Zooplankton communities in doline lakes and pools, in relation to some bathymetric parameters and physical and chemical variables

The zooplankton communities from several lakes and pools inthree zones of a karstic area in central Spain were studiedin spring and early autumn, in relation to morphometric, physicaland chemical characteristics of the lakes. Zooplankton diversitywas higher in autumn than in spring and it was positively correlatedwith lake size (area and depth) in spring, but not in earlyautumn. This effect is partially explained by the sharp zooplanktonstratification in deep lakes, in early autumn. Some morphometriccharacteristics of lake basins were also correlated with thestructure of zooplankton communities. Principal component analyses(PCA) and Two-Way Indicator Species Analysis (TWINSPAN) performedon zooplankton data and a posterior correlation analysis withthe extracted factors and main limnological parameters showedthat trophic state in the first place, and mineralization inthe second place, were the main sources of variance to explainour data. However, the results of these analyses also show thatimportant sources explaining the variance of zooplankton datainclude some factors not quantified in the standard limnologicalanalysis, but evidently related to lake typology, such as shallownessand type of water feeding and flux.     

Functional shifts in lake zooplankton communities with hypereutrophication

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The relative significance of environmental and anthropogenic factors affecting zooplankton community structure in Southeast Wisconsin Till Plain lakes

Zooplankton community composition can be related to natural environmental factors such as lake morphology, lake landscape position, and water chemistry as well as anthropogenic factors such as agricultural and urban land-use. We hypothesized that within-lake factors, such as water chemistry, lake morphology, and human land-use would each be related to zooplankton community structure, but that watershed land-use would be the strongest correlate in southeast Wisconsin lakes. Zooplankton samples, collected every 3 months over a year, from 29 lakes were used to determine how lake and watershed morphology, water quality, and land-use were related to zooplankton community structure in the heavily developed Southeast Wisconsin Till Plain Ecoregion. Forward selection and a variation partitioning procedure were used to determine relative and shared contributions of each suite of variables in predicting zooplankton community structure. Redundancy analysis was used to characterize dominant gradients in pelagic zooplankton communities and related environmental factors and land-use. The major correlates of community structure included summer phosphorus, lake depth and surface area and urban and natural land. Variation partitioning illustrated that phosphorus alone accounts for the greatest part (12%) of community structure. Urban land-uses (residential, commercial and paved land) and lake morphology partially explain zooplankton community variation through combined effects with phosphorus. Small cladocerans and Skistodiaptomus pallidus were associated with higher phosphorus, shallow depth and higher urban land-use, while Daphnia pulicaria dominates in deep lakes with lower phosphorus and less urban land-use. This study contributes to the understanding of factors affecting zooplankton community structure in a largely human developed region and illustrates the importance of eutrophication in structuring zooplankton community composition.     

Influence of hydrophyte abundance on the spatial distribution of zooplankton in selected lakes in Greece

Submerged hydrophyte vegetation consists of a highly important biotic component of maintaining lake ecosystems towards a “clear water” ecological status. Aquatic macrophytes are well known to play a significant multidimensional role in lakes by competing with phytoplankton growth, stabilising sediment and offering refuge to fishes, macro-invertebrates and littoral zooplankton, amongst others. Zooplanktons that are associated with macrophyte beds, in particular, may act as a positive feedback mechanism that contributes to maintaining a clear-water state. Although there are several studies investigating the relationships between macrophytes and zooplankton in European lakes, few have yet been carried out in Greek lakes. Seasonal field sampling was conducted from spring 2006 to autumn 2008 in four lakes of northwestern Greece. Zooplankton samples were collected from within hydrophyte beds in each lake to estimate their relative abundance and species density. Hydrophyte abundance and composition was recorded on a five-point scale. Moreover, water samples were analysed to determine nutrient and chlorophyll-a concentration. Pearson correlations between zooplankton density and key physicochemical variables were conducted to distinguish significant abiotic variables related with major zooplankton groups. Kruskal–Wallis non-parametric analysis was used to test for significant differences in zooplankton composition and environmental variables amongst the five hydrophyte abundance classes. In addition, Canonical correspondence analysis was used to distinguish possible correlations amongst the macrophyte and zooplankton species. Zooplankton density was significantly higher in dense macrophyte vegetation. Small-sized species (e.g. Rotifera) dominated the zooplankton community, indicating the eutrophic nature of the lakes. Large Cladocera were present in low abundance and were mostly littoral. The current research contributes to a better understanding of relationships between biotic groups in selected Greek lakes.     

