Triannual Unionid Report

Report No. 11

March, 1997

A forum for the informal exchange of information on the status of
North American unionid research, management, and conservation

Drawn by an elementary school student as part of a contest to design the character "Russell the Mussel" held by the Tennessee Aquarium, Chattanooga, Tennessee.

Richard G. Biggins
U.S. Fish and Wildlife Service
160 Zillicoa Street
Asheville, North Carolina 28801

NOTE: The intent of this report is to expedite the exchange of information in an
informal format. Report submissions were solicited from individuals and
agencies involved in unionid conservation. The submissions were not edited.
They were copied as received and assembled into the report.
The report was then scanned to create this Web site.

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TABLE OF CONTENTS
TRIANNUAL UNIONID REPORT NO. 11
MARCH 1997

Tankersley, R.
UNIO Listserver.

Knudsen, K.A., and M.C. Hove
Spectaclecase (Cumberlandia monodonta) conglutinates unique, host(s) elusive.

Hove, M.C., and T.W. Anderson
Mantle-waving behavior and suitable fish host of the ellipse.

Hove, M.C.
Ictalurids serve as suitable hosts for the purple wartyback.

Pepi, V.E., and M.C. Hove
Suitable fish host and mantle display behavior of Tritogonia verrucosa.

Mathers, C.M., and J.A.M. Bergmann
News about (Potamilus amphichaenus)

Greenwood, K.S., J.E. Alexander, Jr., and J.H. Thorp
Infestation of Dreissena polymorpha on large prosobranch snails in the Ohio River. 1996 Mississippi River Research Consortium Abstracts.

Krumanocker, N.C., B.L. Sloss, R.V. Anderson, and M.A. Romano
Genetic variation in Dreissena spp. populations in Pools 19 and 20 of the Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Morgan, M., J.S. Cougill, and R.V. Anderson
The occurrence and age structure of zebra mussel populations in Pool 19, Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Havlik, M.E.
A 1994 survey for unionid mollusks from the headwaters of the Root River system, southeastern Minnesota, to the Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Balding, T., D. Kelner, and D. Duchesneau
Ten years of survey data on the lower and mid Chippewa River basin. 1996 Mississippi River Research Consortium Abstracts.

Whitney, S.D., K.D. Blodgett, and R.E. Sparks
Mussel populations in pool 15 of the upper Mississippi River: a decade of change, 1985-1995. 1996 Mississippi River Research Consortium Abstracts.

Jack, J.D., J.H. Thorp, and A.F. Casper
Zebra mussel impacts on the potamoplankton: The differential roles of adult mussels and veligers. 1996 Mississippi River Research Consortium Abstracts.

Casper, A.F., R.B. Summers, T. Sellers, J.H. Thorp, and J. Alaxender
Factors affecting zebra mussel (Dreissena polymorpha) recruitment: seasonal thresholds in large rivers. 1996 Mississippi River Research Consortium Abstracts.

Beckett, D., B.W. Green, and A C. Miller
Changes in zebra mussel densities in the upper Mississippi River: 1995 update. 1996 Mississippi River Research Consortium Abstracts.

Richardson, W.B., L.A. Bartsch, and M.B. Sandheinrich
Growth of a larval fish (Pimephales promelas) is significantly reduced by the presence of zebra mussels and turbulence. 1996 Mississippi River Research Consortium Abstracts.

Anderson, R V., and Jennifer Eichelberger
Epizoic organisms of unionid mussels in channel border habitats of Pool 19, Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Camlin, L.A, J.A. Stoeckel, K.D. Blodgett, and R.E. Sparks
Seasonal patterns in abundance and size distribution of zebra mussels veligers in the Illinois River: 1994-1995. 1996 Mississippi River Research Consortium Abstracts.

Cronin, F.A., J.K. Tucker, and D.W. Soergel
Predation on zebra mussels (Dreissena polymorpha) by common carp (Cyprinus carpio). 1996 Mississippi River Research Consortium Abstracts.

Deuschle, D.R., M.D. Delong, and J.H. Thorp
Effect of zebra mussels on native invertebrate community structure on hard substrata in the upper Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Whitney, S.D., D. Osland, D. Blodgett, and R.E. Sparks
A survey of the unionid mussels of the Illinois River: a recovering resource? 1996 Mississippi River Research Consortium Abstracts.

Vaughn, D.L, R.B. Summers, and J.H. Thorp
Effects of zebra mussels (Dreissena polymorpha) on amphipods in artificial streams. 1996 Mississippi River Research Consortium Abstracts.

Ward, T.B., M.D. Delong, and J.H. Thorp
An in situ experimental study of the population dynamics of zebra mussels in the upper Mississippi River. 1996 Mississippi River Research Consortium Abstracts.

Bruenderman, S.
Mussel news from Missouri.

Cope, G.
Greg Cope joins Toxicology Department at North Carolina State University.

Ahlstedt, S.
Upper Tennessee River NAWQA study for 1997.

Havlik, M.E.
Differences in a Dreissena polymorpha population during a unionid mollusk translocation from a Mississippi River side channel, Mile 725.8, Winona, Minnesota/Buffalo County Wisconsin.

Metcalfe, J.L., S.K. Staton, G.L. Mackie, and N.M. Lane
Biodiversity of freshwater mussels in the lower Great Lakes Drainage basin.

Strayer, D.L., and A.R. Fetterman
Interim report on a resurvey of the unionids of the upper Susquehanna basin in New York.

U.S. Geological Survey, Florida Caribbean Science Center
The national nonindigenous aquatic species geographic information system.

Levey, R., and S. Fiske
On-site cleaning of zebra mussels from unionids on Lewis Creek delta, Lake Champlain.

Roberts, A.D., A P. Farnsworth, J. Sternburg, and M.C. Barnhart
Freshwater mussels in Missouri's Bootheel: Rediscovery of the fat pocketbook mussel.

Barnhart, M.C., and A.D. Roberts
Reproduction and fish host of the fat pocketbook mussel, Potamilus capax.

Barnhart, M.C.
Sterile eggs in unionid mussels and their roles in conglutinate function.

Layzer, J.B.
Current projects at Tennessee Cooperative Fishery Research Unit.

