General patterns of macrozoobenthos distribution in two rivers basins of the Khabarovsky Krai (Far East of Russia)

This article analyses the distribution patterns of macrozoobenthos in watercourses of the basins of the River Bajal and River Anyuy (Khabarovsky Krai, Russia) on the territories of the Bajal Sanctuary and Anyuy National Park. The distance-based linear models (DistLM) method was used to estimate the proportion of distribution of macroinvertebrates explained by the factors considered in the study (river basin, current velocity, substrate, channel width, temperature, pH). All of these factors contributed significantly, together explaining about one-third of the variability of macroinvertebrate distribution. The main explanatory factors were river basin and substrate (9.3% and 10.5%, respectively), as well as the current velocity (5.7%). Based on the cluster analysis, eight statistically significant groups of samples on the basis of similarity of taxonomic composition were identified. A set of indicator taxa was determined for each group and their indicator values were found. Using the Kruskal-Wallis analysis, the environmental factors significantly differing between the obtained groups and subgroups were singled out. There are well-defined patterns in the confinement of taxonomic complexes to certain habitats. Local environmental factors are the strong filter influencing the formation of taxonomic communities. The factor of belonging to the river basin also plays a significant role in the formation of invertebrate communities, which should be considered in the planning of monitoring studies on a large spatial scale. However, the distinguished groups and subgroups are characterised by a low level of internal similarity. Only about a quarter of the total species number belongs to indicator taxa, and samples do not form discrete clusters with obvious hiatus on the ordination diagram. The longitudinal distribution of macroinvertebrates for each river can be characterised as a punctuated gradient.