Sunday, December 11, 2011

Alpine Spiny Crayfish-Euastacus Crassus and Spiny Freshwater Crayfish

The Alpine Spiny Crayfish  Euastacus crassus Riek 1951 is a small to medium Spiny freshwater crayfish with an Occipital – Carapace Length (OCL) of up to 58 mm. Members of the genus Euastacus are distinguished by heavy claws or chelae and a spiny appearance. The species is distinguished from the smaller Victorian species by its lack of a male cuticle partition. This partition is a gap between the membrane running from the body onto the underside of the first joint of the fifth walking leg of the male. The membrane does not reach the male genital pore.  Females reach sexual maturity at around 30-40 OCL. Specimens usually a deep brown colour, occasionally with red tinges dorsally, with orange thoracic spines and tubercles. The underside is orange and green.

The Alpine Spiny Crayfish is one of the most localised species in the  Euastacus  genus and is restricted to the high country occurring in streams in southern NSW, the ACT and in the eastern semi- alpine country of Victoria. The range extends form north-east to south-west approximately 210 km. In Victoria, it extends as far as Mount Beauty and Mount Hotham at elevations above 1 000 m, which may be snow covered in winter. All known sites are located in the Alpine National Park. The most recent records are those of Raadik et al. who found a total of seven individuals from four sites out of a total of 27 sites surveyed in the Upper Murray River Basin.

HabitatLittle is known about the habitat of this species except that it occupies cool streams in alpine and sub-alpine areas. Morgan (1997) describes the vegetation at the type localities as dry sclerophyll forest and heath in largely granite areas with abundant ferns along stream banks at one site. He also notes that the species is patchily distributed in the ACT at sites with relatively undisturbed vegetation.

Life history and ecologyWhile the biology of this species specifically is unknown, in general, mating activity between mature crayfish occurs from May onwards each year, following which females carry eggs under the tail. The eggs hatch from October onwards, depending on seasonal conditions and the species. The dependent juvenile crayfish are carried beneath the tail for some weeks or months after hatching.

The yolk of the egg is retained by the young hatchlings as a yolk sac supplying food during early growth. Once the yolk sac has been completely absorbed, the young disperse to fend for themselves. Most species of Euastacus are moderate burrowers, seeking refuge under rock ledges and amongst submerged, in-stream tree roots. The diet of spiny freshwater crayfish consists primarily of aquatic and  semi-aquatic vegetation, benthic invertebrates.


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