Abstract Juvenile unionid mussels disperse in the water column after detachment from their host fish. The settling velocity (ws) of juvenile mussels is an important component of their dispersion in the water column but has not been measured for unionid mussels. The goal of our study was to measure the ws of juvenile mussels in the laboratory and to examine how ws varied within and among related species. The ws of Actinonaias ligamentina and Ptychobranchus fasciolaris were significantly lower (2.4 ± 0.1 mm/s vs 2.5 ± 0.1 mm/s, respectively) than those of the larger-sized Lampsilis fasciola and Epioblasma triquetra (4.2 ± 0.2 mm/s vs 4.6 ± 0.2 mm/s, respectively). Overall, ws increased with juvenile size, but considerable variation (∼10×) was found within species. Observations indicated that foot movement of juvenile mussels was responsible for reductions in ws, and this behavior may provide a potential mechanism for habitat selection at small-spatial scales. Observed ws differed considerably from ws predicted from Stokes' law using empirically determined shell size and density (ρ = 1.22 ± 0.003 g/cm3 for A. ligamentina), which indicates some of the limitations in predicting ws from size measurements.
We examined seasonal patterns of abundance of mussel larvae (glochidia) in stream drift in a diverse, large-stream mussel assemblage in the Sipsey River, Alabama, across 1 y. We used recently developed techniques for glochidial identification combined with information about mussel fecundity and benthic assemblages to evaluate how well observed glochidial abundance corresponded to expected abundance based on glochidial production. Glochidia from short-term brooding species (Amblema plicata, Elliptio arca, Fusconaia cerina, Pleurobema decisum, Obliquaria reflexa, and Quadrula asperata) were abundant from May to August but did not occur in drift between November and the end of April. Long-term brooders (Lampsilis spp., Medionidus acutissimus, Obovaria unicolor, and Villosa spp.) occurred in several short peaks in spring, summer, and autumn, but generally were less abundant than short-term brooders. We estimated that the benthic assemblage at our study site produced >500,000 glochidia/m(2) annually and production varied widely among species. Abundance of species in the drift was positively related to benthic abundance but was only weakly related to glochidial production. The poor relationship between glochidial production and abundance in the drift suggests that release and transport of glochidia are influenced by a wide variety of abiotic and biotic factors.
Grass litter can be a dominant detritus type in many streams. However, use of this C source in stream food webs often is viewed as insignificant because of its relatively slow breakdown rates and low nutritional quality. We deployed leaf packs containing senesced bluejoint grass (Calamagrostis canadensis) across a natural nutrient gradient of 6 salmon-rearing headwater streams on the lower Kenai Peninsula, Alaska. We hypothesized that litter-colonizing microbes would use dissolved stream nutrients and enhance breakdown rates, litter nutrient concentrations, and densities of macroinvertebrates across streams. Leaf-pack mass and nutrient concentrations were measured on the material at 0 (predeployment), 2, 4, 6, and 8 wk in all streams. Breakdown rates were calculated from the mass measurements with an exponential decay model. Macroinvertebrate composition and abundance were measured at 8 wk in all streams and every 2 wk in 1 stream. Breakdown rates of bluejoint litter were relatively low (20-30% mass loss over 2 mo), but similar to rates found in previous studies of senesced grass litter. Weighted regressions showed that bluejoint breakdown rates in the 6 streams were significantly (p < 0.05) related to dissolved stream nutrient concentrations (r(2) = 0.94 and 0.67 for dissolved inorganic N and PO4-P, respectively), litter nutrient concentration (r(2) = 0.72 and 0.96 for leaf % N and % P. respectively), total macroinvertebrates/g (r(2) = 0.73), and nonmetric multidimensional scaling-axis-1 scores of macroinvertebrate community structure (r(2) = 0.80). Litter nutrients changed after just 2 wk and were increasingly and significantly related to stream nutrient concentrations over time. NMS ordination showed that succession of macroinvertebrates on leaf packs from one stream followed a distinct direction over time, and a large shift in macroinvertebrate community structure occurred between weeks 6 and 8, a result potentially indicating a consumer response to microbial conditioning. The abundance and diversity of macroinvertebrate taxa using bluejoint litter provide evidence that it is an important habitat and energy pathway for consumers in headwater streams of the Kenai Peninsula. In addition, climate change has the potential to change terrestrial vegetation assemblages, which drive differences in stream nutrient concentrations in this region. If N-fixing shrubs become more abundant in the future, litter-decomposition rates will be positively affected by increases in both stream and leaf-litter nutrient concentrations.
