Patterns of Freshwater Mussel Distribution Upstream and Downstream of Tributary Confluences in the Lower Grand River
Location
Hager-Lubbers Exhibition Hall
Description
PURPOSE: Freshwater mussels are ecosystem engineers and keystone species, vital to stream function yet are among the most imperiled group of freshwater fauna. Examining how unionid assemblages are influenced by specific watershed features is critical to conservation and management. Stream confluences often represent ecological hotspots, yet unionid associations with this feature are understudied. SUBJECTS: 1,647 individual unionids were collected from 19 sites. METHODS AND MATERIALS: We collected and analyzed data for freshwater mussels, water quality, habitat, and food resources via semi-quantitative and quantitative methods along an upstream-downstream gradients at tributary confluences in the lower Grand River, Michigan. ANALYSIS: Statistical analysis of mussel and microhabitat data was performed in R studio via multiple parametric and non-parametric univariate tests, NMDS ordination and MRPP, and generalized-linear mixed modeling. RESULTS: Unionid density, richness, and diversity were greater upstream than downstream of confluences. Significant gradient effects were found upstream but not downstream. Unionid density and richness increased along an upstream gradient. Assemblage compositions were distinctly different upstream and downstream of confluence effects. Water depth, Corbicula fluminea abundance, benthic velocity, and gravel embeddedness were important predictor variables of mussel assemblages surrounding tributary mouths. These variables differed between upstream and downstream but did not differ along a longitudinal gradient. CONCLUSIONS: Tributaries represent complex and dynamic areas of stream systems that are influenced by a variety of watershed-level and local influences. Mussel occupation of tributary confluences seems to be a product of local patches of suitable habitat and conditions more than association to confluence effects.
Patterns of Freshwater Mussel Distribution Upstream and Downstream of Tributary Confluences in the Lower Grand River
Hager-Lubbers Exhibition Hall
PURPOSE: Freshwater mussels are ecosystem engineers and keystone species, vital to stream function yet are among the most imperiled group of freshwater fauna. Examining how unionid assemblages are influenced by specific watershed features is critical to conservation and management. Stream confluences often represent ecological hotspots, yet unionid associations with this feature are understudied. SUBJECTS: 1,647 individual unionids were collected from 19 sites. METHODS AND MATERIALS: We collected and analyzed data for freshwater mussels, water quality, habitat, and food resources via semi-quantitative and quantitative methods along an upstream-downstream gradients at tributary confluences in the lower Grand River, Michigan. ANALYSIS: Statistical analysis of mussel and microhabitat data was performed in R studio via multiple parametric and non-parametric univariate tests, NMDS ordination and MRPP, and generalized-linear mixed modeling. RESULTS: Unionid density, richness, and diversity were greater upstream than downstream of confluences. Significant gradient effects were found upstream but not downstream. Unionid density and richness increased along an upstream gradient. Assemblage compositions were distinctly different upstream and downstream of confluence effects. Water depth, Corbicula fluminea abundance, benthic velocity, and gravel embeddedness were important predictor variables of mussel assemblages surrounding tributary mouths. These variables differed between upstream and downstream but did not differ along a longitudinal gradient. CONCLUSIONS: Tributaries represent complex and dynamic areas of stream systems that are influenced by a variety of watershed-level and local influences. Mussel occupation of tributary confluences seems to be a product of local patches of suitable habitat and conditions more than association to confluence effects.