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Trypaea australiensis: larvae inspection and a study on burrowing efficiency on different substrates


Ting Him Wallace Lo 2016

Abstract

Trypaea australiensis, also known as ghost nippers or pink nippers, are also called marine yabbies by fishermen that collect them as bait.  They belong to the infraorder Thalassinidea and are burrowing shrimps that has a distinct shape with an enlarged chela. Burrowing in the sand or mud flats around the coastal intertidal areas. These ghost shrimps play an important role in the ecology of these areas by interacting with various other species that share the same habitat and make nutrients available for the sediment. In the experiment, the burrowing speed of 20 T. australiensis individuals were tested on 3 substrate of increasing grain size. Results showed a positive correlation between time taken to create a burrow and grain sizes. The results showed that there are possibilities that they might look for sediments that are easier to form burrows as their ‘home’. In conclusion, the sediment size does affect T. australiensis individuals and there might be a preference on the substrate when choosing a spot to burrow. This not only affect the abundance of T. australiensis in the area but also other species that rely on the nutrients that T. australiensis makes available.

Introduction

Classification

This species is identified using the key made by K. Sakai (1999).

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Crustacea

Class: Malacostraca

Order: Decapoda

Infraorder: Thalassinidea

Family: Callianassidae

Genus: Trypaea

Species: T. australiensis

Physical description
Adult T. australiensis grows to 80mm in length and has five pairs of pereopods. First and second pair of appendages are chelipeds, and the first pair of cheliped is usually unequal in size in both males and females (Figure 1). Modified appendages for digging and moving substrate particles when burrowing, this is most evident in the third pair of pereopod where the propodus is enlarged (Figure 2). The third pair of maxilliped also shows an enlarged section to hold the substrate particles in place (Figure 3). Only three pair of pleopods as the first two pairs might be absent. The identification of T. australiensis larvae will be discussed at the end of this paper.
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Figure 1
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Figure 2
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Figure 3

Life History and behaviour

Hailstone  and Stephenson (1961) suggested that these ghost shrimps have burrows that has up to 6 openings. And the adults were described to be burrowing in a range of different substrata with sand and mud  in intertidal areas. Burrows varies in size and depth depending on the season and was found to have deeper and bigger burrows in the summer months that reach down to half a meter deep (Butler & Bird, 2008, Stapleton et al. 2002). Rotherham and West (2007) also stated that the population increases during summer and study by Spilmont et al. (2009) has found that diatoms are the main energy source for T. australiensis. And they collect their food directly from the burrow wall. and Stapleton et al. (2002) suggests that they prefer particles that are around 63μm. Rotherham and West (2009) found that these ghost shrimp has an increased fecundity relative to other species in the same family. And has six larval stages before the post larvae stage (Dakin & Colefax, 1940).  And lives for less than four years in average (NSW Government, 2010).

Ecology
Like many other benthic burrowing organisms on the sand flats, ghost shrimps plays an important role in maintaining the organic matter levels in the substrate. A study by Webb and Eyre (2004) stated that increasing the burrow wall surface area in the sediment allows an increase in gaseous exchange for both the ghost shrimp and the bacteria in the surrounding substrata. As a result of the increased ventilation, the metabolism of the sediment such as nitrification, nitrate reduction and nutrition regeneration rate also increases(Jordan et al., 2009; Dunn et al., 2012). However, Jordan et al. (2009) has also found a contradictory level of effect on the sediment metabolic rate  of T. australiensis in different sediments where other organisms might be present. Interactions with other species also include the increased number of Mysella vitrea, a deposit feeding bivalve, around the burrows of T. australiensis (Kerr & Corfield, 1998) and that the larvae of T. australensis are also known to be a food source for glassfish (McPhee et al., 2015). T. australiensis are popular baits among the fishing community and a study by Contessa and Bird (2004) has found that bait collection of T. australiensis has could reduce the population density and would take more than three months to recover. This might pose a problem for popular bait collection spots where disturbance is frequent. There are currently no conservation effort apart from the possession limit of 100 in Victoria and New South Wales, Australia.

