1. Glacier-fed streams are characterised by low spatial but high temporal heterogeneity, manifested in seasonal and diurnal discharge and suspended sediment peaks induced by glacial runoff. These streams shelter macroinvertebrate communities adapted to such harsh environmental conditions. Studies relating macroinvertebrate traits to environmental conditions in glacial streams could provide important insights into the structure and function of glacial stream communities.
2. From data collected in three glacial streams from the central Swiss and southern French Alps, we analysed the relationships among six biological traits to define five groups of macroinvertebrate taxa with similar suites of traits.
3. The longitudinal distribution of the five groups and of individual traits was analysed, as well as their variation according to a glaciality index combining water temperature, conductivity, suspended solids and substrate stability.
4. The trait diversity along the three streams showed a strong upstream-downstream gradient. The upper reaches were dominated by a single group of taxa characterised by small, crawling, deposit feeders. The other trait-based groups appeared progressively downstream.
5. Changes in the relative frequency of trait-based groups along the glaciality gradient highlighted the dominance of all-rounder resistant/resilient traits in the three streams and confirmed that environmental conditions in the glacial streams are too harsh or uniform to allow macroinvertebrate communities to develop alternative suites of traits. The findings are discussed in relation to the question of trait coding in the available literature.