Acid mine drainage (AMD) is a legacy of historical coal mining that affects several thousand stream kilometers around the world by contributing high loads of acidity, SO42-, metals, and other cations. Most research has focused on how AMD affects diversity and structure of various biological assemblages, whereas considerably less has focused on functional processes in streams. We investigated how AMD from abandoned coal mines affects epilithic biofilm development and function. Algal biomass and accrual rates were significantly lower in AMD-affected stream reaches than in control streams. Biomass and accrual rates were lowest at intermediate AMD-affected sites (pH = 5.1-5.9), probably because copious amounts of AlOH3 precipitates smothered the benthic habitat. Ratios of beta-glucosidase (GLU):beta-xylosidase (XYLO) were significantly correlated with algal biomass (r = 0.60, p < 0.01), probably because algae are important sources of C that is readily broken down by bacterial GLU activity, whereas XYLO is mostly associated with C of allochthonous origin. Thus, reduced algal biomass could indirectly exacerbate AMD effects on bacterial function by providing less C needed for cellular functions. Ratios of phosphatase:leucine aminopeptidase significantly increased as pH decreased (R-2 = 0.88, p < 0.01). This increase indicated potential P limitation or stressful conditions for microbial communities because PO4-P readily adsorbs to metal hydroxides, rendering it biologically inaccessible. Ratios in 3 of 4 control streams indicated that N limitation may be more typical in unaffected streams of the region. Low algal biomass and potential P limitation of biofilms may indicate that AMD-affected streams have reduced capabilities to retain nutrients and energy needed to support healthy ecosystems. Considering the links between biofilm structure and function can provide a framework for developing management strategies to restore and conserve ecosystem processes, such as nutrient retention and spiraling, energy flow, food webs, and biodiversity.
Great Plains rivers are characterized by unpredictable, thunderstorm-generated flow events that can abruptly restructure their physical complexity. These morphodynamic disturbances force river organisms to overcome hydrologic challenges. Some organisms surmount these challenges by using refugia, which play a key role in the ecological processes that govern lotic systems. The physical complexity of rivers can determine the availability and diversity of refugia both within and among rivers. However, physical complexity often changes with the hydrologic cycle and position along the river. We determined how the benthic community was affected by changes in the structure and abundance of in-channel refugia created by hydrologic fluctuations. We worked on and around sandbars in the Kansas River (Kaw), a multithread, sand-bed river. The composition of the zoobenthic community was directly related to the complexity of river morphology and flow rates. The community of 1 side channel consistently shifted over time between 2 distinct assemblages depending on whether the side channel was flowing or a disconnected slackwater. The benthic invertebrate community exploits many strategies to survive in the abrasive and continually fluctuating Kaw, including using sandbars as refugia and places for recolonization. The refuge provided by these sandbars will become increasingly important in the future if precipitation regimes become more variable as predicted by climate-change scenarios for the region. However, increased levee and dam construction threaten the persistence of the sandbars and vital habitats that they create.
Island biogeography theory can be used to explain patterns of species richness on various types of habitat islands, including freshwater lake systems. Mollusk production in these systems also has been linked to various water-chemistry variables, such as pH, alkalinity, hardness, and specific conductance. We examined how mollusk diversity patterns were related to geographical and limnological factors in insular lakes of the Beaver and Manitou Archipelagos in Lake Michigan (Laurentian Great Lakes), USA. The strongest correlations observed were with shoreline development (r = 0.80), specific conductance (r = 0.87), and pH (r = 0.87). Principal components analysis revealed that isolation by distance and PO(4)(3-) concentration also may have affected species richness and abundance. Shoreline length was a better predictor of species richness than surface area, but both measures of habitat size were unable to account for much of the variation in species richness. The data suggest that shoreline length and development represent available habitat area more accurately than lake area for primarily littoral-dwelling mollusks. The relatively weak correlations observed with lake area and isolation from Lake Michigan suggest that application of island biogeography theory to predict mollusk species richness using only lake surface area and isolation by distance is limited for freshwater mollusks.
