Benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics: patterns in abundance and diversity

We studied variation in benthic macrocrustacean and insect assemblages in relation to spring habitat characteristics in six springs located in a single groundwater area in south-west Finland. We defined five habitat types in the studied springs according to water flow and benthic substrate characteristicsminerogenic brooks, organogenic brooks, helocrenes, floating moss carpets and limnocrene pools. Most studied invertebrate orders, as well as individual taxa, showed differences in relative abundances between the habitat types, but the most common taxa occurred in all springs and habitat types. The studied macroinvertebrates were most abundant in the moss carpet sites and least abundant in the pool sites, but the difference was not statistically significant. We did not observe significant differences in mean taxonomic richness per sample between habitat classes. The observed taxonomic richness in pooled samples of habitat classes was highest in moss carpet habitat and lowest in pool habitat, and the rarefied richness estimate was lowest in pool habitat. Benthic macrocrustacean and insect assemblages varied more between habitat types than between individual springs. In an Nonmetric Multidimensional Scaling ordination analysis, spring brook sites were separated from the moss carpet and pool sites, whereas helocrene sites were widely scattered among sites in other habitat classes. The strongest ecological gradients were related to water flow and the presence of minerogenic substrate, separating lentic and lotic habitats. Abundances of moss and coarse detritus accounted for most of the within-class variation. We identified several indicator species for minerogenic and organogenic brooks and for moss carpet and pool habitats, but none for the helocrenes. We found several occurrences of two crenobiont insect species considered threatened in Finland. We suggest that combined studies on macroinvertebrate and bryophyte assemblages would be a powerful approach in assessing the biodiversity of springs.