Studies on the zooplankton community of a shallow lagoon of the Southern Baltic Sea: long-term trends,seasonal changes,and relations with physical and chemical parameters

The Darß-Zingst Lagoon, a coastal inlet of the southern Baltic Sea, was subject to extended monitoring. The biomass data of zooplankton from 1969 to 2001 were used to analyze long-term trends and to correlate zooplankton biomass with abiotic factors. The dominant species in the lagoon were the calanoid copepods Eurytemora affinis and Acartia tonsa, and the rotifer Keratella cochlearis f. tecta. In the long-term trend, two pronounced changes in zooplankton biomass and species composition were observed. They are discussed in connection with a shift in dominance from macrophytes to phytoplankton and the invasion of a polychaet species into the lagoon. Significant relations between zooplankton data and abiotic parameters were found. While temperature, precipitation and NAO winter index correlated positively with copepods and negatively with rotifers, the relationships were inversely for pH-value and duration of ice cover.     

<Emphasis Type="Italic">Daphnia</Emphasis> versus copepod impact on summer phytoplankton: functional compensation at both trophic levels

Here we report on a mesocom study performed to compare the top-down impact of microphagous and macrophagous zooplankton on phytoplankton. We exposed a species-rich, summer phytoplankton assemblage from the mesotrophic Lake Schöhsee (Germany) to logarithmically scaled abundance gradients of the microphagous cladoceran Daphnia hyalina×galeata and of a macrophagous copepod assemblage. Total phytoplankton biomass, chlorophyll a and primary production showed only a weak or even insignificant response to zooplankton density in both gradients. In contrast to the weak responses of bulk parameters, both zooplankton groups exerted a strong and contrasting influence on the phytoplankton species composition. The copepods suppressed large phytoplankton, while nanoplanktonic algae increased with increasing copepod density. Daphnia suppressed small algae, while larger species compensated in terms of biomass for the losses. Autotrophic picoplankton declined with zooplankton density in both gradients. Gelatinous, colonial algae were fostered by both zooplankton functional groups, while medium-sized (ca. 3,000 µm³), non-gelatinous algae were suppressed by both. The impact of a functionally mixed zooplankton assemblage became evident when Daphnia began to invade and grow in copepod mesocosms after ca. 10 days. Contrary to the impact of a single functional group, the combined impact of both zooplankton groups led to a substantial decline in total phytoplankton biomass.     

An analysis of long-term winter data on phytoplankton and zooplankton in Neusiedler See,a shallow temperate lake,Austria

In the last 40 years, the shallow steppe lake, Neusiedler See, was ice covered between 0 and 97 days. The North Atlantic Oscillation (NAO) as well as the Mediterranean Oscillation affected the lake and its conditions during winter. Both climate indices correlated negatively with the duration of ice cover and the timing of ice-out. Average winter phytoplankton biomass increased from less than 0.2 (0.05–0.84) mg FM l^?1 in the late 1960s/beginning of 1970s to 3.1 (1.72–5.61) mg FM l^?1 in the years 2001–2004. The increase in annual winter biomass of phytoplankton was associated with a significant shift in the composition of the algal assemblage. In the winter 1997/1998, diatoms contributed between 40 and 80% to the phytoplankton biomass while in 2006/2007 cyanoprokaryotes contributed 46%. Mean chlorophyll-a concentrations during winter were significantly correlated with those of total phosphorus (P_tot). Together with cold-water species (rotifer Rhinoglena fertöensis), perennial, eurythermal ones (copepod Arctodiaptomus spinosus) contributed to the zooplankton community. High zooplankton numbers were encountered when rotifers, particularly when densities of Rhinoglena fertöensis were high (r ² = 0.928). Zooplankton abundance and biomass varied from year to year but correlated positively with Chl-a (biomass ? r ² = 0.69; numbers ? r ² = 0.536). Winter zooplankton populations were primarily influenced by winter conditions, but in early winter also by survival of autumn populations, i.e., the more adults of Arctodiaptomus spinosus survived into winter, the higher was the zooplankton biomass in early winter. Phyto- and zooplankton dynamics in shallow lakes of the temperate region seem to critically depend on the biomass in autumn and on winter conditions, specifically on ice conditions and thus are related to climate signals such as the NAO.     

