Last Updated on Thursday, 13 September 2012 12:56 Written by Douglas David Seifert Thursday, 24 November 2011 13:27
A taste of poison: small and beautiful, Australia's blue-ringed octopus is, however, famed for another reason – its toxic venom. Words and photographs by Douglas Seifert
THERE IS NOTHING so captivating to simple human self-interest than an animal that has made a reputation for itself by causing the death of a human being. The ability to kill is enough to ensure a permanent place in the collective consciousness. Rightly or wrongly, the animal is elevated to the status of something to possibly be feared.Nearly every schoolchild has heard of the deadly blue-ringed octopus of Australia. It is unique among octopuses due to its tiny size – at maturity, its head/body can be smaller than the length of a man’s thumb – and, in dramatic contrast to the mottled camouflage pattern that serves as its daily wear, it exhibits an incredible display of dazzling, iridescent, neon-blue rings when agitated or excited. This octopus also holds within its tissue one of the most lethal neurotoxins known to man: a compound capable of invoking muscular paralysis, respiratory failure and death in humans and other animals many times the diminutive cephalopod’s size.
The vibrant blue rings are considered to be one of nature’s strongest warning signals that this is one creature not to be trifled with. Unfortunately, not every sign in nature is so obvious to humans, and the first discovery of this warning signal came in the form of the first known human fatality, in Australia in 1954.
A 21-year-old sailor, Kirke Dyson-Holland, was spearfishing in shallow water near Darwin. His dive buddy discovered an unusual tiny, colourful octopus, which he tossed to Dyson-Holland, who put it on his shoulder as he waded back to shore. Upon reaching the shore, he threw the octopus back into the ocean and his companion noticed a trickle of blood on the shoulder where the octopus had been resting. Soon, Dyson-Holland experienced the discomfort of a dry mouth and began having trouble breathing. By the time he arrived at hospital, his skin had turned blue and he was not breathing, although he did still have a faint pulse. His companion relayed the man’s last words: ‘It was the little octopus, it was the little octopus.’ Ninety minutes had passed between the octopus bite and the sailor being pronounced dead. The account was published months later in the Medical Journal of Australia, and the news of the odd occurrence of an octopus killing a human began to spread out to the world.
In fact, it would be a nearly a decade before the species of octopus responsible was correctly identified and the causative factor was discovered. The initial suspect was misidentified as a larger and rather common octopus that was known for having a bite capable of causing an effect similar to the allergic reaction to a bee’s sting. As the deceased man had a history of asthma, the assumption was an extreme allergic reaction.
Scientific sleuthing, a re-examination of the pathology reports and an examination of the embalmed specimen of octopus eventually revealed the real facts. The true culprit was determined to be a member of the blue-ringed octopus genus Hapalochlaena (from the Greek meaning ‘soft-cloaked’), a group of ten or so species found in the Indo-Pacific.
There are three well-described species: the southern or lesser blue-ringed octopus (H. maculosa), found in temperate waters from Victoria, South Australia and southern Western Australia; the southern blue-lined octopus (H. fasciata), found in Sydney and along the New South Wales coast to southern Queensland; and the greater blue-ringed octopus (H. lunulata), a tropical species found in Papua New Guinea, Malaysia, Indonesia, the Philippines, the Solomons, Vanuatu and Sri Lanka.
The greater blue-ringed was once thought to be the octopus responsible for the fatality in Darwin, but has now been supplanted by the currently non-taxonomised northern Australian greater blue-ringed octopus (Hapalochlaena sp. 1), one of the many unclassified members of Hapalochlaena. There are also blue-lined octopus species reported from Okinawa and Hong Kong, and a mid-ring blue-ringed octopus (Hapalochlaena sp. 4) known only from Borneo and Sulawesi.
Blue-ringed octopus are diurnal predators, seeking shelter under rocks and in abandoned bivalve shells when not on the hunt for crabs and other crustaceans. They are drab and mottled in coloration, unless (or until) disturbed. When agitated, they turn a cream to pastel yellow shade and display dazzling small, neon-blue rings on black blotches all long their bodies and arms as a warning that this is no ordinary octopus.
The bite from their parrot-like beak transmits a venom that is effective on their crustacean prey, but likely harmless to humans. But the blue-ringed octopus’ saliva, internal organs and tissues carry a paralysing neurotoxin called tetrodotoxin.
