Torrenticolous macroinvertebrate community response to tropical stream water diversions

A legacy of water diversion exists in Hawaii, where water that originally supported native population needs has been co-opted for development, agriculture and tourism.  This change in water usage has resulted in up to 97% of baseflow diversion from some Hawaiian streams. This study assesses the impact of reduced flow from water diversion on instream cascade and coupled riparian insect communities of four West Maui streams.  Cascades were characterized by shallow, high velocity flow over large boulders and support several endemic insect species.  In August 2007 and May 2008, three cascade microhabitats were sampled in upstream and downstream reaches of the first water diversion: benthic, amphibious and aerial microhabitats. Riparian pantraps were set within the same reach. In 2008, two-way ANOVA indicated significant differences in diversity among streams for both cascade (F=3.81, df=3, p=0.0171) and amphibious microhabitats (F=4.319, df=3, p=0.0099).  Significant density differences among streams were also found for the amphibious microhabitat (F=5.994, df=3, p=0.0018), in addition to a significant interaction between stream and upstream or downstream locations (F=4.641, df=3, p=0.0071). Riparian communities were highly variable. These data provide understanding of endemic insect community structure changes in cascade habitats that are often neglected in assessing overall effects of water withdrawal.