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...
Climate change is expected to have important impacts on aquatic ecosystems. On the Boreal Shield,... more Climate change is expected to have important impacts on aquatic ecosystems. On the Boreal Shield, mean annual air temperatures are expected to increase 2 to 4 • C over the next 50 years. An important challenge is to predict how changes in climate and climate variability will impact natural systems so that sustainable management policies can be implemented. To predict responses to complex ecosystem changes associated with climate change, we used long-term biotic databases to evaluate how important elements of the biota in Boreal Shield lakes have responded to past fluctuations in climate. Our long-term records span a two decade period where there have been unusually cold years and unusually warm years. We used coherence analyses to test for regionally operating controls on climate, water temperature, pH, and plankton richness and abundance in three regions across Ontario: the Experimental Lakes Area, Sudbury, and Dorset. Inter-annual variation in air temperature was similar among regions, but there was a weak relationship among regions for precipitation. While air temperature was closely related to lake surface temperatures in each of the regions, there were weak relationships between lake surface temperature and richness or abundance of the plankton. However, inter-annual changes in lake chemistry (i.e., pH) were correlated with some biotic variables. In some lakes in Sudbury and Dorset, pH was dependent on extreme events. For example, El Nino related droughts resulted in acidification pulses in some lakes that influenced phytoplankton and zooplankton richness. These results suggest that there can be strong heterogeneity in lake ecosystem responses within and across regions.
This study identified two scales of pattern in the assemblages of Chydoridae (Crustacea, Branchio... more This study identified two scales of pattern in the assemblages of Chydoridae (Crustacea, Branchiopoda, Anomopoda) in the shallow (<2 m) littoral zone of Plastic Lake, Ontario, Canada in the autumn of 1987. Twenty chydorid species were collected in 15 over-night sets of funnel traps in each of four habitat types. Analysis of variance multivariate analysis of variance, and discriminant function analysis revealed that assemblages differed among the habitats. Alona intermedia, Alona quadrangularis and Chydorus bicornutus were particularly abundant in the most structurally diverse habitat type -muddy, rock-strewn areas with approximately 40% bottom cover by the pipewort, Eriocaulon septangulare. In contrast, Anchistropus cf. minor was caught most often on bare shelves of rock. A second set of analyses demonstrated that chydorid assemblages also differed at a smaller scale, i.e. with local patchiness in bottom cover by the dominant macrophyte (E. septangulare). The abundance of Alona affinis was positively correlated with cover by E. septangulare, whereas Anchistropus cf. minor was caught mainly in microhabitats without vegetation. Alona intermedia and A. quadrangularis were most abundant in microhabitats with intermediate amounts of vegetation, suggesting their abundance is influenced by habitat factors other than vegetation.
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...
Brian Leung is a research assistant professor at the University of Notre Dame. His current resear... more Brian Leung is a research assistant professor at the University of Notre Dame. His current research focuses on ecological forecasting and bioeconomic risk analysis of invasive species, using mathematical, computational, and statistical models. His address: Bill Keller is the senior environmental scientist -Northern Lakes, with the Ontario Ministry of Environment, and is an adjunct professor in the Department of Biology, Laurentian University. His studies focus on documenting and understanding the recovery process in damaged aquatic systems, and on investigating the combined effects of multiple stressors on lakes and on lake recovery. His address: Shelley Arnott is an assistant professor in the Department of Biology at Queen's University. Her research focuses on determining the chemical and ecological factors that influence the recovery of aquatic biota from historical acidification in the face of climatic variability and the spread of nonindigenous species. Her address: John Gunn is a fisheries research scientist with the Ontario Ministry of Natural Resources and heads up the Cooperative Freshwater Ecology Unit at Laurentian University. He specializes in restoration ecology of aciddamaged ecosystems as well as the ecology of salmonid fishes of Ontario. His address:
No other freshwater system contains as many non-native species or has been invaded as frequently ... more No other freshwater system contains as many non-native species or has been invaded as frequently as the Great Lakes-St. Lawrence River basin. Over 180 non-native species have become established in the basin within the past two centuries. Collectively, these invasions have altered biodiversity, habitat structure, productivity, water quality, contaminant cycling and ecosystem services. The composition and rate of discovery of invaders are correlated with changes in dominant vectors, such as transoceanic shipping. We review the invasion history of the basin and identify future invasion threats by considering trends and potential scenarios in changing vectors and pathways. Whereas most non-native species discovered since the opening of the St. Lawrence Seaway in 1959 were attributable to ballast water discharge from transoceanic vessels, recent regulations have apparently reduced the threat of this vector. Nevertheless, non-native species may continue to be introduced through poorly-regulated vectors, particularly those associated with trade in live organisms. The spread and impact of current and future invaders are expected to be exacerbated by interactions with other anthropogenic stressors that are increasing in frequency and spatial extent. Most notably, the continued warming of surface waters of the Great Lakes basin will lift thermal barriers to invasions by warm-water taxa. Contrary to any perception that the "worst is over" (i.e. most harmful invasions have already occurred), the basin remains vulnerable to further ecological and economic disruptions from non-native species.
