Measurement of Diporeia respiration rate for Lake Superior

The freshwater amphipod Diporeia is a dominant macroinvertebrate species in Lake Superior’s benthic community and an important prey item for many fish. A capacity to predict growth and production rates of Diporeia using a bioenergetics model requires information on physiological processes of the species. The objective of this study is to quantify oxygen consumption of Lake Superior Diporeia and to determine if respiration rate changes with body length. Diporeia were collected from Lake Superior and kept over natural sediment maintained at 4 °C. Dissolved oxygen levels for groups of immature (2 mm), juvenile (4 mm), and adult (6 mm) Diporeia in 20 ml microcosms were measured using a polarographic microelectrode. Mass-specific respiration rates for Lake Superior Diporeia ranged from 32.0 to 44.7 mg O₂ g DW^− 1 day ⁻¹. A significant relationship between body length and mass-specific respiration rate (p > 0.1) was not found. The estimate of Diporeia respiration presented here is significantly higher (p < 0.05) than previous findings from populations in Lakes Michigan and Ontario. This study provides new data on respiration rates of Lake Superior Diporeia and compares findings to studies for other connecting Great Lakes.     

Precision of Ages Determined from Scales and Opercles for Yellow Perch Perca flavescens

Scales and opercles were used to age yellow perch Perca flavescens collected in 1989 from Lake Madison (South Dakota), Dauphin Lake (Manitoba), and southern Lake Michigan (Indiana). Three readers aged fish from Lake Madison and Dauphin Lake once and two readers aged fish from Lake Michigan twice. The coefficient of variation (CV) was calculated to compare precision. Ages determined from opercles were as precise as those from scales for fish from Lake Madison (CV = 0 for both structures), and more precise than ages from scales for fish from Dauphin Lake (CV_opercle = 14.0, CV_scale = 27.4, p < 0.001) and Lake Michigan (CV _opercle = 10.6, CV_scale = 13.9, p < 0.001). The high precision of scale and opercle ages for yellow perch from Lake Madison can be attributed to the fast growth rate of fish from that lake and also that only age 1 and 2 fish were aged. The greater precision of opercle ages in comparison to scale ages for Dauphin Lake and Lake Michigan yellow perch can be attributed to ease of recognition of false annuli on opercles as well as to difficulty in distinguishing between false and true annuli crowded on the edge of scales from mature, slower growing fish. Because true annuli are more easily recognized on opercles, ages determined from opercles may be more accurate than ages determined from scales for yellow perch growing at slow or moderate rates.     

Effect of the urbanized embayment Toronto Harbour on the composition and production of zooplankton

To better understand zooplankton dynamics in Lake Ontario’s Toronto Harbour and adjacent coastal area (CA), we sampled zooplankton, phytoplankton, nutrients and physical parameters on six dates in 2016. Despite higher levels of nutrients, chlorophyll and primary production in the inner harbor (IH), the areas supported similar May to November zooplankton biomass (IH = 32 ± 7 and CA = 42 ± 10 mg/m³). IH values were much lower than other nutrient-enriched embayments in Lake Ontario, yet CA biomass was twice that of nearshore sites away from Toronto. Small zooplankton such as rotifers and Bosmina dominated IH; and large taxa (Daphnia, calanoids and predatory cladocerans) were more important in the CA. Daphnia, Bosmina, cyclopoids and calanoids were larger in the CA, and adult cyclopoids had higher egg ratios. This led to low annual IH production estimates for both cyclopoid and calanoid copepods. Total phosphorus and chlorophyll did not appear to regulate zooplankton biomass, but positive relationships were found with bacterial biomass in the IH and with temperature in the cool season. Atypically high fish planktivory rates likely suppressed larger IH zooplankton in 2016, allowing small, resilient Bosmina to flourish and contribute 84% of total production in the IH. Comparing 2016 data to previous zooplankton surveys revealed considerable inter-annual variation in proportions of Daphnia, Bosmina and predatory cladocerans over the 1994 to 2016 period, and the strong top-down controls observed in 2016 were not typical. Elevated microbial production may serve as an important alternate trophic pathway supporting cladoceran populations in Toronto Harbour.     