Abundance,distribution, and territory areas of rock-dwelling Lake Tanganyika cichlid fish species

Lake Tanganyika, the second-oldest and second-deepest lake in the world, harbors an impressive cichlid fish fauna counting about 250 endemic species that are characterized by a great level of ecological, morphological, and behavioral specialization. This study describes and compares cichlid fish communities at two rocky shores with differential human impact in the south of Lake Tanganyika. Species inventories and depth-dependent abundances were elaborated. About 41 and 46 sympatric cichlid species were recorded in the two study sites, respectively. Variabilichromis moorii was the most abundant species (29–60% of total number of fishes), followed by Aulonocranus dewindti (3–19%), Tropheus moorii (12%), Ophthalmotilapia ventralis (4–10%), Eretmodus cyanostictus (6–11%), and Cyathopharynx furcifer (0.01–9%). All other species had abundances below 5%. It further emerged that large cichlids such as Petrochromis species, Cyathopharynx furcifer, and Lobochilotes labiatus were very rare at one location, with frequencies of 0.55% or less. Territorial sizes of three particularly abundant species, Variabilichromis moorii, Aulonocranus dewindti, and Tropheus moorii, were assessed by behavioral observations. We distinguished between territorial core areas and total defended area, yielding average core areas between 0.4 (V. moorii) and 1.6 m² (T. moorii), and total defended areas averaging for each species between 1.6 (V. moorii) and 5.0 m² (A. dewindti) with no significant differences between the two study sites. The data on individual densities are also relevant for evolutionary studies, in that they allow more accurate calculations of effective population sizes.     

Periphyton nutrient content,biomass and algal community on artificial substrate: response to experimental nutrient enrichment and the effect of its interruption in a tropical reservoir

Periphyton plays an important functional role in the retention of nutrients in aquatic ecosystems, especially phosphorus. We evaluated the effects of enrichment with N and P and the effect after 20 days of no additional N and P on periphyton on artificial substratum in open-bottom mesocosms. The aim was to jointly evaluate periphyton, phytoplankton and zooplankton in the presence of macrophytes. Experimental conditions simulated natural conditions and nutrient addition was based on the maximum concentration recorded in mesotrophic reservoir. Our hypothesis is that the periphyton is sensitive to the effects of N and P enrichment and its interruption, despite the positive response of phytoplankton and zooplankton. Two treatments were designed using open-bottom mesocosms (n = 3): control (no nutrient addition); NP+ (combined phosphorus and nitrogen addition). Sampling for the measurement of biotic and abiotic variables was performed, with 10 days of continuous enrichment, on the 3rd, 6th and 11th, and 20 days after enrichment had ended (31st day). Periphyton chlorophyll a, dry mass and algal density increased significantly with the addition of N and P and decreased 20 days after the interruption of the enrichment. The highest periphyton P content was found in the NP+ treatment. The enrichment had a positive effect on Chrysophyceae (Chromulina spp.) and rotifer (Polyarthra spp.) density and the interruption of enrichment favored Bacillariophyceae (Gomphonema sp.) and rotifers (Gastropus stylifer). Phytoplankton responded positively to enrichment. Along with the high macrophyte coverage over the experimental period, we evidenced the positive effect enrichment had on phytoplankton biomass and zooplankton abundance. Therefore, periphyton on artificial substrate was sensitive to effects of N and P enrichment and its interruption, responding promptly to changes in nutrient availability in a scenario of high competition and grazing.     

Alternative egg-feeding tactics in <Emphasis Type="Italic">Telmatherina sarasinorum</Emphasis>, a trophic specialist of Lake Matano’s evolving sailfin silversides fish radiation

