by Louise Goggin
Photo: Jamie Seymour
In 1964, a doctor called Jack Barnes spent hours in a wetsuit
lying in the water near Cairns searching for a jellyfish. He was
trying to find the jellyfish responsible for 'irukandji syndrome'
- a set of symptoms suffered after a jellyfish sting that could
put the victim in hospital. Irukandji is the name of an aboriginal
tribe that once lived in the area around Cairns in north Queensland.
Finally, to Dr Barnes' delight, a thumbnail-sized jellyfish swam
past his mask. He stung himself, his son and a surf life saver
to check that the jellyfish he had caught was responsible for
'irukandji syndrome'. All three ended up in hospital. The tiny
jellyfish was later called Carukia barnesi after the very
dedicated (? and slightly crazy) Dr Barnes.
Carukia barnesi is the only jellyfish proven to cause
'irukandji syndrome'. However, it is now believed that a sting
from at least six different species of jellyfish can produce the
same symptoms which include lower back pain, muscle cramps, vomiting,
restlessness and anxiety. In rare cases, the victim can suffer
pulmonary oedema (fluid on the lungs) or cardiac problems that
could be fatal if not treated.
Are irukandji deadly?
In January 2002, a tourist swimming near Hamilton Island in
the Whitsundays died after being stung by a jellyfish. His death
was reported by the press to have been caused by an irukandji.
The 58-year-old man had a pre-existing medical condition that
made a jellyfish sting fatal. He had a valve replacement and was
taking warfarin to thin his blood. After he was stung, his blood
pressure increased which caused a brain haemorrhage leading to
his death. The jellyfish that stung the man was not collected
and its identity remains a mystery.
In April 2002, a second tourist died after being stung by a jellyfish
while swimming at Opal Reef off Port Douglas in Queensland. The
severe hypertension (high blood pressure) sometimes associated
with irukandji syndrome caused a fatal brain haemorrhage.
The jellyfish which stung the second man was not collected. However,
stinging cells (or nematocysts) collected from the mans
skin do not belong to Carukia barnesi or to any other known
Work is ongoing to find and identify the various types of jellyfish
causing irukandji syndrome, especially those in the offshore islands
and the Great Barrier Reef that cause the life-threatening symptoms
of severely high blood pressure and heart failure.
The difference between Carukia barnesi
and the box jellyfish
Both Carukia barnesi and the larger box jellyfish Chironex
fleckeri are classified as cubozoan jellyfish, commonly called
box jellyfish because they have box-shaped bodies or 'bells'.
There are two main groups of cubozoans - Chirodropidae and Carybdeidae.
Carukia barnesi is a carybdeid jellyfish which are usually
smaller than chirodropid jellyfish, such as the box jellyfish.
Carukia barnesi only grows to about 25 mm across the bell
while the box jellyfish Chironex fleckeri can grow to 30
cm across the bell.
Carybdeid jellyfish, such as C. barnesi, have stinging
cells on their tentacles as well as their body while the chirodropid
jellyfish, such as C. fleckeri, usually only have stinging
cells on their tentacles.
Carybdeid jellyfish usually have a single tentacle hanging from
each of the four corners of their body or 'bell' while chirodropid
jellyfish usually have multiple tentacles hanging from each of
the four corners of their bodies. Carukia barnesi has a
single retractile tentacle, from 50 to 500 mm long, hanging from
each of the four corners of its bell. Chironex fleckeri
can have 60 tentacles (15 on each corner), many of which will
be more than 2m long when extended. Each tentacle can carry about
3,000,000 stinging cells per centimetre of tentacle. A sting from
the box jellyfish can be fatal.
The biology of Carukia barnesi
Little is known about the biology of Carukia barnesi
or any of the jellyfish that cause 'irukandji syndrome'. Carukia
barnesi is a small, transparent jellyfish which is about 25
mm across the body or 'bell' with a single tentacle from each
corner of its box-shaped body.
Carukia barnesi has sense organs which include primitive
eyes on each side of the bell but, because jellyfish do not have
a brain, it is unknown whether the eyes can form an image. In
the box jellyfish Chironex fleckeri, the eyes probably
help to find prey and avoid objects in the water. It is unknown
if the eyes of C. barnesi are used for the same purpose.
Box jellyfish were thought to be at the mercy of water currents
but they have subsequently been found to be fast and agile swimmers.
The large box jellyfish Chironex fleckeri can swim at three
knots. It is not known how fast and well C. barnesi can
Box jellyfish feed on fish and crustaceans and use a strong toxin
that paralyses their prey. Both the body and tentacles on Carukia
barnesi are armed with stinging cells called nematocysts.
