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.     

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.     

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.     

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.     

Revisiting the Great Lakes Water Quality Agreement phosphorus targets and predicting the trophic status of Lake Michigan

LM3-Eutro is a high-resolution eutrophication model with several improved features lacking in historical Great Lakes models. We calibrated LM3-Eutro using a 2-year (1994-1995) dataset and performed a hindcast simulation from 1976 to 1995 to evaluate the model's ability to make predictions over an extended period of time. Results show a reasonable agreement between model output and field data over this time period. The model predicted that an annual loading of 5600 metric tons (MT) would result in a lake-wide annual total phosphorus (TP) concentration of 7.5 μg L^− 1. Using best estimates of future TP loadings, LM3-Eutro forecasts suggest that Lake Michigan will remain oligotrophic and will continue to meet the 7 μg L^− 1 spring TP concentration Great Lakes Water Quality Agreement objective.     

Distribution and abundance of freshwater polychaetes, Manayunkia speciosa (Polychaeta), in the Great Lakes with a 70-year case history for western Lake Erie

Manayunkia speciosa has been a taxonomic curiosity for 150 years with little interest until 1977 when it was identified as an intermediate host of a fish parasite (Ceratomyxa shasta) responsible for fish mortalities (e.g., chinook salmon). Manayunkia was first reported in the Great Lakes in 1929. Since its discovery, the taxon has been reported in 50% (20 of 40 studies) of benthos studies published between 1960 and 2007. When found, Manayunkia comprised < 1% of benthos in 70% of examined studies. In one extensive study, Manayunkia occurred in only 26% of 378 sampled events (1991–2009). The taxon was found at higher densities in one area of Lake Erie (mean = 3658/m²) and Georgian Bay (1790/m²) than in five other areas (mean = 60 to 553/m²) of the lakes. A 70-year history of Manayunkia in western Lake Erie indicates it was not found in 1930, was most abundant in 1961 (mean = 8039, maximum = 67,748/m²), and decreased in successive periods of 1982 (3529, 49,639/m²), 1993 (1876, 25,332/m²), and 2003 (79, 2583/m²). It occurred at 48% of stations in 1961, 58% in 1982, 52% in 1993, and 6% of stations in 2003. In all years, Manayunkia was distributed primarily near the mouth of the Detroit River. Causes for declines in distribution and abundance are unknown, but may be related to pollution-abatement programs that began in the 1970s, and invasion of dreissenid mussels in the late-1980s which contributed to de-eutrophication of western Lake Erie. At present, importance of the long-term decline of Manayunkia in Lake Erie is unknown.     

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.     

Trends in Diporeia populations across the Laurentian Great Lakes, 1997-2009

Benthic communities in the Laurentian Great Lakes have been in a state of flux since the arrival of dreissenid mussels, with the most dramatic changes occurring in population densities of the amphipod Diporeia. In response, the US EPA initiated an annual benthic macroinvertebrate monitoring program on all five Great Lakes in 1997. Although historically the dominant benthic invertebrate in all the lakes, no Diporeia have been found in Lake Erie during the first 13 years of our study, confirming that Diporeia is now effectively absent from that lake. Populations have almost entirely disappeared from our shallow (< 90 m) sites in lakes Ontario, Huron, and Michigan. In Lake Ontario, three of our four deep (> 90 m) sites still supported Diporeia populations in 2009, with densities at those sites ranging between 96 and 198/m². In Lake Michigan, populations were still found at six of our seven deep sites in 2009, with densities ranging from 57 to 1409/m². Densities of Diporeia in 2009 at the four deep sites in Lake Huron were somewhat lower than those in Lake Michigan, ranging from 191 to 720/m². Interannual changes in population size in Lake Huron and Lake Michigan have shown a degree of synchrony across most sites, with periods of rapid decline (1997-2000, 2003-2004) alternating with periods of little change or even increase (2001-2002, 2005-2009). There has been no evidence of directional trends at any sites in Lake Superior, although substantial interannual variability was seen.     

