Colonization of the Laurentian Great Lakes by the invasive mussel Dreissena polymorpha was a significant ecological disturbance. The invasion reached Saginaw Bay, Lake Huron, in 1991 and initially cleared the waters and lowered algal biomass. However, an unexpected result occurred 3 years after the initial invasion with the return of nuisance summer blooms of cyanobacteria, a problem that had been successfully addressed with the implementation of phosphorus controls in the late 1970s. A multi-class phytoplankton model was developed and tested against field observations and then used to explore the causes of these temporal changes. Model scenarios suggest that changes in the phytoplankton community can be linked to three zebra mussel-mediated effects: (1) removal of particles resulting in clearer water, (2) increased recycle of available phosphorus throughout the summer, and (3) selective rejection of certain Microcystis strains. Light inhibition of certain phytoplankton assemblages and the subsequent alteration of competitive dynamics is a novel result of this model. These results enhance our understanding of the significant role of zebra mussels in altering lower trophic level dynamics of Saginaw Bay and suggest that their physical reengineering of the aquatic environment was the major force driving changes in the phytoplankton community composition.

The Great Lakes Water Quality Agreement defines Areas of Concern as geographic areas that fail to meet the general or specific objectives of the agreement where such failure has caused or is likely to cause impairment of beneficial use of the area's ability to support aquatic life. One of the beneficial use impairments, fish tumors or other deformities, is defined by the International Joint Commission to occur when the incidence rate of fish tumors and other deformities exceeds rates at unimpacted or control sites, or when survey data confirm the presence of neoplastic or preneoplastic liver tumors in bullhead or suckers. Brown bullhead, a benthic species with a limited home range, have frequently been used as indicator species in U.S. Areas of Concern. While there is strong field evidence for an association between PAH exposure and hepatic neoplasia in brown bullhead, laboratory investigations would strengthen the association. There is less evidence linking specific classes of chemicals in the environment to orocutaneous neoplasia in brown bullhead. Studies on orocutaneous neoplasia of brown bullhead should focus on assessing the presence or absence of viruses and on epidermal exposure to specific chemicals and chemical mixtures. Lastly, the effects of covariates such as length, age, and gender on the prevalence of liver and skin neoplasms should be investigated. This paper reviews the state of science on the fish tumors or other deformities beneficial use impairment. Subsequent papers address specific issues related to this impairment and provide recommendations for standardized criteria.

Previous studies support the hypothesis that large numbers of infaunal burrow-irrigating organisms in the western basin of Lake Erie may increase significantly the sediment oxygen demand, thus enhancing the rate of hypolimnetic oxygen depletion. We conducted laboratory experiments to quantify burrow oxygen dynamics and increased oxygen demand resulting from burrow irrigation using two different year classes of Hexagenia spp. nymphs from western Lake Erie during summer, 2006. Using oxygen microelectrodes and hot film anemometry, we simultaneously determined oxygen concentrations and burrow water flow velocities. Burrow oxygen depletion rates ranged from 21.7 mg/nymph/mo for 15 mm nymphs at 23 °C to 240.7 mg/ nymph/mo for 23 mm nymphs at 13 'C. Sealed microcosm experiments demonstrated that mayflies increase the rate of oxygen depletion by 2–5 times that of controls, depending on size of nymph and water temperature, with colder waters having greater impact. At natural population densities, nymph pumping activity increased total sediment oxygen demand 0.3–2.5 times compared to sediments with no mayflies and accounted for 2271% of the total sediment oxygen demand. Extrapolating laboratory results to the natural system suggest that Hexagenia spp. populations may exert a significant control on oxygen depletion during intermittent stratification. This finding may help explain some of the fluctuations in Hexagenia spp. population densities in western Lake Erie and suggests that mayflies, by causing their own population collapse irrespective of other environmental conditions, may need longer term averages when used as a bio-indicator of the success of pollution-abatement programs in western Lake Erie and possibly throughout the Great Lakes.

