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This review provides a Canadian perspective on freshwater zooplankton diversity and ecology across scales and systems. It aims at describing how zooplankton are diverse in forms and functions, and constitute a key component of plankton food webs, a model for ecological theories and a sentinel for monitoring ecological integrity and function in lakes facing environmental changes and anthropogenic stressors. These objectives are addressed across a continuum of scales (continental, regional and local) and systems (reservoirs, lakes and ponds). This perspective shows that the environmental control of zooplankton biodiversity, community structure and function in Canada is complex and variable. Zooplankton communities demonstrated a wide range of responses to anthropogenic disturbances across scales and systems due to interactions with watershed biogeochemistry and climate. This review supports the Multiple Forces hypothesis where forcing by abiotic factors (climate, nutrients, morphometry and chemistry) has a fundamental role at continental scale over Canadian ecoregions, and at regional scale in the Boreal ecozones. In contrast, forcing by biotic factors (algal resources and predators) is relatively more influential at local scale, in resort and urban regions. The challenge for future research will be to combine all new concepts and approaches in a global perspective to better understand the responses of freshwater zooplankton to multiple environmental changes and anthropogenic stressors in Canada.

Zooplankton are relevant indicators of changes in lake water quality, used for monitoring the response of aquatic ecosystems to the combined effects of declining acidic deposition and rising air temperatures. First, the current landscape was defined from the recent (2017) spatial patterns of zooplankton communities in 73 Quebec lakes distributed over an 800-km SW–NE gradient, spanning a wide range of water quality, climate, and morphometric characteristics. On a large scale, we identified among-lake clustering of three types of zooplankton assemblages and variation in species composition at fine scale between lake pairs. Dissimilarity in zooplankton assemblages among lake pairs were best correlated (r > 0.400, p < 0.001) with their difference in air temperature, pH, and calcium, reflecting spatial gradients in climate and lake acid–base status. Second, to examine long-term response in the zooplankton community, we compared acidification indicators and abundance of taxa for a subset of 19 lakes sampled in 1982 and 2017. Despite an average threefold drop in sulfate concentration, changes in calcium and pH were relatively small, and consequently, no major changes in zooplankton assemblages were detected since 1982.

Urban ecology is a promising research field in limnology, but we still need to evaluate how urban waterbodies can sustain biodiversity. In this paper, we present a comprehensive foodweb perspective of urban waterbodies in the city of Montreal (Quebec, Canada). The research goals are to evaluate if biodiversity and community structure of foodweb components (phytoplankton, zooplankton, and macroinvertebrates) are valuable tools for assessing the ecological status of urban waterbodies and examine how they are controlled by multiple factors related to trophic status and habitat complexity (origin, water residence, macrophyte cover, fish, and management practices). Multiple factor analysis, correlations, and non-parametric tests were used to examine the relationships between the environmental factors and foodweb biological variables. Our case study confirms that urban waterbodies are important sources of biodiversity and reveals that foodweb-based biological indicators are reliable tools for the biomonitoring of urban waterbodies. Foodweb biodiversity and community structure were more influenced by habitat complexity than by trophic status. The key determinants of variation were the differences in water regime, management of temporary and permanent waterbodies, and contrasts in habitat complexity depending on pond origin (artificial or natural) and macrophyte cover.

Phytoplankton bioindicators were used to assess environmental conditions in urban aquatic systems in a large Canadian city. Sampling was conducted during summers 2010 and 2011 in 20 urban waterbodies on the Island of Montreal (Quebec, Canada). We evaluated 4 indicators: (1) fluorometric estimates of the chlorophyll concentration of the total phytoplankton and of 4 spectral groups, (2) species richness, and (3) biovolumes of taxonomic and (4) functional groups of the microphytoplankton. We assessed how these indicators changed among types of urban waterbodies and determined the limnological features and/or management practices driving their spatial variation. Principal component analysis captured 48% of total environmental heterogeneity, and K-means clustering analyses defined 5 relevant types of waterbodies. Overall, 96 microphytoplankton species (γ diversity) were recorded, and species richness (α diversity) per waterbody varied from 1 to 27. Chlorophyll concentration of the total phytoplankton and the green algae spectral group, as well as the total biovolume of microphytoplankton, dinophytes, and of 2 functional groups (large flagellates, large colonies of green algae, and cyanobacteria) differed among waterbody types. Phytoplankton indicators based on in situ fluorometry and microphytoplankton biovolume of functional and taxonomic groups were fairly coherent and showed potential for monitoring. Implications of our findings are discussed in light of guiding future management practices to sustain biodiversity, ecological integrity, and water quality of urban waterbodies.

Herein, we used zooplankton as a study model for determining how biodiversity components as well as taxonomic and functional attributes reflect lake typology in the natural southern boreal lakes. We estimated the regional and local variation in zooplankton diversity and the community structure across a set of fourteen lakes within a national park. Regional diversity (γ diversity) accounted for 40 species including 20 rotifers, 10 cladocerans and 8 copepods. Local diversity (α diversity) averaged 15 species per lake. Spatial variation in β diversity was inversely related to spatial variation in α diversity. Inter-lake variation in zooplankton communities based on taxonomy, functional traits and biotic indices was explained by two major limnological gradients: namely lake trophic status and fish community. The community structure reflected a gradient of rotifer to calanoid copepod dominance in response to trophic status. Several key species of rotifers (Kellicottia longispina and Conochilus unicornis) and of small (Bosmina and Diaphanosoma birgei) or large (Daphnia catawba and Holopedium gibberum cf glacialis) cladocerans were good indicators of lake zooplankton typology, as in other boreal lakes. We distinguished two main groups of lakes: (1) oligotrophic lakes inhabited by brook trout and dominated by the calanoid copepods and (2) mesotrophic lakes inhabited by northern pike and dominated by rotifers. Overall, our study can help managers better define monitoring and conservation strategies for lake ecosystems in natural parks.

While plants are famously known to use their dormant forms for both temporal and spatial dispersal, animals are generally recognized to use them mostly for periodic survival in unfavourable conditions, despite a plethora of animals (sedentary or inhabiting isolated sites) regularly using their dormant forms for spatial dispersal, too. Freely moving planktonic crustaceans of the genus Daphnia, inhabiting island-like freshwater habitats, are one of the model examples. While they have low chance to cross terrestrial barriers and reach neighbourhood waterbodies in an active form, they have developed adaptations that facilitate spatial dispersal of their dormant forms. In this chapter, we broadly summarize the ultimate reasons of spatial dispersal of freshwater organisms and the modes and routes of their dislocation. We further focus on the morphological, behavioural and life history adaptations that facilitate spatial dispersal of the dormant forms of a model planktonic crustacean, Daphnia. Finally, we evaluate the risks and costs of passive dispersal, assess its effectiveness and describe non-adaptive consequences.

Cyclopoid copepods are a dominant component of freshwater zooplankton and the Cyclopidae is the most diverse family. Dormancy is a fundamental process of cyclopoid life history in permanent lakes and temporary ponds. In boreal lakes, cyclopoid diapause has been documented mainly in Northern Europe but more rarely in Northern America. We present the first assessment on summer diapausing cyclopoids (SDC) in 22 boreal lakes in southern Quebec, which vary in their morphometry, tropic status, and predation pressure by fish or invertebrates. We developed a conceptual model to test the hypothesis that diapausing patterns of SDC in boreal lakes are a complex response depending primarily on morphometric and trophic features and secondly on the intensity of hypolimnetic anoxia and predation by fish or invertebrates. Using morphometric indices, lakes were classified in groups varying by the importance of wind-mixing, the strength of thermal stratification during summer, the potential of meromixis, and the risk of predation by fish or chaoborids. Three cyclopoid species (Diacyclops thomasi, Cyclops scutifer, Mesocyclops edax) dominated in all groups of lakes, while Diacyclops nanus and Acanthocyclops vernalis were found in small abundance and only in few lakes. The highest abundances of SDC (density and biomass) were found in sediments of thermally stratified mesotrophic lakes with intermediate wind-mixing index (Ko) and low potential for meromixis (Pm). Strong positive correlations were found between SDC and meiobenthos abundances in all groups of lakes. High biomass of Chaoborus larvae or presence of large populations of fish negatively affected SDC abundances in meiobenthos. Morphometric features, wind-mixing and thermal stratification, as well as the abundance of Chaoborus and fish predators are the key factors governing species diversity and abundance of summer diapausing cyclopoids in boreal lakes.

