1. BACKGROUND
The diversity of freshwater mussel communities has declined over the past several decades within
watersheds of the Midwestern United States. Fishes play an important role in the life cycle of
freshwater mussels because they serve as hosts for parasitic mussel larvae. Mussel larvae rely on
fish for nutrition and dispersal.
Previous studies have examined the relationships of mussels and host-fish species within
Midwestern watersheds (Watters 1992, Cao et al. 2013). Additionally, previous studies have limited
their evaluations to examining the mussel species richness and abundance with host-fish species
richness (Cao et al. 2013).
Understanding the relationships between mussel and host-fishes can guide the design of mussel
conservation and restoration strategies. I examined the relationships between nine mussel response
variables with ten host-fish variables.
Relationships Between Community Structure of Freshwater Mussels and Host Fishes in a Central Ohio Watershed
Marissa Lauer1 and Peter C. Smiley Jr.2
1College of Engineering, The Ohio State University, 2USDA-ARS, Columbus, Ohio and School of Environment and Natural Resources, The Ohio State University
DISCUSSION AND CONCLUSIONS
RESULTS
METHODS
Mussels were collected using quadrat and visual search techniques in 200-meter long sampling sites.
Eight transects were distributed throughout each site. I searched 16 randomly selected quadrats in
each site to a depth of approximately 13 cm using sieves of sizes 1.2 cm and less. Any mussels that
were less than 1.2 cm were considered too small to identify. Visual searches were performed by two
observers as they waded through each site. Periscopes were used in deeper areas.
Watershed size for each site was obtained from Delaware Soil & Water District.
ACKNOWLEDGEMENTS
I thank the Midwest Area USDA-Agricultural Research Service for funding my summer
internship. I also thank Norman Fausey for logistical and financial support. I thank Karolyn
Stillman and Cody Fleece for their mussel identification assistance. I thank Drew Shafer,
Sarah Hess, Amanda Rapp, and Kyle Seitz for their help and hard work field sampling.
STUDY SITES
Field work was conducted from June to August
2015 in eleven sites in the Upper Big Walnut
Creek Watershed (UBWC). Of these sites, the
land-use surrounding each stream varied from
small agricultural headwaters to large urban
streams. The sites were selected based on
stream type, surrounding land-use, and
watershed size. Five of the eleven sites were
headwater streams. The remaining six sites
were larger tributaries of the UBWC.
REFERENCES
Cao, Y., Huang, J., & Cummings, K.S. 2013. Modeling changes in freshwater mussel
diversity in an agriculturally dominated landscape. Freshwater Science 32:1205-
1218.
Haag, Wendell R. 2012. North American Freshwater Mussels. Cambridge University Press.
Cambridge, New York.
Watters, G. T. Unionids, fishes, and the species-area curve. Journal of Biogeography
19:481-490.
INFLUENCE OF WATERSHED SIZE AND HOST-FISHES
Five mussel species were present
throughout four of eleven sites, which are
larger tributaries of the UBWC. These
species included Lampsilis radiata
(fatmucket), Pyganodon grandis (giant
floater), Toxolasma purvum (lilliput),
Utterbackia imbecillis (paper pondshell),
and Strophitus undulates (creeper). Mussel
size ranged from 68 to 100 mm, and the
number of growth rings ranged from 5 to 12
rings.
Sixteen of 34 host-fish species historically
found in the UBWC were found. The most
common of these host-fish species belonged
to the minnow (Cyprinidae), perch
(Percidae), and sunfish (Centrarchidae)
families.
Mussels were identified and measured lengthwise to the
nearest millimeter using calipers. The number of growth rings
were also recorded. Information on mussel life history and
reproductive strategies was obtained from Haag (2012).
Fishes were collected with a backpack electrofisher in the
same 200-meter long sites the mussels were sampled. All fish
were identified as either host-fish or non-host-fish. Creek chub
and johnny darter species were measured for size before
returning to the stream.
