RECOVERY INFORMATION NEEDED TO PREVENT EXTINCTION OF THE FEDERALLY ENDANGERED WINGED MAPLELEAF: EARLY LIFE HISTORY OF ENDANGERED UPPER MISSISSIPPI RIVER MUSSELS
 

MARK C. HOVE, Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 1980 Folwell Avenue, Saint Paul, MN 55108
612.624.3019, Mark.Hove@fw.umn.edu

ANNE R. KAPUSCINSKI, Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 1980 Folwell Avenue, Saint Paul, MN 55108
612.624.3019, ark@fw.umn.edu and isees@fw.umn.edu

Abstract: Record high flows during 2001 apparently caused the reproductive failure of winged mapleleaf in the St. Croix River. Consultation with the Recovery Team for this species led to a change of the study scope from winged mapleleaf host suitability analysis to early life history requirements of glochidia of the Higgins eye, another federally endangered mussel species. Restoration of Higgins eye in the upper Mississippi River is being accelerated through extensive mussel culture. Increasing the production of Higgins eye juveniles requires information about optimal propagation conditions. To determine the season and water temperature that best facilitate glochidial metamorphosis, 25 largemouth bass were artificially infested with Higgins eye glochidia during fall 2001 and 8 infested during spring 2002. The majority of fish were held in individual aquaria at the University of Minnesota's Fisheries Wet Laboratory. Five fish infested during fall 2001 were held in a cage in the St. Croix River. Bass held in the laboratory survived longer than those in the river. Warm water facilitated more rapid juvenile metamorphosis. Of fish infested in the fall, 82% facilitated glochidial metamorphosis, compared to 33% of spring infested fish.

Increasing the production of juvenile Higgins eye also requires information about the host fishes best suited to facilitate glochidial metamorphosis. Laboratory trials were conducted to identify suitable host species. Twenty-eight fish species (13 families) were infested with glochidia during fall 2001 and seven fish species (2 families) during spring 2002. Black crappie and sauger infested during the fall facilitated glochidial metamorphosis as did black crappie and smallmouth bass infested during the spring. These trials confirm host species identified in earlier studies and show for the first time that sauger and black crappie are suitable host species for Higgins eye glochidia.

INTRODUCTION

Several state and federal agencies are working together to re-establish the federally endangered Higgins eye (Lampsilis higginsii) in the upper Mississippi River. They are propagating this species using intensive culture of juvenile mussels in artificial raceways as well as holding artificially infested largemouth bass or walleye in cages in the Mississippi River. Higgins eye are long-term brooders. Long-term brooders hold young in their marsupia during the fall and winter and release them in the spring (Coker et al. 1921). The best season for facilitating metamorphosis of glochidia in captivity is unknown. It is unclear if glochidia collected during the fall are fully mature for use in culturing juveniles. Higgins eye glochidia collected in the spring are fully mature but fishes and glochidia are significantly more difficult to obtain during this time. Additionally, information is missing regarding the optimal water temperature for culturing juvenile Higgins eye. The objectives of this study were to: (1) determine if juvenile mussel transformation success varies between fall versus spring infested fishes, (2) determine how water temperature influences juvenile transformation success, and (3) identify additional suitable host fishes for Higgins eye glochidia.

Due to the apparent failed reproductive effort among winged mapleleaf in the St. Croix River during 2001, we worked quickly to develop a second research project for fall and winter 2001-2. During spring 2001, the St. Croix River experienced the highest flows recorded in the past 92 years. A large amount of sand appears to have been deposited on the most important winged mapleleaf bed in the river. Winged mapleleaf brood their young for a brief period relative to other mussel species. Over the last four years this species consistently brooded young during the last few weeks in September and first few weeks in October. In fall 2001, we began searching for winged mapleleaf during the expected peak of gravidity, the last week in September. The percentage of gravid mussels can reach 25% during the middle of a typical brooding period. None of 22 individuals observed were brooding at the end of September 2001. We failed to find any gravid animals after searching for brooding females through the remainder of the expected brooding period and beyond. We suspect the sediment deposited during the 2001 spring flood may have directly or indirectly resulted in the reproductive failure of winged mapleleaf adults in the St. Croix River. As we began to suspect this failed reproductive effort, Mark Hove and Pam Thiel called members of the Winged Mapleleaf Recovery Team to collect suggestions for secondary research priorities. The team includes members of state and federal natural resource agencies and a scientist from Macalester College.