The decline of freshwater mussels in the southeastern US emphasizes the need to evaluate the current status of mussel populations. We used the Robust Design, which is a capture recapture sampling design, to estimate demographic parameters (apparent survival and temporary emigration) and capture probabilities of Alasmidonta arcula, Lampsilis dolabraeformis, Lampsilis splendida, and Pyganodon gibbosa in a large lowland river in Georgia. Mussels were sampled in individual habitat units using line-transect methods at similar to 6-wk intervals from summer 2006-2007. We used an information-theoretic approach to evaluate the relative importance of maximum river discharge, habitat characteristics, mussel species, and season on temporary emigration (i.e., proportion of mussels not at the surface), apparent survival, and capture probability. The best-supported models indicated that apparent survival and capture probability varied positively with mussel shell length and among habitat types. Apparent survival (6-wk interval) ranged from 94 to 99% and was greatest in slackwater and lowest in swiftwater habitat. Capture probability ranged from 8 to 20% and was greatest in slackwater and lowest in swift-water habitat. Temporary emigration also varied among species and season and appeared to be related to reproductive behavior, with the largest proportion of mussels occurring at the surface when mussels appeared to be reproductively active. A comparison of catch-per-unit-effort indices to population estimates suggested that the reliability of catch-per-unit-effort indices was influenced by vertical migration behavior and other factors affecting mussel capture probability.
Abstract Nutrient limitation plays an important role in shaping community structure and ecosystem processes in aquatic environments. Many types of nutrient diffusing substrata (NDS) have been used to estimate nutrient limitation in lotic systems. However, whether these various NDS methods produce comparable results is unknown. We evaluated the 3 most commonly used NDS methods—clay pots, plastic cups, and periphytometers—in a single stream to determine if they gave qualitatively similar results. We also examined the effects of initial nutrient ratios on diffusion rates in all 3 types of NDS and periphyton stoichiometry on clay pots. The largest response in chlorophyll a biomass consistently occurred on substrata that simultaneously diffused both inorganic N and P. However, each NDS method produced a significantly different picture of limitation. Clay pots showed that primary producers were colimited by N and P, plastic cups showed primary limitation by N and secondary limitation by P, and periphytometers showed primary limitation by P and secondary limitation by N. Nutrient diffusion rates were very different among methods. Effects of different N∶P ratios were only seen in clay pots. When N∶P was 16∶1, chlorophyll a biomass was low. When N∶P was 1∶1, periphyton had greater %C and %P and low C∶P and N∶P. Our results indicate that further research is required to clarify methodological differences between the types of NDS. Until such discrepancies are addressed, the results obtained with NDS methods should be interpreted with caution.
Flood-pulsing is a key environmental factor that structures biotic communities in large-order river systems, but we focused our study on the effects of flood-pulsing in headwater systems. We used 10 mesocosm wetlands (10 m X 20 m) to test 2 treatments: a flood-pulse regimen in which natural flood events caused water levels to fluctuate and a static regimen in which water levels remained artificially stable. Abiotic characteristics, plants, and aquatic invertebrate communities were monitored from 2002 through 2005 in permanent pools, nonflooded banks in static wetlands, and intermittently flooded banks in flood-pulse wetlands. The flood-pulse treatment had minimal effects on environmental conditions of permanent pools, and submersed plant and aquatic invertebrate communities in permanent pools were similar in both treatments. This result suggested that resource subsidies from the floodplain to the pools were minimal. However, flood-pulsing caused observable changes to plant communities in the intermittently flooded zone (IFZ) above the permanently flooded pool. Overall plant diversity was higher in static wetlands, and % bare ground was higher in flood-pulse wetlands, results suggesting that the short, stochastic floods were a strong environmental stressor. In flood-pulse wetlands, the fluctuating water levels may have reduced the proportion of introduced, weedy, and upland plant taxa. Flood-pulse and static wetlands had distinctly different plant assemblage compositions, indicating that the abiotic stressors caused pronounced changes in the floodplain community. An indicator species analysis showed that taxa classified as obligate wetland plants were indicators in flood-pulse wetlands (e.g., Juncus canadensis, Ludwigia palustris, Dulichium arundinaceum, Eleocharis obtusa, Carex crinita, Carex lupulina, Carex vulpinoidea), but taxa classified as facultative wetland or upland plants were indicators of static wetlands (Cirsium arvense, Eupatoriadelphus maculatus, Plantago lanceolata, Bidens frondosus, Melilotus officinalis, Mentha arvensis, Daucus carota, Poa palustris). Many functional categories of plant species that were common in flood-pulse wetlands (e.g., obligate wetland plants, perennial, native and nonweedy species) are considered beneficial from a management perspective.