Aim We investigated how freshwater microcrustaceans with different susceptibilities to Allee effects differ in the distribution of their geographical range size (GRS) and diversity along latitudinal gradients, evaluating the importance of climatic and historical factors in explaining these differences. We hypothesized that sexual copepods would have a smaller GRS and that their distribution would be linked to historical processes due to mate-finding Allee effects during colonization. Given that cyclic parthenogenetic cladocerans avoid these Allee effects, we predicted that they would exhibit a larger GRS and their distribution would be related to climatic factors rather than dispersal limitation. Location Canadian watersheds, North America. Methods We used a database containing the presence–absence of freshwater zooplankton across 1665 Canadian lakes along a latitudinal gradient of 40°. We computed GRS using minimum convex polygons encompassing all lakes in which each species was present. We pooled the diversity of lakes within watersheds, and computed linear regressions models between watershed diversity and average GRS with the average latitude, distance from a glacial refugium and environmental variables of the watershed. All analyses were performed separately for cladocerans and copepods. Results Cladocerans exhibited, on average, a GRS 70% larger than that of copepods. We found a strong relationship between diversity (negative) and average GRS (positive) with latitude for cladocerans but not for copepods. Cladoceran macroecological patterns were mainly explained by climatic factors, whereas the lack of latitudinal gradients in copepods was potentially due to the influence of a northern glacial refuge and dispersal limitation. Main conclusions Our results show that Allee effects are strongly and negatively associated with GRS, influencing the relative importance of environmental filtering and dispersal limitation on species diversity patterns. We suggest that studies should avoid lumping species with large differences in their susceptibility to Allee effects in order to better disentangle the multiple processes affecting large-scale patterns.

The need to protect and preserve biodiversity is a pressing issue and requires that conservation projects be based on solid foundations. Knowledge of species evolutionary history can serve as a tool to help guide conservation projects on the basis of evolutionary heritage. We used communities of Cladocera (Crustacea, Branchiopoda) in urban waterbodies to identify which sites should be prioritized for phylogenetic diversity conservation. Phylogenetic trees were inferred using DNA sequences from two mitochondrial genes. Furthermore, we also evaluated the consequences of phylogenetic uncertainty for identifying sites for conservation priority. Using results from Bayesian analyses, we considered the effect of uncertainty in the phylogenetic tree on phylogenetic diversity (PD) estimation. When phylogenetic uncertainty was taken into account, the conservation value of individual sites became uncertain and several potential comparisons between sites could not be supported. Consequently prioritization of one site over the other could not be defended in biodiversity conservation projects. Our study highlights the fact that accounting for phylogenetic uncertainty can alter the relative conservation priority of sites, as assessed by their phylogenetic diversity. Therefore, variability in the phylogenetic estimates should be consistently considered and integrated into estimates of phylogenetic diversity and conservation decisions to avoid making suboptimal choices.

Submerged aquatic vegetation (SAV) plays important roles in shallow lakes. In addition to its refuge effect for zooplankton, one key role of SAV is to provide diverse ecological niches to these organisms. The reduction of habitat complexity due to loss of SAV might thus have huge effects on zooplankton communities. The objective of this study was to investigate the relationship between SAV abundance and composition and zooplankton functional diversity and community structure. We used as model system the littoral zone of Lake St. Pierre (Quebec, Canada), a shallow fluvial lake experiencing dramatic changes in SAV cover. Our sampling protocol allowed us to analyse the relationship between SAV and zooplankton along a gradient of SAV abundance. We showed that SAV abundance explained 41% of the variation in the zooplankton community structure and 25% of the variation in zooplankton functional diversity. Our results also indicated that the presence of the benthic cyanobacterium Gloeotrichia sp. in SAV beds had a structuring effect within the dominant family of Chydoridae, being negatively correlated to the abundance of relatively large-bodied species. Our findings suggest that loss in SAV biomass and complexity can affect both community structure and functional diversity of zooplankton in shallow fluvial lakes.

The aim of this study was to evaluate the state of metallic pollution of the sediments of the three main Lakes (Mevia, Ossa and Mwembe) of the Ossa lake complex by the analysis of some heavy metals from May to July 2011. Copper, Nickel, Lead, Zinc, Cadmium and Iron were measured using atomic absorption spectrophotometry method. According to the standard values of GESAMP (group of Experts on the Scientific Aspects of Marine Pollution), lead concentrations were low in Lake Mwembe (4.985±0.060 mg.kg, dry weight), closer to standard values in Lake Mevia (12.935±0.815 mg.kg, dry weight) and very high in Lake Ossa (39.935±2.480 mg.kg, dry weight). Original Research Article Guy et al.; BJAST, 14(6): 1-14, 2016; Article no.BJAST.24001 2 As for Zinc and Cadmium, the contents were superior to standard values in the three lakes. The level of sediment contamination was evaluated using the Pollution Index (PI) and Enrichment Factor (EF). Only cadmium had a PI value greater than 3 and the highest EF (491.456 in Lake Mevia, 480.310 in Lake Ossa and 1761.099 in Lake Mwembe). All heavy metals presented EF values superior to 50 exception being observed for lead in Lake Mwembe (EF value less than 30). Generally, gross values of the different heavy metals measured, associated with EF values, indicated an anthropogenic pollution of these waters. This pollution could be linked to the use of chemical fertilizers and biocides around the neighborhood of Ossa lake complex by the African Forestry and Agriculture Company of Cameroon (SAFACam).

Wetlands of a large fluvial lake in the St. Lawrence River (Quebec, Canada) were visited during 3 years (2004–2006) to collect macroinvertebrates across the belt of emergent vegetation. We tested the hypothesis that hydrology, river landscape, and local environment would explain variations in macroinvertebrates. The 66 taxa collected lake-wide comprised a few abundant but widespread groups (Malacostraca, Oligochaeta, Chironomidae, and Mollusca). Between 2004 and 2006, total abundance at 5 sites monitored annually fell by one order of magnitude, and taxa richness decreased from 19 to 12 taxa. Proportion of amphipods (Gammaridae) dropped sixfold whereas proportion of annelids (Oligochaetes) rose ninefold. The impoverishment of macroinvertebrates coincided with low summer water levels in 2005 and 2006, resulting in the periodic emersion of up-slope sites. Spatial differences in macroinvertebrate communities were less important than inter-annual differences, owing to large variability among sites. Patterns in macroinvertebrate communities were related to water depth, vegetation, and local changes in sediments (31% of variance explained). Gammaridae (Malacostraca) were strongly associated with down-slope sites, whereas Oligochaeta (Annelida) dominated in up-slope sites. Inter-annual changes in water level had major effects on macroinvertebrate communities in Lake Saint-Pierre, above and beyond other environmental variables.

Aquatic ecosystems are common in urban environments. A solid understanding of aquatic species’ distributions in urban habitats will both advance urban ecology and preserve biodiversity in cities. In particular, zooplankton are central components of aquatic food webs and their biodiversity patterns thus warrant further characterization and understanding. We examined sources of variation and biodiversity patterns of zooplankton communities across eighteen waterbodies in the urban landscape of Canada’s large island city of Montreal. We report a total of 80 zooplankton taxa of which rotifers and cladocerans were major contributing taxa to biodiversity. We found a lack of agreement between contributions of individual waterbodies to rotifer and cladoceran beta diversity. Littoral vegetated zones proved to be important habitats for zooplankton biodiversity, contributing considerably to the species richness pool, often with a different species composition. Further variation in zooplankton community composition was attributable to local factors such as waterbody size, algal biomass and composition, and macroinvertebrate predators, but also to urban management practices such as waterbody draining during winter. We show that urban waterbodies can represent important reservoirs of biodiversity. Management practices favoring a large diversity of permanent and temporary habitats with littoral vegetated zones should be incorporated in urban design and conservation plans.

Ecologists have long focused on local-scale phenomena (i.e. local environment variables) and assumed that spatial processes were unimportant factors influencing both the community structure and the functional diversity of aquatic communities. In this paper we used zooplankton assemblages in a typical large river (St. Lawrence River) as a biological model to examine the roles of (1) local environmental conditions (physicochemical characteristics of the water column), (2) broad-scale connectivity (a proxy for dispersion potential), and (3) habitat heterogeneity (a proxy for niche diversity) on the structure and the diversity of lotic communities. Together, these three sets of descriptors explained respectively 52, 49 and 59 % of the variation in zooplankton total biomass, functional diversity and community structure. After partialling out the roles of local environmental conditions and broad-scale connectivity, we demonstrated that habitat heterogeneity alone is a key driver of zooplankton total biomass and functional evenness at the riverscape level. In homogeneous and temporally stable habitats, zooplankton communities had higher biomass and functional evenness but lower species richness. Conversely, zooplankton had lower biomass and higher species richness in heterogeneous and unstable habitats, suggesting that zooplankton species can coexist because disturbances prevent competitive exclusion from occurring. This is the first study to reveal how local environmental conditions, spatial connectivity and habitat heterogeneity operate jointly to determine the functional diversity and structure of aquatic communities in a natural ecosystem.

The objective of the present field experiment was to identify detoxification responses in the gills and digestive gland of a freshwater unionid bivalve, Pyganodon grandis , subjected to a step-change in metal exposure. Adult bivalves were transferred from a reference site (Lake Opasatica) and a metal-contaminated lake (Lake Heva) to a second contaminated lake (Lake Vaudray) in northwestern Quebec, Canada. Changes in organ metal concentrations, in the subcellular distribution of metals and in metallothionein concentrations were followed over time ( t = 0, 132, (400) and 860 days). At each collection time and for each bivalve, the gills and digestive gland were excised and gently homogenized; six sub-cellular fractions were separated by differential centrifugation and analyzed for their Cd, Cu and Zn content, and metallothionein was quantified independently. Metal detoxification strategies were shown to differ between target organs: in the gills, incoming metals were sequestered largely in the granules, whereas in the digestive gland the same metals primarily accumulated in the cytosol, in the metallothionein-like protein fraction. These metal-handling strategies, as employed by the metal-naive bivalves originating in the reference lake, closely resemble those identified in free-living P. grandis chronically exposed in the metal-contaminated lake, suggesting that the ability to handle incoming metals (Cd in particular) is inherent in P. grandis and is not a trait acquired after long-term adaptation of the bivalve to metal-contaminated environments. The bivalves transplanted from both Lakes Opasatica and Heva were able to tolerate their new surroundings during the first 400 days of the transplant experiment, as indicated by the absence of mortality and the presence of gravid animals. Over the final 460 days, mortality remained low for the bivalves transplanted from the reference lake (20%) but reached 100% in the transplanted group from the contaminated lake. It would seem that the Lake Heva bivalves were compromised by their initial exposure to metals in their home lake and that the added stress of being transplanted to and caged in a lake with comparable or slightly higher concentrations of metals was sufficient to cause mortality.

