Cladocerans In Lakes Research Articles

Diel changes in vertical and horizontal distribution of cladocerans in two deep lakes during early and late summer

Temporal and spatial heterogeneity in the distribution of cladocerans in lakes could be caused by abiotic (wind, water currents) and biotic factors (reproduction, food resources, predation). Diel horizontal and vertical distribution of cladoceran assemblages was studied in two deep lakes (Milada and Most Lakes, Czech Republic) in early (June) and late (September) summer. The objective was to study diel vertical migration (DVM) and diel horizontal migration (DHM) of cladocerans under conditions of different macrophyte cover in littoral areas (rich in Milada Lake, poor in Most Lake) and fish assemblages (non-specialised planktivorous species in Milada Lake, and abundant planktivorous fish - maraena whitefish, Coregonus maraena - in open water habitats in Most Lake). Temporal variations in cladoceran assemblages were reported in both lakes in the two sampling periods. DVM was observed in the two lakes, performed by the most vulnerable species to fish predation (the larger Daphnia spp.), but with different patterns (direct and reverse) probably linked with the local fish community and other biotic and abiotic factors in each lake. Horizontal movements were only observed in Most Lake: D. longispina increase its abundance in open waters at night compared to the littoral points; while Ceriodaphnia spp. showed the inverse pattern. In both lakes, higher densities were often found at night in surface layers, producing a great “diurnal deficit”: cladocerans remain undetected in some zones during the day (especially in the littoral areas) moving to surface layers at night.

Cladocera (Crustacea: Branchiopoda) from the state of Mato Grosso, Brazil

Studies on Cladocera biodiversity in Brazilian freshwater ecosystems are intensifying. However, the fauna of some hydrographic regions is still poorly known. We investigated the richness and species composition of cladocerans in lakes of the Pantanal from the state of Mato Grosso (Paraguay hydrographic region), Brazil. In addition, we cataloged the known cladoceran species in each hydrographic region of the state. Occurrence data were obtained from the literature and samples collected from 50 lakes in the northern Pantanal. We recorded 120 cladoceran species from eight families in the state of Mato Grosso. The occurrence of these species was recorded in the Amazon and Paraguay hydrographic regions. We are unaware of studies on cladocerans conducted in the Tocantins-Araguaia hydrographic region. We reported 17 new records in the Pantanal samples (Paraguay hydrographic region). Overall, richness estimates reveal that 72.6% of the state's cladoceran fauna is already known, while for the Paraguay hydrographic region this estimate is 72.2%. In general, the cladocerans from the Amazon and Paraguay regions did not differ. Our findings allow us to infer the need for further studies in the different hydrographic regions found in Mato Grosso in order to improve the knowledge of cladoceran biodiversity. We suggest a greater sampling effort, particularly in the littoral zone of aquatic ecosystems in this state, which can harbor great biodiversity.

Long-term eutrophication affects vertical changes of Daphnia ephippia in the sediments of a subtropical Chinese lake.

Cladoceran remains (e.g., Daphnia ephippia) in sediments are usually able to accurately reflect the historical succession of cladoceran in lakes. However, mechanisms describing the interaction between density changes of empty ephippia and ephippia containing resting eggs in lake sediments and environmental factors remain unclear. The diversity and vertical changes of Daphnia ephippia in the 30-cm sedimentary layer (equivalent to about 90years) were investigated in a subtropical Chinese lake, Lake Chaohu. The ephippia of D. similoides sinensis, D. pulex, and D. galeata were identified in the lake sediments. The densities and accumulation rates of both empty ephippia and ephippia containing resting eggs of three Daphnia species showed similar patterns. The values in the surface sedimentary layers (after the 1970s) were notably higher than in the bottom sedimentary layers (before the 1970s). The densities and accumulation rates of both empty ephippia and ephippia containing resting eggs of D. similoides sinensis were higher than those of D. pulex and D. galeata. Highly significant relationships (P< 0.001) between the TN contents and the ephippial densities and accumulation rates of D. similoides sinensis and D. galeata. TP contents had also significant correlations with the ephippial densities and accumulation rates of D. similoides sinensis and D. galeata, whereas it was not significant correlations with those of D. pulex (P> 0.05). Our results suggested that long-term eutrophication and cyanobacterial blooms might significantly affect the production of Daphnia ephippia and their vertical distribution in the sediments in eutrophic lakes.

A review of the effects ofBythotrephes longimanusand calcium decline on zooplankton communities — can interactive effects be predicted?

Anthropogenic stressors including acid deposition, invasive species, and calcium (Ca) decline have produced widespread damage to Canadian Shield lakes, especially to their zooplankton communities. Here, we review current knowledge on the individual effects on zooplankton by the non-indigenous predator Bythotrephes longimanus and Ca decline; we identify knowledge gaps in this literature and examine the likely interactive impacts of Bythotrephes invasions and Ca decline on zooplankton. The negative impacts of Bythotrephes longimanus on zooplankton communities are well known, whereas current understanding of the effects of declining Ca on zooplankton is restricted to Daphnia spp.; hence, there is a large knowledge gap on how declining Ca may affect zooplankton communities in general. The co-occurring impacts of Bythotrephes and declining Ca have rarely been studied at the species level, and we expect daphniids, particularly Daphnia retrocurva and Daphnia pulicaria, to be the most sensitive to both stressors. We also expect a synergistic negative interaction on cladocerans in lakes with both stressors, leaving a community dominated by Holopedium glacialis and (or) copepods. Our predictions form testable hypotheses but since species and ecosystem response to multiple stressors are difficult to predict, we may actually see ecological surprises in Canadian Shield lakes as Bythotrephes continues to spread and Ca levels continue to fall.