Among several alternatives suggested by Recovery Team members, most people thought the highest priority research objective was to assist with the effort to propagate federally endangered Higgins eye, specifically, to determine whether fall or spring infestation of fishes with Higgins eye glochidia produce more juvenile mussels. Other suggested projects, which we did not pursue but might be helpful in the future were: (1) develop plans to construct a native mussel culture facility at the St. Croix Watershed Research Station, (2) accurately map winged mapleleaf locations on the St. Croix River and distribute a GPS layer to state and federal natural resource agencies, (3) determine how water temperature affects juvenile mussel production, and (4) conduct host suitability analysis on winged mapleleaf congeners.
 
 
 
 
 

METHODS

Juvenile production

We designed a laboratory and field study to determine the best season and water temperature to culture juvenile Higgins eye. During fall 2001 largemouth bass were randomly assigned to one of three temperature treatments in the University of Minnesota’s Fisheries Wet Laboratory, or a field treatment. Laboratory treatments included: (F1) flow-through aquarium at room temperature (approx. 19°C), (F2) flow-through aquarium at well water temperature (approx. 11°C), and (F3) flow-through aquarium at natural river temperatures (followed mean daily temperature of St. Croix River down to 8°C). The field treatment (F4) involved holding fish in a wire cage in the St. Croix River. Five replicates of these treatments were created during fall 2001. During spring 2002 this study design was replicated with some changes. Four replicates of two temperature treatments were produced. The treatments included (S1) flow-through aquarium at room temperature (approx. 19-22°C), and (S2) flow-through aquarium at natural river temperatures (followed mean daily temperature of St. Croix River, 11-22°C). Reasons for changes in the spring study design are described in the last paragraph of this section.

Fish for the fall 2001 study were infested with Higgins eye collected from the Mississippi River. Largemouth bass (Micropterus salmoides) were donated to our laboratory by the Genoa National Fish Hatchery and used as glochidial hosts. Fish were transported to the University of Minnesota’s Fisheries Wet Laboratory and held in flow-through aquaria. Glochidia were obtained from five brooding Higgins eye relocated in a previous state and federal project to a location near Fort Snelling, Minnesota. (The site is approximately 2 miles downstream of the Ford Dam in Minneapolis.) Glochidia and fish were acclimated to laboratory water at 11°C one week prior to infestation. We used a glass pipette to extract a sample of approximately 200 glochidia from each of the following previously marked Higgins eye: 686, C108, C112, DH8, and DH101. Glochidia health was assessed for a group of 10-20 individuals from each brooding Higgins eye. Health was determined by exposing the glochidia to sodium chloride crystals. Greater than 90% of the glochidia closed in response to salt exposure leading us to conclude the remaining glochidia from all five mussels were healthy and usable for the study. Fifty glochidia from each group of 200 glochidia were carefully applied to an individual largemouth bass. Attached glochidia were counted with a dissecting microscope immediately after infestation, 90 min after infestation, and five days after infestation.

Largemouth bass infested during fall 2001 were assigned to one of four treatments. Each of four bass infested with glochidia from one mussel was randomly assigned to one of the following temperature treatments: (F1) flow-through aquarium at room temperature, (F2) flow-through aquarium at well water temperature, (F3) flow-through aquarium at natural river temperatures, or (F4) a cage in the St. Croix River near Hudson, Wisconsin. Infested fish were acclimated to the treatment temperature over a period of 24-48 hours. Fish placed in the St. Croix River were held in a 2’ x 3’ 12" cage with a water current break at the front of the cage. The cage was located above a mussel bed on a bank slope where small fish would likely congregate. Aquaria were siphoned weekly and siphonate checked with a dissecting microscope to count the number of excysted juvenile Higgins eye. The glochidial transformation rate for each fish was calculated as the number of juveniles recovered divided by the number of glochidia that were attached to fish five days after infestation.

The study conducted during fall 2001, with the following few changes, was replicated during spring 2002. Since the largemouth bass in the St. Croix River did not survive the winter, we did not infest fish for the spring field study. We were only able to find four gravid Higgins eye due to high flows and low water clarity in the Mississippi River during 2002. Glochidia were collected from the same group of adults from the Mississippi River at Hidden Falls. Individuals 734, 738, 743, and 1476 were collected at 11°C and used for the spring infestation. We discussed removing the well water temperature (11°C) treatment with Roger Gordon, Genoa National Fish Hatchery mussel culturist. He agreed that it would be unrealistic for a culturist to hold juvenile mussels at 11°C if warmer water were available so we did not replicate the well water temperature treatment during spring 2002. We used glochidia from the four mussels to infest a total of eight largemouth bass. The eight fish were randomly assigned to the following treatments: (S1) flow-through aquarium at room temperature (19-22°C), or (S2) flow-through aquarium at river temperature (11-22°C). When mean daily river temperature exceeded 19°C we increased the water temperature of aquaria in the S2 treatment to follow mean daily river temperature.

