Environmental harshness mediates the quality of periphyton and chironomid body mass in alpine streams

Abstract

Glacier retreat alters physical and chemical characteristics and biological communities of glacier-fed streams. Functional relationships, including effects of different food-source qualities on the density and biomass of primary consumers, are insufficiently known in alpine and subalpine headwaters. We measured: 1) the relative abundance of diatoms 1 chrysophytes, green algae, and cyanobacteria in the periphyton and assemblage patterns of the 2 dominant chironomid subfamilies, Diamesinae and Orthocladiinae, and 2) differences in chironomid body mass as an unexpected response to living conditions in harsh alpine stream ecosystems. Diatoms 1 chrysophytes dominated in harsh environments, and cyanobacteria were abundant in more benign streams. Patterns in algal dominance corresponded to differences in individual body mass of Diamesinae and Orthocladiinae among streams. Body mass of glacial-river specialists Diamesa steinboecki and Diamesa latitarsis gr. was higher in harsh than in benign streams, but other Diamesinae and Orthocladiinae biomass did not differ between harsh or less harsh conditions. Plausible explanations include higher nutritional quality of algal classes in periphyton and less competition for specialists in harsh than in benign streams. Our results indicate that harsh environmental conditions, such as low temperatures and high turbidity, lead to lower taxon numbers and food quality and that food quality influences invertebrate occurrence and body mass in alpine and subalpine headwater streams. Closely related species respond differently to specific environmental conditions and may perform differing functions. This result widens our general understanding of climate-change effects on alpine stream ecosystems and provides additional explanations for species abilities and performance.