A Thesis
entitled
Habitat Use and Community Structure of Unionid Mussels in Three Lake Erie Tributaries
by Jeffrey D. Grabarkiewicz
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the
Master of Science in Biology, Ecology-track
______Dr. Johan Gottgens, Committee Chair
______Dr. Elliot Tramer, Committee Member
______Dr. Daelyn Woolnough, Committee Member
______Dr. Patricia R. Komuniecki, Dean College of Graduate Studies
The University of Toledo
August 2012
An Abstract of
Habitat Use and Community Structure of Unionid Mussels in Three Lake Erie Tributaries
by
Jeffrey D. Grabarkiewicz
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science in Biology, Ecology-track.
The University of Toledo August 2012
Nearly 300 species of freshwater mussels (Bivalvia: Superfamily Unionoidea) have been documented in the United States. Unfortunately, this diversity is in peril, with
76 species currently listed as threatened or endangered under the Endangered Species
Act. This research established unionid population estimates and habitat use within six reaches of three Western Lake Erie tributaries: the Blanchard River, Swan Creek, and
Beaver Creek. Particular emphasis was placed on the federally endangered Rayed Bean
(Villosa fabalis ). Quantitative sampling documented 22 live unionid species and 1,197 live individuals across all reaches and streams. Evidence of recent recruitment was documented for 10 species and size class diversity was found for 15 species. Unionid density and species richness were highest in the Upper Blanchard with a mean reach density of 4.48 unionids per m 2 and 15 live species. Rayed Bean (V. fabalis ) were estimated at 0.29 per m 2 in the Upper Blanchard and 0.13 per m 2 in Middle Swan Creek.
Size class diversity for V. fabalis was found in both reaches, with many young individuals (< 18 mm) present in the Upper Blanchard. Qualitative Habitat Evaluation
Index (QHEI) predicted species richness (R2 = 0.63) and density (R2 = 0.52) at the reach
iii scale. Diversity peaked at an intermediate QHEI. Principal Components Analysis (PCA) suggested patterns in habitat use where Kidneyshell ( Ptychobranchus fasciolaris) and V. fabalis were more common in gravel while White Heelsplitter ( Lasmigona complanata complanata ), Giant Floater ( Pyganodon grandis ), and Fatmucket ( Lampsilis siliquoidea ) were substrate generalists. Components 1 and 2 explained 62.6 % of the data variation.
Different burrowing patterns were observed among species, with V. fabalis, Spike
(Elliptio dilatata ), Wabash Pigtoe ( Fusconaia flava ), Kidneyshell ( P. fasciolaris ), and
Rainbow ( Villosa iris ) present in subsurface samples across most size classes. Shell lengths were significantly shorter for E. dilatata (p < 0.0001) and F. flava (p < 0.0001) found in subsurface samples across all reaches and streams using Mann-Whitney. These patterns appeared to link more with life history than substrate texture. Subsurface sampling highlighted the need to excavate sediments to accurately quantify population size, most notably for V. fabalis which were collected almost exclusively from subsurface samples (93%). This is the first large-scale quantitative unionid assessment of Western
Lake Erie tributaries and the first extensive sampling of subsurface habitat. Future projects may use these data and results as a baseline when assessing changes in population sizes, determining the need to sample subsurface sediments, and identifying areas where populations of V. fabalis may occur.
iv Acknowledgements
I first would like to thank my advisor Dr. Johan Gottgens, whose guiding hand and patience with a part-time graduate student facilitated my academic development and this research project. I also wish to thank my committee members, Dr. Elliot Tramer and Dr.
Daelyn Woolnough, for their valuable suggestions that helped formulate and refine my thesis. A special thanks is warranted to my undergraduate assistant, Craig Krajeski, who endured an intense sampling season during the summer and fall of 2010. I would like to recognize the Lake Erie Protection Fund (grant SG-383-10) for their valuable financial support. I would also like to thank the Department of Environmental Sciences for their support over the course of my graduate education. I remain in debt to the staff and Board of Supervisors at the Lucas Soil and Water Conservation District who gave me the flexibility to complete my degree.
Finally, to my wife Melanie, daughter Nora, and family, for taking care of things I couldn't over the past few years.
v Table of Contents
Abstract iii
Acknowledgements v
List of Tables viii
List of Figures xi
1 Introduction 1
2 Methods 7
2.1 Description of Streams, Reaches, and Sampling Sites 7
2.2 Qualitative Habitat Evaluation Index 9
2.3 Site Sampling Design 12
2.3.1 Site Preparation and Quadrat Sampling 12
2.4 Unionid Processing 15
2.5 Unionid Data Analysis 15
2.6 Habitat Data Analysis 17
3 Results and Discussion 19
3.1 Unionid Data 19
3.1.1 Blanchard River Unionids 20
3.1.2 Swan Creek Unionids 28
3.1.3 Beaver Creek Unionids 34
vi 3.2 Qualitative Habitat Evaluation Index 40
3.3 Microhabitat Use 44
3.4 Subsurface Sampling 50
4 Summary and Conclusions 58
References 63
vii
List of Tables
2.1 Modified Wentworth scale used to classify surface and subsurface 15 substrate samples (Wentworth 1922).
3.1 Sorenson Similarity Index scores for all six reaches and three streams
sampled during 2010. 20
3.2 Population and density estimates of freshwater mussels found in the Middle
Blanchard River. 23
3.3 Population and density estimates of freshwater mussels found in the Upper
Blanchard River. 24
3.4 Recruitment data for the Middle and Upper Blanchard River reaches. All
shell measurements are in millimeters (mm). 25
3.5 Population and density estimates of freshwater mussels found in Middle
Swan Creek. 30
3.6 Population and density estimates of freshwater mussels found in Upper
Swan Creek. 30 3.7 Recruitment data for the Middle and Upper Swan Creek reaches. All shell
measurements are in millimeters (mm). 31
viii 3.8 Population and density estimates of freshwater mussels found in Middle
Beaver Creek. 36
3.9 Population and density estimates of freshwater mussels found in Upper
Beaver Creek. 37
3.10 Recruitment data for the Middle and Upper Beaver Creek reaches. All shell
measurements are in millimeters (mm). 38
3.11 Summary of mean surface substrate quadrat measurements for the eight most 49 common species across all reaches and streams.
3.12 Percentage of individuals found in subsurface samples (Qb) as a percentage 52 of total live individuals found (Q + Qb).
3.13 Mean shell lengths for E. dilatata across reaches and streams for individuals 53 found in surface samples (Q) and subsurface (Qb) samples.
3.14 Mean number of individuals less than 50 mm found in surface (Q) and 53 subsurface samples (Qb) across all reaches and streams.
3.15 Table of mean substrate and penetration data for individuals found in 57 subsurface (Qb) and surface samples (Q) with variance in parentheses.
ix
List of Figures
2-1 The location of field sampling streams, reaches, and sites. 10
2-2 Location maps of sampling reaches and sites: Middle Blanchard River (A),
Upper Blanchard River (B), Middle Swan Creek (C), Upper Swan Creek (D),
Middle Beaver Creek (E), and Upper Beaver Creek (F). 11
2-3 Sampling grid design used throughout this study, based on Smith et al. (2001)
and Strayer and Smith (2003). 13
3-1 Shell length frequency distributions of selected unionid species found in the
Blanchard River. 27
3-2 Shell length frequency distributions of selected unionid species found in the
Upper Blanchard River. 28
3-3 Shell length frequency distributions of selected unionid species found in
Middle Swan Crek (MSWAN). 32
3-4 Shell length frequency distributions of selected unionid species found in
Upper Beaver Creek (UBEAV) and Middle Beaver Creek (MBEAV). 39
3-5 QHEI exploration, linear regression, and 2 nd order polynomial regression for
all sampling reaches. 41
x 3-6 Principal Components Analysis (PCA) of all stream reaches based on mean
surface substrate composition. 43
3-7 PCA of surface substrate use by Giant Floater ( P. grandis ) (A), White
Heelsplitter ( L. c. complanata ) (B), Spike ( E. dilatata ) (C), and Rayed Bean
(V. fabalis ) (D). 45
3-8 PCA of surface substrate use by Fatmucket ( L. siliquoidea ) (A), Fragile
Papershell ( L. fragilis ) (B), Kidneyshell ( P. fasciolaris ) (C), and Wabash
Pigtoe ( F. flava ) (D). 46
3-9 PCA of surface substrate use by Giant Floater ( P. grandis ) (A), White
Heelsplitter ( L. c. complanata ) (B), Spike ( E. dilatata (C) ), and Rayed Bean
(V. fabalis ) (D). 47
3-10 PCA of surface substrate use by Fatmucket ( L. siliquoidea ) (A), Fragile
Papershell (L. fragilis ) (B), Kidneyshell ( P. fasciolaris ) (C), and Wabash
Pigtoe ( F. flava ) (D). 48
3-11 Two-way burrowing histograms. The zero line represents the substrate
surface. White bars indicate the number of mussels captured on the surface
and gray bars represent the number of mussels found in subsurface samples.
The two upper histograms represent Spike ( E. diltatata ) in UBLAN (A) and
MBLAN (B). 51
3-12 Two-way burrowing histograms. The number zero represents the substrate
surface. White bars indicate mussels captured on the surface and gray bars
represent mussels found in subsurface samples. 54
xi Chapter 1
Introduction
Freshwater mussels (Bivalvia: Superfamily Unionoidea) are distributed nearly worldwide, inhabiting every continent except Antarctica. Approximately 780 species belonging to 140 genera have been identified to date, with species diversity maximized in the creeks, rivers, and lakes of North America (Graf and Cummings 2007). Nearly 300 species are known from the United States, the vast majority of which belong to the family
Unionidae. While this diversity is also of conservation concern, with 76 species now listed as threatened or endangered under the U.S. Endangered Species Act (USFWS
2012). The proportion of imperilment within the Unionoidea (Families Unionidae,
Margartiferidae, and Hyriidae) has been reported as greater than any other group of animals in the United States (Riccardi and Rasmussen 1999; Master et al. 2000). In
Ohio, a total of 80 unionid species were recorded historically, with 44 species present in the Lake Erie drainage (Graf 2002; Watters et al. 2009). Five species are now considered extinct and 13 extirpated from Ohio. The Ohio Division of Wildlife lists 37 unionid species as endangered, threatened, or species of concern (ODNR 2010). Unfortunately, even unionids considered relatively common throughout their range are declining or lack
1 evidence of successful reproduction in some Ohio streams (Grabarkiewicz and Crail
2008; Watters et al. 2009).
Ecologically, freshwater mussels play a number of important roles in aquatic ecosystems (Vaughn and Hakenkamp 2001). As sedentary suspension feeders, unionoids remove a variety of materials from the water column, including sediment, organic matter, bacteria, and phytoplankton. Mussels also interact with stream substrates. The burrowing behavior of unionoids mixes sediment pore water, releasing nutrients and oxygenating substrates (Vaughn and Hakenkamp 2001). Particularly dense assemblages of mussels may influence substrate stability while providing nutrients and microrefugia for benthic life (Vaughn and Hakenkamp 2001; Howard and Cuffey 2006; Vaughn and
Spooner 2006; Zimmerman and de Szalay 2007).