Host suitability

Higgins eye glochidia rinsed from each mussel, after removing 200 glochidia for the juvenile propagation study, were used to lightly infest 32 fish species in the laboratory. Species that facilitated glochidial metamorphosis were considered suitable hosts. Most fish used in this study were collected from streams and lakes believed not to hold Higgins eye, in order to avoid testing fish that had acquired immunity from prior exposure to glochidia. Fishes were collected with a seine, trap net, or electrofishing equipment and held in 40 L or 400 L aquaria for approximately two months prior to glochidia infestation. Unionid and fish nomenclature follows Turgeon et al. (1998) and Robins et al. (1991) respectively. Glochidia were used for host tests if * 70% of individuals closed when exposed to a 0.1-1% sodium chloride solution. We infested fishes with glochidia by placing them in a 1-20 L bath, with the glochidia under vigorous aeration. Fish were exposed to glochidia for 15 minutes to 24 hours, depending on the species' susceptibility to infestation. Two to four hours after infestation, we examined the gills of a one to three individuals from each species with a dissecting microscope or by unaided eye to determine if infestation was successful.

After infestation, fish were held in aquaria at 11°C ± 2°C and fed regularly. Small fish were fed frozen brine shrimp (Artemia sp.) or blood worms (Chironomidae) at least three times a week. Fathead minnows (Pimephales promelas) were fed to piscivorous fish once a week and removed from aquaria 5-10 minutes after introduction to minimize the possibility of their consuming glochidia or juvenile mussels lying on the aquarium floor. Small fishes and catostomids were held in suspended nets to prevent them from eating glochidia and juvenile mussels. The trial was ended for a species when glochidia were no longer observed in the aquaria siphonate. At the end of a study the search for juveniles was usually terminated after three consecutive searches failed to reveal a glochidium or juvenile mussel. At this termination point, each fish was anesthetized and searched for attached glochidia using a dissecting microscope. When we found glochidia, the fish was revived and the experiment continued until we no longer observed glochidia attached to the fish. A mussel was considered a juvenile if foot movement was observed. A fish was considered a suitable host if we observed glochidia encystment and metamorphosis to the juvenile stage.

RESULTS

Juvenile production

Largemouth bass infested both during fall 2001 and spring 2002 produced juvenile Higgins eye. Glochidial metamorphosis varied between seasons and temperature treatments. Fall infested fish produced more juvenile Higgins eye than spring infested fish. Between 1-12 juvenile mussels excysted from bass in the F1 treatment 78-134 days post infestation. Juveniles began excysting from F2 treatment fishes at 112 days and F3 treatment fishes at 212 days. Juvenile Higgins eye are still excysting from fishes in treatments F2 and F3. From bass infested during spring 2002, we have only collected juveniles from the two bass in the S2 treatment. Juvenile mussels began excysting approximately 42 days after glochidial infestation and they are still excysting. Trials running through the spring probably have longer glochidial attachment periods than they would have under natural conditions due to our inability to increase water temperature beyond 19°C for over a month starting in June.

There was a difference in the number of fishes facilitating glochidial transformation between seasons. Of eleven surviving bass infested last fall, nine (82%) have produced at least one juvenile Higgins eye. Two of the six surviving bass infested this spring (33%) have supported glochidial metamorphosis. Both fish that produced juveniles this spring were held in the river temperature treatment. Statistical analysis of data for the spring study, which is not yet completed, will be included in our next annual report.

Problems we encountered during this study included low glochidial attachment success, inaccurate glochidia counts, and loss of fish due to disease outbreaks. Initial glochidial attachment success varied from 20-90% across all fall 2001 laboratory treatments. Of 50 glochidia pipetted onto each fish's gills, between 4-34 (mean=16) remained attached 5 days after infestation. Counting attached glochidia was difficult and proved to be inaccurate. We took great care counting the small, transparent glochidia attached to the gill lamellae. We found glochidia that had been encysted for several days were easier to locate than recently attached glochidia. Although we carefully counted the number of glochidia on each fish's gills, we know our counts were inaccurate because we collected more juvenile Higgins eye than originally counted from two fishes. These extra juveniles were probably not from an unplanned glochidial infestation since test fish had been held in a hatchery or wet laboratory for six months prior to this study. Our lack of confidence in the initial glochidial counts precludes statistical testing for significant differences among water temperature treatments. Instead, we present qualitative observations from the juvenile transformation rate data. Finally, the number of replicates in both fall and spring trials were reduced due to multiple fungal outbreaks of Saprolegniaceae. Infected fishes treated with malachite green appeared to benefit from the treatment. The disease outbreaks reduced the number of individuals in the fall trial to four held at room temperature, three in the well water temperature treatment, and four in the river water temperature treatment. Two of eight bass infested with Higgins eye during spring 2002 trial succumbed to two fungal outbreaks.

