Indigenous unionid clam refugia from zebra mussels in Michigan inland lakes.
Abstract: Zebra mussel presence and lake water calcium concentrations were compared to determine if a calcium concentration threshold exists which might preclude colonization of zebra mussels in Michigan inland lakes. The shallow littoral zones of nine northern Michigan inland lakes with calcium concentrations near 28.3 mg/L and considered to have had potential zebra mussel introductions through recreational boating were studied. A survey of native unionids was carried out in the lakes for the purpose of establishing a species inventory list for each lake. Zebra mussel densities were determined for lakes where zebra mussels were detected. Water samples were collected and calcium concentrations determined for each study lake. In five softwater lakes (lakes with calcium concentrations <28.3 mg/L), zebra mussels were not found. Zebra mussels had colonized three of four lakes where calcium concentrations were >28.3 mg/L. Five unionid species were found in seven of the nine lakes surveyed. Unionids were present in four of five lakes where calcium concentrations <28.3 mg/L and where zebra mussels were not detected suggesting a possible unionid refuge from zebra mussel induced mortality and/or extirpation in softwater lakes.
Article Type: Report
Subject: Calcium, Dietary (Distribution)
Zebra mussels (Distribution)
Lakes (Composition)
Authors: Hollandsworth, Donna
Lowe, Rex
Badra, Peter
Pub Date: 10/01/2011
Publication: Name: The American Midland Naturalist Publisher: University of Notre Dame, Department of Biological Sciences Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Earth sciences Copyright: COPYRIGHT 2011 University of Notre Dame, Department of Biological Sciences ISSN: 0003-0031
Issue: Date: Oct, 2011 Source Volume: 166 Source Issue: 2
Topic: Event Code: 690 Goods & services distribution Advertising Code: 59 Channels of Distribution Computer Subject: Company distribution practices
Product: Product Code: 2834791 Calcium Supplements; 2819821 Calcium NAICS Code: 325412 Pharmaceutical Preparation Manufacturing; 325188 All Other Basic Inorganic Chemical Manufacturing SIC Code: 2834 Pharmaceutical preparations
Geographic: Geographic Scope: United States Geographic Code: 1USA United States
Accession Number: 270149505
Full Text: INTRODUCTION

Zebra mussel (Dreissena polymorpha Pallas) invasion into the Great Lakes region has resulted in high mortality or extirpation of native unionids from all or parts of Lake Erie, Lake St. Clair (Schloesser et al., 1998) and the Detroit River (Schloesser et al., 1998). Extirpation of native unionids has occurred primarily in open water, but small remnant populations occur in the Lake St. Clair delta (Zanatta et al., 2002) and three areas of Lake Erie: Presque Isle Bay, Erie, PA (Schloesser and Masteller, 1999), Metzger Marsh near Toledo, OH (Nichols and Amberg, 1999) and near the mouth of the Raisin River, Monroe, MI (Schloesser et al., 1997). In contrast, little is known about impacts of zebra mussels on native mussels in Michigan inland lakes although zebra mussels occur in at least 260 Michigan lakes to date (Michigan Sea Grant, 2008; United States Geological Survey Nonindigenous Aquatic Species Website, 2008).

Studies of zebra mussel habitat requirements have found that pH, temperature, salinity, substrate, nutrients and calcium may limit zebra mussel colonization success (Strayer, 1991; Ramcharan et al., 1992; Stanczykowska and Lewandowski, 1993; Mellina and Rasmussen, 1994; and Hincks and Mackie, 1997). The establishment of zebra mussels and their impact on unionids in European lakes has been well documented. In European lakes, calcium concentrations >28.3 mg/L were required for survival of zebra mussel veligers and to support zebra mussel colonization (Ramcharan et al., 1992). Results of a risk assessment for zebra mussel invasion into 3000 North American streams and rivers showed that most successful zebra mussel colonizations were in regions where calcium concentrations were >28.3 mg/L or where surface water drained high calcium areas into regions where concentrations were <28.3 mg/L (Whittier et al., 2008). However, calcium requirements for successful zebra mussel reproduction and colonization have been reported as low as 20 mg/L in laboratory study (Cohen and Weinstein, 2001).

