This is the fourth time that macro-invertebrates have been sampled in the Majura Dams as part of Project Dragonfly. They were first sampled in spring 2005 to provide a benchmark against which future samples could be compared. As well as our first dragonfly nymph, we found quite a variety of other macro-invertebrates including water boatmen (true bugs), mayfly nymphs, caddis flies, midge larvae, yabbies and freshwater shrimp. The second and third samples were taken in autumn and spring 2006. See earlier reports for more detail. This fourth sample, in autumn 2007, is 18 months after restoration work commenced.
We are using a simple scoring system known as SIGNAL2. Bigger scores indicate a more diverse and healthier water body. The scores for each dam are shown in Figure 1. The total number of macro-invertebrates caught has gone up and down with season (Figure 2) and the range of species has remained more or less the same. It is premature to draw any conclusions about trends over time as the scores are sensitive to sampling conditions and seasonal fluctuations.
Autumn is a quiet time for the insects in our dams, especially in the lower dam. In both years the few animals out and about tended to be the ten-legged decapods – freshwater shrimps and yabbies. It was a similar story for the upper dam with the exception of a super abundance of caddis flies. These are animals that make a protective case out of materials such as gravel and sticks and walk around with it rather like hermit crabs in sea shells. Many of the caddis flies in this sample appeared to be wearing cases made from Carex appressa – a plant that we planted on the edges of the dam as part of the restoration effort. They looked very smart in their smooth green houses.
Jean Chesson
Friends of Mt Majura
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