Giant Cuttlefish - Sepia apama Gray, 1849

Introduction

This species is the largest of all the cuttlefish and an expert at colour change and camouflage. They can change colour in an instant, and by raising parts of their skin, they can also change shape and texture to imitate rock, sand or seaweed. These displays have various interpretations to other marine creatures and may be used for camouflage, mating or even hypnotising prey.

Identification

Sepia apama is the largest of the cuttlefish and can be identified by two rows of three skin flap-like papillae over each eye.
Their cuttlebones can be identified by the lack of a spine and a rough V-shaped thickening (callus) at posterior end. The outer cone is wide and flared in the adult.

Distribution

The Giant Cuttlefish is endemic to southern coastal waters of Australia, and is found as far north as Moreton Bay (QLD) on the east-coast and on the west-coast up to Ningaloo Reef (WA).

Seasonality

Sepia apama spawn from April to September, with a peak spawning period of May-June. Spectacular mass spawning occurs in the Spencer Gulf where thousands of Giant Cuttlefish congregate in relatively small patches of rocky reefs.

Feeding and diet

As like other cuttlefish S. apama feeds on fishes, crabs and other crustaceans

Other behaviours and adaptations

Giant Cuttlefish are mainly active during the day using their excellent camouflage to hide. Colour patterns also play an important part in communication, particularly in the breeding season.

They are reportedly friendly with divers, seemingly curious and attracted to bright colours, and many have been seen following divers around for up to 15 minutes.

Life history cycle

The Giant Cuttlefish has a short life span, it is thought, of just two to four years. In the breeding season, thousands come together to spawn, after which many die. Mass extinctions are therefore commonly observed, with the cuttlebones of dead animals washed up onto beaches in large numbers. Many will show the teeth marks of dolphins, birds, and fish which feed on both the living and dying animals.

Breeding behaviours

Banner-like webs along the margins of their arms are flared to make individuals appear larger, to both appear a more attractive mate to females and intimidate potential rivals. Pulsating zebra stripes also move along the sides of the body, their speed and intensity changing with the situation.

Smaller males have been observed to mimic the colouration and behaviour of females, using this diversion to sneak close to females to mate with them without the awareness of the larger aggressive males.

Mating takes place head to head and spermatophores, or small packages of sperm, are passed from male into an area in the female where fertilisation takes place. Shortly after fertilisation the female will lay between 100 and 300 lemon-shaped, leathery white eggs in subtidal crevices. It is thought the low incubation temperatures needed, around 12°C are one of the potential limiting factors of this species range. Unlike many other cephalopods, female cuttlefish do not guard their eggs and they are left to hatch after 3-5 months.

Economic impacts

Sepia apama is taken as by-catch in trawl fisheries and on a small-scale using jigs, baited hooks or spears. It is sold as food and bait.

References

1. Jereb, P., & C.F.E Roper (eds) (2005) Cephalopods of the World: Chambered Nautiluses and Sepioids, Food & Agriculture Organization of the United Nations Catalogue for Fishery Purposes, Rome, No. 4, Vol. 1
2. Graf, Gary (1987) How I learned to get along swimmingly with the Giant Australian Cuttlefish, Geo, 9(1): 58-71.
3. Norman, M., (2000) Cephalopods- A World Guide, ConchBooks, Germany (Hackenheim)
4. Norman, M & A. Reid., (2000) A Guide to Squid, Cuttlefish and Octopuses of Australasia, CSIRO Publishing, Victoria (Collingwood)
5. Bavendam, F (1995) The Giant Cuttlefish: Chameleon of the Reef, National Geographic, 188(3) 96-106.