Conservation value of waterfalls as habitat for lotic insects of western Victoria, Australia

Abstract

ABSTRACT The conservation significance of waterfalls for insect assemblages is not well known, but there are aquatic insect species known to be waterfall specialists. If waterfalls support distinct insect assemblages, they may make a disproportionately large contribution to regional freshwater insect diversity. The aim of the present study was to determine whether waterfalls in western Victoria, Australia, support distinct insect assemblages compared with other, fast‐flowing habitat (e.g. riffles). Twelve waterfalls were sampled during autumn and winter 2009, with three positions sampled at each waterfall: the vertical rock face; directly below the waterfall rock face; and an adjacent riffle. Insect assemblages on vertical rock faces differed from those in riffles and below waterfalls. Insects positively associated with waterfall rock faces were coleopterans, plecopterans or trichopterans. Turnover (beta‐diversity) of taxa was higher among waterfall rock faces in autumn than among riffles or below waterfalls at either sampling time. The mean (± SE) number of insect taxa was greater in riffles (autumn 11 spp. ± 1.5; winter 15 ± 1.4) than rock faces (autumn 9 spp. ± 0.9; winter 7 ± 0.5). Some species were found only on waterfall rock faces. The total number of taxa was higher on waterfalls with a higher percentage cover of moss. Waterfall habitat appears to support the existence of certain insect species and may provide a refuge for rheophilic species during periods of low flow. Conservation of waterfall habitat is thus important for conserving aquatic insect diversity, and waterfall‐dependent and rheophilic taxa will be threatened by disturbances such as drought and river regulation that reduce stream flows. Environmental water allocations could be used to preserve fast‐flowing waterfall habitat, but flow requirements of waterfall insects need to be further investigated and included in river flow management.Copyright © 2012 John Wiley & Sons, Ltd.