Feeding specialisation is a typical feature of adaptive animal radiations. Different kinds of feeding specialisations have evolved in the endemic sailfin silversides species flock in Lake Matano (Central Sulawesi, Indonesia), including egg-feeding. The present study focuses on Telmatherina sarasinorum, a sailfin silverside species feeding on the eggs of related Telmatherina antoniae. Stomach content analyses supported T. antoniae eggs to be the dominant food item, independent of daytime. We hypothesized that the egg-feeders use alternative tactics for maximising egg consumption under varying densities of both, spawning T. antoniae pairs and competing conspecific egg-feeders. Focal behavioural observations were applied to describe different feeding tactics and to analyse feeding success and the related costs in terms of competitive interactions. Egg-feeders followed single courting pairs of T. antoniae or, alternatively, they switched between different spawning pairs. Following-behaviour, covering one or more spawning events of the host species, was positively related to enhanced egg consumption. Compared to feeding by switching frequently among different spawning pairs, the following tactic came at the cost of likewise increased competition. Behavioural observations suggest that some males monopolize courting pairs of T. antoniae and gain increased amounts of eggs compared to others avoiding competition by switching among pairs. The present results confirm that egg-feeding is a distinct trophic specialisation in T. sarasinorum and increase the scale of behavioural specialisation in Lake Matano’s evolving Telmatherina radiation.     

Discovery of <Emphasis Type="Italic">Ascomorpha ovalis</Emphasis> (Bergendal, 1892) (Rotifera,Gastropodidae), an indicator of oligotrophic conditions,in Glubokoe Lake (Moscow Region,Russia)

The rotifer Ascomorpha ovalis (Bergendal, 1892) was found for the first time in Glubokoe Lake (Moscow Region) in June 2010. Long-term observations of zooplankton dating back to 1897, including our own studies starting in 2004 and carried out on a yearly basis, had never recorded this species before 2010. The density of the population was 25 ind./L in the 0–10 m water layer. In 2011–2012, the species did not disappear but was naturalized in the lake. A. ovalis is an indicator of oligotrophic conditions. The tendency for ongoing oligotrophication of the pelagial of Glubokoe Lake is supported by the penetration and naturalization of Ascomorpha ovalis during recent years and the presence of the oligotrophic rotifer Gastropus hyptopus (Ehrenberg, 1838) detected in the lake earlier.     

The potential of agricultural headwater streams to retain soluble reactive phosphorus

Zooplankton may preferentially graze small, edible diatom species and therefore affect fossils relative to live assemblages by selective removal or increased sedimentation via egestion. Cladoceran zooplankton remains and diatom edibility were analyzed in sediment cores from Moon Lake and Coldwater Lake (North Dakota, USA) to assess changes in potential grazing pressure on algae and influence on diatom-inferred salinity (DIS) reconstructions. Sedimentary zooplankton in Moon Lake were dominated by littoral Cladocera, whereas Coldwater Lake assemblages were primarily small-bodied pelagic and littoral species. Relationships between cladocerans and environmental parameters over the past century varied by site and by species, with Chydorus brevilabris related most closely to drought at Moon and Bosmina sp. related to drought at Coldwater. A higher percentage of inedible diatoms occurred in the sediments of Moon Lake as compared to Coldwater Lake. DIS correlations with drought records improved in Moon Lake when only inedible diatom taxa were used to build a transfer function, but no improvement was seen for Coldwater Lake with this approach. These data suggest grazing pressure on diatoms differed between lakes and that zooplankton–phytoplankton interactions may affect the accuracy of drought reconstructions in the Great Plains.     

Zooplankton abundance in the pelagic region of Lake Kasumigaura (Japan): monthly data since 1980

Microscopic crustaceans (cladocerans and copepods) and rotifers are the principal zooplankton components of the pelagic food webs in lakes. They play important ecological roles, functioning as essential links between primary producers and planktivorous fish. Individuals zooplankton are important nodes of matter flow in pelagic ecosystems. The zooplankton community structure can provide useful indicators of top–down processes, such as the magnitude or strength of planktivorous predators and the extent of zooplankton grazing. Here we report the abundance of zooplankton taxa (crustaceans and rotifers) that were recorded monthly, from January 1980 to September 2015, at two stations on Lake Kasumigaura, a shallow eutrophic lake that is the second largest lake in Japan. The data include information on 12 copepod species (taxa), 20 cladoceran species (taxa), 40 rotifer species (taxa), and the opossum shrimp (Neomysis intermedia). In the 1980s, the plankton of the lake were characterized by cyanobacterial blooms and the co-dominance of Bosmina and Diaphanosoma in the summer. In addition, the two cladoceran genera, Daphnia galeata and Chydorus sphaericus were often prominent. The plankton profile changed dramatically in the middle (1997–2004) of the present long-term monitoring period, when cyanobacteria disappeared and diatoms became dominant even in the summer; concurrently, only the Diaphanosoma cladocerans were evident. However, in the past 10 years, cyanobacterial blooms, the co-dominance of Bosmina and Diaphanosoma, and D. galeata have re-emerged. Zooplankton monitoring forms part of the Lake Kasumigaura Long-Term Environmental Monitoring Program, which has been conducted by the National Institute for Environmental Studies (NIES) since 1977. Data on other planktonic components (phytoplankton and the elements of microbial food webs) noted during monitoring and on primary production were published in Takamura and Nakagawa (Ecol Res 27:839 2012a, Ecol Res 27:837 2012b, Ecol Res 31:287 2016). Lake Kasumigaura is a core site of the Japan Long-term Ecological Research Network, a member of the International Long-term Ecological Research Network. Our quantitative dataset spanning several decades is unique in terms of the work on lakes and the plankton therein, and is freely available. The dataset has been used in ecological and environmental programs, as well as in studies on lake management.     

