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Australian Ghost Shrimp (Yabby)

Lucas Sumpter 2016


The Australian Ghost Shrimp, also known as the yabby, or ghost nipper (Trypaea australiensis) is a small, Decapod, Crustacean that inhabits soft-sand benthic substrates on the east coast of Australia. Part of the order Callianassidae, Australian Ghost Shrimps burrow within these benthic sediments and contribute to their physical, and biogeochemical surroundings as known bioturbators. Yabbies are sexually reproducing, deposit feeders and are a common source of prey for many inshore predatory fish. As a result, they are widely used by recreational fishermen as bait, and are harvested from accessible intertidal zones using a yabby pump or excavation of sediment. This practice has since altered the population dynamics of this native Australian species, though T. australiensis can still be considered abundant within its known habitat range. 

Physical Description

T. australiensis is a relatively small malacostracan crustacean, with a body length of approximately 1.5cm (Holthuis, n.d) to 8cm (Hailstone and Stephenson, 1961). Australian Ghost Shrimps, along with other callianassid shrimps are distinguishable from many other families of decapod by their elongated pleon relative to carapace length (Hyžny and Klompmaker, 2015). Their colouration is largely transparent to white, often with a pink hue (Fig. 1 & 2). A region of orange colouration is often present in the anterior abdominal segments (Fig. 1 & 2). They possess a chitinous cuticle or exoskeleton, subdivided into two distinct tagmata; the cephalothorax and abdominal segments (Ruppert, Fox and Barnes, 2004). Male specimens exhibit an immensely enlarged major cheliped (Fig. 2), and females often possess multitudes of orange eggs adhered to the ventral side of their abdominal segments. For more detailed information on the physical anatomy of T. australiensis, see ‘Anatomy & Physiology’.
Figure 1
Figure 2


Ecosystem Services

Australian Ghost Shrimps are known for their ability in bioturbation (Katrak and Bird, 2003; Bird, Ford and Hancock, 1999; Spilmont et al, 2009; Contessa and Bird, 2004), or the reworking of sediments by animals, in this case due to burrowing. Organisms that create burrows directly affect the transfer of dissolved chemical particulate matter between sediment and the water column (Bird, Ford and Hancock 1999), and thus create conditions facilitative to particular community establishment. 

T. australiensis have been found in many studies to have a notable influence on the biogeochemistry between the sediment strata and the overlying water column. Jordan et al (2009) found the presence of T. australiensis to significantly alter sediment-oxygen-demand, and the residence time/overturning of nitrogen-based nutrients. This finding is likely to be correlated with results obtained by Contessa and Bird (2004), who reported increased chlorophyll-a concentrations in the water column where yabbies were absent. This is likely due to the increased residence time of nutrients in the absence of T. australiensis, facilitating phytoplankton population establishment. The role of yabbies in these two processes suggests that T. australiensis contributes to the localised water quality pertinent to many species in their shallow, intertidal habitats.


Callianassids have been found to inhabit waters of up to 2,400 feet (Hailstone and Stephenson, 1961) however, T. australiensis is found almost chiefly in the intertidal zone, burrowing into soft-sand sediments. Fig. 4 shows the tidal flat sampled within this study, a typical habitat of the Australian Ghost Shrimp.
T. australiensis builds intricate networks of burrows into the substrate, to depths of >50cm (Katrak and Bird, 2003), the entrances to which are visible on the surface of the substrate (Fig. 3).
Figure 3
Figure 4


The facilitative properties of T. australiensis’ burrowing habits also create relationships with other organisms living sharing a common niche. Kerr and Corfield (1998) observed a commensal relationship whereby T. australiensis burrows provided optimal feeding locations for M. vitrea, a species of deposit-feeding bivalve. As a result, while it was shown that M. vitrea was able to survive in the absence of yabbies, the bivalve’s distribution vertically within the benthic strata was altered in the presence of T. australiensis. M. vitrea exhibited a shift to deeper within the sediment in all treatments with T. australiensis populations present, in order to exploit these superior feeding conditions.

