Status of the amphipod Diporeia spp. in Lake Superior, 2006–2016

The amphipod Diporeia spp. has historically been an important component of the benthic food web of the Laurentian Great Lakes. The Great Lakes Water Quality Agreement included its population density as an indicator of ecological condition for Lake Superior, with target values of 220–320 m^?2 in nearshore areas (≤100 m depth) and 30–160 m^?2 in offshore areas (>100 m). To assess the status of Diporeia in Lake Superior, we used a probability-based lake-wide survey design to obtain estimates of Diporeia density and biomass in 2006, 2011 and 2016. A PONAR grab sampler was used to collect Diporeia at 50–53 sites each year, with approximately half in the nearshore (<100 m depth) region of the lake and half in the offshore. The mean area-weighted lake-wide density was 395 ± 56 (SE) m^?2 in 2006, 756 ± 129 m^?2 in 2011, and 502 ± 60 m^?2 in 2016. For all years, both density and biomass were greater in the nearshore than in the offshore stratum. The densities for 2006–2016 were 3–5 times higher than those reported from a lake-wide survey conducted in 1973 by the Canada Centre for Inland Waters. The severe declines in Diporeia populations observed in the other Great Lakes during recent decades have apparently not occurred in Lake Superior. Further research is needed to understand spatial and temporal variability of Diporeia populations in Lake Superior to enhance the utility of Diporeia density as an indicator of benthic condition.     

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.     

Energy Density of Three Fishes from Minnesota Waters of Lake Superior

Energy densities of three salmonine prey species in Lake Superior were determined by bomb calorimetry to examine seasonal trends, differences due to gender and to establish a relation with percent dry weight. These results from April through October for 1992 and 1993 were compared with other studies from the Great Lakes region. Across the 2-year sampling period rainbow smelt Osmerus mordax energy density decreased from April to June and July then significantly increased into September. Lake herring Coregonus artedii energy density was highest in June, decreased significantly by August, and remained stable through October. Bloater C. hoyi energy density was lowest in July, then increased in August and early September before decreasing in late September. There were no significant differences in energy density between males and females for rainbow smelt and lake herring collected on the same date across sampling dates. However, bloater energy density was significantly higher for females than for males on two dates. Energy density estimates for bloater in Lake Superior were lower than those reported from Lake Michigan. Energy density values of rainbow smelt and lake herring fell within the range reported in Lake Michigan and Lake Ontario (rainbow smelt), and from two inland lakes in Minnesota and Lake Mendota, Wisconsin (lake herring). Percent dry weight was a good predictor of energy density (P < 0.001, r² = 0.92–0.99) for all three species for both years. Percent dry weight vs energy density was significantly different between years for bloater and lake herring, and was significantly different for all three species compared with populations in other lakes in the Great Lakes Region.     

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.     

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.     

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.     

Heterotrophic Bacterioplankton Dynamics at a Site off the Southern Shore of Lake Superior

Evolution of the paradigm regarding the relative importance of allochthonous and autochthonous sources of organic matter in aquatic systems has rekindled interest in the role of bacteria in energy transfer. The development of material budget calculations characterizing conditions of net heterotrophy requires knowledge of spatiotemporal dynamics in the bacterial community. Here we present results from three years of measurement of bacterioplankton abundance and production at three locations on the south shore of Lake Superior. In general, bacterial numbers (0.63 × 10⁶ ± 0.29 × 10⁶ cells·mL⁻¹) and production (0.037 ± 0.055 mgC·m⁻³·hr⁻¹) were comparable to those reported previously for Lake Superior and were consistent with the system's place along the trophic gradient. Interannual differences in abundance and production were apparently related to the timing and magnitude of seasonal phytoplankton dynamics. There was no inter-transect variation or systematic nearshore-offshore gradients in bacterial activity despite substantial differences in proximity to sources of terrigenous materials (between transects) and in phytoplankton biomass (with distance offshore). The most striking signals in bacterial activity were those evidenced by peaks in bacterial production associated with the deep chlorophyll maximum and with the decline in the phytoplankton community with the approach to turnover. It is hypothesized that bacterioplankton activity in Lake Superior exists in a near steady state, fueled by labile organic matter produced through phytoplankton excretion and the photolytic processing of refractory terrigenous materials. Superimposed on this rather stable signal are peaks in bacterial production apparently related to senescence of the phytoplankton community and, perhaps, the generation of nutrients by the grazing community.     