Westbrook, O.J., and J.B. Layzer
Survival and growth of hatchery-reared juvenile Lampsilis cardium.

Layzer, J.B., L. Madison, and R. Quinn
Long-term holding of mussels in captivity.

Bogan, A.E.
Art's move to North Carolina Museum of Natural Sciences.

Hardison, B.S.
The relationships between complex hydraulics and mussel density. Thesis, Tennessee Cooperative Fishery Research Unit.

Houslet, B.S.
Age, growth, and stability of a mussel assemblage in Horse Lick Creek, Kentucky. Thesis, Tennessee Cooperative Fishery Research Unit.

Heinricher, J.R.
Reproductive ecology of two species of freshwater mussels in Tennessee. Thesis, Tennessee Cooperative Fishery Research Unit.

Morgan, A.
Feasibility of reintroducing freshwater mussels into Shoal Creek, Alabama and Tennessee. Thesis, Tennessee Cooperative Fishery Research Unit.

Lydeard, C., W. Holznagel, and K. Roe
Ongoing mollusk genetic studies and reprints available at University of Alabama, Tuscaloosa, Alabama.

Howells, R.G.
Taxonomic status of western lilliput (Toxolasma mearnsi).

Neves, R.J.
Success story on bridge replacement in Virginia.

Hubbs, D.
Commercial musseling in Tennessee.

Watters, T.G., and S.H. O'Dee
1. Abstract: Shedding of untransformed glochidia by fishes parasitized by Lampsilis fasciola Rafinesque, 1820 (Mollusca: Bivalvia: Unionidae): evidence of acquired immunity.

2. Surrogate hosts: transformation on exotic and non-piscine hosts.

3. Prolong and glochidial transformation.

Couch, K.J.
An update on the status of the rock pocketbook, Arcidens confragosus (Say, 1829), in the Marais Des Cygnes and Osage River drainages in Kansas.

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Spectaclecase (Cumberlandia monodonta) conglutinates unique, host(s) elusive

Kristian A. Knudsen and Mark C. Hove Univ. of Minnesota, Dept. of Fisheries & Wildlife
1980 Folwell Ave., St. Paul, MN 55108
(612) 624-3019
knudO028@maroon.tc.umn.edu
mh@fw.umn.edu

The host requirements of Cumberlandia monodonta, a federally listed species (Category 2), have not been studied (Watters 1994). Knowledge of host requirements is essential to determine the viability of imperiled mussel populations either in degraded habitats, where they now occur, or in habitats being considered for receiving relocated mussels. As part of a larger study to determine the natural hosts of C. monodonta, we conducted laboratory studies to identify suitable hosts.

Five fish species and larval tiger salamanders were tested in 1996 for host suitability using procedures similar to Hove and Neves (1994). Due to the small size of the glochidia, the glochidial attachment period is defined as the number of days glochidia were observed in tank siphonate. Glochidial metamorphosis was not observed for any of the species tested (Table 1).

Table 1. Species exposed to Cumberlandia monodonta glochidia.

Species Scientific name Number inoculated Number survivors Glochidia attachment period (days) mimic shiner Notropis volucellus 4 0 * longnose dace Rhinichthys cataractae 9 7 20-22 northern redbelly dace Phoxinus eos 8 3 20-22 banded killifish Fundulus diaphanus 8 0 * Iowa darter Etheostoma exile 2 2 24-27 tiger salamander Ambystoma tigrinum 7 7 23-26 *Incomplete study, fish died before completion of experiment.

Cumberlandia monodonta conglutinates collected from three gravid females in the field were flat and white (Figure 1). Unbroken conglutinates were 3 - 6 mm wide and 5 - 13 mm long. Lateral branches were common on many conglutinates, occurring on one or both sides. Branches were 1 to 4 mm long and extended outward from the conglutinate at a 45 degree angle. Some conglutinates had a forked tail.

Figure 1. Outline of branched Cumberlandia monodonta conglutinates.

Literature Cited

Hove, M.C., and R.J. Neves. 1994. Life history of the endangered lames spinymussel Pleurobema collina (Conrad, 1837) (Mollusca: Unionidae). American Malacological Bulletin 11(1): 29 - 40.

Watters, G.T. 1994. An annotated bibliography of the reproduction and propagation of the Unionidae (Primarily of North America). Ohio Biological Survey, Miscellaneous Contributions, No. 1. 162 pp.

Mantle-waving behavior and suitable fish hosts of the ellipse

Mark C. Hove and Tom W. Anderson
Department of Fisheries and Wildlife, University of Minnesota
1980 Folwell Avenue, St. Paul, MN 55108
(612) 624-3019
mh@fw.umn.edu and eO864@maroon.tc.umn.edu respectively

The ellipse, Venustaconcha ellipsiformis, is a small to medium-sized stream dwelling unionid uncommon in the Midwest (Oesch 1984). It is extirpated from Ohio, threatened in Iowa, Wisconsin, and Minnesota, and a species of special concern in Illinois and Indiana (Cummings and Mayer 1992).

We exposed eleven fish species to V. ellipsiformis glochidia collected from females of the North Fork Zumbro River in Goodhue County, Minnesota. Slimy sculpins and Johnny darters, facilitated metamorphosis of glochidia (Table 1). Several fishes did not serve as suitable hosts (Table 2). Juvenile mussels were collected from six walleye just nine days after exposure to V. ellipsiformis glochidia in the first trial. However, juvenile V. ellipsiformis developed for 35 d and 57 d on slimy sculpins and Johnny darters respectively. Subsequent studies on walleyes did not produce any juvenile mussels. We believe the juveniles collected from the walleye were probably from a natural infestation. Additional host suitability studies will be conducted on walleye and other fishes.

Table 1. Suitable fish hosts for V. ellipsiformis glochidia.

Species Number tested Juvenile collection period (d) Johnny darter 6 57-95 slimy sculpin 6 35-59 Average water temperature 19 ~ 2oC

Table 2. Unsuitable fish hosts for V. ellipsiformis glochidia.