Low-flow disturbances are predicted to increase in frequency and intensity because of climate change and extensive human water withdrawal, but the effect of decreased flow on aquatic insect communities is not well understood. I explored the resistance of aquatic insects to reduced flow by creating an experimental low-flow disturbance that diverted similar to 40 to 80% of the water in 3 replicate streams for 2 summers. I sampled the aquatic insect community in control and treatment reaches before and during the 3-mo water diversions. I used a trait-based approach to analyze the data because traits have the potential to increase mechanistic understanding and predictive capabilities. The analysis focused on 6 traits: desiccation resistance, maximum crawling rate, armoring, size at maturity, rheophily, and habit. Community trait composition underwent strong seasonal shifts, but few consistent responses to reduced flow were observed. The 2 trait states that did appear to confer increased resistance were high crawling rate and armoring. These trait states can provide protection from predators. Thus, biotic interactions might be important during low-flow disturbance.
Surveys of freshwater mussel populations are used frequently to inform conservation decisions by providing information about the status and distribution of species. It is generally accepted that not all mussels or species are collected during surveys, and incomplete detection of individuals and species can bias data and can affect inferences. However, considerably less attention has been given to the potential effects of species misidentification. To evaluate the prevalence of and potential reasons for species misidentification, we conducted a laboratory-based identification exercise and quantified the relationships between mussel species characteristics, observer experience, and misidentification rate. We estimated that misidentification was fairly common, with rates averaging 27% across all species and ranging from 0 to 56%, and was related to mussel shell characteristics and observer experience. Most notably, species with shell texturing were 6.09x less likely than smooth-shelled species to be misidentified. Misidentification rates declined with observer experience, but for many species the risk of misidentification averaged >10% even for observers with moderate levels of experience (5-6 y). In addition, misidentification rates among observers showed substantial variability after controlling for experience. Our results suggest that species misidentification may be common in field surveys of freshwater mussels and could potentially bias estimates of population status and trends. Misidentification rates possibly could be reduced through use of regional workshops, testing and certification programs, and the availability of archived specimens and tissue samples in museum collections.
The temporal pattern of river metabolism was estimated for high-order rivers (5-7(th)) in the Daly watershed, tropical Australia, during the dry season (May-October) when discharge was supplied predominantly by groundwater. Rates of photosynthesis (P) and respiration (R) were calculated at 4 sites using the open-channel method based on a model of the river's O-2 budget and Measured diurnal cycles of dissolved O-2 concentrations and temperatures. The rivers were shallow (average depth = 0.8 m), clear (1-2 NTU), and had low concentrations of nutrients (<= 15 mu g/L soluble N and P at most sites) and generally open canopy. At the reach scale, P was limited by light with no evidence of light saturation. An increase in primary producer biomass over the dry season probably underpinned an approximate doubling of P at the 4 sites over the dry season, but increased water temperatures would have contributed, too. P (0.1-4.6 g O-2 m(-2) d(-1)) in the Daly watershed was similar to rates in a shaded tropical Puerto Rican stream and some temperate rivers but was lower than in nutrient-enriched temperate rivers. We surmise that most P resulted in production of dissolved organic C (DOC), rather than growth of primary producer biomass, which was nutrient limited. R exceeded P (P/R approximate to 0.5), and increased approximately linearly with P (r(2) = 0.79-0.99) over the dry season with no statistically significant difference among sites. The similar environmental setting of the 4 sites underpinned their similar temporal pattern of metabolism. Bacterial metabolism of photosynthetically produced DOC (PDOC) could partially explain the tight coupling of R and P but could not account for the river's overall net heterotrophy. The priming effect of bacterial degradation of labile PDOC to increase the mineralization of recalcitrant DOC (e.g., humic acids) provides an explanation for the river's heterotrophy and tight coupling between P and R.
