Effect of toxic riparian weeds on the survival of aquatic invertebrates

In order to ascertain whether introduced weeds have an effect on naturally occurring aquatic fauna, this study assesses the toxicity of 3 introduced weeds that occur along the banks of rivers and ponds in New South Wales, on 4 aquatic invertebrates. Damsel Fly nymphs, Mud Eyes, Mayfly nymphs and Backswimmers were placed in petri dishes with minced leaves from either Crofton Weed, Camphor Laurel or Privet (tests), Black Wattle or Derris dust (comparisons) or no plant material (control). The toxicity of the weeds was determined by the lifespan of the invertebrates exposed to them. Damsel Fly nymphs were adversely affected by Camphor Laurel, Crofton Weed and Derris dust, but not the other treatments. Mud Eyes were most affected by Black Wattle and Crofton Weed, though results were variable and inconclusive. Mayfly larvae were most affected by Crofton Weed and Derris dust. Backswimmers were killed very quickly by all three test weeds and Derris dust. These results show differential toxic effects of the three weeds on different invertebrates, suggesting that the distribution and abundance of aquatic invertebrates may be significantly influenced by the presence of toxic weeds along the waterway. These results add to the understanding of negative impacts of bank disturbance which leads to weed infestation of stream banks.