Enterococcus phages as potential tool for identifying sewage inputs in the Great Lakes region

Bacteriophages are viruses living in bacteria that can be used as a tool to detect fecal contamination in surface waters around the world. However, the lack of a universal host strain makes them unsuitable for tracking fecal sources. We evaluated the suitability of two newly isolated Enterococcus host strains (ENT-49 and ENT-55) capable for identifying sewage contamination in impacted waters by targeting phages specific to these hosts. Both host strains were isolated from wastewater samples and identified as E. faecium by 16S rRNA gene sequencing. Occurrence of Enterococcus phages was evaluated in sewage samples (n = 15) from five wastewater treatment plants and in fecal samples from twenty-two species of wild and domesticated animals (individual samples; n = 22). Levels of Enterococcus phages, F + coliphages, Escherichia coli and enterococci were examined from four rivers, four beaches, and three harbors. Enterococcus phages enumeration was at similar levels (Mean = 6.72 Log PFU/100 mL) to F + coliphages in all wastewater samples, but were absent from all non-human fecal sources tested. The phages infecting Enterococcus spp. and F + coliphages were not detected in the river samples (detection threshold < 10 PFU/100 mL), but were present in the beach and harbor samples (range = 1.83 to 2.86 Log PFU/100 mL). Slightly higher concentrations (range = 3.22 to 3.69 Log MPN/100 mL) of E. coli and enterococci when compared to F + coliphages and Enterococcus phages, were observed in the river, beach and harbor samples. Our findings suggest that the bacteriophages associated with these particular Enterococcus host strains offer potentially sensitive and human-source specific indicators of enteric pathogen risk.     

Diets of Siscowet Lake Trout from the Apostle Islands Region of Lake Superior, 1993

Stomach contents of 384 siscowet lake trout (Salvelinus namaycush siscowet) from the Apostle Islands region of Lake Superior were examined to determine if diets exhibited seasonal trends or shifted with predator size. The information was also used to qualitatively compare siscowet and lean lake trout (S. namaycush) diets. Stomachs from siscowet less than 500-mm total length (TL) contained primarily macroinvertebrates (clams, Mysis relicta, and insects), sculpins (Cottidae; mean TL = 45 mm), and coregonines (Coregonus spp.; mean TL = 120 mm). Stomachs from siscowet between 500- and 699-mm TL contained items similar to smaller siscowet, but burbot (Lota lota; mean TL = 162 mm and a 254-mm siscowet were also present. Stomachs from siscowet longer than 699-mm TL contained fishes such as burbot (mean TL = 246 mm) and coregonines (mean TL = 240 mm). Dietary proportions of coregonines increased significantly with increasing siscowet length groups. The proportion of the total number of identified taxa and frequency of occurrence of terrestrial insects and sculpins declined significantly across all length groups between June and December. Siscowet and lean lake trout diets were not found to be substantially different and a potential for competition exists.     

Accumulation of Contaminant Metals in the Amphipod Diporeia spp. in Western Lake Ontario

Sediment and amphipods (Diporeia spp.) were collected in areas in western Lake Ontario suspected of containing a range of sediment metal contents. The total metal contents (Al, As, Cd, Cr, Cu, Ni, Fe, V, and Zn) of depurated Diporeia tissues were measured and compared to the total metal contents of the surrounding sediment. The fractional bioavailability of As, Cu, Fe, and Zn was determined in those same sediments using a sequential chemical extraction (SCE) procedure and correlated with depurated Diporeia tissue metal contents. Results of these analyses were then used to assess the ability of Diporeia to accumulate sediment metal contamination. A comparison of metal biota-sediment accumulation factors (BSAFs) and sediment metal enrichment factors (EFs) for each metal yielded separate metal groups showing different behavior for tissue accumulation. Aluminum, Cr, Fe, Ni, and V were not enriched in the sediments and were not accumulated in Diporeia tissues, while As, Cd, Cu, and Zn were enriched in the sediments and accumulated in Diporeia tissues. SCE results showed that Cu (3.2 to 8.4 %) and Zn (13 to 19 %) contents in the easily extractable sediment fractions (MgCl₂ and Na-acetate) were significantly correlated with Cu (r = 0.86; P<0.01) and Zn (r = 0.69; P<0.05) contents in depurated Diporeia tissue. In addition, Cu and Zn in Diporeia tissues are also correlated to the total sediment metal content for each respective metal (Cu: r = 0.67, P < 0.05; Zn: r = 0.66, P < 0.05). The high BSAFs for Cu and Zn, in combination with the association of tissue metal contents with easily extracted sediment metal fractions, suggest that Diporeia may be a potential bioindicator for Cu and Zn contamination in sediments.     

