Cephalopods
Giant Australian cuttlefish
Ascarosepion apama (Previously known as Sepia apama)
The world’s largest cuttlefish transforms its colour, pattern and texture in an instant — a remarkable hunter and a celebrated part of the Great Southern Reef.
Scientific Name
Ascarosepion apama
Group
Cephalopod Mollusc
Max Mantle Length
Up to 50cm
Max Weight
Up to 10.5kg
Typical Lifespan
1-2 years
Behaviour & Adaptation
Masters of Disguise
A cuttlefish’s appearance is constantly changing. Pigment cells called chromatophores allow it to alter its colour and pattern, while raised areas of skin change its texture.
These transformations help it blend with rock, sand and seaweed. During breeding, the same abilities become a vivid form of communication, with dramatic displays directed at potential mates and rivals.
Species biology: Australian Museum.
Identification
Recognising A reef Giant
Colour alone is an unreliable guide to a cuttlefish that can change its appearance so quickly. Look instead at its broad body, the fin running around its mantle and the arrangement of its arms.
Giant Australian cuttlefish have distinctive skin folds behind each eye. Inside the body, a lightweight cuttlebone helps control buoyancy.
Broad Mantle
A large, oval body houses the internal organs and cuttlebone.
Fringing Fin
A narrow fin extends along the sides of the mantle.
Arms & Tentacles
Eight arms and two longer feeding tentacles surround the mouth.
Skin Folds
Three folds behind each eye help distinguish this species.
Identification: Fishing Tasmania; Australian Museum.
Distribution & Habitat
AT home on the GSR
Giant Australian cuttlefish occur along southern Australia, from New South Wales around the southern coastline to Western Australia, including parts of Tasmania.
They inhabit rocky reefs, seagrass beds and sandy seafloors. Rocks, ledges and crevices provide shelter and secure surfaces for eggs.
Range and habitat: Australian Museum; Fishing Tasmania.
Feeding Ecology
A hunter hiding in plain site
Giant Australian cuttlefish are carnivores, feeding on crustaceans, fish and other molluscs. Two extendable feeding tentacles seize prey, which is held by the arms and processed by a powerful beak.
Crustaceans
Crabs and other crustaceans form part of their diet.
Fish & Molluscs
They also hunt fish and smaller cephalopods.
Part of the food web
Cuttlefish themselves are prey for dolphins, seals and sharks.
Diet: DCCEEW; predators and biology: Australian Museum.
A Remarkable Winter Gathering
Reproduction & Annual Aggregation
The shallow reefs near Point Lowly and Whyalla in South Australia are renowned for the species’ largest known breeding aggregation. Historically, enormous numbers have gathered here between May and August.
Males compete for females through displays and close guarding. Smaller males may mimic female appearance and posture to approach a potential mate without provoking a larger rival.
Females attach eggs beneath rocks and inside sheltered crevices. These small spaces are a vital part of what makes this stretch of coastline such an important breeding habitat.
Breeding habitat and behaviour: DCCEEW. Recent population changes are covered below.
ADULTS GATHER
Autumn-Winter
Cuttlefish arrive at the breeding reef, and courtship and competition intensify.
Winter
EGG LAYING BEGINS
Females place individual eggs in protected spaces. Adults die after breeding.
Following Months
A NEW GENERATION
Eggs develop over several months. Hatchlings emerge and begin life independently.
A typical seasonal sequence; timing and abundance vary between years.
Breeding STrategies
Size is not the only route to a mating opportunity. While large males display and guard females, smaller males can use stealth or female mimicry to slip past them.
What looks like a colourful gathering is a complex social scene, with changing signals, competing tactics and females that may mate with more than one male.
STrength, Stealth and a clever disguise
Protecting a vulnerable gathering
Conservation
A short lifespan and concentrated breeding event make this population particularly sensitive to poor years. Long-term monitoring is essential to understand changes and guide protection.
Permanent closures prohibit targeting and taking cuttlefish in the Upper Spencer Gulf. Additional cephalopod restrictions apply around the spawning area.
Protecting the Breeding Grounds
The Cuttlefish Coast Sanctuary Zone joined Australia’s National Heritage List in February 2023.
National Significance
Understanding Population Change
Scientists continue to investigate breeding, survival and the environmental pressures that affect the aggregation.
Population Update • 2026
A serious decline under investigation
In August 2026, PIRSA reported that the breeding population had reached a record low. Expanded monitoring and research are investigating the decline, including possible effects of the harmful algal bloom. The causes remain under investigation.
Check current official access advice before planning a visit, as temporary restrictions can change.
For the classroom
Explore the giant Australian cuttlefish lesson and discover the behaviours, breeding strategies and conservation questions behind this remarkable reef animal.
Bring the cuttlefish story to life
Continue Exploring
-
![]()
Citizen Science
Get involved and help researchers better understand and protect the reef.
-
![]()
Cephalopods
Meet the octopuses, squid and cuttlefish of the Great Southern Reef.
-
![]()
Educator Hub
Explore learning resources about Australia’s temperate marine life.
Join Our Community
Sign up to our monthly newsletter to receive the latest updates from around the GSR.
Monthly Great Southern Reef updates. Unsubscribe at any time.