Latitude and elevation as factors controlling occurrence of calanoid copepods in marginal lotic waters in New South Wales,Australia

Freshwater calanoid copepods develop abundant populations in lentic water bodies such as lakes, reservoirs and lagoons. In this study, we examined the potential habitat value of edges in lotic systems such as creeks and rivers where waters tend to stagnate, providing lentic-like environments. We examined a total of 353 edge samples collected from 321 sites across the state of New South Wales, Australia, with latitudes in the range 28.3–37.4°S and elevations in the range 2–1834 m above sea level. Of the total samples examined, calanoid copepods were found in 94 samples, with the frequency of occurrences of species decreasing in the order: Boeckella fluvialis Henry, B. triarticulata (Thomson), Gladioferens spinosus Henry, G. pectinatus (Brady), B. major Searle, B. minuta Sars, and Calamoecia lucasi Brady. The probability of occurrence of the calanoid copepods was related negatively to both latitude (as absolute values) and elevation, based on logistic regression models. We conclude that the edges of many lotic systems provide additional habitats for some species of freshwater calanoid copepods, with constraints on their distributions along latitudinal and elevational gradients.     

Life table demography of <Emphasis Type="Italic">Asplanchna brightwellii</Emphasis> Gosse, 1850 fed with five different prey items

We conducted life table experiments on the freshwater rotifer Asplanchna brightwellii to analyze its demography when fed with prey items from several taxonomic groups (cladocerans, protozoans, and rotifers) and under two different temperature regimes (20 and 25°C); the aim of the study was to determine the preferred prey for A. brightwellii in terms of fitness (evaluated as reproductive success) among five cladoceran, protozoan, and rotifer preys, and to test which temperature (20 or 25°C) is better for life table parameters of Asplanchna. Our analysis identified Brachionus calyciflorus as the preferred prey for A. brightwellii based on life table statistics, ingestion rate and electivity indices. The greatest values for net reproductive rate and intrinsic growth rate were achieved when A. brightwellii was fed B. calyciflorus. Greater reproductive values (R _o and r) were found at 25°C than at 20°C for A. brightwellii across the five prey species. We found significant differences in the ingestion rate and electivity index among zooplanktonic and benthic preys. The influence of temperature, the cost of predation, and how prey selection by A. brightwellii is influenced by: biomass, size, and swimming speed; they are discussed hoping to gain a better understanding of trophic transfers in zooplankton communities.     