In Northwest Ohio, a unionid species of particular interest is the Rayed Bean
(Villosa fabalis ). A diminutive mussel (shell size up to 4.5 cm), V. fabalis has declined over the last century and is now only extant in 28 of the 112 known watercourses where it formerly occurred (Code of Federal Regulations 2012). The range reduction experienced by the Rayed Bean ( V. fabalis ) has been estimated at 73% (Code of Federal Regulations
2012). As such, on March 15th , 2012, V. fabalis was listed as Endangered by the U.S.
Fish and Wildlife Service after maintaining “candidate” status for more than three decades (Code of Federal Regulations 2012). Notwithstanding this recent listing, several
Rayed Bean ( V. fabalis ) populations remain in Northwest Ohio. Within the tributaries of
Western Lake Erie, V. fabalis has recently been found live in the Blanchard River, Fish
Creek, and Swan Creek (Hoggarth et al. 2000; Grabarkiewicz and Crail 2007; Watters et al. 2009; Grabarkiewicz and Gottgens 2011). In addition, Rayed Bean (V. fabalis ) valves
2 were collected during the summer of 1996 from Tymochtee Creek (personal comm.,
Jamie Smith, North Carolina State Museum of Natural Sciences) - although the status of this potential population remains unresolved due to lack of sampling. Rayed Bean (V. fabalis ) is most often found in shallows within or near riffles, where sand and gravel substrates predominate (Ortmann 1919; Watters et al. 2009; COSEWIC 2010;
Grabarkiewicz and Gottgens 2011). Investigators have also noted an association with
“water weeds,” particularly American Water Willow ( Justicia americana ) and other aquatic macrophytes (Ortmann 1919; LaRocque 1967).
Sufficient knowledge of the distribution, size, density, and demographics of mussel populations is important to the conservation of unionid species and communities
(Biggins et al. 1997). Within the tributaries of Western Lake Erie, unionid species distributions have been mapped from collection records and presence-absence surveys
(e.g. Kirsch 1895; Clark and Wilson 1912; van der Schalie 1938; Clark 1944; Hoggarth
1986; Watters 1988; 1996; 1998; Hoggarth 2000; Hoggarth et al. 2000; Badra 2004;
McRae et al. 2004; Grabarkiewicz and Crail 2008; Hoggarth and Burgess 2009). Despite these efforts, knowledge of the distributions of many species is largely incomplete due to poor spatial coverage at the reach or stream scale. This was recently illustrated by the discovery of a population of Rayed Bean ( V. fabalis ) in Swan Creek by Grabarkiewicz and Crail (2007). While distributional gaps are unavoidable - particularly at smaller spatial scales - even less is known about the current population sizes, densities, and demographics of both common and imperiled mussel species. I reviewed survey publications and technical reports and found that no quantitative population studies have been conducted in the tributaries of Western Lake Erie. Without data derived from
3 quantitative or probability-based designs, no baseline or reference dataset is available to contrast populations, assess temporal change with measures of uncertainty, or evaluate and quantify ecological function.
Stream habitat destruction has long been implicated in the decline of freshwater mussels (Ortmann 1909; Bates 1962; Williams et al. 1993; Watters 2000; Downing et al.
2010). Yet, few studies have been able to explicitly define or identify the habitat use of freshwater mussels. For example, Cummings and Mayer (1992) state the habitat of
Fusconaia flava as “creeks to large rivers in mud, sand, or gravel.” Predictive variables have been elusive, with numerous studies attempting to correlate environmental variables
(e.g. sediment particle size, depth, and current speed) with the presence of mussel beds or particular species (Strayer 1981; Huehner 1987; Strayer and Ralley 1993; Morales et al.
2006; Strayer 2008). For example, Strayer (1981) examined mussels and microhabitat use among 22 species of freshwater mussels in small Michigan streams. With only one exception, he found no obvious interspecific differences in microhabitat use (depth, substrate texture, current speed, and distance from shore). Strayer and Ralley (1993) found the predictive power of discriminant models based on microhabitat variables so low that they questioned a traditional approach to describing freshwater mussel habitat.
To this end, Strayer (1999) investigated flow refugia - areas where shear stresses are low during high flow events - within two streams in New York. He was able to demonstrate that mussel densities were significantly higher within flow refuges when compared to areas outside flow refuges. Likewise, Morales et al. (2006) were able to qualitatively model unionid distributions in a 10 km reach of the Upper Mississippi River by combining shear force and substrate texture. While the use of surface substrate texture to
4 predict the distribution and abundance of unionids continues, investigation also persists into alternative methods to identify substrates suitable for unionids. For example,
Johnson and Brown (2000) explored the relationship between substrate penetrability and the occurrence of the Louisiana Pearlshell ( Margaritifera hembeli ). They found M. hembeli more likely to occur in areas of compact substrates and suggested the use of penetrability as a surrogate for sediment stability.
Several malacologists have made observations regarding the burrowing tendencies of freshwater mussels. Ortmann (1919) stated that Rayed Bean ( V. fabalis ) in
West Virginia was “deeply buried in the sand and gravel...” Watters et al. (2009) noted that the Clubshell ( Pleurobema clava ) “may live several inches beneath the surface.”
Likewise, authors over the past several decades have commented on the propensity of
Snuffbox (Epioblasma triquetra ) to bury deeply in the substrate (Ortmann 1919; Baker
1928; Hickman 1937; Buchanan 1980; Parmalee and Bogan 1998). Regardless of these anecdotal observations, few published studies have documented sediment burrowing position across spatial scales (i.e. site, reach, stream, landscape). In my review of publications and technical reports relevant to Ohio and Lake Erie tributaries, I found no studies or surveys that had a considerable subsurface sampling component. Therefore, it is unknown how detectable mussels are at the substrate surface and if sampling results actually represent resident unionid communities. Because so many species are declining or demonstrating little to no recruitment (e.g. Grabarkiewicz and Crail 2008), investigation into the full dimensionality of unionid habitat is needed.
My objective for this study is to establish current abundance and density estimates of freshwater mussels using a reproducible sampling technique within six reaches of three
5 Western Lake Erie tributaries: the Blanchard River, Swan Creek, and Beaver Creek, with particular attention to the federally endangered Rayed Bean ( V. fabalis ). There is a particular need to determine the current status of Rayed Bean ( V. fabalis ) in the Upper
Blanchard which was last studied 18 years ago. At that time, it was well distributed and viable throughout the Upper Blanchard. In addition to the Rayed Bean ( V. fabalis ), I will provide an assessment of demography for each species of conservation concern. Because many mussel species are declining, demographic data are imperative to understanding the status of extant populations. I will examine the relationship of various microhabitat variables to freshwater mussel assemblages, with comparisons across spatial scales. I hypothesize that habitat use varies among species, with substrate and penetrability possible indicators of suitability. Last, I will investigate the burrowing behavior and detectability of different freshwater mussel species across reaches and streams. I anticipate that detectability is a function of species, substrate texture size, and mussel size. Evidence of burrowing has implications for survey protocols as well as for the ecological role of mussels in freshwater ecosystems.
6 Chapter 2
Methods
2.1 Description of Streams, Reaches, and Sampling Sites
Three Western Lake Erie tributaries were identified for study: the Blanchard
River, Swan Creek, and Beaver Creek (Figure 2-1). Two reaches within each stream were selected for sampling. Streams and reaches were chosen based on a suite of factors, including driving distance from the University of Toledo, presence or potential presence of Rayed Bean ( V. fabalis ) populations, stream geology, drainage area, diversification of ecoregions, and limited need to sample using SCUBA. Stream geology and ecoregions were important considerations because I wanted to capture a wide array of till and substrate types. All stream reaches were subdivided into fifteen 100 m sites with each reach totaling 1500 m of possible sampling distance. Where applicable, bridge buffers were applied 100 m upstream and downstream of each bridge to avoid sampling areas of heavy disturbance. Three sites were randomly selected for sampling from each reach
(Figure 2-2). All sites were sampled at low flow conditions from the months of July to early November.
7 The Blanchard River is a tributary of the Auglaize River and drains approximately
1,994 km 2 at the mouth south of Dupont, OH. It rises in the gently rolling terrain of the
Wabash Moraine within Hardin County, just north of the City of Kenton, and meanders north through Hancock County before making an abrupt turn west towards the City of
Findlay. The middle sampling reach was located near this turn - at the intersection of
Township Rd. 208 and Township Rd. 234 - just upstream Findlay (RKM 98.5 – 99.8)
(Figure 2-2). The upper sampling reach was located near U.S Route 30, approximately
4.4 km NE of Forest, OH (RKM 140.9 – 142.2). Both reaches are located within the
Clayey, High Lime Till Plains level IV ecoregion (Griffith et al. 2008) and have watersheds dominated by row cropped agriculture.
Swan Creek is direct tributary of the Maumee River, draining 528 km 2 at the mouth in downtown Toledo. It is a low gradient (0.4 m/km), primarily beach ridge stream best known for draining part of the Oak Openings ecoregion. While the headwaters are chiefly in agricultural land use, much of the lower watershed is suburban or intensely urbanized. The middle sampling reach was located in suburban Monclova
Township (RKM 26.6 – 27.9) - where the creek meanders through a wide, wooded floodplain valley. The upper reach was located within Oak Openings Metropark (RKM
45.0 – 46.3) in Swanton Township. Both reaches are located within the Oak Openings level IV ecoregion (Griffith et al. 2008).
Beaver Creek is also a direct tributary of the Maumee River, draining 497 km2 at the mouth in Grand Rapids, OH. The headwaters rise in the systematically drained agricultural landscape of southern Wood County and eastern Henry County, an area formerly occupied by the Great Black Swamp. Due to problems gaining access on
8 private property, the middle and upper sampling reaches were relatively close, both located in Grand Rapids Township at RKM 2.3 – 3.5 and RKM 4.8 – 6.1. The reaches are located within the Maumee Lake Plains level IV ecoregion (Griffith et al. 2008).
2.2 Qualitative Habitat Evaluation Index
Before transects were laid and quadrat sampling commenced, habitat quality at each site was visually assessed using the Qualitative Habitat Evaluation Index (QHEI) developed by Ohio EPA (Ohio EPA 1987; Ohio EPA 2006). While originally designed to measure physical factors that affect fish communities, QHEI was also thought to apply to other aquatic life (Ohio EPA 1989). The protocol calls for an evaluation of six stream metrics: substrate, instream cover, channel morphology, riparian zone and bank erosion, structural habitat quality (riffle, run, pool, and glide), and gradient. For each metric, several observations are made which result in a total metric score. For example, the
“substrate” metric requires investigators to provide numerical values for substrate type, origin, and quality. The resulting values are summed for an overall substrate metric score. All six metric scores are then summed for a total QHEI score, which ranges from
0 to 100, with higher scores representing higher quality habitats.
9
Figure 2-1. The location of field sampling streams, reaches, and sites. The middle reaches are denoted with bold circles (●) and upper reaches with hollow circles (○).
10
Figure 2-2. Location maps of sampling reaches and sites: Middle Blanchard River (A), Upper Blanchard River (B), Middle Swan Creek (C), Upper Swan Creek (D), Middle Beaver Creek (E), and Upper Beaver Creek (F). Stars denote randomly selected sampling sites and hash marks separate 100 m sites within each reach.