Biodiversity patterns in cladoceran communities were investigated in urban waterbodies in relation with residential land use, pond management, and waterbody environments. We evaluated species richness in the pelagic and littoral zones of eighteen waterbodies of a large Canadian city. Gamma diversity (26 species) observed at a small scale in the urban survey was important comparatively to large-scale surveys of lakes. Beta diversity ranged from 1 to 8 species among waterbodies. We tested if littoral species greatly contributed to regional diversity in urban waterbodies. Littoral species (Chydoridae, Ilyocryptidae, Macrothricidae, Polyphemidae) accounted for 58% of the total species pool. We distinguished five cladoceran assemblages associated to different waterbodies (temporary ponds, permanent lakes, and wetlands). Cladoceran communities were more diverse and variable in permanent lakes than in temporary ponds. Changes in cladoceran species assemblages among waterbodies were driven by variations in waterbody size and phosphorus enrichment, macrophyte and algal biomass, urban density, pond management practices, and the presence of potential predators as fish and macroinvertebrates. Our study indicates that both artificial ponds and lakes and natural wetlands are valuable habitats for the conservation of cladoceran biodiversity and rare endemic species in urban regions. Further research on pond management strategies promoting urban aquatic biodiversity should be undertaken.

Aim We tested the energy and metabolic theories for explaining diversity patterns of crustacean zooplankton in Canadian lakes, and evaluated the influence of regional and local environments on community structure. Location The 1665 studied lakes are distributed across Canada in 47 ecoprovinces. Methods Our database included the occurrence of 83 pelagic crustacean species. The regional species richness in each ecoprovince was estimated using the average local species richness per lake and the first-order jackknife diversity index. Using a principal component plot and forward selection in a multiple regression we identified the most important predictors of regional species richness estimates. We tested the predictions of the species richness-energy hypothesis using climatic variables at regional scale, and of the metabolic theory using the inverse of air temperature. To evaluate the influence of regional and local environmental drivers, we carried out a redundancy analysis between crustacean species occurrences and regional climate and lake environmental factors on a subset of 458 lakes. Results Estimates of pelagic crustacean species richness in Canadian ecoprovinces varied from 3 to 10 species per lake (average local species richness) or 8 to 52 species per ecoprovince (Jackknife diversity index). Our study fully supports the species richness-energy hypothesis and partially the metabolic theory. Mean daily global solar radiation was the most important regional predictor, explaining 51% of the variation in the regional species richness among ecoprovinces. Together, regional climate and local lake environment accounted for 31% of the total variation in community structure. Regional-scale energy variables accounted for 24% of the total explained variation, whereas local-scale lake conditions had less influence (2%). Main conclusions The richness-energy theory explains diversity patterns of freshwater crustacean zooplankton in Canadian ecoprovinces. Solar radiation is the best predictor explaining regional species richness in ecoprovinces and community structure of pelagic crustaceans in Canadian lakes.

We assessed the relative magnitude of various factors (year, preservation method, continent, investigator, and taxonomic level) affecting prediction of invertebrate dry mass (DM) in light of the variability of assessments of invertebrate density. We developed 34 length (L)–DM relationships for Oligochaeta and 17 freshwater invertebrate families belonging to Mollusca, Crustacea, and Insecta. Comparison of our predicted DM for reference-size individuals with values from 120 other published equations revealed that 31% of predicted values were within our 95% CI and 73% were within a 2× DM range (i.e., between 0.5× and 2×). Interannual differences in exponent (slope) or scale factor (intercept) of L–DM relationships were detected for 6 of the 7 taxa investigated, but represented only 3% of total variance in predicted DM. Similarly, preservation methods and measured body dimension each accounted for a small (0–3%) fraction of total variance. Variation among investigators (12–50%) and continents (1–17%) ...

International audience; MeHg biomagnification by the phantom midge Chaoborus in relation to MeHg concentrations in their prey and its migratory behavior was investigated in two Canadian Precambrian Shield lakes. Three Chaoborus species with contrasted migratory behavior were collected in a fishless and a fish-inhabited lake. All species accumulated MeHg through their ontogenic development. In the lake inhabited by fish, all instars of Chaoborus punctipennis displayed a marked migratory behavior and were unable to biomagnify MeHg, whereas in the fishless lake, Chaoborus americanus and Chaoborus trivittatus biomagnified MeHg. Reduced biomagnification capacity of C. trivittatus, the coexisting species living with C. americanus, was also ascribed to a progressive vertical segregation with age. Growth dilution, amount and type of prey items or trophic position could not explain the different patterns of biomagnification. Our findings demonstrate that the most common invertebrate predator of temperate planktonic food webs can biomagnify mercury, contrarily to previous reports.

La composition et la structure du zooplancton de deux lacs du complexe lacustre Ossa (Ossa et Mwembè), site protégé UNESCO situé dans une plaine inondable, ont fait l'objet d'une étude entre septembre 2009 et février 2010. 37 et 41 espèces de zooplancton ont été recensées respectivement dans les lacs Ossa et Mwembè. Les deux milieux, oligotrophes, sont soumis à l'influence du fleuve Sanaga qui leur apporte en temps de crue de nouvelles espèces. La présence de Mesocyclops leuckarti dans ces eaux amène à considérer l'existence de cette espèce sur le continent africain. La densité des organismes zooplanctoniques augmente entre septembre et novembre et chute rapidement en décembre, ce qui s'accorde avec une succession saisonnière des communautés. Les paramètres physico-chimiques, qui permettent de caractériser les plans d'eau comme oligotrophes, ne diffèrent pas significativement entre les deux milieux, ni avec la profondeur de prélèvement, ce qui justifie la valeur de 82 % trouvée pour l'indice de similitude de SÖRENSEN. Quant à la structure des populations de zooplancton, elle est influencée principalement par la saison et par la profondeur de prélèvement, le mois et la station n'ayant pas d'influence sur cette distribution.The composition and the structure of the zooplankton of two lakes of the Ossa lake complex (Ossa and Mwembe) were studied between September 2009 and February 2010. 37 and 41 species of zooplankton were inventoried respectively in the lakes Ossa and Mwembe. The two environments are oligotrophic but subjected to the influence of the river Sanaga that brings them in swelling time new species. Mesocyclops leuckarti found in these lakes suggests the presence of this species on the African continent. The density of the zooplankton organisms increases between September and November and falls quickly in December, in accordance with a seasonal impact on communities. The physicochemical parameters do not differ significantly between the two environments and with the sampling depth. This justifies the value of 82 % obtained with the SÖRENSEN index. The structure of the populations of zooplankton is principally influenced by the season. The sampling depth, the month and the station do not influence this distribution.

We tested if pelagic crustaceans of the genus Daphnia use different anti-predator defences in environmental conditions that do or do not offer deep refuge from planktivorous fish. We kept Daphnia catawba in two series of 9-m deep enclosures with and without caged cyprinid fish Phoxinus eos. In one series of enclosures, Daphnia could select its depth of residence and hide in deep dark water layers to avoid anticipated fish predation, while in another series of enclosures, a plankton net barrier fixed at 2-m depth forced them to stay in subsurface zone exposed to fish kairomones. We compared depth residence and migratory behaviour strategies with life history strategies (body size and size at first reproduction, diapause induction) in Daphnia exposed or not to fish kairomones with or without deep refuge. In deep enclosures with fish, Daphnia spent daytime hours in deep dark layers while at night, they resided closer to the water surface. Yet, no change in life history parameters of migrating individuals was observed compared to the fish-free conditions. In enclosures with fish, where the net barrier forced Daphnia to reside in subsurface zone, they produced smaller offspring, matured at smaller size and achieved lower maximum body length compared to the fish-free conditions. However, they did not produce diapausing eggs. Our experimental study supports the hypothesis that diel vertical migration behaviour with daytime residence in deep, dark water are the preferred antipredator strategy chosen by Daphnia facing anticipated fish predation over life history changes such as reduced size and low growth rate which are used when dark deep refuge is not present or accessible.