DNA barcoding of freshwater zooplankton in Lake Kasumigaura,Japan

Although DNA barcoding is a promising tool for the identification of organisms, it requires the development of a specific reference sequence library for sample application. In the present study we developed a Lake Kasumigaura, Japan, zooplankton DNA barcode library to increase the sensitivity of future zooplankton monitoring for detecting lake ecosystem condition changes. Specifically, the mitochondrial cytochrome c oxidase subunit I (mtCOI) haplotype, i.e., the primary DNA barcode, was examined for each zooplankton taxon. In crustaceans, 37 mtCOI haplotypes were obtained from 99 individuals, representing four and 15 morpho-species of Copepoda and Cladocera, respectively. Comparing these sequences with those in GenBank shows that the lake harbors putative non-indigenous species, such as Daphnia ambigua. In rotifers, 132 mtCOI haplotypes were obtained from 302 individuals, representing 11 genera and one unclassified taxon. The automatic barcode gap discovery (ABGD) algorithm separated these haplotypes into 43 species. Brachionus cf. calyciflorus was divided into five ABGD species, and different ABGD species tended to occur in different seasons. Seasonal ABGD-species succession was also observed within Polyarthra spp. and Synchaeta spp. These seasonal successions were not detected by inspections of external morphology alone. Accepting up to 7% sequence divergence within the same species, mtCOI reference sequences were available in GenBank for three, 13, and 17 species in Copepoda, Cladocera, and Rotifera, respectively. The present results, therefore, reveal the serious shortage of mtCOI reference sequences for rotifers, and underscore the urgency of developing rotifer mtCOI barcode libraries on a global scale.     

The Afromontane Cladocera (Crustacea: Branchiopoda) of the Rwenzori (Uganda–D. R. Congo): taxonomy,ecology and biogeography

The timely characterization of high-altitude freshwater habitats allows an assessment of the diversity of its biota and provides the basis for monitoring community change. In this study, we investigate the Cladocera fauna of 29 water bodies (pools, freshwater lakes, and surrounding swamps sampled at various occasions between 2005 and 2009) in the Rwenzori Mountains (Uganda, D. R. Congo), which are part of the East African Sky Island Complex. All sites except one are located above 3700 m altitude. We include notes on the morphology, taxonomy, distribution, and ecology of each recorded taxon and describe a new species of the Alona rustica-group (Alona sphagnophila n.sp.; Chydoridae). We found 11 species of which seven are restricted to Lake Mahoma, the lowest lake in our study area (2990 m) (Alona affinis barbata, A. intermedia, Alonella exisa, Alonella nana, Daphnia cf. obtusa, Pleuroxus aduncus) and/or Lake Bujuku (Daphnia cf. curvirostris, P. aduncus) (3900 m). Two taxa (Ilyocryptus cf. gouldeni, A. sphagnophila n.sp.) are restricted to Carex/Sphagnum bogs surrounding lakes in the afroalpine zone. Pigmented populations of Chydorus cf. sphaericus occur in all the sites. It is the only cladoceran species surviving the extreme alpine and nival conditions in the Rwenzori. The species is joined by A. guttata at locations at lower altitudes (ca. 3000–4000 m), present in about half of the sites. The Rwenzori Cladocera fauna is characterized by a strong extratropical temperate component and a low level of speciation/endemism. Harboring an impoverished boreal cladoceran community, Lake Mahoma is given closer attention. At 2990 m, the lake is a cold-temperate aquatic island in the tropics and may function as a stepping stone for Palaearctic taxa. We introduce a new term for high-altitude, cold-water habitats in the tropics, which act as climatic islands for extratropical freshwater faunas, Löffler Islands, in honor of Dr Heinz Löffler. In comparison to surveys in 1961, we list five new records in Lake Mahoma, which could indicate cladoceran community changes over the past few decades at ca. 3000 m in the Rwenzori. Since the species distributions correlate to temperature and catchment properties of the lakes, the Rwenzori cladoceran fauna can be expected as sensitive indicators for local changes.     

Adaptations in phytoplankton life strategies to imposed change in a shallow urban tropical eutrophic reservoir,Garças Reservoir,over 8 years