Tetrodotoxin is a deadly substance – various sources state that it’s between ten and 10,000 times more powerful than cyanide – and its effect is to interrupt or block the nerves controlling the contractile muscles essential for the motor processes of respiration. Tetrodotoxin is created by symbiotic bacteria living within the blue-ringed octopus, which are transferred genetically from mother to offspring during the process of conception.
If the victim of a blue-ringed octopus bite is immediately given continuous CPR with heart massage and ventilation until the venom’s effect naturally wears off – generally within 24 hours – the victim will survive. Tetrodotoxin is metabolised rather rapidly and excreted through normal body functions, so long as artificial respiration keeps the body working at its optimum levels. Patients typically make a full recovery, unless a lack of oxygen to the brain has caused permanent damage.
Why does a blue-ringed octopus need such a deadly cocktail in its daily life? The reason is believed to be that the octopus must instantly immobilise its prey or suffer catastrophic damage from the battle. Octopus eat crabs, which are hard-shelled, with strong claws designed to pinch, hold, tear and cut. If the octopus does not immediately disable the crab, its soft tissues would be vulnerable to the crab’s considerable defences and offences.
Call it an overcompensation for an inferiority complex, if you will. It is a matter of survival. Put it this way: if you are that fragile and delicate in physical construction, you have to completely overwhelm, paralyse and annihilate your prey before it can do you physical harm – or your species will not survive.
Like most octopus, blue-ringed octopus do not live long. They breed once, then they die. In laboratory conditions, an entire life cycle of H. maculosa was observed to take place within seven months: four months from hatching to maturity, one month from copulation to egg laying, and two months’ embryonic development of eggs, followed by hatching of offspring, senescence and death.
Unlike other octopus, the female blue-ringed octopus does not lay her eggs attached to a surface in a reclusive den. Rather, she carries the developing eggs with her, cradling the mass of up to 150 eggs between her skirt and body like a vendor of balloons.
The offspring, once born, are miniature, self-sufficient versions of their parents and take on a benthic life of crisis and hunting. They have a functioning ink sac for a few weeks, to be used for last-ditch defence, which then degenerates with maturity and is no longer functional. They have an ample amount of tetrodotoxin in their saliva and are able to hunt successfully as soon as they hatch, but they do not gain their blue rings until they are six weeks old.
When the offspring reach sexual maturity, blue-ringed octopus go wild. Newly mature males are eager but also inexperienced and will attempt to copulate with any other blue-ringed octopus, regardless of its sex. It is not that blue-ringed octopus are sexually confused; they simply cannot visually determine the sex of their conspecifics. Thus, their strategy when they encounter another blue-ringed octopus is to race toward it with all due speed and pounce on the mantle of the other with all their might, grasping around the head with eight arms and hanging on in a tight embrace. There is no mating dance, no courtship, no signalling, no foreplay. The blue-ringed octopus do not seem to recognise whether another octopus is male or female until, at least, they have had a go at copulation.
The ambiguous turns serious once the male inserts its third arm – a modified appendage called a hectocotylus – in through the siphon of its tightly gripped partner and into the mantle cavity. If the male determines the object of his embrace is a female, he will try to copulate by placing a spermatophore packet into the female’s mantle, where she conceives her eggs. If the other octopus turns out to be of the same sex, he withdraws his hectocotylus and the two separate rapidly, without further intimacies.
In male–female copulations, the transfer of spermatophores (typically numbering one to four) into the mantle may take two and a half hours, after which the female has to physically remove the male by reaching back with her arms and pulling the male off, making him break off the amorous embrace. Sometimes she will also cannibalise her former lover.
All in all, there have been fewer than 20 known blue-ringed octopus envenomations worldwide over the past 50 years, resulting in three reported fatalities. It raises the question of how accurately this family of tiny octopus can live up to its deadly reputation.
Is the blue-ringed octopus’ reputation out of proportion to its threat? The answer is yes and no. The octopus has proven to be no threat unless handled – accidentally or deliberately – or otherwise provoked, and brought into contact with fragile human skin and the transport system of the bloodstream beneath. Then, with respect to the body’s indisputable reaction to tetrodotoxin, the question is one of luck. Will medical treatment be administered in time? Or might it just be better to follow a policy of ‘look but don’t touch’?
In the meantime, all people fascinated by this unique family of octopus look forward to scientists further classifying and identifying all the individual species of these beautiful animals, which also happen to carry one of the most lethal neurotoxins to which humans are susceptible. l