Species Number tested Encystment period (d) longnose dace 3 17-20 black bullhead 6 19-23 white sucker 6 19-23 bluegill 6 29-31 walleye I 6 unclear* walleye II 4 7-10 walleye III 4 21-24 walleye IV 5 27-29 golden shiner 6 19-23 yellow perch 6 22-25 logperch 4 45-48 northern pike 4 31-33 *Results were confounded with juvenile mussels from a natural infestation.

In the laboratory, gravid V. ellipsiformis exhibited an interesting mantle display. Ventral to the incurrent siphon are a pair of 10 x 2 mm mantle flaps. The mantle flaps have four to six papillae 3-6 mm long that lie perpendicular to the long axis of the mantle flap. The top side of the mantle flap is the same color as the surrounding mantle. dark mottled brown. One mantle flap lies on either side of the marsupia. Occasionally, inflated marsupia are presented just beyond the perimeter of the valves and just interior to the mantle flaps. During the display period a female mussel displays the cream-colored underside of the mantle flaps. The underside of the mantle also has a small "eyespot" at the posterior end. The mantle is briefly closed and redisplayed whenever the shadow of a small fish or hand passes over the gravid female. Conglutinates are cream-colored, leaf-shaped, and approximately 1 x 5 x 10 mm in size.

Funding for this study was provided by the Minnesota Department of Natural Resources, Natural Heritage & Nongame Research Program, and the University of Minnesota, Undergraduate Research Opportunities Program.

Literature Cited

Cummings, K.S. and C.A. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Illinois Natural History Survey. Manual 5. Champaign, IL. 194 pp.

Oesch, R. D. 1984. Missouri Naiades: A guide to the mussels of Missouri. Missouri Department of Conservation. Jefferson City, MO. 270 pp.

Mark Hove
Department of Fisheries & Wildlife, University of Minnesota
(612) 624-3019
email mh@fw.umn.edu

Cyclonaias tuberculata glochidium

In July 1996 the purple wartyback (Cyclonaias tuberculata) was added to Minnesota's list of threatened species. Identification of fish hosts for C. tuberculata is of interest to Minnesota and Wisconsin natural resource managers charged with conservation of this species.

During 1996 glochidia were obtained from gravid C. tuberculata collected from the St. Croix River, Minnesota and exposed to three species of Ictalurids. All three species, channel catfish, black bullhead, and flathead catfish, were found to be suitable hosts (Table 1). These results confirm my earlier findings on the suitability of channel catfish to serve as hosts for C. tuberculata . This is the first time that flathead catfish and black bullheads have been identified as suitable hosts for this mussel. It is interesting that on three earlier occasions (n=3 individuals) glochidial metamorphosis was not observed on black bullheads (unpublished data).

Table 1. Fish species that facilitated metamorphosis of glochidia.

Species Number of hosts inoculated Number of survivors Junvenile recovery period (days) Number of juveniles recovered Ictalurus punctatus (channel catfish) 3 1 17-29 119 Ameiurus melas (black bullhead) 6 6 12-22 5 Pylodictus olivaris (flathead catfish) 3 3 19-27 3

A disproportionately larger number of juvenile mussels were collected from the channel catfish than from black bullheads and flathead catfish. This may be due the channel catfish serving as a superior host. However, the body length of the surviving channel catfish was four times greater than any of the other individuals tested. To determine if juvenile C. tuberculata production is significantly greater for channel catfish, a more rigorously controlled study is needed.

In the future I plan to conduct host suitability studies on Lasmigona compressa, Ligumia recta, and Anodontoides ferussacianus.

Flathead catfish were obtained from James Hardin, Calhoun City, Mississippi. Partial funding was provided by the Minnesota Department of Natural Resources, Natural Heritage and Nongame Research Program.

Channel catfish

Vanessa E. Pepi and Mark C. Hove
University of Minnesota, Department of Fisheries & Wildlife
1980 Folwell Avenue, St. Paul, MN 55108
(612) 624-3019
pepi003@gold.tc.umn.edu & mh@fw.umn.edu

Tritogonia verrucosa is a widespread but relatively uncommon freshwater mussel in the midwest (Cummings and Mayer 1992). This species is endangered in Iowa, threatened in Wisconsin (Cummings and Mayer 1992), and threatened in Minnesota. T. verrucosa are often found in gravel or rocky substrates (Thiel 1981). In the Upper Mississippi River these already uncommon habitats are becoming extremely rare due to dredge disposal activities and elevated sedimentation rates.

We exposed 9 species of fish to T. verrucosaglochidia collected from the St. Croix River, Interstate State Park, Minnesota. Yellow bullheads facilitated glochidia metamorphosis and dramatic juvenile growth before encystment (Table 1). Flathead catfish have also been reported as suitable hosts for T. verrucosa (Howell 1996).

Table 1. Suitable fish hosts for Tritogonia verrucosa glochidia.

Species Number tested Juvenile collection period (d) yellow bullhead 3 15-22 Average water temperature was 19 ± 2oC

Table 2. Unsuitable fish hosts for Tritogonia verrucosa glochidia.

Species Number tested Encystment period (d) black bullhead 6 10-13 killifish 8 * longnose dace 8 17-24 Iowa darter 5 17-24 spotfin shiner 7 15-17 creek chub 6 22-24 rock bass 6 14-16 tadpole madtoms 6 19-21 Average water temperature was 19 + 2oC * Fish died before end of study

Tritogonia verrucosa presents an unusual mantel during the glochidial release period. The portion of the mantle dorsal to the excurrent siphon is inflated, and crenulated with blue-gray edges and a tan-colored interior. (It really looks like the decorative cream on an eclair.) Although we don't think eclairs are natural food items of Ictalurids, perhaps the mantle is specialized to release a chemical attractant to prospective fish hosts. Additional host suitability studies will be conducted on Ictalurids and other fish families.

Funding was provided by the Minnesota Department of Natural Resources, Natural Heritage and Nongame Research Program, and the University of Minnesota, Undergraduate Research Opportunities Program.

Literature Cited

Cummings, K.S. and C.A. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Illinois Natural History Survey. Manual 5. Champaign, IL. 194 pp.

Howells, R. G. 1996. Pistolgrip and Gulf Mapleleaf hosts. Info-Mussel Newsletter. 4(3): 3.

