Giant cuttlefish  (Sepia apama)

The giant cuttlefish is not yet classified on the IUCN Red List.

The giant cuttlefish (Sepia apama) is the world’s largest cuttlefish, and, like many other cephalopods, it is able to camouflage itself exceptionally well. By changing its skin colour and texture, the giant cuttlefish can convincingly disguise itself against its surrounding environment almost instantaneously (4). Cephalopods, which literally means ‘head-footed’, are a class of marine molluscs which, along with cuttlefish, includes squid, octopuses and nautiluses. Unlike other molluscs, cephalopods have a closed circulatory system, where blood is contained in vessels, and a highly developed nervous system with a large brain (4) (5).

The giant cuttlefish has eight arms and two extended tentacles, which are used for mating and catching prey, as well as to transform and camouflage the shape of the body (6). The giant cuttlefish is reddish brown, with white bars and spots on the arms and the mantle, and pale fins (4).

All cephalopods, and in particular cuttlefish species, have large, highly-developed eyes, and can detect very low light levels, vital in detecting prey and avoiding predation at night (4) (5). Cephalopods are widely considered to be the most intelligent group of invertebrates,with one of the largest brain-to-body size ratios of any invertebrate (7) (8).

The giant cuttlefish is found exclusively around the southern coast of Australia and Tanzania, leading to its alternative common name of the ‘giant Australian cuttlefish’ (3).

Found in coastal waters up to 100 metres deep, the giant cuttlefish generally lives on rocky reefs or among kelp forests, but it can also be found in seagrass meadows (3) (4).

The giant cuttlefish spends a lot of time resting, allowing it to channel more energy into growth, which has been dubbed the ‘live-fast-die-young cephalopod philosophy’ (9). Like all cephalopods, the giant cuttlefish is an active predator, using its excellent camouflage to stalk fishes, crabs and other crustaceans (3) (4).

Thousands of individual giant cuttlefish aggregate every winter to spawn, peaking in May to June, with the number of males outnumbering the females by up to 11:1 (2) (4). During courtship, the male will perform spectacular displays to attract a female, in which bands of colour pass rapidly along the body (4). Males tend to establish territories around the best egg laying sites (3). As larger, aggressive males will often guard females entering their territory, small males, known as ‘sneaker males’, may adopt female colourings to avoid the larger males and achieve a mating (4).

The eggs of the giant cuttlefish are lemon-shaped. Laid in crevices, the eggs hatch after 3 to 5 months (4).

The mantle cavity, a feature common to all molluscs, has adapted to help the giant cuttlefish avoid predation. Water can be rapidly sucked in and ejected from the mantle, and is directed using a moveable ‘funnel’ to create a form of ‘jet propulsion’ which enables the giant cuttlefish to swiftly escape from predators (10). Like many species of squid and octopus, the giant cuttlefish is also able to protect itself by squirting ink, which obstructs the predators view or acts as a diversion. There is also evidence that the ink may block the scent of the cuttlefish, thereby providing protection from predators which hunt by smell (6).

Most species of cuttlefish are able to quickly change the colour and texture of the skin, allowing them to adopt similar shapes, colours and textures to the surrounding environment, such as rocks on the sea-bed. This is also the same technique employed when achieving sneaky matings or luring in prey (11).

The giant cuttlefish is collected as bycatch in trawl fisheries, although relatively low numbers are caught (3). This species is also caught for human consumption and as bait for snapper fishes. Few details on the quantities and origins of catches of the giant cuttlefish are available, and so it is difficult to quantify the effects of this on population numbers (4).

The giant cuttlefish reproduces once in its short lifespan. This means that a decline in one generation will have profound effects on population numbers, as seen in the mid-1990s when mating aggregations of the giant cuttlefish were actively targeted by fisheries (12).

After population numbers began to decline in the 1990s, a ban on fishing was introduced resulting in the recovery and subsequent rise of giant cuttlefish populations (12).

Proposals have been made to protect the Whyalla breeding aggregation site in South Australia as a marine sanctuary (3). Being such an interesting and charismatic animal, there is a degree of public support for the conservation of the giant cuttlefish.

Find out more about the giant cuttlefish and its conservation:

• The Australian Government Department of the Environment, Water, Heritage and the Arts Species Profile and Threats Database - Giant cuttlefish:
  http://www.environment.gov.au/cgi-bin/species-bank/sbank-treatment2.pl?id=69365
• BBC Wildlife Finder - Giant cuttlefish:
  http://www.bbc.co.uk/nature/life/Australian_Giant_Cuttlefish