Comparison of macroinvertebrate assemblages of permanent and temporary streams in an Alpine flood plain, Switzerland

Temporary streams are a common but little studied feature of alpine flood plains. We examined macroinvertebrate assemblages of temporary and permanent alpine streams in the Swiss Alps over a seasonal cycle (spring through autumn). Temporary streams contained fewer taxa and lower zoobenthos abundances than permanent streams, although within stream type variability was high. Temporary streams that dried in early summer were dominated by Chironomidae and Oligochaeta, whereas those that dried later in summer were dominated only by Chironomidae. Permanent streams were dominated by Chironomidae and Turbellaria or Chironomidae and EPT taxa. No seasonal increase in taxon richness was evident in either stream type, but taxa were replaced by other taxa over time. Chironomid assemblages had higher richness in permanent streams. and Orthocladiinae were rare in temporary streams. The life cycle of the common simuliid Prosimulium latimucro was more synchronous. and its development faster, ill temporary than permanent sites. High temperatures and low precipitation caused drought conditions in summer 2003. In one permanent stream, the assemblage was dominated by chironomids in 2002 (a normal weather year), while the turbellarian Crenobia alpina accounted for similar to 50 % of the assemblage in 2003. Temporal changes ill assemblage composition shifted 2-3 weeks earlier in 2003 compared to 2002. Development and growth of P. latimucro was faster in 2003 than in 2002. Although these temporary alpine streams displayed similar biotic characteristics to temporary streams in other biomes, they appear to be highly sensitive to inter-annual changes in climate.