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
We investigated the temporal coherence (i.e., the correlation or synchrony between time series) o... more We investigated the temporal coherence (i.e., the correlation or synchrony between time series) of annual abundances among populations of freshwater zooplankton in eight lakes in Ontario, Canada, from 1980 to 1992. We estimated temporal coherence using the intraclass correlation coefficient (r i ). While values of r i were relatively low among comparisons of all eight lakes, they were statistically significant for three of the seven common cladoceran and copepod taxa (Bosmina longirostris, Leptodiaptomus minutus, and Mesocyclops edax). These significant positive correlations imply that a portion of the interannual variation in abundance was produced by factors operating on a scale larger than the individual lake catchments. Because the eight-lake analysis might obscure strong, but conflicting, patterns among lakes in the region, we identified homogeneous and temporally coherent subsets of lakes for each species using an exploratory stepwise deletion procedure. The resultant homogeneous subsets exhibited much greater temporal coherence, accounting for 47% (Eubosmina) to 84% (Leptodiaptomus) of the interannual variation in abundance. Our results suggest that the factors affecting annual variation in zooplankton abundance must be sought both within lakes and beyond their watersheds.
The biosynthesis of nutritionally important polyunsaturated fatty acids (PUFAs) in phytoplankton ... more The biosynthesis of nutritionally important polyunsaturated fatty acids (PUFAs) in phytoplankton is influenced by environmental temperature. We investigated the potential of climate warming to alter lipid dynamics of Scenedesmus obliquus (Turpin) Kütz. by comparing lipid and fatty acid (FA) profiles as well as FA metabolism (using [1-14 C] acetate) at 20°C and 28°C. We documented an overall decline (53%-37%) in the proportion of n-3 PUFA (in particular, of a-linolenic acid [ALA; 18:3n-3]), and a concomitant increase in saturated fatty acids (SAFAs) in total lipids (TLs) at 28°C, consistent with enhanced incorporation of radioactivity from [1-14 C] acetate into total 16:0, 18:1, and decreased incorporation into 18:2 and 18:3 FA (from 36% to 22% of the total) at 28°C. Glycerophospholipids were also affected by warming; ALA and stearidonic acids (SDAs; 18:4n-3) both decreased (by 13% and 15%, respectively) in phosphatidylcholine (PC) and (by 24% and 20%, respectively) in phosphatidylethanolamine (PE). The characteristic FA in phosphatidylglycerol (PG; 16:1n-13t) increased (by 22%) at 28°C. The activities of desaturases, which add double bonds to FA moieties, comprised the major suite of reactions affected by the temperature increase in TL and polar lipid (PL) classes. Climate modelers predict an increase in the number of extreme heat days in summer at temperate latitudes, with parallel projected increases in water temperatures of shallow water bodies. Our results suggest that the overall decrease in the essential n-3 FA ALA in S. obliquus at higher water temperatures may lower food quality for higher tropic levels, adding another climate-warming stress.
