The role of predation in the regulation of freshwater communities is predicted to decrease along a habitat-duration gradient, from permanent to episodic waters. We tested the role of invertebrate predation in shaping the community structure in a fishless temperate intermittent pond with a three month long hydroperiod by comparing the community structure in two large field enclosures (4.2 m2) with added predators to two enclosures without added predators. The added predators reflected the density and composition of top predators in the pond and comprised weekly additions of dytiscid larvae (for three weeks) followed by weekly additions of odonate nymphs (for five weeks). Compared with the enclosure controls, the predator addition enclosures had fewer dipterans and crustaceans, higher concentrations of benthic ciliates and other protozoans, higher chlorophyll a and bacterial counts, and lower abundance of rotifers. Many treatment effects were temporally variable and this appeared to be linked to predator identity, predator size, and prey availability. Compared with the surrounding pondwater, the enclosed areas had lower abundance of molluscs, ostracods and cladocerans but higher abundance of cyclopoids and higher concentrations of phytoplankton and ciliates. Despite high productivity and seasonally variable predator and prey assemblages, which likely buffered against strong top-down control, we conclude that the top-predators regulate the dipterans and zooplankton in this intermittent pond and that the effects propagated down through the food web to lower trophic levels.

In the natural environment, microbial community structure of river biofilm is controlled by biotic and abiotic factors. This study explored the capacity to manipulate the structure of microbial communities by modifying environmental conditions during the course of biofilm development. River epilithic biofilm was cultivated in situ on artificial substrates placed parallel to river water flow. Substrates were incubated for 3 and 5.5 weeks in river to allow natural biofilm development, at two sites with contrasting physico-chemical characteristics. The first site (Auradé, Gers, France) was located in an agricultural watershed basin and the second site (Larroque, Haute-Garonne, France) was located in a forested watershed basin. After 3 weeks of biofilm development, a subset of substrates was collected from one site and transplanted to the second site where they remained for 2.5 further weeks. Epilithic bacterial community structure (at 3 weeks from each site and at 5.5 weeks from biofilms with and without transplantation) was assessed using PCR-DGGE of 16S rDNA fragment. Biofilm biomass was estimated using ash free dry mass (AFDM). After 3 weeks of development, biofilms from the two sites exhibited comparable AFDM values (average of 1.4±0.2 g.m-2). A difference between the two sites was observed after 5.5 weeks of development: AFDM decreased for biofilms from the agricultural watershed basin (from 1.4 to 0.18 g.m-2) as a consequence of grazing pressure (Bithynia), and increased for biofilms from the forested agricultural watershed (from 1.4 to 2.6 g.m-2). Microbial community analyses revealed a differentiated community structure between biofilms from the different sites and exhibited a change of microbial community structure after 5.5 weeks of biofilm development. These observations confirm a process of ecological succession in microbial communities. Changing the incubation site during biofilm development modified the trajectory of these ecological successions, suggesting that site characteristics mainly conditioned the structure of these microbial communities.

The aim of the study was to test the hypothesis that patterns of cross-Eurasian longitudinal distribution of lotic mayflies are determined by species' ecological requirements and the presence of the West Siberian Lowland. In particular, the objective was to test whether this great lowland is an environmental barrier preventing longitudinal dispersal of the rheophilic (i.e., preferring fast-running highland waters), but not the potamophilic (i.e., preferring slow-current lowland waters) mayflies, as its entire territory contains no rapidly-flowing streams suitable for rheophilic species. This hypothesis was tested indirectly by comparison of altitudinal ranges of species characterised by different cross-Eurasian distribution patterns (mainly East Palaearctic and Transpalaearctic species distributed over the Asian part of Palaearctica and entire Palaearctica respectively). The material used for the analyses was collected in the centre of Eurasia, south-western Siberia, Russia. The region covered both lowland and mountain territories. The studied biogeographical groups of mayflies have distinctly different altitudinal distribution: the Transpalaearctic species inhabit lowland watercourses only, while the East Palaearctic species inhabit the entire altitudinal range with most of the species preferring high elevations (on average 700 m a.s.l.). These results confirmed the stated hypothesis and showed that for most of the East Palaearctic (but not Transpalaearctic) species the West Siberian Lowland can be an environmental barrier preventing their westward dispersal and therefore precluding mixing of the East and West Palaearctic rheophilic faunas. However, possible alternative hypotheses cannot be ruled out, as altitudinal ranges of some of these species do not fall out of the elevation range of the West Siberian Lowland. Remarkably, the East Palaearctic species, which by definition have narrower distribution than the Transpalaearctic species, have broader altitudinal ranges than the Transpalaearctic species. This pattern is related to the altitudinal Rapoport effect recently detected for mayfly distribution over the river systems.