Quantification of invertebrate predation and herbivory in food chains of low complexity

Zooplankton grazing impact on algae, heterotrophic flagellates and bacteria, as well as invertebrate predation on herbivorous zooplankton, were investigated in two sub-Antarctic lakes with extremely simple food chains. The two species of herbivorous zooplankton present in the lakes (the copepods boeckella michaelseni and Pseudoboeckella poppei) exerted substantial grazing pressure on algae. However, the dominant algal species exhibited properties that enabled them to avoid (large size or extruding spines, e.g. Staurastrum sp., Tribonema sp.) or compensate (recruitment from the sediment, Mallomonas sp.) grazing. There are only two potential invertebrate predators on the herbivorous copepods in the two lakes: the copepod Parabroteas sarsi and the diving beetle Lancetes claussi. Vertebrate predators are entirely abscent from sub-Antarctic lakes. Based on our experiments, we estimated that the predators would remove at most about 0.4% of the herbivorous copepods per day, whereas planktivorous fish, if present in the lakes, would have removed 5–17% of the zooplankton each day. Consequently, the invertebrate predators in these high-latitude lakes had only a marginal predation impact compared to the predation pressure on zooplankton in the presence of vertebrate predators in temperate lakes. The study of these simple systems with only two quantitatively functionally important trophic links, suggests that high grazing pressure foreces the algal community towards forms with grazer resistant adaptations such as large size, recruitment from another habitat, and grazer avoidance spines. We propose that due to such adaptations, predictions from food web theory are only partly corroborated, i.e. algal biomass actually increases with increasing productivity, although the grazer community is released from predation. In more species-rich and complex systems, e.g temperate lakes with three functionally important links, such adaptations are likely to be even more important, and, consequently, the observable effects of trophic interactions from top predators on lower trophic levels even more obscured.     

Relationships between zooplankton abundance and trophic state in seven New Zealand lakes

The zooplankton communities of seven Rotorua, New Zealand, lakes of different trophic status were studied in 1977–78. They were generally dominated by the calanoid copepod, Calamoecia lucasi. Bosmina meridionalis occurred in all the lakes and Ceriodaphnia dubia in most. Only small numbers of Macrocyclops albidus ever occurred. Rotifers were not studied in detail. Community composition was similar to that in other northern New Zealand lakes. No well defined patterns of seasonal change in abundance were found and the timing of changes, which were of low magnitude, was different in each lake. Clutch sizes in all species were small. Calamoecia population parameters were analysed using multivariate methods and shown to be related to lake trophic level. Population densities were higher in more productive lakes whereas breeding levels were inversely related to indices of trophic status and population abundance. It is suggested that the populations, as in other northern New Zealand lakes, are food-limited, probably as a consequence of a lack of marked climatic seasonality and the absence of major predation pressures. Groupings of the lakes based on the Calamoecia data are in general agreement with those derived from parallel studies of water chemistry, phytoplankton and macrobenthos.     

Seasonal changes in the biomass,distribution, and patchiness of zooplankton and fish in four lakes in the Sierra Nevada,California

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Influence of benthic and interstitial processes on nutrient changes along a regulated reach of a large river (Rhône River,France)

An enclosure study was conducted in Ranger Lake in south-central Ontario, Canada from 4 July to 5 August 1997 to determine predation effects of the larvae of the phantom midge fly Chaoboruson the zooplankton community. Zooplankton assemblages were established in 12 enclosures (2 m in diameter, 7.5 m deep). Three densities of fourth-instar Chaoborus trivittatus (0 l^–1, 0.1 l^–1 and 0.5 l^–1) were introduced as predator treatments to the enclosures. Temperature, dissolved oxygen and zooplankton community composition were monitored for six weeks. To determine if the zooplankton community composition changed, a repeated measures multivariate analysis was performed on percent biomass of Bosmina and calanoid copepods. There were no significant differences in mean taxon percent biomass among predator treatments. There were significant differences in mean taxon percent biomass between water layers (epilimnion and metalimnion). There were also significant differences in lengths of Bosmina and calanoid copepods among predator treatments at the end of the experiment. Crop content analysis of C. trivittatusshowed that Bosmina constituted 88–98% of the prey items found in the crops. These results demonstrate that the use of deep enclosures, a Chaoborus species which vertically migrates, and lower natural densities of Chaoborus may provide prey with an important natural refuge from predation and so allow a more accurate determination of the predation impact of Chaoborus trivittatusin temperate lakes where fish control Chaoborus densities.     