Life History and Behaviour


T. australiensis is largely a deposit feeder, obtaining its nutrition below the surface of the benthos. It can either feed on food particles within the walls of its burrows, or resuspend particulate matter comprising the burrow walls, and feed on the newly suspended food items (Stapleton, Long and Bird, 2002; Spilmont et al, 2009; Katrak and Bird, 2003). Spilmont et al (2009) observed that T. australiensis exhibits a particular diet, feeding specifically on benthic diatoms, and also noted that the feeding activity of yabbies slowed during the summer months. Fig. 5 shows the anterior end of a collected male T. australiensis specimen, with the elongated rostrum and feeding structures such as the maxilla and mandibular palps visible.
Figure 5

Reproduction & Development

While a distinct lack of information on the reproductive biology of T. australiensis is evident within the literature, it is known that Australian Ghost Shrimps exhibit the same reproductive traits and processes as most species within their family, the Callianassids. As in the majority of decapods, fertilization is external (Encyclopaedia Britannica Online, 2016) and eggs are carried by the female, adhered to the ventral side of the abdominal region (Fig. 8). The fertilized eggs then remain attached here until they have hatched. 

Whilst little information is available on the larval development of T. australiensis, six larval stages have been observed and described (Dakin and Colefax, 1940 as cited in Hailstone and Stephenson, 1961). The Hailstone and Stephenson study (1961) noted the presence of the earliest larval stages within the plankton around one month post-breeding season (late summer), and observed these larval stages to have a carapace length (CL) of approximately 1 millimetre. The latest of the six larval stages were observed in the Hailstone & Stephenson study during spring at a CL of approximately 3 millimetres, and the assumption was made that the post-larval forms would then settle to the benthos during early summer. 

Following maturation, Callianassids are known for displaying distinct sexual dimorphism, distinguished by significant enlargement of the major cheliped in male individuals (Shimoda et al, 2005).  

Sex Ratio Distribution:

While a number of works have investigated the temporal patterns of reproduction in callianassid shrimps, including T. australiensis, our knowledge of how their reproductive patterns vary spatially is lacking. Here, we conduct a small-scale, simple investigation to the sex ratios of yabbies across a singular tidal flat at Dunwich, North Stradbroke Island, Queensland, Australia. The purpose of this experiment was to identify possible spatial dynamics of reproductive activity within the intertidal zone. The objective was also to elucidate the spatial preferences of the shrimps with regards to copulation and sexual reproduction; whether more reproductive activity was likely to occur higher or lower in the intertidal zone. Knowledge of any such patterns may be useful in regulating the collection of T. australiensis as bait by recreational fishermen (see ‘Conservation & Threats), and may allow harvesting of this species at a lesser cost to the overall population due to the preservation of sexually active adults.
In this study, data was collected on the percentage of males and females respectively among the total individuals collected. These data were collected at 10 metre intervals along a 180 metre transect. The respective percentages of the genders were used here as a proxy for sexual interaction between individuals; it was assumed that the closer the sex ratio to 50% males and 50% females, the more reproduction would take place. Thus, assuming this to be the case, it can be inferred that regions within the tidal flat exhibiting the most indifferent proportions of males to females would be areas of highest reproductive activity. 


A transect was marked out, running from the high intertidal (defined as the convergence of beach sands and tidal flat sediments, see Fig. 4) to the low tide waterline at 10:30am on Saturday the 14th of May, 2016. At intervals of 10 metres, T. australiensis specimens were collected using a yabby pump. In order to maintain commonality of sampling methods, 10 pumps were carried out at each interval, and could be from anywhere within a 1marea surrounding the given 10 metre interval mark (e.g. 20m, 70m, 110m). The yabbies obtained from each sample interval were collected and examined; the total number of individuals, the number of males and number of females respectively were recorded before the yabbies were released to re-burrow. This process was repeated every 10m, moving away from the beach in a perpendicular fashion until reaching the waterline. The result was a 180m transect, comprising 18 intervals of 10m where specimens were collected and counted as mentioned above. 

A second transect was attempted at a different location 300m to the south on the same coast, however no specimens were obtained throughout the entirety of the transect despite the presence of burrow entrance holes. This was likely due to the apparent presence of a solid layer of strata approximately 30 centimetres below the surface of the sediment, which likely meant that the area was not ideal habitat for yabbies, which are known to construct burrows of >50cm (Katrak and Bird, 2003). The holes observed at the surface were likely caused by a different burrowing macro-invertebrate, which was not observed during this study. Due to the insufficient data obtained from the second transect, it was subsequently omitted from results. 


