Harvesting an Invasive Bivalve in a Large Natural Lake: Species Recovery and Impacts on Native Benthic Macroinvertebrate Community Structure in Lake Tahoe, USA

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AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) Published online 6 June 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/aqc.2251

Harvesting an invasive bivalve in a large natural lake: species recovery and impacts on native benthic macroinvertebrate community structure in Lake Tahoe, USA

MARION E. WITTMANNa,*, SUDEEP CHANDRAb, JOHN E. REUTERc, ANDREA CAIRESb, S. GEOFFREY SCHLADOWa and MARIANNE DENTONb aTahoe Environmental Research Center, University of California Davis, Incline Village, NV 89451, USA bDepartment of Natural Resources and Environmental Science, University of Nevada, Reno, NV 89512, USA cDepartment of Environmental Science and Policy and Tahoe Environmental Research Center, University of California Davis, CA 95616, USA

ABSTRACT 1. The increasing dispersal and establishment of aquatic invasive species in natural freshwater ecosystems has led to efforts to remove non-native taxa and/or restore native species. An invasive bivalve, Asian clam (Corbicula fluminea), recently (2002) became established in a large, natural subalpine lake (Lake Tahoe, USA). In 2009, experimental efforts were undertaken to harvest C. fluminea from Lake Tahoe sediments using a manually operated suction dredge apparatus. 2. Treatment and control plots were monitored for a 450 day period after dredging to observe target species (C. fluminea) and non-target macroinvertebrate recovery rates. A paired Before-After-Control Impact analysis was used to assess the short- and long-term impacts of suction dredging. 3. Physical harvest resulted in short-term reductions of C. fluminea (1500 individuals m-2 before treatment to 60 individuals m-2 14 days after treatment) with significant disruption to benthic macroinvertebrate community structure. The impact to the target invasive species (C. fluminea) was present 450 days after treatment and community diversity (as represented by Simpson diversity index) did not recover after 1 year (365 days) in dredged sites. Certain non-target macroinvertebrate taxa (Chironomidae and native clam (Pisidium spp.)) increased in suction dredge plots to levels greater than before treatment or in control plot conditions at the end of the study period. 4. Harvesting C. fluminea significantly reduced population densities for a period of 450 days after the removal. Recolonization rates of C. fluminea and non-target species over multiple reproductive seasons will determine the feasibility for this method as a long-term control strategy. Copyright # 2012 John Wiley & Sons, Ltd.

Received 04 December 2011; Revised 20 February 2012; Accepted 01 April 2012

KEY WORDS: lake; littoral; biological control; recolonization; monitoring; benthos; invertebrates; alien species; dredging

INTRODUCTION present costly challenges to natural resource managers. While prevention of invasive species The establishment of aquatic invasive species introductions is considered to be the most effective continues to affect freshwater ecosystems and means to reduce invasive species impacts (Leung

*Correspondence to: Marion E. Wittmann, Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556. E-mail: [email protected]

