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PUBLIC ABSTRACT: Freshwater mussels are the most threatened taxonomic group in North America with extinction rates that exceed those of many species found in both terrestrial and freshwater ecosystems including fish, birds, and amphibians. Part of the reason that mussels are so threatened is because their larvae are parasitic on fish, making the completion of their life cycle dependent upon healthy fish populations. The imperilment of freshwater mussels is a cause for concern because of the benefits that mussels provide to freshwater ecosystems including habitat enhancement, substratum stabilization, nutrient cycling, and water clarification. Restoration and conservation efforts targeting western freshwater mussels have been constrained by a lack of information about habitat requirements. As a result, I was interested in investigating how mussel density and distribution varied with respect to both biotic and abiotic factors at multiple spatial scales. I used a modeling approach to determine which habitat parameters were associated with mussel distribution and density throughout a 55-kilometer (km) of the Middle Fork John Day River, Oregon. Parameters included physical stream habitat characteristics, host fish presence, water quality measures, and mussel food quantity and quality. Results of this analysis indicated that mussels responded to the hierarchical arrangement of physical habitat from the valley segment to the channel unit and that higher densities of mussels were found in parts of the river that were more stable at high flows. I found that the distribution of host fish was not limiting to mussels in this river system and that the overall physical habitat characteristics such as gravel size, silt cover, and woody debris were most important to explaining mussel density and distribution. These results will assist mussel restoration efforts by providing specific guidance about the types of habitat conditions that are suitable for mussels at multiple spatial scales.
Pearly mussels (Unionoidea) live in lakes, rivers, and streams around the world. These bivalves play important roles in freshwater ecosystems and were once both culturally and economically valuable as sources of food, pearls, and mother-of-pearl. Today, however, hundreds of species of these mussels are extinct or endangered. David L. Strayer provides a critical synthesis of the factors that control the distribution and abundance of pearly mussels. Using empirical analyses and models, he assesses the effects of dispersal, habitat quality, availability of fish hosts, adequate food, predators, and parasites. He also addresses conservation issues that apply to other inhabitants of fresh waters around the globe and other pressing issues in contemporary ecology.
As filter feeders, North American freshwater mussels (Unionoida) are important for maintaining the quality of freshwater ecosystems. While North America has the most unionid species in the world, land-use modifications, impoundment of rivers, and invasive species have made unionids some of the most imperiled organisms in North America. It is therefore imperative that we thoroughly examine and understand unionid population and habitat characteristics to better conserve this species and maintain aquatic biodiversity. Macalester College's Aquatic Ecology Lab has monitored unionids in the St. Croix River for almost twenty years. Using their database, I completed a retrospective study investigating habitat and biogeographic variables and their influence associated with mussel distributions. Trends in the data indicated that higher mussel densities were associated with areas of Sub-critical flow (low Froude number), low shear stress, and coarse substrate but not with water depth & velocity. Also mussel species richness declined with greater distance upstream from the Mississippi. While both biogeographic and habitat factors were indicated as significant in determining mussel distributions (i.e. p-value
A new method to map freshwater mussel habitats was developed and tested in the Big South Fork National River and Recreation Area (BISO). The procedure involved using an Underwater Video Mapping System (UVMS) to record river substrate information in conjunction with Global Positioning System (GPS) to create geo-referenced video footage. Simultaneously, the river surface features were video-recorded using a similar geo-referenced video mapping system. Images from both videos were evaluated and used to produce habitat classifications in a Geographic Information System (GIS) format. The focus of the project was on mapping attributes in the river that are significant to freshwater mussel habitats. These attributes characterize river sections as either favorable or unfavorable to freshwater mussel populations. The attributes specifically selected were based on the habitat suitability needs of five federally endangered species of mussels that exist in BISO. By developing a GIS map of the habitat attributes, biologists knowledgeable in the needs of both adult and juvenile mussels of various species can identify locations suitable for augmenting mussel populations and habitat health. This project was conducted in 2004 and involved mapping river habitat in over 27.8 km (17.3 mi) of river in BISO. There are 182.2 km (113.2 mi) of river within BISO, so this assessment encompasses 15 % of the river mileage within the park. Most previous mussel studies have not evaluated long segments of river habitat. This work provides continuous mapping of several contiguous kilometers of river. The findings were stored in a GIS format and used to identify locations for possible re-introduction and management of mussels. Three sections of river in BISO were evaluated. The river segments were chosen to represent river conditions found in different parts of the park. The three sections studied were the Clear Fork Section in the southwest corner of BISO (in TN), Alum Ford Section at the northern park border (in KY), and the Leatherwood Ford Section in