Escherichia coli toxin and attachment genes in sand at Great Lakes recreational beaches

The United States Environmental Protection Agency recommends density thresholds for the fecal indicator organism Escherichia coli in order to ensure the safety of recreational waters. A number of studies published over the past ten years indicate that E. coli is encountered frequently in sand at recreational beaches. While a majority of the sand-associated E. coli may be commensal or environmental strains, the potential for pathogenic strains of E. coli to be present exists. Therefore, the aim of this study was to assess the presence of attachment and virulence genes associated with enteropathogenic and enterohemorrhagic strains of E. coli (EPEC and EHEC) in populations of E. coli recovered from swash zone sand from seven recreational beaches along Lake Huron and Lake St. Clair in eastern Michigan, USA. Genes coding for attachment proteins in EPEC and EHEC were very prevalent in sand E. coli, but genes coding for toxin genes were uncommon. The paucity of genes associated with E. coli toxins suggests that the EPEC and EHEC pathotypes are not common in sand; however, the high prevalence of genes associated with attachment in E. coli pathotypes suggests that these genes are being retained within the beach sand E. coli population.     

Coexistence of the native benthic amphipod Diporeia spp. and exotic dreissenid mussels in the New York Finger Lakes

Populations of the benthic amphipod Diporeia spp. have sharply declined since the early 1990s in all North America's Great Lakes except Lake Superior. The onset and continued decline coincides with the invasion of these lakes by zebra (Dreissena polymorpha) and quagga (Dreissena rostriformis bugensis) mussels and the spread of quagga mussels to deep habitats. The six deepest Finger Lakes of central New York (Seneca, Cayuga, Skaneateles, Canandaigua, Keuka, and Owasco) have historically been Diporeia habitat and have had dreissenids for more than a decade. These lakes represent a wide range of trophic state, maximum depth, and dreissenid invasion history. We hypothesized that Diporeia abundance would be negatively impacted by dreissenid mussel expansion in the Finger Lakes. During 2006–2010, we sampled Diporeia and mussel populations in these six lakes. Diporeia was present in all six lakes, and was abundant (2000/m²) in Owasco Lake that has only zebra mussels and in Cayuga and Seneca Lakes that have had zebra and quagga mussels since 1994. Diporeia abundance was lowest (1000/m²) in Skaneateles, Canandaigua, and Keuka Lakes where quagga mussels have recently expanded. Productivity indicators explained much of the variability of Diporeia abundance. The persistence of Diporeia with quagga mussels in these lakes may be because of available alternative food resources. Fatty acid tracers indicate that Diporeia from Owasco Lake, the lake without quagga mussels, utilize diatoms, but Diporeia from Cayuga Lake that coexist with abundant quagga mussels also use food resources associated with terrestrial detritus that cannot be intercepted by dreissenids.     

Genetic Analysis of the Chinese Mitten Crab (Eriocheir sinensis) Introduced to the North American Great Lakes and St. Lawrence Seaway

The Chinese mitten crab (Eriocheir sinensis) is an invasive organism of concern, with established non-native populations in Europe and California, USA. The species is thought to pose a risk to other North American waterways, including the Great Lakes and St. Lawrence Seaway. Since 1965, there have been sixteen confirmed adult E. sinensis caught in the North American Great Lakes or adjoining waterways. Analysis of their mitochondrial DNA sequence variation for part of the cytochrome c oxidase subunit I gene discerned three haplotypes among seven individuals (caught between 1973 and 2005), identical to common haplotypes in Europe. Analysis of mitochondrial haplotype frequencies and shipping patterns suggests that E. sinensis has been introduced to the Great Lakes from Europe, although we are unable to preclude native Asian populations as putative sources. The species is catadromous, migrating between salt and fresh water to complete its life cycle. This trait makes it unlikely that E. sinensis will establish a breeding population in the Great Lakes proper, which are separated from saltwater by a considerable distance and significant instream barriers such as waterfalls and navigation locks. However, the recent discovery of two confirmed mitten crabs in the St. Lawrence River, which could be more readily colonized, underscores the risk posed by the repeated introduction of this species into the Great Lakes and St. Lawrence Seaway.     

