Orbost spiny crayfish (Euastacus diversus)

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Orbost spiny crayfish in defensive stance
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Orbost spiny crayfish fact file

Orbost spiny crayfish description

KingdomAnimalia
PhylumArthropoda
ClassCrustacea
OrderDecapoda
FamilyParastacidae
GenusEuastacus (1)

The Orbost spiny crayfish (Euastacus diversus) is a small freshwater crayfish named after the location from which it was first described, just north of Orbost in Victoria, Australia (1) (3) (4) (5). It is one of the smallest members of the genus Euastacus (4), and one of Australia’s most threatened crayfish species (6).

Like other Euastacus species, the Orbost spiny crayfish is characterised by its spiny appearance, and it is distinguished from related species by the exact number, location and arrangement of these spines (2) (3) (4). The body of the Orbost spiny crayfish is generally olive-green, with a rusty-orange underside to the large, pincer-like claws (7). However, Euastacus species can be quite variable in appearance, sometimes making identification difficult (8).

As in other crayfish, the body of the Orbost spiny crayfish is covered in a hard, protective carapace. Its abdomen is divided into six segments, and ends in a tail fan composed of a central tail flap (telson) and surrounding flaps called uropods. In addition to the large claws, crayfish have four more pairs of appendages on the thorax, which are known as ‘pereiopods’ and are modified for feeding and walking. The abdomen bears further appendages known as ‘pleopods’ or ‘swimmerets’, which are used in swimming and also by the female for brooding the eggs (9) (10).

On its head, a crayfish has a pair of compound eyes, as well as several feeding appendages and two pairs of antennae, the smaller, central pair of which are known as ‘antennules’ (9) (10).

Also known as
Orbost spiny cray.
Size
Occipital carapace length: up to 3.2 cm (2)
Total length: c. 7 - 7.9 cm (3)
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Orbost spiny crayfish biology

The biology of the Orbost spiny crayfish is poorly known (4). Like other freshwater crayfish, it builds burrows around the margins of the streams it inhabits (3) (4) (9). The diet is likely to include a variety of invertebrates and aquatic and semi-aquatic vegetation, as well as fungi and bacteria found in rotting detritus (4).

Freshwater crayfish do not have long, planktonic larval stages, instead producing large eggs which hatch as miniature versions of the adult. The eggs are incubated on the pleopods of the female before hatching (9) (10). In the Orbost spiny crayfish, females reach maturity at an occipital carapace length of over four centimetres (2).

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Orbost spiny crayfish range

The Orbost spiny crayfish is endemic to Australia. It has one of the most restricted distributions of all Euastacus species, being known from just seven locations in the Brodribb River Catchment, on and around the Errinundra Plateau in East Gippsland, Victoria (1) (4) (5). Its distribution is extremely fragmented (1) (5).

In 1995, this species was also reported in Yandown Creek, in the Queensborough River Catchment (1) (4) (5).

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Orbost spiny crayfish habitat

The habitat preferences of the Orbost spiny crayfish are not well known. However, it inhabits freshwater, and the streams within its range are cool and highly oxygenated, with a bed of cobbles, pebbles or gravel. These streams flow through wet or damp forest or rainforest, and contain abundant debris such as logs and other vegetation (1) (4) (5).

The Orbost spiny crayfish is restricted to headwater streams at elevations of 350 to 1,050 metres (1) (5).

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Orbost spiny crayfish status

The Orbost spiny crayfish is classified as Endangered (EN) on the IUCN Red List (1).

IUCN Red List species status – Endangered

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Orbost spiny crayfish threats

The Orbost spiny crayfish has a highly fragmented and restricted distribution (1) (4), and is uncommon at the sites it inhabits (1) (5). One of the main threats to this freshwater species is a continuing decline in the quality of its habitat, as a result of timber harvesting and forest management activities. Together with associated road building activities, timber harvesting can affect water run-off into the streams this crayfish inhabits, as well as increasing the amounts of sediment and nutrients washing into the water (1) (4) (5).

Burning is often used to regenerate vegetation after timber harvesting, and this can further increase the nutrients and sediment entering streams. The loss of streamside vegetation can also increase light intensity and water temperature (1) (4) (5).

The restricted distribution and small populations of the Orbost spiny crayfish make it particularly vulnerable to any localised events, such as prolonged droughts. It is also likely to be negatively affected by introduced species, such as brown trout (Salmo trutta), cats, foxes, pigs and goats (1) (4) (5). In addition, the Orbost spiny crayfish may be threatened by over-collection in some areas (4).

