Spatial habitat patterning of the freshwater pearl mussel, Margaritifera margaritifera, in the River Rede, North East England.

Abstract

Habitat degradation is prevalent in freshwater ecosystems and acts at multiple scales to impact biodiversity. It has severe consequences for the endangered freshwater pearl mussel (Margaritifera margaritifera). Due to this species’ ecological importance, preservation of the declining population on the River Rede, NE England, is of interest to conservation organisations. Physical habitat parameters in the Rede were assessed across a series of scales relevant to the species’ requirements. Water quality was assessed at the catchment scale. Depth measurements and remotely sensed data on grain size distributions were collected at the meso-scale. Substrate composition, flow type, proximity to the channel edge and adult mussel distribution data were observed at the microhabitat scale. Meso-scale and microhabitat surveys were performed within four 400 m river reaches. A significant contagious distribution of the 310 observed M. margaritifera was identified. All sampled habitat factors related significantly to mussel presence, although flow type displayed a more complex association. Logistic regression and preference modelling further allowed the species’ habitat requirements to be refined, identifying areas of preferred habitat. Mussels were distributed as a function of substrate composition and depth, primarily in areas less than 20 cm deep (above summer low flow). Areas less than 3 m from the bank, run flows, and low turbulence flow types also contributed to the definition of preferred habitat. The Rede M. margaritifera population was found to respond to habitat patchiness. This is in accordance with patchy distributions, related to habitat character, found in recruiting populations and is promising for future conservation efforts. The multiple scale approach employed here could contribute to future catchment management methods.