Copyright # 2012 John Wiley & Sons, Ltd. HARVESTING INVASIVE CLAMS: IMPACT TO THE MACROINVERTEBRATE COMMUNITY 589 et al., 2002; Finnoff et al., 2007; Keller et al., 2008), it Corbicula fluminea is a sediment-dwelling bivalve, is a complex and resource-intensive endeavour that is introduced and invasive to North America and often complicated by undetected propagules, native to temperate and tropical regions of Asia, illegal releases, or accidental introductions that can Africa, and Australia (Counts, 1986). The impacts confound prevention goals. As a result, natural of C. fluminea both on natural and on man-made resource managers are often tasked with controlling systems are known (Isom, 1986) and have been or removing an introduced species after it has observed to affect native invertebrate communities become established. (Karatayev et al., 2003), phytoplankton assemblages Harvesting invasive species has promise as a (Lopez et al., 2006), benthic habitats (Hakenkamp non-chemical means to reduce negative economic and Palmer, 1999) and nutrient cycling (Lauritsen and ecological impacts and increase water quality and Mozley, 1989). This species is considered an and commercial and recreational use of ecosystems economic nuisance because of its ability to biofoul (Simberloff, 1999; Mack et al., 2000). Efforts to water intakes (Eng, 1979), particularly in nuclear physically remove invasive species have been and hydropower production (Isom et al., 1986; attempted for a number of taxa including rusty Williams and McMahon, 1986) where damage crayfish (Hein et al., 2007), dreissenid mussels caused by C. fluminea has been estimated at $1 (Wimbush et al., 2009), aquatic macrophytes billion annually (Pimentel, 2005). fl fi (Tobiessen et al., 1992; Eichler et al., 1993), and Established populations of C. uminea were rst smallmouth bass (Weidel et al., 2007) with varied observed in Lake Tahoe, CA-NV in 2002 and in -2 levels of success. Unintended effects of invasive 2008 high density populations (up to 6000 clams m ) species removal include shifts to native community were observed in nearshore habitats by scientists, structure (Rinella et al., 2009) or increases in natural resource managers, and community population growth rates of the management stakeholders who responded by creating a target (Zipkin et al., 2009). Although rare, science-based rapid response management invasive species management goals have been programme. To explore the feasibility of reducing fl accomplished through long-term programmes of C. uminea abundance with physical harvesting, physical removal (Wimbush et al., 2009) or a dredging experiment was carried out on C. fluminea combining physical removal with other treatment sub-populations of . Benthic substrate removal through diver assisted suction dredging methods (Madsen, 1997). was applied to treatment plots with established Many methods exist to remove species from populations of C. fluminea and monitored for aquatic systems such as hydraulic dredging, hand 450 days. The objectives of this study were to removal, trapping, or electroshocking and each assess the recolonization rates of C. fluminea and has impacts on the surrounding environments co-occurring benthic macroinvertebrate taxa after and biological communities. Dredging or suction suction removal to understand community recovery. removal is a widely used method of species extraction from sediments, and has been used for the removal both of desirable (i.e. commercial) speciessuchastherazorclam(Ensis spp.) and METHODS nuisance benthic macrophytes (Nichols and Cottam, 1972; Tobiessen et al., 1992; Eichler Study site et al., 1993; Hauton et al., 2007). In general, Lake Tahoe (Figure 1) is a large, deep (surface area: dredging in aquatic environments is considered a 495 km2, maximum depth: 501 m) oligotrophic lake major disturbance to benthic systems as it located at a subalpine elevation of 1898 m in the reduces benthic macroinvertebrate populations Sierra Nevada Mountain Range. The Tahoe (Kenny and Rees 1996; Pranovi et al., 1998; Basin’s largely granitic geology, the lake’s large Lewis et al., 2001) and disrupts the population volume (150 km3) and relatively small drainage structure of native communities (Grassle and (800 km2) basin explain its low nutrient Sanders 1973; McCall, 1977; Dernie et al., 2003). concentrations and primary productivity rates These types of disturbances have also been (Goldman, 1988). Annual water temperature observed with dredging activities specifically ranges from 5 to 28 C in the littoral zone, with targeted towards biotic removal (Tuck et al., upper and lower temperature extremes occurring 2000; Morello et al., 2005). in marina locations. The lake is oligomictic,

Copyright # 2012 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) 590 M. E. WITTMANN ET AL.

