Trends of macroinvertebrate community structure in glacier-fed rivers in relation to environmental conditions: a synthesis

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models. 2. Using this information, and data from other recent studies of glacier-fed rivers, a modified conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate fan-Lilies and subfamilies as determined by maximum water temperature (T-max) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure. 3. Where maximum water temperature is below 2 degreesC, Diamesinae chironomids are typically the sole inhabitants, but where T-max > 2 degreesC but C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 degreesC Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe. 4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period. 5. Dispersal constraints influence macroinvertebrate assemblages of many glacier-fed rivers located on islands and in some alpine areas.