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The effects of blackberry (Rubus fruticosus L. agg.) leaf litter on aquatic macroinvertebrates in two urban streams

Wild, Suzi (2002) The effects of blackberry (Rubus fruticosus L. agg.) leaf litter on aquatic macroinvertebrates in two urban streams. Honours thesis, Murdoch University.

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The processing of leaf litter in streams plays a key role in the cycling of energy in aquatic ecosystems. It has been suggested that the invasion of the riparian zone by exotic species such as European willow (Salix babylonica), may affect stream macroinvertebrate communities through the timing of leaf fall, litter quality and litter breakdown rates. This study investigated the effects of European blackberry (Rubus fruticosus), a highly invasive weed of the riparian zone, on macroinvertebrate assemblages in two urban streams, Bannister Creek and Bull Creek, on the Swan Coastal Plain.

The impact of riparian vegetation on macroinvertebrates was investigated using two methods; (A) sweep net samples were collected over two seasons to determine differences in macroinvertebrate assemblages between stream reaches with blackberry or native vegetation in the adjacent riparian zone. (B) breakdown rates and colonisation of blackberry and eucalypt (Eucalyptus rudis) were used to assess preferences of macroinvertebrates for either blackberry or eucalypt as a food source. Furthermore, the relative abundance of the freshwater crayfish Cherax quinquecarinatus at sites with blackberry and native vegetation was quantified and laboratory feeding experiments were conducted to determine preferences of C. quinquecarinatus for either blackberry or eucalypt leaves.

No significant differences were found in macroinvertebrate assemblages between reaches with either blackberry or native riparian vegetation at both Bannister Creek and Bull Creek. However, there was a trend for lower species richness at the sites with blackberry in the riparian zone. The richness of taxa colonising leaf bags containing blackberry and eucalypt leaves was not significantly different at either stream. However, the results indicated a paucity of shredder fauna at Bannister Creek suggesting macroinvertebrates were playing a minor role in leaf litter breakdown.

At Bull Creek, the relative abundance of the fresh water crayfish C. quinquecarinatus, an important shredder, was significantly higher in the blackberry site. The high abundance of C. quinquecarinatus at two of the sites resulted in significantly higher rates of blackberry leaf breakdown. Furthermore, C. quinquecarinatus exhibited a preference for blackberry leaf litter in laboratory experiments. These results suggest that this species plays a significant role in the processing of blackberry leaf litter at Bull Creek.

The removal of blackberry is often a major goal of stream restoration projects, however, this study suggests that in some situations blackberry may contribute significantly to energy cycling in stream ecosystems and its removal should be undertaken with caution.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Environmental Science
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Davis, Jenny and Hobbs, Richard
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