Blue ringed octopus biology

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Biology

Relatively little is known about the biology of blue-ringed octopuses. All three species occur in relatively shallow water from the intertidal to around 30 m. Both H. fasciata and H. maculosa are in-shore species that frequent rock reefs and tide pools. They are also found in sandy areas using mollusk shells as well as bottles and cans for shelter. H. lunulata is found in sandy and silty areas among small corals and clumps of algae. Small crabs, hermit crabs and shrimp make up much of their diet. In the laboratory, the octopuses pounce on crabs, envelope them in their web and bite a hole through the carapace to envenomate prey. The crustaceans quit struggling after a few seconds. The octopus uses its beak to tear off and devour softer pieces of the prey. It partially digests and sucks out the remaining flesh, leaving behind only the hard exoskeleton. There are reports of the blue-lined octopus squirting venom directly into the water to kill prey, but this behavior remains to be confirmed. We have also seen several cases of cannibalism where juveniles have eaten other juveniles and adults have partially consumed other adults. In one case, a female killed and partially ate a male after mating with him.

Like many octopuses, blue-ringed females reproduce just once, laying a single clutch of eggs. When ready to lay their eggs, females of all three species select a suitable shelter such as a mollusk shell or rock cavity- bottles and cans now serve quite well for this purpose. After all the eggs are laid which can take several days, the female remains with them for several weeks until they hatch. She then dies within a couple of weeks. Female H. lunulata attach several festoons of 20 to 30 eggs each to the brood chamber wall. This species produces small eggs, 2.5 to 3.5 mm long. Hatching occurs after about a month and the young enter the plankton, where they remain for an as yet undetermined period before settling.

Female H. maculosa and H. fasciata both produce large eggs, 6-mm long. These eggs take a couple of months to hatch (depending on temperature). The eggs are laid in several unattached clumps. These are carried by the female in her web and arms. The brooding posture typically has the female sitting, mouth down, with her arms and web drawn up around her body, her eyes visible through the folds of the web. The festoons of eggs are held in the brood "basket" formed by the web and arms. When forced to move, three pair of arms hold tightly to the eggs; one pair is used to crawl along the substrate. Immediately after hatching, the young crawl about on the substrate and begin feeding in a day or two. There is no planktonic stage. It appears that H. fasciata reaches sexual maturity in about 4 months. Females with eggs have been reported year round. In the Sydney area, females produce eggs in the spring and fall. This suggests that the generation time may be as short as six months. H. maculosa seems to be an annual species. Near Adelaide, eggs hatch in September and the females lay the following June and July. The life-cycle of H. lunulata is poorly known. In Indonesia and the Philippines, sexually mature females are found primarily in March and April, so this to may be an annual species, although as noted earlier, how long the young spend in the plankton is unknown.

Mating in blue-ringed octopuses involves close contact between males and females. Rather than the male inserting his hectocotylus (third right arm that transfers the sperm package) into the female's mantle cavity from a distance, a male mounts the female, grasps her mantle with his arms, and repeatedly inserts the hectocotylus transferring sperm packets. Mating typically lasts for several minutes, or even hours, and in H. lunulata, is terminated by the female who often has to forcibly remove the male.

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