Changes in Host Use by Unionid Mussels Following River Channelization and Impoundment

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Theses and Dissertations Theses and Dissertations

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Lee Gray Turnage

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Changes in host use by unionid mussels following river channelization and impoundment

Lee Gray Turnage Jr.

A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Biological Sciences in the Department of Biological Sciences

Mississippi State, Mississippi

August 2013

Lee Gray Turnage Jr.

2013

Changes in host use by unionid mussels following river channelization and impoundment

Lee Gray Turnage Jr.

Approved:

______Christopher P. Brooks Eric D. Dibble Assistant Professor of Biological Professor of Wildlife, Fisheries, and Sciences Aquaculture (Major Professor) (Committee Member)

______Gary N. Ervin R. Gregory Dunaway Professor and Graduate Coordinator of Professor and Interim Dean Biological Sciences College of Arts & Sciences (Committee Member)

Name: Lee Gray Turnage Jr.

Date of Degree: August 17, 2013

Institution: Mississippi State University

Major Field: Biological Sciences

Major Professor: Dr. Christopher Brooks

Title of Study: Changes in host use by unionid mussels following river channelization and impoundment

Pages in Study: 39

Candidate for Degree of Masters of Science

More than half the North American freshwater mussel species in the family

Unionidae (unionids) are imperiled or extinct. Alteration of rivers is considered a major contributor to unionid population declines. Losses could occur through disruption of the reproductive cycle. Unionid reproduction requires attachment of larva (glochidia) to host fishes; therefore, changes in the host fish community could alter the reproductive potential in unionid communities. There have been few attempts to compare reproductive success before and after alteration. I examined the pattern of glochidia use on two common host fishes, Lepomis megalotis and Cyprinella venusta, before and after alteration of the Tombigbee River. While both host species declined in the river, the number of glochidia per infested fish and proportion of infested fish increased post- impoundment in L. megalotis but not C. venusta. My results demonstrate the importance of considering reproductive changes as a driver of unionid mussel declines in North

America.

Keywords: Unionidae, Lepomis megalotis, impoundment, Cyrinella venusta, glochidia, Tennessee-Tombigbee Waterway

DEDICATION

For my wife, Jeannie.

ACKNOWLEDGEMENTS

I would like to thank my major professor, Dr. Christopher Brooks, for mentoring me through this process. I would also like to thank my graduate committee members, Dr.

Gary Ervin and Dr. Eric Dibble, for their time and thoughts throughout my time at

Mississippi State. I would also like to thank Dr. Matt Roberts and Dr. Ronn Altig for training, the use of lab space, and guidance. Lastly, I would like to thank the Mississippi

Museum of Natural Science for allowing me the use of specimens to conduct my research.

iii

TABLE OF CONTENTS

DEDICATION ...... ii

ACKNOWLEDGEMENTS ...... iii

LIST OF TABLES ...... v

LIST OF FIGURES ...... vi

CHAPTER

I. INTRODUCTION ...... 1

II. MATERIALS AND METHODS ...... 6

Study System ...... 6 Data Collection ...... 7 Data Analysis ...... 8

III. RESULTS ...... 12

IV. DISCUSSION ...... 17

REFERENCES ...... 22

APPENDIX

A. ABUNDANCES OF SELECT FISHES IN THE TOMBIGBEE AND BUTTAHATCHEE RIVER SYSTEMS...... 28

B. FISH SPECIES PRESENT PRE- AND POST-IMPOUNDMENT OF THE TENNESSEE-TOMBIGBEE WATERWAY ...... 32

C. MUSSEL SPECIES PRESENT PRE- AND POST-IMPOUNDMENT OF THE TENNESSEE-TOMBIGBEE WATERWAY ...... 37

LIST OF TABLES

1 Mean catch per unit effort and variance in distribution of relative abundance for Cyprinella venusta and Lepomis megalotis...... 14

2 Maximum likelihood estimates of mean glochidial load, µ, and overdispersion, k, for Cyprinella venusta and Lepomis megalotis...... 14

3 Number of glochidia on host fish captured in the Buttahatchee and Tombigbee rivers...... 31

4 Variance of distribution of relative abundances for Micropterus salmoides, Campostoma oligoplepis, Lepomis megalotis, and Cyprinella venusta...... 31

5 Fish species in the main channel of the Tombigbee River...... 33

6 Freshwater mussels (Family: Unionidae) in the mainstem of the Tombigbee River...... 38

LIST OF FIGURES

1 Map of Tennessee-Tombigbee Waterway in Northeast Mississippi ...... 10

2 Unionid parasites of Cyprinella venusta and Lepomis megalotis ...... 11

3 Size of catch of Tombigbee Cyprinella venusta and Lepomis megalotis...... 15

4 Relative abundance of Tombigbee Cyprinella venusta and Lepomis megalotis ...... 16

5 Parasitism of Lepomis megalotis by Tombigbee unionids...... 21

CHAPTER I

INTRODUCTION

Impoundment and channelization alter the structure and ecological function of lotic ecosystems by changing their physical and chemical characteristics (Ellis 1936;

Benke 1990; Williams et al. 1992; Watters 2000; Taylor et al. 2008). Channelization has an acute and recurring effect, causing massive disruption of the benthic environment through the removal of the substrate. Changes that occur as a consequence of impoundment are more persistent. Impounded systems become more lentic such that there is slower flow and greater deposition of silt (Ellis 1936; Watters 2000). Pollutants and nutrients which enter the system through runoff adhere to sediment particles and become concentrated in impounded systems, decreasing the fitness of many species of fish and mussels (Family: Unionidae) (Ellis 1936; Bates 1962; Negus 1966; Neves et al.