In contrast, calcium requirements of unionids vary among species and some inhabit softwater lakes (i.e., lakes with calcium concentrations [less than or equal to] 28.3 mg/L) (Boycott, 1936; Mackie and Flippance, 1983). In a study of six low-alkalinity lakes in Ontario, Pyganodon (= Anodonta) grandis and Elliptio complanata were found in Blue Chalk Lake and Harp Lake with calcium concentrations of 2.99 mg/L and 3.15 mg/L respectively (Rooke and Mackie, 1984). A large population of P. grandis has also been reported in Shell Lake, a small arctic lake, with a calcium concentration of 10 mg/L (Green, 1980). Elliptio complanata is known to occur in calcium-poor waters (Hinch et al., 1988) and is found in Mirror Lake, New Hampshire with calcium concentrations of 2-3 mg/L (Strayer et al., 1981).

In this study, Michigan softwater inland lakes were surveyed for native unionids to determine which species occur naturally in these systems and whether these lakes have been colonized by zebra mussels. We also wanted to determine whether a previously determined calcium concentration threshold (i.e., 28.3 mg/L) constrains zebra mussel colonization in Michigan softwater lakes. According to the Michigan Department of Environmental Quality (MDEQ) Surface Water Information Management System (MiSWIMS, 2007) there are Michigan inland lakes that meet the criterion of <28.3 mg/L calcium concentration. We, therefore, hypothesized that while these softwater lakes likely support native unionids populations, they lack sufficient calcium concentrations to support zebra mussel colonization and thus lack resident adult dreissenids.

METHODS

Study lakes.--The nine northern Michigan lakes included in this study have calcium concentration near the target threshold of 28.3 mg/L (MiSWIMS, 2007) and have a historical record of resident native unionids (University of Michigan Museum of Zoology Mollusk Database Website, 2007; D. Hollandsworth, pers. obs.) (Table 1). With the exceptions of Lake Independence and Larks Lake, lakes in this study were chosen because they were judged to experience heavy boating use with multiple public boat accesses and campgrounds and/or parks (Michigan Recreational Boating Information System, 2007; Long Lake Township, Traverse City, Michigan, 2010). All lakes but Lake Independence are in close proximity to lakes and streams that have established zebra mussel populations that could serve as sources of zebra mussels colonists (Michigan Sea Grant, 2007; United States Geological Survey Nonindigenous Aquatic Species Website, 2007). Because zebra mussels can be transported overland from isolated, infested lakes and introduced to non-infested lakes through transient recreational boating activities (Johnson et al., 2001), we considered all of the study lakes to be highly susceptible to zebra mussel introductions.

Unionid surveys.--Native unionids were surveyed in the study lakes to establish a species inventory for each lake. Areas of typical unionid habitat in the littoral zone of each study lake were searched by kayak until unionid shells or trails were visually detected. Upon identifying potentially occupied habitat, three 1-m wide transects were established perpendicular to the shoreline in a shore to lakeward direction with the transect length ranging from 10-20 m as a function of the extent of the visible littoral zone and water depth of each lake. Visual searches were performed along each transect at a depth of 1-2 m where snorkeling could be performed and visibility was sufficient. Because unionid distribution data are sparse or lacking for northern Michigan lakes, this initial survey was used to determine unionid locations in these lakes. Each detected unionid was identified on site and/or photographed for the purpose of species identification. Unionids were then returned into the habitat where they had been collected and placed in the substrate anterior end down. In cases where a sampled unionid was biofouled, zebra mussels were removed and destroyed. Unionids were identified using Cummings and Mayer (1992), Goodrich (1932), Heard and Burch (1966), Thorp and Covich (2001) and by comparisons with taxonomic reference collections (Detroit Edison Company, Detroit, MI).

Zebra mussel surveys.--Areas of substrate suitable for zebra mussel attachment were searched for evidence of zebra mussel colonization. Substrate types in these surveys included cobble, large woody debris, living snails and unionids, spent snails and unionid shells, boat hoists, dock pilings and aquatic macrophytes in water depths <1 m. Zebra mussels were collected through searches within five 0.25 [m.sup.2] quadrats that included cobble and woody debris in the shallow littoral zone.