11 2.3 Site Sampling Design
Following QHEI scoring, all sites were sampled using a probability-based systematic sampling design. This method is similar to Smith et al. (2001) with minor modifications and described in detail by Strayer and Smith (2003). Essentially, the protocol calls for a grid-like design that utilizes three random starts within a defined sampling area (Figure 2-3). As applied to this study, each randomly selected 100 m site was divided into n = number of 0.5 m x 0.5 m squares (0.25 m2 quadrats). Random starts were determined using an x-y coordinate system fixed on the grid, with each of the three randomly determined coordinates repeated at intervals da (across stream) and du
(upstream). A sample size of 150 quadrats (or 150 0.5 m x 0.5 m squares) per 100 m site was targeted to achieve adequate precision while limiting site disturbance and time required to sample each site. As such, the intervals most commonly used were da = 4 m and du = 4 m. Because the target sample size was 150 quadrats per site, sites with larger sampling areas necessitated a slightly increased du. Each random coordinate and subsequent sample represented one systematic sample. Therefore, three systematic samples were collected at each 100 m site, consisting of 50 replicates each. This allows for variance to be calculated properly for population estimates and eliminates the need to make assumptions about the distribution of freshwater mussels within the sampling area.
This general site sampling design was selected for its consistent spatial coverage, ease of implementation in the field, and reproducibility.
2.3.1 Site Preparation and Quadrat Sampling
Site boundaries and transect locations were laid out onsite with a meter tape
12
Figure 2-3. Sampling grid design used throughout this study, based on Smith et al. (2001) and Strayer and Smith (2003). Random coordinates were used to determine sampling squares (each shade of gray), with each coordinate repeated at 4m intervals. Each shade of gray represents a different systematic sample. The heavy black borders denote the sampling interval (4 m x 4 m). The light gray lines (e.g., at 99 m) represent lead core transects laid perpendicular to flow. All values are in meters.
13 and stakes. Leadcore transect lines affixed with colored zip ties (denoting relevant x-axis coordinates) were laid perpendicular to flow at regular intervals. Grid positioning was accomplished using a 2 m aluminum rod with a 0.25 m2 PVC quadrat attached. Once positioning was established, sampling was initiated at the left downstream bank and continued along each transect.
All quadrat sampling followed a predetermined sequence of measurements which was necessary to ensure consistency among all samples. First, a 0.25 m2 PVC quadrat was placed on the streambed and a water depth measurement was taken. A 0.25 m2 was chosen to provide the most localized approximation of habitat conditions and smallest search area. Next, the structural habitat was recorded (i.e. riffle, run, pool, or glide) and a visual assessment of surface substrate was performed across each quadrat diagonal.
Substrate was classified according to a modified Wentworth scale (Table 2.1). Unionids were then collected from the surface and placed in a mesh bag for processing. An ordinal variable was assigned to each unionid based on burrowing depth (2: >50% burrowed, 3: <
50% burrowed, 4: fully exposed). Following unionid collection, a 7.6 cm diameter polycarbonate core with beveled wall edges (wall thickness of 3 mm) was driven into the center of the quadrat until refusal. The resulting subsurface substrates were visually assessed using the modified Wentworth as above and the depth of penetration recorded to the nearest centimeter. The core was then driven four additional times into each corner of the quadrat and depths were recorded. Finally, the quadrat was completely excavated using a metal scoop. Any unionids collected from the excavated material were given a burrowing depth of “1” (wholly burrowed). This process was repeated for each quadrat sample.
14 Table 2.1 . Modified Wentworth scale used to classify surface and subsurface substrate samples (Wentworth 1922).
Size Ranges (mm) Aggregate Class (modified Wentworth)
> 256 Boulder
64 – 256 Cobble
32 – 64 Large Gravel
2 – 32 Small Gravel
0.25 – 2 Sand
<0.25 Fines
2.4 Unionid Processing
All unionids were kept in mesh bags in stream water until processing. Unionids were identified to species, sexed (when possible), and measured with a digital caliper along the x (length), y (height), and z (width) axes to the nearest millimeter. Exceptional or unusual finds were digitally photographed. After identification and measurement, all unionids were returned to the approximate location where they were originally found.
Unionid taxonomy followed Turgeon et al. (1998).
2.5 Unionid Data Analysis
Mussel abundances, densities, and relative abundances were estimated using methods described in Smith et al. (2001) and calculated by the Mussel Estimation
Program (v1.5.2, 2007) created by the U.S. Geological Survey . First, an estimate of population size was determined using:
15
(1)
where an estimate of population size per 100 m ( ) is equal to the possible number of systematic samples (M) divided by the number of chosen systematic samples (m),
th multiplied by the sum (x i) of the counts for all quadrats in the i systematic sample.
Population density (individuals/m 2) is determined by simply dividing the population total by the area sampled. Population size variance is calculated using:
(2) where = (1/m). Confidence intervals were calculated using:
(3)
Reach abundances and densities were estimated by calculating the means of all three sites within a reach. Unionid abundance was defined as unionids per 100 m of linear stream length while unionid density represented the number of individuals per m 2.
Unionid community composition at each site was described using simple species richness and the Shannon Diversity Index (H’). Shannon Diversity Index is calculated according to:
(4)
16 where p i represents the importance value for species i. Shannon Diversity Index reach scores were calculated by pooling the abundances of all species across all sites within a particular reach. Shannon Diversity Index reach scores were calculated by pooling the abundances of all species across all sites within a particular reach.
Unionid community similarities among reaches were analyzed using the Sorensen
Similarity Index. The Sorensen Similarity Index score (QS) is calculated according to:
(5) where A and B are the number of species in samples A and B, and C represents the number of species shared by A and B.
Demographic data were investigated to determine recent recruits and size class diversity. Recent recruits were defined for most species as individuals measuring less than 30 mm, except for Rayed Bean ( V. fabalis ), Slippershell ( Alasmidonta viridis ), and
Lilliput ( Toxolasma parvus ). Recent recruits of these species were defined as individuals measuring less than 20 mm. While this generalizes length-at-age variation among mussel species, it has been reported in the literature as an efficient and consistent field technique
(Mohler et al. 2006; Smith and Crabtree 2010). Size class diversity was used as an approximate surrogate for age diversity. Age diversity was analyzed with shell length (x- axis) histograms and coefficient of variation of these shell lengths using Grabarkiewicz and Crail (2008) as a guide.
2.6 Habitat Data Analysis
Habitat data were investigated and analyzed using the R (build 2.13.1) Foundation
17 for Statistical Computing and Palaeontological Statistics (PAST) version 2.14. Mean reach QHEI scores were calculated by averaging all three sites within each reach. QHEI data were investigated and checked for homoscedasticity by generating box and whisker plots. Linear regression and 2nd order polynomial regression were used to analyze the relationship between QHEI scores and aspects of the mussel community, including species richness, density, and pooled Shannon Diversity scores. Site-reach data were also explored using Principle Components Analysis (PCA) to examine similarities among reaches.
Microhabitat use data were summarized using descriptive statistics. Principle
Components Analysis (PCA) using correlation matrices was used to examine habitat variables in multi-dimensional space. Species with a sample size of 25 or greater and presence across two or more reaches were included for exploration. PCA output was then visually assessed to look for obvious patterns among species.
Burrowing position data were investigated using two-way histograms where surface individuals populated bars above zero and subsurface individuals populated bars below zero. Burrowing ordinal variables were collapsed down to binary responses: “Q” for individuals detectable at the surface and “Qb” found in subsurface samples. Mann-
Whitney was used to test for differences in shell lengths between Q and Qb for species with an adequate sample size. To test for differences in the mean number of small individuals (< 50 mm) found in Q and Qb, t-tests assuming unequal variance were used.
Penetration and substrate data were also analyzed using Mann-Whitney to detect differences in surface substrate characteristics where mussels were present in Q samples versus Qb samples.
18 Chapter 3
Results and Discussion
3.1 Unionid Data
A total of 22 live species and 1,197 live individuals were sampled during 800 person-hours of field work July to early November in 2010. Estimated mean reach densities varied from 4.48 unionids/m 2 in the Upper Blanchard River to 0.22 unionids/m 2 in Upper Swan Creek. While mean densities were highest in the Upper Blanchard, the
Middle Blanchard supported the highest mean abundance due to a consistently larger sampling area (wider channel).
Species richness was highest in the Blanchard River where 17 live species were found and lowest in Swan Creek where a total of eight live species were collected.
Pooled reach Shannon Diversity scores ranged from 1.77 in the Upper Blanchard River to
1.07 in Upper Swan Creek. Sorenson Similarity Index scores were highest ( > 0.61) between reaches within the same stream, indicating that community composition was more similar within streams than among streams (Table 3.1).
19 Table 3.1. Sorenson Similarity Index scores for all six reaches and three streams sampled during 2010. Sorenson scores range from 0 to 1, with higher values indicating greater similarity among reaches.
MBLAN UBLAN MSWAN USWAN MBEAV UBEAV MBLAN - 0.69 0.44 0.40 0.48 0.40 UBLAN 0.69 - 0.52 0.30 0.23 0.37 MSWAN 0.44 0.52 - 0.75 0.13 0.25
Across all reaches and streams several state listed species were found live, including the Ohio species of concern Kidneyshell ( Ptychobranchus fasciolaris ), Creek
Heelsplitter ( Lasmigona compressa ), Deertoe ( Truncilla truncata ), and Round Pigtoe
(Pleurobema sintoxia ). In addition, the Ohio and federally endangered Rayed Bean ( V. fabalis ) was found in the Upper Blanchard River and Middle Swan Creek. Within both reaches of each river, V. fabalis was present at each site – suggesting that it is well distributed throughout the Upper Blanchard River and Middle Swan Creek.
3.1.1 Blanchard River Unionids
Blanchard River field sampling documented a total of 17 live species and 813 live individuals. Mean reach densities (individuals/m 2) were 2.74 in the Middle Blanchard and 4.48 in the Upper Blanchard. Calculating uncertainty for reach means is problematic without making assumptions regarding habitat conditions and mussel distributions through each 100 m site. However, 90% confidence intervals (CIs) were calculated for all site abundances and densities and are presented in Table 3.2 and 3.3. The magnitude of these confidence intervals is the result of site unionid densities and site coverage (area sampled vs. total sample-able area). The number of samples required to generate more
20 accurate estimates of low density unionid populations may be quite high and can be cost prohibitive (Strayer and Smith 2003).
A total of 12 species were found live in the Middle Blanchard, with Shannon
Diversity scores ranging from 0.94 (MBLAN3) to 1.49 (MBLAN2) with a pooled
Shannon Diversity score of 1.24. The most abundant species in the Middle Blanchard were Spike ( Elliptio dilatata ) (66.3%), Fatmucket ( Lampsilis siliquoidea ) (9.7%),
Kidneyshell ( P. fasciolaris ) (8.8%), Creeper ( Strophitus undulatus ) (5.7%), and Fragile
Papershell ( Leptodea fragilis ) (4.7%) (Table 3.2). Recent recruits were documented for
Spike ( E. dilatata ) and Rainbow ( Villosa iris ) (Table 3.4). Size class diversity or recruitment was documented for several species, including Ohio species of concern
Kidneyshell ( P. fasciolaris ) (Table 3.4; Figure 3-1).
Because surveys designed to estimate unionid population sizes have not been published for Ohio streams, these data are difficult to compare with nearby streams.
