Predators
A list of known and suspected predators is presented in the table below, updated from MacArthur (2007).
Teleost fish
Evidence indicates that the western rock lobster makes up only a relatively small proportion of teleost gut contents. As such, no one predator relies heavily on western rock lobster as prey, but many species appear to include them in their diets. Predation appears to be variable with size, with the highest predation rates occurring at smaller sizes, especially 1 and 2 years post-settlement, and lower rates in adults (Howard 1988, Phillips et al. 2003). The only comprehensive study on teleost fish predators of the western rock lobster, was conducted in nursery habitats and found that six common fish species predate on juvenile lobster (Howard 1988). Of these six species, at least two, the breaksea and chinaman cod, have the potential to predate upon larger adult lobsters owing to their large mouth gape relative to body size (Howard 1988). These two species also occur at much greater depths than the study site, which was less than 4 m, and therefore may be important predators on larger lobsters in deeper waters.
Dhufish (Glaucosoma hebraicum) and balchin groper (Choerodon rubescens) are known predators of western rock lobsters, however, in both species, lobster only forms a small portion of their diets. Gut contents analyses have found small amounts (< 5% total prey) of western rock lobster in the guts of dhufish (Robinson 1987, Marr 1980), and pieces of western rock lobster are often observed in the guts of dhufish during fish dissections as part of ongoing research at DPIRD (per. comm. Lek 2022). Two studies have documented western rock lobster in the guts of baldchin groper (Lek 2004, Walker 1983), however in both instances lobster only made up a small proportion of the prey items present.
The overlapping distribution, large size, and potential to consume hard-shelled crustaceans (such as mussels and blue swimmer crabs, as they do in other states), make pink snapper (Pagrus auratus) a potential predator of western rock lobster. While there is no published dietary data to confirm this, pieces of WRL have been observed in the guts of pink snapper during dissections as part of ongoing research at DPIRD (per. comm. Lek 2022) and snapper have been filmed pulling legs off lobster trapped in pots at the Abrolhos Islands. Several other cod and groper species, such as the western wirrah (Acanthistius serratus) and the western blue groper (Achoerodus gouldii), are also considered potential predators of WRL, due to their overlapping distribution, large size, and ability to consume hard shelled invertebrate prey, although no dietary data exists to support or refute this.
Sharks and rays
Several species of sharks are known or thought to consume western rock lobster, although similarly to teleost fish, there is no evidence that lobsters are a singularly important prey item. Both the sandbar shark, (Carcharhinus plumbeus) and the gummy shark (Maculatus antarcticaus) are known to consume western rock lobster, however lobster only make up a very small proportion of each species’ diet: 0.3% in sandbar shark (McAuley et al. 2005) and 2.8% in gummy shark (both western rock lobster and southern rock lobster combined) (Simpfendorfer et al. 2001). Predation by sharks may be most common among larger sharks, as research on gummy sharks has indicated that the occurrence of lobster in the gut increases with increasing size of the shark (Simpfendorfer et al. 2001).
There are several other potential predatory shark species, which co-occur with lobster over at least part of their distribution, occupy similar depths as lobster, and are known to predate upon benthic crustaceans. There is evidence from other states that the whiskery shark (Furgaleus macki) consumes a small amount of southern spiny lobster species, however, a gut contents study of the species in WA found no lobsters present (Simpfendorfer et al. 2001). Bronze whaler sharks (Carcharhinus brachyurus) have been observed to consume lobsters that have been returned to the water after being captured in pots (Davidson 2004). With no Western Australia dietary data published, it is unknown whether, and to what extent, bronze whalers consume western rock lobsters in situ, however dietary studies in other states have not found evidence of lobster predation. Wobbegongs (Orectolobus spp.), are commonly thought to prey on lobsters. They are found on inshore reefs, as well as more offshore reefs, to depths of over 100 m, along the lower west coast of Western Australia (Last and Stevens 1994). They forage in seagrass and reef habitats at night and prey upon benthic prey such as octopus, crabs, small fish and crustaceans (Last and Stevens 1994). However, examinations of the stomach contents of this species in both Western Australia and New South Whales have failed to find any evidence of lobster predation (Chittleborough 1975, Chidlow 2007, Huveneers 2007). Wobbegongs are frequently captured inside lobsters pots, however, the lack of lobster in the gut of the animals would suggest that they are attracted to bait, or octopus inside the pot, rather than the lobster themselves. Several species of large rays found along the west coast at depths similar to western rock lobster, are known to consume benthic invertebrates, and therefore may also prey on lobster. The southern eagle ray (Myliobatis australis), smooth stingray, (Dasyatis thetidis), and black stingray (D. brevicaudata) are all potential predatory rays.