Headwaters (stream orders 1-2) traditionally have been considered depauperate compared to mid-order streams (orders 3-4)-a conclusion that arises from a perception of streams as linear systems and emphasizes change in average alpha (local) diversity along streams. We hypothesized an opposite pattern for beta (among-site) diversity and suggest that headwaters might account for a large degree of basin-scale biodiversity if considered within the more realistic framework of streams as branching networks. We assembled pre-existing biodiyersity data from across the globe to test this hypothesis broadly at the population-genetic (mitochondrial haplotype diversity within species) and community (species/taxonomic diversity) levels, with a focus on macroinvertebrates. We standardized 18 (9 headwater and 9 mid-order) population-genetic and 16 (10 headwater and 6 mid-order) community-level ecoregional data sets from 5 global ecozones for robust comparisons of beta-diversity estimates between the 2 stream-size categories. At the population-genetic level, we applied measures of among-site variation commonly used at both population-genetic (F-ST and Phi(ST)) and community (Sorensen's dissimilarity with both presence/absence and abundance data) levels and developed a novel strategy to compare expected rates of loss of gamma (regional) diversity as individual sites are eliminated sequentially from regions. At the community level, we limited analyses to Sorensen's presence/absence measures. We found that Sorensen's dissimilarity was significantly greater among headwaters than among mid-order streams at both population-genetic and community levels. We also showed that individual headwater reaches accounted for greater proportions of genetic gamma diversity than did mid-order reaches. However, neither F-ST nor (Phi(ST) was significantly different between stream-size categories. These measures, which have been used traditionally for comparisons of population-genetic variation, measure proportions of total variation rather than solely among-site variation (i.e., they also are influenced by within-site variation). In contrast, Sorensen's dissimilarity measures only among-site variation and, therefore, is presumably more useful for reflecting general beta diversity. Overall results suggest that, on average, headwaters probably contribute disproportionately to biodiversity at the network scale. This finding demands a shift in thinking about the biodiversity contributions of small headwaters and has strong conservation implications for imperiled headwater streams around the world.
Quantitative biological assessment protocols are needed for monitoring river status and evaluating river rehabilitation efforts. We conducted a standardized macroinvertebrate survey at 100 sites on 38 nonwadeable rivers in Wisconsin to construct, test, and apply an index of biotic integrity (IBI) intended to be such a bioassessment tool. We assigned independent samples to IBI development (n = 75) and IBI validation (n = 25) data sets. We placed Hester-Dendy artificial substrates at the sites for 6 wk and processed the samples of colonizing macroinvertebrates in the laboratory with a 500-target subsampling procedure plus a large-rare taxon search. Independent of the biota, we assigned an environmental disturbance score to each site based upon water chemistry, land cover, flow modification, and point-source pollution. Ten metrics that represent macroinvertebrate assemblage structure, composition, and function constitute the IBI: the number of taxa in: 1) Insecta or 2) Ephemeroptera, Plecoptera, Trichoptera (EPT); % individuals that were: 3) Insecta, 4) intolerant EPT, 5) tolerant chironomids, 6) gatherers, 7) scrapers, or from 8) the dominant 3 taxa; 9) the mean pollution tolerance value; and 10) the number of unique ecological functional trait niches. Analyses on both the validation subset of sites and all sites inclusive confirmed that least-disturbed sites had the highest IBI scores, severely disturbed sites had the lowest scores, and moderately disturbed sites had intermediate scores. Chironominae and Hydropsychidae taxa known to tolerate nutrient enrichment and overall degraded conditions dominated samples with low IBI scores. In contrast, a diverse assemblage that thrives in relatively undisturbed conditions was present in samples with high IBI scores. Comparison of the new macroinvertebrate IBI with an existing fish IBI suggested that the indices respond to different environmental stressors and illustrated the limitations of using only one taxonomic group for bioassessment. We discuss new macroinvertebrate methods, an IBI development process, and the refinement of metrics that may be useful in tailoring assessment tools for large rivers or wadeable streams in other regions. We also present applications of the IBI, including its potential use in comprehensive large river monitoring programs and for evaluating management efforts.
Stream metabolism at both ecosystem and functional-compartment scales was measured in a low-order Pampean stream (La Choza) over a 3-wk period to characterize metabolic rates and discern the contribution of each functional compartment (submerged macrophytes, benthos, floating macroalgae, water column, and hyporheic zone) to ecosystem metabolism. La Choza stream is an autotrophic ecosystem during low flows and has gross primary production rates of up to 22 g O-2 m(-2)d(-1), which are among the highest reported in the literature and set an upper bound on how productive streams can be in the absence of light and nutrient limitations. Floating macroalgae provided most of the primary production (30-90%), whereas the hyporheic zone provided most of the ecosystem respiration (40-80%). The differential effects of high flows on the different functional compartments depressed the production:respiration ratio, suggesting a strong relationship between flow and metabolism. Thus, low flows enhanced primary production and led to diel dissolved O-2 concentration oscillations between 0 and 25 g O-2/m(3). In contrast, high flow depressed primary production by an order of magnitude and increased ecosystem respiration. High production rates during the low-flow period and extreme physicochemical conditions (anoxia for 7-8 h on a daily basis) may be typical in this type of ecosystem during extended low-flow periods.
