Impact of the Alga Cladophora on the Survival of E. coli, Salmonella, and Shigella in Laboratory Microcosm

E. coli is an indicator of recent fecal contamination of freshwater beaches around the Great Lakes region. Elevated concentrations indicate that a fecal contamination has occurred, and that the risk for contact with fecal pathogenic organisms is heightened. The green algae, Cladophora, harbors populations of E. coli and potentially allows for prolonged survival and even replication of the bacterium in the lake environment. If presence of Cladophora mats on beaches is associated with persistence of E. coli in beach water, then E. coli would be a useful indicator organism only if pathogens also were able to survive and persist in the algae. This study utilized lab microcosms to study the persistence of E. coli, and of the fecal pathogens, Salmonella and Shigella, in lake water with and without the presence of Cladophora. E. coli was able to persist for extended periods in the presence of Cladophora (attached to algal mats for 45 days). Salmonella and Shigella, however, were unable to persist for this time period while in the presence of Cladophora (Salmonella attached to Cladophora was detectable for 10 days and Shigella was detectable for only 2 days). These data imply that E. coli is able to survive in the presence of Cladophora for greater times than are the fecal pathogens and that E. coli may not be an appropriate indicator organism for beaches with accumulations of algal material.     

Response of wetland vegetation to the post-1986 decrease in Lake St. Clair water levels: Seed-bank emergence and beginnings of the Phragmites australis invasion

Water-level fluctuations are critical for maintaining the diversity and resultant habitat value of wetland plant communities in the Laurentian Great Lakes. However, activation of the seed bank can also provide an opportunity for invasive species to displace native species, as occurred when common reed, Phragmites australis, expanded across many wetlands after lake levels receded following highs in 1997. Timing of the invasion process is not clear, however, as Phragmites propagules had to be present to exploit the exposed soils. A data set from Dickinson Island on the St. Clair River delta collected in 1988–1991, 1996 during a previous lake-level decline was analyzed to document prior Phragmites growth, as well as overall seed-bank response. Above-ground biomass was determined for all plants each year in randomly placed quadrats in a 5-ha area exposed when lake levels decreased by 0.65 m from 1986 to 1988. A total of 38 taxa were identified in 1988, but the number decreased, along with biomass of many species, as canopy-dominating Typha angustifolia and Phragmites increased in later years. Although Phragmites did not expand greatly until after the decline from the 1997 high, it likely inoculated the area with viable seed during the previous low. Because post-1997 lake levels were lower than those post-1986, they exposed a greater area for Phragmites colonization from seed; lake levels also remained low for a longer time. Differences in bathymetry below the 1986 and 1997 lake-level elevations likely played a role in greater post-1997 spatial expansion of Phragmites at other sites in the Great Lakes also. The next high lake level will likely be required to displace Phragmites, but the effect will be temporary.     

Fecal indicator organism density in beach sands: Impact of sediment grain size,uniformity, and hydrologic factors on surface water loading

Fecal loading to beach sands and subsequent transport to surface water may result in the degradation of surface water quality. To better understand the relationship between Escherichia coli in sands, beach hydrology, and recreational water quality, we collected surface water, groundwater, and sand samples from three Lake Michigan beaches with varying substrates (fine sand to pebbles, July 2005–June 2006). Sediment cores collected within transects perpendicular to and at fixed distances from the shoreline (0 m, 10 m, 20 m) and surface water samples collected at a depth of 1 m were analyzed for E. coli. Grain size analysis was performed on duplicate core samples to assess the relationship between E. coli density and mean grain size and uniformity. Groundwater samples, collected from shallow drive-point piezometers within the test area, were also analyzed for E. coli. E. coli density in beach sands differed significantly with distance from shore with the highest density occurring at the berm crest (0 m). Mean grain size and uniformity accounted for variation in E. coli density with fine sand of uniform distribution having the highest content. E. coli density in surface water was correlated to E. coli density in beach sand samples at the berm crest. E. coli in groundwater was < 10 to 579 MPN/100 ml (2005); none was detected in 2006. Management interventions, including altered beach grooming practices and slope assessments, may be effective in reducing E. coli content at beaches comprised of fine sands of uniform grain size, hence reducing water quality advisories.     

