Chironex fleckeri (Multi-tentacled Box Jellyfish)
Chironex are often referred to in Australia as Stingers or the northern Australian box jellyfish. Through the Surf Life Saving Association, and though his contact with many organisations, the author is trying to get the general public to realise that there are many varieties of “box-jellyfish” with symptoms varying from mild skin pain (Carybdea sivickisi) to death from respiratory and/or cardiac failure. Thus, it is important to be specific and the name Chironex box-jellyfish is being suggested.
History of investigation into Chironex fleckeri
Dr Ronald Southcott was stationed with the Australian Army in 1944 in the Cairns area. He noticed and described 2 types of stings (Southcott 1959): `Type A’ stings were minor with a small and insignificant skin mark. However they were followed some time later (usually between 20 to 30 minutes) by a number of severe systemic symptoms that often caused prostration, even in the fittest of troops. `Type B’ stings had extreme skin pain with obvious wheal marks visible on the stung area. Although many victims became somewhat sick and lethargic, there were no deaths in this group during the study.
In 1956 in north Queensland, as a result of brilliant field work by Dr Hugo Flecker, Southcott was given a specimen of a chirodropid. He was then able to identify the jellyfish causing Type `B’ stings, naming it, aptly, Chironex fleckeri (Southcott 1956); and in 1967, following similar brilliant field work by Dr Jack Barnes, he identified the jellyfish causing the Type `A’ stings, naming it Carukia barnesi (Southcott 1967).
Dr Hugo Flecker was a Radiologist in Cairns, north Queensland in 1932. On January 20th 1955, when a 5-year-old boy died after being stung in shallow water at Cardwell, north Queensland, Flecker suggested that the police net the area. Three types of jellyfish were caught, one of which was an unidentified, box-shaped jellyfish with groups of tentacles arising from each corner.
Flecker sent it to Dr Ronald Southcott in Adelaide, and on December 29th 1955 Southcott published his article introducing it as a new Genus and species of lethal box jellyfish. He named it Chironex fleckeri, the name being derived from the Greek `cheiro’ meaning `hand’, and the Latin `nex’ meaning `murderer’, and `fleckeri’ in honour of its discoverer.
Flecker was also interested in the Type `A’ stinging and published his article in the Medical Journal of Australia in 1952 naming it the `Irukandji syndrome’ after the “Irukandji” tribe of Aboriginals who lived in the Palm Cove area where the stings were frequently reported (Flecker 1952b). Flecker died in 1957 without finding the jellyfish responsible for the syndrome.*
Flecker’s field and experiment notebook, containing almost certainly valuable information ahead of its time, disappeared with his death. Rediscovery of this notebook would be a major historical and possibly research advance.
Dr. Jack Barnes was a Cairns General Practitioner who then took over the quest for the “Irukandji”. He surmised that the organism had to be a very small jellyfish that swam very quickly, and probably close to the surface. After calculating the most likely time and place to catch the animal Barnes lay on the bottom of the seabed in shallow water wearing his SCUBA gear.
Many hours later his persistence was rewarded when he saw a very small jellyfish swim in front of his mask. He managed to catch this, and another when he saw a fish moving in an erratic fashion which was seen to be caught in the tentacles of another of these tiny jellyfish. To see if they caused the “Irukandji syndrome” Barnes stung himself, his son Nick, and a lifesaver friend. After the characteristic 30-minute delay all three developed the “Irukandji syndrome” and had to be admitted to hospital with severe back pain, muscle cramps, nausea, vomiting and headache (Barnes 1964).
These jellyfish specimens were also sent to Dr Ron Southcott and in 1966 he described them as a new genus and species of box jellyfish called Carukia barnesi. The `car’ from Carybdea, the type of single-tentacled box-jellyfish in whose Family it belonged, and the `ruk’ from “Irukandji”; `barnesi’ named after its discoverer (Southcott 1967).