The “fish tumor or other deformities” beneficial use impairment (BUI) occurs at 9 of the 12 areas of concern (AOC) on Lake Erie. As point sources are mitigated and remediation occurs, AOC are faced with determining delisting criteria. The lack of standardized analyses for this BUI has confounded that process. For orocutaneous tumors, different criteria (presumptive tumors and/or abnormal barbels) and methodology (gross versus microscopic observations) have been used. Hence, this project evaluated tumors at numerous AOC and non-AOC sites and compared methodology. In 1998–2000 the prevalence of presumptive orocutaneous tumors and barbel abnormalities was compared in brown bullhead (Ameiurus nebulosus) collected at eight AOC. The Black (46.7%), Buffalo (29.3%), Cuyahoga (58.9%), and Detroit (26.5%) rivers and Presque Isle Bay (28.6%) had high prevalences of orocutaneous tumors, while the Niagara (10%), Maumee (3.9%) and Ashtabula (4.4%) rivers were lower. From 2002 to 2007 the prevalence of orocutaneous tumors at Presque Isle Bay was consistently near 30%. A variety of non-AOC sites, as potential reference sites, were also monitored during this time. By combining years and sites the prevalence of orocutaneous tumors in bullhead (age 2–12 years) at inland lakes was 6.3%, at Long Point Inner Bay was 8.7%, at other bays and harbors was 14.6% and at tributary sites was 12.5%. Overall, 93% of the raised lesions identified as presumptive tumors grossly were verified as neoplasms microscopically. The prevalence of orocutaneous tumors increased with age at both Presque Isle Bay and Long Point Inner Bay, the sites with the largest sample sizes.

Liver pathology of fishes, including neoplastic and preneoplastic lesions, is widely used as an indicator of exposure to anthropogenic contaminants. By definition, the “fish tumor or other deformities” beneficial use impairment (BUI) at Great Lakes Areas of Concern (AOC) includes neoplastic and preneoplastic liver lesions in brown bullhead (Ameiurus nebulosus) or suckers. Unfortunately, adequate guidelines for defining neoplastic and preneoplastic liver lesions or determining rates at unimpacted control sites were not provided and different criteria have been used. In some cases, only neoplastic changes were used to calculate tumor prevalence, in some both neoplastic and preneoplastic changes and in some it is difficult to determine which changes were included. Using standardized criteria, the prevalence of liver neoplasia was compared at eight AOC during 1998–2000. The Cuyahoga River had the highest prevalence (25.0%), while the Maumee River had the lowest (3.9%). The Buffalo (4.8%), Detroit (5.9%), Ashtabula (6.8%), Niagara (7.5%) and Black (8.9%) rivers were intermediate, as was Presque Isle Bay (7.1%). From 2002 to 2007 the prevalence of liver neoplasia at Presque Isle Bay ranged from a low of 2.1% (2002) to a high of 12.0% (2007). Non-AOC sites, as potential reference sites, also were monitored during this time. By combining years and sites, the prevalence of liver neoplasia in bullhead (aged 2 to 12 years) at inland lakes was 0.7%, at bays/harbors was 1.6% and at tributary sites was 4.1%. This is the same trend (inland lakes<bays/harbors<tributaries<Presque Isle Bay) noted for orocutaneous neoplasms.

