Biodiversity destabilizes substrates at high flows

The concept of ecosystem engineers and the relationship between biodiversity and ecosystem function have been central themes of community ecology research in the past decade. Although streams are a model system to investigate how the diversity of communities can influence physical habitats, few studies thus far have integrated these research areas. We designed an experiment to investigate how stream community structure can influence substrate stability during high flow events. Community structure was manipulated by using 8 freshwater mussel diversity treatments and two mussel density treatments. We used three species of mussels; Actinonaias ligamentina, Amblema plicata, and Quadrula pustolosa. We found that mussel density had significant stabilizing and destabilizing effects on substrate, and found that mussel species richness significantly destabilized substrates. Overall, A. ligamentina destabilized substrates relative to controls, while A. plicata and Q. pustulosa had no overall effect on substrate stability. When all three species were present, mussels had a stronger destabilizing effect on substrates than predicted additively from individual species performances. We think that the protrusion of mussel shells into the water column may increase near-bed turbulence and scouring forces, an effect that we think is strongly influenced by shell morphology and burrowing depth of mussel species.