Barnes – as the Medical Adviser to the Surf Life Saving Association introduced `pantihose’ as an effective protective barrier preventing a serious Chironex sting. It was thick enough to prevent penetration and consequent envenomation by the thread tubes of the stinging cells of Chironex. It became a common site in north Queensland to see Surf lifesavers wearing pantihose on patrol. One pair was worn as usual on the lower half of the body with the feet cut out and taped around the ankles, the other pair had a small hole cut in the crutch and they were pulled over the head with the arms put in the leg part, and the hands free. They were able to safely enter the water to drag long mesh nets through the shallows to see if Chironex were present, allow safer bathing for the general public. The idea was not to rid the area of dangerous jellyfish, but to detect their presence so the beach could be closed to prevent envenomation.
Until recently, this genus and species has been thought to be present in Australian waters only. Stings to humans extend from south of Broome in Western Australia (east Indian Ocean, latitude 18o south) around the northern Australian coastline down to Gladstone, Queensland, on the eastern Australian coastline (west Pacific Ocean, latitude 24o south). Chironex specimens have been reported caught or sighted in the Exmouth Gulf in Western Australia (latitude 22o south) to Bustard Bay, south of Gladstone, Queensland, in the east (latitude 25o south).
Until recently the distribution of Chironex was stated to be Australia only. The author believes this distribution can now be widened to include nearby areas of the Indo-West-Pacific Ocean (see Map 1): –
In 1990 the author examined and identified 6 chirodropid specimens in the Smithsonian Institute, caught by Mayer in the Philippines (1910). Although Mayer had identified them all as Chiropsalmus quadrigatus, in the opinion of the author, who has studied many hundreds of specimens, 2 were actually Chironex fleckeri, 2 fitted the somewhat “vague” description of Chiropsalmus quadrigatus as described by Haeckel (1880), and the other two were too badly damaged, or preserved, for the author to be able to suggest an identification. These observations agree with those of Barnes who stated to the Royal Society in Cairns in 1964 that he had identified specimens of Chironex in the Smithsonian that had been caught by Mayer (1910). The author feels that this is the reason that the description of Chiropsalmus quadrigatus in Mayer (1910) is so confusing – he seems to be actually describing a combination of the features of Chiropsalmus quadrigatus and Chironex fleckeri, even though the latter was only identified as a news genus and species many years later.
In 1993 the author also identified as Chironex fleckeri, the specimens sent by Major T Hooper from Borneo to Phil Alderslade, even though it had never been identified in this area before. These were two of several specimens caught very close to where Major Hooper’s son had sustained an almost fatal jellyfish sting several months previously (see Case Historylink please!).
Also in 1993 the author examined a specimen in the South Australian Museum that came from Vietnam, which he also would identify as Chironex.
These specimens were also reviewed by Rifkin, who also agrees on this identification and that the distribution of Chironex is much wider than previously believed.
Stings occur in shallow water as Chironex swim into this area when the wind is light and hot, and the water calm. Unsuspecting victims usually blunder into tentacles trailing behind the jellyfish bell, which are difficult to see in the water – the tentacles are almost invisible.
Pain is instant and severe and described as being “branded with red hot irons”; victims usually scream with pain. Children will usually stand in the water, trying to pick at the tentacles, thus getting further stings on the hands and arms, increasing the envenomation: adults frequently run out of the water and rub the tentacles. Most stings occur on the lower legs and body.
Adherent tentacles, like sticky threads, usually adhere to the victim: tentacle marks look like the victim has been whipped, or branded with irons. Minor stings cause severe skin pain with raised white wheals with a surrounding red flare. The area may blister and scar. If the victim lives, blistering and skin necrosis occur over the next few hours; scarring often occurs, and lasts for life. Victims may rapidly stop breathing, sometimes within a few minutes of the initial envenomation, with death occurring rapidly unless prompt first aid and medical aid is available.
Sixty seven deaths have been described in tropical Australia since records have been kept from 1883, the latest being the death of a 6 y-o boy near Cairns in December 1999. Such deaths occur rapidly, often within minutes of the initial sting and often far from medical and first aid; as such, assessment of effective first aid and medical treatments is difficult, and as yet, some remains unproven.
