The giant cuttlefish (Ascarosepion apama), also known as the Australian giant cuttlefish, is the world's largest cuttlefish species, growing to in mantle length and up to in total length (that is, including outstretched tentacles). They can weigh over . Like all cuttlefish species, the giant cuttlefish has eight arms and two feeding tentacles, as well as blue blood and three hearts. Using cells known as chromatophores, the cuttlefish can put on spectacular displays, changing colour in an instant. The giant cuttlefish is native to temperate and subtropical waters of Australia, from Brisbane in Queensland to Shark Bay in Western Australia and Tasmania to the south. It occurs on rocky reefs, seagrass beds, and sand and mud seafloor to a depth of . The genetically distinct population in the Upper Spencer Gulf is the most studied population, and has become a tourist attraction.
Physiology and biochemistry
Ascarosepion apama, commonly known as giant cuttlefish or Australian giant cuttlefish, is the largest species of cuttlefish in the world, reaching in mantle length and up to in total length (total length meaning the whole length of the body including outstretched tentacles). Giant cuttlefish can weigh over .Reid, A., P. Jereb, & C.F.E. Roper 2005. Family Sepiidae. In: P. Jereb & C.F.E. Roper, eds. Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 57–152. They have eight arms and two feeding tentacles, as well as blue blood and three hearts, as do all species of cuttlefish.
Genetic studies have shown that little, if any, interbreeding occurs between giant cuttlefish populations. While some genetic divergence is seen, the various populations are not considered taxonomically distinct and are commonly referred to by their location, e.g. Sepia apama upper Spencer Gulf population.Amendment to the list of Threatened Population under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Threatened Species Scientific Committee. The upper Spencer Gulf population is unique in that a permanent salinity gradient in the Spencer Gulf may physiologically exclude other populations from the zone occupied by the upper Spencer Gulf population. This population may in fact be a separate species, as it does show some hallmarks, such as genetic separation, differences in morphology, and different patterns of sexual dimorphism from adjacent populations.Clare Peddie, Heather Kennett The cuttle scuttle The Advertiser 29 September 2012 Pg 67
Giant cuttlefish are a neritic demersal species. They are carnivorous, opportunistic, and voracious predators that feed predominantly on crustaceans and fish. Using neurally controlled cells known as chromatophore organs (red to yellow), iridophores (iridescent: spans the entire visible spectrum from blue to near-IR) and leucophores (white), the cuttlefish can put on spectacular displays, changing colour and patterns in a fraction of a second. Located in three layers under the skin, leucophores make up the bottom layer, with chromatophores the outermost. By selective blocking, the three layers work together to produce polarised patterns. Unlike those in most animals, cuttlefish iridophores are physiologically active; they can change their reflectivity, and the degree of polarisation can also be controlled. Cuttlefish are colourblind; however, the photoreceptors of cuttlefish eyes are arranged in a way that gives them the ability to see the linear polarisation of light. While the mantis shrimp is the only creature known to have true polarisation vision, cephalopods may also. Because the optic lobes of cuttlefish are larger than any other region of the brain and their skin produces polarised reflective patterns, they may communicate through this visual system. By raising elaborate papillae on their skin, S. apama squid can change the shape and the texture of their skin to imitate rock, sand, or seaweed.Alison King The Colourful World of Cephalopods - Cephalopod body patterning II. The Cephalopod Page. A bioenergetics study found that the giant cuttlefish is primarily diurnal and has a small home range () over short recording periods while travelling large distances to breed. They are able to channel most of their energy directly into growth because they spend 95% of the day resting, suggesting bioenergetics more like that of an octopus than a squid. Very little time is spent foraging (3.7% during the day and 2.1% at night); most of their time is spent resting and hiding in crevices from predators. The exception to this behavioral routine is the mass spawning aggregation, where cuttlefish are far more active during the days or weeks that they spend there.Hanlon, R.T. 2008. Australian Giant Cuttlefish - Physiology and Biochemistry . Encyclopedia of Life.
Habitat The giant cuttlefish is native to temperate and subtropical waters of Australia, from Brisbane in Queensland to Shark Bay in Western Australia and Tasmania to the south. It occurs on rocky reefs, seagrass beds, and sand and mud seafloor to a depth of .Norman, M.D. 2000. Cephalopods: A World Guide. ConchBooks.
