Octopus tetricus

Lore & Background

Octopus tetricus was originally discovered in New South Wales and occurs from Lakes Entrance in Victoria to Moreton Bay in southern Queensland, as well as in northern New Zealand including Lord Howe Island. The first sighting in New Zealand was not until 1997, and it has since become one of the most common octopus species there. Gene sequencing confirms that Australian and New Zealand populations come from the same original population, with proposed gene flow via planktonic larvae or adults using floating wood or algae. Warmer waters spreading south of Australia are hypothesized to influence populations to disperse further south in response to climate change.

This species is normally coloured grey to mottled brown with rufous arm faces, orange colouration on arms, funnel, and mantle opening, and white eyes. Its skin is granular with irregular patches and warty structures used for camouflage as seaweed. The second and third arms are longer than the first and fourth, typical of the Octopoda order. The nervous system comprises the brain, optic lobes, and a highly developed arm nervous system containing three-fifths of the octopus's total neurons—350 million neurons distributed equally across its eight arms.

The species epithet tetricus means 'forbidding' or 'gloomy'. The type specimen, collected by the Wilkes Expedition, is thought to be lost. The New Zealand species Octopus gibbsi is considered a synonym of O. tetricus.

Reader's Guide

Octopus tetricus is notable as an ecosystem engineer, altering its habitat by digging dens and using prey remains, including shells, to build shell beds that attract hermit crabs and fish, thereby creating a local ecosystem. It occurs in the intertidal zone along rocky shores and seagrass beds, and at depths up to 70 meters. Adults show high site fidelity, staying in the same location for an average of 3 months, with some aggregating inshore for breeding during spring and summer. The species is semelparous, with females reproducing once in their lifetime, guarding approximately 270,000 eggs per clutch until hatching. Females rarely eat or sleep during nest protection and die shortly after the eggs hatch. Temperature plays a key role in growth: with good food supply, octopuses in cooler waters grow slower but reach larger sizes than those in warmer waters. The species is significant in the Australian fishing industry and contributes to energy flux between trophic levels. Its ability to store viable spermatozoa for up to 114 days and its cannibalistic behaviour of females on males after mating are notable aspects of its reproductive biology.

Did You Know?

• The English translation of Octopus tetricus is 'the gloomy octopus'.
• Each female lays approximately 270,000 eggs per clutch.
• The arm nervous system contains three-fifths of the octopus's total neurons, with 350 million neurons distributed equally across its eight arms.