Thiel, P. 1981. A survey of unionid mussels in the Upper Mississippi River (pools 3l l). Technical Bulletin Number 124. Wisconsin Department of Natural Resources. Madison, WI. 21 pp.

Charles M. Mather
Box 82345
University of Science and Arts of Oklahoma
Chickasha, OK 73018
and
Joseph A.M. Bergmann
110 Scottie Drive
Boerne, TX 78006

According to Neck and Howells (1994) the "Texas heelsplitter has been, and remains, a rather rare species. Only about 150 specimens appear to have been documented since the species was described in 1898. Among these, only about 50 have been found within the last 15 years and among those, only two were alive when found." They also reported that in their surveys, no specimens were found in the Trinity River system.

In the summer of 1996, the present authors visited several sites in the middle reaches of the Trinity River in the vicinity of Houston and Leon Counties, Texas to check on the status of mussel beds that had experienced severe population crashes. In 1981, healthy, very dense mussel beds were sampled in this region. In 1985, large numbers of dead mussels were noted in the region so an effort was made in 1986 to resample one of the earlier sites. During several man-hours of sampling, only a single live mussel (Lampsilis teres) was found and it was too weak to close its shell. In 1996, several of these devastated mussel beds were re-examined to determine if there had been any recovery. Surprisingly, good populations of all the species found previously were found during the 1996 survey. In one area during about two man-hours of sampling, a total of 8 living adults and 49 living juvenile Potamilus amphichaenus were found. Good populations of this species were also found at every other site sampled.

Neck, R W. and R G. Howells. 1994. Status survey of Texas heelsplitter, Potamilus amphichaenus (Frierson, 1898). Special Report, Texas Parks and Wildlife Department, Austin, TX, 47 pp.

1996 Mississippi River Research Consortium abstracts

The following abstracts were selected from presentations made at the 28th annual meeting of the Mississippi River Research Consortium. The next meeting will take place at LaCrosse, WI on April 24-25,1997. All are invited to attend! For more information please contact: Mark Hove at University of Minnesota, Department of Fisheries & Wildlife, 1980 Folwell Avenue, St. Paul, MN 55108, or by phone (612) 624-3019, FAX (612) 625-5299, or email mh@fw.umn.edu.

Kim S. Greenwood, James E. Alexander, Jr., and James H. Thorp

Large River Program, Dept. Biology, University of Louisville, Louisville, KY 40292

We examined the levels of infestation of zebra mussels on two species of snails (Prosobranchia: Pleuroceridae) in five navigation pools of the middle reach of the Ohio River. Using SCUBA, Lithasia obovata, Pleurocera canaliculatum, Lithasia armigera and the infesting mussels were collected at several depths to determine densities, size, and AFDM. Artificial streams and laboratory experiments were used to examine the effects of infestation on snail mobility. Infestation increased with depth and size of snail. L. obovata, which only occurs at shallow depths, has experienced low levels of infestation while Pleurocera and L. armigera have been found to carry as much 5x their own weight in mussels. Heavy levels of infestation result in a decrease in speed, especially under conditions of low flow and warm temperatures. When compared to uninfested individuals of the same size and population, infested snails have lower AFDM. It appears that infestation will have chronic effects on the snail population, such that numbers may be reduced slowly through time by lowering the fitness of individuals and possibly reducing their ability to reproduce.

N. Carol Krumanocker, Brian L. Sloss, Richard V. Anderson, and Michael A. Romano Dept. of Biological Sciences, Western Illinois University, University Circle, Macomb, IL 61455

Collection of Dreissena polymorpha in the summer and fall of 1995 revealed a variety of shell morphologies at 5 collection sites in pools 19 and 20 of the Mississippi River. Sympatrically collected individuals possessed distinguishing phenotypic differences leading to the conclusion that 2 species of Dreissenid were present at each site. Some individuals were rounded ventroposteriorly, had a much more rounded ventral surface with little or no ventrolateral shoulder or ridge, had a higher dorsoanterior slope or winglike extension, possessed a white or black stripe across the middle of the shell from the umbone toward the posterior end, and a difference in the color pattern or marks between the ventrolateral and dorsolateral sides. This description is consistent with previous documentation of D. bugensis. Other individuals had an angulate ventroposterior margin, an arched and flattened ventral surface with an acute shoulder or ridge ventrolaterally, consistent with D. polymorpha. Starch-gel electrophoresis was used to further investigate the possibility that shell morphologies were due to the presence of more than I species. Preliminary electrophoretic data from 11 presumptive loci are consistent for the presence of the 2 mussel species at each sampled site. Allelic variation at key diagnostic loci (Pp, Pgm, Mdh) in combination with corresponding phenotypic variation suggest the presence of the "quagga" mussel, Dreissena bugensis, in the mid-reaches of the Mississippi River.

Melissa Morgan, Jill S. Cougill, and Richard V. Anderson Dept. of Biological Sciences, Western Illinois University, Macomb, IL 61455

Pool 19 of the upper Mississippi River had remained relatively free of zebra mussels until 1994 as indicated by annual surveys at standard sampling locations within the pool. During the 1994 sampling, zebra mussels were present in samples collected from 3 of the 5 sites within the pool. All of the sites were in the lower reach of the pool. In 1994, density of the zebra mussels, where they were collected, was less than 5/m². By 1995 all sites had large populations of zebra mussels with densities at some sites in excess of 50,000/m². Surveying the same habitat type, channel border, there was an upstream to downstream density gradient, with higher zebra mussel densities occurring in the lower reaches of the pool. Frequency of infestation on native unionid mussels was higher at sample sites with coarser substrates and closer proximity to the channel. Infestation density varied between unionid species. Thin shelled species that may burrow more deeply into substrates had very low infestation densities. Consequently heavier shelled unionids which usually have more of the posterior of the shell exposed above the substrate had the highest infestation densities. As many as 3 cohorts were present in the zebra mussel population by mid September with the middle cohort having the highest number of individuals. There was some within pool variation in cohort density which may reflect small differences in habitat characteristics. There is some indication that infestation frequency and density may be lower in shallow channel border areas of previously vegetated habitat, and these sites may serve as a refuge for unionid mussels.