Octopus
While there are several species of octopus located within the range of the western rock lobster, the western rock octopus (Octopus djinda) is the most important predator (Joll 1977). Previously thought to be Octopus tetricus, O. djinda is actually an endemic Western Australian species (Amor & Hart 2021). This species is the principal predator of lobsters in pots, with research indicating that pot-predation by the western rock octopus is far greater than pot-predation by cuttlefish (Sepia apama), or fish predators (Joll 1977). Pots that have been visited by an octopus have significantly reduced catch rates, with one study estimating a 43% reduction in catch (Morgan 1974). Predation is greatest in shallow waters, with rates of predation per 1000 pots, ranging from ~40 in the shallows (< 10 m), to ~5 in depths > 50 m (see figure below) (Hart et al. 2016). Predation rates also increased with pot soak time, and are greatest in warm months (Hart et al. 2016).
While O. djinda is an important predator of lobster in pots, there is no data to suggest that they are a significant predator of lobster in their natural environment, and the importance of western rock lobster as a prey item is unknown. Dietary studies of octopus are difficult as a result of their feeding behaviour, especially with regards to crustaceans and molluscs. Octopus feed by injecting a toxin to paralyse their prey, as well as an enzyme to break down the animal’s flesh. They then use their beaks to tear softened flesh into small pieces, before sucking the meat in through their mouths. As a result, identifying prey items is very difficult. What dietary studies do exist appear to indicate that lobster forms only a minor part of octopus diet. An analysis by Claybrook (2020) found decapods to be a minor but important part of the western rock octopus diet off Fremantle, occurring in the gut about as often as cephalopods, around half as often as teleost fish, and a third as often as crabs, the most abundant prey. The study did not identify more specifically beyond decapods, however because crabs and hermit crabs were identified separately, it is likely that a large proportion of the “decapods” were western rock lobster. Another dietary study found crustaceans made up 33% of gut contents of O. djinda, but did not identify beyond crustaceans (Greenwell et al. 2019).
Rates of predation by octopus in the wild are by and large unknown. Western rock lobsters have been observed to successfully evade O. djinda in the laboratory and the natural environment (Chittleborough 1975, Cobb 1981), and examination of food mounds around octopus shelters have not revealed rock lobster carapaces (Joll 1977). In a predation experiment, octopus were demonstrated to only attack lobster which had been exposed to air for a period of time (Brown & Caputi 1983). Similarly, while Chittleborough (1975) observed octopus predation in the wild, only lobsters being returned after tagging were predated. It seems likely therefore, that octopus rarely attack lobsters in the wild, with most predation occurring when lobsters are injured, stressed, or trapped.
Sealions
The Australian sealion (Neophoca cinerea) is a known predator of the western rock lobster, with remnants of lobster shell identified in gut contents analyses (Richardson & Gales 1987, Berry et al. 2017). Additionally, juvenile sealions have been observed to “steal” lobsters from pots, and historically have, on occasion, been caught in pots as a consequence of this foraging behaviour (Fletcher et al. 2005). Since the introduction of SLEDs (Sea Lion Exclusion Device) in 2006 there have been no reports of sea lions caught in pots, and thus it would appear these devices have successfully prevented sea lion predation in pots (see video below). There is some anecdotal evidence that sea lions are still able to predate through the pots’ escape gaps, but this behaviour is as yet, unconfirmed. The level of natural predation of western rock lobsters by sea lions is not known, however, their ability to dive to depths of ~ 137 m (Lowther et al. 2013), means they can potentially prey on both juvenile and adult lobster populations (Costa and Gales 2003).