1. The d 13 C and d 15 N signatures of zooplankton vary with dissolved organic carbon (DOC), but ... more 1. The d 13 C and d 15 N signatures of zooplankton vary with dissolved organic carbon (DOC), but inconsistent and limited taxonomic resolution of previous studies have masked differences that may exist among orders, genera or species and are attributable to dietary and ⁄ or habitat differences. Here we investigate differences among the isotopic signatures of five zooplankton taxa (Daphnia, Holopedium, large Calanoida, small Calanoida and Cyclopoida) in Precambrian shield lakes with a sixfold range of DOC concentration. 2. d 13 C signatures of Daphnia, small calanoids and large calanoids became more depleted with increasing lake DOC, whereas Holopedium and cyclopoid d 13 C became enriched with increasing DOC concentration. 3. The variability of d 13 C and d 15 N isotopic signatures among zooplankton groups was reduced in high-DOC, compared to low-DOC lakes, especially for d 13 C. Differences in d 13 C and POM-corrected d 15 N accounted for up to 33.7% and 19.5% of the variance, respectively, among lakes of varying DOC concentration. 4. The narrow range of signatures found in higher DOC lakes suggests that different taxa have similar food sources and ⁄ or habitats. In contrast, the wide range of signatures in low-DOC lakes suggests that different taxa are exploiting different food sources and ⁄ or habitats. Together with the variable trends in zooplankton isotopic signatures along our DOC gradient, these results suggest that food web dynamics within the zooplankton community of temperate lakes will change as climate and lake DOC concentrations change.
The ranked acid sensitivities of six common crustacean zooplankton taxa were determined from a mu... more The ranked acid sensitivities of six common crustacean zooplankton taxa were determined from a multilake field survey in Ontario and from laboratory bioassays. The two approaches gave the same ranking (from most to least sensitive): Daphnia galeata mendotae, Daphnia retrocurua, and Skistodiaptomus oregonensis > Diaphanosoma birgei > Mesocyclops edax > Bosmina longirostris. This finding suggests that acidification has caused the widespread damage which has been documented for the zooplankton of Ontario and northeastern U.S. lakes.
The interactive effects of climate change and invasive alien species (IAS) pose serious threats t... more The interactive effects of climate change and invasive alien species (IAS) pose serious threats to biodiversity, ecosystems and human well-being worldwide. In particular, IAS are predicted to experience widespread changes in distribution in response to climate change, with many expanding their ranges into new areas. However, the two drivers of global change are seldom considered together in policy and management. We conducted a knowledge synthesis to assess the state of research on IAS range shifts under climate change in Canada. We found that the study of IAS distribution changes caused by climate change is a relatively new field of inquiry that integrates research in the areas of ecology, conservation biology, and environmental sciences. The multidisciplinary dimensions of the issue are largely overlooked in the scholarly literature, with most studies having a purely natural science perspective. Very little original research has occurred in the field to date; instead literature reviews are common. Research focuses on modeling range changes of current IAS threats, rather than predicting potential future IAS threats. The most commonly studied IAS already occur in Canada as native species that have spread beyond their range (e.g., lyme disease, mountain pine beetle, smallmouth bass) or as established invaders (e.g., gypsy moth). All of these IAS are expected to expand northward with climate change, resulting in widespread negative impacts on forest and freshwater biodiversity, carbon sequestration, and public health. Many barriers to predicting IAS range change under climate change are identified in the literature, including the complexity of the issue, lack of ecological data, and failure to integrate climate change -IAS interactions into research, policy, and management. Recommendations for increased research and monitoring, and the need for policy and management reform predominate in the literature.