Oceanic islands freshwater systems are unique due to their volcanic origin, oceanic situation, catchment morphology and the presence of distinct freshwater communities when compared with continental systems. This study provides an update of Azorean chironomid fauna records, distribution data and includes biogeographical comments, based on collections covering a range of freshwater habitats on several islands over 2005 to 2008. Island species area-relationships or ISAR was performed as a descriptive model for species accumulation patterns in each island in relation to their area. Six new chironimid species records are given for the Azores archipelago: Orthocladiinae:Orthocladius (Eudactylocladius) fuscimanus (Kieffer, 1908), Pseudorthocladius (Pseudorthocladius) curtistylus (Goetghebuer, 1921), Synorthocladius semivirens (Kieffer, 1909), Parachaetocladius abnobaeus (Wülker, 1959); Chironominae:Chironomus (Chironomus) annularis (Meigen, 1818), Parachironomus tenuicaudatus (Malloch, 1915). As a result, the Azorean chironomid fauna has increased from 38 to 44 species, spread across 33 genera. Most recorded chironomids are primarily of western Palaearctic origin; Nearctic, Oriental and Neotropical regions are comparatively poorly represented. A checklist is provided, incorporating and updating previous records. Chirononidae distribution pattern among the islands is analyzed and island species area-relationship (ISAR) analyses, performed to provide a descriptive model for species accumulation patterns in each island, indicated a positive correlation between species richness (number of species) and the area of the Azorean islands, supporting MacArthur and Wilson’s equilibrium theory of island biogeography. Chironomidae could be promising for searching candidate bioindicators to answer the demand of Water Frame Directive.

Difficulties to simply transfer trophic cascade theory from temperate to tropical lakes are now well recognized. Many mechanisms trying to explain top-down divergences between these systems have been proposed, such as lack of key species of herbivorous zooplankton, absence of seasonality in fish reproduction, cyanobacteria development, or differences in fish foraging behaviour. Very few studies have considered bottom-up mechanisms, in particular differences in nutrient recycling and nutrient limitation between the two types of ecosystems. According to the ecological stoichiometry theory, fish-induced alterations of food-web structure could modify the efficiency of consumer-driven nutrient recycling by changing the relative biomass contribution of species in food webs. Consequently, by mostly considering top-down processes, one could underestimate consequences on nutrient availability for phytoplankton growth. In this paper, we compared the results of two mesocosm experiments carried out in temperate and tropical areas, each manipulating food-web structure via the presence or absence of fish. We found trophic cascades in both experiments, but differences between fishless and fish treatments were greater in temperate than in tropical systems. In the tropical experiment, the observed effects could not be supported by classical zooplankton community alteration or by cyanobacteria prevalence. Our results suggest a key contribution of fish nitrogen-excretion to phytoplankton growth in mostly nitrogen-limited tropical systems. Differences in stoichiometric response to food-web structure alteration between temperate and tropical lakes could thus represent a major difference between the two systems. Our study stresses the need for further studies that would allow robust generalization on the functioning of freshwater temperate and tropical ecosystems.

