Zooplankton Communities In Lakes Research Articles

Zooplankton communities of small lakes of the Kuibyshev district Novosibirsk region in the spring and summer

In the course of hydrobiological studies conducted in the spring and summer of 2023 on small lakes of the Kuibyshev district of the Novosibirsk region, zooplankton communities were studied, which is relevant in the field of studying the fish food supply. The purpose of this study was to determine the species diversity and quantitative characteristics of zooplankton communities of lakes. Sampling and in-house processing of samples was carried out according to generally accepted methods. The characteristics of zooplanktonic invertebrates in terms of qualitative and quantitative indicators are considered. The assessment of the trophic and feeding capacity of the lakes is given. 16 species of organisms of 12 genera from 9 families were found in the zooplankton, 5 of which are rotifers, 9 are branched crustaceans and 2 are oar-footed crustaceans. It was found that the greatest species diversity was observed in Lake Tsybovo — 13, the smallest in Lake Maloe Puchkovo — 9 taxa. The average zooplankton abundance and biomass in the studied lakes ranged from 16.0 to 67.645 thousand specimens/m3 and from 652.2 to 7118.5 mg/m3, respectively. The maximum average values of zooplankton abundance and biomass were found in Lake Fedino, the minimum values in Lake Cemetery. In terms of frequency of occurrence and specific abundance, Copepods are mainly dominant. The lowest frequency of occurrence and specific abundance is mainly in Rotifera. According to the average indicators of zooplankton biomass, lakes have different trophic status and feeding capacity of the reservoir: from oligotrophic type (low-fat) to eutrophic type (high-fat). Fedino Lake was classified as a high-grade eutrophic reservoir with an increased productivity class. Cemetery Lake with the lowest abundance and biomass indicators was assessed as an oligotrophic reservoir of low productivity class, from the point of view of feeding opportunities for planktophage fish — low-feeding. Tsybovo and Maloe Puchkovo lakes were assessed as mesotrophic reservoirs.

Effects of dissolved organic carbon gradient on epilimnetic zooplankton communities in lakes

Lake browning is expected to change aquatic ecosystems considerably. The changes that may occur in zooplankton communities with a high concentration of dissolved organic carbon (DOC) are little studied and not yet sufficiently understood. We studied zooplankton communities in Finland in 27 lakes with a wide DOC range. We explored how zooplankton diversity and biomass vary along a DOC gradient and how species belonging to different functional groups respond to varying DOC concentrations. The total biomass of zooplankton was not related to DOC concentration, but diversity decreased and the negative linear trend in diversity coincided with an increase in omnivorous zooplankton taxa, whereas several other herbivorous zooplankton taxa were displaced from the community along the gradient of DOC. The results of our study suggest that some well-adapted taxa, especially omnivorous taxa, can benefit from lake browning, but a larger number of taxa suffer from unfavourable conditions caused by high DOC concentration. DOC-induced changes in predation pressure and changes in phytoplankton community in terms of resource availability for zooplankton should be emphasized in future research to understand the effects of lake browning on zooplankton.

Costs of Daphnia diel vertical migrations under forecasted increase of lake temperature

The aim of our work was to experimentally test the hypothesis that changes in the thermal stratification in lakes of the temperate zone, expected as a result of progressive global warming, will cause an increase in fitness costs in a planktonic cladoceran Daphnia, associated with diel vertical migrations. In a programmable thermostatic chamber, Daphnia magna have been cultured from the first juvenile instar till the first reproduction, in thermal regimes corresponding to the conditions experienced by non-migratory (remaining in epilimnion day and night) and migrating (spending nights in epilimnion and days in hypolimnion) animals. We exposed Daphnia to thermal regimes: corresponding to the temperatures typically reigning stratified lakes nowadays (20 °C in epilimnion and 8 °C in hypolimnion), and expected at the end of this century (28 °C and 12 °C, respectively). The analysis of life-history parameters confirmed the assumption of an increase in metabolic costs resulting from vertical migration of Daphnia along with the expected increase in temperature differences between epilimnion and hypolimnion, which is a daily anti-predator refuge for migrating animals. This may consequently lead to significant changes in the composition of lake zooplankton communities, i.e., to an increase in the share of non-migrating species with small body sizes.