A mid-Holocene buried organic layer 10 to 60 cm thick is present along the Lake Michigan shoreline in southeastern Wisconsin. Named the Southport forest bed for its location in Kenosha County, the unit has yielded abundant wood specimens, including large logs, branches, twigs, stumps, and root material. Roots of truncated in situ oak (Quercus) and elm (Ulmus) trees extend into the underlying till of the late Wisconsin Oak Creek Formation. Nearshore lacustrine sand above the organic layer contains abundant driftwood, overlain by 2 to 3 m of cross-bedded dune sand. More than 50 wood samples have been identified; the assemblage is that of a mixed hardwood forest dominated by oak (Quercus) and hickory (Carya), which account for about 60% of the assemblage. Although the site has been mostly concealed for many years, it was beautifully exposed in the 1960s and early 1970s, when it was initially studied by Phil Sander, who discovered the site and documented it with field notes and numerous photographs. Here we report several new (unpublished) radiocarbon dates and details of the stratigraphy and arboreal flora. Radiocarbon dates suggest that the Southport forest probably lived for 900–1000 ¹⁴C years, possibly longer, reaching its climax at about 5300 B.P. The site is of particular importance because of its proximity to the Nipissing shoreline and provides a significant point on the Nipissing transgression time curve. The unusually large number of identified specimens affords an accurate evaluation of the warm and relatively dry climate that characterized the southern Great Lakes region during the mid-Holocene.

Water movements due to temperature gradients and short-term water level fluctuations control the flushing timescale of the many shallow embayments in the Great Lakes. In this article the water circulation within Frenchman's Bay is reported and estimates made of the hydraulic flushing timescale. This shallow freshwater embayment is permanently connected to Lake Ontario through a channel of width 30 m and depth of 2 m. The water flushing timescale is estimated by using a salt mass budget, leading to a flushing timescale of 7–10 days. During the summer, the exchange of water between the bay and the lake can be driven by a combination of horizontal thermal gradients, and by small but ubiquitous 1–5 cm oscillations in the water level of Lake Ontario. The water movements that are predicted due to water level fluctuations (caused by seiches, storm surges and tides) and due to horizontal thermal gradients leads to estimates of the flushing time of water within Frenchman's Bay in the range of 12–13.5 days, i.e. the same order of magnitude as the salt budget. One consequence of the temperature driven exchange flows is to cause strong and persistent temperature stratification within the bay, which in combination with high nutrient loading and low winds in summer leads to frequent anoxic events.

A two-dimensional (vertical and cross-shore) sediment transport model was applied to several transects in southern Lake Michigan using observations of waves and currents recorded during the spring of 2000. Conditions during this period included several storms that are among the largest observed in the lake. The observations were used to examine the sensitivity of the model to variations in the input parameters (waves, currents, initial bottom sediment size distribution, settling velocity, and bottom stress required for erosion). The results show that changing the physical forcing (waves and currents) or the initial bottom sediment size distribution affected the results more than varying the particle properties (settling velocity and critical shear stress) or the size classes used to describe the size distribution. This indicates that for this model specification of input parameters are of first order importance and should be specified with some confidence before adding additional complexity by including processes such as flocculation and bed consolidation.

Benthic amphipods are a keystone species in food webs of marine and freshwater systems. The amphipod in the phylogroup Diporeia found in the Great Lakes has historically been a dominant member of the benthic community and is critical to the fisheries food web. This study investigates water depth, life stage, sex, production, lipid content, and gut fullness as influences and outcomes of Diporeia distribution in Lake Superior. Samples were collected at 2- to 3-week intervals from May to October 2003 from ten stations along one transect in Lake Superior near the Keweenaw Peninsula of Michigan to determine seasonal trends in abundance and condition. Diporeia comprised, on average, 52% of the benthic macroinvertebrate community. Abundance and productivity of Diporeia is greatest within the slope region (depths of 30 to 125 m) with estimated biomass and annual P/B (production/biomass) values of 0.57 and 0.73 g/m² for this habitat. Young-of-the-year Diporeia were the most abundant life stage in the shelf in the spring while adults were most abundant in the slope and profundal regions in fall. The greatest mean percent gut fullness occurred in September and October while the least full and empty gut occurrences were observed in June and July. The slope of the length-weight relationship for Diporeia in Lake Superior is lower (less biomass per unit length) than that observed for lakes Huron, Michigan, and Ontario. The greatest lipid content was 41% DW in July at 20 m with the overall average lipid content of Diporeia from Lake Superior in 2003 at 32% with a decline observed from September to October. The description of Diporeia abundance, distribution, and life history presented here for Lake Superior, and compared with that of other Great Lakes, will be of use in support of studies of lower food web bioenergetics.