The work of Hartwick and Barnes show Chironex to be a coastal jellyfish. When the air is hot and still (frequently with a gentle northerly wind, common in tropical Australia in the summer months), they will come into very shallow waters at gently-sloping sandy beaches close to creek and river outlets where mangroves are common. Hartwick developed the life-cycle for Chironex after first breeding specimens in the laboratory, and then discovering their polyps in a natural habitat under rocks and mangrove roots, up to 5 kilometres from the sea in mangrove-lined rivers and streams.
For these reasons Chironex are often prevalent around the mouth of these creeks, especially as these are also areas where their prey of prawns and fish occur. Similarly they like the gently sloping, sandy beaches near these creeks. Here they can swim with the tentacles trailing behind them with little fear of them `snagging’ on rocks or other obstacles fishing for their prey, including the prawns and small fish that inhabit these areas. Unfortunately, these are the same areas that humans like and frequent. Chironex fleckeri have been seen and caught over rocks, but this is less common (Fenner et al 1995).
Although Chironex are common in very shallow, calm water they have also been reported out to sea in rougher waters. A surf life saver was stung in deep, rough water near Cairns in 1991 when a Chironex was washed on to the deck of the victim’s surf ski while he was paddling some 200–300 m offshore. Mulcahy (1999, personal communication) also reports that they have been trawled off the bottom by trawlers a couple of kilometres offshore. This observation remains unconfirmed.
Chirodropid fatalities throughout the Indo-Pacific have been documented in every month of the year; some of these may be from Chironex (see above). In the Northern Territory, reports of Chironex stings have occurred in every month of the year except July, but fatal stings have only been registered from September to May.
Appearance and behaviour
Although the bell may grow to 30cm, previously specimens of this size have only been caught in far north Queensland, however, on 4 April 1997 a specimen 25cm diameter was washed up on a beach near Mackay (Figure 7). At the same time, up to 50-60 other specimens were also washed up on to local Mackay beaches. This finding is extremely unusual and cannot be explained. Chironex are very strong swimmers and rarely beached, with just the odd report of its occurrence (Fenner et al 1995). Specimens of sea water have been taken and are to be analysed for pollution and other laboratory tests to see if any explanation can be given.
The maximum size of specimens reported from the Northern Territory is 14cm across the bell; the reason for this is unknown.
The bell is usually transparent, and often very difficult to see, even in very shallow water. It has a box-shape with four corners (pedalia), from which up to 15 thick, flat tentacles may arise. These tentacles may contract to a few cms or extend up to 3 meters or more in length – thus giving a theoretical tentacle length of up to 180 meters on a single large specimen. Hartwick once estimated that up to 4000 million nematocysts may be present in the mature adult. Assuming there may be 180 meters (maximum) of tentacle length, this acquaints to approximately 22 million per meter extended tentacle. Death has occurred from just 1.2 meters of tentacle length – in which case roughly 25 million nematocysts would have caused death, although the approximate number actually penetrating the skin, envenoming and causing death is not yet known.
Chironex fleckeri are the most evolved species of jellyfish having 4 rhopalia, or sense organs that lie mid-way between the pedalia, and at the base of the bell. These rhopalia are organs that: –
|differentiate light and dark using a rudimentary lens
|detect vibration – such as impending danger such as rough water from storms or predators (including humans)
|maintain balance and orientate the jellyfish position in the water.
They feed on small fish and prawns that are quickly killed when they swim into the tentacles. The reason Chironex venom has such tremendous “killing power” is not, as many people believe, to attack and kill humans, but to be able to kill its prey quickly, before the prey struggles too much, breaking off tentacles. Jellyfish, like humans, need to eat to live and breed. If Chironex lose their tentacles then they lose `killing power’, they cannot feed and they die.
Their tentacles are `elasticised’ and may extend out many meters when they are gently swimming along `fishing’ for prey. They can be contracted up to only a few centimetres when they are actively swimming. Chironex are active swimmers, unlike many jellyfish, swimming by a muscular contraction of the bell, which shoots out a jet of water propelling the jellyfish forwards. They can swim at the pace of a walking man, although the energy expended is too great to maintain this for any great length of time (R Hartwick, 1988, personal communication).
