Distribution and Interannual Changes of the Zooplankton of the Durgun Water Basin and Adjoining Water Objects (the Western Mongolia)

The article describes quantitative and structural characteristics of zooplankton of polytypic sites of a water system including a lake, canal, and a water reservoir. It is shown that in the littoral zone of lakes and water reservoirs, the number of species and communities is higher, and biomass, lower. However, in the littoral zone of shallow lake zooplankton in number, took priority due to Rotifera, in the deep part of the water body – Rotifera and Cladocera; in the center of the lake zooplankton dominated by biomass due to Cladocera and Copepoda, in the water reservoir—due to the Copepoda. The dam area of the water reservoir had the highest species richness of zooplankton among all studied sites. The greatest number and biomass of zooplankton within a waterbody are noted in upper part, where a sedimentation zone had formed, and as a whole for the system of the investigated waterbodies, the maximum quantity indices are typical of lake communities. It is revealed that the starkest interannual changes in zooplankton were observed in the shallow lake: the number of species decreased—in the littoral zone at the expense of Rotifera, and in the center, the biomass increased at the expense of Cladocera; in deep-water area of the dam area of the reservoir, conversely, the number of species, as well as the number and biomass of the community, increased due to Copepoda.     

Fluctuations in water level and the dynamics of zooplankton: a data‐driven modelling approach

1. The zooplankton in Lake Kinneret (Israel) have undergone large fluctuations in recent decades, which have been linked to both biotic and abiotic processes. 2. By applying a data‐driven modelling approach to a long‐term database, and focusing on key abiotic (lake‐level change) and biotic (prey abundance) variables, we attempted to identify the possible factors impacting the lake’s zooplankton community. 3. We hypothesised that changes in the predatory zooplankton (adult cyclopoids) assemblage are driven by changes in lake level during years of large changes. We further postulated that lake‐level changes would have a similar impact on the herbivorous zooplankton (cladocerans and cyclopoid copepodites) but an opposite effect on the microzooplankton. In the years of moderate changes to lake level, however, the abundance of predatory zooplankton would determine the size of the herbivore and microzooplankton populations rather than their food sources, that is, top‐down control. 4. The resulting decision trees supported the hypotheses stressing the importance of the annual rate of lake‐level change in shaping the zooplankton community in the lake. In addition, and in contrast to expectations, bottom‐up processes seem to play a role in determining zooplankton abundance.     

The relation between the feeding activity of wintering shovelers (Anas clypeata) and the horizontal distribution of zooplankton in Lake Teganuma,Japan

We investigated seasonal changes in the number and feeding activity of Shovelers wintering in Lake Teganuma in connection with temporal and horizontal fluctuations of zooplankton, and analyzed esophageal contents of a captured Shoveler. Zooplankton community was dominated by rotifers followed by copepods during the study period. Horizontal distribution of both invertebrate taxa differed; rotifers most abundant in the western and eastern parts of the lake in February–March, and cyclopoid copepodids and nauplii more common in the northeast area of the eastern portion of the lake. The number and feeding activity of Shovelers increased from January to March in the northeast area of Lake Teganuma. A Shoveler captured in the area had mostly consumed cyclopoid copepodids despite the fact that rotifers dominated in the zooplankton community at that location. These results suggest that the horizontal distribution and feeding activity of the Shovelers were correlated with the distribution of the cyclopoid copepodids.     

The effect of products of the vital activity of semi-aquatic birds on zooplankton in the littoral of small lakes (Oka River basin)

The zooplankton structure in the littoral of two small lakes that were subjected to the effect of products of the vital activity of birds is described. In the area of birds?? nesting in the zooplankton of the larger lake, the abundance and biomass of copepods reliably increased and the abundance of rotifers decreased, whereas in the smaller lake, a tendency toward the dominant development of rotifers and cladocerans was found. It is suggested that the differences in the zooplankton structure in the littoral of both lakes are determined by the area and the number of nesting birds.     

<Emphasis Type="Italic">Bythotrephes</Emphasis> invasion elevates trophic position of zooplankton and fish: implications for contaminant biomagnification