1997; Watters 2000; Arbuckle & Downing 2002; de Robertis et al. 2003; Corey et al.

2006; Osterling et al. 2008).

Freshwater mussels in the family Unionidae (unionids) are especially sensitive to the changes associated with channelization and impoundment, because they reside in the benthic environment as adults (Ellis 1936; Arbuckle & Downing 2002; Osterling et al.

2008), feed from the water column (Nichols & Garling 2000; Vaughn et al. 2004;

Christian et al. 2004; Nichols et al. 2005; Howard & Cuffey 2006), and rely on both

benthic and pelagic components of the local fish community for reproduction (Kat 1984;

Haag & Warren 1997, 1998; Williams et al. 2008).

Both the importance of unionid mussels to ecosystem function and their decline across North America have been well-documented (Williams et al. 1993; Neves et al.

1997; Lydeard et al. 2004; Wilcove & Master 2005). According to the International

Union for Conservation of Nature, 194 of the 297 North American unionid species (65%) are suffering severe declines, and another 21 species have become extinct in the past 67 years (Williams et al. 1993; Neves et al. 1997; Lydeard et al. 2004; Wilcove & Master

2005). Many of these declines have occurred in lotic systems that have been impounded and/or channelized (Williams et al. 1993; Neves et al. 1997; Watters 2000; Lydeard et al.

2004). It is not clear what role increased adult mortality or reduced reproductive success play in these declines. While siltation and other physical changes reduce survivorship and feeding rates of adults for some species of unionids (Ellis 1936; Box and Mossa

1999; Watters 2000), adults do not always appear to suffer significantly higher mortality in impounded rivers (Bates 1962; Garner & McGregor 2001; Haag 2002).

Impoundment and channelization may have large effects on unionid reproductive success but this effect has been much more poorly studied. Female unionids brood immature life stages called glochidia (larval mussels). Most unionids typically use one of two brooding strategies: bradyticty (long term brooding) or tachyticty (short term brooding; Williams et al. 2008; Haag 2012). Tachytictic unionids release glochidia in one pulse in summer or early fall (June – October) while bradytictic unionids release glochidia in low levels throughout the winter but also release a pulse in the spring or early summer (March – June; Kennedy et al. 2007; Culp et al. 2011). Unionids either

release glochidia into the water column or use elaborate lures to draw the hosts to glochidia as means of infecting host fish (Kat 1984; Haag and Warren 2000; Watters

2002; Corey et al. 2006; Barnhart et al. 2008, Haag & Warren 1997; Haag 2012).

Glochidia usually attach to the hosts gills and metamorphose into juvenile mussels (Kat

1984). Glochidia metamorphosis to the juvenile life stage is dependent on water temperature and can take anywhere from two weeks to six months with some species overwintering on hosts (Zale & Neves 1982; Haag & Warren 1997; Watters & O’Dee

1999).

Regardless of brood strategy, the glochidia of most species are obligately parasitic on the gills of host fish until they metamorphose and settle on the substrate as juveniles

(Arey 1932; Kat 1984). While the glochidia of all species appear to require a host to complete development, the degree of host specialization varies with the mussel species

(Haag & Warren 1997, 1998). As such, the structure of host fish communities plays a critical role in unionid survival, as the glochidia must find a suitable host fish or die

(Arey 1932; Kat 1984).

Physical changes to the habitat can directly influence reproductive success by increasing stress on reproductive adults and by altering the behavior of hosts in the system (Box & Mossa 1999; Corey et al. 2006; Roberts & Taylor 2008). The heavy deposition of silt and organic matter in altered lentic systems combined with stratification can lead to low oxygen conditions that can induce brood failure in gravid mussels and increase mortality in juveniles (Aldridge & McIvor 2003; Osterling et al. 2008).

However, unionids tolerant of conditions associated with lentic habitats (e.g. low dissolved oxygen) would be expected to increase in abundance (Bates 1962; Garner &

McGregor 2001; Haag 2012). Increased turbidity in lentic waters can be due to increased autocthonous production and may also influence reproductive success by disrupting mussel-fish interactions (Corey et al. 2006). Unionids that use conglutinate lures filled with glochidia mimic prey items and attract potential fish hosts rely on the ability of visual predators to detect prey. Bonner and Wilde (2002) provide evidence that high turbidity decreases predation efficiency for fishes adapted to less turbid environments.