Chironex can recognise objects in its path and avoid them. Such obstacles may be objects in the water (ie. rocks and humans), and will often retract their tentacles and swim away from this perceived obstruction or danger.
Through media statements, many people believe that jellyfish `attack’ humans; it is actually the humans `attacking’ the jellyfish, usually by running into the water too quickly, not allowing the innocent jellyfish to be able to retract its tentacles and swim away. Tentacles that are torn off the jellyfish by the victim struggling to get away mean that the jellyfish loses its `killing power’ and consequently, as it cannot catch its prey, it dies.
The tentacles cause instant severe skin pain like being branded by a red-hot iron. Tentacle material is usually avulsed from the animal by the struggling victim, and cling firmly to the victim’s skin which is often diagnostic in chirodropid envenomations and fatalities. These remaining tentacles will contain many thousands of unfired nematocysts. The longer these tentacles remain in contact with the skin, the greater the risk of increasing the envenomation – thus making vinegar such an important immediate, first-aid treatment.
Victims often scream with the pain and children will often stand in the shallow water where they have been stung, pulling at the tentacles, and consequently receiving more stings to their upper limbs. As the keratin of the palms is often too thick for the nematocyst thread tube to penetrate, stings marks will often be confined to the backs of the hands only. Conversely, adults will usually jump back out of the water and run for help, the increased muscular effort increasing heart rate and consequent venom absorption. Thus the first treatment of Chironex stinging may be to `retrieve and restrain’, to prevent further envenomation.
Severe, whip-like marks are visible on the skin with an intense acute inflammatory response developing rapidly. Usually, a `frosted-ladder’ pattern matching the appearance of the nematocyst `batteries’ on the tentacle will be visible, and is of diagnostic value. This appearance is due to millions of discharged and undischarged nematocysts remaining on the skin of the victim, in the same battery lines as are present on the tentacle.
Linear erythematous wheals then rapidly develop, often with a white ischaemic centre. Serious envenomations develop surrounding oedema and darkening of the skin with vesiculation and partial or full thickness skin death, usually resulting in permanent scarring.
Often confusing, victims who die rapidly do not have sufficient time to develop this severe inflammatory response and their skin marks may appear quite insignificant.
Compression bandaging as suggested by Sutherland et al (1979) for snake bite is suggested (see First aid 5.8.3). Although it has not been scientifically proven to be effective in the acute onset of Chironex envenomation, using the principle of holding any remaining venom in the skin (see also, intra-vascular venom injection, 3.3.3), compression bandaging is recommended for major Chironex stings.
Note: it is not recommended for minor stings and then compression immobilisation bandaging must only be used AFTER initial resuscitation and vinegar treatment.
A major sting is defined as one causing: –
|An impaired conscious state, or unconsciousness
|Shallow, slow breathing with central cyanosis, or respiratory arrest
|Reduced pulse strength, irregularities, or asystole
|Covering the equivalent of more than 50% of one limb
There are many other factors that are used to define a major sting, but they will always result in one, or all, of the above signs. An important point stressed to all surf life savers and others treating sting victims is that it is important to realise the significance of a sting victim who was loudly distraught and physically active who suddenly becomes quiet – usually indicating the onset of impaired cerebral perfusion, with a reduced conscious level and possible cardio-respiratory arrest.
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Retrieve the victim from the water and restrain them, if necessary.
If other helpers are available, immediately send them for ambulance / medical help.
Assess the victim’s ABC and treat with EAR or CPR, if necessary.
If others are available to help, or if resuscitation is not needed, pour vinegar over the stung area for a minimum of 30 seconds to inactivate remaining stinging cells on any adherent tentacles left on the skin. Vinegar has been proven to totally prevent further discharge from remaining undischarged nematocysts (stinging cells) and is the cornerstone of first aid treatment. If vinegar is unavailable, the rescuer should pull tentacles off using their fingers (only a faint, harmless prickling will be felt).
