Distribution

1. Coastal areas of the tropical and subtropical Indo-Pacific, from the Bay of Bengal in the west (possible even further west) to the Philippines in the east. Southwards to northern and northeastern Australia.

2a. Coastal areas of the tropical and subtropical Indo-Pacific, from the Maldives and Yangon (Rangoon) in the west to the Philippines in the east. Southwards to northern and northeastern Australia (near Brisbane).

2b. Coastal areas of the western Atlantic, from North Carolina in the USA to the Caribbean and as far as Venezuela and Brazil in the south.

Biology

See also General information on cnidarians. These species, above all Chironex fleckeri, are among the most dangerous jellyfish of all.

Box jellyfish are so called because of the more or less square shape of their bell (Fig. 4.13). In Chironex, the largest species, the bell can reach a width of up to 20 cm. Several tentacles (up to 15) are attached to each of the four lower corners. They carry the dangerous nematocysts and when stretched out can reach a length of up to 3 m in Chironex. There are estimated to be 4 billion nematocysts on a single adult Chironex jellyfish!

Fig. 4.13 Chironex fleckeri

The biology of Chironex has been extensively studied, but little is known about the two other chirodropids. The free-swimming adult animals are found in quiet, shallow coastal waters, while the sessile juvenile stages grow in river estuaries until the first summer rains wash them out into the coastal waters. As a consequence there are frequently mass occurrences of Chironex in the summer months (in Australia from October to May). In contrast to Chironex fleckeri, with its marked seasonal occurrence, C. quadrigatus occurs all year round.

As these species prefer shallow water, in contrast to many other jellyfish, they represent a severe danger for bathers, especially as they are practically transparent and thus very hard to see. However, by wading into the water they have a chance to avoid you, as they possess a simple light-sensory organ (small lens eyes) in their bell and flee from larger objects. 

Stings leave a chaotic mesh of tentacle marks on the skin. On closer observation of the individual tentacle marks, the typical cross-banding can be seen (ladder-like 'cross-hatching' pattern, Fig. 4.11a).

Risk

Due to the extensive skin contact, countless nematocysts are discharged into the hypodermis, which leads to a widespread and rapid accumulation of venom in the tissue and blood vessels. The toxins are mostly proteinaceous and display primarily neurotoxic and cardiotoxic effects in the human body. The amount of venom stored in each individual nematocyst in C. fleckeri and C. quadrigatus is massive compared to other species of jellyfish, and the potent toxins can thus lead to life-threatening envenoming and death within minutes. Contact with approx. 2 m of C. fleckeri tentacles is believed to be sufficient to cause life-threatening envenoming in children. The amount of venom stored in the nematocysts of a single Sea wasp is believed to be sufficient to kill 250 adult humans with an average weight of 70 kg! In terms of the potency of the venom and the speed with which envenoming occurs in humans, C. fleckeri is generally considered the most dangerous venomous animal of all.

Accidents generally occur in bathers in shallow water. To date there have been about 90 fatalities reported due to C. fleckeri, of which 70 alone occurred in Australia. The actual numbers may be much higher, particularly in regions of Southeast Asia and New Guinea, where it is only recently that such accidents are documented. In around one third of the fatalities in Australia, death is said to have occurred in the first 3 minutes! There have been reports of fatal envenoming due to C. quadrigatus from the Philippines, Malaysia and Papua New Guinea. One fatality due to C. quadrumanus was reported from Texas, USA (Bengston et al. 1991).

In regions where Chironex and Chiropsalmus occur, it is strongly recommended to wear diving suits or the thinner "stinger suits", which are available in Australia. In regions with transient increased occurrences of these jellyfish, bathing should be avoided. On Australian beaches where Chironex and Chiropsalmus occur, safe bathing areas are ensured with the use of special nets ("stinger nets") which are attached to floating tubes. It is not safe to bathe beyond these nets and local recommendations should be adhered to!

Literature (biological)

Cleland and Southcott 1965, Endean 1988a, b, Gershwin 2006, Hartwick 1987, Halstead 1988, Heeger 1998, Kinsey 1986, 1988, Storch and Welsch 1997, Warrell and Fenner 1993, Williamson 1988, Williamson and Exton 1985, Williamson et al. 1996

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