Abundance Of Cladocerans Research Articles

Spatial and Temporal Long-Term Patterns of Phyto and Zooplankton in the W-Mediterranean: RADMED Project

It is widely accepted that the Mediterranean is an oligotrophic sea where winter mixing favors the proliferation of diatoms and high values of zooplanktonic biomass, mainly associated with the growth of copepods. Stratified conditions from mid-spring to late autumn are dominated by the picophytoplanktonic groups and the increment of cladoceran abundances. This general picture has important exceptions. A regionalization of the Mediterranean Sea can be established, distinguishing oligotrophic and mesotrophic areas and different blooming periods. The RADMED monitoring program covers a large area from the southwestern limit of the Mediterranean to the Catalan Sea. The analysis of phyto and zooplankton time series extending from 1992 to 2016 in some cases, and from 2007 to 2016 in others, have shown that the Spanish Mediterranean waters have differentiated areas and trophic regimes as a result of the existence of several fertilizing mechanisms which include winter mixing, tidal mixing in the Strait of Gibraltar, cyclonic circulation cells and frontal systems. The present work describes these different mechanisms acting on the Spanish Mediterranean waters, and also the potentiality of monitoring programs for providing statistics suitable for operational activities or the initialization/validation of ecological models.

Climate variability impacts on coastal dune slack ecohydrology

The hydrological regime of freshwater systems plays a crucial role in shaping the dynamics of the different biological communities that inhabit them. Climate change is expected to cause major alterations in the hydrological regime of dune slacks by producing shifts in temperature, precipitation and evapotranspiration. Across seasons, we explore the controls on common water fleas (Cladocera) and aquatic plant communities relative to water level regime, water chemistry, weather and geomorphological setting, in a slack of the Sheskinmore dune system, Co. Donegal, northwest Ireland. Cladoceran abundance and diversity peak in summer, but also vary inter-annually, and drivers for this and hydrological variability are discussed. Vegetation is likewise affected by hydrology in a spatial sense, where distribution follows wet/dry patches of water. Water chemistry is more variable within the same season than across different years, particularly related to the drying out of the slack. Rainfall through 2016-2017 was lower than average and evapotranspiration showed higher values than average for the same time period. The influence on the slack of this decreased precipitation extended across successive seasons. The water table is the most important driver of slack ecology, with incidence on biological communities expressed by the increased variability inter-annually, as opposed to seasonal variation.

Long-term change of the assemblages and abundance of cladocerans in different ecotypes of Lake Taihu