AFTER vinegar application, compression immobilisation bandaging has been suggested for major stings, i.e. those:
a) covering an area more than half of one limb
b) causing impairment of consciousness
c) causing impairment of breathing
d) causing impairment of circulation
The use of compression bandages is unproven but has apparently appeared to offer clinical benefit in major stings.
If available, use Chironex antivenom for all major cases (see above). Three ampoules each containing 20, 000 units may be given intramuscularly, above the bandages, if there is a trained health professional on the beach. Although the IM use of antivenom has been described as being ineffective, its use has appeared to be valuable when used by Ambulance Officers in actual severe envenomation cases.
IV antivenom is the recommended route and qualified Paramedics may administer 1 ampoule. Antivenom also seems to help the severe skin pain of envenomation.
Antivenom has been used for many years and appears clinically effective with no adverse side effects. However, the effectiveness has been questioned because of the preparation of the antivenom: clinically it appears effective in the acute case.
Cold packs may be used (for 15 minutes and repeated when necessary) to help ease the skin pain in conscious victims.
In severe envenomation oxygen is used, if available, to assist with any breathing difficulty; Inhaled analgesia (i.e. entonox or penthrane) can be administered for unremitting pain in conscious, breathing, cooperative patients; its use should be discontinued if the patient’s condition worsens.
Medical Treatment of Chironex stings and Severe Jellyfish stings.
If necessary, continue resuscitation with endotracheal intubation and 100% oxygen (if appropriate) monitoring the oxygen haemoglobin saturation and electrocardiography.
Insert an intravenous line and administer a crystalloid solution, monitoring urine output.
In major chirodropid stings, administer a minimum of 1 ampoule of diluted antivenom (20, 000 units) intravenously. If the clinical response is inadequate, 3 (or more) ampoules may be given intravenously, according to clinical response.
Intermittent positive pressure ventilation with 100% oxygen will also assist in control of pulmonary oedema.
If there is persisting, life-threatening cardiac decompensation or arrhythmia, then consider giving verapamil intravenously (0.1 mg/kg up to 5-mg adult dose) under ECG monitoring until the cardiac arrhythmia reverts or other unwanted effects occur.
Inotropes such as adrenalin or dopamine should be considered for persisting hypotension – however, calcium should not be given.
Cardiopulmonary resuscitation, employing oxygen-enriched air (preferably 100% oxygen) should be continued and not abandoned in the patient with ongoing circulatory arrest until after consideration of further therapy with even more antivenom (at least 6 ampoules total dose, if available) and consideration of more verapamil and inotropes.
Intravenously administered analgesia may be necessary (1 mg/kg of pethidine up to 50 mg adult dose initially). For pain not relieved by cold packs and narcotic analgesia, in chirodropid stings, consider administration of 1 ampoule of antivenom intravenously as above.
Intravenous antivenom (administered as above) may provide cosmetic benefits in stings involving cosmetically sensitive areas (eg. face or neck, especially in females).
Case History 1
Case history written by Fenner (Williamson et al 1984)
At 1000 on 10 March 1984 a healthy 5-year-old girl weighing 2Okg was wading waist-deep in the sea at a beach near Mackay. She received a box jellyfish sting, mainly to her legs, which measured a total of about eight metres of tentacle contact. She was immediately pulled screaming from the water by her grandmother who restrained her hands which had already sustained some additional stings. The victim’s mother doused the adherent tentacles with vinegar within three minutes. The girl who was in great pain, but fully conscious and not cyanosed, was brought to a local GP surgery within 15 minutes of the envenomation. She immediately received an intramuscular injection of pethidine (40 mg), and an intravenous injection of 20 000 units (one ampoule) of box-jellyfish antivenom, diluted 1:2 with water. Within seconds, the pain, and the size and ‘anger’ of the wheals on her limbs, had diminished. On admission to hospital 25 minutes later she was again in some pain, and had obvious tentacle marks. Her vital signs were normal. No compressive bandages were used at any stage.