Marian E. Havlik

Malacological Consultants, 1603 Mississippi Street, La Crosse, WI 54601-4969

Thaddeus Surber (1924) walked 1000 miles to conduct a fish survey of the Root River system, southeastern Minnesota, but he made no mention of unionids even though he commented on other aspects of the River. Since the Root River has never been surveyed for unionids, we sampled from 6 - 17 June 1994 at 117 bridge and road access sites between the Root River system headwaters and the Mississippi River. The main stem of the Root River starts just NE of Lanesboro, MN, at the confluence of the North and Middle Branches, and flows easterly to its confluence with the Mississippi River, between La Crescent and Brownsville, MN. Sampling consisted of wading and shoreline searches in the headwaters and middle reaches of the Root River, and shoreline searches by boat of the lower six miles from Hokah, MN, to the river's mouth. This survey, including the main stem and four major tributaries, yielded 16 unionid species. Only three species were found alive, represented by five living mussels: Venustaconcha e. ellipsiformis (Conrad, 1836), Ellipse (3), and Lampsilis radiata luteola (Lamarck, 1819), Fatmucket (1) were found at a South Branch site, 0.5 mi N of Etna, MN, and one Anodontoides ferussacianus (Lea, 1834) Cylindrical Papershell, was found at a North Branch site, 4 mi NW of Dexter, MN. Several species were represented by fresh-dead shells. The most species (12) were found in the North Branch, Root River among 22 sites; the most shells were found in the South Branch among 40 sites (nine species). Eleven species were found among eight sites on the Middle Branch. No trace of unionids was found on the South Fork, Root River. The most common species found both dead and alive, Venustaconcha e. ellipsiformis, also lives in the Cannon and Zumbro Rivers of southeastern Minnesota, but apparently was not found in western Wisconsin for over 60 years, until 1992 -1994, when it was found in a tributary of the Chippewa River, near Cadott, WI. Data show severe impacts to the Root River system. We were unable to pinpoint the precise impacts, but our preliminary conclusions are that cumulative impacts, primarily agricultural, are apparently responsible. Since the Zebra Mussel is exploding in the Mississippi, we must quickly identify tributary molluscan fauna, or risk losing unique populations before they can be identified. We hope have funding to finish areas not sampled in 1994, including portions of the North Branch, South Branch, Root River main stem, and selected creeks, prioritized from Surber's descriptions. We also sampled sites on the nearby Upper Iowa (2) and Little Iowa Rivers (8), for a total of 127 sites. Project funded by MN Nongame Tax Checkoff Program.

Terry Balding¹, Dan Kelner², and Derrik Duchesneau³

¹University of Wisconsin-Eau Claire, Eau Claire, WI 54702; ²Ecological Specialists, Incorporated, St. Peters, MO 53376; ³Wisconsin DNR, Sheboygan, WI 53081

From 1985 to 1995 we used wading, snorkeling, a glass bottom bucket, and SCUBA to qualitatively sample each 1 or 2 km segment of a 288 km (178.8 mile) reach of the Chippewa River and 82 km (50.9 mile) of selected reaches of some tributaries. We have identified 30 species from among over 25,000 shells that were examined. Of the 30 species, 7 are on the Wisconsin Rare and Endangered Species list: Cumberlandia monodonta, Cyclonaias tuberculata, Plethobasus cyphyus, Quadrula metanevra, Simpsonaias ambigua, Tritogonia verrucosa, and Venustachoncha ellipsiformis. Quantitative data were also collected using 1/4 m² quadrat samples along transects that were systematically placed in certain reaches of the Chippewa and Flambeau Rivers. The highest density recorded was 256 live unionids/m² on the Flambeau River and 104 live unionids for the Chippewa River. Other significant points of interest regarding abundance, distribution and species richness will be presented.

Scott D. Whitney, K. Douglas Blodgett, and Richard E. Sparks Illinois Natural History Survey, River Research Labs, 704 N. Schrader Ave., Havana, IL 62644

During the past ten years mussel populations in Pool 15 have been subjected to a number of stresses, including (1) heavy commercial harvest, (2) pollution from both urban centers and nonpoint sources, (3) increased recreational and commercial navigation, (4) massive mussel die-offs, and (5) recent introduction of the zebra mussel. Since 1985, the Illinois Natural History Survey has evaluated the effects of these stresses on mussel populations by collecting quantitative information at two sites in Pool 15, an Illinois designated mussel sanctuary (Sylvan Slough, RM 485.8) and a commercially harvested bed (Case-IH, RM 488.5). The data collected were used to evaluate changes in species richness and abundance, recruitment, mortality, growth, and age structure at each location. The primary objectives of this study were to detect significant changes, identify possible causal factors, and formulate management recommendations designed to protect, preserve, and enhance mussel populations in this area and elsewhere.

Unionid mussel populations in Pool 15 are extremely rich in both species diversity and abundance, with twenty-six documented species (Table 1) and average densities as high as 290 unionids/m². Pool 15 is also suitable habitat for three threatened and endangered mussel species. Over the past decade there has been a significant (p < 0.001) decline in mussel abundance at both Sylvan Slough and Case-IH. Unionid species show substantial differences in their recruitment patterns ranging from good recruitment every year to once during the past ten years. Overall unionid mortality reached 40% in 1985 during the unexplained mussel dieoff, but has since remained relatively low (14%). We estimate five commercial species required from 19 to 24 years to reach minimum commercial size limit and all reach sexual maturity at an average age of 7 to 8 years (Table 2). Zebra mussel density and infestation of native unionids have both increased significantly in the past two years. In September 1995, average density of zebra mussels was near 500/m² and nearly 50% of the unionids are experiencing some degree of infestation.

J.D. Jack¹, J.H. Thorp², and A.F. Casper²

¹Dept. of Biology, Western Kentucky University, Bowling Green, KY 42101; ²Large River Program, Dept. of Biology, University of Louisville, Louisville, KY 40292

We conducted a series of in-situ experiments using potamocorrals to assess the impacts of zebra mussel adults and veligers on the plankton of the Ohio River. In the first experiment, adult mussels were suspended in the corrals at three different densities (0, 500, 2500 individuals) and incubated 7 days with daily plankton sampling The presence of adult zebra mussels was correlated with a shift toward diatoms or a mixed diatom/bluegreen assemblage and a severe reduction in ciliates and some rotifers Zebra mussel effects on larger zooplankton were taxon-dependent, but bacterial densities showed no trend between treatments. In the second, potamoplankton communities containing veligers were incubated in the presence or absence of the larger macrozooplankton. Zebra mussels will thus have varying impacts on the potamoplankton assemblages at different stages of their life cycle.