It can be observed that between 0 – 30m away from the high intertidal zone, females dominated comprehensively, with zero males obtained at the 0, 10 and 20 metre intervals (Fig. 6, 7). Barre the 40 metre interval, it can be seen that gender dominance remains female, and does not truly fluctuate between genders until 70 metres from the high intertidal. Between 70 and 140m, sex ratio was shown to fluctuate episodically and significantly, with 100% gender dominance occurring at 90, 100, 120 and 130m. From 140 metres onward however, the sex ratio was shown to rapidly approach 50% male, 50% female, and can be observed to fluctuate only slightly from equal proportions. These results suggest that as a general trend, the sex ratio of T. australiensis approaches 1:1 with distance seaward from the high intertidal zone. 


Following qualitative analysis of the results visualized in Fig. 7, it can be inferred that sex ratios of T. australiensis approach 1:1 with distance seaward from the high intertidal zone, and following the assumptions of our proxy, reproductive activity is likely to increase as the ratio approaches 1:1. Based on these findings, T. australiensis appears to exhibit a preference for reproduction in the lower regions of the intertidal zone. 
These results however, must be reinforced by further works before being used to inform management decisions regarding T. australiensis’ population dynamics. While Fig. 7 lends evidence to this relationship, due to a lack of resources, and with sampling opportunities limited due to weather and tides, only one transect was successfully completed. This transect may prove informative of the population dynamics of T. australiensis on the west coast of North Stradbroke Island, however the spatial dynamics of reproductive activity suggested here may not hold true in other locations within the yabby’s distribution. Further studies should seek to collate data from transects such as the one executed here from a multitude of locations along the east coast of Australia. Additionally, while the assumptions of our proxy were outlined, it must be acknowledged that many further factors contribute to the reproductive success of any two individuals and this proxy may not provide absolute accuracy. 
Despite the caveats inherent within this experiment, the results obtained here give rise to a number of future works. The results of these studies are now required, in order to confirm or dispel whether T. australiensis shows a preference for reproductive activity in the lower intertidal zone in all regions of its distribution. 

Figure 6
Figure 7
Figure 8

Moulting (Ecdysis)

As part of the superphylum Ecdysozoa, Callianassid shrimps all inevitably undergo ecdysis, as confirmed in Thessalou-Legaki and Kiortsis (1997) where ecdysis is mentioned in Callianassa tyrrhena. Ecdysis is a form of moulting where the chitinous cuticle or exoskeleton is jettisoned and a new one created. This process is mandatory for the growth of the organism within the exoskeleton, and doubles as an opportunity to repair the exoskeleton following any damages sustained to the previous one (Daley and Drage, 2016). As noted in Hyžny & Klompmaker (2015), Callianassid moulting appears to occur within the burrow, however the discarded cuticle is removed from the burrow. The occurrence of moulting episodes is governed by concentrations of the hormone ecdysone, which is present in all arthropods (Daley and Drage, 2016). In the specific case of T. australiensis, Hailstone and Stephenson (1961) observed three peaks in ecdysis throughout the year, at February, June and October/November. 


T. australiensis has a tendency of building intricately branched, systems of burrows, that have been documented to reach depths of 50cm or more below the surface of the substrate (Katrak and Bird, 2003). It is their burrowing behaviour that renders them crucial in the role of bioturbation of the sediments they inhabit (see ‘Ecosystem Services’ above). Footage was taken of a female T. australiensis specimen re-burrowing, upon being released after specimen collection for this study at Dunwich, North Stradbroke Island (see video below).

Video 1: Female T. australiensis burrowing following release after collection. Video: Lucas Sumpter, 2016.

Anatomy and Physiology

T. australiensis conforms to the general bauplan of Malacostracan Crustacea, with its body divided into 2 distinct tagmata; the cephalothorax, and posterior abdominal segments. At the very front of the cephalothorax, T. australiensis exhibits an elongated rostrum, a pair of antennae, and the feeding mouthparts such as the maxilla and mandibles which (see Fig. 5). In Fig. 9, the five pairs of appendages on the ventral side of the cephalothorax are visible, the anterior-most pair being the chelipeds. T. australiensis displays stark sexual dimorphism in the size of their chelipeds, with the male major cheliped being massively enlarged (Shimoda et al, 2005; Holthuis, n.d) for the purpose of fighting with other individuals. The other of the five pairs of thoracic appendages are biramous and can be used for burrowing (Ruppert, Fox and Barnes, 2004), and Malacostracans differ from other crustacean classes, in that they possess abdominal appendages or pleopods (Fig. 10). These can be seen bordered by orange, on the ventral side of the tail of the specimen shown in Fig. 9. Pleopods, in the case of T. australiensis, can be used for the purpose of locomotion, or generating water flow to aid burrowing. Callianassid shrimps such as T. australiensis differ from many other families of Decapod, in that the pleon is elongated relative to carapace length (Hyžny and Klompmaker, 2015). At the very end of the tail, Malacostracans posess a telson, surrounded by the uropods (Fig. 10) which form the tail fan (Ruppert, Fox and Barnes, 2004) as seen curled towards view by the specimen in Fig. 9. The tail fan, coupled with the musculature present within the abdominal segments, allows malacostracan crustaceans to propel themselves backwards quickly. 