Even when turbidity is not a barrier to reproduction, changes in feeding behavior of particular host species (Roberts et al. 2013) and in the structure of host fish communities may affect the interaction between fish and mussels because unionid community structure appears to be dependent on fish community structure (Watters 1992; Haag & Warren

1998). Ultimately, this may decrease reproductive success for unionids with a high degree of host specialization (Watters 1996).

The foraging behaviors and diets of numerous fish species are known to change after impoundment and channelization (Roberts et al. 2007; Strongin et al. 2011; Roberts et al. 2013). Impoundment can affect the abundance (Smith 1985) and mean fish length in a population (Ross 2001; Rypel 2010) of some host fishes; possibly altering the mean glochidial load they can carry and the distribution shape (described by overdispersion parameter) of glochidial loads (Tedla & Fernando 1969; Blazek & Gelnar 2006; Strayer

2008).

In an effort to assess the degree to which impoundment and channelization might alter unionid reproduction, I examined the patterns of glochidia infection among host species before and after impoundment and channelization of the Tombigbee River in northeast Mississippi. I described effects of these changes on absolute and relative

abundance, mean length of two fish hosts, and glochidial load as a function of host length. I hypothesized that impoundment and channelization of the Tombigbee has altered the pattern of unionid-host fish interaction as measured by the mean glochidial load on infested fish, overdispersion, and the proportion of infested fish in each population.

CHAPTER II

MATERIALS AND METHODS

Study System

The Tombigbee River along with the Tennessee Tombigbee Waterway (TTW) and its main tributaries compose the western portion of the Mobile Basin. This watershed occupies approximately 13,767 square miles (~3,566,000 hectares) in Alabama and Mississippi (Alabama Cleanwater Partnership 2005; Harris 2006). Approximately

300 km of the Tombigbee River was impounded and connected to the Tennessee River via canal in the early 1980’s creating the TTW (Fig 1). Roberts et al. (2013) noted changes in the fish communities along the Tombigbee River and pointed out that the

TTW has higher minimum flows and lower maximum flows than the historic Tombigbee.

Two fishes found in the TTW before and after alteration (Millican et al. 2006) were chosen for the current study because they are omnivorous (Ross 2001) and capable of hosting the majority of unionid species found in this system (Williams et al. 2008).

The longear sunfish (Lepomis megalotis), is capable of hosting glochidia from approximately one-third of the unionids (15 species) in the TTW (Williams et al. 2008;

Fig 2), while the blacktail shiner (Cyprinella venusta) can host twelve (Williams et al.

2008; Fig 2), only four of these being hosted by both host species. Patterns of life history traits of the unionids interacting with each of these hosts differs. A larger fraction of the unionids associated with L. megalotis possess a bradytictic brooding strategy (80% vs. 6

25% for C. venusta), and are more tolerant of lentic conditions (87% vs. 42%; Williams et al. 2008; Haag 2012; Fig 2). All of the mussel species who broadcast their glochidia are also associated with L. megalotis, while a larger proportion of those who use lures are associated with C. venusta (65%).

Data Collection

In order to assess pre- and post-alteration host abundance and infestation patterns, specimens were obtained from the ichthyology collection of the Mississippi Museum of

Natural Science (MMNS) in Jackson, Mississippi. Pre-impoundment museum specimens used to analyze fish abundance were collected in the years 1968 through 1975 and post- impoundment specimens were collected in years 1999, 2001, 2004, 2005, and 2007.

These and additional samples collected in 2010 were used to analyze mean glochidial load and proportion of infested fish. Some years had multiple collections while others did not. Specimens were constrained by availability of museum archives, and by the sampling methods used. All fish specimens used to analyze abundance were captured by a time-constrained collection method to maintain catch per unit effort – specifically, seining for one hour at a site using a 6.1 meter straight seine. Samples collected in 2010 were not collected in this manner and were not used to analyze fish abundances.

Gill arches were dissected from 430 C. venusta (N PRE =269, N POST =161) and

503 L. megalotis (N PRE = 313, N POST =190) specimens under a Fisher Stereomaster

Dissecting Microscope and stored in 70% ethanol prior to processing. In order to clear the soft tissues of the gill arches, each was placed in a 2% KOH solution for 3 to 5 hours and then transferred to a one-to-one solution of de-ionized water and glycerin until they sank (approximately 30 - 45 minutes). Gill arches were then transferred to 100% 7

glycerin for 12 hours to complete the clearing procedure and preserve the tissues

(Dingerkus & Uhler 1977). Specimens were then examined using an Olympus SZH dissection microscope and an external fiber optic light source to determine the number of glochidia on each gill arch.

Data Analysis

Total fish abundance data (catch per unit effort) were used to estimate parameters for a poisson distribution unless data were overdispersed (variance-to-mean ratio (VMR)

> 1). Overdispersed data were fit to a negative binomial model to reflect the presumed gamma-distributed variation in mean catch sizes across samples. Parameter estimates were made by the fitdistr function in the MASS package of R (R Development Core

Team 2012). These parameter estimates and their confidence intervals can be used to determine any change in mean abundance (and if overdispersed, skew) from catch data before and after impoundment (Crawley 2005; Bolker 2008).

