Box Jellyfish - Defense and Feeding Mechanisms

Defense and Feeding Mechanisms

The box jellyfish has been called "the world's most venomous creature," though only a few species in the class have been confirmed to be involved in human deaths and some species pose no serious threat. For example, the sting of Chiropsella bart only results in short-lived itching and mild pain.

Each tentacle has about 500,000 cnidocytes, containing nematocysts, a harpoon-shaped microscopic mechanism that injects venom into the victim. There are many different kinds of nematocysts found in cubozoans. In Australia, the fatal envenomations are most often perpetrated by the largest species of this class of jellyfish Chironex fleckeri, owing to the high potency of the venom carried in their nematocysts. The recently discovered and very similar Chironex yamaguchii may be equally dangerous, as it has been implicated in several deaths in Japan. It is unclear hence which of these species is the one usually involved in fatalities in the Malay Archipelago. In 1990, a 4-year-old child died after being stung by Chiropsalmus quadrumanus at Galveston Island in the Gulf of Mexico, and either this species or Chiropsoides buitendijki are considered the likely perpetrators of two deaths in West Malaysia. At least two deaths in Australia have been attributed to the thumbnail-sized Irukandji jellyfish. Those who fall victim to these may suffer severe physical and psychological symptoms known as Irukandji syndrome. Nevertheless, most victims do survive, and out of 62 people treated for Irukandji envenomation in Australia in 1996, almost half could be discharged home with few or no symptoms after 6 hours, and only two remained hospitalized approximately a day after they were stung.

In Australia, C. fleckeri has caused at least 64 deaths since the first report in 1883, but even in this species most encounters appear to only result in mild envenoming. Most recent deaths in Australia have been in children, which is linked to their smaller body mass. In parts of the Malay Archipelago, the number of lethal cases is far higher (in the Philippines alone, an estimated 20-40 die annually from Chirodropid stings), likely due to limited access to medical facilities and antivenom, and the fact that many Australian beaches are enclosed in nets and have vinegar placed in prominent positions allowing for rapid first aid. Vinegar is also used as treatment by locals in the Philippines.

The box jellyfish actively hunts its prey (zooplankton and small fish), rather than drifting as do true jellyfish. It is capable of achieving speeds of up to 4 knots (1.8 m/s).

Box jellyfish are known as the "suckerpunch" of the sea not only because their sting is rarely detected until the venom is injected, but also because they are almost transparent.

The venom of cubozoans is distinct from that of scyphozoans, and is used to catch prey (small fish and invertebrates, including shrimp and bait fish) and for defense from predators, which include the butterfish, batfish, rabbitfish, crabs (Blue Swimmer Crab) and various species of sea turtles (hawksbill turtle, flatback turtle). Sea turtles, however, are apparently unaffected by the sting and eat box jellies.

In northern Australia, the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.

In Hawaii, box jellyfish numbers peak approximately 7 to 10 days after a full moon, when they come near the shore to spawn. Sometimes the influx is so severe that lifeguards have closed infested beaches, such as Hanauma Bay, until the numbers subside.