These cells are concentrated in rings on the tentacles. The nematocysts
have a miniature harpoon coiled inside which is everted when the
jellyfish contacts its prey (or an unfortunate swimmer). The bulb
of the stinging cell then injects toxin through the shaft and
into the prey. The tentacle is contracted and pulls the prey into
the jellyfish's mouth which is inside the bell.
Box jellyfish are found in tropical waters from Exmouth in Western
Australia to Agnes Water (near Gladstone) in Queensland. Carukia
barnesi has only been collected close to Cairns in north Queensland,
but some of the species that cause 'irukandji syndrome' are found
regularly as far south as Great Keppel Island, or less frequently
as far south as Bundaberg.
Carukia barnesi are found offshore as well as along coastal
beaches near Cairns when northerly or north-easterly winds and
currents carry them onshore. The number of jellyfish in onshore
waters varies between years, probably due to changing wind direction.
In 1999-2000, two scientists sampling north of Cairns every day
for four months caught 250 C. barnesi (most of them were
caught in three days). The following year, only two jellyfish
were caught in the same time.
There are almost 30 species of cubozoans but the life cycles
of only three are known. The life cycle of C. barnesi is
In some cubozoans, the adult jellyfish release sperm and eggs
into the ocean where the egg is fertilised. The eggs develop into
'planulae' which swim for a few days before settling to the bottom
and growing into a polyp. The polyp moves about on the bottom
for about a week before settling in one place. It can bud off
extra polyps. Each polyp develops into a tiny jellyfish or 'medusa'
which swims away from the bottom to begin life swimming in the
Scientists now believe that at least six different species of
jellyfish produce the range of symptoms that have been associated
with a sting from Carukia barnesi. These symptoms are called
'irukandji syndrome.' So far, Carukia barnesi is the only
proven small carybdeid jellyfish to have caused the 'irukandji
syndrome'. There is no antivenom for the syndrome.
In Australia, most cases of 'irukandji syndrome' seem to be restricted
to waters between the Tropic of Capricorn and the northern tip
of Torres Strait. They occur between November and May but cases
have been recorded from the east coast of Australia in most months
except July and August.
Each year, varying numbers of people are stung - from only a
few to more than 200 people. In the summer of 2001-2002, approximately
160 people were stung by mid February (approximately 100 people
in Cairns, 10-15 in Townsville, 20 in the Whitsundays, 10-12 in
Great Keppel, 15 in Agnes Waters).
The initial sting of the jellyfish is usually not very painful.
But about 5-45 (usually 30) minutes after being stung, the person
starts to have a severe backache or headache and shooting pains
in their muscles, chest and abdomen. They may also feel nauseous,
anxious, restless and vomit. In rare cases, the victim suffers
pulmonary oedema (fluid on the lungs) which could be fatal if
The sting should be flushed with vinegar and the patient taken
to hospital as soon as possible if they develop 'irukandji syndrome'
to be treated for the pain.
Preventing the sting
The mesh used in stinger-resistant nets in north Queensland
is broad enough to kept out the box jellyfish Chironex fleckeri
but allows C. barnesi to pass through. On Christmas Day
in 1985, 40 people were taken to the Cairns Base Hospital after
being stung by jellyfish in stinger-resistant enclosures near
A lycra body suit can help protect against stings although people
can be stung where the suit does not cover the skin - around the
feet, neck and head.
- Unravel the life cycle of Carukia barnesi and other
- Identify factors that cause appearance of jellyfish so that
their arrival (and departure) from northern beaches can be predicted.
- Find out how many species of jellyfish cause 'irukandji syndrome'
so that doctors are better able to treat stings.
- Study the action of all the venoms involved in 'irukandji
syndrome' and develop an antivenom or antidote to improve treatment
of all aspects of these stings.
- Develop swimming enclosures which prevent the entry of the
smaller jellyfish like Carukia barnesi.
- Find alternate methods of control or prevention of stings
from jellyfish that cause 'irukandji syndrome'.
- Find if severe symptoms such as hypertension and heart failure
can be predicted and prevented in victims.
For more information
Irukandji Jellyfish Response Taskforce
Dr Peter Fenner's Marine
Lisa-ann Gershwin's website
about jellyfish - Medusazoa
Jamie Seymour at JCU's Tropical
Australian Stinger Research Unit
Thanks to Dr Peter Fenner and Dr Jamie Seymour.