Relative abundance of C. venusta and L. megalotis were calculated for

Tombigbee samples pre- and post-impoundment. The variance of relative abundance distributions for each fish species was calculated pre- and post-impoundment. To test for change in relative abundance from pre- to post-impoundment for each fish species I used a Levene’s test which analyzes the variance of two non-parametric distributions (i.e. distribution of relative abundances of fishes pre- and post-impoundment) to see if they are significantly different from one another (R Development Core Team 2012; Glass

1966). If the F-value from the test (FV) is greater than or equal to the critical value obtained from an F-table (FC) the distributions are significantly different (R Development

Core Team 2012). Changes in mean length of host fishes from pre- to post-impoundment 8

were determined by analyzing the mean fish length using a gamma Generalized Linear

Model (GLM; R Development Core Team 2012). No difference in mean fish length from pre- to post-impoundment was the null hypothesis.

Changes in the association between the unionid community and the host fishes examined could manifest as a shift in the proportion of fish that are infested with glochidia, or as a change in the mean load of glochidia on infested fish. A binomial test was used to determine if the probability of infestation changed after the alteration of the

TTW for each species (R Development Core Team 2012). The pre-impoundment proportion of infested individuals for each species was used as the null hypothesis with which to test the post-impoundment data.

Changes in the mean glochidial load pre- vs. post-alteration were determined by fitting the observed data to a poisson distribution unless data were overdispersed (VMR >

1). Overdispersed data were fit to a negative binomial model to reflect presumed gamma-distributed variation in mean glochidial load across populations and/or dates.

Parameter estimates were made by the fitdistr function in the MASS package of R (R

Development Core Team 2012). These parameter estimates and their confidence intervals can be used to determine any change in mean glochidial load per infested fish

(and if overdispersed, skew) for infestation data before and after impoundment. Changes in load size from pre- to post-impoundment could be related to any changes in host size so I ran a negative binomial GLM (glm.nb) to see if any changes in glochidia load were associated with host length and/or impoundment.

Figure 1 Map of Tennessee-Tombigbee Waterway in Northeast Mississippi

(NOAA 2009; USGS 2002)

Figure 2 Unionid parasites of Cyprinella venusta and Lepomis megalotis

NOTE: Species with ‘a’ are tolerant of lentic conditions, species with ‘b’ known to use a bradytictic reproductive strategy, species with ‘c’ known to broadcast glochidia, Uniomerus tetralasmus has an unkown brood strategy, Utterbackia imbeciliis uses tachytictic and bradytictic brood strategies, Pleurobema curtum and Pleurobema marshalli believed to be extinct.

CHAPTER III

RESULTS

Catch sizes (catch per unit effort) were overdispersed for both species and time periods (Table 1). The mean number of individuals per catch of the blacktail shiner and the long-ear sunfish decreased from pre-impoundment and channelization (473.3 and

20.9 respectively) to post-impoundment and channelization (18.1 and 1.5 respectively,

Table 1, Fig 2).

C. venusta appears to have decreased in relative abundance (FV≥FC; Table 1; Fig

3) while L. megalotis relative abundances appear to be similar (FV

Mean length did not increase in the total population of C. venusta from pre- to post-impoundment (43.4 mm pre-impoundment vs. 43.3 mm post-impoundment; Pre

95% CI = 41.94 – 44.79; Post 95% CI = 41.27 – 45.27; gamma GLM) or for those C. venusta utilized as hosts (43.3 mm pre-impoundment vs. 44.8 mm post-impoundment;

Pre 95% CI = 41.38 – 45.18; Post 95% CI = 41.99 – 47.55; gamma GLM). Mean length of the total population of L. megalotis increased from pre- to post-impoundment (45.8 mm pre-impoundment vs. 59.7 mm post-impoundment; Pre 95% CI = 45.37 – 46.19; Post

95% CI = 58.82 – 60.54; gamma GLM) but mean length did not change for those L.

megalotis used as hosts (58.6 mm pre-impoundment vs. 63.2 mm post-impoundment; Pre

95% CI = 51.6 – 65.5; Post 95% CI = 60.7 – 65.7; gamma GLM).

Potential changes in mussel reproduction were measured by the fraction of host individuals that were infested by glochidia, and mean glochidial load per infested fish.

The proportion of infested C. venusta did not increase (0.491 vs. 0.447; Pre 95% CI =

0.43 – 0.55; Post 95% CI = 0.37 – 0.53; Binomial Test; Table 2), but the proportion of infested L. megalotis increased from pre- to post-impoundment (0.243 vs. 0.5; Pre 95%

CI = 0.196 – 0.294; Post 95% CI = 0.428 – 0.573; Binomial Test; Table 2).

All data for mean glochidial load were overdispersed, so I analyzed the data using a negative binomial distribution. The 95% confidence intervals around the maximum likelihood estimates of the mean glochidial load, µ, and the overdispersion parameter, k, did not overlap for pre- to post-impoundment samples of L. megalotis but they did overlap for C. venusta (Table 2). Because I detected a decrease in the mean length of host fish after alteration of the system, I wanted to determine whether the differences remained after accounting for host length. A negative binomial GLM (glm.nb in MASS package, R Development Core Team 2012) for L. megalotis suggests that differences in load size remain after accounting for host length (p <0.001). Host length accounted for

70% of the change in load size (p<0.001) on L. megalotis from pre- to post-impoundment while impoundment era (pre- vs. post-impoundment) accounted for 20% (p<0.001).