Age and growth of round gobies in Lake Michigan,with preliminary mortality estimation

The round goby (Neogobius melanostomus) is a prevalent invasive species throughout Lake Michigan, as well as other Laurentian Great Lakes, yet little information is available on spatial variation in round goby growth within one body of water. Age and growth of round goby at three areas of Lake Michigan were studied by otolith analysis from a sample of 659 specimens collected from 2008 to 2012. Total length (TL) ranged from 48 to 131 mm for Sturgeon Bay, from 50 to 125 mm for Waukegan, and from 54 to 129 mm for Sleeping Bear Dunes. Ages ranged from 2 to 7 years for Sturgeon Bay, from 2 to 5 years for Waukegan, and from 2 to 6 years for Sleeping Bear Dunes. Area-specific and sex-specific body–otolith relationships were used to back-calculate estimates of total length at age, which were fitted to von Bertalanffy models to estimate growth rates. For both sexes, round gobies at Sleeping Bear Dunes and Waukegan grew significantly faster than those at Sturgeon Bay. However, round goby growth did not significantly differ between Sleeping Bear Dunes and Waukegan for either sex. At all three areas of Lake Michigan, males grew significantly faster than females. Based on catch curve analysis, estimates of annual mortality rates ranged from 0.79 to 0.84. These relatively high mortality rates suggested that round gobies may be under predatory control in Lake Michigan.     

Estimation of Zooplankton Mean Length for Use in an Index of Fish Community Structure and its Application to Lake Erie

Mills et al. (1987) developed an index of zooplankton mean size to assess the state of fish communities. The use of this index was evaluated in an assessment of the fish community structure in 1993 at nearshore and offshore sites in the three Lake Erie basins. Mills et al.’s index was developed using a 153-μm mesh net, while the samples in this study have been collected with 64-μm and 110-μm mesh size nets. Two methods were used to convert the data to 153-μm equivalent collections: (a) regression relationships based on simultaneous collections with three mesh sizes, and (b) elimination of smaller organisms that would have passed through the 153-μm mesh by determining the minimum length of inclusion (MLI). The regressions employed for the conversion of zooplankton mean length (ZML) between the nets were: ZML₁₅₃ = 0.137 + 0.988 ZML₁₁₀ (mm) (r²= 0.804) (n = 10) and ZML₁₅₃ = 0.042 + 1.330 ZML₆₄ (mm) (r² = 0.931) (n = 9). The MLI that resulted in the same mean length as the 153-μm sample averaged (± 1 SE) 0.267 ± 0.016 mm (n =19).The comparison between zooplankton mean length and fish community structure in the western basin of Lake Erie in 1993 showed good agreement with Mills et al.’s index. However, the same was not true for the 1988 to 1990 data. Reasons for this discrepancy are discussed.     

Trends of PCB concentrations in Lake Michigan coho and chinook salmon, 1975–2010

The manufacture and use of polychlorinated biphenyls (PCBs) was banned in the United States in 1977 after it was determined that these compounds adversely affect animals and humans. The Wisconsin Department of Natural Resources has quantified total PCB concentrations in Lake Michigan chinook (n = 765) and coho (n = 393) salmon (Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) filets since 1975. We analyzed these data to estimate trends in PCB concentrations in these fish (1975–2010). We used generalized linear models with a gamma error distribution and log link fit to the untransformed concentrations. Trend patterns were examined using graphical smoothing and generalized additive models. We identified a candidate set of models that included time trend and other predictor variables. Using the Akaike Information Criterion to select among models we found the best models for both species included piecewise linear time trends, total body length, % lipid, and collection season as predictor variables. The intersection of the two trends was 1985 for chinook salmon and 1984 for coho salmon. PCB concentrations in both species increased with body length and % lipid, and were higher for individuals caught in the fall. Our data reveals a dramatic decline in PCB concentrations of − 16.7% and − 23.9% per year for chinook and coho, respectively, up until the intersection year likely reflecting implementation of restrictions on Aroclor-based PCBs. After the intersection year to 2010, PCB concentrations declined at an annual rate of − 4.0% (95% CI: − 4.4% to − 3.6%) and − 2.6% (95% CI: − 3.3% to − 1.9%) for chinook and coho, respectively.     