Andrew F. Casper, R. Brent Summers, Tim Sellers, James H. Thorp, & James Alexander

Large River Program, Dept. of Biology, University of Louisville, Louisville, KY 40292

The strength of zebra mussel recruitment is often inferred from measurement of veliger densities, the implication being that veliger production levels eventually control the abundance and distribution of adult zebra mussels. However, the period when conditions are conducive to settlement can be short in comparison to that for veliger production. Data from the Ohio River in 1995 showed high levels veliger production beginning in early May, when water temperatures remain at or above 18^oC and lasting through September. However, young mussels (<4 mm) do not begin to appear in abundance until mid to late August. This difference between onset of production and significant recruitment suggests that a factor other than temperature limits recruitment. Discharge on the Ohio River drops from an annual peak in March to summer pool by late June. This seasonal decrease in discharge is accompanied by a heavy deposition of suspended sediment. With inorganic suspended sediment at a low and chlorophyll concentrations at a high an optimal environment for initial settlement and growth is created. Summer pool conditions last from late July thru October. This is when most young of the year zebra mussels (<4 mm) first appear. This suggests that while heavy deposition may not affect veliger production, it can limit successful settlement and therefore recruitment into the population. Specific mechanisms may include physical burial of juveniles, clogging of the gills, or low food quality/availability. The occurrence of lower than normal winter precipitation may enhance chances of a strong recruitment whereas late spring flooding which can result in a poor year class recruitment.

David C. Beckett¹, B. Will Green¹, and Andrew C. Miller²

¹Department of Biological Sciences, Box 5018, University of Southern Mississippi, Hattiesburg, MS 39406; ²Environmental Laboratory, U.S. Army Engineer Waterways Experiment Station, 3909 Halls Ferry Rd., Vicksburg, MS 39180

In order to monitor changes in zebra mussel density in the upper Mississippi River we have made yearly collections, since 1991, of rocks and their invertebrate fauna from two wing dams in Pool 10 near Prairie Du Chien (PDC). No zebra mussels were present in the wing dam samples in 1991 or in 1992. Zebra mussels were present in the wing dam samples in 1993, although in low densities. The wing dam collections in 1994 showed a marked increase in zebra mussel densities, e.g. 1994 had a mean of 118 D. polymorpha per m² Of rock surface on the downstream side of wing dam #1, as compared to a density of 6 individuals per m² at the same site in 1993. Results from 1995 reveal a "population explosion" of zebra mussels has taken place in this portion of the upper Mississippi River. Zebra mussel densities on the PDC wing dams in 1995 were approximately 180 times those of 1994. Zebra mussel densities on the bottom of the east channel of the Mississippi River at PDC (where the sampled wing dams are located) were also very high in 1995; approximate densities were 50,000 to 75,000 individuals per m² of bottom. Our results therefore agree with similar studies, e.g. lock chamber studies, which show recent dramatic increases in zebra mussel densities in portions of the upper Mississippi River.

In light of these dramatic increases in zebra mussel density, it is interesting to note that high densities of D. polymorpha are, at present, not a universal phenomenon in the upper Mississippi River. We sampled a wing dam in Pool 9 and one in Pool 11 in 1995 along with the sampling effort at PDC. Although zebra mussels were present on both of these wing dams, their densities were very low (e.g. the mean density on the Pool 9 wing dam equaled less than 10 individuals per m² of rock surface). It should be remembered, however, that zebra mussel densities on the PDC wing dams were very low two to three years ago, and it may take just a few years for zebra mussel numbers to build up on the wing dams (and other habitats) where they are presently scarce.

W. B. Richardson^l,2,3 , L. A. Bartsch¹, and M. B. Sandheinrich²

¹Upper Mississippi Science Center, National Biological Service, La Crosse, WI; ²Department of Biology and Microbiology, University of Wisconsin, La Crosse, WI; ³Research supported by Wisconsin Seagrant

We know that the feeding activities of zebra mussels can significantly reduce both phytoplankton and zooplankton populations. Hypothetically, these reductions in water column trophic resources should result in reduced growth and survival of zooplanktivorous fishes. Several sets of mesocosm experiments previously conducted at the Upper Mississippi Science Center were designed to test this hypothesis. In these experiments, however, we used a facultative zooplanktivore, juvenile bluegills. Contrary to our predictions, bluegills grew better in the presence of zebra mussels because of their ability to switch to benthic prey when plankton became rare. The work we report here describes an experiment using a top predator that is an obligate planktivore (Pimephales promelas larvae) in early life stages then switches to benthic feeding as it matures (as do many fishes). In a 130-d mesocosm experiment we manipulated the presence or absence of (1) zebra mussels (5000/m²), (2) larval fathead minnows (Pimephales promelas: 400/mesocosm), and (3) turbulent mixing (0-5 cm/see). These factors were cross-classified, resulting in 8 treatment combinations, N=3. At the end of the experiment, total mass of fishes harvested from zebra mussel (=Z) or turbulence (=T) treatments was 20% less than that of fish-controls, and 40 % less in the Z+T treatment than in controls. Survival of fishes in the Z+T treatments was 50% less than that in controls. Individual fish from the Z+T treatments were significantly larger than those from other treatments. Turbidity, chlorophyll a concentration, and Daphnia and copepods densities were significantly reduced in Z, T, and Z+T treatments relative to controls. By the last date of the experiment (9/13/95) the fish in the Z+T treatment were ingesting mainly benthos (e.g. amphipods and isopods) while fish in all other treatments were ingesting mainly zooplankton (e.g. rotifers and Bosmina). We suspect that turbulent mixing facilitated increased removal of seston by zebra mussels (by increasing particle contact rates with zebra mussels) resulting in reduced available prey for the fish. Zebra mussels and turbulence also reduced the density of cladocerans, copepod nauplii, and rotifers, valuable as food for larval fishes. Also, turbulent mixing, at rates used here, has been shown to interfere with feeding processes of larval fish resulting in reduced growth. Finally, turbulent mixing in zebra mussel treatments appeared to increase accessibility of macroinvertebrates to larger fish, possibly by moving the invertebrates into the water column where they were consumed.