Table 1 Mean catch per unit effort and variance in distribution of relative abundance for Cyprinella venusta and Lepomis megalotis.

Variance of Host Mean Catch per Critical Impound relative F-value Species unit effort value abundance 473.3 Pre 0.054 Cyprinella (270.0 – 676.6) 15.032 3.996 venusta 18.1 Post 0.016 (7.85 – 28.28) 20.9 Pre 0.0003 Lepomis (9.9 – 31.86) 0.696 3.996 megalotis 1.5 Post 0.0007 (0.65 – 2.25) NOTE: Numbers in parentheses are 95% confidence intervals.

Table 2 Maximum likelihood estimates of mean glochidial load, µ, and overdispersion, k, for Cyprinella venusta and Lepomis megalotis.

Host Impound µ k Infested N Species 3.94 0.21 0.491 Pre 269 Cyprinella (2.89 – 4.99) (0.17 - 0.26) (0.429 – 0.552) venusta 3.91 0.18 0.447 Post 161 (2.46 – 5.36) (0.13 - 0.24) (0.369 – 0.527) 0.99 0.12 0.243 Pre 313 Lepomis (0.65 – 1.33) (0.08 - 0.15) (0.196 – 0.294) megalotis 2.67 0.28 0.500 Post 190 (1.92 - 3.43) (0.20 - 0.36) (0.427 – 0.573) NOTE: Numbers in parentheses are 95% confidence intervals around the parameter estimates. Proportion of infested fish in each host species and time period are in the column labeled Infested.

Figure 3 Size of catch of Tombigbee Cyprinella venusta and Lepomis megalotis

Figure 4 Relative abundance of Tombigbee Cyprinella venusta and Lepomis megalotis

CHAPTER IV

DISCUSSION

The contribution by C. venusta to reproduction across the unionid community in the Tombigbee River appears to be unaltered by impoundment and channelization. Both infestation rates and glochidial loads on L. megalotis have increased following alteration of the system. Change in the glochidial loads on infested L. megalotis is apparent, even after controlling for the effects of host fish size.

One might expect that the observed changes in the pattern of host-mussel interaction are the result of differences in the type of host-mussel contact patterns.

Eleven of the twelve (92%) unionid species in the system that are expected to parasitize

C. venusta are known to use luring strategies, while the last releases, or broadcasts glochidia directly into the water column (Zanatta & Murphy 2006; Williams et al. 2008;

Haag 2012; Fig 2; Appendix C). In contrast, nine of the fifteen unionid species suspected to infest L. megalotis in this system use luring strategies, while the other six broadcast glochidia into the water column (Zanatta & Murphy 2006; Williams et al. 2008; Haag

2012; Fig 2). Contact rate between unionids that lure their hosts by mimicking prey items is likely to be independent of both host and mussel density (frequency dependent contact) because contact is dependent on the host attacking the lure not density of the lures in the water column (Strayer 2008). Interaction with broadcasted glochidia is governed by the

density of both glochidia and hosts in the system (density dependent contact) (Strayer

2008).

The data suggest that C. venusta and L. megalotis have declined in abundance after alteration (Table 1). If observed differences in infestation before and after alteration is governed by the differences in the host attraction strategy employed by mussel communities, the fraction of L. megalotis infested by glochidia would decline after impoundment and the fraction of infested C. venusta would be relatively constant. While the proportion of infested C. venusta did remain the same, the proportion of infested L. megalotis increased after alteration. This suggests that we may need to consider the potential roles of other factors in addition to changes in total abundance to explain the observed changes in infestation probability.

Changes in the size of the glochidial load on these species follow a similar pattern as the proportion of infested individuals. There was no change in the load size on infested C. venusta, but there was an increase in the load size on L. megalotis, even though mean size of host individuals did not change after alteration. This is especially interesting because host length accounted for more of the variation in glochidial load than collection date (pre- vs. post-impoundment) in my samples.

Stressors (e.g., food limitation, turbidity, etc.) can impair immune function of fishes increasing their susceptibility to parasitism (Lafferty 1997; Lafferty & Kuris 1999;

Lafferty & Holt 2003; Strayer 2008). The consequence could be an increasing infestation rate on host fish. Changes in the immune system function of L. megalotis could also explain differences in load size after impoundment and channelization. Decreased immune system function can be induced by increased stress caused by the alteration of

the system (Corbel 1975). Increased turbidity as well as increased autochthonous production in the reservoir, can lower the ability of predatory host fishes to find prey

(Bonner & Wilde 2002; de Robertis et al. 2003), which in turn can lead to decreased immune function in fishes (Corbel 1975), and thus to an increased susceptibility of host fish to glochidial infestation. Typically, once a host fish is parasitized by glochidia a response by the host’s immune system can prevent later glochidial infections (Rogers and

Dimock 2003; Dodd et al. 2005; Rogers-Lowery et al. 2007). Thus, we might expect that smaller fish in a population should be more likely to be infested by unionids and to carry higher glochidial loads in unaltered systems (Strayer 2008), but that more relatively large fish in the population might be infested post-alteration if immune system function was compromised. While this pattern was not observed in the data, further studies are needed to determine whether the immune function of L. megalotis is impaired in the TTW.

