Hydrological and substrate requirements of the thick‐shelled river mussel Unio crassus (Philipsson 1788)

Abstract

ABSTRACT1. Conservation and restoration strategies require knowledge of the autecology of target species. The thick-shelled river mussel Unio crassus is an endangered freshwater bivalve with largely unknown habitat preferences. In this study, hydrological and substrate parameters including shear stress, flow velocity and penetration resistance of substrate were examined in relation to mussel presence/absence data in six streams with recruiting and self-sustaining populations to derive information on the hydrological and substrate habitat requirements of the species. The results indicate that the hydrological and substrate characteristics of U. crassus habitat are broader than expected. In contrast to the assumption that it depends on moderate to high flows (>0.3 m s À1 ), streams with low water flow and soft substrate were also identified as suitable habitats. 6. Functional characteristics of the substrate, especially stability and areas with low shear stress (<1.5 N cm À2 ), seem to be of great importance for the persistence of the species, and monitoring protocols used at present for habitat assessment of U. crassus should be updated.

Joint species models reveal the effects of environment on community assemblage of freshwater mussels and fishes in European rivers

“…). Our results support the previous findings that M. margaritifera has a strong preference to low levels of natural phosphate concentration in undisturbed landscape (Geist & Auerswald, ; Geist, ), while U. crassus can tolerate high levels of nutrient and is likely able to persist in disturbed stream systems (Denic et al ., ; Stoeckl & Geist, ). Furthermore, the negative relationship of M. margaritifera with slope corresponds to a previous study of M. margaritifera in Northern Ireland (Wilson et al ., ).…”

Hydraulic requirements of freshwater mussels (Unionidae) and a conceptual framework for how they respond to high flows

“…() hypothesized that such areas represent places along the streambed with little to no bed mobility. Strayer () and then later Stoeckl and Geist () suggested stable areas in river systems (i.e., low entrainment potential) should be where mussels are chiefly found because individuals are not washed away during floods. Our results and those of Allen and Vaughn (), who used a similar experimental approach, generally support both hypotheses, but there were exceptions as RSS values >1 did not completely eliminate mussels.…”

“…For example, at high flows, mussel species richness and abundance are often maximized in areas where shear stress is low (Morales et al. , Gangloff and Feminella , Allen and Vaughn , Stoeckl and Geist ). In contrast, at low flows, minimum velocity and depth along with complex hydraulic variables such as Froude and Reynolds Roughness numbers are known to be predictive of mussel occupancy and abundance (Gagnon et al.…”

Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish

“…The unionoid thick‐shelled river mussel Unio crassus occurs in soft substratum and sand‐ and gravel‐rich middle watercourses of varying hydrology (Björk, ; Lopes‐Lima et al, ; Stoeckl & Geist, ) where it averages about 8 to 50 years and a maximum life‐span up to 90 years over its distribution area (Helama, Valovirta, & Nielsen, ; Hochwald, ; Lundberg & von Proschwitz, ). The mussel spawns in late spring, and parasitizes on fish species such as minnow Phoxinus phoxinus , bullhead Cottus gobio and chub Squalius cephalus for about 1 month from late spring to early summer (Hochwald, ; Lundberg, Bergengren, & von Proschwitz, ; Maaß, ; Taeubert, Gum, & Geist, ; Taeubert, Martinez, Gum, & Geist, ).…”