Feeding ecology of age-0 lake whitefish in Saginaw Bay,Lake Huron

Age-0 lake whitefish Coregonus clupeaformis (11–160 mm total length) were collected from Saginaw Bay, Lake Huron during April–November 2009 and 2010 for diet analysis and for the evaluation of ontogenetic changes in feeding ecology. Lake whitefish ≤ 50 mm ate mainly zooplankton, after which their diets switched mainly to benthic macroinvertebrates. Cyclopoida were the dominant prey consumed by very small lake whitefish (< 17 mm) and the most frequently selected zooplankton type for individual small fish. Once lake whitefish reached 18–19 mm, Cyclopoida in the diet declined and cladocerans emerged as an important diet item. Daphnia were the most common cladoceran in the diets, but for fish 31–50 mm Bosminidae were also relatively important. Although the shift to Daphnia could represent an ontogenetic point when lake whitefish were large enough to effectively handle this prey, it also took place when the relative availability of Daphnia increased. Once lake whitefish were > 50 mm, Chironomidae larvae became a dominant prey item and this shift to benthivory coincided with a 55% increase in length-adjusted energy content between June and July. However, as fish grew (around 110–120 mm), Sphaeriidae and the benthic zooplankton Chydoridae became increasingly important in the diet. As these less energetically rich prey were incorporated into the diet, there were corresponding 21 and 15% decreases in length-adjusted energy content from July to August and September, respectively.     

Systemic,early-season Microcystis blooms in western Lake Erie and two of its major agricultural tributaries (Maumee and Sandusky rivers)

Recurrent, massive cyanobacterial blooms composed mainly of the genus Microcystis indicate a broad-scale re-eutrophication of Lake Erie. In the past, ameliorating eutrophication relied on intentionally decreasing point-source tributary nutrient, especially phosphorus, loads to the lake. However, recent research has shown that tributaries load not only nutrients but also bloom-levels of phytoplankton, including Microcystis. We built on this previous work by sampling earlier in the year and in much smaller tributaries in both the Maumee and Sandusky systems. We found Microcystis wet biomasses in these tributaries averaged 3.16 mg/L (± 0.59 mg/L, one standard error of the mean) in 2009 and 3.42 mg/L (± 0.55 mg/L) in 2010. Importantly, we found Microcystis in small ditches in March, much earlier than previously observed. Microcystis biomass did not directly correspond to measured phosphorus, chlorophyll, or phycocyanin concentrations likely reflecting complexities associated with lagged physiological responses and/or non-linear growth relationships. Consequently, our findings emphasize that Microcystis blooms form a more broad-scale problem than previously documented, occurring far upstream much earlier in the year.     

Spatial and temporal distribution of the cyanotoxin microcystin-LR in the Lake Ontario ecosystem: Coastal embayments,rivers, nearshore and offshore,and upland lakes

Cyanotoxins, a group of hepatotoxins and neurotoxins produced by cyanobacteria, pose a health risk to those who use surface waters as sources for drinking water and for recreation. Little is known about the spatial and seasonal occurrence of cyanotoxins in Lake Ontario and other lakes and ponds within its watershed. Within the embayments, ponds, rivers, creeks, shoreside, and nearshore and offshore sites of Lake Ontario, microcystin-LR concentrations were low in May, increased through the summer, and reached a peak in September before decreasing in October. Considerable variability in microcystin-LR concentrations existed between and within habitat types within the Lake Ontario ecosystem. In general, the average microcystin-LR concentration was two orders of magnitude lower in embayment (mean = 0.084 μg/L), river (mean = 0.020 μg/L), and shoreside (mean = 0.052 μg/L) sites compared to upland lakes and ponds (mean = 1.136 μg/L). Concentrations in the nearshore sites (30-m depth) and offshore sites (100-m depth) were another order of magnitude lower (mean = 0.006 μg/L) than in the creek/river, bay/pond, and shoreside habitats. Only 0.3% (2 of 581) of the samples taken in Lake Ontario coastal waters exceeded the World Health Organization (WHO) Drinking Water Guideline of 1 μg microcystin/L for humans. In contrast, 20.4% (20 of 98) of the samples taken at upland lakes and ponds within the watershed of Lake Ontario exceeded WHO Guidelines. No significant relationship between nitrate and microcystin-LR concentrations was observed in Lake Ontario even though a significant positive relationship existed between phosphorus and phycocyanin and microcystin-LR concentrations. At an upland lake site (Conesus Lake) in the Ontario watershed, the development of a littoral Microcystis population was not observed despite high nutrient loading (P and N) into the nearshore zone, well-developed nearshore populations of filamentous Spirogyra and Zygnema, the occurrence of Dreissena spp., and the known occurrence of Microcystis and microcystin production in the pelagic waters of Conesus Lake.     