Specimens of the mayfly larva Hexagenia limbata and of the floater mussel Pyganodon grandis were sampled in rivers and lakes contaminated by trace metals in the Abitibi-James Bay region in northwestern Québec. Water samples were collected at each sampling site with in situ diffusion samplers and analyzed for major cations, anions and trace metals (Cd, Cu, Mn, Zn). Surficial sediment samples were also collected at each site and analyzed for Cd, Cu and Zn. In response to Cd contamination at river and lake sites, both sentinel organisms accumulated the metal and synthesized metallothionein (MT), a metal-binding protein synthesized by organisms as a defence mechanism against excess metals in the surrounding media. At the river sites, H. limbata unexpectedly maintained much higher concentrations of MT per unit of accumulated Cd than at the lake sites; this difference between lentic and lotic environments may reflect the response of the species to the more stressful hydrodynamic conditions that prevail in a river. The accumulation of Cd in the mayflies at lake and river sites decreased as a function of the ambient manganese concentration. We hypothesize that dissolved Mn protects against Cd bioaccumulation in H. limbata. The present results support the contention that one cannot extrapolate conclusions drawn from the use of a single sentinel species to a larger set of freshwater invertebrates--both the mayfly and the bivalve are promising biomonitors.

We applied the land-cover cascade (LCC) concept to evaluate whether human disturbance affects crustacean zooplankton community in 13 nutrient-poor lakes of the Laurentian region along a gradient of residential development and land-cover disturbance. Zooplankton biomass responded indirectly to residential disturbances within the watershed based on path analysis. In most LCC models, total phosphorus enrichment was a strong intermediate element linking residential disturbances to increased biomass of small crustaceans ( Bosmina , Ceriodaphnia , and Diaphanosoma ) and Daphnia species ( D. g. mendotae , D. dubia , and D. ambigua ). Zooplanktivory index was also an intermediate element in LCC models of crustacean functional groups and an independent element in daphnid-based LCC models. Low zooplanktivory was associated with higher biomass of large Daphnia ( D. pulicaria and D. catawba ). However, residential disturbance and select environmental factors (phosphate enrichment, zooplanktivory index, lake depth, littoral macrophytes) explained only 42% and 57%, respectively, of among-lake variation in crustacean community and Daphnia assemblages. Variation partitioning analysis suggested that planktivory had a similar or greater influence than human disturbance and phosphate enrichment. Our study improves the knowledge of crustacean zooplankton responses to increasing residential development and land-use disturbances near Canadian Shield lakes.

Summary 1. Strong vertical gradients in light, water temperature, oxygen, algal concentration and predator encounters during summer in stratified lakes may influence patterns of depth selection in crustacean zooplankton, especially Daphnia species. 2. To test how crustacean depth selection varies among lakes along a gradient of catchment disturbance by recent residential development and land use change, we calculated the weighted mean depth distribution of the biomass of crustaceans by day and night in eight nutrient-poor boreal lakes. 3. Generally, the greatest biomass of crustaceans was located at the metalimnion or at the lower boundary of the euphotic zone during thermal stratification in July. The crustacean zooplankton avoided warm surface layers and tended to stay in colder deep waters by both day and night. They also remained at greater depths in lakes with a more extensive euphotic zone. 4. There was some evidence of upward nocturnal migrations of large Daphnia and copepods in some lakes, and one case of downward migration in a lake inhabited by chaoborid larvae. 5. Multivariate regression trees (MRT) were used to cluster crustaceans and Daphnia species in homogeneous groups based on lake natural and disturbance factors. For crustaceans, the depth of the euphotic zone, the sampling depth (epilimnion, metalimnion and hypolimnion), time (day or night) of sampling and the biomass of chlorophyll a were the main driving factors. For Daphnia species, the drainage area, the sampling depth, the cleared land surface area within the catchment and the concentration of total dissolved phosphorus were the main factors.

Previously pristine lakes of the Laurentian region of Quebec, Canada, have faced increasing residential development of their watershed since the 1970s. We tested whether littoral invertebrates respond to this perturbation, even though open-water nutrients and chlorophyll are not yet altered. We examined changes in biomass, size structure, and taxonomic composition of macroinvertebrates living on rocks and sediments in 13 lakes representing a gradient of lakeshore residential development and watershed clearing. Littoral invertebrates provided early indication of lake perturbation, but their response varied according to the substratum. On rocks, total invertebrate biomass increased along the perturbation gradient and size structure shifted towards large organisms. These changes were likely mediated by a concomitant increase in epilithon biomass, suggesting a bottom-up control. No significant change in total biomass and size structure was observed for invertebrates in sediments. In contrast, taxonomic composition changed with lake development in sediments, but not on rocks. Taxonomic shifts were likely related to changes in sediment heterogeneity due to a decline of woody litter and increased fine particle deposition. Oligochaetes were positively associated to perturbation, whereas mayflies were negatively associated; these taxa could be used as indicators. Sediments were a better sentinel substratum than rocks for biomonitoring the impact of lake residential development.

We evaluated the potential of vegetation and sediment habitats in wetlands of the St. Lawrence River for developing a macroinvertebrate bioassessment program with reference conditions. During September 2004, we collected macroinvertebrates in emergent vegetation and sediment in both fluvial sites (reference) and tributary-plume sites (impacted) in waters of the north and south shores of Lake Saint-Pierre (St. Lawrence River). In each habitat, we compared taxa richness, abundance, and community structure of macroinvertebrates between reference and impacted sites, and used multivariate models to relate macroinvertebrate community to environmental conditions. Each habitat was suitable for discriminating reference fluvial sites from impacted tributary-plume sites based on macroinvertebrate communities. In emergent vegetation, macroinvertebrates were dominated by epibenthic fauna such as crustaceans (Gammaridae, Asellidae) and molluscs (Valvatidae) at fluvial sites, and insect larvae (Chironomidae, Caenidae) at tributary-plume sites. In sediment, macroinvertebrates comprised a greater proportion of endobenthic fauna such as Oligochaeta and Sphaeridae. Crustaceans and molluscs were still dominant at fluvial sites and Oligocheata and Chironomidae at tributary-plume sites. No strong difference was depicted in macroinvertebrate composition between north and south shore water masses. Environmental variables explained a higher proportion of variance in macroinvertebrate community composition in emergent vegetation than in sediment (68% versus 44%). Macroinvertebrate composition in sediment was more related to metal contamination, whereas macroinvertebrate composition in emergent vegetation was related primarily to vegetation type and water quality. Relevance of the study for bioassessment of macroinvertebrates in the St. Lawrence River using the reference condition approach is discussed.

The contribution of metaphyton and submerged and emergent macrophytes as support to phytophilous organisms was compared from the standpoint of epiphytic chlorophyll and of invertebrate biomass, taxonomic composition and size distribution. This study was carried out in a fluvial lake of the St. Lawrence River (Lac Saint-Pierre, Quebec) at 5 sites with chemically and physically distinct water masses. Invertebrate and epiphyton biomass were consistently higher in complex filamentous mats (overall mean: 61 ± 5 [SE] mg and 124 ± 18 μg Chl a /g vegetation dry mass, respectively) and submerged plants (overall mean: 48 ± 7 mg and 195 ± 56 μg Chl a /g vegetation d.m.) than in the simple emergent stems (overall mean: 4 ± 1 mg and 45 ± 15 μg Chl a /g vegetation d.m.). Taxonomic composition of the invertebrate communities varied largely among types of vegetation and sites. Sampling site (and hence water physical and chemical characteristics) explained a larger fraction of the variation in invertebrate composition (28%) than vegetation type (9%). Overall, metaphyton hosted an invertebrate fauna more abundant and more diverse, with larger organisms and more semi-aquatic taxa, than that of nearby vascular macrophytes. However, at the scale of this river segment (~ 300 km2), metaphyton contributed < 1% to total phytophilous invertebrate biomass compared to 96% and 4% for submerged and emergent plants, respectively. In the river trophic network, vascular plants thus appear to support the bulk of the food supply, which is periodically enriched and diversified by the appearance of metaphyton blooms.

This study examined the formation of morphological defences by two coexisting Daphnia species, the large-sized D. pulicaria (2 mm) and the small-sized D. mendotae (1.4 mm), in response to the presence of young-of-the-year (YOY) yellow perch (Perca flavescens) and invertebrate predators (Chaoborus, Leptodora) during summer in a mesotrophic lake. We hypothesized that due to differential size-selective predation risk by YOY fish and invertebrates, the large-sized and the small-sized Daphnia species would show different morphological responses to predation threats. We followed changes in two morphological traits (relative length of the tail spine in D. pulicaria and of the helmet in D. mendotae) among different periods during summer according to YOY fish and invertebrate predation. We defined four YOY fish predation periods based on the presence of YOY perch in the pelagic zone of the lake and the relative abundance of Daphnia preys in their gut contents, and two invertebrate predation periods based on exclusive or mutual occurrence of the invertebrate predators. The large-sized (D. pulicaria) and the small-sized (D. mendotae) species showed different morphological responses to YOY fish and invertebrate predators, respectively. The tail spine ratio of the juveniles and adults of D. pulicaria did not change in response to YOY fish predation or to invertebrate predation. A gradual increase in the helmet ratio was observed in the small-sized D. mendotae over the summer period. This change was related to the co-occurrence of the invertebrate predators (Chaoborus and Leptodora) and to YOY fish predation. The warmer temperature cannot be accounted for helmet elongation since it was constant across depths, and not related with the co-occurrence of D. mendotae and YOY perch.

