Abstract

Benthic macroinvertebrates are commonly used to monitor the condition of rivers and streams. Predictive models and biological objectives used in environmental policies, two tools for assessing stream condition, rely on the assumption that the communities from which the invertebrates are derived are sufficiently stable or persistent over time for valid comparisons to be made with test sites sampled years afterwards. There has only been limited testing of this in Australia and there has been no formal programme established to assess long-term changes in aquatic ecosystems. In this paper, data sets collected from the Latrobe and Yarra river systems in south-eastern Australia, sampled over periods of up to 20 years between initial and final samplings, were examined. Using multivariate analyses, it was found that stream communities were persistent at the taxonomic level of family, but significant temporal changes were apparent using species-level data. Tests of rank abundance (Friedman's and Spearman rank correlation) gave mixed results but generally lead to the same conclusions. The implications of these results are discussed with regard to changes in faunal composition, stability of rank abundances, impacts on the use of predictive models and biological objectives, and possible links to major environmental features.