Trophic Roles and Ecological Functions Provided by a Multi-Species Assemblage of Freshwater Mussels

EPA Grant Number: FP917377
Title: Trophic Roles and Ecological Functions Provided by a Multi-Species Assemblage of Freshwater Mussels
Investigators: Atkinson, Carla L
Institution: University of Oklahoma
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2011 through August 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Aquatic Systems Ecology


Complex feedback interactions within communities can maintain processes that ensure ecosystem services, including ecosystem processes that maintain clean water. Without these complex multi-step pathways, the flux of nutrients and materials can destabilize an ecosystem leading to unsustainable and undesired ecosystem response. Consequently, research on the nutrient processing of the speciose assemblages of freshwater mussels has significant implications for key regulating ecological processes in stream systems and will inform the conservation planning of these highly endangered groups. This research project will investigate the roles of diverse freshwater mussel assemblages in river food webs and nutrient cycling via these critical filter-feeding invertebrates.


Nutrient limitation is a key factor that structures biotic interactions within ecosystems. In stream environments, nutrients are taken up by organisms and cycled through the system downstream. Organisms like freshwater mussels may have a strong influence on nutrient cycling and alter ecosystem dynamics. Alteration of the nutrients in the environment influenced by large aggregations of mussels will be studied. This research will combine information on trophic partitioning of a diverse assemblage of freshwater mussels and relate the fixed internal nutrient requirements to the ratios of nutrients these organisms release back into the stream environment. This approach combines Physiology, Biogeochemistry and Ecosystem Ecology. During the summer of 2010, nutrient diffusing substrates (NDS) were used to determine the nutrients that limit primary production in areas of high mussel densities and no mussels. This was used to determine how mussels may influence nutrient dynamics. Controlled mesocosm experiments with NDS will further elucidate how mussels change nutrient dynamics. To investigate the diet of freshwater mussels, natural abundance stable isotopes (13C and 15N), a very powerful approach in determining patterns of energy flow and food web linkages in ecosystems, will be incorporated with stoichiometric analysis (%C, %N, %P and the molar ratios of these elements), available food resources and their excretion products to construct a mass balance model of nutrient flux. The combination of diet analysis and the stoichiometric analysis will lead to further understanding of the dietary requirements of multiple species of freshwater mussels. This research will lead to further understanding of the requirements of organisms and how this influences their environment.

Expected Results:

With an estimate of the impact freshwater mussels have on nutrient flux, this research will allow quantification of an important ecosystem function mussels provide. Initial results show significant differences in the nutrients that limit primary production that occurred in areas with mussels (co-limitation) in comparison to areas without mussels (N-limitation). This suggests that mussels, through preferential uptake and excretion, are altering nutrient dynamics. The results also suggest mussels store large quantities of nutrients in their tissue that would otherwise be carried to downstream watersheds. To determine the contribution of freshwater mussels to nutrient storage and flux, a parameterized model will be developed to estimate the contribution of mussels to nutrient flux and storage using the estimates on nutrient composition and retention. The strength of this approach is that the model will combine information from high resolution laboratory experiments and more realistic field experiments. Additionally, mussels occur as speciose, dense aggregations known as mussel beds. This research also will investigate if trophic partitioning, through the use of stable isotope analysis, facilitates high species diversity in these high density mussel beds. In combination with this information, 15N-enriched mussels will be used as tracers to determine how mussel-derived nutrients travel through the stream food web. Through the combination of these approaches, information of the influence of organisms on aquatic ecosystem function will be gained.

Potential to Further Environmental/ Human Health Pro tection

This research will examine the roles of freshwater mussels, the most endangered faunal group in North America, in relation to ecosystem services (i.e., nutrient flux, nutrient storage and support of the food web). A stronger understanding of the linkages between biodiversity and ecosystem services in freshwaters is needed. This will have immediate applicability to understanding the value of freshwater mussels in the role of supporting higher trophic levels and providing ecosystem services.

Supplemental Keywords:

ecosystem services, nutrient storage, nutrient flux, freshwater mussels, water quality, stoichiometry, trophic partitioning, nutrient limitation,

Progress and Final Reports:

  • 2012
  • 2013
  • Final