Engaeus Granulatu

Engaeus Granulatus 
 
Kingdom : Animalia
Phylum : Arthropoda
Subphylum : Crustacea
Class : Malacostraca
Order : Decapoda
Infraorder : Astacidea
Family : Parastacidae
Genus : Engaeus

Species : Engaeus Granulatus 

Engaeus granulatus is a Tasmanian endemic burrowing crayfish occupying a restricted distribution in the Central North. The specific name of the crayfish refers to the prominent granulations found on its claws, which makes it one of our more easily identified Engaeus species. Within its distribution, the species seldom exhibits the vigorous colonies that are often typical of the other named species in the genus. For this reason as well as the fact that this crayfish often occurs in areas that are experiencing considerable development with subsequent habitat loss, E. granulatus is probably even less secure than the other threatened species of Engaeus currently listed.

Engaeus granulatus has been assessed as Critically Endangered under criterion. This species is thought to have undergone a decline of 80% or greater in the last ten years. It has an estimated area of occupancy of less than 0.5 km² with a severely fragmented distribution. It is subject to a range of threats which are resulting in a continuing decline in the quality of habitat. A species recovery plan has been developed, however urgent action is needed to protect some of the remaining subpopulations as none are protected at the present time.

Countries / Native: Australia (Tasmania)

Habitat and Ecology:     This species occupies seeps, wetlands and stream banks in relatively undisturbed habitats. It is only rarely seen above ground or in standing water. This species is often found in clayey soils with deeper burrows than other Engaeus species. It is believed to eat rotting wood, detritus, root material and, occasionally, animal material. The dispersal of this species through waterways may be limited, leading to restricted ranges and a high degree of local speciation (Doran 1999). The largest male recorded was 25.5 mm carapace length, and mature females ranged form 18.8 to 29.6 mm carapace length. The largest non-reproductive female was 19.6 mm carapace length (Horwtiz 1990).

Range Description:     This species is endemic to central north Tasmania. It is found in an area running southwest from Port Sorell to the Railton area and north to Quoiba, near Devonport (Nelson 2003). The historical distribution of this species is difficult to determine. Based on the distribution and abundance of other burrowing crayfish, it is likely that this species was quite common throughout its range prior to its habitat becoming highly modified (Nelson 2003). This species has an estimated extent of occurrence of 515 km² (N. Doran pers. comm. 2009).  Surveys conducted in 2002-03 found that this species had a restricted, fragmented population with limited connectivity between populations. Occupancy within its range is estimated to be between 0.2 - 0.5 km² (Threatened Species Scientific Commitee 2004). This estimate is based on known locations, with a 10 m (0.2 km²) or 20 m (0.5 km²) buffer applied to waterways and suitable wet areas within each colony to give an overall estimate of potentially occupied habitat (Threatened Species Scientific Commitee 2004). This is thought to be a conservative estimate (Threatened Species Scientific Commitee 2004). It is still not clear how much available suitable habitat is unsampled (Threatened Species Scientific Commitee 2004). It is highly probable that known populations will remain isolated due to the modified environments separating them and the continuing threatening processes operating throughout the range of the species (Nelson 2003).