Degree Name

Doctor of Philosophy


Department of Biological Sciences


The type and number of macrofauna present in streams changes markedly in space and time. Accurately and informatively describing changes in the composition of macrofaunal assemblages requires well replicated, quantitative sampling and the use of qualitative and quantitative descriptive and statistical techniques. I used a hierarchical design to quantitatively sample the benthic macroinvertebrate assemblages of pool habitats in five adjacent, temperate coastal streams of the Illawarra region of New South Wales between 1997 and 1999. Sampling was replicated spatially (3 sites on each stream) and temporally (12 sampling occasions per year). The collected macrofauna were identified to the lowest taxonomic level possible with available keys. I used quantitative and qualitative univariate and multivariate statistical techniques to describe how the type and number of macroinvertebrates I collected changed in space and time. I also used multivariate hypothesis testing techniques (Analysis of Similarities) to test hypotheses regarding how these assemblages changed over a number of temporal scales and at two relatively small spatial scales, within and among adjacent streams.

Aquatic insects dominated the diverse benthic macroinvertebrate fauna that I collected from the five study streams, with (82.7%) of individuals and 110 (82.1%) of the 134 taxa identified being insects. Dipterans (mainly the Chironomidae), and Ephemeropterans were particularly numerous. I also collected 24 non-insect taxa. Twenty taxa, mostly insects, accounted for 95.4% of the total number of individuals I collected.

I detected significant spatial variability in the composition of the assemblages I sampled. This finding represents an important demonstration of fine scale spatial variability in the macrofaunal assemblages of pool habitats in temperate Australian streams. Interestingly, the complex pattern of variability displayed by major taxonomic groups (mainly insect orders) at the finest spatial scale sampled here, within creeks, was not evident at the among creeks scale. These assemblages also exhibited considerable temporal variability. I detected differences among years, among seasons in each year, within seasons, and among this study and Gregory's (unpublished data) earlier study of the same sites. Differences among seasons were a reflection of the generally high degree of temporal variability present during the study and did not indicate specifically seasonal variability.

Abnormally severe climatic fluctuations experienced during this study appear to have been influential in structuring the macrofaunal assemblages that I sampled. I detected dramatic declines in the density of macrofauna after two flash flood events. Severe drying, which occurred during the 1997/98 El Nino induced drought, substantially altered not only the number but also the type of macrofauna I sampled. Air-breathing taxa dominated the shrinking pools of water that formed when flow ceased in late 1997. The response to drying and flooding detected here was similar to that documented for the macrofaunal assemblages of running water systems worldwide.

This study also represented the post-development sampling stage of an assymetrical Beyond-BACI impact assessment that was designed to assess the potential impact of the construction phase of a major housing development at Horsley Park on the macrofauna of two streams adjacent to the development. The assemblages of four potentially impacted sites were compared to eleven control sites to determine whether changes occurring between pre-development (Gregory - unpublished data) and postdevelopment (this study) periods indicated that an impact had occurred. The impact assessment design used to conduct this study is unique in that it contains both multiple putatively impacted and multiple control sites.

Neither the univariate or multivariate impact assessments provided evidence that an impact had occurred at any of the four putatively impacted sites. The high degree of temporal variability exhibited by these assemblages and associated with the severe climatic fluctuations that occurred during this study may have limited the study's ability to detect an impact and made a statistically valid univariate test for impact impossible. Differences in the macrofaunal composition and degree of variability exhibited by one putatively impacted site, Robin's Creek Site 1, can not be attributed to the effect of the Horsley Park housing development. Rather, they appear to reflect differences in substratum composition and flow variability between this site and all other sites I sampled. The results of this study highlight the difficulties inherent in detecting human impacts in spatially and temporally dynamic stream systems.