Materials and Methods

The substrate was obtained from the beach of Wellington Point, Redland City. Three types of substrate with different grain size were used. Different coarseness of substrate were obtained by running them through sand filters with different pore sizes. The diameter of the particles were 250μm - 1mm, 1mm - 2mm and 2mm - 4mm. A total of 20 adult T. australiensis  were tested individually. Seven in each of the 250nm - 1mm and 1mm - 2mm substrates and six in the 2mm - 4mm substrate. Four centimeters  of the substrate was placed inside a container (18cm x 10m x 8cm) and then filled with saltwater until it has a water depth of one centimeter (Figure 4).  The timer was started when the individual starts digging as they might swim around the container when placed. Speed of burrowing was measured by the time taken to dig a burrow that could accommodate the head either in depth or volume without taking the large chela into account (Figure 5, 6). I also defined burrow as a hole that would not collapse without the support of anything (Figure 7, 8).

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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8

Results

Every T. australiensis individual made a burrow under laboratory conditions and most of them started burrowing once they were placed in the container. Due to time constraints two of the individuals in the 2mm substrate group did not manage to finish their burrow in the time limit of 25 minutes and the maximum time of 25 minutes is recorded. The smallest value in the sediment size range is taken for the ease of the statistical analysis. Figure 9. shows the time taken to burrow with the increase in sediment particle size. The association was tested to be significant in a linear regression model with p=0.0124. The multiple R-squared value showed that 30% of the variation is explained by sediment particle size.
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Figure 9

Discussion

Burrowing experiment

It was believed that sediment grain size affects the efficiency of burrowing in T. australiensis and the results of the experiment supports this hypothesis. From the observations, there were usually two approaches for digging a burrow, the first being simply excavating the substrate by holding them together with their appendages and placing them outside the burrow (Figure 10). The second usual practice was to dive into the substrate and then pressed down on the walls to secure the particles, forming a burrow (Figure 11). The slowered burrowing speed of the T. australiensis might be due to the coarser substrate not able to hold shape. The 2mm sediment was noticeably more loose than the other substrate and would not hold shape. While digging, T. australiensis secreted a mucous which stick the particles together, this is also most evident in the 2mm substrate. Both the individual that did not finish within the 25 minute minute were using the first approach on the 2mm substrate, forming a “pit” instead of a burrow. This again probably relate to the coarse substrate not holding in place and would collapse, thus, the excavating method was used and a pit was formed. When burrowing, the large chela was used to support the initial hole while the other appendages secures the walls (Figure 13). The linear regression model only explained 30% of the variation in the data. Other sources of variation in the data which was not recorded might include the gender of the individual, size and maybe the size of the enlarged chela as it clearly aids the building of a burrow. Temperature might also be a factor contributing to the burrowing speed as Butler and Bird (2008) suggests warmer months increases the activity level of T. australiensis and will result in deeper and bigger burrows. It is also important to note that in a natural environment the substrate consists of a range of different sized particles. To conclude, T. australiensis are present in a lot of sediment types (Hailstone & Stephenson, 1961) but there might be a difference in distribution even at one location as the sediment type differs, which may affect its efficiency in digging a burrow and affect energy expenditure. Further studies might find out if there are any preferred substrate types and map out their abundance.

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Figure 10
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Figure 11

Larvae identification

The larvae is identified using a guide by Dakin and Colefax (1940). Females T. australiensis with eggs were caught and the hatching occurred in a bucket during transportation back to the laboratory. The newly hatched larvae were transferred into 4% PFA solution to fix within 30 minutes of the hatching. However, according to Dakin and Colefax (1940) a stage one, or newly hatched larvae does not have a rostrum, dorsal spines, feathering on the telson spines and median terminal spine. And the newly hatched larvae we collected (Figure 12) were in fact stage two larvae, which has every feature listed above (Figure 13, 14, 15). This could be explained by either T. australiensis larvae having a quick moulting interval (<30 minutes) from first to second stage, or if Dakin and Colefax (1940) has gotten larvae that hatched prematurely.
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Figure 12
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Figure 13
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Figure 14
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Figure 15

Acknowledgements

I would like to thank all the tutors and peers that helped with this project. Special thanks to Sophia Chan putting in solid effort pumping the yabbies out for the experiment.