Distribution of nuisance Cladophora in the lower Great Lakes: Patterns with land use, near shore water quality and dreissenid abundance

Selected shorelines and offshore shoals in Lakes Erie, Huron and Ontario were surveyed with a high frequency hydroacoustic system to investigate current spatial patterns of nuisance benthic filamentous algal (e.g., Cladophora) cover and stand height. Cladophora reached nuisance levels at all sites in Lakes Erie and Ontario, but not in Lake Huron or Georgian Bay. Despite clear gradients in coastal land cover, near shore water quality gradients were generally weak, and for Lakes Erie and Ontario, measures of near shore water quality were similar to that at offshore shoals. Hierarchical partitioning analysis suggested that while dreissenid mussel abundance appeared to be important in determining the magnitude of Cladophora standing crop, the joint contribution of catchment land cover, near shore water quality (nutrient levels and suspended matter) and dreissenid mussel abundance explained nearly 95% of the total variance in nuisance Cladophora standing crop observed in this study. Although the results from this study are necessarily correlative in nature and definition of causal relationships is not possible, these results provide corroborating evidence from sites across a gradient within and across the lower Great Lakes that is consistent with the operation of the near shore shunt model.     

Is reduced benthic flux related to the Diporeia decline? Analysis of spring blooms and whiting events in Lake Ontario

Benthic monitoring by USGS off the southern shore of Lake Ontario from October 1993 to October 1995 provides a detailed view of the early stages of the decline of the native amphipod Diporeia. A loss of the 1994 and 1995 year classes of Diporeia preceded the disappearance of the native amphipod at sites near Oswego and Rochester at depths from 55 to 130 m. In succeeding years, Diporeia populations continued to decline in Lake Ontario and were nearly extirpated by 2008. Explanations for Diporeia's decline in the Great Lakes include several hypotheses often linked to the introduction and expansion of exotic zebra and quagga mussels (Dreissena sp.). We compare the timeline of the Diporeia decline in Lake Ontario with trends in two sources of organic matter to the sediments — spring diatom blooms and late summer whiting events. The 1994–95 decline of Diporeia coincided with localized dreissenid effects on phytoplankton in the nearshore and a year (April 1994 to May 1995) of decreased flux of organic carbon recorded by sediment traps moored offshore of Oswego. Later declines of profundal (> 90 m) Diporeia populations in 2003 were poorly associated with trends in spring algal blooms and late summer whiting events.     

Evidence for Remote Effects of Dreissenid Mussels on the Amphipod Diporeia: Analysis of Lake Ontario Benthic Surveys, 1972–2003

The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m² at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m² to 63/m² between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces.     

The Great Lakes Cladophora Model: Development,testing, and application to Lake Michigan

A recent review of the Great Lakes Water Quality Agreement has concluded that while controls on phosphorus inputs to Lake Michigan achieved the desired effect in offshore waters, the nearshore region continues to suffer from elevated phosphorus levels. Failure to achieve trophic state goals in the nearshore is manifested in nuisance growth of Cladophora and attendant impacts on property owners, utilities, and the public health and welfare. This study focuses on a site in Lake Michigan near Milwaukee, Wisconsin, where nuisance growth of Cladophora and associated beach fouling occur regularly. A mechanistic model simulating Cladophora growth, suitable for guiding nutrient management in the Great Lakes nearshore, is presented. The model represents an update of the Canale and Auer framework, reflecting current understandings of Cladophora ecology and offering a user-friendly interface making the software more widely available to decision makers. This Great Lakes Cladophora Model (GLCM) is first validated for the Auer/Canale data set collected in 1979 at a site on Lake Huron and then for a data set developed in 2006 for a site on Lake Michigan. Model performance under the strikingly different forcing conditions (depth, light, phosphorus levels) characteristic of these two sites affirms the widespread applicability of the tool. The GLCM is then extended to examine the impacts of ecosystem perturbation (dreissenid colonization) on Cladophora growth and to future approaches to monitoring and management.     