This study aimed at evaluating the phytoplankton adaptive strategies of phytoplankton in a shallow urban eutrophic tropical reservoir, Garças Reservoir, over temporal and vertical scales. Samples were taken monthly for eight consecutive years (1997–2004) at a fixed set of depths in the water column. At the beginning, the reservoir was eutrophic with 20% of its surface covered by water hyacinth Eichhornia crassipes (phase I). Then, in phase II, water hyacinth grew to cover up to 40–70% of the surface. In phase III it was mechanically removed. After macrophyte removal the limnology changed, drastically. This removal modified nutrient dynamics, drastically reduced water transparency, and increased both primary production and phytoplankton biomass, the latter impeding light penetration. Phytoplankton life strategies during water hyacinth dominance (phase II) responded promptly to this environmental disturbance in conditions of low dissolved oxygen (DO) and soluble reactive phosphorus (SRP) and high free CO₂ values. After macrophyte removal, a permanent cyanobacterial monoculture was established. Phase I was dominated basically by Sphaerocavum brasiliense, mainly during the stratified months, represented by non-flagellate colonies, the M functional group, S-strategists, and greater biomass of species with high maximal axial linear dimension (MLD) and cell volumes. Phase II was dominated by Cryptomonas curvata, C. erosa, C. marssonii, Trachelomonas sculpta, T. volvocinopsis, T. kelloggii, T. hispida, Peridinium spp., Aphanocapsa spp., and Aphanothece spp., and was represented by unicellular flagellate species, Y, W2, K, L_O functional groups, and C-strategists, greater biomass of species with intermediate MLD and cell volumes. Phase III was dominated by Microcystis aeruginosa, M. panniformis, Cylindrospermopsis raciborskii, Planktothrix agardhii, and Aphanizomenon gracile, represented by non-flagellate colonies, M, S, H1, S functional groups, and S and R-strategists, greater biomass of species with high MLD and cell volumes (>50 μm and >10⁴ μm³, respectively).     

Plankton community composition and vertical migration during polar night in Kongsfjorden

The polar night in the Arctic is characterized by up to six months of darkness, low temperatures and limited food availability. Biological data on species composition and abundance during this period are scarce due to the logistical challenges posed when sampling these regions. Here, we characterize the plankton community composition during the polar night using water samplers and zooplankton net samples (50, 64, 200, 1500 μm), supplemented by acoustics (ADCPs, 300 kHz), to address a previously unresolved question–which species of zooplankton perform diel vertical migration during the polar night? The protist community (smallest plankton fraction) was mainly represented by ciliates (Strombidiida). In the larger zooplankton fractions (50, 64, 200 μm) the species composition was represented primarily by copepod nauplii and small copepods (e.g., Microcalanus spp., Pseudocalanus spp. and Oithona similis). In the largest zooplankton fraction (>1500 μm), the euphausiid, Thysanoessa inermis, was the most abundant species followed by the chaetognath Parasagitta elegans. Classical DVM was not observed throughout the darkest parts of the polar night (November–mid-January), although, subtle vertical migration patterns were detected in the acoustic data. With the occurrence of a more distinct day–night cycle (i.e., end of January), acoustical DVM signals were observed, paralleled by a classical DVM pattern in February in the largest fractions of zooplankton net samples. We suggest that Thysanoessa spp. are main responsible for the acoustical migration patterns throughout the polar night, although, chaetognaths and copepods may be co-responsible.     

Winter ecology of shallow lakes: strongest effect of fish on water clarity at high nutrient levels

While the structuring role of fish in lakes is well studied for the summer season in North temperate lakes, little is known about their role in winter when fish activity and light irradiance potentially are lower. This is unfortunate as the progressing climate change may have strong effects on lake winter temperature and possibly on trophic dynamics too. We conducted an enclosure experiment with and without the presence of fish throughout winter in two shallow lakes with contrasting phosphorus concentrations. In hypertrophic Lake Søbygård, absence of fish led to higher biomass of zooplankton, higher grazing potential (zooplankton:phytoplankton ratio) and, accordingly, lower biomass of phytoplankton and chlorophyll a (Chl a), while the concentrations of total nitrogen (TN), total phosphorus (TP), oxygen and pH decreased. The average size of egg-bearing Daphnia and Bosmina and the minimum size of egg-bearing specimens of the two genera rose. In the less eutrophic Lake Stigsholm, zooplankton and their grazing potential were also markedly affected by fish. However, the decrease in Chl a was slight, and phytoplankton biovolume, pH and the oxygen concentration were not affected. TN was higher when fish were absent. Our results indicate that: (i) there is a notable effect of fish on zooplankton community structure and size during winter in both eutrophic and hypertrophic North temperate lakes, (ii) Chl a can be high in winter in such lakes, despite low light irradiance, if fish are abundant, and (iii) the cascading effects on phytoplankton and nutrients in winter may be more pronounced in hypertrophic lakes. Climate warming supposedly leading to reduced winter mortality and dominance of small fish may enhance the risk of turbid state conditions in nutrient-enriched shallow lakes, not only during the summer season, but also during winter.     

