Manly Dam Crustaceans
Crustaceans are invertebrates with a hard exoskeleton (carapace), a segmented body that is bilaterally symmetrical, more than four pairs of jointed appendages ("legs") and an open circulatory system (the "blood" does not flow in a closed loop).
There are two large species of crayfish present at Manly Dam, the Giant Sydney Spiny Crayfish and the Sydney Spiny Crayfish, both profiled below.
Although they are often referred to as Yabbies, they are distinctively different from the true Yabbie (Cherax destructor) and have very different natural histories and environmental requirements.
For example, yabbies are found west of the Great Dividing Range in rivers, creeks and dams. Some have been introduced into other areas as they are a valuable source of food to some who enjoy yabby fishing. They mature at a young age (~18 months), breed profusely, and can tolerate poor quality and warmer water. Their introduction to waterways poses a serious threat to other species of crayfish.
Video: Sydney Giant Spiny Crayfish and Climbing Galxias fish in Manly Dam catchment. Video credit: Greg Wallis.
Spiny Crayfish (Euastacus sp.) are slow growing, can take 5-10 years to reach sexual maturity and can live to a very old age in excess of 40 years.
They also produce relatively few young, and require cool, clean, well oxygenated water in natural environments and may then become the dominant predator within a creek system.
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Sydney Spiny Crayfish
Species: Euastacus australasiensis
Image credit: RB McCormack, The Australian Crayfish Project -
Giant Sydney Spiny Crayfish
Species: Euastacus spinifer
Image credit: Greg Wallis
Other crustaceans
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Freshwater Shrimp
Species: Paratya australiensis
These small freshwater shrimp are very common at the dam and are otherwise widespread. It is an important food source for fish and platypus (none in Manly Dam, locally extinct).
Image credit: Jiri Lochman/Lochman Transparencies -
Long-armed shrimp
Macrobrachium species
These are much larger than the small freshwater shrimp and are easily recognised by their very long first arms/claws
Image credit: Tolderi -
Riffle Shrimp
Species: Australatya striolata
There have been reports of Riffle Shrimp in Mermaids Pool below the Manly Dam wall. Riffle shrimp are fan feeders, and so like to sit in the current and filter the water that flows past them. They can grow up to 5-6cm. All Shrimp are born Male and change sex to female at about 3-4cm.
Image Credit: Fishmosy (Dr. Benjamin Mos) and Northboy