However, all sites sampled within the Blanchard River supported higher mussel densities compared to Swan Creek and Beaver Creek during this study. In addition to my results, a recent study conducted in 2009 documented a total of 17 live unionid species in the vicinity of Findlay (Hoggarth and Burgess 2009). The survey area of this study was just west of my lowest site (MBLAN1) downstream through the City of Findlay and west approximately 8.0 km. Interestingly, just four live Spike ( E. dilatata ) were reported by
Hoggarth and Burgess (2009) after searching six reaches. Spike was by far the most abundant species during my study, accounting for 66.3% of all mussels sampled in the
Middle Blanchard. Densities were as high as 16 per 0.25 m2 in the gravelly riffles of
MBLAN3. Methods were different between the two studies, with a variety of techniques
21 employed by Hoggarth and Burgess (2009), including transect and quadrat sampling, general collecting techniques, and timed searches. These differences, however, do not explain such a large disparity between the number of E. dilatata detected. Such an abrupt change in distribution and density may be a result of barriers to dispersal (impounded sections through Findlay), alteration of habitat, changes in host fishes distributions, or water quality issues (Watters 2000).
The Upper Blanchard River was found to support a total of 15 live species, with
Shannon Diversity scores ranging from 1.52 (UBLAN6) to 1.84 (UBLAN5) and a pooled
Shannon Diversity score of 1.77. The most abundant species were Spike ( E. dilatata )
(41.5%), Fatmucket ( L. siliquoidea ) (23.7%), Giant Floater ( Pyganodon grandis ) (9.9%),
Wabash Pigtoe ( F. flava ) (7.3%), and Rayed Bean ( V. fabalis ) (6.5%) (Table 3.3).
Recent recruits were documented for Slippershell ( A. viridis ), Cylindrical Papershell
(Anodontoides ferrusacianus ), Spike ( E. dilatata), Wabash Pigtoe ( F. flava ), Fatmucket
(L. siliquoidea ), Giant Floater ( P. grandis ), and Rayed Bean ( V. fabalis ). In addition, all species except White Heelsplitter ( Lasmigona complanata complanata ) exhibited age class diversity (C V > 0.20) (Table 3.4).
Rayed Bean ( V. fabalis ) was found at each site in the Upper Blanchard, suggesting that it is well distributed through the reach. Estimated site densities for V. fabalis were as high as 0.58 per m 2 (0.42-0.79, 90% CI). While V. fabalis was relatively abundant in the Upper Blanchard, the mean densities at which it occurred were generally lower than those recently reported from several sites in French Creek (Pennsylvania,
Ohio River drainage) by Smith and Crabtree (2010). Mean densities in French Creek at nine sites ranged from 0 to 3.02 V. fabalis per m 2, with five sites supporting greater than
22
Table 3.2. Population and density estimates of freshwater mussels found in the Middle Blanchard River. Site abundances are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (MBLAN) are means calculated from all three sites (MBLAN1, MBLAN2, and MBLAN3). Species with an asterisk (*) are Ohio species of concern.
MBLAN1 MBLAN2 MBLAN3 MBLAN Relative Scientific Name Abundance Density Abundance Density Abundance Density Abundance Density Abundance Anodontoides ferussacianus 31 (6-155) 0.03 (0.01-0.13) 10 0.01 0.3 Elliptio dilatata 1227 (824-1828) 1.05 (0.71-1.57) 3212 (2387-4324) 2.03 (1.51-2.73) 2770 (1449-5294) 2.40 (1.26-4.59) 2403 1.83 66.3 Fusconaia flava 42 (8-215) 0.03 (0.01-0.14) 14 0.01 0.4 Lampsilis siliquoidea 368 (292-465) 0.32 (0.25-0.40) 507 (338-761) 0.32 (0.21-0.48) 185 (116-295) 0.16 (0.10-0.25) 353 0.27 9.7 Lasmigona c. complanata 61 (27-138) 0.05 (0.02-0.12) 42 (8-215) 0.03 (0.01-0.14) 34 0.03 0.9 Lasmigona compressa* 42 (8-215) 0.03 (0.01-0.14) 14 0.01 0.4 Lasmigona costata 61 (27-138) 0.05 (0.02-0.12) 42 (8-215) 0.03 (0.01-0.14) 31 (6-155) 0.03 (0.01-0.13) 45 0.04 1.2 Leptodea fragilis 61 (27-138) 0.05 (0.02-0.12) 423 (221-810) 0.27 (0.14-0.51) 31 (6-155) 0.03 (0.01-0.13) 172 0.12 4.7 Ptychobranchus fasciolaris* 215 (135-341) 0.18 (0.12-0.29) 465 (314-687) 0.30 (0.20-0.43) 277 (149-516) 0.24 (0.13-45) 319 0.24 8.8 Pyganodon grandis 31 (6-155) 0.03 (0.01-0.13) 42 (8-215) 0.03 (0.01-0.14) 24 0.02 0.7 Strophitus undulatus 92 (36-234) 0.08 (0.03-0.20) 254 (54-426) 0.16 (0.08-0.26) 277 (203-378) 0.24 (0.18-0.33) 208 0.16 5.7 Villosa iris 31 (6-155) 0.03 (0.01-0.13) 62 (12-310) 0.05 (0.01-0.27) 31 0.03 0.9
23
Table 3.3. Population and density estimates of freshwater mussels found in the Upper Blanchard River. Site estimates are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (UBLAN) are means calculated from all three (UBLAN4, UBLAN5, and UBLAN6) sites. Species with an asterisk (*) are Ohio species of concern while two asterisks (**) denote federally endangered species.
UBLAN4 UBLAN5 UBLAN6 UBLAN Relative Scientific Name Abundance Density Abundance Density Abundance Density Abundanc e Density Abundance Alasmidonta viridis 38 (17-85) 0.05 (0.23-0.12) 13 0.02 0.4 Amblema plicata 120 (76-191) 0.16 (0.10-0.26) 19 (4-94) 0.03 (0.01-0.13) 46 0.06 1.4 Anodontoides ferussacianus 100 (43-234) 0.14 (0.06-0.32) 57 (23-144) 0.08 (0.03-0.20) 52 0.07 1.6 Elliptio dilatata 1604 (1362-1890) 2.18 (1.85-2.57) 1446 (1286-1626) 1.99 (1.77-2.23) 1029 (856-1237) 1.41 (1.18-1.70) 1360 1.86 41.5 Fusconaia flava 241 (104-554) 0.33 (0.14-0.75) 343 (262-447) 0.47 (0.36-0.62) 136 (86-215) 0.19 (0.12-0.30) 240 0.33 7.3 Lampsilis cardium 19 (4-94) 0.03 (0.01-0.13) 6 0.01 0.2 Lampsilis siliquoidea 722 (391-1332) 0.98 (0.53-1.81) 1161 (904-1491) 1.60 (1.24-2.05) 447 (338-590) 0.61 (0.46-0.81) 777 1.06 23.7 Lasmigona c. complanata 60 (24-152) 0.08 (0.03-0.21) 57 (23-144) 0.08 (0.03-0.20) 39 0.05 1.2 Lasmigona costata 114 (34-388) 0.16 (0.05-0.53) 78 (52-116) 0.11 (0.07-0.16) 64 0.09 2 Pleurobema sintoxia* 20 (4-100) 0.03 (0.01-0.14) 38 (8-189) 0.05 (0.01-0.26) 58 (23-147) 0.08 (0.03-0.20) 39 0.05 1.2 Ptychobranchus fasciolaris* 100 (53-190) 0.14 (0.07-0.26) 95 (69-131) 0.13 (0.10-0.18) 65 0.09 2 Pyganodon grandis 321 (184-561) 0.44 (0.25-0.76) 457 (301-693) 0.63 (0.41-0.95) 194 (127-297) 0.27 (0.01-0.13) 324 0.44 9.9 Strophitus undulatus 20 (4-100) 0.03 (0.01-0.14) 7 0.01 0.2 Villosa fabalis** 80 (28-232) 0.11 (0.04-0.31) 419 (305-575) 0.58 (0.42-0.79) 136 (108-171) 0.19 (0.15-0.24) 212 0.29 6.5 Villosa iris 20 (4-100) 0.03 (0.01-0.14) 19 (4-94) 0.03 (0.01-0.13) 19 (4-96) 0.03 (0.01-0.13) 19 0.03 0.6
24
Table 3.4. Recruitment data for the Middle and Upper Blanchard River reaches. All shell measurements are in millimeters (mm). Recent recruits were individuals < 30 mm, except for V. fabalis and A. viridis which were < 20 mm. Coefficient of variation was only calculated for individuals with a minimum sample size of n = 5. Species with an asterisk (*) are Ohio species of concern while two asterisks (**) denote federally endangered species.
MBLAN UBLAN Min Max Mean Coefficient Recent Min Max Mean Coefficient Recent Scientific Name Length Length Length of Variation Recruits Length Length Length of Variation Recruits Alasmidonta viridis 16 18 17 N/A 2 Amblema plicata 32 121 74 0.40 0 Anodontoides ferussacianus 52 52 52 N/A 0 18 72 51 0.31 1 Elliptio dilatata 21 122 77 0.25 4 13 106 82 0.23 5 Fusconaia flava 73 73 73 N/A 0 10 101 59 0.28 1 Lampsilis cardium 35 35 35 N/A 0 Lampsilis siliquoidea 39 125 91 0.19 0 17 115 90 0.20 1 Lasmigona c. complanata 97 119 110 0.10 0 98 131 111 0.13 0 Lasmigona compressa* 87 87 87 N/A 0 Lasmigona costata 81 129 110 0.19 0 43 131 106 0.25 0 Leptodea fragilis 48 98 72 0.22 0 Pleurobema sintoxia* 40 100 69 0.33 0 Ptychobranchus fasciolaris* 48 98 72 0.22 0 61 111 83 0.22 0 Pyganodon grandis 36 101 75 0.31 0 23 119 88 0.27 1 Strophitus undulatus 33 53 43 N/A 0 64 64 64 N/A 0 Villosa fabalis** 12 29 21 0.24 8 Villosa iris 27 74 54 N/A 1 34 46 39 N/A 0
25 1.0 per m 2. French Creek supports one of the largest remaining V. fabalis populations
(Code of Federal Regulations 2012). It should also be noted that French Creek is nationally recognized for supporting a diverse freshwater mussel community and large populations of federally listed mussel species. Very little quantitative information is available regarding other V. fabalis populations throughout its range (Code of Federal
Regulations 2012).
From 1994 to 1996, a survey was conducted of the Upper Blanchard by
Hoggarth et al. (2000). Two sites were located near my Upper Blanchard reach, although the precise locations are difficult to determine. Hoggarth et al. (2000) reported a large and diverse mussel community from these sites, including substantial numbers of Rayed Bean ( V. fabalis ). However, it is unclear how many V. fabalis were enumerated as shell and how many were found live. Because the sampling methods differ so greatly between Hoggarth et al. (2000) and my sampling during 2010
(qualitative search vs. quantitative quadrat-based survey), it is difficult to compare results. Despite this, the five most abundant species reported by Hoggarth et al. (2000) were the same five species found during my study. Two species were found during the previous study that I did not encounter, however. These two species were the Lilliput
(T. parvus ) and the Ohio endangered Purple Lilliput ( Toxolasma lividus ). It is unclear from the methods described by Hoggarth et al. (2000) if these species were found as shell or live. It should also be noted here that quadrat surveys may not be as efficient at detecting low density species (< 0.01 per m 2) as qualitative surveys ( Strayer et al. 1997;
Vaughn et al. 1997; Obermeyer 1998; White and Gangloff 2008). Furthermore, I randomized my sites and therefore was not necessarily expending effort sampling the
26 most suitable habitat. Both of the Toxolasma species reported by Hoggarth et al.