Temporal trends of phytoplankton and zooplankton stable isotope composition in tropical Lake Malawi

Stable isotope ratios of three seston size classes (20–100 μm, 2–20 μm, and 0.2–2 μm) and zooplankton species were analyzed to determine the plankton food web structure of Lake Malawi. Over an annual cycle, seston δ¹³C varied between ?20.41‰ and ?27.43‰ with a mean value of ?24.27‰ ± 1.2 while δ¹³C values for zooplankton fluctuated between ?22‰ and ?25‰ with a mean of ?23.84‰ ± 0.77. Seston δ¹³C fluctuations appeared to be related to changes in physical and meteorological conditions in the lake that ultimately control nutrient availability. The highest seston δ¹³C values observed during the rainy and mixed seasons likely result from high phytolankton growth rates. δ¹⁵N of plankton was temporally variable, suggesting short term changes in N cycling dynamics that control the supply of N to phytoplankton. Very low seston δ¹⁵N values recorded during the mixing season suggest excess NO₃^? availability resulting from upwelling and vertical mixing. In contrast to expectations the calanoid Tropodiaptomus cunningtoni appeared to feed at a trophic level higher than that of all other zooplankton species, including the cyclopoid, Mesocyclops aequatorialis aequatorialis. δ¹⁵N values indicate that zooplankton were nearly 2 trophic levels above seston in the early stratified season. This implies that adult zooplankton could be utilizing forms of food other than phytoplankton during this period, such as nauplii or protozoans. This extra step in the food web, and the trophic positions of large zooplankton species, may alter estimates of food web efficiency and potential fish production for Lake Malawi.     

Contaminant Concentrations and Reproductive Rate of Lake Superior Bald Eagles, 1989–2001

We investigated the trend in contaminant concentrations in Lake Superior bald eagles (Haliaeetus leucocephalus) from 1989–2001, and examined the relationship of contaminant concentrations to eagle reproductive rate during that time. Concentrations of dichloro-diphenyl-dichloroethylene (DDE) and total polychlorinated biphenyls (PCBs) in nestling blood plasma samples decreased significantly from 1989-2001 (p = 0.007 for DDE, p = 0.004 for total PCBs). Mean contaminant concentrations in eaglet plasma, 21.7 μg/kg DDE (n=51) and 86.7 μg/kg total PCBs (n = 54), were near or below the estimated threshold levels for impairment of reproduction as determined in other studies. A preliminary assessment of polybrominated diphenyl ether (PBDE) concentrations indicated a mean of 7.9 μg/kg total PBDEs in Lake Superior eaglet plasma (n = 5). The number of occupied bald eagle nests along the Wisconsin shore of Lake Superior increased from 15 to 24 per year, between 1989 and 2001 (p < 0.001, r² = 0.70, n = 13 years). Eagle reproductive rate did not increase or decrease significantly between 1989 and 2001 (p = 0.530, r² = 0.037, n = 13 years, mean productivity = 0.96 young per occupied nest). The lack of correlation between reproductive rate and contaminant concentrations, as well as the comparison of contaminant concentrations to the estimated thresholds for impairment of reproduction, suggest that DDE and PCBs no longer limit the reproductive rate of the Lake Superior eagle population in Wisconsin.     

A model for determining satellite-derived primary productivity estimates for Lake Michigan

A new MODIS based satellite algorithm to estimate primary production (PP) has been generated and evaluated for Lake Michigan. The Great Lakes Primary Productivity Model (GLPPM) is based on previous models that required extensive in situ data but it can utilize remotely sensed observations as input for some model variables and therefore allows greater spatial resolution for primary productivity estimates. The Color Producing Agent Algorithm (CPA-A) is utilized to obtain robust chlorophyll a values and the NASA KD2M approach is used to obtain the diffuse attenuation coefficient (K_d). Only incident PAR and carbon fixation rates are additionally needed to generate the primary productivity estimate. Comparisons of the satellite derived PP estimates from single monthly images to average monthly field measurements made by NOAA/GLERL found good agreement between estimates. Satellite derived PP estimates were used to estimate a preliminary Lake Michigan annual primary production of 8.5 Tg C/year. The new algorithm can be easily adapted to work on all the Great Lakes and therefore can be used to generate time series dating back to late 1997 (launch of SeaWiFs). These time series can contribute to improved assessment of Great Lakes primary productivity changes as a result of biological events, such as Dreissenid mussel invasions, climatic change and anthropogenic forcing.     