References

Butler, S.N. & Bird, F.L. 2008, "Temporal changes in burrow structure of the thalassinidean ghost shrimps Trypaea australiensis and Biffarius arenosus", Journal of Natural History, vol. 42, no. 31, pp. 2041-2062.

Contessa, L. & Bird, F.L. 2004, "The impact of bait-pumping on populations of the ghost shrimp Trypaea australiensis Dana (Decapoda: Callianassidae) and the sediment environment", Journal of Experimental Marine Biology and Ecology, vol. 304, no. 1, pp. 75-97.

Dakin, W.J., and Colefax, A.N. 1940, “The plankton of the Australian coastal waters off New South Wales”, Monograph No.1, Department of Zoology University of Sydney.


Dunn, R.J.K., Welsh, D.T., Jordan, M.A., Arthur, J.M., Lemckert, C.J. & Teasdale, P.R. 2012, "Interactive influences of the marine yabby (Trypaea australiensis) and mangrove (Avicennia marina) leaf litter on benthic metabolism and nitrogen cycling in sandy estuarine sediment",Hydrobiologia, vol. 693, no. 1, pp. 117-129.

Hailstone, T.S. & Stephenson, W. 1961, “The biology of Callianassa (Trypaea) australiensis Dana 1852 (Crustacea, Thalassinidea)”, University of Queensland Press, St. Lucia.

Jordan, M.A., Welsh, D.T., Dunn, R.J.K. & Teasdale, P.R. 2009, "Influence of Trypaea australiensis population density on benthic metabolism and nitrogen dynamics in sandy estuarine sediment: A mesocosm simulation", Journal of Sea Research, vol. 61, no. 3, pp. 144-152.

Kerr, G. & Corfield, J. 1998, "Association between the ghost shrimp Trypaea australiensis Dana 1852 (Crustacea: Decapoda) and a small deposit-feeding bivalve Mysella vitrea Laserson 1956 (Mollusca: Leptonidae)", Marine and Freshwater Research, vol. 49, no. 8, pp. 801-806.

McPhee, J., Freewater, P., Gladstone, W., Platell, M. & Schreider, M. 2015, "Glassfish switch feeding from thalassinid larvae to crab zoeae after tidal inundation of saltmarsh", MARINE AND FRESHWATER RESEARCH, vol. 66, no. 11, pp. 1037-1044.

NSW Government, 2010, “Ghost nipper (Trypaea australiensis)”, Status in fisheries in NSW, pp. 143-144.

Rotherham, D. & West, R.J. 2007, "Spatial and temporal patterns of abundance and recruitment of ghost shrimp Trypaea australiensis across hierarchical scales in south-eastern Australia", Marine Ecology Progress Series, vol. 341, pp. 165-175.

Rotherham, D. & West, R.J. 2009, "Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales", Marine Biology, vol. 156, no. 6, pp. 1277-1287.

Sakai, K. 1999, “ Synopsis of the family Callianassidae, with keys to subfamilies, genera and species, and the description of new taxa (Crustacea: Decapoda: Thalassinidea)”, Zool. Verh. Leiden, vol.  326(30:VII), pp. 1-152

Spilmont, N., Meziane, T., Seuront, L. & Welsh, D.T. 2009, "Identification of the food sources of sympatric ghost shrimp (Trypaea australiensis) and soldier crab (Mictyris longicarpus) populations using a lipid biomarker, dual stable isotope approach", Austral Ecology, vol. 34, no. 8, pp. 878-888.

Stapleton, K.L., Long, M. & Bird, F.L. 2002, "Comparative feeding ecology of two spatially coexisting species of ghost shrimp, Biffarius arenosus and Trypaea australiensis (Decapoda: Callianassidae)", Ophelia, vol. 55, no. 3, pp. 141-150.

Webb, A.P. & Eyre, B.D., 2004, “Effect of natural populations of burrowing thalassinidean shrimp on sediment irrigation, benthic metabolism, nutrient fluxes and denitrification”, Marine Ecology Progress Series, vol. 268, pp. 205-220

Bonus picture of a T. australiensis larvae section under the microscope .