(2000) may still occur in the Upper Blanchard regardless of not being found during my
Figure 3-1. Shell length frequency distributions of selected unionid species found in the Blanchard River. The top two histograms represent shell length data for the Ohio species of concern Kidneyshell ( P. fasciolaris ) in the Middle Blanchard (A) and Upper Blanchard (B). The bottom two histograms represent shell length data for the Spike ( E. dilatata ) in the Middle Blanchard (C) and Upper Blanchard (D).
27
Figure 3-2. Shell length frequency distributions of selected unionid species found in the Upper Blanchard River. The left histogram represents shell length data for the Ohio species of concern Round Pigtoe ( P. sintoxia ) (A) and the right histogram shell length data for the federally endangered Rayed Bean ( V. fabalis ) (B).
sampling efforts. Despite this, using Hoggarth et al. (2000) as a reference condition, the presence of recent recruits, numerous young individuals, and a diversity of age classes suggests that the community has been relatively stable since Hoggarth (2000) sampled from 1994 to 1996.
3.1.2 Swan Creek Unionids
Swan Creek field sampling documented a total of eight live species and 181 live individuals. Mean reach densities (individuals/m 2) were 1.38 in Middle Swan Creek and 0.22 in the Upper Swan Creek. Site abundances and estimates were also calculated with 90% confidence intervals and are presented in Table 3.5 and Table 3.6.
A total of six species were found live in Middle Swan Creek, with Shannon
28 Diversity scores ranging from 1.04 (MSWAN1) to 1.43 (MSWAN3) with a pooled
Shannon Diversity score of 1.24. The most abundant species in Middle Swan Creek were Spike ( E. dilatata ) (60.9%), Fatmucket ( L. siliquoidea ) (11.8%), Rayed Bean ( V. fabalis ) (10.2%), Rainbow ( V. iris ) (8.9%), and Wabash Pigtoe (F. flava ) (5.6%) (Table
3.5). Recent recruits were documented for Slippershell ( A. viridis ), Fatmucket ( L. siliquoidea ), and Rayed Bean ( V. fabalis ) (Table 3.7). Although I did not detect recent recruits for Spike ( E. dilatata ), Wabash Pigtoe ( F. flava ), and Rainbow ( V. iris ), each of these species did exhibit some age class diversity (C V > 0.15) (Figure 3.3).
Grabarkiewicz and Crail (2007) and Grabarkiewicz (2008) reported results of qualitative unionid surveys from Swan Creek conducted during 2006 to 2008. Five sites were located near or within my 1500 m Middle Swan Creek sampling reach. Several species, including Threeridge ( A. plicata ), White Heelsplitter ( Lasmigona complanata ),
Flutedshell ( L. costata ), Pink Heelsplitter ( P. alatus ), Giant Floater ( P. grandis ),
Creeper ( S. undulatus ), and Deertoe ( T. truncata ), found during those surveys were not found during my study in 2010. However, most of the missing species sampled between 2006 and 2008 were at very low abundances (< 5 individuals per site). As previously stated in the discussion of the Upper Blanchard, qualitative searches are generally more efficient at locating species than quadrat-based, quantitative sampling methods. Considering these species were rare during 2006 to 2008, it is reasonable that my quadrat sampling did not detect them considering site coverage was generally less than 7%. The Middle Swan Creek reach sampled during my study is the “jewel” of the system as described by Grabarkiewicz (2008). However, it should be noted that the methods employed during this study were designed to replicate reach sampling effort,
29
Table 3.5. Population and density estimates of freshwater mussels found in Middle Swan Creek. Site abundances are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (MSWAN) are means calculated from all three sites (MSWAN1, MSWAN2, and MSWAN3). Species with two asterisks (**) are federally endangered.
MSWAN1 MSWAN2 MSWAN3 MSWAN Relative Scientific Name Abundance Density Abundance Density Abundance Density Abundance Density Abundance Alasmidonta viridis 15 (3-72) 0.03 (0.01-0.13) 36 (7-176) 0.05 (0.01-0.26) 20 (4-101) 0.03 (0.01-0.13) 24 0.04 2.7 Elliptio dilatata 692 (597-802) 1.25 (1.0.8-1.45) 729 (593-896) 1.10 (0.89-1.34) 163 (96-276) 0.21 (0.13-0.36) 528 0.85 60.9 Fusconaia flava 74 (54-101) 0.13 (0.10-0.18) 71 (48-106) 0.11 (0.07-0.16) 48 0.08 5.6 Lampsilis siliquoidea 44 (18-110) 0.08 (0.03-0.20) 160 (71-361) 0.24 (0.11-0.54) 102 (74-140) 0.13 (0.10-0.18) 102 0.15 11.8 Villosa fabalis** 44 (18-110) 0.08 (0.03-0.20) 160 (94-273) 0.24 (0.14-0.41) 61 (24-154) 0.08 (0.03-0.20) 88 0.13 10.2 Villosa iris 118 (32-433) 0.21 (0.06-0.78) 53 (11-264) 0.10 (0.02-0.40) 61 (12-303) 0.08 (0.02-0.40) 77 0.12 8.9
Table 3.6. Population and density estimates of freshwater mussels found in the Upper Swan Creek. Site abundances are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (USWAN) are means calculated from all three sites (USWAN4, USWAN5, and USWAN6).
USWAN4 USWAN5 USWAN6 USWAN Relative Scientific Name Abundance Density Abundance Density Abundance Density Abundance Density Abundance Lampsilis siliquoidea 74 (39-140) 0.13 (0.07-0.25) 40 (8-198) 0.05 (0.01-0.27) 38 0.06 38.6 Lasmigona c. complanata 119 (70-201) 0.21 (0.13-0.36) 20 (4-99) 0.03 (0.01-0.13) 36 (16-79) 0.05 (0.02-0.12) 58 0.10 31.6 Pyganodon grandis 45 (18-112) 0.08 (0.03-0.20) 60 (24-151) 0.08 (0.03-0.20) 18 (4-88) 0.03 (0.01-0.13) 41 0.06 29.8
30
Table 3.7. Recruitment data for the Middle and Upper Swan Creek reaches. All shell measurements are in millimeters (mm). Recent recruits were individuals < 30 mm, except for V. fabalis and A. viridis which were < 20 mm. Coefficient of variation was only calculated for individuals with a minimum sample size of n = 5. Species with two asterisks (**) are federally endangered species.
MSWAN USWAN
Min Max Mean Coefficient Recent Min Max Mean Coefficient Recent Scientific Name Length Length Length of Variation Recruits Length Length Length of Variation Recruits Alasmidonta viridis 14 29 23 0.28 1 Elliptio dilatata 40 105 65 0.20 0 Fusconaia flava 46 67 54 0.20 0 Lampsilis siliquoidea 15 85 56 0.45 6 90 112 100 0.06 0 Lasmigona c. complanata 67 95 79 0.12 0 Pyganodon grandis 70 86 77 0.08 0 Villosa fabalis** 20 33 25 0.14 1 Villosa iris 36 63 48 0.17 0
31
Figure 3-3. Shell length frequency distributions of selected unionid species found in Middle Swan Creek (MSWAN). The top two histograms represent shell length data for the Spike ( E. dilatata ) (A) and Wabash Pigtoe ( F. flava ) (B). The bottom two histograms represent shell length data for the Rayed Bean ( V. fabalis ) (A) and Rainbow (V. iris ) (B).
32 estimate population sizes, and calculate relative abundances. These methods removed effort from some of the most optimal locations at the reach and site scale. Despite this, it also led me to a new site (MSWAN2) where I found many Rayed Bean ( V. fabalis ).
This result highlights the potential impact randomization can have when sampling rare species. This technique may introduce sites that may not otherwise be considered with more selective sampling strategies.
Upper Swan Creek was found to support a total of three live species, with
Shannon Diversity scores ranging from 0.64 (USWAN6) to 1.02 (USWAN5), with a pooled score of 1.07. The species encountered were Fatmucket ( L. siliquoidea )
(38.6%), White Heelsplitter ( L. c. complanata ) (31.6%), and Giant Floater ( P. grandis )
(29.8%) (Table 3.6). Recent recruits were not documented for any of the three species and each species exhibited low age class diversity (C v < 0.12) (Table 3.7). Despite few live species, several species were present as shell only, including Cylindrical Papershell
(A. ferussacianus ), Threeridge ( A. plicata ), Wabash Pigtoe (F. flava ), and Creeper ( S. undulatus ).
Upper Swan Creek supported the fewest mussels and least number of species.
These results support the data reported by Grabarkiewicz (2008) for sites near my sampling reach. Sampling was difficult throughout Upper Swan Creek due to large amounts of woody debris – the worst of which was found at USWAN6. While my reach was located within Oak Openings Metropark, QHEI scores were consistently poor at all three sites. This was due to the absence of riffles, consistently poor channel development, sparse canopy cover, and indicators of channel instability, such as scour down to hardpan, abundant woody debris, and bank erosion.
33 3.1.3 Beaver Creek Unionids
Beaver Creek field sampling documented a total of 12 live species and 205 live individuals. Mean reach densities (individuals/m2) were 0.89 in Middle Beaver and
0.92 in Upper Beaver Creek. Site abundances and estimates were also calculated with
90% confidence intervals and are presented in Table 3.8 and Table 3.9. Overall, unionid diversity and density within Beaver Creek was lower than the Blanchard River but similar to Middle Swan Creek.
Middle Beaver Creek was found to support a total of nine live species, with
Shannon Diversity scores ranging from 1.24 (MBEAV2) to 1.50 (MBEAV3) and a pooled Shannon Diversity score of 1.39. The most abundant species were Wabash
Pigtoe ( F. flava ) (44.9%), Fragile Papershell ( L. fragilis ) (17.8%), Pink Heelsplitter ( P. alatus ) (14.4%), White Heelplitter ( L. c. complanata ) (7.2%), and Mapleleaf ( Quadrula quadrula ) (4.6%) (Table 3.8). Recent recruits were documented for Wabash Pigtoe ( F. flava ) (Figure 3-4) and Pimpleback ( Quadrula pustulosa ). Considerable age class diversity was exhibited by Fragile Papershell ( L. fragilis ) (Figure 3.4) and Pink
Heelsplitter ( P. alatus ) (C V > 0.15).
Upper Beaver Creek was found to support a total of 10 live species, with
Shannon Diversity scores ranging from 1.51 (MBEAV4) to 1.68 (MBEAV5) and a pooled Shannon Diversity score of 1.58. The most abundant species were Wabash
Pigtoe ( F. flava ) (40.4%), Fragile Papershell ( L. fragilis ) (22.8%), White Heelplitter ( L. c. complanata ) (10.6%), Pink Heelsplitter ( P. alatus ) (7.6%), and Giant Floater ( P. grandis ) (5.2%) (Table 3.9). Recent recruits were documented for Ohio species of concern Deertoe ( T. truncata ) (Table 3.10). Some diversity of size classes was
34 documented for Wabash Pigtoe ( F. flava ), Fatmucket ( L. siliquoidea ), White
Heelsplitter ( L. c. complanata ), and Fragile Papershell ( Leptodea fragilis ) (C V > 0.15)
(Table 3.10; Figure 3-4).