枝角类作为淡水湖泊生态系统中的初级消费者之一，对生存环境的改变极为敏感.本文分析了太湖西、中和东部等湖区的钻孔沉积物、表层沉积物以及春夏秋季活体枝角类的组成与丰度.结果表明：活体枝角类组成以象鼻溞（Bosmina spp.）为优势种，秋季枝角类属种数量最多.太湖不同生态型湖区表层沉积物枝角类组成均以象鼻溞为优势种，其中西部与中心湖区的枝角类组成与丰度较为相似，种类单一，枝角类绝对丰度高；东部湖区枝角类属种较为丰富，绝对丰度低，优势种由浮游种象鼻溞以及沿岸种圆形盘肠溞（Chydorus sphaericus sl）和西方笔纹溞（Graptoleberis testudinaria）等种属构成.百年以来，太湖枝角类组成与丰度随着营养水平增加而改变，富营养指示种（Bosmina longirostris）丰度的增加与贫营养指示种（Bosmina longispina）丰度的下降，响应了湖区生态环境的演变过程.1970s末期，太湖西部与中心湖区在进入富营养化阶段，枝角类组成单一，象鼻溞占有绝对优势，与东部湖区相比，沿岸种、底栖种稀少.东部湖区在1960s以后，枝角类属种数量增加，但丰度下降，响应了1960s以来该区域营养水平提高、沉水植被生物量增加以及沼泽化加剧的环境过程.;Cladoceran, as one of the primary consumers in freshwater lake ecosystem, is sensitive to environmental change. So far, fruitful researches of subfossil cladocerans have been applied in many fields, such as paleoclimate reconstruction, food web, and nutritional changes and so on. However, most of studies focused on the lakes in boreal, temperate and subarctic zones, especially the alpine and deep lakes. Few works paid attention to freshwater shallow lakes in the middle and low latitudes of subtropics in Asia. Lake Taihu, located in the south of the Yangtze River Delta, is a large shallow lake covering over 2000 km² area which is also the third largest freshwater lake in China. Lake Taihu is ecologically divided into different basins. The west and north parts of Lake Taihu are observed increase of nutrient which has led to the emergence of non-N₂ fixing Microcystis sp. cyanobacterium causing serious cyanobacterial blooms and reduced biodiversity. The eastern part of Lake Taihu is also a mild eutrophic lake under the condition of growing large number of submerge plants. Those changes had influence on cladoceran composition and abundance. In this paper, we analysed the composition and abundance of cladoceran assemblages from cores and surface sediments and modern waters in spring, summer and autumn of the western, central and eastern parts of Lake Taihu. The results showed that Bosmina spp. was the dominant cladoceran of the sediments and water in different ecotypes of Lake Taihu. The composition of modern cladoceran was basically the largest number of cladoceran species in autumn. The cladoceran composition was single but with a high-level abundance in the western and central Lake Taihu. The cladoceran species in the eastern Lake Taihu were relatively rich but with a low-level abundance. The dominant species in the east part of Lake Taihu were composed of several species such as Bosmina spp., Chydorus sphaericus sl and Graptoleberis testudinaria. Over the past century, the composition and abundance of cladoceran in Lake Taihu had changed with the change of ecological environment. Especially, the change of the relative proportion of the eutrophic species (Bosmina longirostris) and the poor nutrient species (Bosmina longispina) indicated the evolution process of the eutrophication in Lake Taihu. At the end of 1970s, the western and central regions of Lake Taihu entered the eutrophication stage. The composition of cladoceran assemblages was single with a high-level abundance of Bosmina spp. and scarce littoral and benthic species compared with the eastern Lake Taihu. After 1960s, the cladoceran community in eastern Lake Taihu became relatively abundant but with a decrease of the abundance of cladocerans, which responded to the expansion of submerged vegetation biomass, swampiness and the aggravating eutrophication since 1960 AD.

Factors of Dynamics of Plankton Crustacean Communities under Eutrophic Conditions

It has been shown that the main drivers of the dynamics of cladoceran and copepod abundances can be predators (fish), the quantity and/or quality of food in terms of the contents of eicosapentaenoic acid, phosphorus and nitrogen in the seston under eutrophic conditions. In experimental mesocosms under eutrophic conditions, we found that, fish did not affect the quantity and quality of food resources for crustaceans. In the second half of experiments, however, dominance shifted from copepods to cladocerans. This was due to the improvement of the food quality for cladocerans in terms of the carbon-to-phosphorus ratio in the seston rather than to fish predation. Under eutrophic conditions, fish reduced the biomass of both cladocerans and copepods without changing the ratio between them.

Climate variability impacts on coastal dune slack ecohydrology

The hydrological regime of freshwater systems plays a crucial role in shaping the dynamics of the different biological communities that inhabit them. Climate change is expected to cause major alterations in the hydrological regime of dune slacks by producing shifts in temperature, precipitation and evapotranspiration. Across seasons, we explore the controls on common water fleas (Cladocera) and aquatic plant communities relative to water level regime, water chemistry, weather and geomorphological setting, in a slack of the Sheskinmore dune system, Co. Donegal, northwest Ireland. Cladoceran abundance and diversity peak in summer, but also vary inter-annually, and drivers for this and hydrological variability are discussed. Vegetation is likewise affected by hydrology in a spatial sense, where distribution follows wet/dry patches of water. Water chemistry is more variable within the same season than across different years, particularly related to the drying out of the slack. Rainfall through 2016-2017 was lower than average and evapotranspiration showed higher values than average for the same time period. The influence on the slack of this decreased precipitation extended across successive seasons. The water table is the most important driver of slack ecology, with incidence on biological communities expressed by the increased variability inter-annually, as opposed to seasonal variation.