In hospital critical care unit, she received IV hydrocortisone (30 mg at once, then every four hours) by the intravenous route; IM pethidine (20 mg) and vinegar ‘soaks’ to the sting area.’ Within six hours, and while breathing inspired oxygen, she developed central cyanosis with tachypnoea, but no audible moist lung sounds.
Eight hours after the envenomation, she received further IV injections of hydrocortisone (100 mg) and of box-jellyfish antivenom (20 000 units), with no improvement in her condition. She had oliguria and her chest x-ray showed interstitial pulmonary oedema. The oxygen was increased but central cyanosis persisted. Over the next three hours the patient began to pass urine through the indwelling catheter, and a rapid improvement in her clinical condition was noted. Twelve hours after envenomation she was no longer cyanosed, had passed 800 ml of urine, and no analgesia was required. The next morning, while breathing room air, bilateral bronchial breathing was heard on auscultation, and the sting areas were swollen and tender. All other signs and symptoms had resolved. and her condition was obviously much improved. She was discharged from hospital well on the fifth day after admission.
Unfortunately, secondary infection with Staph. aureus developed in her right popliteal fossa over the next two weeks treated by the author with co-trimoxazole, 7.5 ml twice a day and topical applications of an antibiotic preparation [Neosporin) and hydrocortisone [1%1 cream) with a seemingly good result. However, scarring developed which remains obvious 12 years later.
Case history 2
Case history written by Williamson and Fenner (Lumley et al 1988)
On January 20, 1987, a healthy five-year-old boy who weighed 20 kg was bathing waist-deep in the sea at Barney Point beach near Gladstone, central Queensland. The weather was hot and still, the sea calm, and the water temperature was 29.5 ‘C. At about 1000 he ran from the water, shrieking and attempting to pull at adherent, translucent tentacles on his legs. His grandmother, who had accompanied him to the beach, assisted in this process with a towel, and in so doing sustained minor stings to her own forearms.
The child’s screams attracted attention. This person came to the patient’s assistance and doused vinegar over the sting area on the child’s legs, which were already showing red wheals. The estimated elapsed time between the initial envenomation and this first-aid manoeuvre was four to five minutes.
The grandmother ran for her car, and the child, who was described as “pale and sobbing”, was placed, sitting up in the back scat, with the helper. The elapsed post-envenomation time now was approximately 10 min. The grandmother drove to the ambulance centre in less than three minutes by ignoring all traffic signals. The condition of the child, who still sat upright, was “gradually deteriorating”. Just before reaching the ambulance centre the householder observed that the child had ‘ ‘blue lips” even though “respiratory sounds” were still apparent.
On arrival at the ambulance centre at 10. 15 a.m., the patient was described by the ambulanceman as unconscious, with a ghostlike pallor ‘ pulseless and with “fixed, dilated pupils”. The child was transferred to an ambulance vehicle where single-operator cardiopulmonary resuscitation with oxygen was commenced. The victim was then rushed to the casualty department of the hospital, where it arrived at 1018.
An initial assessment showed an unconscious apnoeic child with peripheral and central cyanosis, no palpable pulse, and urticarial wheals on his legs, hands and lower abdomen. The child was intubated, IV access obtained and 100% oxygen and ECC given. An ECG showed pulseless idioventricular rhythm which failed to respond to any therapy. After 20 min of continuous resuscitation, and approximately 40 min after the initial sting, further resuscitation was abandoned.
Post-mortem examination and investigations.
Conducted 25hrs after death a post-mortem showed urticarial lesions with tentacle imprints on both wrists, legs, thighs, and the lower abdomen, width 4-5mm and total length 4 m. Skin biopsy showed many nematocysts with a concentration from zero to clusters of more than 4000/mm2, presumably corresponding to the “batteries” of nematocysts that are grouped on the epithelium; most had discharged, and their threads had penetrated the mid-dermis, with trajectories that ranged from 0. 1 mm to 0.7 mm. A cellular inflammatory reaction was not present, which reflected the lack of time for such a response to occur.