A review of published literature and technical reports finds no references for the mussels of Beaver Creek. The only information available is through seven voucher specimens housed at the Ohio State University Museum of Zoology (Division of
Molluscs). The shells document six species, with collection dates ranging from 1949 to
1997. All species present in the Ohio State collection were found live during 2010 field work. No records for Beaver Creek exist at the University of Michigan Museum of
Zoology (Division of Mollusks).
Overall, Middle Beaver Creek and Upper Beaver Creek were found to support a low to medium density mussel assemblage noticeably different in composition than
Swan Creek or the Blanchard River. Sorenson Similarity values presented in Table 3.1 suggested that the species composition found in Beaver Creek was most dissimilar to the community found in the two reaches with Rayed Bean (V. fabalis ): the Upper
Blanchard and Middle Swan Creek. Many of the species found in Middle and Upper
Beaver Creek, such as Pink Heelsplitter ( P. alatus ), Pimpleback ( Q. pustulosa ), and
Mapleleaf ( Q. quadrula ), are commonly found in lake, reservoir, or “big river” habitats
(Parmalee and Bogan 1998; Watters et al. 2009). This may be due to associated host species, such as Channel Catfish ( Ictalurus punctatus ) and Freshwater Drum
(Aplodinotus grunniens ), which are often more abundant in rivers and lakes. Due to the proximity of both reaches to the Maumee River, the current Maumee fauna probably has a strong influence on the community of the Beaver Creek sampling reaches.
35
Table 3.8. Population and density estimates of freshwater mussels found in Middle Beaver Creek. Site abundances are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (MBEAV) are means calculated from all three sites (MBEAV1, MBEAV2, and MBEAV3). Species with an asterisk (*) are Ohio species of concern. MEAV1 MBEAV2 MBEAV3 MBEAV Relative Scientific Name Abu ndance Density Abundance Density Abundance Density Abundance Density Abundance Fusconaia flava 150 (67-336) 0.16 (0.07-0.36) 396 (279-561) 0.53 (0.38-0.76) 674 (419-1084) 0.5 (0.31-0.80) 407 0.40 44.9 Lasmigona c. complanata 20 (4-98) 0.03 (0.01-0.13) 177 (75-418) 0.13 (0.06-0.31) 66 0.05 7.2 Lasmigona compressa* 35 (7-180) 0.03 (0.01-0.13) 12 0.01 1.3 Leptodea fragilis 200 (117-341) 0.21 (0.13-0.36) 178 (131-242) 0.24 (0.18-0.33) 106 (21-539) 0.03 (0.01-0.13) 161 0.18 17.8 Potamilus alatus 199 (34-290) 0.11 (0.04-0.31) 79 (27-228) 0.11 (0.04-0.31) 213 (95-479) 0.16 (0.07-0.36) 131 0.12 14.4 Pyganodon grandis 75 (30-190) 0.08 (0.03-0.20) 40 (8-197) 0.05 (0.01-0.27) 38 0.04 4.2 Quadrula pustulosa 25 (5-125) 0.03 (0.01-0.13) 20 (4-98) 0.03 (0.01-0.13) 71 (14-359) 0.05 (0.01-0.27) 39 0.04 4.3 Quadrula quadrula 20 (4-98) 0.03 (0.01-0.13) 106 (21-539) 0.08 (0.02-0.40) 42 0.04 4.6 Toxolasma parvus 35 (7-180) 0.03 (0.01-0.13) 12 0.01 1.3
36
Table 3.9. Population and density estimates of freshwater mussels found in Upper Beaver Creek. Site abundances are per 100 m and densities represent individuals per m 2. Values in parentheses represent 90% confidence intervals. The final three columns (UBEAV) are means calculated from all three sites (UBEAV4, UBEAV5, and UBEAV6). Species with an asterisk (*) are Ohio species of concern. UBEAV4 UBEAV5 UBEAV6 UBEAV Relative Scientific Name Abundance Density Abundance Density Abundance Density Abundance Density Abundance Fusconaia flava 280 (85-375) 0.31 (0.21-.40) 524 (355-773) 0.61 (0.41-0.91) 138 (69-275) 0.16 (0.08-0.32) 314 0.36 40.4 Lampsilis cardium 23 (5-114) 0.03 (0.01-0.13) 8 0.01 1.0 Lampsilis siliquoidea 68 (27-173) 0.08 (0.03-0.20) 46 (18-116) 0.05 (0.02-0.14) 38 0.04 4.9 Lasmigona c. complanata 40 (17-164) 0.06 (0.02-0.22) 137 (61-305) 0.16 (0.07-0.36) 69 (40-118) 0.08 (0.05-0.14) 82 0.10 10.6 Leptodea fragilis 165 (80-316) 0.18 (0.08-0.30) 228 (165-314) 0.27 (0.19-0.37) 138 (80-235) 0.16 (0.09-0.28) 177 0.21 22.8 Potamilus alatus 40 (17-164) 0.06 (0.02-0.22) 137 (61-305) 0.16 (0.07-0.36) 59 0.08 7.6 Pyganodon grandis 74 (35-172) 0.08 (0.04-0.29) 46 (18-116) 0.05 (0.02-0.14) 40 0.04 5.2 Quadrula pustulosa 46 (20-102) 0.05 (0.02-0.12) 15 0.02 1.9 Quadrula quadrula 68 (14-341) 0.08 (0.16-0.40) 23 0.03 3.0 Truncilla truncata* 40 (17-164) 0.06 (0.02-0.22) 23 (5-114) 0.03 (0.01-0.13) 21 0.03 2.7
37
Table 3.10. Recruitment data for the Middle and Upper Beaver Creek reaches. All shell measurements are in millimeters (mm). Recent recruits were individuals < 30 mm, except for T. parvus which was < 20 mm. Coefficient of variation was only calculated for individuals with a minimum sample size of n = 5. Species an asterisk (*) are Ohio species of concern.
MBEAV UBEAV
Min Max Mean Coefficient of Recent Min Max Mean Coefficient Recent Scientific Name Length Length Length Variation Recruits Length Length Length of Variation Recruits Fusconaia flava 24 96 66 0.28 2 26 99 69 0.27 0 Lampsilis cardium 110 110 110 0 Lampsilis siliquoidea 78 92 84 0.18 0 Lasmigona c. complanata 90 108 99 0.06 0 89 145 112 0.19 0 Lasmigona compressa* 93 93 93 N/A 0 Leptodea fragilis 31 101 68 0.28 0 34 114 85 0.26 0 Potamilus alatus 72 140 100 0.23 0 112 141 124 0.11 0 Pyganodon grandis 67 85 76 0.11 0 70 74 72 N/A 0 Quadrula pustulosa 15 67 51 N/A 1 46 61 54 N/A 0 Quadrula quadrula 74 114 91 N/A 0 66 73 70 N/A 0 Toxolasma parvus 28 28 28 N/A 0 Truncilla truncata* 29 33 31 N/A 1
38
Figure 3-4. Shell length frequency distributions of selected unionid species found in Upper Beaver Creek (UBEAV) and Middle Beaver Creek (MBEAV). The top two histograms represent shell length data for Wabash Pigtoe ( F. flava ) (A) and Fragile Papershell ( L. fragilis ) (B) in Upper Beaver Creek. The bottom two histograms represent shell length data for Wabash Pigtoe ( F. flava ) (C) and Fragile Papershell ( L. fragilis ) (D) in Middle Beaver Creek.
39 3.2 Qualitative Habitat Evaluation Index
Mean reach QHEI scores ranged from 65 (SD +4.4) in the Middle Blanchard
River to 44 (SD +1.2) in Upper Swan Creek. The amount of variability among sites within reaches differed - with one sample standard deviation ranging from 5.5 in Upper
Beaver Creek to 1.2 in Upper Swan Creek (Figure 3-5). In general, the Middle
Blanchard scored higher QHEIs than other reaches due to greater substrate diversity, the presence of riffles, and overall greater habitat heterogeneity. Reaches that scored lower consisted of sites with fine substrates, homogenous channel structure (e.g., dominated by glide habitat), and indicators of instability.
QHEI has been positively correlated with the biological integrity of fish communities throughout Ohio (Ohio EPA 1987). If habitat quality is a useful predictor of fish community integrity, it may also be a useful predictor of unionid species richness and density due to the obligate fish parasite stage shared among unionids.
Therefore, I examined the relationship between QHEI and mean unionid species richness, density, and Shannon Diversity. Linear regression was used on unionid species richness and density because it provided the same approximate fit as 2 nd order
nd polynomial regression. A 2 order polynomial regression provided the best fit for
Shannon Diversity (Figure 3-5).
Although my study possessed a limited number of data points, the initial results
2 suggest a positive relationship between QHEI scores and unionid species richness (R
2 2 = 0.63), unionid density (R = 0.52), as well as Shannon Diversity (R = 0.51). Clearly, more samples are needed from Ohio creeks and rivers to determine the predictive ability of QHEI. Within the range of QHEI values examined (44 to 67), increases
40
Figure 3-5. QHEI exploration, linear regression, and 2 nd order polynomial regression for all sampling reaches. The boxplot (A) illustrates intersite variability for each reach. The box represents the interquartile range which contains values between the 25 th and 75 th percentile. The line within the box represents the median QHEI score while the whiskers denote the upper and lower adjacent values. Graphic B examines mean species richness as a function of mean QHEI score. Graphic C depicts mean unionid density as a function of mean QHEI score. Graphic D depicts pooled Shannon Diversity as a function of mean QHEI score.
in habitat quality would provide more suitable habitat conditions for mussels and associated fish species. However, I would expect mussel habitat to become less
41 suitable as QHEI values exceed 70 due to the QHEI scoring methodology. This is partly due to QHEI scaling by substrate particle size, awarding more points for large sediment grain sizes and fewer points for smaller grain sizes. For example, boulder receives a “10” while small gravel receives a “6” in the substrate metric. Additional examples can be found throughout the metric where more points are awarded for cobble and boulder versus smaller substrates. Additionally, stream gradient and related measures (e.g. current velocity) are also scaled so moderate to high gradient streams receive more points than low gradient streams. Therefore, with other factors being equal, the highest scoring streams will be high gradient, large substrate streams.
Considering the results of my field research and the QHEI scoring methodology, caution should be applied when using QHEI to predict unionid communities.
The PCA presented in Figure 3.6 further explores QHEI scores and substrate similarities across reaches. Component 1 explained 65.5% of the data variation while
Component 2 explained 20.6% of the variation. The Middle Blanchard (MBLAN), which contained the largest mean percentages of cobble and large gravel, orients far to the left of the other study reaches. The Middle Blanchard also had the highest mean QHEI score. Upper Swan Creek (USWAN), which was comprised of mostly silt, sand, and organic matter, orients far to the right. Upper Swan Creek had the lowest mean QHEI score. The other reaches, where small gravel dominated the particle size distribution, lie in between MBLAN and USWAN. Interestingly, the two sites where Rayed Bean ( V. fabalis ) occurs are relatively close together.