Environmental Factors Controlling Zooplankton Communities in Thermokarst Lakes of the Bolshezemelskaya Tundra Permafrost Peatlands (NE Europe)

Environmental physical and chemical factors controlling the abundance and biodiversity of zooplankton in permafrost-affected lakes are poorly known yet they determine the response of aquatic ecosystems to on-going climate change and water warming. Here, we assess the current status of zooplankton communities in lakes of the Bolshezemelskaya Tundra (permafrost peatlands of NE Europe), and provide new information about the composition and structure of zooplankton. The results demonstrate that the structure of zooplankton communities is influenced by the morphometric features of lakes and the degree of lake overgrowth by macrophytes. According to the level of quantitative development of zooplankton, most tundra lakes were of the oligotrophic type with an average wet biomass of up to 1 g/m3. The largest number of species was observed in zooplankton communities of small thaw ponds with an area of up to 0.02 km2 and overgrown with macrophytes. The analysis of factors that influence the formation of the lake zoocenosis demonstrated that the species composition and quantitative characteristics of zooplankton are chiefly controlled by pH and water mineralization. A comparison of the results obtained with the literature data on the lakes of this region collected 60 years ago suggests that the ecosystems of these lakes are in a stable state. Overall, these new insights will improve our knowledge of factors controlling the zooplankton spatial dynamics in unique but quite abundant thermokarst lakes of NE European Tundra, subjected to on-going climate warming.

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

The short-term effects of planktivorous fish foraging in the presence of artificial light at night on lake zooplankton.

Numerous studies have revealed that artificial light at night alters the natural patterns of light in space and time and may have various ecological impacts at different ecological levels. However, only a few studies have assessed its effect on interactions between organisms in aquatic environments, including predator-prey interactions in lakes. To fill this gap, we performed a preliminary enclosure experiment in which we compared the foraging effect of juvenile perch (Perca fluviatilis) on a natural lake zooplankton community in the absence and presence of light of high-pressure sodium (HPS) lamps mimicking artificial light emitted by a boat. The results revealed that even short-lasting exposure to HPS lamps may result in increasing fish predation, which in turn decreased the mean body size in zooplankton populations (e.g. Bosmina thersites) and affected the relative proportion between different taxa in zooplankton communities.

Taxonomic and functional differences between winter and summer crustacean zooplankton communities in lakes across a trophic gradient

AbstractDespite increasing interest in winter limnology, few studies have examined under-ice zooplankton communities and the factors shaping them in different types of temperate lakes. To better understand drivers of zooplankton community structure in winter and summer, we sampled 13 lakes across a large trophic status gradient for crustacean zooplankton abundance, taxonomic and functional community composition and C/N stable isotopes. Average winter zooplankton densities were one-third of summer densities across the study lakes. Proportionally, cladocerans were more abundant in summer than winter, with the opposite pattern for calanoids and cyclopoids. In green (eutrophic) lakes, zooplankton densities were higher under the ice than in brown (dystrophic) and blue (oligotrophic) lakes, suggesting better conditions for zooplankton in productive lakes during winter. Overall, zooplankton communities were more similar across lakes under the ice than during the open water season. Feeding group classification showed a decrease in herbivore abundance and an increase in predators from summer to winter. C/N stable isotope results suggested higher lipid content in overwintering zooplankton and potentially increased reliance on the microbial loop by winter zooplankton. Our results show substantial variation in the seasonality of zooplankton communities in different lake types and identify some of the factors responsible for this variation.

Abiotic and biotic drivers of temporal dynamics in the spatial heterogeneity of zooplankton communities across lakes in recovery from eutrophication.