The benthic community of a braided reach of a lowland river was studied with the aim to identify functional habitats through the assessment of potential habitats. Functional habitats were defined considering physical and biological characteristics. Three reaches of the Chocancharava River (Córdoba, Argentina) were selected and six potential habitats were sampled during high and low water periods. Hydraulic and environmental variables were also registered in each sampling occasion. Taxonomic composition, macroinvertebrate abundance, richness, diversity and evenness were estimated for each identified functional habitat. TWINSPAN analysis was applied separately for two data sets (high water and low water period). This analysis showed that samples of the low water period were mainly grouped in relation to three habitats units: vegetated habitats, unvegetated habitats and habitats related to bars. These three habitats were considered functional habitats. The whole biological and environmental data sets were ordinated by Canonical Correspondence Analysis (CCA) showing a significant relationship between benthic assemblages and environmental variables. This analysis grouped samples in relation to the functional habitats identified by TWINSPAN and indicated that the most influential environmental variables explaining the ordination were: current velocity, depth, substrate size and cover percent of rooted emergent macrophytes. Faunal composition determined by CCA for each functional habitat was in agreement with the results obtained by the Relative Preference Index (RPI). Factorial ANOVAs showed that abundance, taxonomic richness, diversity and evenness were different among the functional habitats and that the community attributes were influenced by the effect of the hydrological period and habitat. As the functional habitat approach provides useful tools in management and river rehabilitation the use of this methodology may allow to develop more appropriate restoration strategies to be applied in altered lowland reaches.

We studied assemblages of littoral chironomids from three alpine lakes in the High Tatra Mountains (Slovakia) along an altitude range of 1725–2157 m. The study sites were selected in order to emphasize differences in their thermal regimes. Littoral samples were taken quantitatively in the ice-free seasons of 2000 and 2001. In total, 3468 chironomid larvae and pupae were collected and 32 taxa were identified. Some parameters of the littoral chironomid assemblages showed clear patterns along the altitude gradient. The number of taxa and Shannon diversity increased markedly with decreasing altitude. Density, however, did not show any correlation with altitude. Even though gatherers highly dominated in all sites, their relative abundance decreased with decreasing altitude. The ratio of scrapers and predators correlated negatively with altitude. According to the results of a Detrended Correspondence Analysis, Pseudodiamesa arctica and Micropsectra radialis were chosen as indicator species for alpine lakes >2000 m a.s.l. Typical subalpine lake inhabitants are Zavrelimyia sp., Prodiamesa olivacea, Corynoneura scutellata group, Cricotopus polaris, Micropsectra bavarica and Paratanytarsus austriacus. A single species, Micropsectra junci, seemed to be characteristic of alpine lakes <2000 m a.s.l. This “gradient lake concept” could be used to predict changes in mountain lake fauna under expected climate change scenarios. Generally, an upward shift of subalpine species would be expected. The thermal regime of lakes, however, also depends on several local factors. Consequently, the schemes outlined here would not be valid for the entire Tatra lake district.

In the present work, based on material from several localities in Brazil, we present a contribution to the taxonomy of the Terpides lineage, a monophyletic group of Neotropical mayflies that encompasses three genera: Terpides, Tikuna, and Fittkaulus. A new species of Terpides is described from the States of Espírito Santo and Mato Grosso, based on nymphs, male and female imagos. The male imago of the type species of Terpides, T. guyanensis, the nymph and male imago of Tikuna bilineata, and the nymph of Fittkaulus cururuensis are described for the first time.

The impact of repeated hydropeaking events was assessed in the Alpine stream Noce Bianco (Trentino, NE Italy). Three stations were selected, one upstream and two at 0.25 km and 6 km downstream from a hydropower plant which causes 7-fold discharge increases. We collected hyporheic invertebrates for two years. Taxa diversity and abundance were reduced in the impacted sites, especially affecting the stygobites, which were significantly less abundant at the impacted sites, whereas stygoxene invertebrates increased exponentially. Repeated hydropeaking events alter the physical-chemical characteristics of the hyporheic habitat, resulting in the recorded faunistic pattern. The deposition of the fine sediment transported by the turbinated water downstream of the power plant and the absence of natural peak floods which remove fine sediments, probably cause a reduction of the interstitial space interstitial habitat available to stygobitic taxa. Surface water natural thermal regime is altered by the hypolimnetic discharges, and such alterations propagate into the hyporheic, affecting the stenothermic taxa. Some benthic taxa used the hyporheic habitat as a refuge to avoid catastrophic drift during hydropower production operation. The main trophic roles represented in the hyporheic assemblages do not support an important role for biological interactions such as predation in determining the fine-scale patchiness of the hyporheos.