42
Figure 3-6. Principal Components Analysis (PCA) of all stream reaches based on mean surface substrate composition. Values in parentheses indicate mean reach QHEI scores. Component 1 explained 65.5% of the data variation while Component 2 explained 20.6% of the variation.
43 3.3 Microhabitat Use
Microhabitat data were investigated using Principle Components Analysis
(PCA). I selected substrate surface texture for exploration because it was consistently quantified. All substrate measures were initially entered into the analysis. Vectors that possessed little variance and were correlated with other vectors were removed. I finished with two different ordination frameworks: one that included organic matter and one that did not. The term “organic” during this study denoted the presence of organic debris or macro-sized detritus as a constituent of the surface substrate. The amount of woody debris encountered during field work within all reaches and streams was substantial.
While the PCA diagrams (Figures 3-7 – 3-10) represent exploration and not analysis, they do suggest patterns in the data that are supported by Table 3.10. I noticed a general pattern where several species, including Spike ( E. dilatata ), Wabash Pigtoe ( F. flava ), Kidneyshell ( P. fasciolaris ), Rayed Bean ( V. fabalis ), and Rainbow (V. iris ), aligned along the small gravel vector. Kidneyshell ( P. fasciolaris ) and Spike ( E. dilatata ) were among the few species that displayed several points along large gravel. Overall,
Kidneyshell ( P. fasciolaris ) seemed to align strongest along coarse sediments, although a few individuals were found in quadrats with a substantial amount of sand. Rayed bean
(V. fabalis ) were found in quadrats with the highest mean of small gravel percentage
(60.2%) and lowest variation (SD 22). They were most often found in well sorted gravel glides at the head of riffles or shoals. The “arch effect” was also apparent in the PCA output. This may be because PCA interprets shared zeros as a positive relationship
(McCune and Grace 2002).
44
Figure 3-7. PCA of surface substrate use by Giant Floater ( P. grandis ) (A), White Heelsplitter ( L. c. complanata ) (B), Spike ( E. dilatata ) (C), and Rayed Bean ( V. fabalis ) (D). The independent substrate variables used include percent surface silt, sand, organic, small gravel (sgravel), and large gravel (lgravel). The black dots represent quadrat samples where the species was found while gray dots represent all samples across all reaches and streams.
45
Figure 3-8. PCA of surface substrate use by Fatmucket ( L. siliquoidea ) (A), Fragile Papershell ( L. fragilis ) (B), Kidneyshell ( P. fasciolaris ) (C), and Wabash Pigtoe ( F. flava ) (D). The independent substrate variables used include percent surface silt, sand, organic, small gravel (sgravel), and large gravel (lgravel). The black dots represent quadrat samples where the species was found while gray dots represent all samples across all reaches and streams.
46
Figure 3-9. PCA of surface substrate use by Giant Floater ( P. grandis ) (A), White Heelsplitter ( L. c. complanata ) (B), Spike ( E. dilatata (C) ), and Rayed Bean ( V. fabalis ) (D). The independent substrate variables used include percent surface silt, sand, small gravel (sgravel), and large gravel (lgravel). The black dots represent quadrat samples where the species was found while gray dots represent all samples across all reaches and streams.
47
Figure 3-10. PCA of surface substrate use by Fatmucket ( L. siliquoidea ) (A), Fragile Papershell ( L. fragilis ) (B), Kidneyshell ( P. fasciolaris ) (C), and Wabash Pigtoe ( F. flava ) (D). The independent variables used include percent surface silt, sand, small gravel (sgravel), and large gravel (lgravel). The black dots represent quadrat samples where the species was found while gray dots represent all samples across all reaches and streams.
48 Table 3.11. Summary of mean surface substrate quadrat measurements for the eight most common species across all reaches and streams. Values in substrate columns represent mean percentages of substrate present and values in parentheses indicate ±1 SD. Sample sizes (N, minimum = 20) were calculated based on the number of quadrats where the species was present. Small gravel is represented by sgravel and large gravel by lgravel.
N Silt Sand sgravel lgravel Organic
Elliptio dilatata 271 5.9 (7.1) 21.7 (20.6) 52.9 (25.3) 8.6 (11.6) 3.3 (9.5) Fusconaia flava 106 10.9 (6.4) 24.4 (22.3) 53.1 (24.1) 4.6 (7.9) 4.3 (8.2) Lampsilis siliquoidea 141 8.9 (7.5) 26.2 (22.1) 46 (26.9) 5.6 (9.1) 7.2 (16.5) Lasmigona c. complanata 29 10 (6.6) 35.5 (30.1) 36.2 (30.8) 1.7 (4.1) 13.8 (25.5) Leptodea fragilis 28 8.9 (6.9) 22 (19.4) 43.9 (27.2) 8.8 (8.8) 3.6 (7.6) Pyganodon grandis 65 12.6 (6.5) 27.1 (21.7) 37.8 (25.6) 3.6 (8.4) 16.3 (24.9) Ptychobranchus fasciolaris 35 3.7 (6.0) 20.3 (25.3) 53.9 (25.1) 10.1 (13.3) 1.3 (3.1) Villosa fabalis 30 8 (7.1) 22.3 (16.2) 60.2 (22.0) 2.3 (4.5) 2.2 (6.0) Villosa iris 21 8 (10.6) 23.5 (24.7) 51.3 (23.3) 6.3 (7.8) 2.5 (7.0)
In contrast to the species that aligned with gravel, several species occupied a wide range of vectors, including White Heelsplitter ( L. c. complanata ), Giant Floater (P. grandis ), and Fatmucket ( L. siliquoidea ). These species are widespread in Ohio and may occupy habitats where other species do not occur. All three were present in gravel glides and shoals like the former species that aligned along the gravel vector, but also in margin areas of sand, silt, and woody debris.
While organic debris is not traditionally thought of as a substrate type, I included it as part of the PCA due to its abundance throughout my field research. Much of the organic debris was embedded in the sediment. When included in the PCA, the “margin areas” used by L. c. complanata , P. grandis , and L. siliquoidea became visible when compared with species that were more abundant in gravel substrates (Figure 3-7 and 3-8).
A stricter interpretation of substrate was also performed by removing organic debris and simply including the traditional texture categories (Figure 3-9 and 3-10).
49 3.4 Subsurface Sampling
Approximately 61% of all live mussels were found on the substrate surface (Q) while 39% were collected from subsurface (Qb) samples. In total, just 8% of all recent recruits (< 30mm; < 20mm for A. viridis , V. fabalis , and T. parvus ) were found on the surface. Differences in surface detectability were observed across streams but were somewhat less variable across reaches where sample sizes were large. For example, only
26.3% of Spike ( E. dilatata ) was detected at the substrate surface in Swan Creek while
64.6% and 68.1% were found at the surface in the Middle Blanchard and Upper
Blanchard, respectively (Figure 3-11). Middle Swan Creek harbored the greatest percentage of mussels in subsurface samples but was also dominated by species that exhibited a propensity for burrowing into the substrate.
Interspecific differences in surface detectability were evident at the reach and stream scales (Table 3.12). Spike ( E. dilatata ) (Figure 3-11), Wabash Pigtoe ( F. flava )
(Figure 3-11), Kidneyshell ( P. fasciolaris ), and Rainbow ( V. iris ) were all present in subsurface samples across most size classes. Despite this, I did find a general trend that shell lengths were routinely smaller in subsurface samples when compared to surface samples among these species. To demonstrate this, I tested whether the mean shell length differed among E. dilatata and F. flava collected from surface (Q) and subsurface samples (Qb). Spike ( E. dilatata ) and Wabash Pigtoe ( F. flava ) were selected due to consistently large sample sizes across spatial scales. Because shell length data were not normally distributed, I used Mann-Whitney to test the null hypothesis that there was no difference in mean shell length ranks for individuals collected from the surface (Q) and individuals collected from the subsurface (Qb). I rejected the null hypothesis at
50
Figure 3-11. Two-way burrowing histograms. The zero line represents the substrate surface. White bars indicate the number of mussels captured on the surface and gray bars represent the number of mussels found in subsurface samples. The two upper histograms represent Spike ( E. dilatata ) in UBLAN (A) and MBLAN (B). The middle row represents E. dilatata in the MSWAN (C) and E. dilatata (D) across all reaches and streams. The bottom row represents Wabash Pigtoe ( F. flava ) in UBLAN (E) and F. flava across all reaches and streams (F).
51 Table 3.12. Percentage of individuals found in subsurface samples (Qb) as percentage of total live individuals found (Q + Qb). Values in parentheses represent total individuals found (Q + Qb).
Species Qb MBLAN UBLAN MSWAN USWAN MBEAV UBEAV
V. fabalis 93.3 (45) - 93.3 (30) 93.3 (15) - - - V. iris 66.7 (16) 33.3 (3) 50.0 (2) 72.7 (11) - - - F. flava 51.2 (117) 0 (1) 67.9 (28) 77.8 (9) - 55.0 (40) 31.0 (39) E. dilatata 42.2 (457) 35.4 (203) 31.9 (159) 73.7 (95) - - - P. fasciolaris 39.3 (33) 33.3 (27) 66.6 (6) - - - - P. grandis 17.8 (73) 23.5 (17) 15.8 (38) - 14.3 (7) 20.0 (5) 16.7 (6) L. siliquoidea 10.0 (150) 3.2 (31) 7.8 (90) 35.3 (17) 14.3 (7) - 0 (5) L. fragilis 9.3 (54) 0 (13) - - - 15.0 (20) 9.5 (21) L. c. complanata 5.7 (35) 0 (3) 0 (5) - 0 (10) 2 (6) 0 (11) L. costata 3.2 (13) 0 (4) 11.1 (9) - - - - P. alatus 0 (22) - - - - 0 (14) 0 (8)
α = 0.05 across all reaches and streams for Spike (p < 0.0001) and across reaches for
Wabash Pigtoe ( F. flava ) (p = 0.02 and p <0.0001) (Table 3.13). These results suggest that sampling these species without a subsurface component may misrepresent population demography if shell length is used as a surrogate for age. As noted above, this trend was evident in other species (e.g. P. fasciolaris and V. iris ) but I did not test for differences due to small sample sizes or limited distributions. It should be noted that Mann-Whitney does not require normally distributed data but may be sensitive to data with unequal variances. While the variances for some reaches were similar, there are others that are substantially different.
I also tested whether small individuals were more abundant in subsurface samples than surface samples. To do this, I examined abundance in subsurface and surface samples for individuals less than 50 mm for the following species: F. flava , E. dilatata , L. siliquoidea , and P. grandis . These species were chosen for their large sample size across spatial scales and large maximum shell size of 100 mm or more (Watters et al. 2009). I used a two-tailed t-test assuming unequal variance at α = 0.05 to test the null hypothesis
52 that there was no difference in the mean number of small individuals present in subsurface versus surface samples among reaches and streams.
Table 3.13. Mean shell lengths for E. dilatata and F. flava among reaches and streams for individuals found in surface samples (Q) and subsurface (Qb) samples. Mann- Whitney values are included indicating significant differences in ranked values at α = 0.05.