Cannibalism
Although the shell fragments found in the guts of wild-caught lobsters have been commonly considered the result of consuming exuvia, cannibalism is known to occur, especially in a laboratory setting. Cannibalism in aquaria has been documented in juveniles and appears to be most common in recent moults and smaller animals (especially post puerulie), and increases at higher density or when food is supply insufficient or of poor quality (Johnston et al. 2006, Moyle et al. 2009). Additionally, observations of cannibalism of recently moulted adults in that laboratory confirm its occurrence in larger animals (per. obs. Emma-Jade Tuffley). It is unknown how much, if any, cannibalism occurs in the wild, however, cannibalism in wild populations has been observed in other spiny lobster species, and it is likely that at least some of the density-dependent mortality of western rock lobster, especially in post puerulus, is the result of cannibalism.
| Common name | Scientific name | Known/Potential |
| Teleost Fish | ||
| Sand Bass | Psammaperca waigiensis | K |
| Sea Trumpeter | Pelsartia humeralis | K |
| Brown-spotted wrasse | Pseudolabrus parilus | K |
| Breaksea cod | Epinephelides armatus | K |
| Chinaman cod | Epinephelus homosinensis | K |
| Gold-spotted sweetlips | Plectorhyncus flavomaculatus | K |
| Dhufish | Glaucosoma hebraicum | K |
| Baldchin groper | Choerodon rubescens | K |
| Pink Snapper | Pagrus auratus | P |
| Blue groper | Achoerodon gouldii | P |
| Large trevally | Carangidae | P |
| Large cod | Epinephelus spp. | K |
| Shark sand Rays | ||
| Gummy shark | Mustelus antarcticus | K |
| Whiskery shark | Furgaleus macki | K |
| Bronze whaler | Carcharhinus brachyurus | P |
| Sandbar shark | Carcharhinus plumbeus | K |
| Wobbegongs | Orectolobus spp. | P |
| Rays | Dasyatis spp., Myliobatis australis | P |
| Mammals | ||
| Australian sea lion | Neophoca cinera | K |
| Cephalopods | ||
| Octopus | Octopus tetricus and Octopus spp. | K |
| Cuttlefish | Sepia apama | K |
Parasites and disease
Shell Disease
Western rock lobster are rarely found with obvious parasites or disease. Possibly the most common is shell disease, which is a progressive chitinolysis (dissolving of the shell) and necrosis (bioerosion) of the exoskeleton of crustaceans and is caused by numerous chitinoclasitic, gram-negative bacteria (Shields 2011). Shell disease presents as large, brown or black, irregularly shaped lesions, commonly on the uropods (tail-fan) of the lobster, and for this reason, is sometimes called “tail-fan necrosis”. The bacteria usually enter the cuticle of the exoskeleton via some sort of mechanical abrasion or damage to the shell (Shields 2011). While shell disease can penetrate beyond the exoskeleton, into the underlying tissue, it rarely does, usually developing laterally, further eroding the cuticle. Lobsters are able to overcome shell disease by moulting, however, lobsters that moult less frequently can presumably succumb to infection. A survey of 150 juveniles western rock lobster detected shell disease in 8% of animals examined (Evans 1987). Various species of bacteria were isolated from the lesions, including; Aeromonas sp., Alcaligenes sp., and Vibrio sp..
Strictly speaking, “shell disease” is defined as necrosis caused by bacteria, however, fungal infections can present very similar to shell disease, and are therefore often identified as such. An outbreak of fungal shell disease in the western rock lobster was recorded by McAleer & Baxter (1983). Lesions occurred on the abdomen, uropods, telson and pereopods. The fungus, identified as Fusarium solani, was isolated from both the lobsters and the seawater from locations with diseased lobsters. The authors suspected that environmental factors facilitated the outbreak, and given the location of the lesions around the uropods and telson (tail-fan), it is likely that water quality was an issue (Shields 2011). Another fungal infection has been recorded in the gills of juvenile western rock lobster. In 1987, seven of the 150 sampled juveniles had the fungal gill infection, however, the species of fungus was not identified (Evans 1987).