Richard V. Anderson and Jennifer Eichelberger

Dept. of Biological Sciences, Western Illinois University, Macomb, IL 61455

Much of the channel border habitat in navigation pools of the Mississippi River has a soft silty substrate. As such it is not a good habitat for organisms which need a solid substrate on which to attach. Live unionid mussels which occur in this habitat provide an optimum type of epizoic substrate since their shells offer a hard surface and the mussels maintain their position at the water substrate interface, thus preventing attached organisms from being buried by sedimentation. Eighteen species of epizoic organisms were found on the surfaces of unionid mussels collected in mid to late summer. Other than zebra mussels, the dominant epizoic organism was the leptocerid caddisfly, Oecetis. Bryozoans and freshwater sponges were also common. Fish, insect, and other invertebrate eggs were also frequently present on shell surfaces. Of the 1200 mussels examined, over 70% contained epizoic organism. Mussel size and species was related to frequency of occurrence of epizoon. Small shells, less than 5 cm in length often had no epizoic organisms. The threeridge, Amblema plicata, had the highest frequency of epizoon with 96% of the shells over 5 cm in length containing attached organisms. The presence of unionid mussels in channel border habitat may significantly increase benthic community diversity in these areas.

Lori A. Camlin¹, James A. Stoeckel², K. Douglas Blodgett¹, and Richard E. Sparks²

¹Illinois Natural History Survey, LTRMP La Grange Field Station, 704 N. Schrader Ave., Havana, IL 62644; ²Illinois Natural History Survey, River Research Laboratory, 17500 ECR 1950N PO Box 590, Havana, IL 62644

In river systems, an understanding of dispersal patterns of zebra mussel (Dreissena polymorpha) veligers can aid in the development of effective management strategies for adult zebra mussel populations. The main objective of this study was to determine veliger abundance and size distribution fluctuations throughout the year. This information will help us gain insight into locations of upriver source populations and potential downriver settlement patterns. From May 1994 through December 1995, zebra mussel veliger drift was monitored twice weekly at a single site on the Illinois River at Havana, Illinois (river mile 121.12. Veligers were collected by filtering a known volume of depth-integrated river water through a 60-Em plankton net. Veligers were identified using polarized light microscopy, then enumerated and measured using Optimas imaging and analysis software.

In 1994, live veligers were found in all samples from May to October (Figure 1) when water temperatures were greater than 12^oC and sporadically from November to December when water temperatures were less than 12^oC. In 1995, veligers were found continuously from May to August (water temp > 12^oC), but sporadically in September and October (water temp > 12^oC). While the duration of spawning seasons differed, total veliger production was similar with an estimated 2.0 x 1014 and 2.4 x 1014 veligers drifting past our site in 1994 and 1995 respectively. Size distributions of veligers were also very similar, the average-sized veliger being 109.7 Em in 1994 and 109.0 Em in 1995. For both years, approximately 80% of veligers were between 95 and 135 Em (Figure 2). This suggests the majority of veligers we saw throughout our study were coming from the same upstream population(s).

Locations of source and destination populations were estimated assuming a development time of 48 hours to reach D-stage at 95 Em, growth rates of 6-13 Em/day, a settling size of 180-250 Em, and an average flow rate of 0.5 m/s. Based on these assumptions, the majority of veligers passing our site were produced upriver of Illinois River mile (IRM) 185.2 and would settle downriver of IRM 37.9. Veliger abundances as high as 70 million/second indicated that the potential for significant settlement downriver from our site was high. While we saw little settlement in the lower Illinois River in 1994, significant settlement occurred in 1995. These populations suffered high mortality and virtually disappeared by fall 1995. If total veliger production follows the same pattern in coming years, potential for recolonization of downriver reaches will be high.

Frederick A. Cronin, John K. Tucker, and Dirk W. Soergel

Long Term Resources Monitoring Program Pool 26, Illinois Natural History Survey, 4134 Alby Street, Alton, Illinois 62002

We examined the gut contents from 31 common carp (Cyprinus carpio) collected at Mississippi River Mile 217 in late August 1995 for evidence of predation on zebra mussels (Dreissena polymorpha). We found between 1 and 407 zebra mussel beaks in 83.9% of the fish we examined. For all fish examined, common carp contained 118.2 beaks per fish or about 59 zebra mussels per fish. Excluding fish that did not contain one or more beaks, we found 140.9 beaks per fish or about 70 zebra mussels per fish. The survey did not indicate that larger fish consumed more zebra mussels than smaller fish. Estimated valve length for zebra mussels consumed by common carp ranged from 1.48 to 42.52 mm with a mean 11.79 mm (SE = 0.10 mm). Individual variation existed among the 24 fish in mean valve length of zebra mussels consumed. We found that large fish tend to prey on larger zebra mussels than small fish. The general size range of zebra mussels consumed by common carp overlapped the upper portion of the size range of young-of-the-year zebra mussels living at the site and the lower portion of the size range of older zebra mussels living at the site. Other prey items found included fingernail clams (Sphaeriidae), the Asiatic clam (Corbicula fluminea, Corbiculidae), and Lampsilis teres (Unionidae). Notwithstanding the possible impact that the common carp may have on zebra mussel demographics, our study bears directly on the controversy surrounding proposals to import other exotic molluscivorous fishes such as the black carp (Mylopharyngodon piceus) to effect long-term control of zebra mussel populations. If predation by the common carp is found to be widespread where zebra mussels are numerous, then there is no reason to import other fishes. Further studies of the common carp in other areas with high zebra mussel densities are critically needed.