In addition to differences in contact structure and the immune system function of host fishes, seasonal patterns in mussel life history may play a role in this difference as well. Infestation of L. megalotis is not evenly distributed across months (Fig 4). My data show that after alteration of the system, there is apparent increase in glochidial loads from August through October and a relative decrease in load size in May and June suggesting that unionids utilizing a bradytictic brood strategy may be driving the change in parasitism (Fig 4).

The timing of the tachytictic pulse coincides with low flows in the TTW (Morris

1991). Of the lentic adapted unionids that broadcast their glochidia, half (three of six) are bradytictic unionids and half are tachytictic (Williams et al. 2008; Haag 2012; Fig 2).

The release of tachytictic glochidia during low flows would increase the relative density

of host fish and glochidia in the water column, thereby increasing the chances of contact.

These lentic-adapted unionids are more likely to have persisted in impounded systems

(Isom 1969; Parmalee et al. 1982; Parmalee & Hughes 1993; Garner & McGregor 2001;

Haag 2012). The potential increase in their relative abundance over time could have also contributed to the observed changes in infestation.

The data suggest that impoundment and channelization of the Tombigbee have altered resident unionid demographic structure (Williams et al. 1992). Further, changes in host fish community structure, immune system function, unionid brood strategy, or habitat preference may have facilitated those changes. Unionid declines resulting from decreased recruitment is suspected in other impounded systems, but this hypothesis has proven problematic to test due to difficulties in finding glochidia on field-collected fishes, and in sampling for juvenile unionids in the benthos (Negus 1966; Neves &

Widlak 1987). These data emphasize the need for similar studies to be conducted to test the hypotheses presented here and to examine other host species in this and other aquatic systems to determine the extent of reproductive changes induced by impoundment and to identify the mechanism(s) driving these changes.

Figure 5 Parasitism of Lepomis megalotis by Tombigbee unionids.

NOTE: White boxplots are pre-impoundment and shaded boxplots are post- impoundment. The numbers in row labeled ‘prop. zeros’ are proportion of uninfested host individuals in that time period.

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APPENDIX A

ABUNDANCES OF SELECT FISHES IN THE TOMBIGBEE AND

BUTTAHATCHEE RIVER SYSTEMS

Comparisons in host use by freshwater mussels in the family Unionidae

(unionids) were started in two rivers in Northeast Mississippi: one altered, the

Tombigbee, and one unaltered, the Buttahatchee. The Tombigbee was impounded and channelized to construct the Tennessee-Tombigbee Waterway (TTW). Construction took

12 years and was completed in 1985 (Boschung 1989). In comparison, the Buttahatchee is relatively unchanged and flows into the TTW near Columbus, MS. The goal of my research was to analyze the effect of impoundment and channelization on the unionid reproductive process. Samples from the Buttahatchee were meant to be used as a reference to test samples from the Tombigbee and TTW against. However, relatively low numbers of specimens captured in the Buttahatchee compared to the other waterbodies

(Table 3) resulted in specimens from this river being dropped from my research. In lieu of this, the Tombigbee samples were the reference to test the TTW samples against.

Initially, three host fish species were examined for the presence of glochidia in these two rivers: Micropterus salmoides (Largemouth bass), Campostoma oligolepis

(Largescale stoneroller), and Lepomis megalotis (Longear sunfish). These species occupy different parts of the water column, have different foraging habits (bass – piscivorous, sunfish – omnivorous, stoneroller – insectivorous; Ross 2001) and thus would be expected to come in contact with a variety of unionid lures and glochidia. A lack of bass and stoneroller specimens in museum collections coupled with low glochidia counts (Table 3) resulted in discontinuation of research on these two host fish species. I added another host fish species, Cyprinella venusta (Blacktail shiner), to get a broader sampling of the unionid communities’ infestation of hosts. The shiner is omnivorous,

present in the Tombigbee before and after alteration, and occupies a different part of the water column than the sunfish (Ross 2001).

Relative abundance of M. salmoides, C. oligolepis, L. megalotis, and C. venusta were calculated for Tombigbee samples pre- and post-impoundment. The variance of relative abundance distributions for each fish species was calculated pre- and post- impoundment (Table 4). To test for change in relative abundance from pre- to post- impoundment for each fish species I used a Levene’s test which analyzes the variance of two non-normal distributions (i.e. distribution of relative abundances of fishes pre- and post-impoundment) to see if they are significantly different from one another (R

Development Core Team 2012). If the F-value from the test is greater than or equal to the critical value obtained from an F-table the distributions are significantly different (R

Development Core Team 2012; Table 4). The increase in variance of M. salmoides was significant (FV≥FC; Table 4) suggesting that this species has increased in relative abundance post-impoundment. C. oligolepis and L. megalotis relative abundances appear to be similar (FV

Table 3 Number of glochidia on host fish captured in the Buttahatchee and Tombigbee rivers.