Seasonal and annual dynamics of the zooplankton community in lakes are affected by changes in abiotic drivers, trophic interactions (e.g., changes in phytoplankton and fish communities and abundances) and habitat characteristics (e.g. macrophyte abundance and composition). However, little is known about the temporal responses of the zooplankton community to abiotic and biotic drivers across lakes at the regional scale. Using a comprehensive 20-year dataset from 20 Danish lakes in recovery from eutrophication, we assessed the seasonal and annual trends in the spatial heterogeneity of zooplankton community across lakes and related it to abiotic and biotic drivers. We found significant seasonality and inter-annual decreases in spatial zooplankton heterogeneity in both shallow and deep lakes, with the decrease in the spatial turnover dominating the temporal dynamics of the beta diversity. For the inter-annual changes, decreased spatial heterogeneity of phytoplankton, macrophytes and fish were important biotic drivers at the regional scale. Using a series of ordinary least squares regressions and model selection with model averaging approaches, we revealed that both local (e.g., total phosphorus, total nitrogen, pH, Secchi depth, alkalinity, Schmidt stability, water temperature) and regional drivers (e.g., air temperature, solar irradiance) were important variables influencing the spatial zooplankton heterogeneity, although the directions depended on the beta diversity measures and water depth. Our results highlight an important role of bottom-up forces through phytoplankton community as well as macrophytes and top-down forces via fishes in driving the temporal changes in zooplankton community composition patterns at the regional scale.

Biogeographic patterns of planktonic and meiobenthic fauna diversity in inland waters of the Russian Arctic

Abstract Broad‐scale assessment of biodiversity is needed for detection of future changes across substantial regions of the Arctic. Presently, there are large data and information gaps in species composition and richness of the freshwater planktonic and meiobenthos communities of the Russian Arctic. Analysis of these data is very important for identifying the spatial distribution and temporal changes in species richness and diversity of rotifers, cladocerans, and copepods in the continental Russian Arctic. We investigated biogeographic patterns of freshwater plankton and meiobenthos from c. 67° to 73°N by analysing data over the period 1960–2017. These data include information on the composition of rotifers, cladocerans, and copepods obtained from planktonic and meiobenthic samples, as well as from subfossil remains in bottom sediments of seven regions from the Kola Peninsula in the west, to the Indigirka River Basin (east Siberia) in the east. Total richness included 175 species comprised of 49 rotifer genera, 81 species from 40 cladoceran genera, and 101 species from 42 genera of calanoid, cyclopoid, and harpacticoid copepods. Longitudinal trends in rotifer and micro‐crustacean diversity were revealed by change in species composition from Europe to eastern Siberia. The most common and widespread species were 19 ubiquitous taxa that included Kellicottia longispina (Rotifera), Chydorus sphaericus s. lat. (Cladocera), Heterocope borealis, Acanthocyclops vernalis, and Moraria duthiei (Copepoda). The highest number of rare species was recorded in the well‐studied region of the Bolshezemelskaya tundra and in the Putorana Plateau. The total number of copepod and rotifer species in both Arctic lakes and ponds tended to increase with latitude. Relative species richness of copepods was positively associated with waterbody area, elevation, and precipitation, while relative species richness of cladocerans was positively related to temperature. This result is consistent with known thermophilic characteristics of cladocerans and the cold tolerance properties of copepods, with the former being dominant in shallow, warmer waterbodies of some western regions, and the latter being dominant in large cold lakes and waterbodies of eastern regions. Rotifers showed a negative association with these factors. Alpha‐ and β‐diversity of zooplankton in the Russian Arctic were strongly related to waterbody type. Lake zooplankton communities were more diverse than those in pond and pool systems. Moreover, the highest β‐diversity values were observed in regions that showed a greater breadth in latitude and highly heterogeneous environmental conditions and waterbody types (Bolshezemelskaya tundra and Putorana Plateau). Redistribution of freshwater micro‐fauna caused by human activities occurred in the 1990s and 2000s. As a result of climate warming, a few cladoceran species appear to have extended their range northward. Nevertheless, the rotifer and micro‐crustacean fauna composition and diversity of the majority of Arctic regions generally remain temporally conservative, and spatial differences in composition and species richness are chiefly associated with the differences between the warmer European and colder east Siberian climates.