net power output, 196 cm3 displacement, 12.4 Nm @2500 rpm net torque) was used to remove treatment plot sediments to a depth of 13 cm at Marla Bay (9.5 m3 removed) and a depth of 8 cm (depth of sediments above a clay hard pan boundary) at Lakeside (8.5 m3 removed). To collect benthic macroinvertebrates, sediment grab samples (N = 3) were collected in each of the treatment and control plots using a petite Ponar grab sampler (2.4 L volume, 231 cm2 sample area, Wildlife Supply Company, Yulee, FL, USA) at 7 days before and 14, 90, 240, 365, and 450 days after dredging. Upon collection all samples were screened (500 mm mesh) and the retained sediment was then placed in a super-saturated sugar solution to float invertebrates (Anderson, 1959). Samples were then picked manually to remove all macroinvertebrates. All organisms were preserved fi Figure 1. Location of C. fluminea treatment plots in Lake Tahoe, CA-NV. in 70% ethanol until identi cation (Merritt and Two treatment plots (surface area: 36 m2)atMarlaBay,NV(A)andthree Cummins, 1996; Thorp and Covich, 2001) Average at Lakeside, CA (B) were dredged to remove C. fluminea containing sediments in April 2009. Both plot locations were at 5 m water depth particle size distribution of Marla Bay and in the south-eastern portion of Lake Tahoe where C. fluminea populations Lakeside sediment types was determined using a have been established since 2002. wet sieve method (Gordon et al., 1992) and described using a Wentworth scale. Temperature samples were collected using in situ loggers (4 h mixing completely only in years of intense spring W sampling interval) (iButton #DS1922L, 0.5 C storms (Goldman et al., 1989; Wetzel, 2001). The accuracy, Embedded Data Systems, Lawrenceburg, photic zone extends to an approximate depth of KY, USA). 100 m, and the entire water column is oxygenated Total macroinvertebrate abundance, abundance throughout the year (Coats et al., 2006). Lake Tahoe by taxonomic grouping and Simpson Diversity supports an assemblage of benthic invertebrates Index (Simpson, 1949) was calculated for each dominated by oligochaetes, amphipods, ostracods, sample. Abundance was calculated by dividing the and dipteran larvae (Frantz and Cordone, 1996). number of species individuals per sample by the volume of the petite ponar grab sampler. Impact of sediment removal on the invertebrate Methodology community was assessed using Paired Before-After Control-Impact (BACIP) analysis (Stewart-Oaten Diver-assisted suction dredging was applied in 5 m et al., 1986; Underwood, 1991, 1994; Guerra- water depth at two sites, Marla Bay and Lakeside, García et al., 2003). Effect size was calculated by which both have established C. fluminea forming differences between site-specificpairs: populations – with Marla Bay representing a high density C. fluminea population (average abundance ¼ ¼ m þ ’ þ e Dik XiCj XiIk i ik (1) ~2000 m-2) and Lakeside representing a region with lower densities (average abundance ~500 m-2). At where X represents taxonomic abundance or each site, three suction removal plots and one diversity index values, m is the mean difference 2 control plot (surface area: 36 m ) were delineated between control and impact, ’i the change in on the lake bottom to guide the dredging diver and difference from before to after, and eik the error to demarcate sampling areas for monitoring associated with the differences (Stewart-Oaten purposes (Figure 1). Owing to field resource et al., 1986). Differences (Dik), were then compared limitations, only two plots were suctioned at Marla for before and after periods using a two-sample Bay and three at Lakeside. In March 2009 a t-test. Both sites (Marla Bay and Lakeside) were suction dredge apparatus (4 cm diameter hose, combined to calculate the overall mean difference engine specifications: 5.5 HP (4.1 kW) @3600 rpm in effect size while maintaining site-specificpairing

Copyright # 2012 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) HARVESTING INVASIVE CLAMS: IMPACT TO THE MACROINVERTEBRATE COMMUNITY 591 between control and treatment plots. A significant (78 19 m-2) comprised 1% of the population at change in the mean difference (m) after the onset of Marla Bay compared with more than 13% the perturbation was considered strong evidence of (536 58 m-2) of the population at Lakeside. The an environmental impact. All statistical analysis was dominant groups at Lakeside were Amphipoda carried out using program R 2.12.1. (1354 188 m-2; 34%) and Chironomidae (559 74 m-2; 14%) (Figure 2). Sediment substrate at the Lakeside site was RESULTS characterized as coarse to medium sand with a Before treatment, average total macroinvertebrate median sediment particle size, Me = 0.375 mm and abundance (P < 0.001, t-test, n = 12, df = 22) was very coarse sand at Marla Bay, Me = 1.180 mm. lower at Lakeside (mean abundance standard Water temperature at the sediment–water interface error: 4014 280 m-2) compared with Marla Bay ranged from 5.6 to 17.9 C during the course of (6995 684 m-2). Common taxonomic groupings the 450 day monitoring period. were observed at both sites: Amphipoda (Hyalella Immediate (14 days after treatment) impacts of sp.), Chironomidae, Oligochaeta, Gastropoda suction removal were similar among most (Planorbidae and Physidae), and non-native and taxonomic groupings (Table 1, Figure 3). There native bivalves, Corbiculidae (C. fluminea) and was no significant difference in taxonomic Sphaeriidae (Pisidium casertanum and compressum; abundances and diversity indices between control hereafter referred to as Pisidium spp.), respectively. and treatment plots before suction removal Other less common taxonomic groups observed at (Table 1). At 14 days (April 09) after suction both sites were Trichoptera (Leptoceridae, removal treatment, average total invertebrate Lepidostomatidae), Ceratopogonidae (Palpomyia abundance (combined between two sites) was 410 sp.), Ostracoda, Copepoda, Hydracarinidae, (140 S.E.) individuals m-2; a 93% reduction Cladocera, Hirudinea and Nematoda, and were compared with pre-treatment condition (5892 594). not included in the analysis because of rare The initial impact on C. fluminea was significant fl occurrence. C. uminea was dominant in Marla with a 96% reduction from 1484 (472) to 59 (34) Bay, with average relative abundance of 35% individuals m-2 in the treatment site. Amphipoda -2 (2450 343 m ), compared with Lakeside where also showed a dramatic reduction in abundance, fl C. uminea abundances represented 8% decreasing 96% from 1022 (143) in the -2 (485 95 m ) of the community (Figure 2). pretreatment condition to 44 (23) individuals m-2 Chironomids were the other dominant taxonomic at 14 days. While average abundances of both -2 group at Marla Bay (2527 145 m , 31%), and chironomids and gastropods on day 14 in treatment -2 Amphipoda (669 76 m ; 10%), Oligochaeta plots did significantly decline after dredging -2 -2 (676 126 m ; 10%), and Gastropoda (779 214 m ; (Figure 3), BACIP results showed that there was no 11%) represented secondary groups. Pisidium spp. significant impact on mean effect size (Table 1). Simpson diversity index values were significantly affected immediately after treatment, with mean effect size increasing more than two orders of magnitude compared with pre-treatment and control conditions (Table 1). Mean effect size varied during the monitoring period with differences observed among the taxonomic groups. Abundance of the management target C. fluminea in dredged plots was significantly less than in control plots at 450 days (July 2010) after treatment (Figure 3). However, at 365 days (April 2010) after treatment BACIP results showed that effect size in dredged plots was not significantly different from control or before Figure 2. Proportion of macroinvertebrate taxa at site A (Marla Bay) conditions. Total invertebrate abundance effect and site B (Lakeside) in Lake Tahoe before suction removal treatment. fi Proportions are based on average abundance of taxonomic grouping size was not signi cant at 240 days (December based on benthic sampling carried out in March 2009. 2010) after treatment. However, Simpson diversity