Contaminants Associated with Suspended Sediments in Lakes Erie and Ontario, 1997–2000

Sediment traps were installed at individual index stations in the western basin of Lake Erie and the Mississauga (central) basin of Lake Ontario, and refurbished seasonally during the period 1997–2000. In Lake Ontario, sediment down flux rates and corresponding contaminant down flux rates were highest in winter and increased with depth due to the influence of resuspended bottom sediments. Sediment down flux rates in western Lake Erie (22 to 160 g m⁻² d⁻¹) were far greater than in Lake Ontario (0.19–3.0 g m⁻² d⁻¹). Suspended material in western Lake Erie was characterized as predominately resuspended bottom sediments; down flux rates were roughly 5- to 10-fold higher in spring and fall, compared to summer. Suspended sediment concentrations of PCBs and other organochlorine contaminants, represented by both annual means and individual seasonal values, were higher in Lake Ontario throughout the duration of the study, compared to Lake Erie. The mean annual concentration of PCBs in suspended sediments over the period 1997–2000 was 330 ng/g in western Lake Erie and 530 ng/g in Lake Ontario. Based on a comparison with historical data from Lake Ontario, mean contaminant concentrations over the period 1997–2000 for PCBs, hexachlorobenzene, and mirex corresponded to decreases of 38%, 74%, and 40%, respectively, since the mid-1980s. Corresponding down flux rates for PCBs, hexachlorobenzene, and mirex decreased by approximately 70%, 90%, and 80%, respectively, since the 1980s.     

Lake Erie Central Basin Total Phosphorus Trend Analysis from 1968 to 1982

The total phosphorus data from 1968 to 1982 in the Lake Erie central basin trend study area was analyzed to determine in-lake responses to the Great Lakes Water Quality Agreement (GLWQA) phosphorus loading reduction program. The available data for each year were divided into five subsets according to time of year and depth of the water column. Each data subset was regressed as a function of time and total phosphorus loadings to Lake Erie. Linear regression analysis indicates that the in-lake phosphorus concentrations have been decreasing and are well correlated with decreased loadings to the lake. The highest rate of phosphorus decrease with time (0.56 ± 0.10 mg · m⁻³ yr⁻¹) was obtained by using epilimnetic concentrations from April to December for each year. This data subset also shows the best correlation with decreasing phosphorus loadings. From 1968 to 1982, Lake Erie offshore phosphorus concentrations responded to decreasing external phosphorus loadings at a rate of 0.45 ± 0.09 mg · m⁻³ per thousand metric tonnes.     

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.     

Trends in Mysis diluviana abundance in the Great Lakes, 2006–2016

With the large Diporeia declines in lakes Michigan, Huron, and Ontario, there is concern that a similar decline of Mysis diluviana related to oligotrophication and increased fish predation may occur. Mysis density and biomass were assessed from 2006 to 2016 using samples collected by the Great Lakes National Program Office's biomonitoring program in April and August in all five Great Lakes. Summer densities and biomasses were generally greater than spring values and both increased with bottom depth. There were no significant time trends during these 10–11 years in lakes Ontario, Michigan, or Huron, but there was a significant increase in Lake Superior. Density and biomass were highest in lakes Ontario and Superior, somewhat lower in Lake Michigan, and substantially lower in Lake Huron. A few Mysis were collected in eastern Lake Erie, indicating a small population in the deep basin of that lake. On average, mysids contributed 12–18% (spring-summer, Michigan), 18–14% (spring-summer, Superior), 30–13% (spring-summer, Ontario), and 3% (Huron) of the total open-water crustacean biomass. Size distributions consisted of two peaks, indicating a 2-year life cycle in all four of the deep lakes. Mysis were larger in Lake Ontario than in lakes Michigan, Superior, and Huron. Comparisons with available historic data indicated that mysid densities were higher in the 1960s–1990s (5 times higher in Huron, 2 times higher in Ontario, and around 40% higher in Michigan and Superior) than in 2006–2016.     

A Comparison of Photosynthate Allocation in Lakes

We compared the relationships between photosynthate allocation to protein, carbohydrate, lipid and low molecular weight (LMW) fractions and the variables daylength and water temperature in Lakes Huron, Michigan, and Ontario as well as three smaller headwater lakes in the Lake Ontario drainage. In all lakes investigated the allocation of recently produced photosynthate to carbohydrate was strongly related to daylength (% carbohydrate = −3.5 * daylength (hr) + 72.8; n = 59, r² = 0.56). The percentage of photosynthate allocated to protein was a function of water temperature in all lakes although the y-intercept for the protein-temperature relationship was much lower in the three headwater lakes and Lake Ontario (% protein = 0.50 * temperature (°C) + 6.1; n = 37, r² = 0.52) than in Lake Huron and Lake Michigan (% protein = 0.68 * temperature (°C) + 24.2; n = 23, r² = 0.49). The increase in allocation to protein was related to a decrease in allocation to low molecular weight material (% LMW = −1.1 * % protein + 57.13; n = 60, r² = 0.72). The percentages of photosynthate in lipid and LMW material were not related to any of the environmental variables measured. Assuming that photosynthate allocation is related to biochemical composition, the phytoplankton in Lakes Huron and Michigan were more protein rich for a given temperature than those in Lake Ontario and in the smaller inland lakes. The protein deficit was due to an increase in allocation to LMW material.     