Parasites can regulate host abundance and influence the composition and structure of communities. However, host-parasite interactions might be context-specific if environmental conditions can alter the outcome of parasitism and disease. An understanding of how host-parasite interactions might change in different contexts will be useful for predicting and managing disease against a background of anthropogenic environmental change. We examined the ecology of Myxobolus cerebralis, the parasite that causes whirling disease in salmonids, and its obligate host, Tubifex tubifex, in geothermally variable stream reaches in Yellowstone National Park. We identified reaches in 4 categories of geothermal influence, which were characterized by variable substrates, temperatures, specific conductivities, and pH. In each reach, we measured aspects of host ecology (abundance, relative abundance, size, and genotype of T. tubifex), parasite ecology (infection prevalence in T. tubifex and abundance of M. cerebralis-infected T. tubifex), and risk to fish of contracting whirling disease. Tubifex tubifex abundance was high all in reaches characterized by geothermal influence, whereas abundance of M. cerebralis-infected T. tubifex was high only in reaches characterized by intermediate geothermal influence. We suggest that habitat had a contextual effect on parasitism in the oligochaete host. Abundance of infected hosts appeared to depend on host abundance in all reach types except those with high geothermal influence, where abundance of infected hosts depended on environmental factors.
Taxonomic identification of benthic macroinvertebrates is critical to protocols used to assess the biological integrity of aquatic ecosystems. The time, expense, and inherent error rate of species-level morphological identifications has necessitated use of genus- or family-level identifications in most large, statewide bioassessment programs. Use of coarse-scale taxonomy can obscure signal about biological condition, particularly if the range of species tolerances is large within genera or families. We hypothesized that integration of deoxyribonucleic acid (DNA) barcodes (partial cytochrome c oxidase subunit I sequences) into bioassessment protocols would provide greater discriminatory ability than genus-level identifications and that this increased specificity could lead to more sensitive assessments of water quality and habitat. Analysis of DNA barcodes from larval specimens of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa collected as part of Maryland's Biological Stream Survey (MBSS) revealed similar to 2 to 3x as many DNA-barcode groups or molecular operational taxonomic units (mOTUs) as morphologically identified genera. As expected, geographic distributions for several mOTUs were tighter than for the parent genus, but few mOTUs showed closer associations with water-quality variables or physical-habitat features than did the genus in which they belonged. The need for improved protocols for the consistent generation of DNA barcodes is discussed.
Differences in the raw data used in bioassessments and choices regarding how those data are analyzed and summarized can affect inferences regarding the status of ecological resources and, thus, the degree to which we can trust individual ecological assessments, compare assessments across different programs and regions, or share data when developing or refining new endpoint indices. Progress in addressing these issues has been hindered by lack of consensus regarding what a general definition of comparability should be in the context of bioassessments and what measures of comparability are appropriate for ecological data. In this paper, we review the state of knowledge regarding the comparability of assessments as affected by differences in raw data (composition and relative abundance of taxa), derived measures (biotic metrics and endpoint indices), and assessment levels (condition classes). We specifically address the extent to which the comparability of assessments can be compromised by systematic differences in data, discuss the factors known to affect data comparability, and consider the techniques available to evaluate and improve comparability. Rigorous assessment of data comparability should be a standard aspect of quality assurance when developing and applying biological indices.
The North American spiny-cheek crayfish, Orconectes limosus (Rafinesque, 1817), a widespread invader in Europe, seems to have been introduced there successfully only once. According to available literature, 90 individuals of unclear origin were released in Poland in 1890. Despite this apparent bottleneck, the species has successfully colonized various aquatic habitats and has displaced native crayfish species in many places. To test whether different European populations were likely to have come from a single source and to identify their possible origin, we analyzed the diversity of the mitochondrial gene for cytochrome c oxidase subunit I (COI) of O. limosus individuals from Europe and from its original range in North America, including the presumed source region of European populations, the Delaware River watershed (eastern USA). Two haplotypes were found in European populations. One haplotype was widespread; the other was present in a single population. In contrast, 18 haplotypes were detected in North America. This result supports the hypothesis of a single overseas introduction of O. limosus and suggests that the high invasion success of this species was not limited by an introduction bottleneck. Two divergent clades were detected in North American O. limosus populations. One, which includes the dominant haplotype in Europe, was found in a large part of the species' present range. The 2(nd) (diverging by >1%) was mostly restricted to a limited area in southeastern Pennsylvania. Orconectes limosus populations in the northern part of the species' North American range, at least some of which are nonindigenous themselves, may share the source area with European O. limosus. The endangered status of O. limosus populations in southeastern Pennsylvania and northeastern Maryland, where much of the species' genetic diversity resides, should be considered in conservation management.