Our study showed for the first time in nature that two coexisting Daphnia adopted alternative life history and behavioural strategies to cope with negative size-selection predation by gape-limited young-of-the-year (YOY) perch. We evaluated the phenotypic plasticity in life history and behavioural traits of two coexisting Daphnia species, D. pulicaria (2 mm) and D. galeata mendotae (1.4 mm), in response to seasonal changes in predation by YOY yellow perch (Perca flavescens) in a mesotrophic lake. We expected that the large-sized D. pulicaria, the most likely subjected to sizeselective predation by YOY perch, will show stronger antipredator responses than the small-sized D. galeata mendotae. To test this hypothesis, we examined changes in life history and behavioural traits in juveniles and adults of both species during four YOY fish predation periods that were selected based on the presence of YOY perch in the pelagic zone and the relative abundance of Daphnia prey in their gut contents. Our study supports the scenario of negative size-selective predation by gape-limited YOY perch on both Daphnia species. The electivity index indicated that no daphnids with a body length .1.75 mm were predated by YOY yellow perch. Coexisting Daphnia exhibited phenotypic plasticity in their antipredator defenses based on their vulnerability to seasonal changes in size-selective predation of YOY perch. Juvenile Daphnia were the targeted prey and they responded by a decreased body length. Behavioural defenses were the dominant strategy used by both adult Daphnia populations to withstand high predation. A decreased size at maturity was not employed by Daphnia, except at the very end of the predation period. Behavioural defenses are short-term strategy adopted to avoid predation. Both antipredator defenses became unnecessary expenses and were no longer sustained after the predation period.

The relative effects of top-down and bottom-up drivers of zooplankton size structure were examined in three limnologically diverse regions of Quebec, Canada. Lake productivity drove biomass of small-sized zooplankton (300–1000 µm) in the Eastern Townships and Laurentian regions, which have high total phosphorus gradients, but was not significant in the low-productivity region, Gouin. Fish species composition was found to affect biomass of large-sized (>1000 µm) zooplankton and was the primary factor affecting zooplankton size structure in the low productivity region. When size structure of the zooplankton communities were described as normalized biomass size spectra, only bottom-up factors were significant, as increasing productivity resulted in higher curve peaks and increased parabola curvature. No factors were significantly related to any parameter of the Pareto distribution to describe size spectra. Overall, bottom-up forces were stronger drivers of zooplankton size structure, particularly in regions with wide ranges in lake trophy, while fish predation was more important in regions with low productivity variability.

The body size of zooplankton has many substantive effects on the function of aquatic food webs. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, calanoids, and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74 degrees latitude and encompassing a temperature range of 2-30 degrees C. Cladoceran body size declined with temperature, in a marginally significant manner (P = 0.10). For cyclopoids, the decline was more significant (P = 0.05). In both cases, there was considerably more variation around the regression lines than previously observed; suggesting that other variables such as fish predation played a role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclopoids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation.

Temporal monitoring studies are needed to detect long-term trends in ecosystem health. In the present study, we tested metallothionein (MT) as a potential biomarker for long-term variations in trace metal levels in lakes subject to atmospheric metal inputs from a nearby copper smelter. Over a 13-year period, we estimated on several occasions ambient free Cd 2+ , Cu 2+ and Zn 2+ concentrations at the sediment–water interface in six lakes with contrasting metal levels, and measured metal and metallothionein concentrations in gills of bivalves ( Pyganodon grandis ) living in these lakes. All but one of the study lakes had comparable drainage ratios, so inter-lake differences in hydrological export of metals from contaminated watersheds to receiving waters were likely minimal. Declines in the metal emissions from the smelter (especially for Cd and Zn) during the 1980s led to appreciable decreases in both calculated free Cd 2+ ion concentrations in the study lakes (− 59 ± 21% between 1989 and 1998) and accumulated Cd levels in their clam populations (− 46 ± 12% between 1989 and 2002). Taking all lakes into account, MT concentrations in bivalves have comparatively dropped by 44% (± 10%) since 1989. In contrast to what we found for Cd, there were no significant reductions in the calculated free Cu 2+ and Zn 2+ concentrations in the various lakes during our study period (− 2 and − 10%, respectively, with 95% confidence intervals spanning zero). Overall, observed decreases in MT in bivalves over time were best correlated with similar decreases in both ambient and accumulated Cd levels ( r = 0.77, P = 0.0003 and r = 0.79, P P -values corrected for temporal autocorrelation), suggesting that long-term trends in gill MT concentrations in P. grandis may be useful as predictors of temporal changes in environmental Cd contamination in lakes.

Changes in phytoplankton and zooplankton communities were studied in 16 lake-years during a large-scale experimental before–after study as part of the Terrestrial Riparian Organisms Lakes and Streams (TROLS) project. After forest harvesting, phytoplankton biomass and especially cyanobacterial biomass increased in some of the experimental lakes, up to an order of magnitude. Although the response of phytoplankton was not directly related to the intensity of forest harvesting, this large-scale experiment provided a unique opportunity for studying the effects of an increasing gradient in cyanobacterial biomass on zooplankton communities. Cladoceran size structure and biomass were negatively correlated with cyanobacterial biomass, suggesting that large cladocerans and especially daphnids were inhibited by the increase in cyanobacterial biomass. The increase in cyanobacterial biomass seems to have caused a significant reduction in the size structure of zooplankton communities. As no correlation was found between cladocerans and cyanotoxins, our results point more towards feeding inhibition by filamentous and colonial cyanobacteria as a possible cause for the decline in the size structure and biomass of zooplankton communities. These results suggest that the increase in cyanobacterial biomass is likely to cause a shift in the size of zooplankton communities, which will lead to a profound change in functioning of lake systems.

The effectiveness of the optical particle counter (OPC) to estimate zooplankton biomass depends on the variability in zooplankton shape and the presence of interfering particles. In marine environments where zooplankton are composed of similarly shaped copepods, an average shape is relatively easily obtained. However, in freshwater environments, spheroid cladocerans mix with ellipsoid copepods and make the application of a single morphometric model difficult. To expand the use of the OPC to freshwater environments, we developed new ellipsoid models for three common lake types (eutrophic, mesotrophic, and oligotrophic). In addition, we assessed how closely different size fractions of seston corresponded to zooplankton biomass. When expressed in common dry mass units, OPC- and seston-derived zooplankton biomass estimates showed a 1:1 correspondence with taxonomically derived estimates in productive lakes (r > +0.70, P 200 mm) than in eutrophic or oligotrophic lakes (>500 mm). The presence of algae and rotifers had no detectable influence on OPC and size-fractionated seston estimates. Overall, these analyses suggest that OPC and seston provide reliable estimates of lacustrine zooplankton biomass as long as region-specific ellipse models and size fractions, respectively, are used.

The importance of top-down effects of piscivorous fish on phytoplankton in natural oligotrophic lakes is still debated. In this study, we analyzed patterns in phytoplankton and zooplankton abundance in 37 oligotrophic Canadian Shield lakes in relation to variations in both piscivorous fish predation and resources (total phosphorus; TP). Zooplankton community structure (but not total biomass) was partially affected by the variation in fish predation while the phytoplankton community structure and total biomass showed no response. Carbon isotope analyses revealed that the lack of topdown effects is due to the uncoupling of the littoral and the pelagic food webs. We found that the fish community depends mostly on benthic resources, suggesting that only low planktivory occurred in our study lakes. Due to the absence of specialized zooplanktivorous fish, zooplankton is poorly exploited in these lakes and thus able to control phytoplankton by grazing. A comparison of our data with published studies on the TP � /chlorophyll a relationships in both natural and manipulated systems shows that the phytoplankton biomass per unit of TP is relatively low in Canadian Shield lakes.