The WHAM-F TOX model quantifies the combined toxic effects of protons and metal cations 29 toward... more The WHAM-F TOX model quantifies the combined toxic effects of protons and metal cations 29 towards aquatic organisms through the toxicity function (F TOX ), a linear combination of the 30 products of organism-bound cation and a toxic potency coefficient for each cation. We 31 describe the application of the model to predict an observable ecological field variable, 32 species richness of pelagic lake crustacean zooplankton, studied with respect to either 33 acidification or the impacts of metals from smelters. The fitted results give toxic potencies 34 increasing in the order H + < Al < Cu < Zn < Ni. In general, observed species richness is lower 35 than predicted, but in some instances agreement is close, and is rarely higher than 36 predictions. The model predicts recovery in agreement with observations for three regions, 37
We tested the sampling methods of a volunteer-based monitoring program designed to detect the non... more We tested the sampling methods of a volunteer-based monitoring program designed to detect the non-indigenous spiny water flea, Bythotrephes longimanus, and found that the program could detect the majority of Bythotrephes invasions. Volunteers take two vertical hauls with a 30 cm diameter net at each of three pelagic stations. To determine if the volunteers were using a large enough net at their three stations, we performed a 17-lake comparison of the volunteer's net with a 75 cm diameter, research-grade net. We found no difference in the number of stations at which Bythotrephes was detected (paired t-test, p = 0.155) with the two nets, because Bythotrephes densities were above the detection limits for both nets. To determine if three stations were sufficient to detect the invader with the volunteer's net, we deployed it at 30 stations in two lakes with average (Harp Lake, 4.17 Bythotrephes m −3 ) vs. low Bythotrephes densities (Sugar Lake, 0.92 m −3 ). In Harp Lake, repeated randomized sampling of the 30 sets of data indicated that only three stations were needed for 100% capture success. In Sugar Lake, seven stations were needed for 100% capture success, but three stations, the current program design, failed to detect the invasion only 14% of the time.
We used multiple linear regression analysis to investigate relationships between latesummer epili... more We used multiple linear regression analysis to investigate relationships between latesummer epilimnion thickness, transparency, lake area, acidity and summer weather conditions in a large (n = 116) multi-year data set for 9 small Boreal Shield lakes. Dissolved organic carbon (DOC) was the best individual predictor of late summer epilimnion thickness (r 2 = 0.69). Total chlorophyll a, the number of days between ice-out and late-summer stratification, and lake area collectively explained an additional 14% of the variation in epilimnion thickness. The three attributes of summer weather that we examined, mean daily temperature, mean daily wind speed, and mean daily hours of bright sunshine, did not add to the predictive ability of our regression model. Lake acidity also did not add directly to the predictive ability of the model, likely because DOC concentrations already reflected the effects of pH. Our study supports an increasing body of evidence indicating that the dominant effects of climate change on lake thermal structure in small lakes will be through effects on processes that affect lake transparency.
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...
Climate change is expected to have important impacts on aquatic ecosystems. On the Boreal Shield,... more Climate change is expected to have important impacts on aquatic ecosystems. On the Boreal Shield, mean annual air temperatures are expected to increase 2 to 4 • C over the next 50 years. An important challenge is to predict how changes in climate and climate variability will impact natural systems so that sustainable management policies can be implemented. To predict responses to complex ecosystem changes associated with climate change, we used long-term biotic databases to evaluate how important elements of the biota in Boreal Shield lakes have responded to past fluctuations in climate. Our long-term records span a two decade period where there have been unusually cold years and unusually warm years. We used coherence analyses to test for regionally operating controls on climate, water temperature, pH, and plankton richness and abundance in three regions across Ontario: the Experimental Lakes Area, Sudbury, and Dorset. Inter-annual variation in air temperature was similar among regions, but there was a weak relationship among regions for precipitation. While air temperature was closely related to lake surface temperatures in each of the regions, there were weak relationships between lake surface temperature and richness or abundance of the plankton. However, inter-annual changes in lake chemistry (i.e., pH) were correlated with some biotic variables. In some lakes in Sudbury and Dorset, pH was dependent on extreme events. For example, El Nino related droughts resulted in acidification pulses in some lakes that influenced phytoplankton and zooplankton richness. These results suggest that there can be strong heterogeneity in lake ecosystem responses within and across regions.
This study identified two scales of pattern in the assemblages of Chydoridae (Crustacea, Branchio... more This study identified two scales of pattern in the assemblages of Chydoridae (Crustacea, Branchiopoda, Anomopoda) in the shallow (<2 m) littoral zone of Plastic Lake, Ontario, Canada in the autumn of 1987. Twenty chydorid species were collected in 15 over-night sets of funnel traps in each of four habitat types. Analysis of variance multivariate analysis of variance, and discriminant function analysis revealed that assemblages differed among the habitats. Alona intermedia, Alona quadrangularis and Chydorus bicornutus were particularly abundant in the most structurally diverse habitat type -muddy, rock-strewn areas with approximately 40% bottom cover by the pipewort, Eriocaulon septangulare. In contrast, Anchistropus cf. minor was caught most often on bare shelves of rock. A second set of analyses demonstrated that chydorid assemblages also differed at a smaller scale, i.e. with local patchiness in bottom cover by the dominant macrophyte (E. septangulare). The abundance of Alona affinis was positively correlated with cover by E. septangulare, whereas Anchistropus cf. minor was caught mainly in microhabitats without vegetation. Alona intermedia and A. quadrangularis were most abundant in microhabitats with intermediate amounts of vegetation, suggesting their abundance is influenced by habitat factors other than vegetation.