Copyright # 2012 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) 592 M. E. WITTMANN ET AL.

Table 1. CI and BACI analysis results for taxonomic groups collected before suction dredge treatment (Before) and after treatment (days 14–450). The ﬁrst value for each taxon indicates the mean effect size: between control and impact sites (CI) in the Before column, and in subsequent columns (days 14–450) before/after and control/impact (BACI). The second entry shows the t-statistic (H0: EffectSizeBefore =EffectSizeAfter)withsigniﬁcance level indicated: *** = P < 0.001, ** = P < 0.01, * = P < 0.05

Before (Mar 09) 14d (April 09) 90d (Jul 09) 150d (Sep 09) 240d (Dec 09) 365d (Apr 10) 450d (Jul 10)

Total invertebrates 1230 4372 3255 2674 2248 1850 1565 0.06 5.30*** 4.11* 3.29* 2.54 1.94 1.54 Amphipoda 34 551 322 180 218 185 177 0.33 2.11** 1.37 0.83 0.98 0.86 0.84 Chironomidae 651 742 332 63 134 268 442 0.13 0.31 1.06 1.97* 2.43* 2.95** 3.59*** Oligochaeta 69 808 754 682 652 706 677 0.99 4.69*** 4.75*** 4.42*** 4.15*** 4.38*** 4.33*** Gastropoda 138 310 147 98 63 34 29 0.87 1.11 0.09 0.45 0.89 1.28 1.39 Corbicula ﬂuminea 453 1471 1343 1285 1206 1033 1013 0.22 1.82* 2.01* 2.00* 1.88* 1.48 1.45 Pisidium spp. 31 369 286 316 236 147 111 1.26 3.22** 3.07** 3.64*** 2.94** 1.67 1.24 Simpson Index (diversity) 0.007 0.405 0.355 0.336 0.310 0.256 0.258 0.02 3.77*** 5.16*** 6.00*** 6.69*** 6.26*** 7.13***

Figure 3. Temporal changes of the abundance (number of individuals m-2) of each taxonomic group in suction dredge treatment (dashed line) and control (solid line) plots from March 2009 (before treatment) to July 2010 (after treatment). Error bars represent one standard error. Time of sampling is indicated by days after treatment and month/year in which the sampling event occurred. index remained significantly different from the change in effect size for total invertebrate pre-impact condition throughout the entire abundance, C. fluminea abundance, native clam sampling period (450 days; July 2010) suggesting (Pisidium spp.) abundance, and Simpson diversity that community dynamics were altered by index. By the end of the sampling period, both harvesting. Chironomids had a significant positive Pisidium spp. and total invertebrate abundance effect size at day 240 (December 2009), indicating show the greatest reductions in effect size, that abundances in treatment plots at this time declining from 0.92 at 14 days to 0.28 at 450 days surpassed abundances in control and impact plots and 0.78 at 14 days to 0.28 at 450 days, before treatment. All other taxonomic groups had respectively. C. fluminea effect size was no longer negative, but reducing, effect sizes at the end of significant at the end of the monitoring period, the sampling period – indicating a trend towards with a decrease from 0.76 to 0.53, while species a return to background and pre-treatment diversity remained affected, with a proportional abundances. Figure 4 shows the proportional reduction to 0.63 at 450 days.

