oEPA
www.epa.gov/ada
EPA/600/F-13/231

BRIEF
science
BUILDING A SCIENTIFIC FOUNDATION FOR SOUND ENVIRONMENTAL DECISIONS
Native Mussels Alter Nutrient Availability and Reduce Blue-Green Algae Abundance
Background:
Freshwater mussels (Bivalvia: Unionidae) (Figure 1)
are an important group of filter feeding and long-lived (6 to
100 years) mollusks that live and burrow in river sediments.
Freshwater mussels occur in large multi-species groups
(mussel beds). Flowever, the biodiversity of these sentinel
organisms continues to decline rapidly in many rivers across
the United States and they are considered North America's
most imperiled faunal group. These valuable filter feeders
remove nutrients and particulates from the water column.
They make limited nutrients more locally available for other
species while reducing total rates of downstream nutrient
export. Trans-location (movement) and transformation of
nutrients by animals is an important biogeochemical process
that can enhance primary production across ecosystems
and may have large effects on community composition
and ecosystem function. Mussels can even generate spatial
heterogeneity to support habitat in rivers and subsidize
adjacent terrestrial ecosystems. As part of EPA's ongoing
work to evaluate how natural and engineered structures in
rivers alter nitrogen processing, determining the influence of
mussels on nitrogen ecosystem sendees is critical to better
management and decision making in aquatic ecosystems under
anthropogenic and climatic stress. Since dense aggregations
of consumers like mussel beds can create biogeochemical
hotspots of nitrogen processing in aquatic ecosystems, we
wanted to understand the importance of mussels to streambed
nutrient dynamics, to determine whether mussels enhance
benthic algae composition in rivers.
Findings and Implications:
In a collaborative effort between The University of
Oklahoma and the EPA's Office of Research and
Development, recent cutting edge research shows that mussels
greatly influence ecosystem processes by modifying nutrients
that limit primary productivity m rivers of southern Oklahoma
(Figure 2). Sites without mussels were nitrogen limited with
-26% higher relative abundances of N-fixing blue-green
algae, while sites with high mussel densities were co-limited
(N and P) and dominated by diatoms. Blue-green algae are
known for forming toxic algal blooms, while diatoms are typi-
cally a high quality food for grazing invertebrates. This sug-
gests that through the formation of biogeochemical hotspots,
native mussels reduce blue-green algae populations while
promoting diatoms, thus creating better habitat patches for
other aquatic organisms.
This work shows that translocation of nutrients by mussel
aggregations are important to nutrient dynamics and algal
species composition in rivers. Tlie findings demonstrate that
nitrogen translocation and transformation by a biologically
diverse, imperiled faunal group controls nutrient limitation,
community assemblages, and highlights the importance of
native consumers in aquatic ecosystems. Entire assemblages
of mussels have been extirpated from many rivers due to a
variety of anthropogenic and climatic causes like dams, dredg-
ing, sedimentation, and prolonged drought. The full ramifi-
cations of past and future losses are yet unknown, but these
results suggest that further loss of species could dramatically
change community composition and ecosystem properties of
riverine ecosystems, potentially damaging water quality.
Figure 1. Native unionid mussels in rivers convert water column nitrogen to more bioavailable forms to support algal
community structure, actually slow nitrogen movement downstream, and potentially enhance sustainable water quality for
healthy communities.

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Figure 2. Rivers are under multiple stressors from human pollutants and climatic e ffects. These systems support diverse
ecosystem services, including those of native mussels, which can enhance sustainable healthy communities and improve
water quality.
Publications:
Atkinson, C. L.. C. C. Vaughn, K. J. Forshay, and J. T. Cooper.
2013. Aggregated filter-feeding consumers alter nutrient
limitation: Consequences for ecosystem and community
dynamics. Ecology doi.10.1890/12-1531.1.
otrA Robert S. Kerr Environmental Research Center
/ National Risk Management Research Laboratory
www.epa.gov/ada j
Contacts:
Kenneth J. Forshay, United States Environmental Protection
Agency, Robert S. Kerr Environmental Research Center,
919 Kerr Research Drive, Ada. OK 74820, (580) 436-8912,
Forshay.Ken@epa.gov
Carla L. Atkinson Oklahoma Biological Survey, University of
Oklahoma, 111 E. Chesapeake St., Norman, OK 73019,
carlalatkinson@gmail.com
Caryn C. Vaughn, Oklahoma Biological Survey, University of
Oklahoma, 111 E. Chesapeake St., Norman, OK 73019,
cvaughn@ou.edu

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