Number Number of River Host species Impoundment captured glochidia Micropterus Pre 0 – salmoides Post 20 2 Campostoma Pre 0 – Buttahatchee oligolepis Post 46 3 Lepomis Pre 0 – megalotis Post 48 145 Micropterus Pre 40 14 salmoides Post 7 4 Campostoma Pre 13 0 oligolepis Post 14 0 Tombigbee Lepomis Pre 313 311 megalotis Post 190 509 Cyprinella Pre 269 1060 venusta Post 161 630

Table 4 Variance of distribution of relative abundances for Micropterus salmoides, Campostoma oligoplepis, Lepomis megalotis, and Cyprinella venusta.

Pre- Post- F- Critical Species impoundment impoundment value value variance variance Micropterus 1.42e-05 0.0017 9.188 3.996 salmoides Campostoma 1.68e-06 0.0002 2.538 3.996 oligolepis Lepomis megalotis 0.0003 0.0007 0.696 3.996 Cyprinella venusta 0.054 0.016 15.032 3.996

APPENDIX B

FISH SPECIES PRESENT PRE- AND POST-IMPOUNDMENT OF THE

TENNESSEE-TOMBIGBEE WATERWAY

A total of 108 fish species were known to occur in the mainstem of the

Tombigbee river pre-impoundment (Table B1; Boschung 1989). A total of 67 fish species are known to be in the Tennessee-Tombigbee Waterway post-impoundment

(Table 5; Boschung 1989; Millican et al. 2006; Ross 2001).

Table 5 Fish species in the main channel of the Tombigbee River.

Pre- Post- Species Common Name impoundment impoundment Scaphirhynchus Alabama sturgeon B suttkusi Polyodon spathula Paddlefish B O Lepisosteus oculatus Spotted gar B M Lepisosteus osseus Longnose gar B M Amia calva Bowfin B Anguilla rostrata American eel B Alosa alabamae Alabama shad B Alosa chysochloris Skipjack herring B Dorosoma cepedianum Gizzard shad B M Dorosoma petense Threadfin shad B M Hiodon tergisus Mooneye B Esox americanus Grass pickerel B M Esox niger Chain pickerel B M Campostoma oligolepis Largescale stoneroller B M Cyprinella callistia Alabama shiner B M Cyprinella venusta Blacktail shiner B M Cyprinus carpio Common carp B M Ericymba buccata Silverjaw minnow B Hybognathus hayi Cypress minnow B X Mississippi silvery Hybognathus nuchalis B minnow Luxilus chrysocephalus Striped shiner B M Lythrurus bellus Pretty shiner B M Macrhybopsis Speckled chub B M aestivalis Macrohybopsis Silver chub B storeriana Nocomis leptocephalus Bluehead chub B M Notemigonus Golden shiner B M crysoleucas Notropis ammophilus Orangefin shiner B M 33

Table 5 (continued)

Notropis atherinoides Emerald shiner B M Notropis baileyi Rough shiner B Notropis candidus Silverside shiner B M Notropis edwardraneyi Fluvial shiner B M Notropis maculatus Taillight shiner B Notropis stilbius Silverstripe shiner B Notropis texanus Weed shiner B M Notropis volucellus Mimic shiner B M Notropis winchelli Clear chub B M Opsopoeodus emiliae Pugnose shiner B M Pimephales notatus Bluntnose minnow B M Pimephales vigilax Bullhead minnow B M Semotilus Creek chub B atromaculatus Carpiodes cyprinus Quillback B M Carpiodes velifer Highfin carpsucker B M Southeastern blue Cycleptus meridionalis B sucker Erimyzon oblongus Creek chubsucker B M Hypentelium etowanum Alabama hog sucker B M Ictiobus bubalus Smallmouth buffalo B Minytrema melanops Spotted sucker B Moxostoma carinatum River redhorse B Moxostoma erythrurum Golden redhorse B M Moxostoma poecilurum Blacktail redhorse B M Ameiurus melas Black bullhead B Ameiurus natalis Yellow bullhead B Ameiurus nebulosus Brown bullhead B Ictalurus furcatus Blue catfish B M Ictalurus punctatus Channel catfish B M Noturus funebris Black madtom B Noturus gyrinus Tadpole madtom B Noturus leptacanthus Speckled madtom B Noturus munitus Frecklebelly madtom B Noturus nocturnus Freckled madtom B Pylodictis olivaris Flathead catfish B R Aphredoderus sayanus Pirate perch B Strongylura marina Atlantic needlefish B M Fundulus dispar Starhead topminnow B M Fundulus notatus Blackstripe topminnow B Blackspotted Fundulus olivaceus B M topminnow 34

Table 5 (continued)