Mapping cyanobacterial blooms in Lake Champlain's Missisquoi Bay using QuickBird and MERIS satellite data

C-phycocyanin (C-PC) and chlorophyll-a (Chl-a) concentrations for the eutrophic waters of Missisquoi Bay, Lake Champlain (VT–QC) were retrieved from Envisat's MERIS radiance data (300 m spatial resolution) and validated against coincident georeferenced transect observations. Pigment concentrations were also predicted from empirically calibrated QuickBird data (2.4 m spatial resolution) using selected band ratios and principal components analysis. The QuickBird NIR/Red band ratio accounted for approximately 80% of the variability in observed Chl-a concentration, allowing for detailed mapping of phytoplankton spatial distributions. C-PC concentrations, in contrast, were somewhat poorly modeled (R² = 0.68). Use of these data for monitoring purposes, however, is also limited by the need for coincident field observations. Chl-a concentrations were also accurately retrieved from the MERIS data (Mean Relative Error = -0.6%) despite high concentrations of suspended particles and dissolved organic matter in the bay waters. C-PC concentrations were underestimated on average by 2.1%, but by 10–20% at high C-PC concentrations (≥ 80 μg/L) and as the proportion of cyanobacteria in the phytoplankton community decreased. The relatively high overall accuracies observed, however, attest to the robustness of the MERIS semi-analytical retrieval algorithms used to quantify potentially toxic cyanobacteria cell densities without the need for coincident field data. Our analyses over a 17 day period captured the peak and collapse of a late summer cyanobacterial bloom, illustrating the value of remote sensing to provide synoptic and timely information on the abundance and distribution of cyanobacterial populations that, in turn, can facilitate public health risk assessment.     

Rapid Increase and Subsequent Decline of Zebra and Quagga Mussels in Long Point Bay,Lake Erie: Possible Influence of Waterfowl Predation

Distribution and density of two introduced dreissenid species of mollusks, the zebra mussel Dreissena polymorpha and quagga mussel D. bugensis, were monitored in the Inner Bay at Long Point, Lake Erie, 1991–1995. Since populations of certain waterfowl species have been reported to alter their dietary intake and migration patterns in response to the ready availability of zebra mussels, the percent occurrence of zebra mussels in the diet of 12 duck species (552 birds) was studied concurrently, and several spring and fall aerial waterfowl surveys were flown between 1986 and 1997 (n = 75), to document changes in duck populations at Long Point. The first reproductive population of zebra mussels on the bay most likely appeared in 1990. After an initial rapid increase in density and colonization of the Inner Bay, zebra mussels began to steadily and consistently decline in absolute numbers, density per station and occupied area. Mean density per station in 1995 was 70% less than in 1991, the first year of rapid colonization, and 67% less than in 1992, the year of peak abundance in the bay (P < 0.05). Occupied area peaked in 1992, with 80% of sampling stations supporting mussels; the following 3 years showed consistent declines in the proportion of stations supporting mussels: 1993 = 75.9%, 1994 = 63.2% and 1995 = 57.1% (P < 0.05). Mussels in size class 0 to 5 mm were most abundant in 1991, 1993 and 1995, whereas those in size class 6 to 10 mm predominated in 1992 and 1994 (P < 0.05). Very few mussels over 15 mm were found. Lesser Scaup Aythya affinis (75.4 to 82.5 % occurrence), Greater Scaup A. marila (66.7 to 81.5 % occurrence), and Bufflehead Bucephala albeola (46.7 to 60 % occurrence) were the only three waterfowl species that consistently incorporated zebra mussels in their diet, and the mussel decline coincided with a substantial increase in the populations of these species at Long Point. Waterfowl days for Lesser and Greater Scaup combined increased rapidly from 38,500 in 1986 (prior to the zebra mussel colonization of Long Point) to 3.5 million in 1997 (P = 0.012). Bufflehead days increased from 4,700 to 67,000 during the same period (P = 0.001). Oligotrophication of Lake Erie, through reduced plankton and chlorophyll concentrations, has occurred since the invasion of zebra mussels, probably a result of filtering activities of introduced mussels. While a reduction in plankton availability may have contributed to the zebra mussel decline, high rates of waterfowl predation probably had the most substantial effect on mussel densities at Long Point. Waterfowl predation also probably influenced the size structure of the zebra mussel population, since waterfowl are size-selective foragers, and increased water clarity would have facilitated their ability to select preferred medium and large size classes of mussels. Quagga mussels, which were first detected in 1993, experienced a decline in both density and area occupied over the next two years. Quagga mussels rarely attached to soft substrates, and their decline is possibly related to the decline of suitable hard substrates, such as zebra mussels, as well as to predation by waterfowl.     

