Hydrology, hydraulics and scale influence macroinvertebrate responses to disturbance in tropical streams

Despite much research on the influence of disturbance on stream macroinvertebrates, comparative information on tropical streams is limited. We assessed disturbance influence on assemblages under different conditions of hydrology (aseasonal and seasonal) and hydraulics (pools, riffles and stream morphology) by sampling a stream in the Australian Wet Tropics (AWT) pre- and post-flood, and by undertaking experiments at whole-riffle and single-stone scales in several streams in the AWT and Papua New Guinea (PNG). The fauna was very mobile in all streams, facilitating recolonisation. Resilience (recovery) was strongly related to scale - rapid in single-stone experiments (2-4 d) and least following whole-stream disturbance (similar to 45 d, comparable with some temperate systems), indicating the importance of scale in understanding disturbance. Local undisturbed patches and pools acted as refugia and provided colonists at least partly via drift. The presence of all life stages of most species through the year and rapid development would facilitate recovery. Multiple disturbances had similar impact to single events, resulting in a reduced but resilient fauna. Resilience was not greatly different in more regularly disturbed sites, but richness was lower in PNG than AWT possibly due to their different disturbance regimes. Disturbance selects a sustained fauna that is resilient (or tuned) to the prevailing disturbance regime.