Gambusia affinus Mosquitofish B M Labidesthes sicculus Brook silverside B M Menidia audens Mississippi silverside M Morone chrysops White bass B M Morone mississipiens Yellow bass M Ambloplites ariommus Shadow bass B Centrarchus Flier B X macropterus Lepomis cyanellus Green sunfish B M Lepomis gulosis Warmouth B M Lepomis humilis Orangespotted sunfish B M Lepomis macrochirus Bluegill B M Lepomis marginatus Dollar sunfish B M Lepomis megalotis Longear sunfish B M Lepomis microlophus Redear sunfish B M Lepomis miniatus Redspotted sunfish M Lepomis punctatus Spotted sunfish B Micropterus Spotted bass B M punctulatus Micropterus salmoides Largemouth bass B M Pomoxis annularis White crappie B M Pomoxis Black crappie B M nigromaculatus Elassoma zonatum Banded pygmy sunfish B Ammocrypta beani Naked sand darter B M Ammocrypta meridiana Southern sand darter B M Crystallaria asprella Crystal darter B M Etheostoma Bluntnose darter B chlorosoma Etheostoma fusiforme Swamp darter B Etheostoma gracile Slough darter B Etheostoma histrio Harlequin darter B Etheostoma lachneri Tombigbee darter B Etheostoma nigrum Johnny darter B M Etheostoma parvipinne Goldstripe darter B Etheostoma proeliare Cypress darter B Etheostoma rupestre Rock darter B Etheostoma stigmaeum Speckled darter B M Etheostoma swaini Gulf darter B Etheostoma whipplei Redfin darter B Etheostoma zonifera Backwater darter B Percina kathae Mobile logperch B M 35

Table 5 (continued)

Percina maculata Blackside darter B M Percina sciera Dusky darter B M Percina shumardi River darter B Percina suttkusi Gulf logperch B M Percina vigil Saddleback darter B Stizostedion vitreum Walleye B Aplodinotus grunniens Freshwater drum B M NOTE: Species with a ‘B’ are found in Boschung (1989), those with ‘M’ are found in Millican et al. (2006), those with ‘O’ are found in O’Keefe et al. (2007), those with ‘R’ found in Ross (2001), and those with ‘X’ are present in Mississippi Museum of Natural Science archives.

APPENDIX C

MUSSEL SPECIES PRESENT PRE- AND POST-IMPOUNDMENT OF THE

TENNESSEE-TOMBIGBEE WATERWAY

A total of 45 freshwater mussels species in the family Unionidae (unionids) were known to be in the mainstem of the upper Tombigbee prior to construction of the

Tennessee-Tombigbee Waterway (TTW; Williams et al. 1992; Williams et al. 2008;

Table 6). Post-impoundment 44 unionids have been found in the mainstem (TTW, impoundments, and bendways of old Tombigbee), however many of their ranges are poorly understood and some appear to be declining while others are increasing in abundance (Williams et al. 2008; Table 6).

Table 6 Freshwater mussels (Family: Unionidae) in the mainstem of the Tombigbee River.

Pre- Post- Species Common name impoundment impoundment Amblema plicata Three ridge X X Anodonta sp. Cypress floater X X Anodonta Flat floater X X suborbiculata Anodontoides radiatus Rayed creekshell X Arcidens confragosus Rock pocketbook X X Ellipsaria lineolata Butterfly X X Elliptio arca Alabama spike X X Elliptio arctata Delicate spike X X Elliptio crassidens Elephantear X X Epioblasma penita Southern combshell X Fusconaia cerina Gulf pigtoe X X Fusconaia ebena Ebonyshell X X Hamiota perovalis Orangenacre mucket X X Lampsilis ornata Southern pocketbook X X Lampsilis straminea Southern fatmucket X X Lampsilis teres Yellow sandshell X X Lasmigona Alabama heelsplitter X X alabamensis Leptodea fragilis Fragile papershell X X Ligumia recta Black sandshell X X Ligumia subrostrata Pondmussel X

Table 6 (continued)

Medionidus Alabama X X acutissimus moccasinshell Megalonaias nervosa Washboard X X Obliquaria reflexa Threehorn wartyback X X Obovaria jacksoniana Southern hickorynut X X Obovaria unicolor Alabama hickorynut X X Plectomerus Bankclimber X X dombeyanus Pleurobema curtum Black clubshell X Pleurobema decisum Southern clubshell X X Pleurobema marshalli Flat pigtoe X Pleurobema perovatum Ovate clubshell X X Pleurobema taitianum Heavy pigtoe X X Potamilus inflatus Inflated heelsplitter X X Potamilus purpuratus Bleufer X X Pyganodon grandis Giant floater X X Quadrula apiculata Southern mapleleaf X X Quadrula asperata Alabama orb X X Quadrula metanevra Monkeyface X X Quadrula nobilis Gulf mapleleaf X X Quadrula rumphiana Ridged mapleleaf X X Quadrula stapes Stirrupshell X Quadrula verrucosa Pistolgrip X X Strophitus subvexus Southern creekmussel X X Toxolasma parvum Lilliput X X Truncilla donaciformes Fawnsfoot X X Uniomerus tetralasmus Pondhorn X X Utterbackia imbecillis Paper pondshell X X Villosa lienosa Little spectaclecase X X Villosa vibex Southern rainbow X X