Understanding variation in fish populations is valuable from both a management and an ecological perspective. Great Lakes sea lampreys are controlled primarily by treating tributaries with lampricides that target the larval stage. Great Lakes streams were divided into four categories based on their regularity of parasitic lamprey production inferred from the historic regularity of chemical treatments. This categorization was intended to direct future assessment efforts, but may also reflect differences in early demographics. We analyzed assessment data collected from 1959 to 2005 using mixed-effects models and variance components analyses to test for differences in recruitment and growth to age 1 among stream categories. Recruitment was twice as large in regularly treated streams as in irregularly treated streams, indicating that age-1 year-class strength is correlated with consistent chemical treatments. We found no differences in length at age 1 among stream categories; however, Lake Superior streams with irregular treatment histories exhibit more variation in length at age 1 than streams that are treated regularly. The majority of variation in length at age 1 was due to within-year variation, which was fairly consistent across stream types within each lake. Our results indicate that early life history differs among subsets of the Great Lakes sea lamprey population, and management practices should be modified to account for these differences. Mixed-effects models and variance components analyses are useful tools for analyzing large historical datasets for patterns of demographic variation within and among populations, whether the ultimate goal is pest control, harvesting, or conservation.

We examined the feeding ecology of larval lake whitefish (Coregonus clupeaformis) in Chaumont Bay, Lake Ontario, during April and May 2004–2006. Larvae were collected with towed ichthyoplankton nets offshore and with larval seines along the shoreline. Larval feeding periodicity was examined from collections made at 4-h intervals over one 24-h period in 2005. Inter-annual variation in diet composition (% dry weight) was low, as was spatial variation among collection sites within the bay. Copepods (81.4%), primarily cyclopoids (59.1%), were the primary prey of larvae over the 3-year period. Cladocerans (8.1%; mainly daphnids, 6.7%) and chironomids (7.3%) were the other major prey consumed. Larvae did not exhibit a preference for any specific prey taxa. Food consumption of lake whitefish larvae was significantly lower at night (i.e., 2400 and 0400 h). Substantial variation in diet composition occurred over the 24-h diel study. For the 24-h period, copepods were the major prey consumed (50.4%) and their contribution in the diet ranged from 29.3% (0400 h) to 85.9% (1200 h). Chironomids made up 33.4% of the diel diet, ranging from 8.0% (0800 h) to 69.9% (0400 h). Diel variation in the diet composition of lake whitefish larvae may require samples taken at several intervals over a 24-h period to gain adequate representation of their feeding ecology.

Although the round goby, Neogobius melanostomus, is widespread in the Great Lakes and has an extended breeding season with a high reproductive rate; its spawning behaviour remains elusive. We present the first reported accounts of spawning by the round goby in the laboratory. By simulating winter conditions and restoring spring conditions, we induced round gobies to spawn in October 2007, March 2008, May 2008, and January 2009. In one case, fanning by the nest-holding male began 10 days before egg deposition and, during this period, the male rubbed secretions along the ceiling of the nest. Males were choosy about which gravid females entered the nest and prevented entry by some females. Spawning involved repeated inversions by females and males releasing gametes on the ceiling of the nest. Males guarded the nest by blocking the entrance, producing agonistic vocalizations and chasing intruders. Inside the nest, eggs were regularly inspected by the males and constantly ventilated using pectoral and caudal fins. Up to three gravid females spawned sequentially in a nest. Peak ventilation occurred after egg deposition and declined with time until the parental male ate the eggs. The decline of parental care and egg cannibalism was likely an artifact of laboratory conditions and small brood size. Our findings offer new information on the reproductive habits of the invasive round goby. Because the reproductive sequence in the laboratory seems easy to disrupt, the procedures may lead to a management tool to control the spread of the species into new areas.