Impact of enhanced summer temperatures on the distribution and structure of zooplankton communities in the heated stratified lakes: Implications for climate change

Long-term studies demonstrated that temperature increases of 3–6 °C above natural levels caused reduction in zooplankton biomass. We hypothesized that large-bodied species would respond more strongly to temperature increases than small-bodied species because they are less adapted to high temperatures. Studies were conducted in three similar stratified meso-eutrophic lakes with different thermal regimes. Enhanced temperature, migrations, food abundance and dissolved oxygen concentrations were analyzed as potential factors that could affect zooplankton biomass. The warmest lake differed from the other lakes by lower total biomass of zooplankton less abundance of large-bodied zooplankton species, smaller population body sizes of abundant cladoceran species and higher food concentrations. Day and night abundances of zooplankton did not differ between the vertical strata and between the pelagic and littoral zones in the three study lakes suggesting that zooplankton did not vertical or horizontal migrations. We suggest that decreases of dissolved oxygen below the epilimnion prevented zooplankton from vertically migrating. As a result, zooplankton accumulated in the epilimnion where temperatures were higher than in the lower strata. Regression analysis showed that temperature had a significant negative impact on the total biomass of zooplankton in the epilimnion of the warmest study lake. Therefore, our results are in accordance with the ecological Bergmann’s and James’ rules dealing with the temperature-size relationships.

Composition, abundance, and diversity of limnetic cladocerans (Crustacea: Anomopoda and Ctenopoda) in a black-water lake in the Negro River basin, Amazonas State, Brazil

Abstract For the past 10 years, studies have contributed greatly to knowledge regarding the composition and distribution of the planktonic cladocerans of Tupe Lake in Amazonas State, Brazil, but comparisons between these studies have not been made, and this would increase the comprehension of the ecology of these organisms and their environment. Periodically the hydrological conditions in Tupe Lake change, due to its connecting channel with the Negro River. The purpose of this study was to determine the composition, abundance and diversity of cladocerans in the limnetic zone of Tupe Lake and compare the results with previous studies performed there. Samples were taken in April, June, September, October, November/08 and February/09 in 4 stations located in different areas of the lake. Ceriodaphnia cornuta G.O. Sars, 1886, Bosminopsis deitersi Richard, 1895 and Bosmina cf. longirostris (O.F. Muller, 1785) were the most abundant and frequent species of cladocerans among the 25 recorded species. Higher abundance and richness were observed during the low water phase (October/08). A relationship between the number of samples taken, as well as the type of sampling gear used, and the species richness was observed, when comparing this and previous studies performed in the lake.

Seasonal Abundance of Cladocerans and their Relation to Physico-chemicalparameters of Pond Ecosystem in Palampur, Dist. Kangra, (H.P.)

The physico-chemical parameters and cladocerans diversity are an important measure for evaluating the suitability of water for drinking purposes and irrigation. The investigation was undertaken to estimate the physico-chemical characteristics and to record the presence and abundance of cladocerans in relation to the physico- chemical regime of the pond ecosystem. The water samples were analyzed for temperature, pH, electrical conductivity, dissolved oxygen, total dissolved solids, total solids, total suspended solids, total-alkalinity, nitrate-nitrogen, potassium, total phosphate-phosphorus, chlorides,sodium, and cladocerans were estimated and recorded respectively on monthly basis for the period of one year from April 2014 to March 2015. The present study revealed the presence of seven species namely Moinamucronata, Bosminalongirostris, Daphnia pulex, Daphnia magna, Simocephallusexpinosus, Sidacrystalline andDiaphanosomabrachyurum of cladocerans.

