TROPICAL ACID STREAMS - THE CHIRONOMID (DIPTERA) RESPONSE IN NORTHERNAUSTRALIA

1. Chironomidae, sampled by interception of drifting cast pupal exuvia e, responded to inputs of acid, heavy metal-rich waters in a seasonall y flowing tropical stream in northern Australia. 2. Responses included gain of distinctive (indicative) taxa, loss of some species typical o f pristine conditions, and increase in species richness. 3. Experiment al manipulation (upstream diversion) of a mine adit entry showed that these responses were the result of change in water quality. 4. The hig her species richness at low pH, which is contrary to temperate studies , may be explained by the large tropical (Australian and south-east As ian) pool of species tolerant of naturally occurring acidic aquatic ha bitats. 5. The structure and responses of the exuvial-assessed chirono mid community matched long-term larval data.