Development of a Bioenergetics Model for the Round Goby (Neogobius melanostomus)

The round goby (Neogobius melanostomus) was introduced into the Great Lakes in the 1990s through ballast water transfer. Gobies are potential vectors for material transfer between the benthic and pelagic zones. A bioenergetics model was developed for round gobies to enable us to quantify the flow of energy, contaminants, and nutrients from the benthos to pelagic fishes. Weight- and temperature-dependent coefficients for metabolism and consumption were derived. Food consumption increased with temperature up to 26°C before sharply decreasing, and weight-specific consumption decreased with increasing fish weight (allometric coefficient = −0.256, SE = 0.160). Specific oxygen consumption was inversely related to body mass (allometric coefficient = −0.157, SE = 0.025) and increased exponentially with temperature. Estimated Q₁₀ for respiration was 1.84. Additional parameters were obtained from the literature to describe specific dynamic action, egestion, excretion, and reproductive losses. The bioenergetics model explained growth of round gobies in Lake Erie and in their native range.     

A status assessment and review of the herpetofauna within the Saginaw Bay of Lake Huron

Amphibians and reptiles are key bioindicators of environmental health and habitat quality and can be used to provide baseline information to help assess habitat conditions and evaluate restoration success. In 2011 and 2012 we conducted comprehensive herpetological surveys throughout the Saginaw Bay area and assessed community composition, species richness, and spatial distribution. We also compared current distributions to historic observations and habitat conditions. A total of 25 taxa (13 species of reptiles and 12 species of amphibians) were observed within the Saginaw Bay area during this study. Herpetofauna were conspicuously unobserved in areas where Phragmites australis dominates the vegetation community and were concentrated in remaining areas of suitable habitat adjacent to Phragmites. Herpetofauna observations were clustered in areas where Phragmites and other invasive plant species were rare or absent. We were able to relate categorization of Phragmites invasion (i.e., 1 = 0–10% colonization detected, 2 = 10–50%, 3 > 50%) to both a biologically and statistically significant decrease in amphibian and reptile species richness. Our results indicate that Saginaw Bay can support a diverse herpetofauna community and there is potential to restore and improve this region for rare and common amphibian and reptile species. Removal of invasive plant species would greatly improve herpetofaunal communities within Saginaw Bay. Our results will help this region's resource professionals assess the quality of habitat and set goals for restoration of amphibian and reptile habitats.     

Ice–water heat exchange during ice growth in Lake Baikal

Using a custom-made thermistor chain frozen into the ice cover we obtained the first detailed information on distribution of temperature within ice and structure of the ice–water boundary layer during ice growth in Lake Baikal. A mathematical model of the heat transport in a multilayer ice–water system (Stefan problem) was developed and verified on results of in situ measurements. Effective coefficients of thermal diffusivity and ice–water heat fluxes were estimated from the inverse solution of the model and compared with direct flux estimates from the flux-gradient method. Both estimations agreed on flux values of 1–10 W m^− 2 and demonstrated strong synoptic variability in ice–water heat exchange. We estimated the thickness of viscous laminar sublayer under ice, as well as the thickness of the transitional layer on top of the turbulent water column. The thickness of the viscous sublayer of 1–1.5 cm in Lake Baikal was several times smaller than values reported previously from small lakes, suggesting high magnitudes of convective velocities and/or of the under-ice currents in Lake Baikal. Significant growth of the thermal diffusivity coefficient with increasing distance from the ice bottom was detected: its value at the top of the transition layer of under ice water was 10–40 times higher compared with its value in viscous laminar sublayer. This is also significantly higher than previous estimations in smaller freshwater lakes.