Polymethylene-interrupted fatty acids: Biomarkers for native and exotic mussels in the Laurentian Great Lakes

Freshwater organisms synthesize a wide variety of fatty acids (FAs); however, the ability to synthesize and/or subsequently modify a particular FA is not universal, making it possible to use certain FAs as biomarkers. Herein we document the occurrence of unusual FAs (polymethylene-interrupted fatty acids; PMI-FAs) in select freshwater organisms in the Laurentian Great Lakes. We did not detect PMI-FAs in: (a) natural seston from Lake Erie and Hamilton Harbor (Lake Ontario), (b) various species of laboratory-cultured algae including a green alga (Scenedesmus obliquus), two cyanobacteria (Aphanizomenon flos-aquae and Synechococystis sp.), two diatoms (Asterionella formosa, Diatoma elongatum) and a chrysophyte (Dinobryon cylindricum) or, (c) zooplankton (Daphnia spp., calanoid or cyclopoid copepods) from Lake Ontario, suggesting that PMI-FAs are not substantively incorporated into consumers at the phytoplankton-zooplankton interface. However, these unusual FAs comprised 4-6% of total fatty acids (on a dry tissue weight basis) of native fat mucket (Lampsilis siliquoidea) and plain pocketbook (L. cardium) mussels and in invasive zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels. We were able to clearly partition Great Lakes' mussels into three separate groups (zebra, quagga, and native mussels) based solely on their PMI-FA profiles. We also provide evidence for the trophic transfer of PMI-FAs from mussels to various fishes in Lakes Ontario and Michigan, further underlining the potential usefulness of PMI-FAs for tracking the dietary contribution of mollusks in food web and contaminant-fate studies.     

Historical changes and current status of crayfish diversity and distribution in the Laurentian Great Lakes

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although O. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. O. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions.     

Dominant glacial landforms of the lower Great Lakes region exhibit different soil phosphorus chemistry and potential risk for phosphorus loss

Phosphorus (P) losses from agricultural soils are a growing economic and water-quality concern in the Lake Erie watershed. While recent studies have explored edge-of-field and watershed P losses related to land-use and agricultural management, the potential for soils developed from contrasting parent materials to retain or release P to runoff has not been examined. A field-based study comparing eight agricultural fields in contrasting glacial landscapes (hummocky coarse-textured till-plain, lacustrine and fine-textured till-plain) showed distinct physical and geochemical soil properties influencing inorganic P (P_i) partitioning throughout the soil profile between the two regions. Fields located on the coarse-textured till-plain in mid-western Ontario, Canada had alkaline calcareous soils with the highest Total-P_i concentrations and the majority of soil P_i stored in an acid-soluble pool (up to 91%). In contrast, loosely to moderately soluble P_i concentrations were higher in soils of the lacustrine and fine-textured till-plain in southwestern Ontario, northeast Indiana and northwestern Ohio, US. Overall, soils on the lacustrine and fine-textured till-plain had a greater shrink swell-capacity, likely creating preferential flow to minimize P_i interaction with the more acidic, lower carbonate and lower sorption capacity soils. These differences in soil P_i retention and transport pathways demonstrate that in addition to management, the natural landscape may exert a significant control on how P_i is mobilized throughout the Lake Erie watershed. Further, results indicate that careful consideration of region-specific hydrology and soil biogeochemistry may be required when designing appropriate management strategies to minimize P_i losses across the lower Great Lakes region.     

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.     

The Zebra Mussel Dreissena polymorpha Found in North America in 1986 and 1987

The zebra mussel Dreissena polymorpha was first detected in the western basin of Lake Erie, Ontario, Canada, on natural gas wellheads and well markers between April and November 1986. It was found again in 1987 on the north shore of Lake Erie in a water treatment plant, and in vessel fouling. The population increased in Lake Erie in 1988. Dreissena may have spread from Lake Erie to Lake St. Clair, where it was then discovered on 1 June 1988.     