We studied the effect of point-source and non-point-source pollution on the retention capacity of the stream and its link with the metabolic state (primary production and respiration) and invertebrates assemblages in a third order Mediterranean stream. Two experimental sites were chosen: one in the upper part of the catchment (Montégut site) characterized by low concentrations in nitrate and phosphate and one in the lower part of the catchment (Lézat site) characterized by high nitrate and phosphorus concentrations. Both experimental sites were located on reaches that included a Waste Water Treatment Plant (WWTP) point nutrient source allowing discussion of the relative effects of point-source and non-point-source nutrients loads on ecosystem function (respiration and uptake rates) and aquatic organism assemblages. NH4 +-N, and PO4 3 −-P uptake rates were determined using solute additions conducted at constant rates (short-term nutrient addition procedure) and NO3 −-N uptake rates were determined using instantaneous solute addition (slug addition procedure). Rates of gross primary production (GPP) and ecosystem respiration were determined using the open system, two-stations diurnal oxygen change method. Benthic invertebrate communities were investigated for species and functional feeding groups diversities measurements. Results show that autotrophy in the river results from nutrients of two distinct origins: point sources for phosphorus (urban area and WWTP) and non-point sources for nitrogen (agricultural zones) with local additions from WWTP inputs. Comparison between the two sites shows that the WWTP did not affect uptake rates, respiration or primary production of the ecosystem in the low-nutrient Montégut reach despite increase of invertebrates communities biomass density. Inputs from the WWTP, in the high nitrate and phosphate Lézat reach, increased respiration, lower benthic biomass and led to changes in the species composition and did not affect uptake rates.

Cyanobacterial blooms cause extensive ecological damages in aquatic environments. Heterotrophic nanoflagellates (HNF) play an important role in controlling the populations of cyanobacteria in natural water bodies. In this study, we report a HNF, NF-WJ05, which grazes efficiently on the toxic cyanobacterium Microcystis aeruginosa strain PCC 7806. The morphological characteristics of the nanoflagellate observed by optical microscope and confocal microscope showed that NF-WJ05 could be a Paraphysomonas. The sequences of the internal transcribed spacer (ITS) regions of rDNA including the 5.8S rDNA region was determined and compared with sequences available in databases. The 5.8S rDNA sequence showed a high degree of similarity to those belonging to species of Chromophyta. However, sequences similar to that of its ITS were not found in the databases. Several environmental factors affecting the grazing efficiency of NF-WJ05 on cyanobacteria were evaluated. The more suitable conditions for grazing were 30°C and pH 5.0 with stirring. Ammonia inhibited the grazing, whereas low concentrations of phenol increased the grazing rate with an optimal concentration at 50 µg.L-1.

In the present paper, based on the rearing of nymphs in the field, we present for the first time the description of the adult stage of Rivudiva Lugo-Ortiz and McCafferty and of its type species, R. minnatena Lugo-Ortiz and McCafferty. Adults of Rivudiva can be distinguished from the other genera of Baetidae by the following combination of characters: (1) hindwings present or absent, when present with two longitudinal veins and with costal projection pointed, placed in the basal fourth of anterior margin; (2) forceps three-segmented, segment III long, about 2× as long as wide; (3) distal margin of subgenital plate with small pointed projection. Besides that, R. coveloae (Traver, 1971 [Proc. Entomol. Soc. Washington, 73, 58–63]), new combination, and R. venezuelensis (Traver, 1943 [Bol. Entomol. Venezolana, 2, 79–98]), new combination, are proposed based on the characteristics listed above, specially the distal margin of subgenital plate with a small pointed projection. Comments on the biology of the nymphs are also provided.

The changes in the dynamics of cladocerans in Lake Vela (Portugal), as well as the morphologic and life history traits of the small-bodied cladoceran Ceriodaphnia pulchella, were studied intensively during one month characterized by deep and fast changes in the phytoplankton community: the beginning of the cyanobacteria dominance. Lake Vela, located in the Mediterranean region, is a polymictic shallow lake exhibiting characteristics typical of an advanced trophic status, namely the permanently turbid water, the reduction in biodiversity and the occurrence of cyanobacteria blooms. The density and composition of the cladocerans populations varied considerably during the short-term period analyzed. Coincident with the increase of cyanobacteria, the density of Daphnia longispina decreased drastically, associated with an increase of Bosmina longirostris and Chydorus sp. The constant density of C. pulchella, even during the cyanobacteria dominance, and the strong relationship found between weight and size, suggests that the low quality of phytoplanktonic food in Lake Vela did not play an important role in its fitness. Besides the small size of C. pulchella, this fact could be also related to its diversified diet. Nevertheless, a closer examination of the life history parameters of C. pulchella revealed a reduction in the fecundity, size at first reproduction, mean size of ovigerous females and maximum size of the population, which suggest an increase of the fish pressure after the decline of Daphnia. C. pulchella showed also a short-life cycle and a fast turnover of individuals, which constitutes also an advantage, allowing a fast adaptive response of the population.