Water Transparency Drives Intra-Population Divergence in Eurasian Perch (Perca fluviatilis)

Trait combinations that lead to a higher efficiency in resource utilization are important drivers of divergent natural selection and adaptive radiation. However, variation in environmental features might constrain foraging in complex ways and therefore impede the exploitation of critical resources. We tested the effect of water transparency on intra-population divergence in morphology of Eurasian perch (Perca fluviatilis) across seven lakes in central Sweden. Morphological divergence between near-shore littoral and open-water pelagic perch substantially increased with increasing water transparency. Reliance on littoral resources increased strongly with increasing water transparency in littoral populations, whereas littoral reliance was not affected by water transparency in pelagic populations. Despite the similar reliance on pelagic resources in pelagic populations along the water transparency gradient, the utilization of particular pelagic prey items differed with variation in water transparency in pelagic populations. Pelagic perch utilized cladocerans in lakes with high water transparency and copepods in lakes with low water transparency. We suggest that under impaired visual conditions low utilization of littoral resources by littoral perch and utilization of evasive copepods by pelagic perch may lead to changes in morphology. Our findings indicate that visual conditions can affect population divergence in predator populations through their effects on resource utilization.

Environmental and spatial factors influencing the distribution of cladocerans in lakes across the central Canadian Arctic treeline region

We examine the role of local environmental and spatial factors in explaining variation in the composition of cladoceran assemblages from surface sediments within a set of 50 lakes spanning a broad southwest to northeast transect across the central Canadian Arctic treeline region from Yellowknife (Northwest Territories) to the northern boundary of the Thelon Game Sanctuary (Nunavut Territory). Within each lake, the cladoceran fauna was identified based on the subfossil exoskeletal remains preserved in recently deposited lake sediments. Physical and chemical limnological data were measured in August of 1996 and 1998. Spatial data were generated based on latitude and longitude using Principal Coordinates of Neighbors Matrices analysis (PCNM). The relationships between cladocerans and the measured environmental and spatial variables were examined using both unconstrained (Principal Components Analysis, PCA) and constrained (Redundancy Analysis, RDA) ordination techniques. Variance partitioning, based on partial RDAs, was used to identify the relative importance of significant environmental and spatial explanatory variables. Three environmental variables were identified as significantly influencing cladoceran community structure: surface water temperature, dissolved organic carbon (DOC), and total phosphorus (TP). Five PCNM-generated spatial variables were also significant in explaining cladoceran distributions. Variance partitioning attributed 14% of the variance in the distribution of Cladocera to spatial factors, an additional 10% to spatially-structured environmental variables, and 8% to environmental factors that were not spatially-structured. Within the central Canadian Arctic treeline region, spatial and other environmental processes had an important influence on the distribution of cladoceran communities. The strong influence of spatial factors was related to the large ecoclimatic gradient across treeline. The distribution patterns of cladocerans suggest that they have potential for use in paleoenvironmental assessments of northern ecosystems, a region of considerable interest for environmental change research.

Grazing on bacteria by flagellates and cladocerans in lakes of contrasting food-web structure

We tested the hypothesis that grazing on bacteria would vary between lakcs with differing plankton community structures. Paul and Tuesday lakes (Gogebic County. MI) are respectively dominatcd by piscivorous and planktivorous fish. Consequcntly, zooplankton in Paul are primarily large daphnids, while zooplankton in Tuesday are primarily small cladocerans and copepods. Wc measured flagellate grazing on bacteria using a fluorescent minicqll method, while cladoceran grazing was estimated from the relationship between body length and filtering rate. We predicted that cladoceran grazing on bacteria would bc higher in Paul, and f'lagellate grazing would be highcr in Tuesday. Cladoceran grazing on bacteria was important in both lakes contrary to our initial expectation. Large populations ofthe small cladoceran, Bosmina longirostris, in Tuesday exertcd a grazing pressure (0.18-35 x 106 bacteria I ' h ') approximately equal to that of thc large cladoceran, Daphnia pulex, in Paul (0.34-30 x 106 bacteria I ' h ').Flagellate grazingwas higher in Tuesdayaspredict ed(range: Paul,0.l 6 x l06bacterial rh rlTuesday.0.2-20 x 10('bacterial I h '). Hrrwever, there was not a simple relationship bctwcen total abundance of flagellates and total grazing rates. High community grazing by flagellates occurred when attached choanoflagellates were present. These flagellates had higher ingestion rates than free forms. We find no clear evidcnce that differences in food-web structure between the two lakes influence the process ofgrazing on bacteria. Instead, our results emphasize the significance ofcladocerans and attached tlagellates as consumers of bactena in freshwater ecosvstems.

Zooplankton and its grazing as indicators of trophic status in Dutch lakes

The existing data on the species composition of zooplankton and grazing intensities of crustacean plankton are discussed in the light of trophic status, particularly in the Dutch lakes of varying trophy. Several species of rotifers in northern Europe and North America are considered to indicate eutrophic environments. However, unanimity is less regarding crustacean zooplankton, since several species are encountered in lakes varying widely in trophic degree.The zooplankton to seston (33 μm) biomass ratio may provide information about the ecological transfer efficiency and trophic status. In the Dutch lakes the ratio decreases sharply with increase in food concentration during eutrophication, namely from ca 0.4 in oligotrophic lakes to about 0.05 in the hypertrophic ones.The zooplankton community grazing is high and variable in lakes of low trophy but low and relatively constant in lakes of high trophy. The fluctuations in the filtering rates of Daphnia sp. (e.g. D. magna) may provide information both on trophic degree as well as dissolved substances in lake waters. The dominance of small cladocerans in lakes may be due to quality of food and trophic level, besides fish predation. The recurrent clear-water phase in lakes would indicate oligo-mesotrophic situations in which the zooplankton plays an important role in the phytoplankton wax and wane.