Deric R. Deuschle¹, M.D. Delong¹, and J.H. Thorp²

¹Large River Study Center and Biology Dept., Winona State University, Winona, MN 55987; ²Large River Program and Dept. of Biology, University of Louisville, Louisville, KY 40292

The zebra mussel, Dreissena polymorpha, has entered the upper Mississippi River, and is expected to have an impact on the ecology of the river, as it has in the Great Lakes. The objective of this study was to examine between the zebra mussel and native invertebrate communities, and how invertebrate communities may change as zebra mussel densities increase. A total of 20 cages were placed in the main channel of the Mississippi River. Half of the cages were enclosed with 1.5-cm diameter mesh to exclude large fish, while the remaining cages were left open. Two types of substrata were used; one type consisted of 12 unglazed clay tiles, while the other type consisted of 12 bundles of willow branches. The two types were used to mimic natural rock, and snag substrate respectively. This combination of factors allows a total of 4 experimental treatments. Cages were placed into the river in June 1994. This report pertains to the second year (1995) of the study. One sample from each cage was removed monthly from June to October 1995. Preliminary analysis indicated that zebra mussel densities were highest on the tiles compared to the snags. Densities were also higher in the closed cages than the open ones. These two observations seem to indicate that zebra mussels are more successful on rocky areas, a substrate of limited abundance in the Mississippi River. Invertebrate communities showed marked changes as zebra mussel densities increase. Colonization by the mussels creates new micro-habitats that become favorable for some species, and detrimental to others. Community composition varied greatly in response to differing habitats. Chironomidae populations increased as zebra mussel densities increased. The numbers and variety of predator species (e.g. Odonata, Megaloptera) that feed on Chironomidae also increased.

Scott D. Whitney, Darin Osland, Douglas Blodgett, and Richard E. Sparks

Illinois Natural History Survey, River Research Labs, 704 N. Schrader Ave., Havana, IL 62644

The last comprehensive mussel survey of the Illinois River, conducted in 1966-69, indicated 25 of the 49 species once found in the river had been extirpated; extensive stretches of the upper river, once densely populated with mussels, did not yield a single living specimen. What was once the most productive mussel resource per river mile in the United States, had been severely degraded by habitat loss, exploitation, and pollution. In the past three decades mussel populations in the Illinois River have been subject to three major changes: (1) renewed commercial exploitation for the Japanese cultured pearl industry; (2) dramatic improvements in water quality; and (3) the recent invasion of two nonindigenous bivalves, the Asiatic clam (Corbicula fluminea) and the zebra mussel (Dreissena polymorpha). In 1993, we began a comprehensive survey to assess the impacts of these changes and determine the current status of mussel populations in the Illinois River. Wading and brailing were used for preliminary site assessment and for comparisons with previous studies. However, the majority of the collections were made by divers using quantitative and qualitative sampling techniques. The information we have collected indicates that mussel populations in some areas of the river are showing signs of recovery after decades of decline. The most dramatic improvements were recorded in the upper reaches of the river, where we found live mussels representing 12 unionid species, including juveniles; a live mussel had not been reported from this part of the river since the early 1900's. Throughout the entire river, we collected a total of 23 species, including five species once listed as extirpated. Average densities ranged from less than 1 live mussel/m² to 38/m², with population density and species abundance at our sample sites showing an increase in the downriver direction. Most mussel beds in the lower river arc now comprised of several abundant species rather than one or two dominant species reported in past surveys. The age and size structure of mussel populations indicate higher growth rates than mussels collected from Pool 15 of the Upper Mississippi River and stable recruitment patterns for most species. Despite signs of improvement in unionid density and species diversity at some sites, the future of Illinois River mussels remains questionable. The recent invasion and proliferation of the zebra mussel coupled with increased anthropogenic demands on the river and its resources may set back years of recovery of the Illinois River mussel populations.

D.L. Vaughn, R. Brent Summers, and James H. Thorp

Large River Program, University of Louisville, Louisville, KY 40292

We examined the effects of zebra mussel and non-zebra mussel (gravel) substrates on amphipod densities, biomass, and size-class distributions. Equal amounts of substrate (either zebra mussels or gravel) were placed in independent channels of an artificial stream mesocosm. Equal amounts of similar sized substrate were used to ensure that any differences encountered were not artifact of differences in habitat heterogeneity. Water was pumped directly from the Ohio River to the stream mesocosm, which allowed for amphipod colonization of the channels. Amphipods were allowed to colonize and grow in the channels for a four week period. At the end of the four week period, amphipods were removed and enumerated for densities, biomass, and size-class distributions. The data is currently being analyzed, however, initial trends indicate that channels with zebra mussel substrates support higher amphipod densities and biomass than channels with gravel only. This difference may be due to the retention of organic matter, to include faeces and psuedofaeces produced by the zebra mussels which in turn may result in a higher quality detrital food source for the amphipods thus resulting in higher densities and biomass.

Thomas B. Ward¹, Michael D. Delong¹, and James H. Thorp²

¹Large River Studies Center, Biology Dept., Winona State University, Winona, MN 55987; ²Large River Program, Dept. of Biology, University of Louisville, Louisville, KY 40292

Zebra mussels, Dreissena polymorpha, have invaded the upper Mississippi River and have established themselves as a major macroinvertebrate species inhabiting hard substrata. An experiment was designed to examine the population dynamics and possible predation effects in the upper Mississippi River. The experiment entailed use of two types of cages: open cages, on which only the upstream side was covered with 1.5 cm diameter mesh; and closed cages, which were completely covered with 1.5 cm diameter mesh. Each cage was fitted with either 12 clay tiles or 12 bundles of willow dowels (snags) to serve as hard substrata. The resulting design consisted of four combinations of experimental units. Cages were initially deployed in June 1994. Data for this report discuss the second year of the project. One substratum was removed from each cage monthly from June to October 1995. Zebra mussels and other invertebrates were removed from substrata and preserved for later taxonomic separation, counting and measurement. Zebra mussel colonization was higher on tiles than on snags, and was much greater in closed than open cages. The greater abundance on tiles suggests that cobble substratum are preferred over woody debris. Similarly, their abundance in the closed cages compared with that of the open cages suggest that fish predation may be a factor influencing population size. Zebra mussel densities were approximately the same in open and closed cages for zebra mussels 0-8 mm long. Densities of mussels greater than 8 mm are much lower in open cages than in closed cages, suggesting size-specific removal of mussels by fish predators.

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