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The Australian Giant Cuttlefish

Abigail Rose Natusch 2021


The Australian Giant Cuttlefish, Sepia apama, is a large carnivorous, solitary marine mollusc that can be found along the Southern coast of Australia ranging from Exmouth in Western Australia to Fraser Island in Queensland ("Sepia apama Gray, 1849,"). It is the largest species of cuttlefish in the world and is most abundant in the Upper Spencer Gulf in South Australia where they go to spawn annually in winter(Hall & Hanlon, 2002). They live for about 1 year and at the end of their life cycle, they spawn and die (O'dor, 1998) however there is evidence that male cuttlefish can live for more than 2 years and spawn more than once in their lifetime (Hall & Hanlon, 2002).  


Cuttlefish like other shell-less cephalopods (coeloids) have a cuttlebone that they use mainly for buoyancy and movement with the assistance of jet propulsion. Cuttlefish have evolved lighter cuttlebones for better lift in their movement (M. Norman & Reid, 2000). They are also a popular sight as they show extravagant displays in different situations and can sometimes be very friendly to humans (Runck).

Physical Description

The Giant Australian cuttlefish can have a mantle length of about 1 metre ("Sepia apama Gray, 1849,") and can weigh up to 6 kg (Gales, Pemberton, Lu, & Clarke, 1993). They can be distinguished by having 3 flaps of skin above each of their eyes as well as a total of 10 arms ("Sepia apama Gray, 1849,"). Although being colour-blind, colour and displays plays a vital part (Bucking, 2011) in mating, hunting and even in everyday life; for example cuttlefish have been seen to respond to bright colours shown by divers (Runck).


Difference between other species

The Giant Australian Cuttlefish, like other species, have chromatophores which they use to change their appearance and to match their substrate. However, the method in which they achieve this crypsis differs amongst species; Sepia officinalis (the Common Cuttlefish) use disruptive colouration which breaks up the outline of the individual; this is what militaries use for their uniform or when painting their vehicles. Sepia pharaonic (the Pharaoh Cuttlefish), achieve crypsis by blending in with their surroundings (Hansford, 2008). Sepia apama are like the latter.

Figure 1


The Sepia genus are carnivorous and eat mainly fish, crustaceans (Runck), sharks and other cuttlefish (Lu, Zheng, & Lin, 1998). While hunting, they display an extravagant and continual moving pattern which is used to distract their prey (Lu et al., 1998).


The Australian Giant Cuttlefish is the second-most dominant prey of Australian fur seals. These fur seals target and consume large and mature individuals especially in the spawning season when they are the most abundant (Gales et al., 1993).  The Indo-Pacific bottlenose dolphin is another common predator of Sepia apama. After catching and killing the cuttlefish, the dolphin will thrash the cuttlefish to remove the ink and drag the body along the sand to remove the tough outer skin and cuttlebone (Finn, Tregenza, & Norman, 2009).

Life History and Behaviour

Reproduction & Development

Like other many other cephalopods, Sepia apama are known to spawn once in their lifetime (Rodhouse, 1998).  However, there has been evidence suggesting that male cuttlefish are able to live longer than 1 year and visit spawning sites twice (Hall & Hanlon, 2002).


During the spawning season, which is usually in southern hemisphere winter ("Sepia apama Gray, 1849,"), both male and female cuttlefish will progress to rocky reef areas (Hall & Hanlon, 2002). These areas are very popular tourist attractions as you can see cuttlefish in very high densities. A popular site is the Upper Spencer Gulf in South Australia where this species is the most abundant ("Sepia apama Gray, 1849,").


Cuttlefish species are known to have extraordinary sperm competition characteristics; one of them being the ability of females to store and choose certain sperm out of those stored when it comes to fertilisation. They are also able to choose when they fertilise their eggs (Eberhard, 1996) . With this in mind, studies show that sperm longevity is a vital part of a cuttlefish’s life and that it plays a role in the female’s choice of sperm after copulation (Naud & Havenhand, 2006). There is controversy surrounding the use of “semelparity” and “iteroparity” when it comes to describing an animal’s spawning cycle especially when an animal can spawn multiple times in one spawning event (Rocha, Guerra, & González, 2001) therefore the use of these words will be avoided in this webpage. After mating with about 17 times with different males, females will lay about 5 – 39 eggs daily (totalling 200 eggs) on the undersides of flat rocks where they are not accessible by predators (Hanlon, Naud, Shaw, & Havenhand, 2005). The female will lay one egg at a time which would take about 8 minutes (Hall & Hanlon, 2002).