A model laboratory system to study the synergistic interaction and growth of environmental Escherichia coli with macrophytic green algae

Escherichia coli, an important fecal indicator bacterium, is known to persist and reproduce in association with Cladophora and other macrophytic algae and environmental substrates. Recent increases in the growth of Cladophora and other macrophytic algae in many of the Laurentian Great Lakes result in the accumulation of large amounts of algal biomass along the shoreline and on beaches. While the Cladophora–E. coli association may pose substantial public health risks, detailed laboratory-based studies have not been done to investigate the bases of the interaction. This is due, in large part, to past inabilities to culture many macrophytic algae under near axenic conditions. Here we describe the development and experimental use of laboratory microcosms to study the synergistic interaction and growth of the green alga Pithophora, a close relative of Cladophora, with environmental E. coli. In the absence of exogenous organic carbon supply, the E. coli population attached to algal filaments increased approximately three orders of magnitude within 72 h of inoculation. Growth of E. coli on Pithophora appeared to be limited by dissolved nitrogen with a concentration of ≥ 66 μg/mL N allowing maximal bacterial growth. In contrast, an environmental strain of Salmonella did not grow under identical conditions in the microcosms, suggesting that this bacterium requires additional growth factors not provided by Cladophora. Since the alga can be maintained in the laboratory for long periods of time, this system allows for further experimentation and understanding of macroalga–microbe interactions.     

Spatiotemporal patterns of water quality in Lake Ontario and their implications for nuisance growth of Cladophora

This study, motivated by a resurgence in Cladophora, investigates changes in the nutrient environment in the littoral zone of Lake Ontario. We measured nutrient concentrations from 2004 to 2008 at two littoral zone (2–12 m) sites on the north shore of Lake Ontario where Cladophora has experienced a resurgence and compared concentrations with data collected in the late 1970s. Spring total phosphorus (TP) and soluble reactive P (SRP) concentrations have significantly declined at these two sites. Furthermore, P loading from the major tributaries to our study sites declined between 1964 and 2008. Upwelling events were not detectably associated with increases in P concentrations at our sites. We conclude that a recent upsurge in nuisance Cladophora, at least at these sites, cannot be explained by deteriorating littoral zone water quality in terms of P concentrations or by changes in catchment loading. For additional context, we also examined trends in coastal (14–20 m) and offshore (> 50 m) nutrients using Environment Canada epilimnetic surveillance data, 1975–2008. Significant declines in TP and SRP concentrations have occurred in north coast waters, concurrent with declines in the offshore. However, nutrient concentrations, notably spring SRP, have not decreased among south coast stations, potentially reflecting greater coastal entrapment of catchment-derived waters. We infer that EC-monitored north coast stations reflect integrated interannual water quality, while south coast stations are more strongly influenced by catchment loading. The effects of higher nutrient concentrations along the south coast, which co-occur with lower water transparency, on benthic algal growth have yet to be determined.     

Spatial and temporal variation in the distribution of burrowing mayfly nymphs (Ephemeroptera: Hexagenia limbata and H. rigida) in western Lake Erie

In the early 1990s, burrowing mayfly species reappeared in sediments of the western basin of Lake Erie after an absence of over 30 years due to episodic hypoxia at the sediment–water interface. Long-term monitoring of adult mayflies at shoreline areas had revealed that Hexagenia rigida was more abundant than Hexagenia limbata during the initial recolonization period, but was gradually replaced by H. limbata. We hypothesized that this shift in dominance would be confirmed by the distribution and abundance of nymphs. We identified nymphs collected each spring throughout western Lake Erie from 1997 to 2004. The relative abundances of H. rigida and H. limbata nymphs exhibited the same temporal sequence as adults. Furthermore, the number of sites in the western basin in which H. rigida occurred decreased as the occurrence frequency of H. limbata increased. H. limbata were dominant in the basin by 2004. Hexagenia limbata nymphs persisted in the center-most part of the basin, whereas H. rigida did not, possibly due to differences in tolerance to hypoxia. There were no significant differences in body size between the two populations. Differences in dispersal distance from source populations and the timing and success of egg hatching likely accounted for the initial colonizing success of H. rigida, but the differential ability of H. limbata eggs to overwinter in sediments and possible tolerance of nymphs to hypoxia has possibly led to its current dominance in the western basin.     

