My primary research interest is the influence of biotic and abiotic factors on the distribution, food web structure, and ecosystem processing of aquatic organisms. I currently use freshwater mussel assemblages as my target organisms to investigate these factors. Freshwater mussels are an interesting and important group to work with because they are relatively large (biomass), long lived (2 - 30+ years), sessile organisms that have unique life histories in that they use a fish host during part of their larval development. In addition, freshwater mussels are one of the most imperiled groups in North America with nearly 70% of the nearly 300 species being extinct, endangered, or of some special concern. My research interest in the role of freshwater mussels in aquatic systems can be broken down into three different aspects: distribution, food resources/food webs, and nutrient recycling. These interests are an expansion of my dissertation research investigating the role of freshwater mussels in low order streams by asking additional questions and moving into larger stream systems.
Distribution:
I am interested in the factors that influence the spatial and temporal patterns of organisms across multiple scales (i.e. watershed, stream system, stream segment, stream reach, pool/riffle and microhabitat). To do so, we have sampled streams to determine community numerical standing crop estimates, population estimates, and size frequency distributions of mussel assemblages. We are also interested in determining the fish host of several endangered and threatened mussels and relating that to the distribution of the fish host at the pool/riffle to the stream system distribution.
What are the biotic and abiotic factors that may influence freshwater mussels at a variety of scales? At the microhabitat to stream reach scale, my colloraborators and I have been investigating abiotic and biotic factors that may be important to the distribution of freshwater mussels (and other aquatic organisms) and while incorporating the size and biomass distribution of freshwater mussels across these scales. At the reach, pool/riffle and microhabitat scale, we have used spatial statistics to determine the relationship between the distribution of mussels and abiotic factors such as water depth, water velocity, and substrate composition and biotic factors such as other macro-invertebrates and biofilm communities. At the stream system and stream segment scale, I am collaborating with another mussel biologist and two geomorphologists looking at stream segment and stream reach geomorphological features that may influence mussel distribution and abundance in high-order lowland streams. In the future, we plan to use GIS technology more in depth to address some of these questions at larger spatial scales and involving multiple spatial scales.
Food Resource/FoodWebs:
I am also interested in determining the food composition of freshwater mussels in terms of quality (e.g. composition) and quantity (e.g. nutrients). What is the food resource of freshwater mussels and what is its quality and quantity? To answer these questions my collaborators and I have used multiple methods to determine the food quality and quantity such as nutrient analysis (CNP), organics analysis (NVSS/AFDM), C and N stable isotopes, chlorophyll concentrations, microbial biomass and community structure, and mussel gut fluid enzyme analysis. During previous work, we have found that stable isotopes do not provide the appropriate resolution to pinpoint the source of freshwater mussel food. Therefore, I plan to continue research on identifying the food source(s) of freshwater mussels by radiolabeling autotrophic and heterotrophic microbes and feeding labeled microbes to freshwater mussels in controlled laboratory settings to determine if mussels incorporate microbial cells, microbial exopolymers, both, or neither. I also plan to continue my collaboration with a microbial ecologist for the seston microbial biomass and community structure. This work has food web implications determining which trophic level freshwater mussels feed and also can be used to determine if different species of mussels are using the same food source (functional redundancy) or partitioning the resources. Our previous research using stable isotopes and gut fluid enzyme activities showed that two co-occurring species of mussels had similar gut fluid enzymes and stable isotope signatures indicating that they were using a similar low protein diet as indicated by high protease activity. In addition to radiolabeling, we plan to move down the stream continuum from small to large streams to determine if and how mussel food use changes down the continuum.
Ecosystem Processes/Nutrient Recycling:
A third area I am interested in is ecological stoichiomety and measuring the rates and ratios that freshwater mussels recycle food (seston) nutrients to soluble and fecal nutrients. This aspect integrates my first two research areas by determining the influence of freshwater mussel nutrient recycling.
Are there spatial and temporal patterns in nutrient recycling by individual mussel species?
Since seston (food source) quality and quantity change from season to season, event to event, and from site to site, it is important to know and understand the spatial and temporal patterns of mussel nutrient recycling rates and ratios.
Are there taxonomic differences in nutrient recycling?
Because species have different size structure and nutrient composition of tissues, the concentrations, ratios, and demand for nutrients are different. Therefore, it is possible two freshwater mussels feeding on the same general resource with the same nutrient composition may assimilate different amounts of nutrients due to their body content and demand, i.e. they are stoichiometrically different. The implications of differences in demand will result in different rates and ratios of soluble and fecal nutrients being recycled into the water column. Therefore, even though mussels are feeding on similar food items, they may recycle the nutrients in different rates and ratios, providing different ecosystem functions, providing for a unique ecosystem function. Conversely, two or more species may be redundant in recycling nutrients, providing for more stability in the system if one or more species should become extinct.
What is the significance of nutrient recycling of mussels in terms of their contribution to nutrient fluxes in streams and to meeting the demand for nutrients by other organisms such as primary producers or heterotrophic bacteria?
During my dissertation work, I found that the mussel assemblage in the Ouachita River headwaters (Arkansas) provided ~10% of the N and P flux of the stream during low flow conditions in the fall and that nutrients were limiting to primary producer growth during this time. The next step in determining the role of mussels in streams is to conduct nutrient spiraling experiments in reaches with and without mussels. I predict that reaches without mussels will have shorter nutrient spirals than those with mussels providing nutrients to the reach. Furthermore, I will determine the demand for these nutrients by incorporating primary production and possibly heterotrophic production estimates.
Ultimately, this research can be put into the context of understanding how freshwater mussel nutrient recycling influences population, community, and ecosystem processes of other aquatic organisms as freshwater mussel biomass and assemblage composition change from small to large streams. Furthermore, all of this information will lead to a better understanding of basic mussel biology and ecology for better conservation and management of this imperiled fauna.
Secondary Interest:
Two secondary research areas that I have been involved with for several years include molecular ecology and biomonitoring / biosurveying. My collaborators and I have used molecular ecology to investigate genetic variation at the population and species levels. For example, I have been part of a collaborative team determining the genetic structure of freshwater mussel, mayfly and caddisfly populations. In addition to population level questions, I have also collaborated on the development of molecular markers or keys to identify morphologically cryptic midge flies, important indicators of water quality. I am also part of a collaborative team funded to use molecular and morphological techniques to determine the conservation status (i.e. species determinations) of Lampsilinae mussel taxa of Arkansas streams. My other secondary research interest, biomonitoring, uses fish and aquatic macro-invertebrate richness, abundance, community structure to determine biological integrity of stream communities and water quality.
16 July 2003