Combined effects of fish and macroinvertebrate predation on zooplankton in a littoral mesocosm experiment

Whether macrophytes offer an effective refuge for zooplankton in all shallow lakes is subject to debate. To explore potential constraints between different predator threats and the related habitat choice by zooplankton, we conducted a mesocosm experiment in 12 large-sized pools mimicking the nearshore environment with part of its length being covered by submersed macrophytes (Egeria densa) and holding a mixed zooplankton community. Four treatments were used: (i) young zooplanktivorous fish (3 silverside, Odontesthes bonariensis) in the “open-water” zone; (ii) macroinvertebrate predator (31 grass shrimp, Palaemonetes argentinus) in the vegetated zone; (iii) both, fish in the open-water and shrimp in the vegetated zones; and (iv) control with no predators. Our results show specific effects of each predator on the abundance, composition, and size of cladocerans. Regarding distribution, in control and shrimp mesocosms, no differences were found between the two zones, while cladocerans were clearly more abundant in the vegetated side in the presence of fish. When both fish and shrimp were present, cladocerans preferred the vegetated zone too, but in a smaller proportion, and their abundance was less. The presence of predatory macroinvertebrates in vegetated littoral zone reduces the refuge value of this habitat, at least for cladocerans.

Spatial changes in zooplankton communities in a strong human-mediated river ecosystem.

River damming causes a decrease in water current velocity which leads to an increase in richness and abundance of organisms atypical for running waters. Zooplankton is a representative example of such organisms. The influx of zooplankton from carp ponds is an additional factor that increases richness and abundance of zooplankton in rivers. We hypothesized that zooplankton dispersing from the carp ponds colonize the impoundments in river and the richness of zooplankton increase in impoundments by development of new species, not observed in the upstream. The zooplankton was collected monthly from April to September of 2013 and 2014. Sampling sites were located in the Barycz river (in the lotic sections and in the dam impoundments), as well as in its tributaries, which are the outlets of carp ponds. The most changes in zooplankton richness and abundance were observed at sites located within the dam impoundments, especially in relation to the lower values of the current velocity. Since the abundance of pelagic rotifers, cladocerans and copepods in the carp pond outlets was similar to that at lower sites in the Barycz, the influence of the carp pond outlets on the abundance in the dam and lotic sections was significant. The river itself in its impounded sections provides advantageous conditions for retention and colonization by a high abundance of zooplankton dispersing from the carp ponds, and for the development of species not occurred in the upstream, which, in turn, increases richness.

Effects of zebra mussels on cladoceran communities under eutrophic conditions

The purpose of this study was to determine how zebra mussels affected cladoceran community structure under eutrophic conditions. We conducted a mesocosm study where we manipulated the presence of zebra mussels and the presence of large-bodied Daphnia (Daphnia magna and Daphnia pulicaria). We also conducted a complimentary life-table experiment to determine how water from the zebra mussel treatment affected the life history characteristics of the cladoceran species. We anticipated that small- and large-bodied cladoceran species would respond differently to changes in algal quality and quantity under the effects of zebra mussels. Large-bodied Daphnia successfully established in the zebra mussel treatment but failed to grow in the control. We did not observe positive relationships between food concentrations and cladoceran abundances. However, the phosphorus content in the seston indicated that food quality was below the threshold level for large-bodied cladocerans at the beginning of the experiment. We believe that zebra mussels quickly enhanced the phosphorus content in the seston due to the excretion of inorganic phosphorus, thus facilitating the development of large-bodied Daphnia. In conclusion, our results suggest that zebra mussels can alter the phosphorus content of seston in lakes and this can affect the dynamics of crustacean zooplankton.

Correspondence of zooplankton assemblage and water quality in wetlands of Cachar, Assam, India: Implications for environmental management

Abstract The zooplankton assemblage of selected wetlands of Assam, India was assessed to deduce the structural variation in the context of water quality parameters. A two year study between 2012 and 2014 comprising of 530 samples from the five wetlands revealed the presence of 46 taxa, 26 Rotifera, 15 Cladocera, 4 Copepoda and 1 Ostracoda, in varying density. The rotifers dominated in terms of abundance (48 ind. cm−3) followed by the cladocerans (28 ind. cm−3) and the copepods (19 ind. cm−3) and showed significant (p <0.05) correlations with turbidity, alkalinity, hardness and phosphate contents of the water samples. The diversity and the richness of the zooplankton showed an increasing trend with the water temperature. Among the different taxa, Brachionus sp. was most abundant followed by Mesocyclops sp. while Beauchampiella sp. was represented in the least numbers. Application of the cluster analysis allowed the segregation of the different zooplankton based on the similarities of abundance in the samples. The water quality parameters like temperature, alkalinity, turbidity, magnesium and calcium were observed to be significant contributors in shaping the zooplankton community composition of the wetlands, revealed through the correlations and canonical correspondence analysis. As an extension, the information can be used in monitoring the quality of the freshwater habitats of the concerned and similar geographical regions, using the zooplankton as the major constituents. The variations in the abundance of cladoceran, copepod and rotifer zooplanktons can be used to understand the mechanisms that sustain the food webs of the aquatic community of the freshwater bodies.