We estimated the effects of Bythotrephes longimanus invasion on the trophic position (TP) of zooplankton communities and lake herring, Coregonus artedi. Temporal changes in lacustrine zooplankton communities following Bythotrephes invasion were contrasted with non-invaded reference lakes, and along with published information on zooplankton and herring diets, formed the basis of estimated changes in TP. The TP of zooplankton communities and lake herring increased significantly following the invasion of Bythotrephes, whereas TP in reference lakes decreased (zooplankton) or did not change significantly (lake herring) over a similar time frame. Elevated TP following Bythotrephes invasion was most prominent in lakes that also supported the glacial relict, Mysis diluvania, suggesting a possible synergistic interaction between these two species on zooplankton community composition. Our analysis indicated that elevated TPs of zooplankton communities and lake herring are not simply due to the presence of Bythotrephes, but rather reflect changes in the zooplankton community induced by Bythotrephes; namely, a major reduction in the proportion of herbivorous cladoceran biomass and a concomitant increase in the proportion of omnivorous and/or predatory copepod biomass in invaded lakes. We demonstrated that increases in TP of the magnitude reported here can lead to substantial increases in fish contaminant concentrations. In light of these results, we discuss potential mechanisms that may be responsible for the disconnect between empirical and theoretical evidence that mid-trophic level species invasions (e.g., Bythotrephes) elevate contaminant burdens of consumer species, and provide testable hypotheses to evaluate these mechanisms.     

Zooplankton seasonal dynamics in a recently filled mine pit lake: the effect of non-indigenous <Emphasis Type="Italic">Daphnia</Emphasis> establishment

We examined the temporal and vertical dynamics of zooplankton in Weavers Lake, New Zealand, between October 2004 and October 2005, at a time when it was colonised by a non-indigenous Daphnia species. Zooplankton community composition changed during the study from one of rotifer dominance (e.g. Asplanchna, Polyarthra, Brachionus and Keratella species) to cladoceran (Daphnia dentifera) dominance. Temporal changes in zooplankton community composition were strongly associated with a gradual increase in lake water clarity, and were attributable to the highly efficient filter feeding of D. dentifera. The corresponding reduction in rotifer densities may have resulted from the superior competitive abilities of the newly established Daphnia. As Daphnia were rare inhabitants of New Zealand lakes before 1990, the arrival and rapid spread of the non-indigenous D. dentifera has lead to widespread changes in both water clarity and zooplankton community composition. An apparent lack of mixing in the lake was facilitated by the lake’s extremely small surface area:depth ratio. However, we conclude that physical features of the lake had minimal influence on water clarity relative to the invasion of D. dentifera.     

The effects of a colony of the Armenian gull (<Emphasis Type="Italic">Larus armeniacus</Emphasis> Buturlin) on zooplankton in the Lake Sevan littoral zone (Armenia)

The zooplankton of the open and semi-protected parts of Lake Sevan littoral zones that have been affected by the products of vital activity of the colony of the Armenian gull (Larus armeniacus Buturlin) were studied. It was shown that in the open coastal area the number of species is higher as compared to a similar reference site. However, the impact of wave-driven mixing of the water resulted in the lack of significant changes in the number and biomass of invertebrates at the compared observation sites. At the semi-protected part, the number of species, as well as the number and biomass of zooplankton, are significantly higher compared to the reference site. At the nesting area at both types of shoals copepods compose the basis of the zooplankton number and biomass, with Calanoida being part of the dominant complex. At the reference sites of the open shoal Copepoda also prevail; at the semi-protected sites, it is Cladocera that prevail. The basic differences between the effect of the products of the birds’ vital activities and anthropogenic eutrophication on zooplankton were revealed.     

Horizontal variations in associations of zooplankton in Lake Kariba

The horizontal distribution of the zooplankton in Lake Kariba was sampled by means of vertical hauls using 55 and 250 μm meshed nets. Crustacea were sparse in the main lake, but increased dramatically in the very shallow water at the end of Crocodile Creek. The composition of the zooplankton is influenced by the presence in the main lake of the Tanganyika sardine, Limnothrissa miodon , and by the large size of the dominant diatom in the phytoplankton. In the creeks the distribution can be explained by the zooplankton occurring in open spaces into which planktivorous fish do not enter because of the possibility of predation by Tiger fish ( Hydrucyori ) and birds.
The systematic composition of the zooplankton in L. Kariba is reviewed and compared with two natural lakes and another man-made lake. It is concluded that the zooplankton and the fishes in L. Kariba have reached approximately the specific diversity that one would expect from a similar sized natural lake in the same geographical area.     

The role of light for fish–zooplankton–phytoplankton interactions during winter in shallow lakes – a climate change perspective

1. Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light.
2. We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November–March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light).
3. In both lakes total zooplankton biomass and chlorophyll- a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish.
4. When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak.
5. Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes.     