Influence of trophic status and conductivity on zooplankton composition in lakes and ponds of Torres del Paine National Park (Chile)

The Torres del Paine National Park is located in the southern Chilean Patagonia. This park has numerous and heterogeneous lakes and ponds with different trophic status and zooplankton composition. The aim of this study was to analyze the influence of trophic status and conductivity on zooplankton assemblages in lakes and ponds within the Torres del Paine National Park. The water bodies described in the present study were previously classified in three groups. The first group consisted of large, deep and oligotrophic lakes with fish populations, low zooplankton species diversity and high predominance of calanoid copepods of small body size. The second group contained small mesotrophic lakes with fish populations and relatively high predominance of small sized daphnids. The third group consisted of fishless ponds of different trophic status, wide conductivity gradient and with zooplankton species of relatively large body size. The results show that Daphnids abundance was directly related to chlorophyll-a concentration and inversely associated with conductivity. Calanoids abundance was also directly associated with conductivity.     

The influence of catchment size on lake trophic status during the hemlock decline and recovery (4800 to 3500 BP) in southern Ontario lakes

We investigated the ecological effects of terrestrial ecosystem change during the hemlock decline and recovery (4,800–3,500 BP) on lake communities (diatoms and chrysophytes). This study specifically assessed the role of catchment area and slope in determining the magnitude of lake eutrophication during the hemlock decline by analyzing sediment cores from five alkaline, holomictic lakes in southeastern Ontario, Canada. The study lakes were similar in most limnological aspects, but differed widely in the relative sizes of their catchments. Diatoms were used to quantitatively infer past lake-water total phosphorus (TP) concentrations.All five lakes showed shifts in their algal communities during the hemlock decline, but most lakes exhibited only minor changes in trophic status. The magnitude of the limnological response appears to be related to catchment size and slope. Long Lake, Burridge Lake, and Gunter Lake possess the smallest catchments and exhibited the weakest responses to the hemlock decline. The catchment area of Flower Round Lake is considerably larger and steeper than these lakes, and was the only lake to show a marked eutrophication. Aulacoseira ambigua bloomed and diatom-inferred TP concentration increased by 14 µg 1^–1.Catchment slope appears to have influenced the type of material exported into the lakes. Lake basins draining catchments with gentle relief received proportionally greater amounts of organic matter, whereas steeper catchments supplied relatively greater proportions of mineral matter. Faster water flow associated with steeper catchment slope may have enhanced mineral erosionFollowing the hemlock decline, nutrient supplies to most of the study lakes were reduced. The period of forest recovery was associated with an 11 µg 1^–1 reduction in diatom-inferred lake-water TP concentration in Flower Round Lake, and algal populations decreased. Our results generally support the ecological theory of forest ecosystem development and secondary succession developed from long-term data collected at the Hubbard Brook Experimental Ecosystem.     

Physical-chemical influences on vernal zooplankton community structure in small lakes and wetlands of Wisconsin,U.S.A.

We sampled zooplankton communities from 54 small water bodies distributed throughout Wisconsin to evaluate whether a snap-shot of zooplankton community structure during early spring could be used for the purpose of differentiating lakes from wetlands. We collected a single set of zooplankton and water chemistry data during a one-month time window (synchronized from south to north across the state) from an open water site in each basin as a means to minimize and standardize sampling effort and to minimize cascading effects arising from predator–prey interactions with resident and immigrant aquatic insect communities. We identified 53 taxa of zooplankton from 54 sites sampled across Wisconsin. There was an average of 6.83 taxa per site. The zooplankton species were distributed with a great deal of independence. We did not detect significant correlations between number of taxa and geographic region or waterbody size. There was a significant inverse correlation between number of taxa and the concentration of calcium ion, alkalinity and conductivity. One pair of taxa, Lynceus brachyurus and Chaoborus americanus, showed a significant difference in average duration of sites of their respective occurrence. All other pairs of taxa had no significant difference in average latitude, waterbody surface area, total phosphorus, total Kjeldahl nitrogen, alkalinity, conductivity, calcium ion, sulfate, nitrate, silicate or chloride. Taxa were distributed at random among the sites – there were no statistically significant pairs of taxa occurring together or avoiding each other. Multivariate analysis of zooplankton associations showed no evidence of distinct associations that could be used to distinguish lakes from wetlands. Zooplankton community structure appears to be a poor tool for distinguishing between lakes and wetlands, especially at the relatively large scale of Wisconsin (dimension of about 500 km). The data suggest that a small body of water in Wisconsin could be classified as a wetland if it persists in the spring and summer for only about 4 months, and if it is inhabited by Lynceus brachyurus, Eubranchipus bundyi, and if Chaoborus americanus and Chydorus brevilabris are absent.     

