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Donald W. Schloesser

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Length-frequency distribution curves of Hexagenia limbata nymphs collected in May, August, and October 1974 and May 1975 in the St. Marys River between Lakes Superior and Huron were bimodal for each sampling period. These curves, combined with interpretation of nymphal emergence period and mean surface water temperatures, indicate that the population of Hexagenia nymphs in the St. Marys River is composed of two year classes or cohorts. One cohort emerges per season, 2 years after egg deposition.
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Long-term trends in the abundance of unionids in the western basin of Lake Erie were examined from data collected at 17 stations in 1961, 1972, and 1982. The mean number of unionids at these stations declined over this time period, decreasing from 10 m−2 in 1961, to 6 m−2 in 1972, down to 4 m−2 in 1982. This decline in abundance was reflected in the decrease in the number of stations where mussels were found; unionids were found at 16 of the 17 stations in 1961, but at only 6 stations in 1982. Reasons for the decrease in the unionid population are not generally apparent, but are probably related to the decline in water quality and periods of low oxygen levels over the time period of the surveys.
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We examined Manayunkia speciosa individuals from the Klamath River, Oregon/California and Lake Erie, Michigan, USA for the presence of Microsporidia. We identified microsporidian spores and sequenced their SSU, ITS, and part of the LSU rDNA. Phylogenetic analysis of SSU rDNA indicated spores from both populations belonged to the Nosema/Vairimorpha clade. PCR showed an infection prevalence in Lake Erie M. speciosa of 0.6% (95% CI = 0.5%, 0.7%). This represents the first known example of molecularly characterized Nosema/Vairimorpha isolates infecting a non-arthropod host.
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We sampled benthos from the St. Marys River in May 1974 and May 1975 to determine visibly the occurrence of sorpted oil and the distribution of nymphs of the burrowing mayfly Hexagenia in the bottom of the Lake George and Lake Nicolet channels. Results of our survey showed that, between 1967 and 1974-75, the occurrence of oil in the substrate of the Lake George Channel had advanced from 16 km to 30 km downstream from the point where oil is discharged at Sault Ste. Marie, Ontario. Absence or low densities of nymphs coincided with the presence of oil in the sediments. In the Lake Nicolet Channel, evidence of oil pollution was meager and the density of Hexagenia nymphs was generally high.
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Dreissena polymorpha (Pallas), a small mussel common throughout most of Europe, was discovered in June of 1988 in the southern part of Lake St. Clair. Length–frequency analyses of populations from the Great Lakes and review of historical benthic studies suggest that the mussel was introduced into Lake St. Clair in late 1986, probably as a result of the discharge of ballast water from an ocean-crossing vessel. Following the 1990 reproductive season, Dreissenapopulations ranged from the head of the St. Clair River, through Lake St. Clair, the Detroit River, Lake Erie, the Welland Canal, and the Niagara River to the western basin and southern shoreline of Lake Ontario. Isolated populations were found in the St. Lawrence...
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