Largemouth bass held in the laboratory had higher survivorship than bass held in the St. Croix River. Fishes held in the St. Croix River over the winter did not survive to spring 2002. In early May 2002, a month before the juvenile excystment period, a review of the fish cage revealed that the largemouth bass had been dead for at least one month. Fish in the cage were decomposed and covered in fungus, preventing our reviewing the gills for attached Higgins eye glochidia.

Host suitability

We infested twenty-eight fish species (thirteen families) during fall 2001 and seven fish species (two families) during spring 2002 with Higgins eye glochidia. Higgins eye glochidia did not attach to eight species (gizzard shad, emerald shiner, fathead minnow, bluntnose minnow, mimic shiner, spottail shiner, brook silverside, and banded killifish) last fall. This may have been due to the small number of glochidia used in the infestation. Of those successfully, infested seventeen species (ten families) either did not facilitate glochidial metamorphosis or died before the end of the study (Table 1). Two species, black crappie and sauger, facilitated metamorphosis of Higgins eye glochidia (Table 2). Spring host suitability trials are still running. To date, we have collected juvenile Higgins eye from black crappie and smallmouth bass.

DISCUSSION

Juvenile production

Glochidial transformation rate is influenced by water temperature. Villosa nebulosa glochidia artificially placed on the gills of Cottus spp. and held at 18°C metamorphosed in half the time it took glochidia to metamorphose at 13°C (Neves et al. 1985). Juvenile Amblemines excysted from two darter species held at 21°C in roughly one-third the time it took them to excyst from darters held at 11°C (Hove et al. 1999). In this study, we also observed a negative relationship between water temperature and glochidial metamorphosis period. At 19°C juvenile Higgins eye excysted from fall infested fish between 78-134 days. At 11°C and 8°C juveniles began to excyst at 112 and 212 days respectively. (Comparison of temperature treatments from the spring trial is not yet possible since we have only collected juveniles from the river temperature treatment.) The amount of thermal input, as measured by degree-days, facilitating glochidial metamorphosis is not equivalent at different temperatures. Encysted V. nebulosa held at 13°C took approximately 970 degree-days to metamorphose while those held at 18°C took approximately 570 degree-days (Table 3). Similarly, darters held at 11°C took approximately 1650 degree-days to facilitate juvenile metamorphosis compared to 630 degree-days for darters held at 21°C. When this study is complete, we will determine if our data follow the trend in the other studies where roughly a one degree Celsius drop in water temperature results in an additional 100 degree-days needed to complete glochidial metamorphosis.

Host suitability

Our results confirm and expand our understanding of Higgins eye glochidial host requirements. Many species in the genus Lampsilis utilize Centrarchids and Percids to facilitate glochidial metamorphosis (Watters 1994). Waller and Holland-Bartels (1988) showed that walleye, yellow perch, smallmouth bass, largemouth bass, and green sunfish are suitable host species for Higgins eye and that northern pike and bluegill appear to be marginal hosts. Our results confirm largemouth bass is a suitable host species for Lampsilis higginsii. We tested three Centrarchids (orange-spotted sunfish, pumpkinseed, and rock bass) and one Percid (blackside darter) not previously tested but they did not facilitate glochidial metamorphosis.

This study shows for the first time that sauger and black crappie are suitable hosts for Higgins eye glochidia. Previous studies showed that sauger are infested with Higgins eye under natural conditions (Coker et al. 1921, Surber 1913, Wilson 1914). Additional field and laboratory studies should be conducted using crappie and additional darter species to determine their importance in the early life history of Higgins eye.

Plans for 2002-3

Higgins eye early life history studies will be concluded during 2002. Aquaria will be siphoned and juvenile mussels counted through completion of the glochidial excystment period. We will use this information to compare glochidial metamorphosis success between season and temperature treatments, and describe suitable host fishes.

We will study glochidial host requirements of winged mapleleaf during 2002-3. Preparations for conducting host suitability trials during 2002 using flathead catfish, channel catfish, blue catfish, and slender madtom are nearly complete. To determine if larger fish facilitate a higher glochidial metamorphosis rate than smaller fish we plan to compare winged mapleleaf glochidial transformation success between small (less than 20 cm) and large (40-60 cm) channel catfish. Finally, we will collect fishes from the St. Croix River at Interstate State Park, Minnesota during fall 2002 and spring 2003 to identify fishes naturally infested with winged mapleleaf glochidia.

