Inter-annual patterns in macroinvertebrate communities of wilderness streams in Idaho, USA

This study examined the inter-annual variation in macroinvertebrate assembl ages in six wilderness streams in central Idaho over a 6-year period (1990- 1995). Benthic macroinvertebrates and associated environmental correlates w ere sampled during baseflow each summer. Little environmental change, as as sessed using coefficients of variation (CVs) for substrate size and embedde dness, width, depth and periphyton standing crops, occurred in the streams over the period of study. There was also little temporal change in macroinv ertebrate assemblages based on the relative abundance of the 10 most abunda nt taxa, all shredder taxa and all plecopteran taxa. CVs for individual tax a were substantially greater than those of most community measures, with ra re taxa contributing 30-50% of the variation for any one stream. Frequency distributions for taxa CVs excluding rare taxa were more normally distribut ed. Differences in assemblage structure among streams were attributed to st ream size (shift in shredder assemblages) and temperature (shift in plecopt eran taxa). These data indicate a long-term (multi-year) persistence in the macroinvertebrate composition of these pristine streams, thus supporting t he premise that such streams are excellent references for use in long-term biomonitoring programs.