Dynamics of habitats and macroinvertebrate assemblages in rivers of the Australian dry tropics


R. G. Pearson, School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811, Australia.
E-mail: richard.pearson@jcu.edu.au


1. The dry tropics are characterised by episodic summer rainfall such that the majority of annual river flow occurs in a short period of time. This dryland hydrological cycle leads to variably connected channels and waterholes along the length of a river bed.

2. We investigated the seasonal changes in biophysical characteristics and macroinvertebrate assemblage composition in dry-tropics rivers at 15 sites on four rivers, each sampled five times (representing one annual hydrological cycle), in the Burdekin catchment, north Queensland, Australia.

3. Assemblages and their temporal trajectories differed among seasons, sites and habitats, even within the same habitat and/or river. Wet season flooding did not appear to ‘reset’ assemblages, with post-wet season assemblages differing between years.

4. We found no consistent pattern in taxonomic richness over time, and sites within rivers showed no consistent convergence or divergence (i.e. turnover) in macroinvertebrate assemblage composition. However, biophysical variables associated with the rigours of the late dry season had significant effects on macroinvertebrate assemblages, highlighting the variable and often harsh conditions of dry-tropics rivers. Underlying these patterns were different resistance and resilience traits of invertebrates (such as colonisation and establishment abilities), as well as the local-scale effects of biophysical variables.

5. The dynamic nature of dryland rivers presents major challenges to monitoring programmes, and our results suggest a more complex scenario for monitoring and management than previously described.