Lyngbya wollei in western Lake Erie

We report on the emergence of the potentially toxic filamentous cyanobacterium, Lyngbya wollei as a nuisance species in western Lake Erie. The first indication of heavy L. wollei growth along the lake bottom occurred in September 2006, when a storm deposited large mats of L. wollei in coves along the south shore of Maumee Bay. These mats remained intact over winter and new growth was observed along the margins in April 2007. Mats ranged in thickness from 0.2 to 1.2 m and we estimated that one 100-m stretch of shoreline along the southern shore of Maumee Bay was covered with approximately 200 metric tons of L. wollei. Nearshore surveys conducted in July 2008 revealed greatest benthic L. wollei biomass (591 g/m² ± 361 g/m² fresh weight) in Maumee Bay at depth contours between 1.5 and 3.5 m corresponding to benthic irradiance of approximately 4.0–0.05% of surface irradiance and sand/crushed dreissenid mussel shell-type substrate. A shoreline survey indicated a generally decreasing prevalence of shoreline L. wollei mats with distance from Maumee Bay. Surveys of nearshore benthic areas outside of Maumee Bay revealed substantial L. wollei beds north along the Michigan shoreline, but very little L wollei growth to the east along the Ohio shoreline.     

Occurrence of the Great Lake's most recent invader, Hemimysis anomala, in the diet of fishes in southeastern Lake Ontario

The Ponto-Caspian mysid, Hemimysis anomala, was first observed in southeastern Lake Ontario in May 2006. During July and August 2007, gill nets were fished in 6 to 8 m of water at two locations of known Hemimysis colonization in southeastern Lake Ontario to determine if fish that consume macroinvertebrates were beginning to include this new invasive mysid in their diets. Of nine fish species captured in August, September, and October 2007, three species had consumed Hemimysis: alewife (Alosa pseudoharengus), rock bass (Ambloplites rupestris), and yellow perch (Perca flavescens); and six species had not: round goby Apollonia melanostoma, smallmouth bass Micropterus dolomieu, spottail shiner Notropis hudsonius, gizzard shad Dorosoma cepedianum, white perch Morone americana and log perch Percina caprodes. Diets of alewives from all samples were composed predominantly of Hemimysis (69.6% -100% frequency of occurrence, 46.0%–74.5% dry weight diet composition). Two of 6 rock bass stomachs sampled in August contained ≥ 98.9% Hemimysis (10 and 40 individuals each) and one of 61 yellow perch stomachs sampled in September contained 10.0% Hemimysis (6 individuals) and 90.0% fish. While Hemimysis were observed only sparsely in the diet of most nearshore fish, their predominance in alewife diets and their omnivorous feeding behavior indicated that they have the potential to alter energy flow in Great Lakes' foodwebs.     

Predicted Atrazine Concentrations in the Great Lakes: Implications for Biological Effects

Atrazine is an herbicide used extensively throughout the Midwest corn belt, including the agricultural regions within the Great Lakes basin watershed. Measurements of atrazine concentrations in the Great Lakes are few, however, so knowledge of its current concentrations, persistence, and trends in this ecosystem is limited. A dynamic annual time step model was used to predict atrazine concentrations over time in the Great Lakes based on varied atrazine loading rates to the lakes (“most-likely” and “high” loading conditions). Four degradation scenarios were evaluated: no degradation, and atrazine degradation with half-lives of 2 years, 5 years, and 10 years. Predicted steady-state concentrations for all of the scenarios and all the Great Lakes ranged from 0.0024 to 0.88 μg/L. The number of years until steady-state conditions were achieved ranged from 4 to over 400 years. The most-likely loading rate and two-year half-life scenario had the lowest concentrations (0.0024 to 0.13 μg/L) and the fewest years (4 to 13 years) to achieve steady-state conditions. Available monitored atrazine concentrations in the Great Lakes are very similar to the most-likely loading rate and 2-year half-life scenario predicted values. Monitored and predicted concentrations in the Great Lakes indicate atrazine does not currently pose a toxicological risk to humans or aquatic organisms, and under current and expected lower loading rates should remain well below criteria values.