Austrothelphusa transversa

Austrothelphusa transversa (von Martens, 1868), also known as the freshwater crab, inland crab, or tropical freshwater crab[3] is a species of freshwater crab endemic to Australia.[1] A. transversa is the most dispersed species out of this genus as it has adaptations that allow it to have a higher tolerance to drought and arid conditions.[4]

Austrothelphusa transversa
Austrothelphusa transversa from Queensland
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Brachyura
Family: Gecarcinucidae
Genus: Austrothelphusa
Species:
A. transversa
Binomial name
Austrothelphusa transversa
Synonyms[1][2]
  • Telphusa crassa
    (Milne-Edwards, 1869)
  • Telphusa leichardti
    (Miers, 1884)

Taxonomy & Description

A. transversa has had numerous changes to the presentation of the species name, changing genera, and subgenera, and subfamily, including Parathephusa, Liotelphusa, and Holthuisana.[4] Due to losses of type specimens, similarities between similar genera, and relatively recently, molecular testing, the species is currently under the genus Austrothelphusa alongside six other species.[4] The coloration of A. transversa varies amongst individuals, as they have a single brown, maroon, and grey coloring to the exoskeleton, or a similar shade.[5] The Inland crab has a relatively smooth carapace which grows to around 5 cm (2.0 in) in diameter.[5] Like other decapods, The Inland crab has a pair of claws, one longer than the other, and four pairs of legs with a relatively round carapace.[5]

Distribution & Habitat

A. transversa is endemic to the Australian mainland and is widely distributed throughout the North-Western half of Australia, occupying the inland arid conditions of central Australia and the tropical and sub-tropical rivers of northern Australia.[4] The inland crab is predominantly found throughout ephemeral rivers, creeks, and waterholes throughout Queensland (QLD) and the Northern Territory (NT), whilst located in pockets in the north-eastern parts of Western Australia (WA) and South Australia (SA), and parts of north-western New South Wales (NSW).[4][6]

Behaviour

Aestivation

The inland crab is thought to estivate into the deep underground burrows in which the crab builds in clay or sediment banks as a way of dealing with prolonged droughts, waiting for the rain to restore the creeks, rivers, and water holes, allowing them to exit estivation.[6] The burrowing habit of the crab is vital for its survival as it allows them to find moist substrate closer to the water table in which it with remain, keeping them alive during the drier winter months, that much similar to the common yabby.[4] The burrows range on average of 50–100 cm (20–39 in) in-depth and contain a plug over the top, this creates a chamber in which the moisture remains trapped in preventing the crab from drying out, prolonging the time the crab can remain in the burrow.[1]

Diet

The restoration of water in the ephemeral rivers throughout the wet season supports a temporary abundance of aquatic life in these creeks, such as algae, and fish.[6] Though the inland crab being an omnivore, they feed primarily on algae that accumulates in these rivers when the water returns.[6][5] The Inland crab is an opportunistic scavenger that can feed on decaying animals in which it encounters.[6]

Amphibious

Modified gills of A. transversa work as lungs when exposed to the atmosphere allowing them to become amphibious, this is also a common trait amongst some other crustacean species.[7] This adaptation allows the inland crab to leave the water helping it thermoregulate, as small pools of water can fluctuate throughout the day becoming intolerable, hence the crab can leave the water and seek shelter amongst roots, leaf litter, and other debris.[6]

Reproduction

The female crab carries the fertilized eggs under the abdomen plate, which itself is tucked under the thorax of the carb and can lay anywhere from 100 to 350 eggs.[8][9] The eggs are held throughout the development of the egg stage and into early the juvenile stage, where the mother will then disperse the young into the close surroundings where they will then fend for themselves.[8] The mother crab is believed to hold onto her young during the estivation period in the burrows, releasing the young crabs when she exits the estivation period taking full advantage of this estivation, giving the young optimal chance for success as waterways return.[6]

Conservation actions

Although considered to be of 'Least Concern' by the IUCN, the Austrothelphusa transversa occurs in several protected areas, including Sturt National Park.[3] The Inland crab is seen as of 'Least Concern' due to its wide distribution but, to what extent the species will remain at this level will depend on further studies.[1] More Recent studies are predicting that due to its wide disruption, it could be more specious than originally expected.[4]

Threats

Urbanization and modifications to natural rivers are a few factors that are threatening A. transversa. Altering the natural flow of creeks and modifying the structure of the banks, replacing natural substrate with concrete channels has a direct impact on the specie's ability to burrow and aestivate.[8] Along with prolonged drought, agriculture, and climate change, it is of consideration that the inland crab could further have to face even longer periods without water.[6]

References
  1. Esser, L. & Cumberlidge, N. (2008). "Austrothelphusa transversa". IUCN Red List of Threatened Species. 2008: e.T134922A4036588. doi:10.2305/IUCN.UK.2008.RLTS.T134922A4036588.en.
  2. "Austrothelphusa transversa (von Martens, 1868)". Atlas of Living Australia. Retrieved 28 September 2018.
  3. "Sturt National Park: Plan of management" (PDF). NSW National Parks & Wildlife Service (PDF). Government of New South Wales. January 2018. ISBN 978-1-76039-991-7. Retrieved 28 September 2018.
  4. Naser, Murtada D (2018). "Molecular and morphological investigations into two species-complexes within the Australian freshwater crab genus Austrothelphusa Bott, 1969 (Crustacea: Decapoda: Gecarcinucidae)": 1–126. doi:10.25904/1912/421. Cite journal requires |journal= (help)
  5. "Austrothelphusa transversa (Martens, 1868)". Atlas of Living Australia. Retrieved 25 October 2020.
  6. Waltham, Nathan J (2016). "Unravelling life history of the Inland Freshwater Crab Austrothelphusa transversa in seasonal tropical river catchments". Royal Zoological Society of New South Wales. 38 (2): 217–222. doi:10.7882/AZ.2016.034.
  7. Taylor, H. H; Greenaway, Peter (1979). "The structure of the gills and lungs of the arid‐zone crab, Holthuisana (Austrothelphusa) transversa (Brachyura: Sundathelphusidae) including observations on arterial vessels within the gills". Journal of Zoology. 189 (3): 1. doi:10.1111/j.1469-7998.1979.tb03969.x.
  8. Waltham, Nathan; Hughes, Jane; Davie, Peter (2014). "Freshwater crabs occupying tropical north Queensland coastal creeks". Royal Zoological Society of New South Wales. 37 (2): 256–262. doi:10.7882/AZ.2014.005.
  9. "Inland Freshwater Crab". Queensland Museum. Queensland Government. Retrieved 25 October 2020.
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