Sedimentary losses of phosphorus in some natural and artificial Iowa lakes

Phosphorus sedimentation in four natural and four artificial Iowa lakes was measured by using sediment traps to determine if sedimentary phosphorus losses were greater in artificial lakes than in natural lakes and the limnological factors influencing phosphorus loss rates. Mean phosphorus sedimentation rates ranged from 13.3 to 218 mg · m^–2 day^–1. Although phosphorus sedimentation rates for the natural lakes as a group did not differ significantly from the rates for artificial lakes, there were significant differences among individual lakes. Phosphorus sedimentation rates also varied significantly during different seasons at different locations within a lake and at different depths within a location. Despite the variance, phosphorus sedimentation rates were strongly correlated with inorganic sediment concentrations and inorganic matter sedimentation rates, thus suggesting that inorganic sediments influence phosphorus sedimentation rates. When Iowa data were combined with data from published studies, mean sedimentation rates were directly correlated with mean chlorophyll a concentrations of the lakes. These data strongly suggest that sedimentation rates as measured by sediment traps are strongly influenced by the trophic status of a lake. Though sedimentation rates were higher in the more productive lakes, it is suggested that these rates represent only gross sedimentation rates rather than net sedimentation rates because of resuspension and resedimentation of bottom sediments.     

Response of microcosm zooplankton to acidification

Zooplankton community transformation in response to soft water acidification was studied in two experimental series using the microcosm method. The dynamics of total abundance, changes in the proportions of the main zooplankton groups, stability of the dominant complex, and species diversity were evaluated. Zooplankton population proved to decrease at all studied low pH (5–6, 4–5, and 3–4) within the first two weeks relative to the control. At water pH 5–6, either Rotifera-Copepoda or Cladocera-Copepoda zooplankton complex was established depending on the initial community composition; while at pH 4–5, Copepoda predominated in the established zooplankton community. The community edificator species was replaced at pH 4–5. The lowest diversity index was also observed at this pH (1.0–1.5 bit/ind.). In addition, the proportion and absolute population of copepod nauplii and cladoceran Scapholeberis mucronata increased at low pH. A decrease in water pH to 3–4 proved to be disruptive for the zooplankton community.Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 1, 2005, pp. 100–108.Original Russian Text Copyright © 2005 by Kurbatova.     

Planktonic copepods of Boston Harbor,Massachusetts Bay and Cape Cod Bay, 1992

Zooplankton were collected by vertical tows with 102 µm mesh at ten stations in Boston Harbor, Massachusetts Bay and Cape Cod Bay in February, March, April, June, August, and October, 1992. This study was part of a larger monitoring program to assess the effects of a major sewage abatement project, and sampling periods were designed around periods of major phytoplankton events such as the winter-spring diatom bloom, the stratified summer flagellate period, and the autumn transition from stratified to mixed waters. There was considerable seasonal variation in total zooplankton abundance, with minimal values in April (1929–11631 animals m^–3) during a massive bloom of Phaeocystis pouchetii, and maximum values (67 316–261075 animals m^–3) in August. There were no consistent trends of total abundance where any particular station had greater or lesser abundance than others over the entire year. Zooplankton abundance was dominated by copepods (adults + copepodites) and copepod nauplii (30.4–100.0% of total zooplankton, mean= 83.2%). Despite the large seasonal variation in zooplankton and copepod abundance, the copepod assemblage was dominated throughout the entire year by the small copepod Oithona similis, followed by Paracalanus parvus. Other less-abundant copepods present year-round were Pseudocalanus newmani, Temora longicornis, Centropages hamatus, C. typicus, and Calanus finmarchicus. Two species of Acartia were present, primarily in low-salinity waters of Boston Harbor: A. hudsonica during cold periods, and A. tonsa in warm ones. Eurytemora herdmani was also a subdominant in Boston Harbor in October. The potential role of zooplankton grazing in phytoplankton dynamics and bloom cycles in these waters must be considered in view of the overwhelming numerical dominance of the zooplankton by Oithona similis which may feed primarily as a carnivore. Furthermore, it seems unlikely that eutrophication-induced alteration of phytoplankton assemblages could cause significant trophic domino effects, reducing abundances of Calanus finmarchicus that are forage of endangered right whales seasonally utilizing Cape Cod Bay because C. finmarchicus has long been known to be a relatively unselective grazer, and most importantly, it is a trivial component of total zooplankton or total copepod abundance in these waters.     

Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa,a tropical rift valley lake in Ethiopia

The zooplankton of a Rift Valley lake in Ethiopia, Awasa, was sampled at 3 stations for 2 years (1986 and 1987) concurrently with various meteorological and limnological measurements. The spatial and temporal variation in abundance of some numerically dominant crustaceans, Mesocyclops aequatorialis similis (Copepoda), Thermocyclops consimilis (Copepoda) and Diaphanosoma excisum (Cladocera) is discussed. Temporal (months, sampling dates) rather than spatial (station) variability accounts for more than 50% of the total variance in zooplankton abundance but horizontal patchiness exists during periods of high zooplankton density. Sampling errors were generally low, except for counts of cyclopoid nauplii (subsampling) and Diaphanosoma (inter-replicate variance). Zooplankton showed distinct seasonality associated with the mixing cycle of the lake. Total numbers increased to more than 200 000 m⁻³ during the unstratified period (July to September). Low numbers were evident during stratification (February to May) when zooplankton numbers did not exceed 15 000 m⁻³. Individual zooplankton species and age classes showed variable seasonal amplitudes, ranging from 6.4 (nauplius 3) to 44.8 (copepodite 3 of Mesocyclops). We discuss some possible causes for zooplankton seasonality in Lake Awasa, and also review zooplankton seasonal cycles in other tropical lakes, especially African ones.     

Nutrient enrichment experiments in three central Florida lakes of different trophic states

Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated in situ in clear polyethylene bags for 3 to 6 days. The 2⁵ factorial design employed two levels (ambient and enriched) of each of five nutrients [NH₄ ⁺, PO _inf4 ^sup3− , Fe⁻ -EDTA, SiO _inf3 ^sup2− and a cation (Ca²⁺ or K⁺) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors and predictive models.     

Limnological and morphometrical data of eight karstic systems `cenotes' of the Yucatan Peninsula,Mexico, during the dry season (February–May, 2001)

The karstic nature of the Yucatan Peninsula allows the formation of natural sink-holes from the dissolution of calcareous rock. These systems are almost the only epigean source of fresh water available in this region. In spite of their biological importance, little is known about the morphometric and limnologic characteristics of these karstic systems. We measured limnological variables in eight cenotes in central Quintana Roo during February–May, 2001. Zooplankton biomass and chlorophyll a were also measured in order to determine if the behavior of primary and secondary production was related to environmental parameters. Important short-term changes were observed in nutrients (NO₃ ^–, NO₂ ^–, PO₄ ^3-), biomass, and chlorophyll a. The morphometrically conditioned productivity (MCP), which evaluates the cumulative effect of several morphometric variables on production (area, maximum length, shoreline development, perimeter), showed a negative correlation with respect to zooplankton biomass, as did also both pH and temperature. Conversely, NO₃ ^– and NO₂ ^– had a positive correlation with zooplankton biomass. No correlation was found for chlorophyll a. Significant differences in NO₃ ^– (F = 61.52, p<0.001), NO₂ ^– (F = 7.36, p<0.001), zooplankton biomass (F = 17.57, p<0.001), chlorophyll a (F = 62.19, p<0.001), and conductivity (F = 497.49, p<0.001) were found among the systems. These results indicate the existence of sharp differences between these karstic systems (oligotrophic, with smaller area, deep and less productive) and non-karstic ones, (eutrophic, larger area, shallow and more productive) but are similar to previous data from other karstic systems of Mexico and other parts of the world. However, understanding of these fragile tropical systems is in the initial phase. It is necessary to increase the intensity of these studies in order to allow a full explanation of their limnological behavior.     