Microsporidiosis – “Cotton Tail”
Microsporidia is a phylum of small, spore-forming, unicellular parasites, capable of infecting a range of both vertebrate and invertebrate species. Once considered protozoans, they are now classed as a type of fungi. In crustaceans, these parasites infect the muscle tissue, causing a distinctive liquefactive and coagulative necrosis, that often causes the muscle to turn from a translucent grey to a creamy white, resulting in a cooked appearance. It is this appearance that has led to the colloquialism “cotton tail”. Research has indicated that infections in western rock lobsters are caused by Ameson sp., and occur at a rate of around 1-2% in juveniles (Evans 1987).
Microphallidea
Western rock lobsters are susceptible to a gonad infection by a parasitic trematode of the family Microphallus. Several species of microphallidae use crustaceans as an intermediate host for the encysted metacercariae stage. The cysts are usually quite small, < 1 mm in diameter, and can be detected using a microscope. Infections of Thulakiotrema genitale, a species of micrphallidea, have been observed in the gonads of juvenile and adult western rock lobster in the wild (Evans 1987, Deblock et al. 1990). Infection rates can be quite high, ranging from 47% to 87%. This trematode, in large infestations, can cause the lobster to become sterile, however infestations of this magnitude appear to be rare.
Worms
The eggs of brooding female western rock lobsters are susceptible to infection by a nemertean worm, Carcinonemertes australiensis (Campbell & Gibson 1989). The species is translucent white and approximately 7 mm long and 1 mm wide. Rates of infection can be quite high, with one study noting infestation in 67% of berried females (Evans 1987). Their effect on the female and/or her eggs has not been documented.
Bacterial egg infection
Filamentous bacteria are common on the eggs of marine crustaceans, including spiny lobsters, especially in aquaria (Shields 2011). There are no documented cases of filamentous bacterial infections in the western rock lobster in the wild or in aquaria. However, in 2019, the eggs of one of 11 lobsters housed in aquaria at DPIRD, become infested with what appears to be filamentous bacteria, causing the entire brood to fail (see image below) (pers. Obs. Emma-jade Tuffley). Unfortunately, the species was not identified.
Pink Lobster
There are some reports in the literature of an unusual syndrome occurring in western rock lobster known as pink lobster syndrome (Phillips & Melville-Smith 2006, Shields 2011). The flesh of affected animals is said to become pink or orange and have a bitter flavour, making them unpalatable. Affected lobsters apparently show signs of lethargy and can die from the syndrome. Although there is very little information available in the literature, observations of this syndrome are often reported to DPIRD and appear to occur more often in summer.
References
Last PR, Stevens JD (1994) Sharks and Rays of Australia. CSIRO.
Marr, F., 1980. Growth, reproduction and dietary preference of the Jewfish Glaucosoma hebraicum. Unpublished B.Sc. project report. Biology Department, Curtin University., Perth, Western Australia.
McAleer R, Baxter M, (1983) Black shell disease of the western rock lobster caused by Fusarium solani. In: Proc. 8th Cong. Internat. Soc. Human Anim. Mycol., Massey University, Palmerston North, New Zealand, 1982, pp. 378–382.
Robinson, R.G., 1987. The morphology and histology of the alimentary tract: the dietary preference of the Western Australian Jewfish; Glaucosaom hebraicum. Final report – Western rock lobster ecosystem processes – September 2007 31 Unpublished B.Sc. project report. Biology department, Curtin University, Perth, Western Australia.
Shields JD (2011) Diseases of spiny lobsters: a review. J Invertebr Pathol 106:79–91.
Walker (1983), In: MacArthur L, Hyndes G, Babcock R (2007) Western rock lobster in ecosystem processes of south-western Australia. Final Report to Department of.