We characterized phytoplankton community succession at different depths of a shallow hypertrophic reservoir in relation to physical and chemical environmental variables. The phytoplankton community was sampled biweekly at three different water depths (surface, middle and bottom) in the reservoir from November 2002 to February 2004. A range of 18 environmental variables including temperature, electrical conductivity (EC), total phosphorus (TP) and total nitrogen (TN) were measured to assess their influence on phytoplankton community succession. As well, combined multivariate analyses with a cluster analysis and a nonmetric multidimensional scale (NMDS) were conducted. Microcystis aeruginosa was the dominant species in all seasons except spring. Thus, Cyanophyceae was a dominant taxonomic group. In spring, Bacillariophyceae dominated, followed by Cryptophyceae and Chlorophyceae. The succession was relatively delayed at the middle and bottom layers compared with at the surface layer. Abundance and species richness of phytoplankton were also higher in the surface layer than in the bottom layer. Cluster analysis classified the phytoplankton community into four clusters at each depth, and the changes were also well reflected in the NMDS ordination. Each cluster showed seasonal patterns characterized by indicator species, as well as environmental variables such as temperature, conductivity, and nutrients including N and P. Seasonal dynamics of the phytoplankton community was the strongest at the surface layer and weakest at the bottom layer. These depth-variable environmental variables are likely to be the key factors driving changes in the phytoplankton community composition.

Performance of the prescribed gear of the European Standard (i.e. 1.5 m deep Nordic gillnet) was compared with gillnets deep enough to cover the whole water column (WWCG) for characterizing fish assemblages in a large and shallow lake (Lake Balaton, Hungary). Differences in species number, relative abundance and biomass, and length distribution of fish were examined in both inshore and offshore habitats of the lake. Nordic gillnet samples provided comparable information to that of WWCG for both species richness and abundance and biomass of benthic species. However, substantial differences were found between the two net types in the representation of pelagic fish species (i.e. bleak, razor fish and asp). Overall, the WWCG provided different information with more precise (less variable) data on fish assemblage structure than the Nordic gillnet. Results suggest that identification of neither horizontal nor vertical gradients in within lake fish assemblage structure can be guaranteed with the Nordic gillnet alone even in such shallow lakes, like Lake Balaton. It was concluded that benthic Nordic gillnet samples should be complemented with information on fish occurring in the upper water layers (i.e. pelagic species) even in very shallow lakes either by using pelagic or floating gillnets or by whole water column gillnetting.

The macroinvertebrate fauna of twenty-one ponds (thirteen temporary and eight permanent) located in four protected areas in Central Italy were studied in March, May and June 2002, with the aim to bring out relationships between environmental variables and the functional characteristics (functional feeding groups, habits and resistance to drought) of communities. Macroinvertebrates were collected in three mesohabitat types (macrophyte beds, littoral sediments, central sediments). Overall, the functional attributes of temporary and permanent pond communities did not differ greatly. However, at the mesohabitat scale, collector-gatherers, burrowers and permanent residents capable of passive dispersal were more abundant in sediments. Scrapers and shredders, sprawlers and climbers, swimmers and divers, and organisms capable of active dispersal which lack drought resistance were more abundant in macrophyte beds. Although hydroperiod is the main driving factor affecting community structure, our results suggest that it remains an unimportant factor in controlling functional traits, which appeared to be more influenced by substratum types. Moreover, the positive relationship between taxonomic and functional diversity metrics indicates that an increase in taxonomic richness induces a satisfactory partitioning of the ecological resources among taxa, thus maintaining the ecological complexity of the ponds regardless of their hydroperiod length.