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...
Brian Leung is a research assistant professor at the University of Notre Dame. His current resear... more Brian Leung is a research assistant professor at the University of Notre Dame. His current research focuses on ecological forecasting and bioeconomic risk analysis of invasive species, using mathematical, computational, and statistical models. His address: Bill Keller is the senior environmental scientist -Northern Lakes, with the Ontario Ministry of Environment, and is an adjunct professor in the Department of Biology, Laurentian University. His studies focus on documenting and understanding the recovery process in damaged aquatic systems, and on investigating the combined effects of multiple stressors on lakes and on lake recovery. His address: Shelley Arnott is an assistant professor in the Department of Biology at Queen's University. Her research focuses on determining the chemical and ecological factors that influence the recovery of aquatic biota from historical acidification in the face of climatic variability and the spread of nonindigenous species. Her address: John Gunn is a fisheries research scientist with the Ontario Ministry of Natural Resources and heads up the Cooperative Freshwater Ecology Unit at Laurentian University. He specializes in restoration ecology of aciddamaged ecosystems as well as the ecology of salmonid fishes of Ontario. His address:
No other freshwater system contains as many non-native species or has been invaded as frequently ... more No other freshwater system contains as many non-native species or has been invaded as frequently as the Great Lakes-St. Lawrence River basin. Over 180 non-native species have become established in the basin within the past two centuries. Collectively, these invasions have altered biodiversity, habitat structure, productivity, water quality, contaminant cycling and ecosystem services. The composition and rate of discovery of invaders are correlated with changes in dominant vectors, such as transoceanic shipping. We review the invasion history of the basin and identify future invasion threats by considering trends and potential scenarios in changing vectors and pathways. Whereas most non-native species discovered since the opening of the St. Lawrence Seaway in 1959 were attributable to ballast water discharge from transoceanic vessels, recent regulations have apparently reduced the threat of this vector. Nevertheless, non-native species may continue to be introduced through poorly-regulated vectors, particularly those associated with trade in live organisms. The spread and impact of current and future invaders are expected to be exacerbated by interactions with other anthropogenic stressors that are increasing in frequency and spatial extent. Most notably, the continued warming of surface waters of the Great Lakes basin will lift thermal barriers to invasions by warm-water taxa. Contrary to any perception that the "worst is over" (i.e. most harmful invasions have already occurred), the basin remains vulnerable to further ecological and economic disruptions from non-native species.
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
We investigated the temporal coherence (i.e., the correlation or synchrony between time series) o... more We investigated the temporal coherence (i.e., the correlation or synchrony between time series) of annual abundances among populations of freshwater zooplankton in eight lakes in Ontario, Canada, from 1980 to 1992. We estimated temporal coherence using the intraclass correlation coefficient (r i ). While values of r i were relatively low among comparisons of all eight lakes, they were statistically significant for three of the seven common cladoceran and copepod taxa (Bosmina longirostris, Leptodiaptomus minutus, and Mesocyclops edax). These significant positive correlations imply that a portion of the interannual variation in abundance was produced by factors operating on a scale larger than the individual lake catchments. Because the eight-lake analysis might obscure strong, but conflicting, patterns among lakes in the region, we identified homogeneous and temporally coherent subsets of lakes for each species using an exploratory stepwise deletion procedure. The resultant homogeneous subsets exhibited much greater temporal coherence, accounting for 47% (Eubosmina) to 84% (Leptodiaptomus) of the interannual variation in abundance. Our results suggest that the factors affecting annual variation in zooplankton abundance must be sought both within lakes and beyond their watersheds.
