Hapalochlaena fasciata Click to enlarge image
Blue-lined Octopus, Hapalochlaena fasciata Image: Dr Isobel Bennett
© Australian Museum

Fast Facts

  • Classification
    Species
    fasciata
    Genus
    Hapalochlaena
    Subfamily
    Octopodinae
    Family
    Octopodidae
    Order
    Octopoda
    Class
    Cephalopoda
    Phylum
    Mollusca
    Kingdom
    Animalia
  • Size Range
    4.5 cm

The Blue-lined Octopus is one of the blue-ringed octopuses, which are reputed to be among the most dangerous animals in the sea.

Identification

There are several species of blue-ringed octopuses in Australia, with the most common one found in Sydney being the Blue-lined Octopus. All species are brown and it is only when they are disturbed that the vibrant blue markings appear as a warning.

Habitat

The Blue-lined Octopus is found on intertidal rocky shores and in coastal waters to a depth of 15 m.

Distribution

The Blue-lined Octopus is found from Southern Queensland to southern New South Wales.

Other behaviours and adaptations

Blue-ringed Octopuses are reputed to be some of the most dangerous animals in the sea. In some respects this is true because they have an extremely powerful venom that they use to kill their prey of crabs and small fishes. On the other hand, they are very shy and non-aggressive creatures that prefer to hide under ledges and in crevices. Encounters with humans usually result in the octopus quickly darting for cover. It is only when an animal is picked up that it may 'bite' and inject its paralysing venom, known as tetrodotoxin.

Danger to humans

The big danger is that small children who are attracted to their bright colour displays may be tempted to pick them up. There have been several fatalities in Australia from this octopus.

The blue-ringed octopuses, including the Blue-lined Octopus, may 'bite' if handled but, because of the small size of the injecting apparatus, the 'bite' may not be felt. However within minutes symptoms include numbness of the lips and tongue, difficulty in breathing, followed by complete paralysis of the breathing muscles. Victims appear to lose consciousness as they cannot respond to their name being called. However, after recovering, they have reported being able to hear everything around them. Call for help, monitor breathing and airways. Apply mouth-to-mouth resuscitation.