Can dispersal buffer against salinity‐driven zooplankton community change in Great Plains' lakes?

Abstract The North American Great Plains contains thousands of lakes that vary in salinity from freshwater to hypersaline. Paleolimnological studies show that salinity levels in these lakes are tightly linked with climate, and current projections point to a more arid future in the region due to natural and anthropogenic climate change, potentially influencing lake salinity. Many zooplankton species are sensitive to changes in salinity, and their position near the base of the aquatic food web makes it important to understand how they might respond to increasing salinity levels. Zooplankton communities in lakes with rising salinity levels may exhibit changes in structure, including a shift toward more salinity‐tolerant species and a reduction in abundance, species richness, and diversity. However, it is possible that dispersal of zooplankton among lakes could mitigate such community changes when migrant populations replace sensitive zooplankton with those that are locally adapted to higher salinities. To test if dispersal could reduce salinity‐induced changes in zooplankton communities, we ran a field enclosure experiment at a freshwater lake in southern Saskatchewan where we manipulated salinity levels and zooplankton dispersal. We evaluated how salinity and dispersal influenced species identities and relative abundances (community structure) using multivariate statistics and comparing taxonomic and functional compositions among the different treatments (richness, diversity, and evenness). We found that increasing salinity levels in our enclosures above that in our study lake resulted in lower zooplankton abundances and species richness levels, primarily due to the loss of cladoceran species. However, patterns in our multivariate analyses suggested that cladocerans were maintained in enclosures with salinity levels of 2.5 and 5.0 g/L when those enclosures received immigration from nearby lakes. In contrast, our univariate analyses failed to find evidence that immigration affected community structure (richness, diversity, evenness). The lack of significant statistical differences could suggest that dispersal does not have an effect, or it may have been a problem with statistical power, as a power analysis suggested that fairly large effect sizes would have been required to achieve statistical significance. Based on our results, we were unable to reach a definitive conclusion on the role that dispersal might play in buffering zooplankton communities against salinity‐driven changes. However, our study provides two important insights for planning future work. First, our power analyses indicated that more replication may be needed given the variability among our experimental enclosures. Second, the patterns in our multivariate analyses suggested that cladocerans could be maintained in lakes undergoing salinity increases if they receive immigration from surrounding lakes with higher salinities. Future work examining how inter‐ and intraspecific salinity tolerance varies across lakes with a gradient of salinities would be helpful for understanding the role that dispersal might play in buffering against salinity‐driven losses of cladoceran zooplankton.

Hydrological variability, zooplankton availability and the shift between planktivore-benthivore feeding behaviour in the visual predator fish, Odontesthes bonariensis

Hydrology is a key factor in the dynamic of zooplankton community in lakes with high water renewal rate. Crustaceans’ zooplankton biomass can sharply decline during flooding periods as consequence of wash-out effect. The hydrologically induced changes in zooplankton community may certainly affect the feeding behaviour of planktivorous fishes, but this has not been studied yet. The inland silverside, Odontesthes bonariensis (Valenciennes, 1835), is the main visual planktivorous fish in temperate shallow lakes of South America. We analyzed the diet composition and feeding strategy of O. bonariensis in a large run-of-the-river shallow lake, along two consecutive spring-summer periods with contrasting hydrological conditions. Water residence time varied one order of magnitude between flood and drought period. As it was expected, silversides showed size selective feeding on large cladocerans during drought period when zooplankton biomass was high. On the other hand, during high flushing period, zooplankton abundance decreased noticeable and silversides drastically changes its feeding behaviour from visual planktivore to benthivore. The analysis of the feeding strategy of O. bonariensis showed that this species largely behaves as a specialist irrespective of the hydrological conditions. However, the main involved prey varied from large Daphnia during low flow conditions to large Ostracoda during floods. Our study reveals that the variation in the availability of suitable prey induced by hydrological variability is associated with a drastic change in feeding grounds and prey selection of O. bonariensis. This flexible predatory behaviour may have consequences on food web dynamics of shallow lakes that are further discussed.

