EN: Blue-ringed Octopus
DE: Blauring-Krake
Family
Octopus
(Octopodidae)
Size
max. 15 cm
Diet
Carnivore;
Small Crustaceans & Molluscs
Distribution
Indo-Pacific
So far, at least ten different Blue-ring octopus are known to science, but it is not yet clear whether they are different species, or whether some of them are merely a variation of others.
Two of the confirmed and most common species are Hapalochlaena lunulata (this species is usually mentioned in the identification) and H. maculosa. The species can be distinguished from each other by measuring the size and number of blue rings. Another hint is the body length. H. maculosa is the larger species and has a body length of max. 5 cm and a tentacle length of approx. 10 cm, while the body length of H. lunulata usually measures less than 5 cm and has a tentacle length of max. 7 cm. H. maculosa has 10 brown spots per tentacle, which are bordered with blue rings, and a total of 50-60 rings on its coat, while H. lunulata usually has less than 25 rings on its coat. The rings are 8 mm in diameter, larger than in H. maculosa.
Blue-ringed octopus live mainly on sandy and rocky bottoms in temperate waters of the Indo-Pacific near the tidal zone at depths of up to 50 meters. Like most cephalopods they have a life expectancy of about 2 years, but the males die already after the mating ritual. They like to hide in shells, bottles or cans.
They are carnivorous and feed mainly on small crabs, hermit crabs, shrimps and molluscs. Like all cephalopods they have a parrot-like beak, with which they bite only when catching prey or as a defense against predators. The bite is poisonous (see more about this under “Poison”), which might be caused by the lack of an ink sack – another way to deter predators. However, the evolution of the poison vs. the ink sac is unknown. H. lunulata is said to have enough poison in it to kill 26 adult humans within minutes. Blue-ringed octopuses are rather rare, so a sighting is always a nice surprise.
Behavior
Blue-ringed octopus are solitary animals and hunters, which when left undisturbed have a very inconspicuous coloration in the sandy gray area, which is adapted to the background. If the animal is disturbed – for example by the nasty habit of some dive guides to hold a fist over the animal and then suddenly open their hand, i.e. to imitate an attack by another octopus – the animal shows its blue rings as a warning and as a deterrent. This reaction is also shown when the animal is followed stubbornly at a constant distance. Then it loses patience and tests the effect of its warning rings. So no reason to scare the animal unnecessarily for it to display its blue rings. By the way, the octopus can not only change the color intensity and thickness of its blue rings, but also let them pulsate to a small color spectacle.
How do the rings work?
In 2012, a report by an American biologist was published in the “Journal of Experimental Biology”, which explains how the Blue-ringed Octopus can display its glowing blue rings, i.e. how this works biologically. Other octopuses have chromatophores (small bags filled with dye) in their skin that can be stretched abruptly by the muscles. However, the blue-ring octopus has developed its own special effects, which we humans usually do not appreciate: Wrinkles! Simply put, the rings are created by light reflection in the octopus’ densely packed tissue layers. One part of the skin houses the light-reflecting cells, which are covered by a ring-shaped skin fold when at rest. When the octopus wants to show its rings, it abruptly relaxes some muscles, tenses others, and the fold gives way to the glowing ring, only accentuated by some dark skin in the center of the rings and around them. And all this within a remarkably short third of a second. According to the researcher, no other comparable system is known in nature.
Gift
The species of Blue-ringed Octopus have one thing in common in any case: the highly effective and deadly poison Tetrodotoxin. In case of a bite (the tentacles are not poisonous, only the beak) it can kill a full-grown human being and is considered to be one of the most deadly poisons in the marine animal kingdom due to the severity of the toxin. The same toxin is also found in other underwater species, even outside the octopus family, such as puffer fish. So far no antidote has been developed. The toxin is produced in the salivary glands by certain bacteria. Blue-ringed Octopus are actually very peaceful, non-aggressive animals. Most poisonings are caused by humans who have “played” with the animal… go figure….
The bite is usually not painful. Nevertheless, you should signal for help immediately and go ashore. Gradually more symptoms appear, which can include the following: Reddening at the bite site, weakness, tingling in the face/limbs/neck, nausea, vomiting, inability to move (paralysis), paralysis with swallowing and speaking difficulties, apparent apathy (person appears to be unresponsive while fully conscious, but cannot communicate either acoustically or mimically) and finally respiratory paralysis. As a first aid, mouth-to-mouth is particularly important until the patient receives medical treatment. In general, quick first aid and especially ensuring continuous breathing is crucial for a positive outcome. The paralysis symptoms always extend rapidly to the respiratory center. If the patient is still in the water, he should be brought ashore immediately.
Another very critical measure is to apply a compression bandage. Do not apply alcohol to the wound under any circumstances! The heart is probably the least worrying organ in the whole poisoning chain, as the toxin has no effect on the heart functions. However, the pulse must be monitored at all times, as a sharp drop in blood pressure can lead to circulatory failure.
