of all jellyfish with its disc-shaped bell sometimes growing to over one metre long and its tentacles reaching more than 10m.  The bell top is usually white but is often yellow, brown or reddish underneath the bell.  It can inflict a painful sting and swimmers can often find it difficult to avoid their fine tentacles.  If stung, relieve the pain by applying a cold pack and seek medical attention if necessary.

Less common is the Little Mauve Stinger but it can be found Australia-wide.  It has a small mushroom-shaped body two to six centimetres in diameter with many warty lumps containing nematocysts covering its body.  The colour of the bell is pink or mauve with eight pale brown tentacles about 10-30cms long.  It is sometimes called ‘the purple people eater’ because, despite its attractive appearance, it can inflict a nasty sting.

The Tamoya (also known as Fire Jelly and Moreton Bay Stinger) is distributed throughout tropical Australian waters, all Queensland and northern NSW waters and is often found in open water.  There are some sub-species which are common at Mackay, Moreton Bay and Northern NSW.  It has a large transparent box-shaped bell which is approximately six to 18cms in diameter.  A single thick, ribbon shaped tentacle that can be up to one metre long hangs from each corner.  There is no antivenom but vinegar is effective as first aid. 

So when you are cruising the Queensland coast and want to drop over the side for a swim, dive or even checking the anchor you will be able to do so in confidence.  You will now know what to look for regarding jellyfish and if you should be unlucky enough to be stung you will know how to treat it.


The information in this article has been sourced from various agencies.  While doing the research I found many conflicting opinions.  Dr. Lyndon Llewellyn, Research Manager from Australian Institute of Marine Science in Townsville explained it to me as follows:  “Part of the reason for the conflicting information in the public domain is that it can be a controversial field.”  So while all care has been taken to ensure the information supplied is true and correct the author, Rosemary Jilderts, takes no responsibility for the accuracy of the information or for any typographical errors.

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