Engaeus Yabbimunna

Saturday, February 18, 2012

Engaeus Yabbimunna

Burnie Burrowing Crayfish

Engaeus Yabbimunna

Engaeus Yabbimunna
Burnie Burrowing Crayfish

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

Species : Engaeus Yabbimunna

Engaeus Yabbimunna was unknown until 1992, when a population was located at Burnie on the North West Coast of Tasmania (Doran & Richards, 1996). For this reason E. yabbimunna was given the name "Burnie Burrowing Crayfish". E. yabbimunna is distinguished from similar species by slight morphological differences including the presence of only one row of tubercules ("bumps") on the chelae ("claws"), an upturned spine on the rostrum and the pattern of pores on the sternum (Horwitz, 1994).

Doran and Richards (1996) note that E. yabbimunna live in burrows which always reach the water table. This corresponds to Horwitz & Richardson's (1986) Type 2 burrows. The species is thought to feed on rotting vegetation and perhaps aquatic macroinvertebrates (Doran & Richards, 1996). At the time of its discovery in 1994, it was considered to have an extremely restricted distribution and was initially known from only three creeks in the Burnie area ((Doran & Richards, 1996). However, further work has revealed a wider distribution, with the species having been recently identified from several catchments west of Burnie (J. Nelson, A.M.M. Richardson, pers. comm.). Nevertheless, E. yabbimunna is considered to be a rare species whose survival is threatened by many pressures, including habitat removal and disturbance as well as decreased water quality (Doran & Richards, 1996).

Marist Regional College's Burnie Burrowing Crayfish Project consisted of a group of Year 10 students who monitored water quality and mapped vegetation and the distribution of crayfish burrows along a creek flowing through the City of Burnie. The aim of the project was to assess the habitat available to E. yabbimunna in the area with a view to developing a recovery plan for the species.

The Burnie Burrowing Crayfish is a freshwater crayfish which grows to an average of 6 cm long. This species is distinctive as it has only one row of tubercles on the back of the claw, a smooth 'palm' of the claw and an upturned tip of the rostrum (projection between the eyes) (Bryant & Jackson 1999).

Australian DistributionThe Burnie Burrowing Crayfish is known only from Burnie and the area immediately to the west, in Tasmania. The species was first discovered in 1992 in Burnie Park. It has been recorded at 34 sites in Shorewell, Romaine, Cooee, Seabrook, Camp and Distillery Creeks (Doran 1999b; Doran & Richards 1996). The extent of occurrence is 130 km² (Richardson et al. 2006).

The species has a fragmented distribution, as only those subpopulations in Romaine Creek are interconnected (Doran & Richards 1996).

Population InformationThe population size of the Burnie Burrowing Crayfish has been estimated at 229 000 to 1 650 000. This was calculated using the density/occupancy estimates determined for the related Scottsdale Burrowing Crayfish (Engaeus spinicaudatus) coupled with known locations and projected habitat for the Burnie Burrowing Crayfish (Doran 1999b).

Land Tenure of PopulationsThe Burnie Burrowing Crayfish is not known to occur in any conservation reserves (Doran 1999b).

HabitatThe Burnie Burrowing Crayfish prefers well covered, slowly draining strips of fern dominated native riparian vegetation. It is known from stream banks and seepages retaining remnant riparian vegetation within Burnie, and, outside the city, in open and grassy sheep pasture, farm dams, roadside seeps and culverts, sedgey marsh, and some moderately disturbed stream sides (Doran 1999b).

The Burnie Burrowing Crayfish usually constructs burrows which are connected to the water table (Doran 1999b). Burrows can be complex and extensive and may often be the product of several generations of crayfish activity (Doran & Richards 1996).

Life CycleBurrowing crayfish live their entire lives within their burrow systems (DPIW 2007). Males and females are not found in the same burrow system (Horwitz 1990a). They occasionally appear on the surface at night and in damp, overcast conditions. All burrowing crayfish have gills under their carapace, making them dependent on water to breathe (DPIW 2007).

Burnie Burrowing Crayfish are believed to mate in early September (Doran 1999b). Females have been found in early December carrying eggs in an early stage of development under their tails (Doran 1999b).

FeedingBurrowing crayfish feed on rotting wood, detritus, root material and occasional animals material (Bryant & Jackson 1999b). Ferns (Dicksonia antarctica), tea-tree, other vegetable material and aquatic invertebrates are likely food sources for the Burnie Burrowing Crayfish (Doran & Richards 1996).

Movement Patterns
Breeding and dispersal between different subpopulation of the Burnie Burrowing Crayfish is likely to be very limited in most cases (Doran & Richards 1996).

Species identification
In areas where only one burrowing crayfish species occurs, the presence of crayfish burrows confirms the presence of that species. However, in some areas, more than one crayfish species may be present (that is, the species occur together). In an area of overlapping distributions, further investigation is needed once burrows have been located to determine the species occupying a particular microhabitat. This will usually involve burrow excavation. Burrow excavation surveys must be designed and implemented in a way that minimises the disturbance to habitat at the site and should only be conducted in consultation with burrowing crayfish experts. Survey methodology should include protocols for appropriate hygiene controls to avoid the spread of pathogens such as chytrid fungus and Phytophthora in crayfish habitat. Permits may be needed for burrow excavation surveys (Tasmanian Burrowing Crayfish Workshop 2010).

ThreatsWater pollution, water diversion and habitat removal are the greatest threats to the Burnie Burrowing Crayfish (Doran 1999b). Removal of vegetation from creek banks is likely to reduce the food available to this species (Doran & Richards 1996).

The species is thought to be particularly threatened by processes associated with increasing urbanisation and industrial pollution in the Burnie urban area. Populations are also threatened by agricultural and forestry activities through changes to hydrology, construction of dams and roads, streamside land clearance, soil compaction, sedimentation and changes to water quality (LEC 2007).

Due to its limited dispersal capacity, the Burnie Burrowing Crayfish is at risk from inbreeding depression. It is also less likely to be able to recolonise areas in which the local subpopulation has become extinct (Doran & Richards 1996).