Q Qb Mann-Whitney Values mean variance mean variance U Z P Elliptio dilatata MBLAN 82.9 320.9 62.9 353.4 4378 -7.5 < 0.0001 UBLAN 90.9 303.4 49.4 752.4 2671 -11.4 < 0.0001 MSWAN 68.8 323.8 53.1 233.4 896.5 -4.4 < 0.0001 ALL REACHES 85.2 518.2 54.6 345.7 21870 -16.5 < 0.0001
Fusconaia flava UBLAN 69.3 287.7 54.3 275.2 89 1.4 0.15 MBEAV 74.6 132.0 58.1 426.1 123.5 2.4 0.02 UBEAV 69.3 287.7 54.3 275.2 99 2.4 0.02 ALL REACHES 70.8 276.5 55.9 244.6 11015 4.7 <0.0001
I found significantly more small individuals in subsurface samples for Spike ( E. dilatata )
(p = 0.03). This was not statistically significant using the test method selected for other species (Table 3.14). I suspect this was because of small sample size.
Table 3.14. Mean number of individuals less than 50 mm found in surface (Q) and subsurface samples (Qb) across all reaches and streams. T-test values are included indicating significant differences in means at α = 0.05.
Mean Q Mean Qb df T Stat P E. dilatata 3.0 12.3 3 3.8 0.03 F. flava 1.5 5.5 6 2.4 0.06 L. siliquoidea 0.3 3.3 2 2.4 0.14 P. grandis 0.3 1.7 3 1.8 0.17
As noted above, several species were found in subsurface samples across size classes. However, some species were collected from subsurface samples only when young. Species that demonstrated this pattern included Fatmucket ( L. siliquoidea ),
53 Fragile Papershell ( L. fragilis ), and Giant Floater ( P. grandis ) (Figure 3-12). These species were found almost exclusively on the surface at 75 mm or more in length.
Figure 3-12. Two-way burrowing histograms. The number zero represents the substrate surface. White bars indicate mussels captured on the surface and gray bars represent mussels found in subsurface samples. The two upper histograms represent Fatmucket ( L. siliquoidea ) in UBLAN (A) and across all reaches and streams (B). The middle row represents Giant Floater ( P. grandis ) in UBLAN (C) and across all reaches and streams (D). The bottom row represents L. fragilis in MBEAV (E) and across all reaches and streams (F).
54 The data and analysis above focused on trends related to species and size.
I also investigated the relationship between substrate texture, substrate penetrability, and surface detectability. For this, I used E. dilatata and F. flava again due to their large sample size and presence across multiple reaches (n = 271 and n = 106, respectively) and streams (n = 3 and n = 5, respectively). For both species, I analyzed the mean substrate texture and core penetration depth of quadrats where they were found in subsurface samples and compared them to surface samples. Because the data were non-parametric, I used Mann-Whitney to examine differences between ranked values at α = 0.05. While I found evidence that ranked values differed for two comparisons at the reach scale, overall there were not strong significant relationships among reaches and streams. Penetrability data did suggest that there was a trend where mussels were more abundant in substrates that had a higher penetrability, this was significant for both F. flava and E. dilatata across all streams and reaches but was not consistent at the reach scale.
These summary statistics and analyses suggest that freshwater mussel burrowing and surface detectability may be influenced by species and associated life history traits.
Patterns were evident that subdivided species into those present in subsurface samples across size classes, those present in subsurface samples primarily when young, and those species that were found mostly above or below the surface no matter the size class (e.g.,
V. fabalis ). I found no strong evidence that suggested surface detectability was a response to surface substrate texture for the species examined. However, substrate penetrability did differ when all samples across all reaches and streams were included for E. dilatata – with Spike ( E. dilatata ) more common in subsurface samples with higher penetrability.
Obviously, these results are a snapshot of detectability during summer, low flow
55 conditions. Since sampling programs typically survey mussels during low flow conditions, these results highlight the need to investigate subsurface sediments when conducting sampling designed to accurately assess population or community characteristics. The results also raise questions regarding why mussels burrow into subsurface sediments. Possible explanations include additional stability, pedal or deposit feeding, and protection from predators.
56
Table 3.15. Table of mean substrate and penetration data for individuals found in surface (Q) and subsurface samples (Qb) with variance in parentheses. Core penetration values are in centimeters. Ranked means were compared using Mann-Whitney tests and p- values were considered significant at α = 0.05. Surface Sand Surface Gravel Surface Organic Core Penetration Q Sand Qb sand P Q gravel Qb gravel P Q organic Qb organic P Q Core Qb Core P E. dilatata UBLAN 27.2 (271) 17.8 (203) 0.300 58.7 (500) 55.6 (511) 0.410 3.1 (72) 1.2 (10) 0.400 3.0 (3.7) 2.7 (4.9) 0.267 MBLAN 16.8 (350) 19.8 (250) 0.050 65.8 (702) 65.9 (443) 0.522 0.8 (9.2) 0.7 (13) 0.857 1.7 (3.6) 2.4 (5.9) 0.114 MSWAN 24.6 (567) 28.1 (564) 0.491 62.3 (916) 66.9 (653) 0.665 4.2 (135) 1.0 (9) 0.147 4.1 (9.3) 5.4 (5.8) 0.020 ALL REACHES AND STREAMS 19.4 (343) 22.2 (365) 0.078 62.6 (646) 63.5 (553) 0.917 2.1 (48) 0.9 (10) 0.164 2.5 (4.8) 3.6 (7.5) <0.001
F. flava UBLAN 18.9 (536) 30.9 (608) 0.160 65 (630) 37.9 (442) 0.007 0.5 (2.8) 2.9 (36) 0.624 2.9 (2.5) 4.1 (6.8) 0.170 UBEAV 25.7 (91) 27.5 (110) 0.631 57.3 (480) 60.8 (74) 0.660 1.3 (15.6) 1.6 (6.7) 0.562 3.5 (3.0) 3.4 (3.6) 0.370 3.5 6.7 MBEAV 26.9 (692) 13.8 (120) 0.900 69.3 (895) 52 (172) 0.197 9.0 (304) 6.1 (47) 0.704 (14.9) (16.4) 0.060 ALL REACHES 5.2 AND STREAMS 21.9 (338) 27.6 (539) 0.317 59.4 (486) 51.3 (581) 0.161 3.2 (99) 3.7 (36) 0.148 3.5 (6.4) (12.2) 0.017
57 Chapter 4
Summary and Conclusions
No quantitative unionid population studies have been conducted in the
tributaries of Western Lake Erie. My work represents the first of this kind. The
reaches I studied during 2010 were found to support locally and globally important
populations of freshwater mussels. The federally endangered Rayed Bean (V.
fabalis ) was well distributed in both the Upper Blanchard River and Middle Swan
Creek, present at all sites within each reach. In addition, within both reaches a
variety of size classes were found, with many young V. fabalis individuals present
in the Upper Blanchard River. The Upper Blanchard also supported the highest
species richness and highest mussel densities among the six reaches studied.
Beaver Creek, which had a relatively undocumented fauna prior to my 2010 field
sampling, was found to support 13 species and two Ohio species of concern.
Several of the species found in Beaver Creek are more often associated with big
river habitats and may have source populations in the nearby Maumee River
mainstem.
58 Several future projects could be conducted to better understand the community structure within the study reaches and streams. First, the current range of Rayed Bean ( V. fabalis ) in both the Upper Blanchard River and Middle Swan
Creek could be investigated further. I suspect the current range of V. fabalis in
Swan Creek is a mere five RKM in length while the Upper Blanchard may be as high as 33 RKM. Once determined, methods could be designed to estimate population sizes for each stream with measures of uncertainty. Revisions to the methods used in this study would be necessary to provide estimates across such a comparatively large spatial scale. This would likely require a two-phase sampling method, where timed searches and habitat assessments were conducted during
“phase I” and quadrat sampling was conducted during “phase II.” Methods might also include using Geographic Information Systems (GIS) to assist with habitat identification similar to the study conducted by Smith and Crabtree (2010). Long- term monitoring could also be performed using the current study or an expanded version as detailed above. Because my methods are reproducible and the data reported included measures of uncertainty for individual sites, monitoring goals could involve assessing temporal changes related to species richness, abundance, density, and demography. Site randomization could also locate new sites where populations of rare species occur similar to the results from Middle Swan Creek during this research.
In addition to further quantifying and monitoring the Middle Swan Creek and Upper Blanchard V. fabalis populations, the patterns of habitat use identified
59 during this research could be helpful in determining future areas to search for
Rayed Bean ( V. fabalis ). For example, distribution maps presented in Watters et al.
(2009) suggest that V. fabalis may still be present in tributaries of the Auglaize
River and the Sandusky River or tributaries. Using GIS and a database of independent variables, areas where V. fabalis may still occur could be identified by overlaying independent variables associated with known Rayed Bean populations.
To expand on this, QHEI data examined through Ohio EPA records could be used to locate small gravel glides and riffles where QHEI scores ranged from 55 – 70.
Other useful independent variables might include the presence of co-occurring species (e.g., A. viridis and E. dilatata ), identified host species presence, stream size, and the presence of J. Americana or Saururus cernuus .
While QHEI may prove useful in the capacity described above, caution should be applied until more data are analyzed to fully understand its predictive ability for unionid communities. To obtain data from sites with QHEI scores above
70, streams outside Northwest Ohio may have to be evaluated where gradients are higher and substrates larger. Collecting these data could be part of a project aimed at further understanding the utility of QHEI to predict richness and diversity of freshwater mussel communities or populations.
Data exploration using PCA was an effective method to visualize unionid surface substrate use. Because 2,700 quadrat samples were taken during my research, PCA was necessary to examine habitat use with all the samples collected from my universe as the backdrop. Substrate use patterns were evident where species such as Kidneyshell ( P. fasciolaris ) and Rayed Bean ( V. fabalis ) were more
60 common in gravel habitats while White Heelsplitter ( L. c. complanata ), Fragile
Papershell ( L. fragilis ), Giant Floater ( P. grandis ) were substrate generalists.
Future work could include sampling more habitats (e.g., large rivers, coastal marshes, etc.) to fully develop the range of surface substrates currently used by different species.
The subsurface sampling performed during this study provided a snapshot of three dimensional habitat use of different freshwater mussel species. Such sampling provides an accurate assessment of the composition of freshwater mussel communities when compared to surface assessments (or presence-absence surveys).
I was able to demonstrate different patterns among species and evidence that subsurface burrowing may be driven more by life history traits than surface substrate texture for the species examined. As a natural extension of these results, the habitat use of juvenile individuals of different species could be examined. A possible research question could be “do juvenile freshwater mussels use different microhabitats than adults?” Unfortunately, the sample size collected during my study was limited in terms of juveniles and recent recruits. This would require some a priori knowledge or pre-sampling to determine the optimal sampling locations. One additional challenge presented by such a study would be how to define “juvenile” for the species under consideration.
The unionid populations and communities identified during this study will require protection if they are to persist. Unlike fish or other aquatic organisms, mussels are especially vulnerable to mechanical disturbance (e.g., dredging, logjam removal, or “dipping out”) because they move very slowly. Such disturbance is
61 common in Northwest Ohio and is a threat to bivalve mollusk communities.
Watershed management and restoration are also critical. Several tools are available for natural resource agencies and environmental managers to protect creeks and rivers. These include conservation easements and programs through the USDA
Farm Bill (buffer strips and wetland restoration). My research contributed a quantitative assessment of the community composition of freshwater mussels on the surface and burrowed in the sediments of three tributaries to Lake Erie. Without effective protection and proactive watershed restoration, freshwater mussels will continue their downward spiral of diversity loss.
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