Functional shifts in lake zooplankton communities with hypereutrophication

Abstract Functional variation among consumer communities can alter ecosystem nutrient cycling. These impacts on ecosystem function can be specifically driven by interspecific variation in stoichiometric traits; thus, functional trait‐based approaches can be used to explain the processes controlling ecosystem stoichiometry. However, eutrophication may reduce the functional importance of consumers in ecosystems by eliminating heterogeneity in nutrient recycling among taxa. To test whether zooplankton functional diversity, i.e. aspects of the stoichiometric trait space occupied by zooplankton communities, varies over gradients in trophic state and nutrient stoichiometry, we examined functional and taxonomic variation in the zooplankton communities of 130 lakes in the agriculturally dominated state of Iowa (U.S.A.) over 7 years. Stoichiometric functional dispersion decreased with trophic state index, supporting the trait abundance shift hypothesis that hypereutrophic lakes are characterised by different combinations of functional traits than their less eutrophic counterparts. Zooplankton communities became increasingly N‐rich relative to P as TSI increased. Specifically, P‐poor Bosmina, Chydorus, and cyclopoid copepods increased in abundance with eutrophication. Stoichiometric trait distributions of zooplankton shift with eutrophication, which implies that the unique functioning of hypereutrophic lakes could be due in part to the consumers inhabiting them. As zooplankton N:P increased with trophic state while lake total nitrogen to total phosphorus ratio decreased with trophic state, P‐poor zooplankton taxa may exacerbate excess P availability in these hypereutrophic systems by differentially recycling P at higher rates.

Temporal dynamics and relationship between climate, limnological variables and zooplankton composition in climate-sensitive Lake Bosumtwi, Ghana

The community composition and the factors affecting seasonal and interannual dynamics of zooplankton in Lake Bosumtwi were studied biweekly at a central index station during 2005 and 2006. The lake zooplankton community was species poor. Mesocyclops bosumtwii was numerically superior seasonally and interannually and was endemic to the lake. Minor constituents included Moina micrura, six rotifer species (except for Hexarthra intermedia) and Chaoborus ceratopogones larvae. Low variance of cyanobacteria-dominated phytoplankton biomass underlined stable zooplankton community structure. Emergence of rare species of rotifers occurred seasonally. The climatic signature on the lake’s stratification and mixing regime was strongly influenced by atmospheric temperature, but weakly by wind strength, because of sheltering of the lake by high crater walls. Increasing mixing depth entrained high TP concentrations from below the thermocline seasonally, but reflected poorly in the phytoplankton biomass behaviour. Total zooplankton abundance did not differ seasonally, but varied markedly from year to year in its timing and magnitude. Herbivores were squeezed between food limitation and high predation pressure from Chaoborus all year round. The low fish planktivory (high fishing pressure) on Chaoborus may create a trophic bottleneck restricting energy transfer efficiency from zooplankton to fish.

Crustacean zooplankton assemblages in inland waters of southern Patagonia (Alacalufes National Reserve), Chile (49-51°S)

The inland water crustacean communities in southern Chilean Patagonia (46-55°S) are characterized by their marked low species number, and many recurrent species among a wide ecological and geographical gradient, that is due to oligotrophy of lakes and lagoons and the fluvial parameters (i.e., high flow velocities) in rivers. The aim of the present study was to describe the zooplankton communities in lakes and respective outflow river estuaries in Alacalufes National Reserve on islands of Chilean southern Patagonia (49-51°S). Species abundance and presence/absence were considered. The results obtained revealed the presence of a low number of species and also multiple sites in which zooplankton was not recorded at all. This is probably due the low zooplankton diversity of cold lakes at these high latitudes and the often turbulent flow of the outflow rivers studied.