La métallothionéine (MT) est un ligand protéinique intracellulaire important à cause de son implication dans les processus de régulation des métaux traces essentiels et non-essentiels. Bon nombre de travaux ont été conduits en laboratoire pour bien comprendre les mécanismes de synthèse de cette protéine, mais les études réalisées en milieu aquatique sont beaucoup plus rares, particulièrement dans les rivières (milieu lotique). Dans ce contexte, la présente étude avait deux objectifs principaux : (1) identifier en milieu lotique les métaux traces (argent "Ag", cadmium "Cd", cuivre "Cu", nickel "Ni", plomb "Pb" et zinc "Zn") susceptibles d'induire la synthèse de la MT chez trois espèces sentinelles, soit le mollusque bivalve Pyganodon grandis, la larve d'éphémère Hexagenia limbata et le grand brochet du nord Esox lucius ; (2) définir les variables physico-chimiques ou toxicologiques pouvant influencer la prise en charge des métaux traces et conséquemment les concentrations en MT chez le mollusque P. grandis et l'éphémère H. limbata. Deux rivières de la région de l'Abitibi ont été échantillonnées à l'été 2001 afin de récolter les espèces sentinelles à 21 stations. Les concentrations en métaux traces, ainsi qu'en métallothionéine, ont été mesurées dans les branchies des mollusques, dans le rein des brochets et dans le corps entier des éphémères. La métallothionéine a été mesurée à l'aide d'une technique de saturation au mercure. D'après nos résultats, le cadmium tissulaire semble être le meilleur prédicteur de la concentration de MT chez les trois espèces sentinelles. Cependant, l'implication d'autres métaux est également possible. Dans le cas de P. grandis, la concentration de manganèse (Mn) dans les sédiments pourrait influencer la prise en charge du Cd et la synthèse de MT., Metallothionein (MT), an intracellular metal binding protein, is recognized for its role in the regulation of essential and non-essential trace metals. The mechanisms of synthesis of this protein have been studied in the laboratory but much less work has been carried out in the field, particularly in lotic environments. According to the literature, metallothionein protects tissues from metal damage, and may be used as a direct measure of the biochemical state of the affected tissue. Metallothionein shows high affinity for group IB and IIB metals ions (e.g. Cd, Cu, Zn), and consequently can sequester and detoxify metals. The use of MT as a biomarker for elevated levels of trace metals in aquatic environments has therefore been proposed as a tool in ecotoxicological studies. Changes at the biochemical level offer distinct advantages as biomarkers, since molecular alterations are normally the first detectable responses to environmental changes.The present study focused on two objectives, the first of which was to identify which trace metals (silver "Ag", cadmium "Cd", copper "Cu", nickel "Ni", lead "Pb" and zinc "Zn") may induce MT synthesis in three sentinel species collected in two northern Quebec rivers (Colombière River, close to Val d'Or, and Matagami River close to the town of Matagami) in a mining region (Abitibi, Québec). The three sentinel species were the adult bivalve Pyganodon grandis, the larval mayfly Hexagenia limbata, and the adult great northern pike Esox lucius. The second objective was to define variables that could influence the uptake of these trace metals and consequently the concentrations of MT in the sentinel species. The selection of these sentinel species was based on the following criteria: their relative abundance in the aquatic systems studied; their relative immobility; the ease of sampling; metal tolerance; metal bioaccumulation capacity; dynamics of metal accumulation; capacity to synthesize metallothionein; and availability of physiological and behavioural data.In 2001, physico-chemical conditions (e.g.: temperature, oxygen, transparency, phosphorus, chlorophyll a, etc.) were monitored during two sampling campaigns at 21 stations. Trace metals were measured in water and sediment in all stations, and in tissues of the sentinel species that were collected when present at the station (P. grandis - gills; H. limbata - whole body; E. lucius - kidney). Dialysis cells were used to collect water samples for the determination of concentrations of total dissolved metals, major anions and cations, humic and fulvic acids, and dissolved organic carbon. At each sampling site, divers collected three replicate sub-samples from two sediment cores for metal analyses. The cores were extruded in the boat and samples taken from the uppermost 0.5 cm, i.e. from the oxidized layer.The two rivers differ in their morphometry, their physico-chemistry, and their biology. The Allard River is larger (200 m vs. 7 m) and deeper (30 m vs. 3 m) than the Colombière River. The Colombière River is slightly more acid (pH: 6.2 - 6.7) and less productive (14 - 32 µg total P L-1) than the Allard River (pH: 6.7 - 7.4; 24 - 45 µg total P L-1). However, the rivers present some similarities such as slow current conditions and limited water transparencies. The range of Ag, Cu and Ni concentrations in water and sediment was greater in the Colombière River, whereas Pb concentrations were higher in the Allard River and Cd concentrations were similar in the two rivers. Zinc was the dominant metal in both rivers, but variations were more significant in water in the Colombière River. Although trace metal and MT concentrations were highly variable among species, stations and rivers, no consistent spatial gradients were detected in animals collected downstream from mining activities.As was the case for the ambient environment, Zn was also the dominant metal in organisms of both rivers. Zinc concentrations were similar in mayflies from the two rivers, but higher in molluscs and lower in pike collected from the Colombière River than in comparable animals from the Allard River. Following Zn, Cu was the second metal in importance in species from the two rivers, whereas the concentrations of Ag were low in all organisms and were undetectable in pike. Cadmium was more concentrated in mayflies and molluscs from the Colombière River than in those from Allard River, and also higher in the pike collected in the contaminated zone of the Colombière River. The concentrations of Ni in all species were comparable between rivers, but were more elevated in mayflies than in the other sentinel species.The range of Pb concentrations was comparable between rivers for all species, but concentrations were lower in the pike (kidney). The concentration of MT was higher in the pike than in the two other species. Mayflies had higher MT levels in the Allard River, while MT concentrations were higher in molluscs of the Colombière River. The relationships between metals and MT were very variable between rivers and species. Nevertheless, MT concentrations were most strongly related to those of accumulated Cd in the three sentinel species. The relationships between MT and Cd for all three species were stronger in the Allard River than in the Colombière River. In the case of P. grandis, because the number of stations where the bivalves could be collected from the Colombière River was low (n=4), no statistically significant relationship was observed between MT and Cd in the tissues, in spite of the high correlation coefficient (r=0.98). For the bivalves, manganese (Mn) concentrations in the sediment were negatively correlated with accumulated Cd concentrations and with MT levels. In H. limbata, in addition to Cd, other metals such as Cu (-) and Zn (+) also exhibited weak relationships with MT. Finally, in bivariate analyses, Pb concentrations in pike liver were significantly correlated with those of MT in this species, but based on multiple regression models, no variable other than Cd affected the level of MT in E. lucius.

Cet article vise à évaluer les effets à moyen terme des feux et des coupes de forêt sur la biomasse, la richesse spécifique et la composition du zooplancton des lacs de la forêt boréale au Québec. L'étude a été réalisée durant trois ans (1996-1998) après les perturbations sur 3 sous-ensembles de lacs similaires au niveau de leur morphométrie, incluant 7 lacs naturels non perturbés sur leur bassin versant, 7 lacs affectés par des coupes sur plus de 43% de la surface du bassin versant et 7 lacs affectés par des feux sur plus de 50% de la surface du bassin versant. Notre étude indique que le zooplancton a une forte résilience aux perturbations des lacs de la forêt boréale par les feux et les coupes. Les assemblages d'espèces sont très stables et varient peu entre les lacs naturels et les lacs perturbés. Les Rotifères sont le seul groupe affecté par les perturbations; leur richesse spécifique et leur biomasse sont plus fortes dans les lacs perturbés que dans les lacs naturels. Les feux ont un effet d'eutrophisation plus marqué que les coupes. Dans les lacs affectés par les feux, les apports accrus de nutriments favorisent la croissance du phytoplancton puis des rotifères. Toutefois, dans les lacs affectés par les coupes, la forte couleur de l'eau due aux apports accrus en carbone organique dissous est un facteur limitant, et la hausse du phytoplancton et des rotifères est moins accentuée. La richesse spécifique et la biomasse des Crustacés (Cladocères, Copépodes Calanoïdes et Cyclopoïdes) ne varient pas avec les perturbations. Sur l'ensemble du suivi, le niveau de perturbation n'est pas fortement relié aux changements dans la biomasse des groupes taxinomiques qui s'expliquent plutôt par les variations annuelles de la température de l'eau et des concentrations en chlorophylle a., This paper aims to evaluate mid-term impacts of forest wildfires and harvesting on the biomass, species richness and assemblages of zooplankton communities in boreal lakes in Québec. The research was carried out during a post-perturbation 3-year survey (1996-1998) on three subsets of lakes (natural, cut, burnt lakes). It complements previous short-term studies conducted 1 year after perturbations in the same region by PATOINE et al. (2000, 2002a) on different subsets of lakes, which failed to detect significant effects. This comparative study attempts to minimize the spatial variability among natural and perturbed lakes by selecting lakes with similar morphometric conditions. For this selection, we applied a multivariate approach developed by DUHAIME and PINEL-ALLOUL (2005). Making sure that natural and perturbed lakes have similar morphometric features allows minimization of the confounding effects of lake and watershed conditions on organic carbon and nutrient exports from perturbed watersheds, and subsequently on lake water quality and biota.The initial 3-year survey was conducted on 31 lakes including 15 natural lakes without any perturbation in their watershed over the past 70 years, and 9 burnt lakes with more than 50% of their watershed intensively burnt, and 7 logged lakes with more than 43% of their watershed clear-cut. Lakes were visited three times per summer (May-June, July, August-September) between 6:00 to 15:00h, during the 3 years (1996-98) following the fires and harvesting of 1995. Watershed and lake morphometry, and water quality, and algal communities were monitored and studied by CARIGNAN et al. (2000) and PLANAS et al. (2000). Fish communities were sampled and studied by SAINT-ONGE and MAGNAN (2000). Zooplankton was sampled using a cantilever net (53 µm mesh size) on vertical hauls from 1 m above the sediments to the lake surface. Sampling methods and analysis of zooplankton were previously described by PATOINE et al. (2000, 2002a). We estimated species richness and assemblages, as well as the biomass of each zooplankton group (Rotifera, Cladocera, Copepoda Cyclopoida and Calanoida) and of the total community in each year and each lake. Simple ANOVA were used to evaluate global changes over the mid-term survey in zooplankton attributes among the three subsets of lakes (natural, cut, burnt). RMANOVA (analysis of variance with repeated measures) were used to test the effects of watershed conditions related to perturbations (natural, cut, burnt lakes), the effects of annual variations during the survey and their interaction. Redundancy analysis (RDA) served to evaluate the relationships between changes in the biomass of zooplankton groups during the survey in the three subsets of lakes and the changes in environmental factors and perturbation intensity. Environmental factors retained for the analysis were the drainage ratio (ratio of watershed area to lake area), lake water transparency, concentrations of total phosphorus, total nitrogen and dissolved organic carbon, water temperature in the euphotic zone, chlorophyll a concentrations, and biomass classes of dominant fish (yellow perch, white sucker). The perturbation intensity, expressed as the percentage of watershed area clear-cut or burnt, was also included in the model.Based on their similarity in morphometric variables (drainage ratio, lake volume, area and maximum depth, percentage of wetlands in the watershed), we retained for the study 7 cut lakes (C2, C9, C12, C23, C24, C29, C48), 7 burnt lakes (FBP9, FBP10, FP2, FP24, FP30, FP31, FP32), and 7 natural lakes (N5, N16, N56, N70, N82, N88, N109). Variations in morphometric characteristics were found within each subset of lakes (reference, burnt, logged), and we did not detect significant variation among groups. However, we did find significant differences in water quality variables among subsets of lakes. Thus, in our study, we have minimized the effects of variable morphometry among watersheds and lakes that could confound the responses of lakes to perturbations, while maintaining the same effects of fires and harvesting on water quality, as previously observed (CARIGNAN et al. 2000). This allowed us to test scaling-up effects of these changes on zooplankton communities.Our study shows that zooplankton communities in boreal lakes have strong resilience to environmental perturbations by wildfires and clear-cut logging. Species assemblages were very stable and varied little between natural and perturbed lakes. Some rotifer species such as Keratella taurocephala, known as a species adapted to acidic and humic lakes, had higher abundance in the cut lakes most enriched in dissolved organic carbon. Another rotifer species, Polyarthra vulgaris, adapted to eutrophic lake and reservoir ecosystems, was more abundant in the burnt lakes that were the most enriched in nutrients. Only short life-span and r-strategic species such as rotifers showed increases in species richness in the perturbed lakes compared to natural lakes. Compared to previous studies, our study showed that this increase in the number of rotifer species lasted for the 3-year survey. Rotifers also showed higher biomass in perturbed lakes (especially burnt lakes), but only during the first two years of the survey. In general, fires had greater eutrophication effects than did clear-cut harvest. In lakes impacted by fires, increases in nutrient inputs (total phosphorus, total nitrogen) favoured phytoplankton and rotifer growth, while in lakes impacted by logging, increases in dissolved organic carbon and water color limited the increase of phytoplankton and rotifers. For the crustaceans (Cladocera, Calanoida, Cyclopoida), neither species richness nor biomass was related to watershed perturbations. In general, our study indicates that natural sources of temporal variation between years had greater effects on the biomass of some zooplankton groups than did the perturbations. Overall, increases in Rotifera biomass were primarily related to higher mean summer water temperature whereas increases in Cyclopoida biomass were related to higher chlorophyll a concentrations. Perturbation intensity, nutrient concentrations, and drainage ratio also tended to increase the responses of these zooplankton groups, but their influence over the mid-term survey was not significant. A higher biomass of Calanoida was observed in lakes (mainly natural ones) with high water transparency and low nutrients. Variation in Cladocera biomass was not related to lake enrichment, higher temperature or perturbation intensity. Our mid-term study generally confirms the effects of wildfires and logging, as previously suggested, but not significantly detected by other studies (PATOINE et al. 2000, 2002a) conducted only during the first year after the perturbations. It shows the usefulness of mid-term monitoring to better assess the ecological impacts of natural and anthropogenic perturbations on aquatic ecosystems.