The biosynthesis of nutritionally important polyunsaturated fatty acids (PUFAs) in phytoplankton ... more The biosynthesis of nutritionally important polyunsaturated fatty acids (PUFAs) in phytoplankton is influenced by environmental temperature. We investigated the potential of climate warming to alter lipid dynamics of Scenedesmus obliquus (Turpin) Kütz. by comparing lipid and fatty acid (FA) profiles as well as FA metabolism (using [1-14 C] acetate) at 20°C and 28°C. We documented an overall decline (53%-37%) in the proportion of n-3 PUFA (in particular, of a-linolenic acid [ALA; 18:3n-3]), and a concomitant increase in saturated fatty acids (SAFAs) in total lipids (TLs) at 28°C, consistent with enhanced incorporation of radioactivity from [1-14 C] acetate into total 16:0, 18:1, and decreased incorporation into 18:2 and 18:3 FA (from 36% to 22% of the total) at 28°C. Glycerophospholipids were also affected by warming; ALA and stearidonic acids (SDAs; 18:4n-3) both decreased (by 13% and 15%, respectively) in phosphatidylcholine (PC) and (by 24% and 20%, respectively) in phosphatidylethanolamine (PE). The characteristic FA in phosphatidylglycerol (PG; 16:1n-13t) increased (by 22%) at 28°C. The activities of desaturases, which add double bonds to FA moieties, comprised the major suite of reactions affected by the temperature increase in TL and polar lipid (PL) classes. Climate modelers predict an increase in the number of extreme heat days in summer at temperate latitudes, with parallel projected increases in water temperatures of shallow water bodies. Our results suggest that the overall decrease in the essential n-3 FA ALA in S. obliquus at higher water temperatures may lower food quality for higher tropic levels, adding another climate-warming stress.
1. The d 13 C and d 15 N signatures of zooplankton vary with dissolved organic carbon (DOC), but ... more 1. The d 13 C and d 15 N signatures of zooplankton vary with dissolved organic carbon (DOC), but inconsistent and limited taxonomic resolution of previous studies have masked differences that may exist among orders, genera or species and are attributable to dietary and ⁄ or habitat differences. Here we investigate differences among the isotopic signatures of five zooplankton taxa (Daphnia, Holopedium, large Calanoida, small Calanoida and Cyclopoida) in Precambrian shield lakes with a sixfold range of DOC concentration. 2. d 13 C signatures of Daphnia, small calanoids and large calanoids became more depleted with increasing lake DOC, whereas Holopedium and cyclopoid d 13 C became enriched with increasing DOC concentration. 3. The variability of d 13 C and d 15 N isotopic signatures among zooplankton groups was reduced in high-DOC, compared to low-DOC lakes, especially for d 13 C. Differences in d 13 C and POM-corrected d 15 N accounted for up to 33.7% and 19.5% of the variance, respectively, among lakes of varying DOC concentration. 4. The narrow range of signatures found in higher DOC lakes suggests that different taxa have similar food sources and ⁄ or habitats. In contrast, the wide range of signatures in low-DOC lakes suggests that different taxa are exploiting different food sources and ⁄ or habitats. Together with the variable trends in zooplankton isotopic signatures along our DOC gradient, these results suggest that food web dynamics within the zooplankton community of temperate lakes will change as climate and lake DOC concentrations change.
The ranked acid sensitivities of six common crustacean zooplankton taxa were determined from a mu... more The ranked acid sensitivities of six common crustacean zooplankton taxa were determined from a multilake field survey in Ontario and from laboratory bioassays. The two approaches gave the same ranking (from most to least sensitive): Daphnia galeata mendotae, Daphnia retrocurua, and Skistodiaptomus oregonensis > Diaphanosoma birgei > Mesocyclops edax > Bosmina longirostris. This finding suggests that acidification has caused the widespread damage which has been documented for the zooplankton of Ontario and northeastern U.S. lakes.