Effect of Fasting under Different Temperature Conditions on Nucleic Acid Ratios in the Opossum Shrimp Mysis relicta: a Calibration Approach

The opossum shrimp Mysis relicta is an important component of the diet of benthivorous and planktivorous fish in the Great Lakes. The invasion of the Great Lakes by exotic invertebrates (Bythotrephes longimanus, Cercopagis pengoi, Dreissena polymorpha, and D. bugensis) has altered the base and intermediate levels of the foodweb. Thus, information about the condition of M. relicta may reveal the extent of indirect effects of these changes on this trophically-important invertebrate. Biochemical indices based on nucleic acid ratios have been shown to be suitable proxies for the growth and condition of aquatic organisms. These indices are affected by multiple factors, such as; food level, temperature, body size, sex/life stage, maturation, and moult stage and need to be calibrated before field data can be interpreted on a quantitative basis. In this study, we investigated the effect of fasting under different temperature conditions on the nucleic acid ratios RNA/DNA, RNA/protein and protein/DNA in M. relicta. Juvenile M. relicta were exposed to fasting conditions for 11 and 21 d in two controlled laboratory experiments at 3°C and 8°C. Several effects of time and temperature on the condition indices of fasting M. relicta were observed; however, we concluded that, of the various metrics tested, only RNA/DNA ratios provide a suitable index of metabolism and condition in fasting animals. RNA concentrations declined in response to fasting on the order of 3–4 d at 8°C and between 4 and 11 d at 3°C. Juvenile M. relicta with RNA/DNA ratios < 1.5–1.8 were clearly identified as fasting animals. Field-caught animals having RNA/DNA ratios near these levels are demonstrating clear signs of metabolic stress.     

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns (Sterna hirundo) and Caspian terns (Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (− 19.1%) and colony sites (− 23.2%) between the first and third censuses. An increase in numbers at US sites (+ 26.6%) did not compensate for losses (− 33.1%) at Canadian sites. Caspian terns increased in nest numbers (+ 65.9%) and colony sites (+ 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.     

Seasonal abundance,community composition,and silica content of diatoms epiphytic on Cladophora glomerata

The establishment of dreissenid mussels in the Great Lakes has been implicated in causing a resurgence of benthic macroalgae, notably Cladophora glomerata (L.) Kützing. The seasonal proliferation and nutrient retention of epiphyton on Cladophora may be important to littoral zone processes. In this study, peak diatom epiphyte density (601 diatoms μg^− 1 dry mass) co-occurred with peak Cladophora biomass. The exceptionally adhesive Cocconeis pediculus came to dominate the epiphyton to the near exclusion of all other diatoms by early summer, indicating powerful constraints on the epiphyte assemblage. There was a strong relationship between epiphytic silica content and epiphyte abundance, but the relationship was different between seasons. In the spring and fall when Cladophora was growing vigorously, silica content of the diatom epiphytes was 20.1–25.6 pmol Si diatom^− 1. In the summer, during Cladophora senescence, silica content was 6.5–10.0 pmol Si diatom^− 1 and valves were visibly thinner. These observations suggest that diatom epiphytes may be limited by Si during peak Cladophora biomass. Areal estimates of silica content of Cladophora epiphyton was strongly related with Cladophora biomass: at 2 m depth, silica content increased from 22.7 mmol Si m^− 2 in the spring to 490 mmol Si m^− 2 during peak Cladophora biomass. Silica content can be a valuable proxy for diatom epiphyte abundance if the vitality of the Cladophora substrate is considered. Future work needs to assess the seasonality of pelagic versus benthic silica demand and the interannual variability of epiphyte silica content to assess how changes in Cladophora biomass may affect nearshore Si cycling.     

Laboratory-derived temperature preference and effect on the feeding rate and survival of juvenile Hemimysis anomala

Hemimysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile Hemimysis, using individuals acclimated to mid (16 °C) and upper (22 °C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0 °C (SE 0.25) when acclimated to 16 and 21.9 °C (SE 0.38) when acclimated to 22 °C, with the σ-values of the curves at 2.6 and 2.5 °C, respectively. No mysids were observed in temperatures below 10 or above 28 °C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32 °C, all mysids died within 8 h at 30.2 °C for 16 °C acclimated mysids, and at 31.8 °C for 22 °C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5 °C to 19 Bosmina eaten per hour at 27 °C. The results of our experiments indicate an optimal temperature for Hemimysis between 21 and 27 °C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.     