Spatial patterns reveal strong abiotic and biotic drivers of zooplankton community composition in Lake Mývatn, Iceland

Spatial patterns in the abundance of species are determined by local abiotic and biotic conditions, and by the movement of individuals among localities. For species distributed among discrete habitat “islands”, such as zooplankton distributed among lakes, local conditions within lakes often dominate low movement rates among lakes to determine the composition of communities. Here, we ask whether the same abiotic and biotic environmental conditions can generate spatial patterns in the distribution of zooplankton within a lake where there are high horizontal movement rates. We conducted three spatial surveys of zooplankton communities in Lake Mývatn, Iceland, a moderately sized (37 km2) shallow lake with a high outflow rate. The pelagic zooplankton community showed strong spatial structure (spatial autocorrelation), with species composition varying with spatial variation in chlorophyll‐a, the abundance of Anabaena (cyanobacteria), lake depth, light extinction coefficient, and temperature. These factors are known from other studies to be strong drivers of among‐lake variation in freshwater zooplankton communities. However, in contrast with among‐lake studies, fish (stickleback) abundance had no measureable effect on the abundance or species composition of the zooplankton community, although high local stickleback abundance was associated with low zooplankton:phytoplankton biomass ratios. Finally, a parallel study of the underlying benthic crustacean community showed much finer spatial variation (spatial autocorrelation to a range ≤0.6 km vs. 9 km for pelagic zooplankton), suggesting that the stationary character of the benthos allows finer grained spatial patterns. Given the high flow rate of water in Mývatn (>200 m/d), the generation of spatial patterns suggests very strong effects of variation in abiotic and biotic environmental conditions on the population dynamics of zooplankton in the lake.

Feeding response of <i>Daphnia</i> cf.<i> similis</i> to different concentration gradients of <i>Microcystis</i> and its implication for preventing algal blooming

Daphnia are important components of zooplankton communities in lakes, ponds and reservoirs. Currently freshwater ecosystems are affected worldwide by Cyanobacterial blooms through the process of eutrophication. The objective of this study was to provide experimental evidence to the response of Daphnia to various concentrations of Microcystis . The experiment contained four treatments and two controls each with three replicates. The first control contained D . cf. similis without Microcystis and the second control contained Microcystis without D .cf. similis . The remaining four treatments contained both D . cf. similis and Microcystis at different concentration of Microcystis .. The results showed a significant negative relationships between D . cf. Similis and Microcystis across the treatments (F=294.5; p<0.00). From the four Microcystis concentration gradients, we found mortality of D. cf. Similis in HMC (high Microcystis concentration) and 67% of the original HMC gradient while in the other treatments, in 43% and 22% original HMC treatment, D . cf. Similis reproduce and attain high density. Therefore, from these results it is concluded that D . cf. similis can control the growth of Microcystis if the concentration is low but they cannot reduce an already existing bloom. Keywords : Concentration gradient, D. cf. Similis, Feeding-treatment, Microcystis, Ethiopia.

Effects of winter surface aeration on pelagic zooplankton communities in a small boreal foothills lake of Alberta, Canada

Winter aeration is often used to prevent fish winter-kill among lakes supporting recreational fisheries and is often used in conjunction with trout stocking as trout are sensitive to hypoxia.We collected limnological data as well as pelagic microcrustacea and rotifers one year before and one year after aeration was initiated in Birch Lake, located in the boreal foothills ecozone of Alberta, Canada. Using a Before-After-Control-Impact design, we compared changes in Birch Lake to those in two nearby and similarly mesotrophic, stocked control lakes (one aerated for more than six years, one unaerated). During winter, surface aeration increased the depth of well-mixed water in Birch Lake, maintaining levels of dissolved oxygen suitable for supporting stocked trout. Linear mixed model analyses indicated that among May–August water quality parameters, only phosphorus concentrations showed a marginally significant treatment × year interaction, increasing only in the unaerated control lake. Aeration did not affect the spring–summer abundance, biomass, or sizes of Birch Lake's zooplankton community. Once aerated, the microcrustacean community in Birch Lake showed partial overlap with the community in the aerated control, although this could not be statistically linked to changes in specific taxa. Ours is the first study to investigate impacts of winter surface aeration on zooplankton communities despite the numerous lakes managed under this strategy.

Contrasting patterns of allochthony among three major groups of crustacean zooplankton in boreal and temperate lakes.

