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Abstract: Salt, primarily NaCl, is commonly used to de‐ice winter roads. The usage of road salt is steadily increasing as the area of urbanised land expands, and chloride concentrations in many lakes and flowing waters near roads have been steadily increasing through time. In some waterbodies, these concentrations are reaching levels that are toxic to freshwater organisms, such as zooplankton which are integral to the structure and function of freshwater communities. We currently have a poor understanding of the impact of road salt contamination on zooplankton communities, and particularly the variation in response among lakes. Zooplankton communities differ in factors that could influence the impacts of elevated chloride, such as local species composition, exposure history and regional connectivity. Assessing and predicting how increasing road salt usage affects natural, freshwater zooplankton communities requires studies that investigate how communities vary in the impacts of elevated chloride, and in their response to dispersal. We conducted a field mesocosm experiment that examined the effects of salt (NaCl) addition on two different zooplankton communities, which were also subjected to repeated introductions of zooplankton dispersers from the regional species pool. These treatments allowed us to determine whether communities differed in the impacts of salt, and how the effects of salt differed between communities that did and did not receive zooplankton dispersers. We found variation in the effects of salt and dispersal between our experimental communities. For one lake community, salt drove zooplankton species composition towards dominance by littoral cladocerans. Zooplankton dispersal into this community ameliorated these impacts of salt by returning species composition to a state more similar to our “Control” communities. Conversely, for the other lake community, salt alone had minimal effects on zooplankton, while the combination of salt and dispersal led to declines in adult copepods. Our experiment found that the impacts of salt varied between two zooplankton communities, causing a range of negative, positive and neutral community effects, and that dispersal from the regional species pool could serve as an ameliorating or exacerbating influence. Efforts to understand and predict the impacts of road salt on freshwater communities would therefore benefit from an evaluation of the potential role played by local (e.g., exposure history and biotic interactions) and regional (e.g., connectivity to possible sources of immigrants) context in the response of communities to elevated chloride. [ABSTRACT FROM AUTHOR]

Northern regions are expected to experience large environmental change over the next few decades. The response of biota will depend on changes in the local environment, regional processes that influence lake connectivity, and species interactions. In 2008, we surveyed 92 lakes and ponds across Wapusk National Park, located on the southwestern shore of Hudson Bay. At each site we assessed water chemistry and zooplankton community composition. In an effort to understand how the aquatic ecosystems will respond to future environmental change, we determined local characteristics (e.g., water chemistry), regional spatial factors (e.g., dispersal), and biotic interactions (e.g., species associations) influencing community composition. Important environmental variables included lake area, pH, ionic composition, total phosphorus, and chlorophyll a; however, spatial variables explained more variation than environmental variables, suggesting that dispersal is an important driver of zooplankton composition in this region. Additionally, species exhibited negative co-occurrence patterns, suggesting biotic interactions are important in structuring the zooplankton communities. As environmental conditions change and the distribution of habitat (i.e., coastal fen, interior peatland, and spruce forest) shifts, evidence that the park's zooplankton community is spatially structured coupled with our suspicion that zooplankton are likely to experience high dispersal levels in Wapusk leads us to suggest zooplankton may indeed be able to track changing environmental conditions within the park, although it remains unclear how species interactions will modify this expectation. [ABSTRACT FROM AUTHOR]

Identifying factors that influence the foraging ability of an introduced predator is essential for assessing its potential impact on the invaded community. We conducted a series of in situ enclosure experiments to determine the effect of light on the foraging ability and community-level effects of the invasive cladoceran Bythotrephes longimanus in lakes., In 1-L enclosures with only Daphnia prey, a strong effect of predation under ambient light conditions was observed. There was no evidence of predation in dark treatments, suggesting that Bythotrephes is unable to feed by mechanoreception alone., A subsequent experiment using larger enclosures exposed an assemblage of prey from an uninvaded lake to Bythotrephes predation across a similar light gradient. Consistent with regional lake surveys, Bythotrephes reduced cladoceran abundance under ambient light conditions., At the community level, predation effects were overall strongest under ambient light; however, the influence of light on predation varied across trials that differed in initial community structure of prey. Also, some predation under dark conditions was possible on Ceriodaphnia and Bosmina, suggesting that Daphnia, in particular, may be less vulnerable under low-light conditions., Our results suggest that light refuges for some prey taxa could play an important role in mediating the impact of Bythotrephes. [ABSTRACT FROM AUTHOR]