Presque Isle Bay, Lake Erie, was listed as an Area of Concern (AOC) by the International Joint Commission in part because of the high incidence of external tumor in brown bullheads. Verifying the source of the possible contaminant exposure is critical to addressing the AOC designation. We used telemetry tracking (n = 49 fish) to test the hypothesis that adult bullheads captured within the bay during spawning season do not exit the bay during the post-spawning summer and fall months. We analyzed genetic variation at 15 microsatellite loci for 112 adult fish from 5 locations, 4 inside the bay and 1 outside, in order to test for possible differences. Data from fixed-station receivers suggested fish did not leave Presque Isle Bay during the study period. Predicted locations outside Presque Isle Bay were only 0.1% of all predicted locations and were below the 0.2% error rate based on known manual relocations. However, there was evidence for movement within Presque Isle Bay. Most movement was between Misery Bay or Lagoons and the open bay area. Whereas telemetry results showed tendency for adult site fidelity, genetic results showed no differences among locations, indicating that there is a single panmictic population. Our telemetry data suggest that brown bullheads are likely a useful indicator species for environmental conditions in Presque Isle Bay, since adults likely are retained in the system.

Restoration of lake trout Salvelinus namaycush stocks in Lake Huron is a fish community objective developed to promote sustainable fish communities in the lake. Between 1985 and 2004, 12.65 million lake trout were stocked into Lake Huron representing eight different genetic strains. Collections of bona fide wild fish in USGS surveys have increased in recent years and this study examined the ancestry and diet of fish collected between 2004 and 2006 to explore the ecological role they occupy in Lake Huron. Analysis of microsatellite DNA revealed that both pure strain and inter-strain hybrids were observed, and the majority of fish were classified as Seneca Lake strain or Seneca Lake hybrids. Diets of 50 wild age-0 lake trout were examined. Mysis, chironomids, and Zooplankton were common prey items of wild age-0 lake trout. These results indicate that stocked fish are successfully reproducing in Lake Huron indicating a level of restoration success. However, continued changes to the benthic macroinvertebrate community, particularly declines of Mysis, may limit growth and survival of wild fish and hinder restoration efforts.

The nonindigenous mottled fingernail clam, Eupera cubensis is reported from the Upper Mississippi River Basin for the first time. This record represents a significant northern range expansion for the species in the United States. It appears to be presently confined to a 35-km stretch of the Chicago Sanitary and Ship Canal (CSSC), an artificial waterway that connects the Mississippi River drainage to the Great Lakes. Although the introduction of this species to the Great Lakes basin poses uncertain risks to the general aquatic community, the immediate effects of Eupera cubensis on the fauna of the CSSC are expected to be minimal.

Fallfish (Semotilus corporalis) are the largest native cyprinid in the northeastern United States and are the most abundant native species in the Salmon River, New York. The Salmon River is a high-quality spawning and nursery river for Pacific salmon (Oncorhynchus spp.) migrating from Lake Ontario. Because of the large number of Pacific salmon spawning in the river in the fall extensive redd superimposition occurs resulting in salmonid eggs being available on the substrate. We examined the fall diet of 647 fallfish in 2007 and 2008 to determine the extent of predation on Pacific salmon eggs. The contribution of eggs in the diet significantly increased once fallfish attained a size of 100 mm total length. The largest size category of fallfish examined (≥150 mm) had the highest proportion (86.1%) of salmon eggs in their diet. The contribution of Zooplankton and chironomids in the diet of fallfish decreased with fish size. Except for the two largest groups of fallfish examined (i.e., 100–149 mm and ≥150 mm) diet overlap among size groups was low. The high contribution in the diet during the fall and high caloric value of Pacific salmon eggs could increase growth and survival of this species in the Salmon River.