Assessment of Microcystis growth rate potential and nutrient status across a trophic gradient in western Lake Erie

Plankton tow samples collected from 2002 through 2009 indicate that Microcystis biovolume in western Lake Erie is often most dense in transition zone (TZ) waters between Maumee Bay and the center of the western basin. TZ waters are generally high in nutrients and turbidity, and concentrations of each decrease with distance from Maumee Bay. High Microcystis biovolume in the TZ suggests the possibility that the conditions in these waters support a greater Microcystis growth rate relative to the open lake. To test this hypothesis, during the 2008 bloom, Microcystis was collected from western Lake Erie for measurements of total protein content (TPC) as an indicator of growth rate potential and cellular nutrient content to indicate nutrient deficiencies. TPC results indicate that Microcystis in the TZ had a higher potential growth rate compared to offshore waters. TPC values in Maumee Bay were intermediate but not significantly different from the TZ and offshore. Nitrogen content of Microcystis remained high over the summer at all sites, despite very low dissolved nitrate concentrations and low total nitrogen-to-total phosphorus ratio in late summer in the lake. Ammonium level in the lake was constant during the summer, and likely provided the nitrogen source for Microcystis. Cellular phosphorus content varied between site and sample date suggesting that Microcystis was moderately phosphorus deficient. Quotas of micronutrient indicated that Microcystis was not deficient of micronutrients. Results of this study suggest the waters in and adjacent to Maumee Bay provide more favorable growth conditions for Microcystis than offshore waters.     

The establishment of the nuisance cyanobacteria Lyngbya wollei in Lake St. Clair and its potential to harbor fecal indicator bacteria

Lyngbya wollei is a filamentous cyanobacterium which forms large nuisance mats and has infested eastern and southeastern U.S. Lakes and reservoirs for over 100 years. Lyngbya was recently identified in the Great Lakes system in the St. Lawrence River, and Western Lake Erie. Here we report on large deposits of L. wollei washing onshore at a popular recreational beach in Lake Saint Clair, part of the Great Lakes system. The amount of L. wollei deposited on shore was quantified and evaluated for the presence of fecal indicator bacteria (FIB). High concentrations of Escherichia coli, enterococci and Clostridium perfringens were found in the L. wollei in nearshore waters. The densities of E. coli (MPN), enterococci (MPN) and C. perfringens (CFU) attached to L. wollei averaged 3.5, 3.2 and 3.2 log/g, respectively. In contrast, nearshore waters contained nearly 10 times less FIB, averaging 2.6, 2.4 and 2.6 log/100 ml of E. coli (MPN), enterococci (MPN) and C. perfringens (CFU), respectively. DNA fingerprint analysis was used to examine the population structure of E. coli isolates obtained from L. wollei mats. The L. wollei-borne E. coli strains were genetically diverse, suggesting a causal relationship between E. coli and L. wollei. Results from this study indicate that in addition to the macroalga such as Cladophora, cyanobacteria like L. wollei also harbor FIB, potentially impacting water quality and human health in the Great Lakes.     

Development and Evaluation of a New Predictive Model for Metamorphosis of Great Lakes Larval Sea Lamprey (Petromyzon marinus) Populations

Accurate forecasts of the number of larval sea lamprey (Petromyzon marinus) within a stream that will enter into metamorphosis are critical to currently used methods for allocating lampricide treatments among streams in the Great Lakes basin. To improve our ability to predict metamorphosis we used a mark-recapture technique, involving the marking of individual larval lamprey with sequentially coded wire tags, to combine information regarding individual and stream level parameters collected in year t, with direct observations of metamorphic outcome of lamprey recaptured in year t+1. We used these data to fit predictive models of metamorphosis. The best model demonstrated excellent predictive capabilities and highlighted the importance of weight, age, larval density, stream temperature and geographic location in determining when individual lamprey are likely to transform. While this model was informative, it required data whose measures are not practical to obtain routinely during the larval sea lamprey assessment program. A second model, limited to data inputs that can be easily obtained, was developed and included length of larvae the fall prior to metamorphosis, stream latitude and longitude, drainage area, average larval density in type-2 habitat, and stream lamprey production category (a measure of the regularity with which treatments are required). This model accurately predicted metamorphosis 20% more often than current models of metamorphosis; however, we recommend further validation on an independent set of streams before adoption by the Great Lakes Fishery Commission for ranking streams.     

