Macroinvertebrate sampling methods for lowland Australian rivers

The macroinvertebrate communities of large lowland rivers are little studied, partly because of the lack of suitable collection methods. In this study, four macroinvertebrate collecting methods: two artificial substrates, snags and onion-bag baskets; air-lift sampling of soft sediments; and sweep net sampling of edges (including macrophyte stands where they occurred) were trialed in four lowland rivers within the Murray-Darling Basin in southeastern Australia. The subset of the macroinvertebrate community collected by each method was determined and the number of replicates needed for a given degree of precision was estimated. Sweep samples were dominated by hemipterans and were the best method for collecting decapods and beetles. The other three methods collected mostly chironomid, caenid mayfly and ecnomid caddisfly larvae and oligochaetes. The artificial snag and basket samples had surprisingly similar compositions but the snag samples did contain some taxa, such as Dicrotendipes, Paratanytarsus and wood-boring beetles, that basket samples did not. The densities of macroinvertebrates collected by artificial snags, sweep and air-lift samples were similar. We concluded that each of the methods could be used in lowland rivers but for different purposes. For example, if quantitative data are needed, only air-lifts and snags would be appropriate, whereas if a species list is required, snags and sweeps would be most effective.