Cladoceran abundance in relation to water quality parameters of Chakki Talab, Bodhan, Telangana

In the present study an attempt has been made to evaluate water quality and related density of Cladocerans for a period of one year, October 2015 to September 2016. Water quality parameters such as temperature, PH, total dissolved solids, dissolved oxygen, biological oxygen demand, total alkalinity, total hardness, chlorides, phosphates, and nitrates are presented here to relate with the abundance of Cladocerans. The Cladoceran abundance reflects the eutrophic nature of the Chakki talab.

SPATIAL AND TEMPORAL DISTRIBUTION OF MARINE CLADOCERAN SPECIES IN THE SURFACE WATERS OF ISKENDERUN BAY

Cladocerans are important member of pelagic ecosystem and they serve as good sources of food for fish and fish larvae during the warm periods. The aim of this study was to determine species composition of marine cladocerans and their temporal and spatial distribution in the surface waters of coastal and offshore waters of Iskenderun Bay. The study was conducted at the four stations in Iskenderun Bay between November 2005 and August 2006. The samples were collected horizontally with WP-2 net (200 mesh size). Six species of cladocerans ( Penilia avirostris, Evadne spinifera, Pseudoevadne tergestina, Evadne nordmanni, Pleopis polyphamoides and Podon intermedius ) were found. Among these, Evadne nordmanni was observed for the first time in Iskenderun Bay. With regard to annual abundance of cladoceran species, Evadne spinifera was the most abundant and followed by P. avirostris and P. tergestina . While the maximum abundance of cladoceran was observed in May-06, the minimum abundance was in November-05. It can be concluded that results of this study could provide a significant contribution to the future studies on cladoceran diversity in the region.

Disentangling food webs interactions in the littoral of temperate shallow lakes

Elucidation of food web interactions provides better understanding of ecosystem functioning, indicates anthropogenic impacts which often cause alterations in environmental conditions and detoriorations in feeding network in terrestrial and aquatic ecosystems. The importance of microfauna and macroinvertebrates in littoral zones of shallow waters has poorly been studied regarding their trophic interactions. This study compares invertebrate assemblage and food web interactions among epiphyton, zooplankton and benthic macroinvertebrates across structural heterogeneity in the littoral zone of three temperate shallow water bodies. Submerged and structurally-complex stands of Ceratophyllum demersum inhabited higher abundance of cladocerans and supported higher diversity and biomass of epiphytic protozoans and invertebrates in comparison to floating-leaved Nuphar lutea stands. Analysis of the ecosystem functioning illustrated the increased biomass of macroinvertebrate predators and a preference of predation over planktonic crustaceans in more complex macrophyte stands. Food webs displayed higher complexity and size with habitat heterogeneity, while epiphyton and zooplankton shared the important fraction in food resources among the invertebrate trophic network. Results of food web modelling indicated zooplankton and epiphyton as more vulnerable to invertebrate predation in the complex submerged macrophytes than in floating-leaved macrophyte stands. Integrated community, ecosystem and food web approaches in explanation of complex trophic interactions in the littoral zones justified an increase in diversity and food-web functional complexity with structural heterogeneity of microhabitats.