Mussel Response
Variable
Watershed Size % Headwater Host-Fishes
p-value pR2 p-value pR2
Presence/Absence 0.144 37.13 0.998 100
% Giant Floaters <0.0001 24.30 0.008 7.87
% Fatmucket <0.0001 21.37 0.003 11.81
% Periodic <0.0001 19.79 0.002 13.6
% Generalists and
Broadcast
<0.001 23.31 0.005 9.53
Species Richness 0.011 22.44 <0.0001 57.56
Abundance <0.0001 47.85 <0.0001 29.56
Mean Size <0.0001 25.02 <0.0001 32.72
Mean Growth Rings 0.0002 19.26 <0.0001 24.36
My research question
was:
What are the
relationships between
the community structure
of freshwater mussels
and host fishes in the
Upper Big Walnut Creek
watershed, Ohio?
Mussel Response Variables Host-Fish Variables
Presence or Absence Species Richness
Percentage of Giant Floater Abundance
Percentage of Fatmucket Percentage from Sunfish Family
Percentage with Periodic Life History Strategies Percentage from Minnow Family
Percentage of Generalists and
Broadcast Glochidial Dispersers
Percentage of Darters
Species Richness Percentage of Creek Chub
Abundance Percentage of Adult Creek Chub
Mean Size Percentage of Johnny Darter
Mean Number of Growth Rings Number of Headwater Host-Fish
Percentage of Headwater Host-Fish
I used generalized linear model regression analysis to examine the relationships of mussel community
variables with host-fish variables. Generalized linear models were used because they are robust to
non-normally distributed data sets with large numbers of zero values. Poisson distribution was used to
examine count data and binomial distribution was used for proportional or percentage data. I
conducted 90 generalized linear model tests using R and all combinations of each mussel and host-
fish variables are listed below.
I also used generalized linear model regression analysis to determine the relationships of nine
mussel community variables with watershed size. I then compared these observed relationships to
those relationships found with percentage of headwater host-fishes.
• No significant relationships occurred between the presence or absence of freshwater mussels
and ten host-fish variables.
• Eight of ten host-fish variables exhibited significant relationships with the percentage of giant
floaters. The same eight host-fish variables exhibited significant relationships with the
percentage of mussels that are generalists and broadcast glochidial dispersers. The strongest
positive relationships that occurred were the percentage of giant floaters with host-fish species
richness (Figure 1) and the percentage of generalists and broadcast glochidial dispersers with
host-fish species richness (Figure 4).
• Eight of ten host-fish variables exhibited significant relationships with the percentage of
fatmucket. Nine of ten host-fish variables exhibited significant relationships with the percentage
of mussels with a periodic life history strategy. The strongest negative relationships were
observed of the percentage of fatmucket with host-fish species richness (Figure 2) and the
percentage of mussels with a periodic life history with host-fish species richness (Figure 3). Five
of ten host-fish variables exhibited significant relationships with mussel species richness. Of
these relationships, the strongest was observed with the percentage of headwater host-fish and
it exhibited a negative relationship (Figure 5).
• One host-fish variable, the percentage of headwater host-fish, exhibited a significant relationship
with mussel abundance (Figure 6). The percentage of headwater host-fish was also the only
variable that exhibited a significant relationship with mean size (Figure 7) as well as with mean
number of growth rings (Figure 8). All three of these relationships were negative.
• The host-fish variable with the greatest number of significant relationships with
mussel response variables was the percentage of headwater fish, followed by host-
fish species richness, percentage of host-fishes from the minnow family, and
percentage of host-fishes from the sunfish family.
• The percentage of giant floaters, percentage of fatmucket, percentage of mussels
with a periodic life history strategy, percentage of mussels that are generalists and
use the broadcast glochidial dispersal method, and abundance, were more strongly
related to watershed size than to the percentage of headwater fish.
• Freshwater mussels within UBWC exhibited significant relationships with host-fishes.
Specifically I documented that mussel community structure exhibited significant
relationships with host-fish community structure.
• My results are consistent with those who have observed positive relationships between
mussel species richness and abundance with host-fish species richness and
abundance (Watters 1992, Cao et al. 2013). However, my results are unique because I
documented relationships for a greater number of mussel and host-fish response
variables.
• My results suggest that future research needs to evaluate a greater number of mussel
and host-fish response variables.
• My observed relationships of mussel community structure with watershed size suggest
that mussel conservation and restoration efforts should be targeted within larger
subwatersheds in the UBWC and watersheds in Ohio with similar land use patterns.
Figure 1 Figure 2
Figure 3 Figure 4
Figure 5 Figure 6
Figure 7 Figure 8