Development in cuttlefish heavily depends on the condition that they face such as temperature, salinity, etc. As temperature rises, the hatching rate of cuttlefish eggs decreases however this occurs to an extent (Dickel, Chichery, & Chichery, 1997). The average development period for Sepia apama is anywhere from 3 to 5 months long (Cronin & Seymour, 2000).


When it comes to behaviour, these animals are quite extraordinary. They are known for their use of chromatophores to avoid predators, lure prey and even attract mates (Lu et al., 1998). Males are also known to impersonate females to avoid male-male competition. Research shows that these female-impersonating males have a higher reproductive success and lower competition encounter rate compared to those that don’t impersonate (M. D. Norman, Finn, & Tregenza, 1999). The Giant Australian Cuttlefish are anisogamous where females produce small quantities of large and high-quality eggs, which they spend a lot of energy on, and males produce large quantities of small sperm (Hall & Hanlon, 2002).



The species in this genus has similar behavioural characteristics when it comes to finding and attacking prey. Sepia is known to stalk their prey and by quickly extending their tentacles out, they grab the prey (Lu et al., 1998). Once prey are located and targeted, cuttlefish carry out a display (Lu et al., 1998) which is described as “a subtle unilateral passing cloud” by (Hall & Hanlon, 2002) where the chromatophores seem to be passing over the mantle. Male cuttlefish use this prior to courtship with females (Hall & Hanlon, 2002). Once they have captured their prey, they will use their beak to consume their prey (M. Norman & Reid, 2000). Some cuttlefish have toxic saliva that paralyses the prey(Nixon, 1985) but there is no evidence that Sepia apama has this trait.


The developmental period is an important time for all cuttlefish where studies have shown that individuals pick up on visual cues that they were exposed to in the egg once they have hatched. This means that the developmental period is where cuttlefish learn their prey and act upon their learnt skills once their juveniles (Darmaillacq, Lesimple, & Dickel, 2008).


Figure 2
Figure 3

Anatomy and Physiology


Respiration in these cuttlefish happens in the mantle cavity where jet propulsion occurs (M. Norman & Reid, 2000). Once water enters the mantle cavity, it is expelled through the siphon (Bone, Brown, & Travers, 1994). Cuttlefish have a highly efficiently respiratory system where oxygen is exchanged form the water into their blood (JOHANSEN, Brix, & LYKKEBOE, 1982). In their blood, there is haemocyanin which is a protein that transports oxygen in the blood (M. Norman & Reid, 2000).



Cephalopods excrete primary urine containing ammonia into the water around them. They do actually retain a fair amount of ammonia in their organs in order to assist with neutral buoyancy (Wilbur & Clarke, 2013).

Biogeographic Distribution

We can see from the figure that these cuttlefish can be found throughout the southern coasts of Australia. This sparks interest as there are different habitats at all of these locations and we know that cuttlefish prefer rocky reefs, seagrass beds and coral regions (Beeton, 2011). These cuttlefish seem to prefer very active environments.

Figure 4

Evolution and Systematics

Cuttlefish have evolved to be shell-less. The first few cephalopods were Nautilus-like animals which have an outer hollow shell which provides lift but as time passed, coeloids have evolved to have internal shells which produce less drag. Having an internal shell allows for these coeloids to inhabit higher depths with a smaller risk of implosion due to lower water pressure (M. Norman & Reid, 2000). Nautilus ancestors were shaped differently. The first nautiluses had a conical gas-filled shell rather than a curved one, like modern Nautiluses, and through time that shell slowly curved in (Wilbur & Clarke, 2013).