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Otermin et al., 2002). In addition, chironomids were not completely removed after suction treatment, leaving behind 10% of the initial population abundance as primary recolonizers. In comparison, other taxa, such as amphipods and gastropods, were more completely removed, with 4% of their original population abundance remaining in treatment plots. The rapid chironomid recolonization could also be attributed to potential migration from adjacent untreated plots given its high abundance compared with other taxa observed in Lake Tahoe. Amphipods had rapid recovery relative to control plot Figure 4. Temporal changes (days after treatment, calendar date) in proportional effect size for three taxonomic groups and one diversity conditions, which was probably attributable to their index: total invertebrate abundance, native bivalve species (Pisidium mobility, and similar to chironomids, a high spp.) abundance, invasive clam species (Corbicula fluminea, i.e. treatment target) abundance, and the Simpson Diversity Index. Changes in effect potential for migration from adjacent, untreated size are standardized by differences in effect size before treatment. areas. Temporal patterns of amphipod abundance mimicked control plot conditions, and by 150 days (September 2009) effect sizes were insignificantly DISCUSSION different from controls. Similar to amphipods, While physical harvesting can decrease the oligochaete abundances in treatment plots showed abundance of a target species, it can also disrupt increases correlated with control plots, but with soft-sediment benthic communities by reducing many fewer individuals throughout the entire diversity and abundance of some taxa. Dredging to 450 day monitoring period, suggesting that migration remove C. fluminea populations in Lake Tahoe of new individuals from adjacent areas was not as reduced benthic macroinvertebrate abundances and frequent for oligochaetes as it was for other more produced variable recolonization patterns that were mobile taxa. Timing of reproductive cycles for these dependent on environmental parameters and taxa is unknown, but it was also possible that early individual taxon responses. At the end of this recolonization rates during the spring and early study’s monitoring period, total invertebrate summer periods for chironomids and amphipoda abundances in treatment plots were not significantly were optimal in comparison with oligochaetes, different from control or pre-treatment plot Pisidium spp., or C. fluminea, all of which did not conditions, whereas diversity indices remained show significant increases in abundance until at significantly decreased, suggesting that community least 240 days (December 2009) after treatment. dynamics were still altered 450 days after treatment. Slight increases in the abundance of the target In general, dominance of a few groups is a invasive species C. fluminea in treatment plots did common feature of macroinvertebrate communities not begin until 240 days (December 2009) after in the early stages of the recolonization process treatment, and treatment plot densities were (Ladle et al., 1980; Otermin et al., 2002), in part statistically different from control plots at 450 days because they are either able to persist in sediments (July 2010). However, during the April 2009 or can migrate into disturbed areas (Yount and sampling (365 days after treatment), C. fluminea Niemi, 1990). In this study, chironomids were treatment and control plots did not significantly among the first recolonizers in treatment plots, with differ. This reduction of control plot abundances a 50% recovery rate in abundances at 90 days (July could have been attributed to sampling effects 2009). In contrast, the abundances of some taxa given the naturally heterogeneous distribution of such as amphipods and oligochaetes did not begin C. fluminea in space, or potentially from a to recover until 150 days (September 2009) after winter-time decrease in the abundances as a treatment. At 150 days after treatment amphipod result of a low temperature mortality event (Werner abundances increased more rapidly than those of and Rothhaupt, 2008). Subsequent sampling on oligochaetes. Chironomids are ubiquitous in Lake 450 days after treatment (July 2010) showed Tahoe, and have been similarly observed as early continued increases in both the control and colonizers in other systems because of their treatment plot abundances of C. fluminea, once r-selected traits (Gray, 1981; Malmqvist et al., 1991; again returned to a significant difference between