Lifecycle and reproduction Giant cuttlefish live for one to two years. Breeding takes place with the onset of the southern winter. Males abandon their normal cryptic colouring and set out to dazzle the females by adopting rapidly changing bright colours and striking patterns. Females are polyandrous, and collaborative research indicates the tendency for females to reproduce using male genetic material deposited in spermatangia more favorably than in sperm receptacles directly. Females then attach their eggs to the undersides of rocks in caves or crevices, where they hatch within three to five months. A. apama is semelparous, and death follows shortly after a single mating cycle and laying of eggs that will spawn the next generation. A. apama has poor anaerobic capability compared to most aquatic invertebrates and a lack of food leads to catabolism. Stomach-content analysis indicates fasting during the breeding season, and as A. apama can catabolise no more than 50% of its body weight, it slowly loses physical condition as the season progresses and eventually dies. Throughout their range, these cephalopods breed in pairs or small groups, laying eggs in suitable caves or rock crevices. Loose spawning aggregations can form, but rarely exceed 10 animals in any one location, with one known exception; hundreds of thousands aggregate along rocky reefs between Whyalla and Point Lowly in the Upper Spencer Gulf. While surveys suggest that juveniles leave these spawning grounds after hatching, nothing is known of their subsequent movement or lifestyle strategies as a juvenile. Adults return to the aggregation site the following winter, or may delay their return by an additional year.
Predators The Australian giant cuttlefish is preyed upon by a variety of marine predators. In South Australia's Spencer Gulf, Indo-Pacific bottlenose dolphins have been observed using a specialized technique to remove the ink and cuttlebone before consuming the cuttlefish.Catch cuttlefish, drain off the ink, then fillet. Serves five (dolphins): Scientists stunned by mammals' elaborate culinary preparations
Long-nosed fur seals (Arctocephalus forsteri) are also known predators, and various cephalopods—including cuttlefish—are taken by yellowtail kingfish (Seriola lalandi).
The predation of cephalopods by yellowtail kingfish has raised ecological concerns in Spencer Gulf, particularly regarding the potential impact of aquaculture escapees on wild species, including the giant Australian cuttlefish and their eggs.
Conservation status In 2009 the species was listed as "near threatened" on the IUCN Red List of Threatened Species due to an observed declining trend at that time.
Upper Spencer Gulf population
Unpublished scientific data indicated that several genetically distinct populations of giant cuttlefish are living in Australian waters. Discovered by divers in the late 1990s, the upper Spencer Gulf population is the best studied, largely because it is the world's only known mass cuttlefish-spawning aggregation. It has also become a popular ecotourism attraction for divers and snorkelers.
Hundreds of thousands of giant cuttlefish gather on subtidal reefs around Point Lowly near Whyalla between May and August. While outside of the breeding season, the sex ratio is one to one, Spencer Gulf males outnumber females by up to 11 to one in the spawning aggregation. If this is due to fewer females taking part or to males breeding for a longer period of time than females is not known. With densities of , covering about , the sheer numbers of giant cuttlefish make this breeding aggregation unique in the world. As the cuttlefish are oblivious to divers while spawning, they are now a major regional tourist attraction for divers from around the world. Professor Roger Hanlon of the Woods Hole Oceanographic Institution has called the breeding aggregation "the premier marine attraction on the planet."
The upper Spencer Gulf population displays two alternative lifecycles in both sexes (growth pattern polymorphism). The first involves rapid growth with maturity reached in seven to eight months with small adults returning to spawn in the first year. The second involves slow growth with maturity reached in two years, with large adults returning to spawn in the second year. The upper Spencer Gulf population displays reproductive behaviours unique to this population, possibly as a result of the high spawning densities. Large males defend females and egg-laying sites, while small males, "sneakers"Life. Extraordinary Animals, Extreme Behaviour by BBC Books, Martha Holmes & Michael Gunton, 2009 , pg 28. mimic female colouring and form to gain access to the females being protected by the dominant males, which are extremely territorial. Male genetic material is deposited in sperm receptacles directly. The females, which potentially lay hundreds of eggs, extract one egg at a time and fertilise it by passing it over the sperm receptacle before attaching it to the underside of a rock at depths of .
Conservation
An unsuccessful application to list this population of giant cuttlefish as a threatened species under Australian law was made during the government's consideration of BHP Billiton's Olympic Dam mine expansion project. The application was made following an observed and unexplained population decline and public concerns about future risks posed by industrial pollution. On 2 February 2011, the Australian government's Threatened Species Scientific Committee ruled that the species was not eligible for listing, as the affected population was not taxonomically distinct from the rest of the species for the purposes of the act.Conservation Assessment. Advice to the Minister for Sustainability, Environment, Water, Population and Communities from the Threatened Species Scientific Committee (the Committee) on Amendment to the list of Threatened Population under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) 2 February 2011. Further scientific work has determined the cuttlefish of northern Spencer Gulf to be genetically distinct from other giant cuttlefish populations in Australian waters, although the results remain unpublished.
The Upper Spencer Gulf Marine Park covers a large area, within which lies several sanctuary zones, including the Cuttlefish Coast Sanctuary Zone, which was inscribed on the National Heritage List on 24 February 2023.
Commercial fishing