Seasonal quantitative dynamics and ecology of pelagic rotifers in an acidified boreal lake

Lake Gjerstadvann is a dimictic, oligotrophic, slightly acidified boreal lake in southern Norway (northwest Europe). The planktonic rotifer community of this lake was studied quantitatively during one year in order to investigate the impacts of the local environment and biotic interactions on seasonal succession and habitat selection. Pure suspension feeders (mainly Keratella spp., Conochilus spp., and Kellicottia longispina) together with raptorial graspers or specialised feeders (mainly Polyarthra spp. and Collotheca spp.) dominated the rotifer community over prolonged periods, whereas carnivorous/omnivorous species (mainly Asplanchna priodonta) were extremely uncommon. Low bicarbonate buffering capacity resulted in a distinctive seasonal oscillating pH between 5.0 and 5.6, defining a special acid-transition lake category. The pH values were highest in the productive period during summer, and lowest during ice break-up coinciding with the peak reactive aluminium concentrations of 250-300 mg L-1. As in typical Norwegian boreal perch lakes, the most abundant cladoceran was Bosmina longispina due to perch predation on the genus Daphnia. Rotifer community structure was significantly related to temperature and oxygen (P=0.001 and P=0.022), illustrating the important effects of the seasonal cycle and vertical density stratification. The most significant competition indicator species were B. longispina and Eudiaptomus gracilis (both with P=0.001). A variance partitioning indicated that 14% of the total community composition variance could only be explained by biotic interactions, while 19% of the variance could be attributed to environmental gradients. Of the variance, 23% could not be resolved between biotic interactions and environmental gradients, while a residual of 44% was not explainable by any of the variables. Acid conditions alone cannot account for all the observed changes in the rotifer community of this lake with low humic content, since resource limitation and food competition are also important factors shaping rotifer population dynamics and the community structure.

Analyzing the effects of four submerged macrophytes with two contrasting architectures on zooplankton: A mesocosm experiment

<p>Increases in the structural complexity of submerged macrophytes are often shown to be linked to higher invertebrate abundance and diversity, but a number of studies have demonstrated, however, that this is not always the case. The objective of this study was to analyze the effects of four macrophyte species with two contrasting architectures (simple architecture with broad leaves: <em>Vallisneria spiralis</em> L. and <em>Potamogeton malaianus</em> Miq. and complex architecture with finely dissected leaves: <em>Ceratophyllum demersum</em> L. and <em>Myriophyllum verticillatum </em>L.) on zooplanktons. We hypothesized that structurally more complex macrophytes would support more zooplanktons and higher diversity, species richness, abundance and biomass, and to test our hypotheses, zooplankton samples within the above-mentioned macrophytes were collected to analyze the variances at different times. Contrary to our expectations, we found that the zooplankton’ responses were independent to the macrophyte architecture. Specially, although finely dissected<em> M</em>.<em> verticillatum</em> could significantly increase total zooplanktons, diversity, species richness, rotifers and cladocerans than the other three macrophytes, the effects of finely dissected <em>C</em>.<em> demersum</em> on these parameters exhibited no significant differences compared to two broad leaved macrophytes (<em>V</em>.<em> spiralis</em> and <em>P</em>.<em> malaianus</em>). Moreover, broad leaved macrophytes even increased more abundance zooplanktons than finely dissected <em>C</em>.<em> demersum</em>. In addition, the effects of macrophytes on zooplanktons also varied with zooplankton species. For example, the four tested macrophytes could significantly increase cladoceran abundance and biomass. Yet for copepods, the density was significantly increased<em> </em>in presence of <em>V</em>.<em> spiralis</em> and <em>C</em>.<em> demersum</em>, but<em> P</em>.<em> malaianus </em>and<em> M</em>.<em> verticillatum</em> did not show significant effects on copepod density. Moreover, all the tested macrophytes except for <em>V</em>.<em> spiralis</em> even significantly suppress copepod biomass. Therefore, our results did not support the hypothesis that structurally complex macrophytes harbor more zooplanktons, and showed that the effects of the investigated macrophytes on zooplanktons were not likely to depend on their architectures, but seemed to rely on complex relationships between macrophyte and zooplankton species.</p>

Changes in the inflow of saline water into the Bornholm Basin (SW Baltic Sea) during the past 7100 years – evidence from benthic foraminifera record