ACKNOWLEDGMENTS

Several people and organizations contributed to this effort. Tessa Diedrich, Nick Dillon, Vikash Kanodia, Marissa McGill, Carrie Nelson, Daniel Schriever, Whitney Taylor were instrumental in completing the field and laboratory portions of this project. Members of the Winged Mapleleaf Recovery Team recommended and strengthened the design of the research project. Roger Gordon and Jeff Lockington, Genoa National Fish Hatchery, provided the largemouth bass for the study. We thank Dan Kelner and Mike Davis for assisting with collection of gravid mussels. Mike Davis, Minnesota Department of Natural Resources, provided the fish cage and recommended the location for holding fish in the St. Croix River. We also thank Pam Thiel, Hattie Curtner, Jo Schroeder, and Bruce Vondracek for administering the project. Bruce Vondracek and Dave Andersen made several suggestions that improved this report. This project was made possible through funding from the U.S. Geological Survey and the University of Minnesota Undergraduate Research Opportunities Program. Support for A. R. Kapuscinski came from the Department of Fisheries, Wildlife, and Conservation Biology and from the Minnesota Sea Grant College Program, at the University of Minnesota.

LITERATURE CITED

Coker, R. E., A. F. Shira, H. W. Clark, and A. D. Howard.  1921.  Natural history and propagation of fresh-water mussels.  Bulletin of the Bureau of Fisheries 893: 76-181.

Hove, M. C., J. L. Weiss, J. R. Berkner, and A. R. Kapuscinski.  1999.  Juvenile Amblemines appear to excyst more rapidly in warm water.  Triannual Unionid Report 17: 9.

Neves, R. J., L. R. Weaver, and A. V. Zale.  1985.  An evaluation of host fish suitability for glochidia of Villosa vanuxemi and V. nebulosa (Pelecypoda: Unionidae).  American Midland Naturalist 113(1): 13-19.

Robins, C. R., R. M. Baily, C. E. Bond, J. R. Brooker, E. A. Lachner, R. N. Lea, and W. B. Scott.  1991.  A list of common and scientific names of fishes from the United States and Canada.  American Fisheries Society Special Publication 20, Bethesda, Maryland.  183 pp.

Surber, T. 1913. Notes on the natural hosts of fresh-water mussels. U. S. Bureau, Fisheries 32: 110-116. Separately issued as Bureau of Fisheries Document No. 778.

Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks, 2nd edition. American Fisheries Society, Special Publication 26, Bethesda, Maryland. 509 pp.

Waller, D. L., L. E. Holland-Bartels. 1988. Fish hosts for glochidia of the endangered freshwater mussel Lampsilis higginsi Lea (Bivalvia: Unionidae). Malacological Review 21: 119-122.

Watters, G. T.  1994.  An annotated bibliography of the reproduction and propagation of the unionoidea (primarily of North America).  Ohio Biological Survey Miscellaneous Contributions, Number 1.  vi + 158 pp.

Wilson, C. B.  1914.  Copepod parasites of fresh-water fishes and their economic relations to mussel glochidia.  Bulletin of the Bureau of Fisheries 34: 331-379.
 

Table 1. Fishes that did not facilitate Higgins eye metamorphosis or that died before the end of the trial.
 

Species	Number infested	Number of survivors	Attachment period (days)
Acipenseridae
lake sturgeon	3	3	1-6
Lepisosteidae
longnose gar	11	11	1-6
Cyprinidae
common shiner	1	1	1-6
creek chub	1	1	1-6
hornyhead chub	1	1	1-6
spotfin shiner	7	7	1-6
Catostomidae
northern hognose sucker	2	2	1-6
Ictaluridae
channel catfish	20	20	1-6
flathead catfish	2	1	6-34
tadpole madtom	4	4	1-6
yellow bullhead	4	4	1-6
Percopsidae
trout-perch	1	1	1-6
Gadidae
burbot	2	2	1-6
Percichthyidae
white bass	1	0	*
Centrarchidae
orange-spotted sunfish	5	5	6-34
pumpkinseed	1	1	34-43
rock bass	5	5	43-56
Percidae
blackside darter	8	8	1-6

* - Incomplete trial, fish died prior to the end of the trial.
 
 

Table 2. Fishes that facilitated Higgins eye glochidia metamorphosis.
 
 

Species	Number infested	Number of survivors	Excystment period	No. juveniles recovered
Centrarchidae
black crappie	9	9	102-126 d	4
Percidae
sauger*	2	0	35-63 d	28

* - Incomplete trial, fish died prior to the end of the trial.
 
 
 

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