Patterns of invertebrate diversity in streams and freshwater springs in Northern Spain

Abstract

Invertebrate diversity patterns were examined in six rheocrene springs and six nearby, runoff-fed streams in Cantabria, Northern Spain. Periphyton biomass, organic matter and biomass of moss were always higher in springs than streams. Species densities (number of species/area) and rarified species richness (number of species/number of individuals) were lower and invertebrate densities greater in spring habitats. Of 22 variables chlorophyll-a was the best predictor of species richness, whereas total organic matter was the best predictor of invertebrate density, although neither relationship was strong. Spring habitats had invertebrate communities dominated by non-insect taxa (e. g., Echinogammarus, and Hydrobiidae and Neritidae snails), in contrast to the insect dominated communities in runoff-fed streams (e. g., Baetis, Ecdyonurus, Elmis, Prosimulium, Scirtes and Chironomidae). Echinogammarus had the highest densities in springs; an order of magnitude greater than any other taxa. The effects of biotic processes, such as predation from Echinogammarus on community structure may be more marked in springs because predated individuals cannot be as readily replaced by drifting animals from upstream reaches. The reduced diversity in springs compared to streams could be a result of several factors including increased predation from animals such as Echinogammarus or the unusually constant thermal characteristics.