As a high altitude species, the Orbost spiny crayfish is also likely be under threat from the potential effects of climate change. This may cause increased temperatures, altered water regimes, more severe weather events and a loss of suitable highland habitat, as well as increasing the potential for bushfires (1) (5).

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Orbost spiny crayfish conservation

There are no specific conservation measures currently aimed at the Orbost spiny crayfish. However, it is indirectly protected by fishing restrictions in Victoria, which have a minimum crayfish catch size that is greater than the largest individuals of this species (1) (5).

One of the most important measures for the protection of the Orbost spiny crayfish will be the protection of its habitat. There are plans to establish ‘Linear Reserves’ consisting of undisturbed zones of at least 100 metres on each stream bank, extending up to 1 kilometre upstream and downstream from sites at which this species occurs. These protected areas should be monitored to determine how effective they are at mitigating the threats to the crayfish’s habitat (1) (4) (5). Further research is also needed into the populations, distribution, biology and life history of the Orbost spiny crayfish (1) (4) (5).

In 2005, the Australian Crayfish Project (ACP) was started, with the aim of surveying, identifying and documenting all of Australia’s freshwater crayfish species. It is hoped that the information generated by this project will help in the conservation of crayfish species and their fragile habitats (6) (8). Once further information on the Orbost spiny crayfish is available, it may need to be raised to a higher category of threat (1) (5).

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Find out more

Find out more about the Orbost spiny crayfish and its conservation:

More information on freshwater crayfish conservation in Australia:

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Glossary

Abdomen
In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustacea (such as crabs) some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen.
Antennae
Pair of sensory structures on the head of invertebrates.
Carapace
In arthropods (insects, crabs, etc), the fused head and thorax (the part of the body located near the head), also known as the ‘cephalothorax’.
Detritus
Litter formed from fragments of dead material.
Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Genus
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
Incubation
The act of incubating eggs; that is, keeping them warm so that development is possible.
Invertebrates
Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones) and echinoderms.
Larval
Of the stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Occipital carapace length
A measurement used for species such as crayfish, taken as the length between the eyes and the rear of the carapace.
Plankton
Aquatic organisms, usually tiny, that drift passively with water movements; may be phytoplankton (plants), zooplankton (animals), or other organisms such as bacteria.
Thorax
Part of the body located between the head and the abdomen in animals.
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References

  1. IUCN Red List (June, 2011)
    http://www.iucnredlist.org/
  2. Coughran, J. (2008) Distinct groups in the genus Euastacus? Freshwater Crayfish, 16: 123-130.
  3. Riek, E.F. (1969) The Australian freshwater crayfish (Crustacea: Decapoda: Parastacidae), with descriptions of a new species. Australian Journal of Zoology, 17(5): 855-918.
  4. Murray, A. (2003) Action Statement. Orbost Spiny Cray, Euastacus diversus. Department of Sustainability and Environment, Victoria, Australia. Available at:
    http://www.dpi.vic.gov.au/CA256F310024B628/0/9DE0D82A0E909834CA2570ED000A56FA/$File/128+Orbost+spiny+cray+2001.pdf
  5. Coughran, J. and Furse, J.M. (2010) An Assessment of Genus Euastacus (49 Species) Versus IUCN Red List Criteria. A Report Prepared for the Global Species Conservation Assessment of Lobsters and Freshwater Crayfish for the IUCN Red List of Threatened Species. Environmental Futures Centre, Griffith University, Queensland, Australia. Available at:
    http://iz.carnegiemnh.org/crayfish/IAA/docs/Coughran_and_Furse_2010.pdf
  6. Australian Aquatic Biological Pty Limited: Project No. 100016 - The Orbost Spiny Crayfish Euastacus diversus (Riek 1969) (June, 2011)
    http://www.aabio.com.au/documents/TheOrbostSpinyCrayfishEuastacusdiversusresearchproposal_final2_.pdf
  7. SpinyCrayfish.com: Euastacus diversus - Orbost Spiny Crayfish (June, 2011)
    http://www.spinycrayfish.com/?page_id=326
  8. Australian Aquatic Biological Pty Limited - Australian Crayfish Project (June, 2011)
    http://www.aabio.com.au/crayfish.html
  9. Identification and Ecology of Australian Freshwater Invertebrates (June, 2011)
    http://www.mdfrc.org.au/bugguide/index.htm
  10. Campbell, A. and Dawes, J. (2004) Encyclopedia of Underwater Life. Oxford University Press, Oxford.
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Image credit

Orbost spiny crayfish in defensive stance  
Orbost spiny crayfish in defensive stance

© Jason Coughran

Jason Coughran
jcoughran@croakingenvironment.com.au
http://www.croakingenvironment.com.au/staff/jc.html

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