Riparian eucalypts and willows and their significance for aquatic invertebrates in the River Murray, South Australia

The exotic weeping willow Salix babylonica is compared to the native river redgum Eucalyptus camaldulensis as a modifier of invertebrate habitats in the littoral zone of the River Murray. Net samples indicated minor differences in the composition and diversity of invertebrate assemblages at three willow and three redgum sites. Packs of redgum and willow leaves in mesh bags were used to assess rates of leaf breakdown. Willow leaves (half-life 14-26 days) decomposed more quickly than redgum leaves (27-50 days), although they were affected more by physical abrasion than biological decomposition. Willow leaves in 2.5-cm mesh bags lost more weight than those in 300 μm bags, indicating that feeding by invertebrates was also a factor. Microbial activity was the main agent of weight loss in redgum leaves. After 8 weeks' incubation there were distinctive invertebrate assemblages associated with leaf packs at redgum and willow sites. At redgum sites, but not willow sites, there were different assemblages in willow and redgum packs. Feeding trials showed that the common atyid shrimp Paratya australiensis preferred microorganism-colonized redgum leaves over colonized willow leaves and fresh leaves, although this may reflect preferences for the associated biofilms. Leaf biofilms at redgum sites had relatively high density and diversity of diatoms; redgum leaves generally attracted greater densities of bacteria, and fungi were not prominent on either leaf type. © 1997 John Wiley & Sons, Ltd