Cet article présente une première synthèse comparative des impacts des feux et des coupes forestières sur la qualité des eaux et les communautés aquatiques des lacs de l'écozone boréale de l'est du Canada. La recherche a été réalisée de 1996 à 1998 dans le cadre d'un projet du Réseau de centre d'excellence sur la gestion durable des forêts (RCE-GDF) et porte sur 38 lacs du Bouclier Canadien du Québec. Les changements dans la qualité de l'eau ainsi que dans la diversité, la biomasse et la structure des communautés de plancton et de poissons ont été suivis pendant trois ans dans 20 lacs dont les bassins versants étaient non perturbés, dans 9 lacs qui avaient subit des coupes forestières et dans 9 lacs qui avaient subit des feux de forêt.Notre étude montre que les feux et les coupes ont des impacts significatifs qui diffèrent selon le type de perturbation. En général, les lacs affectés par les coupes et les feux ont des concentrations de phosphore 2 à 3 fois plus élevées que les lacs de référence. Toutefois, les lacs affectés par les feux montrent des concentrations en nitrates beaucoup plus élevées tandis que les lacs affectés par les coupes sont moins transparents et ont des eaux plus colorées, très riches en carbone organique dissous. Les feux et les coupes affectent aussi de façon différente la minéralisation des eaux et les concentrations des ions majeurs. Les feux et les coupes n'ont pas d'effet sur la biodiversité des communautés planctoniques, sauf dans les lacs ayant un grand bassin versant et plus de 40 % de perturbation. Aucune différence n'a été observée entre les lacs de référence et les lacs perturbés au niveau de l'occurrence, l'abondance et la croissance des espèces de poissons. En revanche, les feux et les coupes affectent la production et la structure des communautés aquatiques. Dans les lacs affectés par les feux, l'enrichissement en azote et phosphore provoque une hausse de la concentration en chlorophylle a, et de la biomasse du phytoplancton et du limnoplancton (seston > 53 µm), en particulier des diatomées, des rotifères et des gros crustacés, pendant deux à trois années après les feux. En revanche, dans les lacs affectés par les coupes, l'enrichissement en phosphore n'entraîne qu'une augmentation très faible et limitée à un an de la biomasse des algues et pas de changement dans les biomasses du limnoplancton, en raison de la forte couleur et de la transparence réduite des eaux, qui limite la production biologique. Les coupes ont un impact négatif sur les copépodes calanoïdes, un groupe de zooplancton caractéristique des lacs oligotrophes et transparents. Une diminution significative de la proportion des individus de petite taille a été observée chez les populations de perchaude et de meunier noir des lacs perturbés (lacs de coupe et de feux formant un seul groupe). Les impacts observés dans la qualité des eaux et la production du plancton augmentent avec l'importance relative des perturbations au niveau du bassin versant. Cependant, la variabilité dans les caractéristiques des bassins versants et des lacs, en particulier le rapport de drainage et le temps de résidence des eaux, a des effets confondants sur les réponses des écosystèmes lacustres aux perturbations par les feux et les coupes., This paper presents a comparative review on ecological impacts of wildfires and harvesting on water quality and aquatic community attributes of boreal lakes in eastern Canada. This project was carried out from 1996 to 1998, as part of the research program of the Sustainable Forest Management Network Centre of Excellence (NCE-SFM), on 38 lakes of the Boreal Canadian Shield (Québec, Canada). Changes in water quality, and in diversity, biomass and community structure of pelagic plankton and fish populations were monitored for 3 years in 20 reference lakes, 9 cut lakes and 9 burnt lakes.Our study shows that wildfires and logging have significant impacts on water quality as well as primary and secondary producers in boreal lakes. However, fire and logging does not have similar impacts. In general, cut and burnt lakes showed higher concentrations of total phosphorus (TP: 2-3 folds) than reference lakes. However nitrates concentrations (NO3-) were higher in burnt lakes than in reference and cut lakes, whereas dissolved organic carbon (DOC), light extinction coefficient (e PAR) and water colour were higher in cut lakes than in reference lakes, burnt lakes showing intermediate values. Wildfire and logging also affect ionic composition of lake water. Both burnt and cut lakes had higher concentrations of potassium (K+), chloride (Cl-) and calcium (Ca2+) than reference lakes, while sulphates (SO42-) and magnesium (Mg2+) increased only in burnt lakes. The observed increases in organic and mineral elements reflect their export from the watershed and were related to the drainage ratio. As mobile ions are rapidly flushed from the perturbed watersheds, ionic water composition returned to normal levels within three years after the perturbation. In contrast, some changes in water quality (P and N enrichment in perturbed lakes; DOC increase in cut lakes) seems to be on longer term and might have a more important effect on limnological features of lakes such as thermal stratification, mixed and euphotic depth, plankton biomass and bioaccumulation of mercury in zooplankton and fish.Wildfires and logging do not have significant impacts on species richness of planktonic communities, except for lakes with large drainage basins and those where the perturbation was higher than 40% of the watershed area. However, wildfires and logging affect biomass of plankton communities. In burnt lakes, the nutrient enrichment induced important increases in Chl. a concentration and phytoplankton biomass, and a small increase in limnoplankton biomass (seston > 53 µm). Diatoms, rotifers and large crustaceans showed significant increases. In burnt lakes, increases in phytoplankton were observed during the three years of the survey and were highest in the first 2 years after fires. Limnoplankton increases lasted only 2 years and were highest the second year after fires. In cut lakes, nutrient enrichment was not reflected in a proportional increase in plankton production due to increase in DOC concentrations and lake water colour that reduced water transparency. Phytoplankton slightly increased only the first year after logging and no increase was observed for limnoplankton and zooplankton. Logging negatively affect calanoids, a zooplankton group characteristic of clear and oligotrophic lakes. No significant differences were observed in the occurrence, abundance and growth of fish populations among reference and perturbed lakes. However, the proportion of small yellow perch and white sucker were significantly lower in populations of impacted lakes (burned and logged lakes pooled). In most cases, impacts on water quality and plankton communities were related to the intensity of fire or logging, when expressed as the percent area of watershed harvested or burnt divided by the lake surface or volume. Simple models may then be developed and help to predict the effect of harvesting practices on lake ecosystems. However, environmental variation in watershed and lakes characteristics, especially drainage ratio and lake water residence time, are important confounding factors in the responses of lakes to watershed perturbations by fire or logging. Lakes with drainage ratio > 4 and with more of 30% of their watershed perturbed are the most sensitive to fire and logging. These factors should be considered when developing lake management models in the boreal forest impacted by fire and logging.