Prey size selection and feeding ecology of an omnivorous invader: Hemimysis anomala

We studied the feeding ecology of the Ponto-Caspian mysid Hemimysis anomala, a recent invader to the Great Lakes that is expanding to other bodies of water. Experimentally we found that H. anomala's prey consumption rates were affected by prey size and by illumination. Juvenile H. anomala fed at similar rates under soft light and darkness, while adults fed more in complete darkness, indicating reliance on different prey-receptors. Small prey was preferred by juvenile and medium-size H. anomala, but large H. anomala also exploited larger prey sizes. Juveniles also consumed a large proportion of algae, but they became more carnivorous as size increased indicating an ontogenetic diet shift from juvenile (4.5 mm length) to young adult (6.5 mm length). Results from field-collected (wild) H. anomala juveniles showed that they consumed similar quantities of algae and zooplankton. The juvenile δ¹³C corresponded to pelagic algae consumption; however, larger wild H. anomala had enriched δ¹³C from benthic algae, indicating different habitat utilization than juveniles. The δ¹⁵N for the largest wild H. anomala collected was 1‰ above that of juveniles, pointing to an increased reliance on animal food with size. Wild H. anomala also fed on large amounts of detrital material, possibly deriving a nutritional benefit from them. H. anomala is an adaptable organism capable of exploiting pelagic and benthic regions of the littoral zones of lakes. H. anomala's preference for small prey puts it in competition with larval fish and could potentially impact both upper and lower trophic levels.     

The invasion of a large lake by the Eurasian genotype of common reed: The influence of roads and residential construction

The Eurasian genotype of common reed (Phragmites australis) is one of the most aggressive plant invading North American wetlands. There is, however, little published evidence on establishment patterns of populations along lakes of the St. Lawrence River–Great Lakes watershed. We tested the hypothesis that the recent invasion of Great Lake Saint-François (Québec, Canada) by common reed was facilitated by a dense road system and by an intense residence construction activity along lakeshores. A total of 345 and 2914 reed stands were mapped along lakeshores, and along the road system of the study area, respectively. The probability of finding a reed stand on a lakeshore increases with the proximity of the lake's outlet, and of a paved road, but decreases with the proximity of a residence built since 1990. It is likely that common reed first spread along the road system, and that wind dispersal of seeds then favored the establishment of populations on lakeshores. Our model does not support the hypothesis that residential construction facilitated the establishment of reed stands, probably because the recent residential construction boom occurred essentially in the southern part of the lake, where the number of roadside reed populations is much lower than in the northern part (lower seed rain). The invasion of Great Lake Saint-François shows that the spread of the plant is not restricted to major river or road systems. Large or small lakes, if submitted to intense diaspore pressure, can also be at risk.     

Burrowing mayfly (Ephemeroptera: Ephemeridae: Hexagenia spp.) bioturbation and bioirrigation: A source of internal phosphorus loading in Lake Erie

Traditional lake eutrophication models predict lower phosphorus concentrations with decreased external loads. However, in lakes where decreased external phosphorus loads are accompanied by increasing phosphorus concentrations, a seeming “trophic paradox” exists. Western Lake Erie is an example of such a paradox. Internal phosphorus loads may help explain this paradox. We examined bioturbation and bioirrigation created from burrowing mayfly, Hexagenia spp., as a possible source of internal phosphorus loading. Phosphorus concentrations of experimental microcosms containing lake sediments, filtered lake water, and nymphs (417/m²) collected from western Lake Erie were compared to control microcosms containing sediments and lake water over a 7-day period. Phosphorus concentrations in microcosms containing Hexagenia were significantly greater than microcosms without nymphs. Further, we estimate the soluble reactive phosphorus flux from the sediments due to Hexagenia is 1.03 mg/m²/day. Thus, Hexagenia are a source of internal phosphorus loading. High densities of Hexagenia nymphs in western Lake Erie may help explain the “trophic paradox.” Furthermore, Hexagenia may be a neglected source of internal phosphorus loading in any lake in which they are abundant. Future studies of phosphorus dynamics in lakes with Hexagenia must account for the ability of these organisms to increase lake internal phosphorus loading.