Scale‐dependent longitudinal patterns in mussel communities

Abstract

Summary 1. Species richness and assemblage patterns of organisms are dictated by numerous factors, probably operating at multiple scales. Freshwater mussels (Unionidae) are an endangered, speciose faunal group, making them an interesting model system to study the influence of landscape features on organisms. In addition, landscape features that influence species distributions and the scale at which the factors have the greatest impact are important issues that need to be answered to conserve freshwater mussels. 2. In this study, we quantified freshwater mussel communities at 16 sites along three mid‐sized rivers in the south‐central United States. We addressed the following questions: (i) Are there predictable longitudinal changes in mussel community composition? (ii) What landscape variables best explain shifts in community composition? and (iii) At what scale do landscape variables best predict mussel community composition? 3. After controlling for the influence of longitudinal position along the stream, we compared mussel distributions to a suite of hypothesised explanatory landscape variables across multiple scales – catchment scale (entire drainage area), buffer scale (100‐m riparian buffer of the entire catchment) and reach scale (100‐m riparian buffer extending 1 km upstream from the sampling site). 4. We found a significant and consistent longitudinal shift in dominant mussel species across all three rivers, with community composition strongly related to distance from the headwaters, which is highly correlated with stream size. After accounting for stream size, variables at the buffer scale were the best predictors of mussel community composition. After accounting for catchment position, mean channel slope was the best explanatory variable of community composition and appeared in all top candidate models at the catchment and buffer scales. Coverage of wetland and urban area were also correlated with community composition at the catchment and buffer scales. 5. Our results suggest that landscape‐scale habitat factors influence mussel community composition. Landscape features at the buffer scale performed best at determining community composition after accounting for position in the catchment; thus, further protection of riparian buffers will help to conserve mussel communities.

Modeling changes in freshwater mussel diversity in an agriculturally dominated landscape

“…Within a habitat, substrate size, shear stress, and near-riverbed turbulence are important factors to explain mussel patchiness (Strayer 1999, Brim Box et al 2002, Steuer et al 2008, Fulton et al 2010. At a spatial scale between these 2, such as the watershed, changes in mussel assemblages have been related to land use (Arbuckle and Downing 2002, Diamond et al 2002, McRae et al 2004, Poole and Downing 2004, Brown et al 2010, Hopkins and Whiles 2011, Atkinson et al 2012, channel morphology (Gangloff andFeminella 2007, Brainwood et al 2008), stream-flow stability (McRae et al 2004, Morales et al 2006), water quality, and overloading of fine sediments (see reviews by Strayer et al 2004, Downing et al 2010. However, unlike most other aquatic species, freshwater mussels also depend strongly on a separate group of animals, fishes, for recruitment and dispersal (Haag and Warren 1998, McNichols et al 2011, Schwalb et al 2011.…”

Implications of species addition and decline for nutrient dynamics in fresh waters

“…Mussel beds at this location are diverse and dense, and species composition changes longitudinally along the river (Atkinson et al 2012). Mussels at this site support primary and secondary production ( Vaughn andSpooner 2006, Spooner andVaughn 2009; Table 1).…”

“…Density and biomass (using length-mass regressions) were estimated with previously described methods (Vaughn et al 2004, Atkinson et al 2012, Spooner et al 2012. These data were combined with density data to scale biomass from quadrat to reach scale for 2010 and 2012 (Vaughn and Spooner 2006).…”

The process domains concept as a framework for fish and mussel habitat in a coastal plain river of southeastern North America

“…The cumulative impact of riparian degradation that accumulates downstream of the middle reach may lead to this geomorphic degradation and/or reduced water quality (Allan, 2004). Such land use impacts on mussel communities have been recently documented in similar-sized rivers of southeastern Oklahoma (Atkinson et al, 2012). In summary, mussel abundance and richness appear to be strongly limited by dam effects in the upper reach, communities recover in the hydrogeomorphically favorable middle reach, and then richness is again reduced by less favorable hydrogeomorphic conditions in the lower reach.…”