The importance of terrestrial-derived organic matter for lake zooplankton communities remains debated, partly because little is known about the basic pathways by which allochthonous carbon is transferred to zooplankton, and whether these vary among the major taxonomic and functional groups. We quantified allochthony of three zooplankton groups (Cladocera, Calanoida, and Cyclopoida) across 18 lakes in Quebec, spanning broad gradients of dissolved organic matter (DOM) and lake trophy, using a multi-isotope (delta2H + delta13C), multi-source (terrestrial, phytoplanktonic, benthic) approach. All three zooplankton groups had significant levels of allochthony, but differed greatly in their respective patterns across lakes. Allochthony in Calanoida and Cyclopoida was linked to detrital food chains based on particulate organic matter (POM) and on DOM, respectively, whereas in Cladocera it appeared related to both pathways; not surprisingly this latter group had the highest mean allochthony (0.31; compared to 0.18 in Cyclopoida and 0.16 in Calanoida). This study highlights the complexity of the pathways of delivery and transfer of terrestrial organic matter in freshwaters, and underscores the role that microbial food webs play in this transfer.

Recovery of acid damaged zooplankton communities: measurement, extent, and limiting factors

Anthropogenic acidification has affected biota in thousands of lakes in eastern North America and Europe. To measure the degree and extent of biological recovery following pH recovery in acidified lakes, many studies have assessed changes occurring in acid-damaged zooplankton communities. In this review we synthesize studies of zooplankton recovery from regions severely affected by acidification. In doing so, we provide a critical overview of: (1) the design of studies used to detect recovery; (2) the status of communities in acidified regions; and (3) our current understanding of the factors that limit recovery. The design of most studies assessing zooplankton recovery fall into three categories based on their selection of data to be used for recovery benchmarks: (1) historical; (2) reference-lakes; and (3) temporal. Within these study designs, the most commonly used metrics include species richness, indicator species, and relative species abundances. Many studies have used species richness as the sole indicator of recovery; however, we argue that additional metrics should be considered in analyses to make conclusions more robust. Studies conducted in eastern North America and Northern Europe have demonstrated significant, though often incomplete, recovery of zooplankton communities in lakes that reach a pH &gt; 6.0. Data collected in central Europe indicate little recovery in the heavily affected Bohemian Forest lakes, but complete recovery of species richness in the moderately acidified Tatra Mountain lakes. Factors limiting biological recovery, including slow chemical recovery, dispersal limitation, and community resistance, vary in importance among and within regions, suggesting that region- and lake-specific management approaches may be required.

Discriminating zooplankton communities in lakes with brook trout (Salvelinus fontinalis) and in fishless lakes

Natural geographic barriers and escarpments inhibited the post-glacial colonization of many lakes by fish on the eastern Canadian Boreal Shield. Hence, fishless lakes containing freshwater communities that evolved without fish predation are commonly found on the Boreal Shield next to fish-present lakes. The aim of this study was thus to assess how different top-down control from fish or invertebrate predation structure zooplankton communities in eastern Canadian Boreal Shield lakes throughout the ice-free season. We examined zooplankton community characteristics using univariate indices such as abundance, richness (S), evenness (J'), diversity (H'), and multivariate species assemblages (Bray—Curtis dissimilarity) in 5 lakes with a single fish population, brook trout, Salvelinus fontinalis, and in 5 naturally fishless lakes throughout the ice-free season. The total abundance of zooplanktonic organisms was significantly higher in fishless lakes over the whole sampling period; this was related to the presence of small herbivorous species such as rotifers. Species assemblages of zooplankton were also significantly different between the 2 types of lakes throughout the season, principally due to the high abundance of rotifers and the scarcity of immature and mature daphnids in fishless lakes. Our results suggest that the low intensity of selective predation by brook trout on large herbivores and the heavy predation by Chaoborus americanus larvae on daphnids in fishless lakes appear to be the key factors for structuring the zooplankton community. Multivariate indicators identified patterns that were not revealed with the usual univariate indices, showing the importance of selecting appropriate indicators for the assessment of community structure.