Macrophytes as dispersal vectors of zooplankton resting stages in a subtropical riverine floodplain

The resting stages of freshwater zooplankton constitute a special mechanism for passive dispersal, often displaying a variety of adaptations so as to ease transport. In floodplain systems, macrophytes are one of the most representative biotic groups showing interactions with the zooplankton community. The annual fluctuations in the hydrometric level of the Paraná River favour the displacement of this aquatic vegetation in floodplain environments. This paper hypothesizes that the roots and submerged portions of different macrophytes contain zooplankton resting stages which are able to hatch when environmental conditions are favourable. In turn, this contributes to the dispersal of zooplankton by plants when they are displaced by the flood pulse. Six macrophyte species were sampled (Eichhornia crassipes, Azolla filiculoides, Limnobium spongia, Pistia stratiotes, Eichhornia azurea and Nymphoides indica) from lakes within the Paraná River floodplain. Roots and submerged portions of vegetation were stored (90 days) at 4 °C then incubated at 25 °C for 90 days. Hatchling emergence was recorded at 2-day intervals during this period. In total, 70 zooplankton taxa were recorded in all macrophyte samples; rotifers were the most representative group (69%) followed by cladocerans (28%) and copepods (3%). The roots and submerged parts of aquatic vegetation house viable zooplankton resting stages. This phenomenon allows the dispersal of resting stages and therefore colonization of new habitats during the displacement of macrophyte species.     

Above- and belowground competition between two submersed macrophytes

Several studies have shown that submerged macrophytes provide a refuge for zooplankton against fish predation, whereas the role of emergent and floating-leaved species, which are often dominant in eutrophic turbid lakes, is far less investigated. Zooplankton density in open water and amongst emergent and floating-leaved vegetation was monitored in a small, eutrophic lake (Frederiksborg Slotssø) in Denmark during July–October 2006. Emergent and floating-leaved macrophytes harboured significantly higher densities of pelagic as well as plant-associated zooplankton species, compared to the open water, even during periods where the predation pressure was presumably high (during the recruitment of 0+ fish fry). Zooplankton abundance in open water and among vegetation exhibited low values in July and peaked in August. Bosmina and Ceriodaphnia dominated the zooplankton community in the littoral vegetated areas (up to 4,400 ind l^?1 among Phragmites australis and 11,000 ind l^?1 between Polygonum amphibium stands), whereas the dominant species in the pelagic were Daphnia (up to 67 ind l^?1) and Cyclops (41 ind l^?1). The zooplankton density pattern observed was probably a consequence of concomitant modifications in the predation pressure, refuge availability and concentration of cyanobacteria in the lake. It is suggested that emergent and floating-leaved macrophytes may play an important role in enhancing water clarity due to increased grazing pressure by zooplankton migrating into the plant stands. As a consequence, especially in turbid lakes, the ecological role of these functional types of vegetation, and not merely that of submerged macrophyte species, should be taken into consideration.     

Zooplankton Composition,Diversity and Physicochemical Features of Bandam Kommu Pond,Medak District,Telangana, India

The present investigation aims to study the zooplankton composition, diversity along with physicochemical profile in a chosen pond at Medak district from December, 2010 to November, 2012. The study revealed the occurrence of 80 zooplankton species including 60 rotifers, 18 cladocerans and 02 copepods. Zooplankton density fluctuated between 119 and 26,463/L, diversity H′ = 0.89–2.68, species richness 5–21 and dominance 18.6–74.1 % over the 2 years study period. Rotifers were more predominant than other zooplankton communities, especially family Brachionidae and Lecanidae. High density of the overall zooplankton community was due to more rotifer population and the numerical dominance of the species Brachionus angularis, B. calyciflorus, B. caudatus, Keratella tropica, Filinia terminalis and Epiphanies mucronata. It was observed that the zooplankton density significantly correlates with pH values of the pond. Physicochemical profile of the pond shows tropical climate, hard water and alkaline in nature. Chloride content was found to be high may be due to the anthropogenic pressure and influx of sewage. The high content of phosphate and nitrate reveals that the pond is enriched with nutrients. This has significant correlation with zooplankton dominance. The present findings clearly indicates the eutrophication of the pond.