Vinegar and Chironex box jellyfish
The use of vinegar as a first aid treatment for Chironex fleckeri stings was introduced in 1980 by Dr Bob Hartwick. While experimenting with tentacles from Chironex fleckeri he observed that methylated spirits caused a mass firing of the nematocysts. Field research was carried out in Gove, NT, and Townsville, Qld, when volunteers (including surf life savers, and Drs Barnes, Callanan, Hartwick, Unwin and Williamson) were stung under controlled conditions—an experimental procedure not currently recommended by many scientists and all Ethics Committees.
Various treatments were assessed in the laboratory and in the field, leading to the classic paper by HARTWICK and colleagues in the Medical Journal of Australia in 1980. This work demonstrated that 2-10% acetic acid in water (including household vinegar [4-6% acetic acid in water]) irreversibly inhibited stinging cell (nematocyst) discharge in Chironex fleckeri and several other species of box jellyfish. This would prevent further envenomation of the victim from remaining adherent tentacles material on the skin, the usual occurrence with Chironex fleckeri sting victims. A paper by the same authors in the Medical Journal of Australia described a case where a pregnant woman was saved on a Townsville beach by EAR alone, without immediately available antivenom, after a severe Chironex fleckeri sting.
These two papers exerted probably the greatest single influence on the Surf Life Saving Association at the time. After a meeting between the Queensland State Centre representatives, Dr Jack Barnes and the three authors of these two articles, the use of methylated spirits was abandoned and vinegar was adopted as the standard Australia-wide first aid treatment for box jellyfish nematocyst discharge inhibition.
Life cycle of Chironex box jellyfish
BROWN (1973) was the first to suggest that Chironex may breed close inshore, after he caught 24 tiny Chironex juveniles only 6–9 mm diameter in shallow water in Horseshoe Bay, Magnetic Island, near Townsville, north Queensland, in the summer of 1972. His investigations of that island were prompted by the island residents, denial of any Chironex sightings, during a year of particularly high prevalence of Chironex in north Queensland generally. His documentation contains other valuable observations, including the then `silent opposition’ of tourist organisations to the publicising the dangers of chirodropids in north Queensland waters and the need for protective clothing against both sunburn and chirodropid stings.
Confirmation of Brown’s suggestion, together with further understanding of the life cycle, have been brilliantly obtained by Hartwick and colleagues.
Although much remains to be learned and directly observed, the adult medusae at season’s end probably swim up coastal estuarine saltwater creeks to habitats of the polyp forms where the male and female adults reproduce sexually, probably by semelparous spawning. However, it may be that a single adult animal reproduces sexually, as planula larvae that subsequently developed into polyps have been found live in the bell cavity of a mature Chironex (RIFKIN 1992, unpublished observations). The resultant planulae (those that survive) develop into creeping (`roving’) polyps that look for suitable habitats before attaching to the rocks and debris of the creek bottom, where they develop into sessile (fixed) polyps.
On the way to adult maturation, these fixed polyps fall prey to various predator creatures, as a normal part of the biological food chain. Nevertheless they are surprisingly hardy and capable of asexual reproduction by budding, under favourable environmental conditions. The polyp forms need little food during the food-scarce winter period, but the growth rate of polyps (and medusae) varies with the food source and not the weather—although the food source is related to weather to some extent, and so there may be a range of sizes of jellyfish in the one area (HARTWICK 1990, unpublished observations).
Larger numbers of polyps develop if the food supply (planktonic animals) is good and there is no overgrowth of other polyp species (HARTWICK 1990, unpublished observations). Eventually (typically during September in northern Queensland) the surviving polyps detach to become small free-swimming juvenile medusae the survivors among which become the adult Chironex medusae. Rains flush through the creeks stimulating the polyps and they start to grow until they break off and are carried to sea as small box jellyfish. January rains will kill off any remaining polyps in creeks.
The emergence of part-grown Chironex medusae in large numbers from selected saltwater estuarine creek mouths, in response to favourable environmental conditions, has been directly observed on occasions in far north Queensland.
As with other life-cycle stages (planulae and polyps), the Chironex medusae fall prey to natural predators at all stages in their maturation. These predators include hawksbill turtles, butterfish, batfish and spinefoot fish.