Calcium concentration measures.--Water samples were collected from each lake to determine calcium concentrations (mg/L). Calcium concentration varies minimally with lake depth or seasonally in softwater lakes (Wetzel, 1975), so two 250 mL samples were collected at a single site in each lake at a depth of 0.25 m below the surface in water >1 m deep. Water samples were collected directly using clean, acid-washed polyethylene bottles that had been previously rinsed in lake water at the site. Following collection, water samples were treated with concentrated HN[O.sub.3] to a pH [less than or equal to] 2. Samples were stored at 4 C and transported to the laboratory. Calcium concentrations were determined using atomic absorption spectrometry with a Varian Spectra AA-600 Flame instrument (accuracy = [+ or -] 4% of actual values) following methodology provided in Standard Methods for the Examination of Water and Wastewater (1998).

Data analysis.--Student t-test with a significance level of alpha = 0.05 was used to determine if there was a difference in mean calcium concentrations of lakes where zebra mussels were absent vs. lakes where zebra mussels were present using Minitab 14.

RESULTS

Unionid surveys.--A total of 143 individual unionids representing five species were found in seven of the nine lakes surveyed (Table 2). Lampsilis siliquoidea was found in five of the seven lakes and Pyganodon grandis occurred in six of the seven lakes surveyed. Zebra mussels and unionids were found coexisting in Houghton Lake, and three of the eight unionids collected were biofouled with zebra mussels. Of the 143 unionid individuals collected, 55.5% were from Lake Independence in Michigan's Upper Peninsula.

Zebra mussel survey.--Zebra mussels were found in three of the nine lakes surveyed, including Houghton, St. Helen and Douglas Lakes; however, this survey was limited to the shallow littoral zone of the study lakes. Zebra mussel densities in the visible littoral zone were 50.4 individuals/[m.sup.2] in Lake St. Helen and 8.8 individuals/[m.sup.2] in Houghton Lake. No zebra mussels were detected on sandy substrate in the sampling area of Douglas Lake; however, zebra mussels were covering unionids, cobble and woody debris during the summer of 2006 (D. Hollandsworth, pers. obs.) (Fig. 1). Zebra mussels were found also on live or spent snails and/or unionids in Houghton Lake, and on live or spent snails and unionids in Douglas Lake. Zebra mussels were found on woody debris and cobble in Lake St. Helen.

Calcium concentrations.--Total calcium concentrations in the nine study lakes ranged from 17-34 mg/L (Fig. 2). The mean calcium concentration of lakes with zebra mussels present (32 mg/L) differed significantly from the mean calcium concentration of lakes where zebra mussels were absent (24 mg/L) (P = 0.008, df = 6) (Fig. 3).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

DISCUSSION

Our results suggest that there is a significant difference in mean total calcium concentrations in Michigan lakes with and without zebra mussel colonization. Specifically, mean calcium concentration for lakes with zebra mussels present was 32 mg/L and for lakes without zebra mussels was 24 mg/L. Calcium concentrations presented here for our study lakes were determined based on a single sampling event, although calcium content is reported to vary minimally with depth and seasonality in softwater lakes (Wetzel, 1975). In laboratory studies, minimum calcium requirements for zebra mussel reproductive and colonization success has been reported as 20 mg/L (Cohen and Weinstein, 9001). However, zebra mussels were not found in lakes with calcium concentrations [less than or equal to] 28.3 mg/L in a study of European lakes (Ramcharan et al., 1992). In this study, zebra mussels were absent from six lakes, and five of those lakes had calcium concentrations [less than or equal to] 26 mg/L. Our results therefore agree with those observed in European lakes and suggest that there is a calcium concentration threshold for zebra mussel colonization success between 26 and 32 mg/L.

Zebra mussels piggyback on macrophytes entangled on the trailers and motors of boats, and boating is considered a primary vector of zebra mussels transported overland to isolated inland lakes not colonized by zebra mussels (Johnson et al., 2001). All study lakes have multiple public boat accesses and/or campgrounds/parks, lakes and/or streams nearby that are colonized by zebra mussels and with the exceptions of Lake Independence and Larks Lake are judged to be used heavily for recreation. Lake Mitchell (calcium concentration = 20 mg/L) is frequently fished by anglers who also launch their fishing boats <35 mi away in the Manistee River at Tippy Dam. Tippy Dam has been heavily infested with zebra mussels since 1997 and could be a source of colonists to Lake Mitchell; however, Lake Mitchell has remained zebra mussel free to date (Larry Solce, Unit Supervisor, Mitchell State Park, Cadillac, MI, pets. comm., 2008; United States Geological Survey Nonindigenous Aquatic Species Website, 2008). In Long Lake (calcium concentration = 26 mg/L) Myriophyllum spicatum, Eurasian water-milfoil, another invasive species that is transported between water bodies on boat trailers and motors (Johnson et al., 2001), has been established since 2006 (Michigan Sea Grant, 2009). It is likely that zebra mussels have been introduced into Long Lake as well although there is no evidence of successful colonization. Zebra mussels are absent from Larks Lake (calcium concentration = 31 mg/L); however, it is not a heavily-used lake and may not have received potential colonists.

