Ambient calcium is declining in thousands of soft-water lake habitats in temperate regions as a c... more Ambient calcium is declining in thousands of soft-water lake habitats in temperate regions as a consequence of unsustainable forestry practices, decreased atmospheric calcium deposition, and acidic deposition. As their exoskeleton is heavily reinforced with calcium, freshwater crustaceans have a high specific calcium requirement relative to other aquatic organisms. Daphnia in particular, is an ideal crustacean for investigating the consequences of calcium decline because it is an abundant and important member of freshwater zooplankton communities. Although it has been established that adult and juvenile Daphnia have different tolerances to low ambient calcium as a result of their different life stage specific calcium requirements, the consequences of declining calcium on embryonic development have never been investigated. Here we describe the distribution of calcium in embryonic stages of D. magna and introduce a novel and easy to use staging scheme. We then tested whether calcium c...
The annual population growth of the exotic invader Bythotrephes cederstroemi was calculated from ... more The annual population growth of the exotic invader Bythotrephes cederstroemi was calculated from the spatial distribution and rate of accumulation of its diagnostic caudal processes in the sediments of Harp Lake, Ontario. To our knowledge, this is the first use of the sediment record to quantify the annual population growth of a zooplankton species on a whole-lake scale with confidence
Road deicing operations have raised chloride (Cl) levels in many temperate lakes in Europe and No... more Road deicing operations have raised chloride (Cl) levels in many temperate lakes in Europe and North America. These lakes vary widely in trophic status, but to date, no one has quantified the interaction between food quantity and road salt toxicity. We examined the effects of food quantity (particulate algal C concentration (C)) on the chronic toxicity of Cl to Daphnia in soft-water bioassays. There was a strong positive linear relationship (r(2) = 0.92 for NaCl and r(2) = 0.96 for CaCl2) between food quantity and Cl LC50. As food quantity increased from 0.2 to 1.0 mg C/L (levels characteristic of oligotrophic to eutrophic lakes, respectively), the chronic Cl LC50 increased from 55.7 to 284.8 mg Cl/L. Salt type (NaCl or CaCl2) did not affect the Cl LC50, Daphnia life history parameters, or the intrinsic rate of population increase (r). The life history parameter most sensitive to Cl was neonate production. Cl did not inhibit egg production, nor was the maternal lipid investment in e...
Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake pr... more Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake primary production. Disturbances that change these inputs may affect how aquatic ecosystems function and deliver services vital to humans. Here we test, using a forest cover gradient across eight separate catchments, whether disturbances that remove terrestrial biomass lower organic matter inputs into freshwater lakes, thereby reducing food web productivity. We focus on deltas formed at the stream-lake interface where terrestrial-derived particulate material is deposited. We find that organic matter export increases from more forested catchments, enhancing bacterial biomass. This transfers energy upwards through communities of heavier zooplankton, leading to a fourfold increase in weights of planktivorous young-of-the-year fish. At least 34% of fish biomass is supported by terrestrial primary production, increasing to 66% with greater forest cover. Habitat tracers confirm fish were closely...
Canadian Journal of Fisheries and Aquatic Sciences, 2003
The nonindigenous predatory cladoceran Bythotrephes longimanus is spreading rapidly among Canadia... more The nonindigenous predatory cladoceran Bythotrephes longimanus is spreading rapidly among Canadian Shield lakes, but only one case study of its impacts exists. In Harp Lake, the abundances of several cladoceran and one cyclopoid species fell after the invasion, and far fewer species benefited. To determine if Harp Lake provides typical results, we compared the summer crustacean zooplankton communities of 17
Ambient calcium is declining in thousands of soft-water lake habitats in temperate regions as a c... more Ambient calcium is declining in thousands of soft-water lake habitats in temperate regions as a consequence of unsustainable forestry practices, decreased atmospheric calcium deposition, and acidic deposition. As their exoskeleton is heavily reinforced with calcium, freshwater crustaceans have a high specific calcium requirement relative to other aquatic organisms. Daphnia in particular, is an ideal crustacean for investigating the consequences of calcium decline because it is an abundant and important member of freshwater zooplankton communities. Although it has been established that adult and juvenile Daphnia have different tolerances to low ambient calcium as a result of their different life stage specific calcium requirements, the consequences of declining calcium on embryonic development have never been investigated. Here we describe the distribution of calcium in embryonic stages of D. magna and introduce a novel and easy to use staging scheme. We then tested whether calcium c...
The annual population growth of the exotic invader Bythotrephes cederstroemi was calculated from ... more The annual population growth of the exotic invader Bythotrephes cederstroemi was calculated from the spatial distribution and rate of accumulation of its diagnostic caudal processes in the sediments of Harp Lake, Ontario. To our knowledge, this is the first use of the sediment record to quantify the annual population growth of a zooplankton species on a whole-lake scale with confidence
Road deicing operations have raised chloride (Cl) levels in many temperate lakes in Europe and No... more Road deicing operations have raised chloride (Cl) levels in many temperate lakes in Europe and North America. These lakes vary widely in trophic status, but to date, no one has quantified the interaction between food quantity and road salt toxicity. We examined the effects of food quantity (particulate algal C concentration (C)) on the chronic toxicity of Cl to Daphnia in soft-water bioassays. There was a strong positive linear relationship (r(2) = 0.92 for NaCl and r(2) = 0.96 for CaCl2) between food quantity and Cl LC50. As food quantity increased from 0.2 to 1.0 mg C/L (levels characteristic of oligotrophic to eutrophic lakes, respectively), the chronic Cl LC50 increased from 55.7 to 284.8 mg Cl/L. Salt type (NaCl or CaCl2) did not affect the Cl LC50, Daphnia life history parameters, or the intrinsic rate of population increase (r). The life history parameter most sensitive to Cl was neonate production. Cl did not inhibit egg production, nor was the maternal lipid investment in e...
Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake pr... more Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake primary production. Disturbances that change these inputs may affect how aquatic ecosystems function and deliver services vital to humans. Here we test, using a forest cover gradient across eight separate catchments, whether disturbances that remove terrestrial biomass lower organic matter inputs into freshwater lakes, thereby reducing food web productivity. We focus on deltas formed at the stream-lake interface where terrestrial-derived particulate material is deposited. We find that organic matter export increases from more forested catchments, enhancing bacterial biomass. This transfers energy upwards through communities of heavier zooplankton, leading to a fourfold increase in weights of planktivorous young-of-the-year fish. At least 34% of fish biomass is supported by terrestrial primary production, increasing to 66% with greater forest cover. Habitat tracers confirm fish were closely...
Canadian Journal of Fisheries and Aquatic Sciences, 2003
The nonindigenous predatory cladoceran Bythotrephes longimanus is spreading rapidly among Canadia... more The nonindigenous predatory cladoceran Bythotrephes longimanus is spreading rapidly among Canadian Shield lakes, but only one case study of its impacts exists. In Harp Lake, the abundances of several cladoceran and one cyclopoid species fell after the invasion, and far fewer species benefited. To determine if Harp Lake provides typical results, we compared the summer crustacean zooplankton communities of 17
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