Copyright # 2012 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) 594 M. E. WITTMANN ET AL. control and treatment plots densities, but an The 450 day monitoring period of the treatment insignificant effect size as represented in the BACIP plots revealed several important factors of results. While BACIP analyses have frequently been recolonization dynamics in this system. First, used to assess the impact of dredging on while total invertebrate abundance recovered to macrobenthic communities (Morello et al., 2005), pre-disturbance levels, species diversity (as natural changes in control populations and timing represented by the Simpson index) was significantly of monitoring events can affect results and different from pre-treatment and control plot value interpretations of recovery. This is particularly throughout the entire post-dredging monitoring important in relation to management scenarios, period (14–450 days). This suggests a modified where the determination of invasive species control community structure, which was most strikingly programmes are often based on monitoring results highlighted through shifts in chironomid that are limited in extent. abundances in treatment plots. Second, multiple It is possible that recolonization by C. fluminea linear regression results suggest that, similar to was influenced by the following: (1) minimum other pulse-disturbed freshwater soft-sediment thermal thresholds for reproduction/juvenile benthic communities (Lake, 2000), time since release, and (2) the coarse sediment type at Marla treatment was a consistent predictor of C. fluminea Bay, compared with the clay substrate at Lakeside and total invertebrate abundances, as well as remaining after removal. C. fluminea population Simpson diversity index effect sizes. Third, at densities remained low at both sites until the the end of this study period (450 days; July 2010), minimum temperatures required for reproduction (i. the Simpson diversity index in the treatment e. gametogenesis, juvenile release) were approached plots remained significantly different from both during the spring and summer periods. Through pre-treatment and control conditions. This has either juvenile release, or movement of adults from several implications: (i) continued monitoring is adjacent plots, recolonization of C. fluminea required to understand whether the macrobenthic occurred in the summer months, but with higher invertebrate community can fully recover to abundances observed in Marla Bay as a result of pre-treatment or control conditions, and (ii) further sediment type (coarse sediments in Marla, and clay studies relating to inter- and intra-specificdynamics pan remaining after suction removal at Lakeside) in treatment plots that can have longer-term that provided more favourable habitat in which impacts on community recovery are warranted. to recolonize. In contrast, through site surveys Recovery times of macroinvertebrate taxa after using SCUBA, Pisidium spp. were observed disturbance in lentic habitats have been observed to inhabiting the upper clay and re-sedimented range from days to years and are dependent on layers at Lakeside after dredging. environmental condition, community composition, Unlike the invasive target species, C. fluminea, and magnitude of the perturbation (Cowell, 1984; abundances of native bivalves Pisidium spp. Van de Meutter et al., 2006; Sychra and Adamek, increased to levels greater than or equal to those 2011). Understanding benthic community dynamics observed in the treatment plots by day 365 (April under a pulse disturbance scenario can further 2010) compared with control plot conditions. C. indicate whether suction dredging is an effective fluminea is well known for its temperature-dependent method for invasive species control of molluscs reproductive rates (Williams and McMahon, 1989), in lentic habitats. generalist feeding preference (Way et al., 1990; Several control strategies for invasive molluscs, Hakenkamp and Palmer, 1999), and tolerance to a namely dreissenid mussels, have been developed wide variety of environmental conditions (Williams and in some cases, have been successful (Nalepa and McMahon, 1989). The relative recolonization and Schloesser, 1993; Claudi and Mackie, 1994; success of Pisidium spp. compared with the slower D’Itri, 1997). Removal of adult C. fluminea and recolonization rates of opportunist C. fluminea, other invasive molluscs has been used primarily in suggests that C. fluminea is perhaps not as well power generation settings where biofouling of adapted to low water temperatures, limited food important structures incurs significant costs and availability, and other environmental variables not removal was necessary for proper plant measured here. Further study of inter-specific functioning (Connelly et al., 2007). However, for competition in Lake Tahoe is needed to understand open water bodies these approaches are generally this relationship. not suitable as they can be ecologically damaging,

Copyright # 2012 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 22: 588–597 (2012) HARVESTING INVASIVE CLAMS: IMPACT TO THE MACROINVERTEBRATE COMMUNITY 595 expensive, and ineffective (Wimbush et al., 2009). work was provided by the Southern Nevada There have only been two reports of bivalve Public Lands Management Act, the Lahontan eradication (using chemical treatment) in open Regional Water Quality Control Board and the water bodies (Bax, 1999; Virginia Department Nevada Division of State Lands. of Game and Inland Fisheries, 2009) and one non-chemical treatment that reduced but did not eradicate a dreissenid mussel population REFERENCES (Wimbush et al., 2009). In general, the only accepted practical approach for managing molluscan Anderson RO. 1959. A modified flotation technique for sorting bottom fauna samples. Limnology and Oceanography invasions in open waters is thought to be by 4:223–225. prevention-oriented management (Frischer et al., Bax NJ. 1999. 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