Analysis of phytoplankton-zooplankton relationships in an oligotrophic lake under natural and manipulated conditions

During August, 1987, we performed a series of Limnocorral experiments in lake La Caldera, a small winter-kill lake in which phytoplankton is strikingly nutrient-limited. The effects of biomanipulation on zooplankton-phytoplankton relationships were assessed by monitoring both individual species and whole-assemblage responses. Two sizes of enclosures were used (15 and 350 litres) and two treatments were assayed: 1) removal of zooplankton by 45 μm filter net and 2) doubling the natural grazing pressure by increasing the zooplankton concentration. Results show the two enclosure types to differ strikingly: flagellates disappeared from the small enclosures, resulting in four- to six-fold changes in chlorophylla concentration and three- to four-fold changes in number of individuals. Most species were grazed (a prey selectivity based on criteria other than size was observed) and their net growth rate increased with zooplankton concentration, causing a net increase in the phytoplankton growth, a stimulatory effect probably through nutrient regeneration that overrides the losses due to grazing.     

Ecology and role of zooplankton in the fishery of Lake Naivasha

Taxonomic composition, distribution, community structure and seasonality of Lake Naivasha zooplankton between 1978 and 1980 are described. The ecological status of the zooplankton in relation to prevailing ecological factors and the lakes fishery are discussed. Species composition of the zooplankton community in Lake Naivasha has been remarkably constant since first observations between 1929 and 1931. The community structure and distribution of the zooplankton in the lake varied little from July 1978 to July 1980, however, there was evidence of species succession among the larger zooplankters, especially the cladocerans. In the littoral area zooplankton contribute significantly to the food and production of juvenile fish. There is an absence of fish zooplanktivores in the limnetic area of the lake. Consequently the limnetic zooplankton is not utilised by higher trophic levels.     

Zooplankton and environmental factors of a recovering eutrophic lake (Lysimachia Lake, Western Greece)

The present study investigates the zooplankton community dynamics and the abiotic environment in the eutrophic Lake Lysimachia (western Greece). The lake is considered to be recovering from eutrophication after the termination of an urban sewage inflow in 2000, and its waters are replenished constantly from the nearby oligotrophic Lake Trichonis. The results show that, although a decrease in nutrient concentrations was observed compared to the past, the lake still has eutrophic characteristics. This was reflected in the zooplankton community which is typical of those found in eutrophic lakes where rotifers prevail. Similarities among this lake and other nearby lakes were found considering the zooplankton community composition and seasonal variation. However, Lake Lysimachia is inhabited also by a number of different and even unique species (e.g., Moina micrura), suggesting that this ecosystem may be an important biodiversity refuge. Most of the zooplankton species were correlated with water temperature and, to a lesser extent, eutrophication key-water quality variables. Although there are few available data on the zooplankton of the lake, the abundance and composition of the community presenting characteristics indicative of intermediate trophic conditions and suggesting that the lake is probably under a kind of “biological” recovery.     

Experimental whole‐lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole‐lake manipulation, in which DOC concentration was increased from 8 to 11 mg L^?1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC‐mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon‐to‐phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).     

The recovery of crustacean zooplankton from acidification depends on lake type

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface-water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large-scale assessments of long-term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid-sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid-sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long-term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification.     

The zooplankton communities of an artificially divided subtropical coastal estuarine–lake system in South Africa

Nhlabane coastal lake and estuary system in South Africa is divided by a permanent barrage constructed at the outlet of the lake. This study compared the zooplankton assemblages of the lake and estuary systems after 15 years of separation. Before sampling commenced the mouth of the estuary closed and remained so throughout the duration of the study. The lake was completely fresh and the estuary had a low salinity not exceeding 4‰. Both the estuary and lake are shallow systems (less than 2 m) and were well mixed. Turbidity levels were generally below 10 NTUs. Temperature fluctuated seasonally between 18.5 and 30°C. Oxygen levels ranged between 4.3 and 9.9 mg/l but were mostly above 5 mg/l for both systems. The estuarine and lake plankton was dominated by copepod instars, especially of the calanoid Pseudodiaptomus hessei. During the entire study period the lake also supported high densities of rotifers. Rotifers only appeared in the estuarine plankton at the end of the sampling period. During the first sampling sessions zooplankton diversity in the estuary was higher but declined thereafter to levels within the range calculated for the lake. Estuarine relict species recorded reflect the estuarine history of the lake. Multivariate analyses indicated a change in the composition of the zooplankton community in the estuary during the duration of the study, while that of the lake remained comparatively stable. Species composition analyses showed that this change in the estuary was due to a shift from an estuarine to a more freshwater zooplankton assemblage. During this change some estuarine species declined in abundance or were not recorded anymore. These changes in the zooplankton community of the estuary may well illustrate the changes that occurred in the lower (south) section of the lake after completion of the barrage which isolated it from the estuary. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water chemistry,landscape, and spatial controls of δ13C and δ15N of zooplankton taxa in boreal lakes: One size does not fit all

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Invertebrate food sources for waterbirds provided by the reconstructed wetland of Nyirkai-Hany,northwestern Hungary

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