The interactive effects of climate change and invasive alien species (IAS) pose serious threats t... more The interactive effects of climate change and invasive alien species (IAS) pose serious threats to biodiversity, ecosystems and human well-being worldwide. In particular, IAS are predicted to experience widespread changes in distribution in response to climate change, with many expanding their ranges into new areas. However, the two drivers of global change are seldom considered together in policy and management. We conducted a knowledge synthesis to assess the state of research on IAS range shifts under climate change in Canada. We found that the study of IAS distribution changes caused by climate change is a relatively new field of inquiry that integrates research in the areas of ecology, conservation biology, and environmental sciences. The multidisciplinary dimensions of the issue are largely overlooked in the scholarly literature, with most studies having a purely natural science perspective. Very little original research has occurred in the field to date; instead literature reviews are common. Research focuses on modeling range changes of current IAS threats, rather than predicting potential future IAS threats. The most commonly studied IAS already occur in Canada as native species that have spread beyond their range (e.g., lyme disease, mountain pine beetle, smallmouth bass) or as established invaders (e.g., gypsy moth). All of these IAS are expected to expand northward with climate change, resulting in widespread negative impacts on forest and freshwater biodiversity, carbon sequestration, and public health. Many barriers to predicting IAS range change under climate change are identified in the literature, including the complexity of the issue, lack of ecological data, and failure to integrate climate change -IAS interactions into research, policy, and management. Recommendations for increased research and monitoring, and the need for policy and management reform predominate in the literature.
The WHAM-F TOX model quantifies the combined toxic effects of protons and metal cations 29 toward... more The WHAM-F TOX model quantifies the combined toxic effects of protons and metal cations 29 towards aquatic organisms through the toxicity function (F TOX ), a linear combination of the 30 products of organism-bound cation and a toxic potency coefficient for each cation. We 31 describe the application of the model to predict an observable ecological field variable, 32 species richness of pelagic lake crustacean zooplankton, studied with respect to either 33 acidification or the impacts of metals from smelters. The fitted results give toxic potencies 34 increasing in the order H + < Al < Cu < Zn < Ni. In general, observed species richness is lower 35 than predicted, but in some instances agreement is close, and is rarely higher than 36 predictions. The model predicts recovery in agreement with observations for three regions, 37
We tested the sampling methods of a volunteer-based monitoring program designed to detect the non... more We tested the sampling methods of a volunteer-based monitoring program designed to detect the non-indigenous spiny water flea, Bythotrephes longimanus, and found that the program could detect the majority of Bythotrephes invasions. Volunteers take two vertical hauls with a 30 cm diameter net at each of three pelagic stations. To determine if the volunteers were using a large enough net at their three stations, we performed a 17-lake comparison of the volunteer's net with a 75 cm diameter, research-grade net. We found no difference in the number of stations at which Bythotrephes was detected (paired t-test, p = 0.155) with the two nets, because Bythotrephes densities were above the detection limits for both nets. To determine if three stations were sufficient to detect the invader with the volunteer's net, we deployed it at 30 stations in two lakes with average (Harp Lake, 4.17 Bythotrephes m −3 ) vs. low Bythotrephes densities (Sugar Lake, 0.92 m −3 ). In Harp Lake, repeated randomized sampling of the 30 sets of data indicated that only three stations were needed for 100% capture success. In Sugar Lake, seven stations were needed for 100% capture success, but three stations, the current program design, failed to detect the invasion only 14% of the time.
We used multiple linear regression analysis to investigate relationships between latesummer epili... more We used multiple linear regression analysis to investigate relationships between latesummer epilimnion thickness, transparency, lake area, acidity and summer weather conditions in a large (n = 116) multi-year data set for 9 small Boreal Shield lakes. Dissolved organic carbon (DOC) was the best individual predictor of late summer epilimnion thickness (r 2 = 0.69). Total chlorophyll a, the number of days between ice-out and late-summer stratification, and lake area collectively explained an additional 14% of the variation in epilimnion thickness. The three attributes of summer weather that we examined, mean daily temperature, mean daily wind speed, and mean daily hours of bright sunshine, did not add to the predictive ability of our regression model. Lake acidity also did not add directly to the predictive ability of the model, likely because DOC concentrations already reflected the effects of pH. Our study supports an increasing body of evidence indicating that the dominant effects of climate change on lake thermal structure in small lakes will be through effects on processes that affect lake transparency.
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