There is a lot of conflicting arguments on how cephalopods evolved especially surrounding what their ancestors looked like. Recent research (Smith & Caron, 2010) has found that the early Cambrian was home to some potential soft-bodied primitive cephalopods. A specimen, Nectocaris pteryx, had been found in Mid-Cambrian Burgess shale, in mud-like sediment. This tells us that this animal inhabited environments near the benthos, like modern cephalopods (Boyle & Rodhouse, 2008). There are some characteristics of N. pteryx that are not seen in modern cephalopods negative buoyancy however the presence of large fins in the N. pteryx support the active nature of cuttlefish (Smith & Caron, 2010).


Phylum: Mollusca

Class: Cephalopoda (Cuvier, 1797)

Subclass: Coleoidea (Bather, 1888)

Superorder: Decabrachia (Boettger, 1952)

Order: Sepiida (Zittel, 1895)

Family: Sepiidae (Leach, 1817)

Genus: Sepia (Linnaeus, 1758)

Subgenus: Sepia (Linnaeus, 1758)

Species: Sepia apama (Gray, 1849)

Figure 5
Figure 6

Conservation and Threats

3 major threats:
  • Fishing
  • Ocean Acidification
  • Changing environmental conditions

Sepia apama are listed as “Near Threatened” in the IUCN Redlist (Barratt, 2012). They are heavily impacted by climate change, direct anthropogenic activities, and changing environmental conditions.


The Upper Spencer Gulf is a popular fishing and tourist attraction due to the presence of Australian Giant Cuttlefish’s mass spawning aggregations in winter. The population started to decline because of this so fishing in the spawning area was banned however fishing the outside of the area is still allowed. They are often commercially fished and are bycatch (Barratt, 2012) during the period of time right before the spawning season where the cuttlefish are busy feeding in preparation for spawning (Barratt, 2012).

Ocean Acidification

When it comes to climate change, rising carbon dioxide levels cause the pH of the ocean to decrease, this is called ocean acidification. Studies show that increased carbon dioxide has caused increased calcification of cuttlebones in several cuttlefish species. This would therefore negatively affect their buoyancy (Gutowska, Melzner, Pörtner, & Meier, 2010). Increased carbonification in the water affects cuttlefish differently depending on the stage of their life cycle they are in and their availability of food (Otjacques et al., 2020). Figure 1 from that paper shows the relationship between the cuttlebone weight and the number of days the cuttlefish eggs were exposed to the treatment before hatching. We can see that the longer the eggs were exposed to the carbon dioxide treatment, the heavier the cuttlebone became. This study further concluded that cuttlefish exposed to high carbon dioxide treatments at early developmental stages were affected significantly in terms of calcification of their cuttlebones (Otjacques et al., 2020).


A less buoyant body plan would mean that more energy would be invested into movement in aggregating and in hunting rather than using that energy for reproduction (for females, when creating high quality eggs) or competing (for males) (Gutowska et al., 2010).

Changing environmental conditions

Cuttlefish are heavily impacted by the environment they are in; conditions include salinity, temperature, and water content thus pollution (Beeton, 2011). Too low or high of a salinity has been seen to decrease the hatch rate of cuttlefish eggs where the eggs do not make it past the early stages of development (Peng et al., 2017). Other conditions that these cuttlefish are heavily influenced by are temperature, turbidity, and consequently, algal blooms. Temperature has been recorded to not cause changes in the hatch rate of cuttlefish eggs by (Palmegiano & d'Apote, 1983) but (Beeton, 2011) states that rising temperatures does cause declines in population density and an increase in algal blooms which reduces oxygen levels. Turbidity causes poor visibility when it comes to mating as males often use extravagant displays which females choose from (Lu et al., 1998).


All of these factors were found to have contributed to a decline in population density in the Upper Spencer Gulf in past surveys (Beeton, 2011; "Sepia apama Gray, 1849,").



From 2013 to 2017, a temporary fishing ban on these cuttlefish was implemented in the Upper Spencer Gulf. Since then, cuttlefish numbers have stopped declining but they have not returned to those prior to fishing events ("Sepia apama Gray, 1849,"). Now, there is a seasonal ban on these cuttlefish in South Australia (Giant Cuttlefish

Sepia apama).

Figure 7


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