[FIGURE 3 OMITTED]

Zebra mussel densities were high in Douglas Lake, low in Houghton Lake and Lake St. Helen Lake, and absent altogether in the remaining six lakes surveyed. Zebra mussel establishment was reported for Houghton Lake, Lake St. Helen and Douglas Lake in 1993, 1994 and 2001, respectively (USGS Nonindigenous Aquatic Species Website, 2008; University of Michigan Biological Station Website, 2008). Houghton Lake, Lake St. Helen and Douglas Lake experienced population explosions in 2006, and zebra mussel populations have declined since their explosion in Houghton Lake and Lake St. Helen especially where water depths are shallower than 1 m (Pam Tyning, Progressive AE, Grand Rapids, MI, pers. comm.; Pete Rieli, Lake St. Helen Lake Association, St. Helen, MI; D. pers. obs.). Zebra mussel density in a dozen European lakes has fluctuated over a 30 y period, and population declines after population explosions with large zebra mussel individuals has occurred (Stanczykowska and Lewandowski, 1993). Zebra mussel density in Houghton Lake and Lake St. Helen may experience similar fluctuations and explain present low densities. Pam Tyning reported zebra mussel presence on macrophytes at depths of 2-3 m in Houghton Lake (Progressive AE). Regardless, zebra mussels have successfully colonized these lakes and zebra mussel invasion has resulted in unionid mortality in Douglas Lake (Rex Low, pers. comm.; D. Hollandsworth, pers. obs.). The presence or establishment of zebra mussels has not been documented for the remaining six lakes surveyed (Michigan Sea Grant, 2008; United States Geological Survey Nonindigenous Aquatic Species Website, 2008). Although this survey did not detect zebra mussels in these lakes, this survey was limited to the shallow littoral zone, and maximum zebra mussel densities are reported to occur at depths >2-4 m (Stanczykowska and Lewandowski, 1993),

Live Anodonta ferussacianus, Elliptio complanata, Lampsilis siliquoidea, Ligumia nasuta and Pyganodon grandis were found in six of the nine lakes studied, and five of the six lakes where unionids were present have calcium concentrations below the reported zebra mussel colonization calcium concentration requirement (Ramcharan et al., 1992). Additional unionids and/or unionid species may be present at depths >2-m; however, this study would not have detected such individuals as it was limited to the shallow littoral zone. The results of this study suggest that lakes with calcium concentrations [less than or equal to] 26 mg/L may serve as refugia from zebra mussel induced mortality and/or extirpation for A. ferussacianus, E. complanata, L. siliquoidea, L. nasuta and P. grandis. However, Michigan has many hardwater lakes and few calcium poor lakes that have been identified. Thus, the refuge potential of calcium poor lakes for these species is limited in Michigan.

Lakes in Michigan's western Upper Peninsula (UP) region are low in calcium because of underlying igneous bedrock (Dorr and Eschman, 1970; Rapp et al., 1987), although calcium concentrations of lakes in the remainder of the state are generally high because they are situated in lacustrine deposits or limestone that contain calcium carbonate (Dorr and Eschman, 1970). In a study of 12 lakes along Lake Superior, three lakes found to have lower buffering capacities were situated in sandy lacustrine deposits while nine lakes having higher buffering capacities were situated in lacustrine deposits with a clay component (Rapp et al., 1987). Softwater lakes in the Lower Peninsula (LP) may be calcium poor because they are shallow and/or seepage lakes and situated in glacial sand ranging from 201-1100 ft thick (Akers, 1938; Western Michigan University, 1981). Lake water calcium concentration in Houghton Lake may be greater than that of other lakes in this study because a lacustrine clay, one derived from limestone, underlies the lake's margins just below a layer of sand a few inches thick (Dennis Albert, pers. comm.).

