Tuesday, May 27, 2008
233

Changes in the macroinvertebrate fauna of debris dams in three headwater streams across a gradient of drying

Amber Clarke1, P.S. Lake1, Nick R. Bond2, and Ralph Mac Nally1. (1) Australian Centre for Biodiversity, School of Biological Sciences, Monash University, Clayton, Australia, (2) School of Biological Sciences & eWater CRC, Monash University, Victoria, Australia

While flow-ecology relationships in streams are well studied, less is known about the effects of drying and drought on stream biota.  Many environmental variables have been shown to influence macroinvertebrate assemblages, however the length of the aquatic phase is emerging as a critical factor.  Drying is an important form of local and regional disturbance in Australia because freshwater systems are characterized by low total discharge, highly variable flow and both seasonal and supra-seasonal drought.  This disturbance is likely to be amplified in headwater streams because of their small size and vulnerability to climate change.  This project investigates changes in the macroinvertebrate fauna of debris dams in three headwater streams across a gradient of drying following a period of drought in Victoria, Australia lasting at least eleven years.  Taxonomic richness of macroinvertebrates was significantly different among the three streams.  As expected, a higher proportion of terrestrial taxa were found as the severity of drying increased.  Despite this, several fully aquatic taxa were found to inhabit debris dams in stream channels with a total absence of surface flow.  Debris dams may be an important refuge for macroinvertebrates in headwater streams during periods of seasonal or supra-seasonal drought.

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