In the event of an environmental disturbance, dispersal of native taxa may provide species and genetic diversity to ecosystems, increasing the likelihood that there will be species and genotypes present that are less vulnerable to the disturbance. This may allow communities to maintain functioning during a disturbance and may be particularly important when the perturbation is novel to the system, such as the establishment of an invasive species. We examined how dispersal of native species may influence crustacean zooplankton communities in freshwater lakes invaded by the invertebrate predator, Bythotrephes longimanus. Using large enclosures, we experimentally tested the effect of dispersal on zooplankton community abundance, richness, and composition in (1) a community invaded by Bythotrephes, (2) the same community with the invader removed, and (3) a community that was never invaded. Dispersal increased zooplankton community abundance and richness; however, these effects were usually only significant in the invader-removed treatment. Dispersal tended to make the invader-removed communities more similar to never-invaded communities in abundance, richness, and composition. Dispersal had little effect on zooplankton abundance in the invaded community; however, richness significantly increased, and the community composition changed to resemble a never-invaded community by the end of the experiment. Our results have implications for understanding the role of dispersal during transitory states in communities. Dispersal of native taxa may be particularly important during the period between the arrival and broad-scale establishment of Bythotrephes, as dispersal through space or time (i.e., from resting eggs) may rapidly increase zooplankton abundance when the, invader is absent or in low abundances. Overall, our results suggest that communities with strong local predatory and competitive interactions may be closed to immigration from colonists, but that invasive species may alter the conditions under which species can establish. These results have implications for the interaction of native and invasive species across broad spatial scales, as regional dispersal of native taxa may forestall the local extirpation of native species. In particular, transient phases that result from variable persistence of invaders within habitats or across a region may permit native colonists to successfully establish, and thus increase local and regional resistance to future disturbance. [ABSTRACT FROM AUTHOR]

We employed zooplankton resting eggs to track population-level shifts in acid tolerance over the last century in a boreal shield lake recovering from acidification. Shifts in mean and variance of ecological tolerances of species that occupy ecosystems recovering from anthropogenic stress are important to consider because of their potential to influence eco-evolutionary dynamics at community and ecosystem levels. In a laboratory experiment, we compared juvenile survival of Leptodiaptomus minutus copepods hatched from resting eggs from three time periods (80- to 100-year- old: pre-industrial, 20- to 50- year- old: lake acidification, and 8- to 10-year- old: recovery of lake-water back to pH ≥ 6.0) under several pH treatments. Mitochondrial DNA was used to confirm species identity and to test for population bottlenecks as a possible mechanism to explain our results. We expected that nauplii hatched from eggs deposited prior to industrialization (lake-water pH ≈ 6.0) and from the period of pH recovery (lake-water pH ≥ 6.0) would have lower mean and more variable survival at acidic pH compared to nauplii hatched from the period of peak lake acidification (lake-water pH ≈ 4.7). Our results, which are likely a combination of both genetic and environmental effects, suggest support for this hypothesis. Nauplii hatched from eggs deposited during the period of acidification in George Lake had reduced variation in pH tolerance compared to the recovery period. This was likely driven by strong selection rather than genetic drift because we found no evidence of a population bottleneck. However, we could not detect differences in the variance of naupliar survival between pre-industrial and acidic time periods. Trends in mean naupliar survival from different time periods matched findings from other field-based studies that detected a relationship between lake acidification history and acid tolerance in L. minutus. [ABSTRACT FROM AUTHOR]

Ecological linkages between species diversity in communities and genetic diversity in populations have potential to influence the assembly of communities in habitats recovering from human disturbance, but few studies have attempted to synthesize relationships between these levels of biological organization, especially for locally adapted species. No such studies have been done in freshwater ecosystems despite the plethora of environmental stressors plaguing aquatic communities around the world. We present the first study to test (I) whether diversity and dissimilarity among communities and populations of a locally adapted species are correlated and (2) whether communities and population haplotypes respond differently to environmental selection and spatial structure of habitats. We used a fragment of mitochondrial DNA (mtDNA) belonging to the gene cytochrome oxidase subunit I (COl) as a neutral tag to discriminate among different population haplotype variants. In boreal lakes with different histories of exposure to anthropogenic acidification, diversity and dissimilarity metrics for crustacean zooplankton communities and locally adapted populations of an abundant and broadly distributed calanoid copepod species, Leptodiaptomus minutus, did not correlate. This discord was likely because zooplankton communities responded more strongly to acidity and acidity-related environmental variables than spatial structure of lakes, whereas the distribution of L. minutus haplotypes' was more strongly governed by spatial structure of lakes than environmental selection. Although spatial structure was the dominant driver of haplotype structure among L. minutus lake populations, there were similarities in the types of environmental variables that influenced the distributions of species in communities and haplotypes in populations. How haplotype diversity among populations relates to community diversity depends on the relative influence of spatial structure of habitats and selection at each of these scales of biological organization. [ABSTRACT FROM AUTHOR]