The Baltic Sea (~393 000 km2) is the largest brackish sea in the world and its hydrographic and environmental conditions are strongly dependent on the frequency of saline water inflows from the North Sea. To improve our understanding of the natural variability of the Baltic Sea ecosystem detailed reconstructions of past saline water inflow changes based on palaeoecological archives are needed. Here we present a high‐resolution study of benthic foraminiferal assemblages accompanied by sediment geochemistry (loss on ignition, total organic carbon) and other microfossil data (ostracods and cladocerans) from a well‐dated 8‐m‐long gravity core taken in the Bornholm Basin. The foraminiferal diversity in the core is low and dominated by species of Elphidium. The benthic foraminiferal faunas in the central Baltic require oxic bottom water conditions and salinities >11–12 PSU. Consequently, shell abundance peaks in the record reflect frequent saline water inflow phases. The first appearance of foraminiferal tests and ostracods in the investigated sediment core is dated to c. 6.9 cal. ka BP and attributed to the first inflows of saline and oxygenated bottom waters into the Bornholm Basin during the Littorina Sea transgression. The transgression terminated the Ancylus Lake phase, reflected in the studied record by abundant cladocerans. High absolute foraminiferal abundances are found within two time intervals: (i) c. 5.5–4.0 cal. ka BP (Holocene Thermal Maximum) and (ii) c. 1.3–0.75 cal. ka BP (Medieval Climate Anomaly). Our data also show three intervals of absent or low saline water inflows: (i) c. 6.5–6.0 cal. ka BP, (ii) c. 3.0–2.3 cal. ka BP and (iii) c. 0.5–0.1 cal. ka BP (Little Ice Age). Our study demonstrates a strong effect of saline and well‐oxygenated water inflows from the Atlantic Ocean on the Baltic Sea ecosystem over millennial time scales, which is linked to the major climate transitions over the last 7 ka.

Distribution and fluctuations of backswimmers (Notonectidae) in a tropical shallow lake and predation on microcrustaceans.

Notonectids are widely distributed in freshwaters and can prey on zooplankton in temperate lakes. However, its role in structuring the zooplankton community is unknown in tropical lakes. Thus, our objective was to study the notonectid Martarega uruguayensis in a Brazilian tropical shallow lake to evaluate its potential as a zooplankton predator. Its horizontal distribution was analized in the lake throughout one year in fortnightly samplings. Backswimmers were more abundant (mean density 162.9 ± 25.8 ind.m-2) in the cool-dry season, with a strong preference by the littoral zone (mean density 139.9 ± 17.5 ind.m-2). Laboratory experiments were undertaken with young and adult notonectid and the two most abundant cladocerans, Daphnia gessneri and Ceriodaphnia richardi, as prey. Predation by backswimmers in the laboratory showed that only juveniles fed on microcrustaceans (mean ingestion rate of 1.2 ± 0.2 Daphnia and 1.0 ± 0.2 Ceriodaphnia per predator per hour), without size selectivity. Adult insects probably have difficulties in detecting and manipulating small planktonic organisms. On the other hand, young instars might influence zooplankton community, especially in the littoral zone of the lake. This study does contribute to a better understanding of trophic interactions in tropical shallow lakes and is the first to investigate the predation of a notonectid on microcrustaceans from Lake Monte Alegre.

Effect of suspended solids on interaction between filter-feeding fish Aristichthys nobilis and zooplankton in a shallow lake using a mesocosm experiment

ABSTRACTSuspended solids (SS) resulting from sediment resuspension (SR) can impact ecosystems through direct and indirect effects on freshwater organisms and their interactions. This study was conducted to determine whether the SS can affect the interaction between filter-feeding fish (Aristichthys nobilis) and zooplankton using a mesocosm experiment with sediments from Lake Taihu, a large shallow lake in China. SR using pump was divided into three intensities: strong, weak and no SR representing different concentrations of SS. Zooplankton abundance was significantly higher in the no-fish treatments than in the fish treatments under all three SR conditions. SR intensity had significantly negative effect on zooplankton abundance. There were interactions between fish and SR intensity on abundances of copepod, rotifer, total zooplankton and dominant zooplankton species except cladoceran abundance. The results indicate that SS had a lesser effect on zooplankton predation by filter-feeding fish, which suggests that zooplankton communities in shallow lakes can be affected by the filter-feeding fish even under high level of SS condition.