the middle of the park (in TN). In-stream physical habitat characteristics were captured by video cameras at the water surface and underwater. The images were then classified into habitat categories that are either favorable or unfavorable to the mussel populations. Applying UVMS technology was a unique way to gather habitat attributes and create maps. Five primary habitat attributes were evaluated. These attributes were: flow characteristics of the river (pool, run, and riffle), river depth, substrate classification, embeddedness of the substrate, and the presence of coal contamination. The UVMS above-water camera system was very successful in evaluating the flow characteristics of the river (distinguishing between pool, run, and riffle) in the three study sections in BISO. The UVMS underwater video footage was used to classify substrate characteristics. The evaluation for the presence of coal deposits indicated the Clear Fork Section did not have coal deposits in the video footage, whereas the Leatherwood Ford and Alum Ford sections had a significant amount of coal in the river. The UVMS was successful at locating areas of possible habitat for the five mussel species of interest. These areas are mostly in clusters along the river. There is significant overlap in the suitable habitat areas identified among the five species, largely because several of the species prefer similar habitat attributes. Four of the species require riffles for optimal habitat, and the flow characteristics in the Clear Fork and Leatherwood Ford sections provided this type of habitat. The other species was a pool-loving species, which had more optimal habitat in the pool segments in the Leatherwood Ford Section. The Alum Ford Section did not have any suitable mussel habitat because the impounded river forms a reservoir. The intermittent substrate classification points on the lake bottom showed continuous silt, which does not provide suitable habitat for any of the five species of endangered mussels. Out of the total 1,207 sites evaluated for habitat suitability, the majority were unsuitable as mussel habitat. The total number of suitable habitat sites identified per species ranged from 109 to 548 (this is the combined total for optimum, suboptimum and marginally suitable habitat). Mussels are very specific in terms of the habitat they thrive in, so a method to systematically identify these locations is a valuable tool. Overall very few areas of optimal habitat were identified. For the four species that thrive in riffle habitats, two (or less) optimal habitat sites were identified per species. The fifth species, the Cumberland Elktoe, thrives in pools. Over the length of the mapped rivers there was considerably more length of pool than riffle, so there were more opportunities for desirable habitat for this pool-loving species; 19 optimal habitat sites were identified. When the habitat criteria were expanded to encompass suboptimal and marginal criteria, the number of suitable habitat sites increased dramatically for all of the species. For each of the four riffle-loving species the expanded criteria identified suitable habitat in approximately 10% of the classified points. For the pool-loving Cumberland Elktoe, the expanded criteria identified suitable habitat in almost 50% of the classified points.
"By identifying relationships with abiotic and biotic factors, output from species distribution models can help to identify the boundaries of aquatic species at risk critical habitat, direct inventories, and define the spatial units for long-term population monitoring. In this study, we tested whether SDMs can be developed from existing southern Ontario occurrence data for five mussel species at risk using MaxEnt software, a program for modelling species distributions with presence-only species records. Models were built using species presence and abiotic attribute data for the Ausable, Bayfield, Grand, Thames, and Sydenham rivers. Abiotic attributes included: channel slope, riparian and catchment forest cover, summer water temperature, surficial geology, and upstream catchment area. Attributes were based on the provincial Aquatic Ecosystem Classification (AEC) scheme. Strongly supported distribution models were developed for all five mussel species, with 2 to 4 influential predictor variables being identified for each species. Predictors identified consistently across species as influencing habitat suitability were summer water temperature and upstream contributing area. Other informative variables (i.e., geology and tree cover) were only identified for more widespread species (e.g., Wavy-rayed Lampmussel). The number of informative predictor variables for rarer species (e.g., Fawnsfoot) may be limited by the small number of species records, which could be addressed through future inventories. Incorporating the influence of anthropogenic stressors and host fish availability would also improve MaxEnt models but does require the compilation of additional databases"--Abstract, page vi.
The objectives of this study were to determine the importance of a variety of physical and chemical habitat variables, and host fish populations, to the mussel community in Sinking Creek, a fourth order tributary to the Rockcastle River in Laurel County. Eight species of mussels inhabit Sinking Creek, including the federally endangered Villosa trabalis and Alasmidonta atropurpurea. Mussels were sampled, fish collected and physical and chemical habitat variables measured at eleven sites. Relationships among physical and chemical variables with the mussel community and relationships between mussel and fish community composition were determined by testing for correlations between distance matrices. Several habitat variables were found to be correlated with mussel community composition, i.e., flow, temperature, percent canopy, turbidity, and acidity. No correlation was found between habitat variables and fish populations. Of note was that only two specimens of Alasmidonta atropurpurea were collected during the study (July-September 2002).