The testate amoebae communities living among different species of mosses in Sphagnum peatlands in eastern Poland were studied. Sampling was done on a monthly basis from April to November 2005-2007. To assess the importance of the vertical distribution of testate amoebae within the mosses, each sample was cut into two parts: the upper living part (1-5 cm) and the lower dead part (5-10 cm). The highest species richness occurred in hollows dominated by Sphagnum angustifolium, Sphagnum flexuosum and Sphagnum palustre. Lower numbers of taxa were observed in hummocks dominated by Sphagnum magellanicum, Polytrichum strictum and Polytrichum commune. There was a distinct horizontal micro-zonation of the abundance of testate amoebae occurring among Sphagnum mosses, but only a small difference ascertained among Polytrichum. The number of testate amoebae was significantly greater in the deeper samples. The results demonstrated that depth to water table, pH and total organic carbon can strongly regulate the abundance and taxonomic composition of testate amoebae.

We studied the spatiotemporal trends of Eragrostis curvula (Schrad.) Nees in a flood meadow of a regulated river. The response variables, including the abundance of colonies, colony sizes, flowering spikes, biomass and root structure were checked against a set of environmental variables. These variables included distance from the river, substrate conditions (stony to sandy), soil nutrients (total nitrogen, phosphorous and calcium) and soil moisture. Relationships were evidenced using redundancy analysis. Response variables were found to be distinctive and based on substrate conditions (i.e. stony or sandy). The variables ‘distance from the river’ and ‘soil phosphorous’ contributed significantly to the overall variance. Stony habitats were observed to have lower soil nutrient levels and were characterised by monospecific stands of E. curvula, while the high nutrient levels of sandy habitats promoted heterogeneous herbaceous vegetation growth. Primary production, especially belowground, was measured to be significantly higher (t-test, P<0.05) in stony habitats. Spatiotemporal trends suggested that, irrespective of the number of colonies, E. curvula demonstrated significant levels of adaptation to micro-environments through biomass allocation and the morphological plasticity of its roots. The study results suggest that river regulation and the subsequent reduction in the frequency of inundation, in addition to the reduction of nutrients and fine sediment supply downstream, give a competitive edge to E. curvula over other herbaceous species.

The spatial and temporal distribution of zooplankton and environmental parameters in Kasseb, Mornaguia and Ghdir El Goulla reservoirs (North of Tunisia) were studied monthly from July to December 2002 in order to establish seasonal patterns, biotic and abiotic relationships for these reservoirs. In Kasseb reservoir, the zooplankton community was dominated by Acanthocyclops sp. (37.3% of total zooplankton density) and Bosmina longirostris (32.6% of total zooplankton density). In Mornaguia and Ghdir El Goulla, Copidodiaptomus numidicus was the most abundant species with 62.1% and 97.5% of total zooplankton density respectively. Our study indicated that the zooplankton community of Ghdir El Goulla reservoir was influenced by the impact of internal environmental factors and artificially introduced water from the two Kasseb and Mornaguia reservoirs. Highest density of zooplankton species was recorded in Kasseb reservoir, which indicated an increased tendency for eutrophication. Mornaguia and Ghdir El Goulla are oligo-mesotrophic reservoirs. Understanding the relationship between the zooplankton community and temporal distribution is important for the understanding of trophic interactions within these reservoirs.

The population dynamics of the red swamp crayfish (Procambarus clarkii Girard, 1852) was studied from May 2005 to May 2006 in a pond (PCD) subjected to drought between June and December and in a continuously flooded rice field drainage channel (PMG) located in the Tejo river basin, Portugal. The proportion of females in the population was not independent from the season and was negatively correlated with both female and male maturation status. Male and female maturation was synchronous but males remained in a reproductive form after recruitment while females reverted quickly to lower maturation indexes. At PCD and PMG, respectively 2 and 5 cohorts were detected by modal analysis. Large crayfish were abundant in spring, summer and early autumn and juveniles were abundant in autumn, especially at PCD. Crayfish density at PCD was lower than at PMG and mortality rate (Z) was 3.99 at PCD and 2.43 at PMG. The average lifespan of the crayfish populations was 91 days at PCD and 150 days at PMG. Our study indicated faster growth and larger maximum sizes at the site with the more stressed environment and lowest relative crayfish densities (PCD), suggesting that any exploitation or control strategies for these two populations should consider management of the hydroperiod and of maximum crayfish densities.