Our study results suggest that calcium poor lakes may serve as important refuges for native unionids in a landscape where zebra mussels are rapidly spreading among lakes as a result of boating activity. While the natural calcium concentration of these lakes appears to preclude colonization by zebra mussels, measures should still be taken to limit the introduction of zebra mussels to these lakes in the future. Additional research is also needed to identify other calcium poor lakes that could provide temporary or permanent refuges for threatened mussels with calcium requirements below 28 mg/L. Ligumia nasuta is listed as endangered by the Michigan Department of Natural Resources and the Michigan Natural Features Inventory (2010); however, only one individual was found in our study in Houghton Lake (calcium concentration = 34 mg/L). Although other unionid species identified in our study are not threatened with extinction they play vital roles in lake ecosystems. For example, unionid shells provide habitat for epizoic algae that have no other substrate than mollusk shells (Francoeur, et al., 2002). The loss of these species may have important ramifications for other members of their community, and it is important that we conserve these unionids.

Acknowledgments.---Thank you to Sheryn Lowe, Dennis Albert, Ted Bambakidis, Michael Grant, Pat Kocioleck and William Kovalak for technical support, and to Ali Bazzi and Linda Grimm, University Michigan Dearborn, for laboratory space, equipment and instrument use as well as technical support. Thank you to Phil Meyer and Alison, Shane, Barry and Linda Lishawa, Mary Ellen Williams, and Larry Solce for assistance in sampling. Thank you to Knute Nadelhoffer, Karie Slavik, Peg Meade, Mary Anne Carroll, David Karowe, Lisa Readmond and Pam Ballard for the opportunity to do this work and for your support. Thank you to my family and friends for your support and assistance. This project was funded by University of Michigan Biological Station and National Science Foundation Research for Teachers.

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SUBMITTED 21 SEPTEMBER 2009

ACCEPTED 23 MAY 2011

DONNA HOLLANDSWORTH

University of Michigan Biological Station, 2541 Chemistry Building, 930 North University Avenue, Ann Arbor, Michigan 48109

REX LOWE

University of Michigan Biological Station, 2541 Chemistry Building, 930 North University Avenue, Ann Arbor, Michigan 48109 and Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403

AND

PETER BADRA

Natural Features Inventory, 530 West Allegan Street, Lansing, Michigan 48933
TABLE 1.--Latitude and longitude, surface area, glacial drift
thickness, maximum depth, inlets and outlets for Lower Peninsula
lakes

                                                  Surface
                                                   area
       Lake name            Latitude/longitude    (acres)

Mitchell (Wexford Co.)     44.259726/-85.482504     2580
Otsego (Otsego Co.)        44.930297/-84.691848     2012
Round (losco Co.)           44.34028/-83.85695        91.5
Long (Grand Traverse Co.)  44.724727/-85.756115     2966
Douglas (Cheboygan Co.)    45.570353/-84.713684     3395
Larks (Emmet Co.)          45.60417/-84.925837       591
Houghton (Roscommon Co.)   44.307504/-84.713337   20,044
Lake St. Helen
  (Roscommon Co.)          44.359726/-84.478059     2390

                           Glacial drift                 Parking spaces
                               drift         Maximum       at public
       Lake name           thickness (ft)   depth (ft)      launches

Mitchell (Wexford Co.)         801-1000         20            125
Otsego (Otsego Co.)            801-1000         23             47
Round (losco Co.)              201-400          19             10
Long (Grand Traverse Co.)      401-600          80             12
Douglas (Cheboygan Co.)        201-400          89              5
Larks (Emmet Co.)              201-400           9              0
Houghton (Roscommon Co.)       401-600          21            200
Lake St. Helen
  (Roscommon Co.)              401-600          27             90

* This boat launch site is located at a picnic site in a Center
Township, Emmet Co. park. The park does not have designated car
or car with boat trailer parking

TABLE 2.--Species lists of unionids mollusks in Michigan inland lakes
surveyed

Unionid species   Anodontoides     Elliptio    Lampsilis    Ligumia
and lake names    ferussacianus   complanata   siliquoidea   nasuta

Douglas                                             *
Houghton                                                        *
Independence                          *             *
Larks                                               *
Long                    *
Mitchell                                            *
Round                                               *

Unionid species   Pyganodon
and lake names      grandis

Douglas                *
Houghton
Independence           *
Larks                  *
Long                   *
Mitchell               *
Round                  *
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