Bythotrephes longimanus is an invertebrate predator that has invaded the North American Great Lakes and a number of inland lakes, where it preys on crustacean zooplankton. We examined the effect of Bythotrephes on two measures of ecosystem function during a four-month observational study of freshwater lakes on the boreal shield. Bythotrephes-invaded lakes had significantly lower epilimnetic zooplankton abundance and production compared to reference lakes. On average, Bythotrephes consumed 34% of zooplankton production when it was present in lakes. There was some evidence of changes in the timing of zooplankton production, as well as shifts to cooler, less productive habitats, which may lessen the overall effect of the invader on the transfer of energy to higher trophic levels. We experimentally demonstrated a weak trophic cascade where invader predation reduced zooplankton biomass, and subsequently increased phytoplankton growth. However, the response was small in magnitude and not biologically relevant at the whole lake-scale. The most conspicuous effect of Bythotrephes that we measured was a diversion of energy away from native predators at higher trophic levels. [ABSTRACT FROM AUTHOR]

Analyses of temporal patterns of diversity across a wide range of taxa have found that more diverse communities often show smaller compositional changes over time. This generality indicates that high diversity is associated with greater temporal stability in species composition. We examined patterns of diversity and community stability in zooplankton time series data from 36 lakes sampled over a combined 483 years. The species–time relationship was flatter in more species-rich lakes in the temperate zone. However, high-latitude lakes had both low richness and low turnover. These patterns were consistent for turnover both within and among years. Daily, annual and long-term richness were all higher in large lakes while turnover was unaffected by the surface area. Richness on all time scales, as well as turnover within and among years, all declined at high latitude. Species–area relations and latitudinal gradients in richness therefore reflect different temporal components of diversity. Our results suggest that diversity shows strong associations with compositional stability that vary qualitatively across biogeographical provinces. Community stability increases with diversity among lakes in the temperate zone; however, the two are negatively correlated across latitudinal gradients. These patterns indicate that either the direct effects of diversity on stability or their covariance with environmental fluctuations vary with latitude. [ABSTRACT FROM AUTHOR]

The article investigates the roles of local environmental conditions and dispersal limitation in crustacean zooplankton recovery from acidification in Swan Lake, Ontario, a historically acidified, metal-contaminated lake. Mesocosm and emergence trap experiments were conducted. The preindustrial pH of the lake was estimated to be between 5.6 and 6.1 but sulphur dioxide emissions from nearby smelters caused a reduction in pH to 4.0 in 1977. Three colonist species-C. b. thomasi and S. ore-gonensis and, to a lesser extent,. M. edax-were not affected by the pH treatment in the enclosure experiment but were reduced in abundance by the resident zooplankton community indicating an effect of local biotic conditions. The results suggests that local and regional processes are instrumental in zooplankton community assembly. This indicates that a multifaceted management solution will be required for complete restoration of acidified ecosystems. Recovery of some - taxa, such as Ceriodaphnia and Daphnia, will be affected without further reductions in acid deposition and subsequent increases in take pH.

Invasive species introductions into freshwater ecosystems have had a multitude of effects on aquatic communities. Few studies, however, have directly compared the impact of an invader on communities with contrasting structure. Historically high levels and subsequent reductions of acid deposition have produced landscapes of lakes of varying acidity and zooplankton community structure. We conducted a 30-day enclosure experiment in Killarney Provincial Park, Ontario, Canada, to test the effects of Bythotrephes longimanus, an invasive invertebrate predator, on two contrasting zooplankton communities at different stages of recovery from acidification: recovered and acid damaged. Bythotrephes significantly decreased zooplankton biomass and abundance in both communities but had a greater negative effect on the abundance of zooplankton in the recovered community. Bythotrephes reduced species diversity of the recovered zooplankton community but not of the acid-damaged community. Species richness of both community types was unaffected by Bythotrephes predation. The effect of Bythotrephes on small cladocerans, a preferred prey type, differed between the community types and appeared to be related to density-dependent predation by Bythotrephes. Both community- and species-level results suggest that recovered and acid-damaged zooplankton assemblages may be negatively affected by an invasion of Bythotrephes but that the specific response is dependent on the original community structure. [ABSTRACT FROM AUTHOR]

Examines conceptual frameworks in order to understand the sequence of ecological steps needed for the recovery of biotic communities and on where and how to intervene in this process should recovery stall. Description of decision tree, highlighting the sequence of processes necessary for ecological recovery; Analysis of process bottlenecks such as inadequate water quality; Details of the framework for the integration of ecological processes in a larger management context.

Assesses the importance of rotifers in lake ecosystems which increases the acidicity level during the experimental manipulation in Little Rock, Arkansas. Nature of species-specific responses among habitats; Observation of the total rotifer biomass; Indication of hydrogen-ion concentration.