The influence of trophic status on the crustacean zooplankton community was investigated in lakes and reservoirs in temperate and subtropical-tropical regions. We tested if there is a consistent relationship between crustacean species richness, assemblages, and abundance and trophic indices such as total phosphorus and chlorophyll a. We also examined if these patterns differ between regions. Cumulative species richness and assemblages varied among regions. The greatest number of crustacean species was found in the temperate oligotrophic region with the largest number of lakes sampled. However, cumulative species richness was similar in temperate and subtropical–tropical regions when comparing subsets with a similar number of lakes and reservoirs. The relationships between species richness and latitude or trophic status were difficult to assess owing to imbalance among regions in number of lakes and reservoirs sampled and to biogeography and fish predation potential influences. Trophic status was associated with changes in abundance of all major crustacean zooplankton groups. Eutrophic ecosystems supported greater crustacean abundances at all latitudes. However, cladocerans and cyclopoids were more abundant in eutrophic lakes and reservoirs, whereas calanoids were more abundant in temperate oligotrophic lakes. Total phosphorus was found to be a better predictor of the biomass of major crustacean groups than chlorophyll a in all regions.

The efficiency of a cantilevered bridle net was tested in comparison with a Wisconsin net and a pumping system to sample zooplankton organisms in three water layers (epi-, meta- and hypolimnion) of three Canadian Shield lakes. Variations among samplers were compared to variations due to within-lake vertical distribution of zooplankters and among lake variations. For each lake and water layer, we also assessed the efficiency of the three methods according to the catches of zooplanktonic taxa. The highest percentages of variationweregenerallyduetolakeorwater-layereffects;interactionbetweensamplinggearsandwaterlayers wasabove50%formosttaxa,exceptcladoceran.Samplingmethodsexplainedmorevariationthanthelake effect for some zooplankton taxa, indicating that using different sampling devices could potentially alter the among-lake variation interpretation of zooplankton abundance. The pumping system captured higher densitiesofanimalspertaxathanthecantileverandtheWisconsinnets.Thecantilevernetgenerallycaptured mobile taxa more efficiently (Polyarthra vulgaris, copepods, Daphnia sp., Diaphanosoma brachyurum and chaoborids) than the Wisconsin net and the pumping system, but its efficiency varied among water layers.

This study documents for the first time both vertical and horizontal distribution patterns of the zooplankton community in Lake Kinneret during the period of thermal stratification. The zooplankton distribution patterns were explored in relation to abiotic (temperature, oxygen) and biotic (picocyanobacteria, ciliates, flagellates, phytoplankton, fish) environmental gradients. Sampling was carried out on 6–7 July 1992 at five stations and six depths from nearshore to offshore. Zooplankton abundance and biomass varied from 5 to 267 ind. l−1(mean: 95 ind. l−1), and from 0.1 to 65 d.w. mg m−3(mean: 24 d.w. mg m−3). Zooplankton taxonomic groups (Rotifera, Cladocera, Cyclopoida, Calanoida) and size classes (micro-, meso- and macrozooplankton) showed peaks of maximal density and biomass in the epilimnetic and metalimnetic strata (5 and 14 m). Depth, accounting for 31–39% of total spatial variation, reflected the vertical distribution of zooplankton in relation to temperature and oxygen declines, and the higher concentration of food resources (protists and phytoplankton) in the epilimnion and metalimnion. Onshore–offshore distance, accounting for 17–22% of the total spatial variance, reflected different distribution patterns shown among zooplankton groups and size classes. The macrozooplankton (Copepoda, Cladocera) was more abundant offshore, whereas microzooplankton (Rotifera and nauplii) predominated nearshore. These horizontal distribution patterns were related to small increases in temperature and phytoplankton biomass, and higher concentrations of fish in the littoral zone. Although limited to a short temporal scale, our study indicated that zooplankton spatial distribution in Lake Kinneret during the period of thermal stratification was related to physicochemical, food and predation factors, manifested differently along the vertical and nearshore–offshore gradients.

We investigated the mechanisms behind the negative effects of cyanobacteria on zooplankton by comparing the effects of Microcystis aeruginosa single cells, colonies, and toxins on the feeding behavior of Daphnia pulicaria in three independent experiments. The animals were fed a mixture of Scenedesmus supplemented by increasing proportions (0, 20, 50, 80, 100%) of Microcystis or concentrations (0, 50, 500, 5,000 ng ml 21 ) of purified microcystin-LR. The changes in feeding behavior, as indicated by the appendage beat, mandible or labrum movement rates were evaluated by a direct observation method that coupled video recording and computerized image analysis. Daphnia responded in a different manner to the presence of single cells and colonies. In the case of the single cells, the mandibular movement rate (MMR) declined more than appendage beat rate (ABR), suggesting that Daphnia have the ability to discriminate between Microcystis and Scenedesmus. Colonies, on the other hand, produced a typical feeding interference response: the animals increased their labral rejection rate (LRR) and showed starvation signs. LRR increased in the presence of both unicellular and colonial Microcystis. In both cases, the changes in MMR and ABR were rapidly reversible and hence unlikely to be caused by intoxication from the presence of cellbound microcystins. In contrast, the addition of purified microcystin-LR at the concentration of 5,000 ng ml 21

The present study was designed to assess the environmental effects of metals in a field setting. We explored exposure--bioaccumulation--effects relationships in freshwater molluscs exposed to metals in their natural habitat. Indigenous floater mussels (Pyganodon grandis) were collected from ten limnologically similar lakes located along a Cd, Cu and Zn gradient. Ambient free-metal ion concentrations were estimated as a measure of metal exposure. Metallothionein (MT) was measured in mussel gills and metal partitioning among the various cytosolic protein pools was determined by size exclusion chromatography. Various biomarkers were also measured, including malondialdehyde (MDA) concentrations in the gills and in the digestive gland, glutathione-peroxidase and glutathione-reductase activities in the digestive gland, and lipid concentrations in the gonad. Cadmium and MT concentrations in the gill cytosol increased along the contamination gradient, but Cu and Zn levels were independent of the ambient free-metal ion concentrations. The distribution of Cd among the various cytosolic complexes remained quite constant: 80% in the MT-like pool, 7% in the low molecular weight pool (LMW1.8 kDa) and 13% in the high molecular weight pool (HMW18 kDa). For these chronically exposed molluscs there was thus no threshold exposure concentration above which spillover of Cd occurred from the MT pool to other cytosolic ligands. However, the presence of Cd in the LMW and HMW fractions suggests that metal detoxification was imperfect, i.e. that P. grandis was subject to some Cd-related stress at low chronic exposure concentrations. Consistent with this suggestion, MDA concentrations, an indicator of oxidative stress, increased with gill cytosolic Cd. In the digestive gland, MDA concentrations were unrelated to any of the measured metals, but glutathione-peroxidase and glutathione-reductase activities increased with gill cytosolic copper. We speculate that cytosolic Cu catalyses the production of reactive oxygen species, to which the organism reacts by increasing activities of the two enzymes, thus preventing the accumulation of reactive oxygen species. Lipid concentrations in the gonad did not decrease with any of the measured toxicological parameters, suggesting that energy reserves for reproduction were not compromised in the metal-contaminated mussels. The results of the present study, where chronically exposed bivalves were collected from their natural habitat along a metal contamination gradient, contrast markedly with what would have been predicted on the basis of experimental metal exposures, and clearly demonstrate the need to study metal exposure--bioaccumulation--effects relationships in natural populations.

SUMMARY 1. Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (� 5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes. 2. In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species – Aphanizomenon flos-aquae, Anabaena flos-aquae and Microcystis aeruginosa – which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos-aquae. The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology. 3. Standardised concentrations of the hepatotoxic microcystin-LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced. 4. Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited.

In Canada, disturbance of boreal forests has increased due to expanding anthropogenic activities, particularly forestry. A first attempt was made to evaluate impacts of forest harvesting and wildfire on changes in water quality and biota of lakes. We present case studies in two major geological and climatic subregions of the boreal ecozone in Canada: the Boreal Plain and the Boreal Shield. Responses of lake ecosystems to wildfire and logging differed. In upland Boreal Plain lakes, total phosphorus (P), inorganic nitrogen (N) and algal biomass were higher in lakes with burned watersheds, whereas, only total P increased in lakes with watershed logging. Logging on the Boreal Shield and wildfire in wetland-and permafrost-dominated watersheds on the northern Boreal Plain were associated with increases in dissolved organic carbon (DOC) and water colour, possibly causing light-limitation of algae in both regions, and a decrease in calanoid biomass in eastern Boreal Shield lakes. The number of water qual...