The Impact of Fish Predation and Cyanobacteria on Zooplankton Size Structure in 96 Subtropical Lakes

Zooplankton are relatively small in size in the subtropical regions. This characteristic has been attributed to intense predation pressure, high nutrient loading and cyanobacterial biomass. To provide further information on the effect of predation and cyanobacteria on zooplankton size structure, we analyzed data from 96 shallow aquaculture lakes along the Yangtze River. Contrary to former studies, both principal components analysis and multiple regression analysis showed that the mean zooplankton size was positively related to fish yield. The studied lakes were grouped into three types, namely, natural fishing lakes with low nutrient loading (Type1), planktivorous fish-dominated lakes (Type 2), and eutrophic lakes with high cyanobacterial biomass (Type 3). A marked difference in zooplankton size structure was found among these groups. The greatest mean zooplankton size was observed in Type 2 lakes, but zooplankton density was the lowest. Zooplankton abundance was highest in Type 3 lakes and increased with increasing cyanobacterial biomass. Zooplankton mean size was negatively correlated with cyanobacterial biomass. No obvious trends were found in Type 1 lakes. These results were reflected by the normalized biomass size spectrum, which showed a unimodal shape with a peak at medium sizes in Type 2 lakes and a peak at small sizes in Type 3 lakes. These results indicated a relative increase in medium-sized and small-sized species in Types 2 and 3 lakes, respectively. Our results suggested that fish predation might have a negative effect on zooplankton abundance but a positive effect on zooplankton size structure. High cyanobacterial biomass most likely caused a decline in the zooplankton size and encouraged the proliferation of small zooplankton. We suggest that both planktivorous fish and cyanobacteria have substantial effects on the shaping of zooplankton community, particularly in the lakes in the eastern plain along the Yangtze River where aquaculture is widespread and nutrient loading is high.     

Changes and drivers of zooplankton diversity patterns in the middle reach of Yangtze River floodplain lakes,China

Anthropogenic habitat alteration interferes the natural aquatic habitats and the system''s hydrodynamics in the Yangtze River floodplain lakes, resulting in a serious decline in freshwater biodiversity. Zooplankton communities possess major position in freshwater ecosystems, which play essential parts in maintaining biological balance of freshwater habitats. Knowledge of processes and mechanisms for affecting variations in abundance, biomass, and diversity of zooplankton is important for maintaining biological balance of freshwater ecosystems. Here, we analyzed that the temporal and spatial changes in the structure of zooplankton community and their temporal and spatial variations respond to changes in environmental factors in the middle reach of Yangtze River floodplain lakes. The results showed that zooplankton samples were classified into 128 species, and Rotifera was the most common taxa. Significant seasonal differences were found among the abundance and diversity of zooplankton. Similarly, we also found significant seasonal differences among the biomass of zooplankton functional groups. The spatial turnover component was the main contributor to the β diversity pattern, which indicated that study areas should establish habitat restoration areas to restore regional biodiversity. The NMDS plot showed that the structure of zooplankton community exhibited significant seasonal changes, where the community structure was correlated with pH, water temperature, water depth, salinity, total nitrogen, chlorophyll‐a, and total phosphorus based on RDA. This study highlights that it is very important to ensure the floodplain ecosystem''s original state of functionality for maintaining the regional diversity of the ecosystem as a whole.     

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos in hypertrophic Lake Teganuma

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos were intensively surveyed in Lake Teganuma during May 1983–April 1984. The annual mean chlorophyll a concentrations were as high as 304 µg · l^–1–383 µg · l^–1. The daily gross primary production of phytoplankton was high throughout the year. The peak production rate was recorded in August and September, when blue-green algae bloomed. The annual gross primary production was estimated as 1450 g C · m^–2 · y^–1, extremely high as compared with other temperate eutrophic lakes. Zooplankton was predominantly composed of rotifers. The annual mean standing crop of zooplankton was 0.182 g C · m^–2 around the middle between the inlets and the outlet and was lower than in most other temperate eutrophic lakes. Zoobenthos was mostly composed of Oligochaeta and chironomids. The annual mean standing crop of zoobenthos ranged from 0.052 g C · m^–2 to 0.265 g C · m^–2, the lowest values among temperate eutrophic lakes, which is in contrast to the high primary production.