Sedimentation Rates and Depositional Processes in Lake Superior from 210Pb Geochronology

Sedimentation rates range from 0.01 to 0.32 cm/yr in 17 sediment box cores from Lake Superior, as determined by ²¹⁰Pb geochronology. Shoreline erosion and resuspension of nearshore sediments causes moderate to high (0.05–0.11 cm/yr) sedimentation rates in the western arm of Lake Superior. Sedimentation rates are very high (> 0.15 cm/yr) in marginal bays adjoining Lake Superior; and moderate to very high (0.07–0.19 cm/yr) in open lake regions adjacent to marginal bays. Resuspension of nearshore and shoal top sediments in southern and southeastern Lake Superior by storms is responsible for depositional anomalies in ²¹⁰Pb profiles corresponding to 1905, 1916–1918, and 1940 storms. Sedimentation rates are very low (0.01–0.03 cm/yr) in the central basins due to isolation from sediment sources. These data indicate that sedimentation rates and processes vary significantly in different regions of Lake Superior. The sedimentation rates provided by this study, in conjunction with previously-reported sedimentation rates, yield a better understanding of the Lake Superior depositional environment.     

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.     

Contemporary diets of Lake Superior lake whitefish off the Keweenaw Peninsula and changes in condition from the 1980s to 2010s

Over the last two decades, declines in lake whitefish (Coregonus clupeaformis) recruitment and growth in many areas of the Laurentian Great Lakes have raised concerns about the status of this important species. Although Lake Superior populations have been less affected than those in other Great Lakes, these populations still face multiple threats. We characterized lake whitefish diets collected off the Keweenaw Peninsula between 2015 and 2017 and compared results to previous Lake Superior studies. We additionally estimated length-weight relationships to determine whether lake whitefish body condition (i.e., expected weight-at-length) had changed since the 1980s. Diet diversity was low, although individual specialization was moderate to high. Fish transitioned from consuming Diporeia in the spring to Mysis and fish eggs during fall and winter; sphaeriids composed 20–30% of diets across all seasons. Compared to findings for other Lake Superior regions, lake whitefish diets comprised lower percentages of high energy items (e.g., Diporeia, Mysis) and higher percentages of low energy items (e.g., sphaeriids). Expected weights in the 2000s and 2010s were lower in the 400- and 500-mm length groups but similar in larger lengths groups compared to the 1980s; condition was highest across all lengths in the 1990s. The observed decline in condition since the 1990s in the 400- and 500-mm length groups, in combination with possibly greater consumption of less energetically profitable items, suggests that lake whitefish <600 mm or preferred prey resources in this lake region may be experiencing stressors leading to condition declines, although what these stressors are remain unknown.     

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.     

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.     

Monitoring of Trace Organic Contaminants in Atmospheric Precipitation

The design and use of a year-round sampler for trace organic contaminants in wet precipitation are described. The sampler is electronically controlled and features a 0.25-meter-square stainless steel funnel with a 4-L amber glass bottle. The whole assembly is insulated and equipped with heating elements which permit collection of ice/snow samples. The samples are preserved in situ with methylene chloride and extracted again with methylene chloride in the laboratory. A small network of four sampling stations was established in the Great Lakes basin for the purpose of obtaining a refined estimate of atmospheric loading of trace organic pollutants to the Great Lakes. A total of 93 rain/snow samples was collected from the network during 1986. These samples were analyzed for organochlorine pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. The most significant organochlorine pesticides found were alpha-HCH, gamma-HCH (lindane), and methoxychlor with concentrations in the range of 7–10 ng/L, 4–5 ng/L, and 2–7 ng/L, respectively. Other organochlorinated pesticides were measured occasionally at sub-nanogram levels. Polychlorinated biphenyls were also widely detected with mean concentrations of 7–10 ng/L. Polycyclic aromatic hydrocarbons were detected in about 50% of the samples. Some of the prevalent polycyclic aromatic hydrocarbons were phenanthrene, methylnapthalene, fluoranthene, and pyrene with mean concentrations of 50–200 ng/L. Deposition of agricultural chemicals (HCHs) was higher in Lake Superior and Huron but precipitation at Lake Erie and Lake Ontario contained more varieties of domestic pesticides.     

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.