While little mention is given to the internal anatomy of T. australiensis or callianassidae specifically, the species does again display the generalized internal anatomy of malacostraca. The malacostracan digestive system includes an oesophagus, where food is transported to the proventriculus (stomach possessing two chambers) for digestion, and then absorbed within the ceca (Ruppert, Fox and Barnes, 2004). Digestion in the stomach occurs via chewing, courtesy of the gastric mill (Ceccaldi, 1989), and also chemical breakdown of food. 
Figure 9
Figure 10

Biogeographic Distribution

Australian Ghost Shrimps are found in intertidal, benthic sand sediments along the majority of the eastern coast of Australia. Their distribution was observed in a pioneering study by Hailstone and Stephenson (1961) as between Port Phillip Bay, Victoria at the southern extremity, to the Low Isles at the northern, offshore from Port Douglas, Queensland. Holthuis (n.d) describes the same distribution, though with the northern extremity defined as Townsville, Queensland. The definitive boundaries of this distribution are ill-defined however, likely due to the non-exhaustive nature of sampling in a geographic sense. 
Figure 11

Evolution and Systematics

The phylogeny of Callianassid ghost shrimps to date is generally incomplete and ill-defined (Hyžny and Klompmaker, 2015). While the fossil record is extensive enough on temporal and spatial scales, over half of the described taxa were done so based on trace fossils of the cheliped (Hyžny and Klompmaker, 2015) and hence, confident reconstruction of the Callianassids’ phylogenetic tree is difficult. However, one such phylogenetic diagram was produced by Hyžny and Klompmaker (2015), and has been included here with the positions of the subfamily Callianassinae and genus Trypaea highlighted (see Fig. 12).

Kingdom: Animalia

Subkingdom: Bilateria

Infrakingdom: Protostomia

Superphylum: Ecdysozoa

Phylum: Arthropoda 

Subphylum: Crustacea

Class: Malacostraca 

Subclass: Eumalacostraca

Superorder: Eucarida

Order: Decapoda

Suborder: Pleocyemata

Infraorder: Thalassinidea

Superfamily: Callianassoidea

Family: Callianassidae

Subfamily: Callianassinae

Genus: Trypaea

Species: T. australiensis
Figure 12

Conservation and Threats

Trypaea australiensis is commonly harvested for use as bait, by recreational fishermen on Australia's east coast (Contessa and Bird, 2004; Butler and Bird, 2008; Hailstone and Stephenson, 1961). Extraction of yabbies from intertidal benthic sediments is carried out at low-tide when intertidal flats can be accessed on foot, using a suction-pump (Fig. 14) or by digging. This practice been observed to be extensive in many locations on the east coast of Australia, and has been demonstrated to correspond with a marked decrease in population numbers (Contessa and Bird, 2004).
The effect of collection of T. australiensis has also been suggested to be three-fold. The removal of individuals, coupled with the alteration of benthic sediments due to physical disturbance by excavation (Fig. 13), and removal of yabbies as bioturbators, all contribute to the population decline of T. australiensis caused by bait collection(Contessa and Bird, 2004). The role of T. australiensis as bioturbators is well documented (Katrak and Bird, 2003; Bird, Ford and Hancock, 1999; Spilmont et al, 2009; Contessa and Bird, 2004) and as a result, the collection of yabbies for the purpose of bait has been shown to result in decreased sediment porosity (Contessa and Bird, 2004) and ultimately, changes in local biogeochemistry. For example, Contessa and Bird (2004) found increased chlorophyll-a concentrations in conjunction with areas of yabby pumping. The culmination of these flow-on effects makes it difficult for T. australiensis to re-establish in areas that have experienced pumping, and population declines ensue. 
Figure 13
Figure 14


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