North coast burrowing crayfish, Engaeus granulatus

The north coast burrowing crayfish, Engaeus granulatus, remains the only confirmed threatened animal species resident on the property. These crustaceans need water to breathe. They live in burrows in the wetter parts of the property with access to the water table below. Their food is said to be rotting vegetation with some small invertebrates, They frequently build a hollow "chimney" upwards from the opening of their burrows out of small mud pellets. The functions of the chimneys are unknown but Engaeus sometimes close them off in hot weather, perhaps to conserve moisture.

Engaeus granulatus mate in mid to late Spring, producing eggs that hatch into larvae in mid-late summer. Females fold their tails forwards, creating a pocket in which they carry their orange eggs or young larvae. The juveniles are released from the burrows when the water levels are high. It is thought to take three years for the larvae to reach maturity and breed themselves.

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This photo shows the only live specimen of Engaeus granulatus that we have ever seen at Rubicon.

 

 

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It was sheltering within a "chimney" above a burrow that was accidentally knocked over.

 

 

 

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Our burns reveal Engaeus granulatus holes and chimneys, generally in the wetter areas.

 

We are conducting a long-term study to record changes in the number and distribution of active Engaeus granulatus holes over time, in an area that we burnt in April 2011.

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Method

After the burn, we set up 1 metre square quadrats within a 5 m x 4 m area and mapped all the Engaeus burrows in that area. In this photo, tennis balls show the positions of the holes in one of the twenty quadrats in the study.

 

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Every six months since then, we have returned to the site to record all the burrows present in the 5 m x 4 m area and to monitor whether each is new, active or closed. Numbered aluminium tags mark the positions of the holes.

 

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The vegetation has thickened considerably since 2011 and it would be very hard to find the holes if they had not been marked previously.

 

 

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Between 2011 and 2015, three new burrows have been found and numbered, and six burrows have closed. These figures include one burrow newly discovered and one burrow newly closed in 2014.

 

 

We have also surveyed for holes along two metre wide transects across several areas soon after burning. The patchy distribution of the holes makes it hard to estimate the total number of holes accurately but we surmise that there are well over 10,000 burrows on the property.

Disturbance map 2015

Location map showing Engaeus records, the Engaeus experiment and transects sued to count Engaeus holes at Rubicon. Map data: Google