We explored the spatial and temporal variability of benthic macroinvertebrate communities (density, taxon richness, evenness and taxonomic composition) in a tropical Panamanian stream that is potentially affected by organic and chemical pollution resulting from human activities. As predicted, pristine headwaters of Site 1, located within the Altos de Campana National Park, showed the lowest macroinvertebrate densities, suggesting an increase in pollution-tolerant taxa at downstream sites located near human settlements and agricultural land. Moreover, Site 1 had higher accumulated taxon richness than downstream sites (except Site 5), although evenness was higher at Site 3. Density and taxon richness were higher and more variable in the dry season, while evenness was only higher in the dry season at Site 1. Multivariate analysis showed that the fauna responded to a natural longitudinal gradient, but there was also a strong water quality signal associated with human settlements. Community composition was related to abiotic variables commonly associated to pollution, such as alkalinity, dissolved solids, phosphates, and total organic carbon.

This work represents a concerted effort aimed at understanding the microbiological and chemical evolution of a small boreal lake during the diurnal cycle of photosynthesis. We studied diurnal variation of ∼40 dissolved macro- and trace elements, organic carbon and bacterial population dynamics in the surface and bottom water layer of the shallow Vilno Lake in the White Sea basin. Four-days continuous measurements with 6 h sampling steps both at the surface (0.5 m) and on the bottom (4.0 m depth) during no-bloom periods revealed constant concentrations (within ±20–30%) of all major elements (Na, Mg, Si, K, Ca), organic and inorganic carbon and most trace elements (B, V, Cr, Fe, Cu, Ga, As, Rb, Sr, Y, Zr, Sb, Cs, Ba, all REEs, Hf, Pb, Th, U). At the same time, the concentration of some biologically important trace metals (Mo, Mn, Co, Cd) was subjected to variations partially reflecting the change of bacterioplankton concentration. This work enables two types of element behavior to be distinguished during photosynthesis in the water column – constant concentration and sinusoidal variations – depending on their speciation in solution and their affinity to aquatic microorganisms.

Four experiments were serially carried out conducted to study foraging activity in the freshwater gastropod Lymnaea stagnalis in the absence and presence of predators (crayfish or fish) under daylight and in the dark. The snails were either parasitized by digenean trematodes (Diplostomum pseudospathaceum or Plagiorchis elegans) or remained unparasitized. The snails had an evident circadian foraging rhythm: they preferred diurnal foraging notwithstanding the predators and parasites. However, the snail's parasite status and the predation risk had an interaction effect on the number of feeding events per snail individual so that especially the snails parasitized by D. pseudospathaceum were more active in the presence of a fish predator than in the absence of predators. Some of the snails responded to cues from a crayfish predator by crawling out of the water. The results suggest that D. pseudospathaceum may be capable of manipulating the behaviour of its first intermediate snail host in ways that enhance its success of transmission to the parasite's second intermediate fish host. The results also indicate that the effects of biotic stressors, such as predation risk and parasitism, on the foraging pattern in the snails L. stagnalis may be interactive and highly specialized rather than generalized.

Nitrogen stable isotope composition (δ15N) of particulate organic matter (POM) has been used to infer dominant nitrogen cycling processes in lakes. However, very few studies have compared the isotope variations in lakes along trophic state and other biogeochemical gradients. Here we report an analysis of δ15NPOM and selected environmental variables from 96 subtropical lakes to assess the patterns and controls of isotope variations. Results indicate that δ15NPOM values varied from −2.8 to 13.2‰ and were not significantly correlated with total phosphorus (TP), total nitrogen (TN) and chlorophyll a (Chl a). The 15N depletion in POM was found across the entire trophic gradient and likely reflected contributions from planktonic nitrogen fixation. The 15N enrichment was attributed to high primary production and the contributions of anthropogenic wastes in eutrophic lakes, and the presence of microzooplankton in the water samples of the oligotrophic lakes. The δ15NPOM was negatively correlated with water color and positively correlated with pH. Because water color is indicative of light availability which affects phytoplankton growth and pH is significantly correlated with Chl a concentration in the study lakes, the close relationship between water color, pH and δ15NPOM therefore suggests primary productivity-driven isotope fractionation. Results from this study did not reveal the importance of trophic state, nitrogen concentration and surface area to the variations of δ15NPOM and points to the complex interactions of nitrogen cycling processes in lakes with diverse biogeochemical features.

We assessed the effect of small dams on stream habitats and on the structure and function of benthic macroinvertebrate communities in mountain streams of Córdoba, Argentina. Two streams with small dams (impacted streams) and two streams without dams (control streams) from the Carcarañá River upper sub-basin were selected. Dominant hydraulic units were identified and benthic samples were collected in each of these units during high and low water periods. According to this study small dams may have impact on the function and structure of the invertebrate community, though hydraulic habitats would not be affected. Fourteen hydraulic units were found and changes due to dams were not observed as assessed by the detrended correspondence analysis. The canonical correspondence analysis grouped samples mainly in relation to hydraulic habitats whereas TWINSPAN grouped samples according to the presence of dams. Nested ANOVAs showed changes in richness and diversity, in the abundance of filterers and shredders and in the abundance of certain species. Small dams generate quite small reservoirs and their permeability may be greater than those of large dams. The behaviour of macroinvertebrate populations in drift and colonization processes, the continuity of the riparian structure and the discharge of planktonic algae downstream the dams may be some factors determining the ecological changes produced by small impoundments.

Using field experiments, we investigated the effects of fish carcasses (so called ‘food falls') on benthic fauna. We simulated food falls using freshly killed fish during two different seasons (spring and summer) in the littoral zone of a large, pre-alpine meso-oligotrophic lake in central Europe (Lake Constance, Germany). This study provides evidence that input in the form of fish carcasses may play an important role in nutrient dynamics within this ecosystem. The benthic communities in the vicitinity and underneath the food fall were strongly influenced by the food fall. The results show that this supply of organic matter has a significant influence on the relationships within the communities, which are clearly dominated by bacteria, followed by copepod nauplii, cyclopoid copepods, chironomids, and ostracods. Total decomposition was obtained between days 80 and 68 of the experiments. The food fall had a positively but not significant effect on meiofaunal assemblages in these experiments. Furthermore, the results showed a negative relationship between bacteria and meiofauna abundance, indicating grazing by the meiobenthos on the bacterial community. These findings support other studies that found that the meiofauna exerted a grazing pressure on the microbial community, where this process was important in the decomposition of carcasses. Moreover, this study shows the potential importance of fish carcasses in Lake Constance, where food falls may generate high abundances and diversity of the benthic fauna and support high bacterial activities in this littoral ecosystem.

The biomass and composition of the phytoplankton was studied at seven sampling stations located at different water bodies (open water, inner pond and canal) of a large, shallow turbid lake (Lake Fertő, Neusiedlersee). The open water was characterized by picocyanobacteria and meroplanktonic diatoms, the artificial canal by epiphytic diatoms, cryptophytes and chlorophytes. The inner ponds, based on the phytoplankton composition, were positioned between these water bodies. High picoplankton abundance (>106 cells.mL−1) and predominance (up to 80% contribution to the total phytoplankton biomass) were detected in the open water and the inner ponds, which was hypothesized to be the result of the turbid environment by the suppression of the top down control and by light-limitation. Information on the diversity of the picoplankton in the open water of the lake has been presented first time in this study. Based on molecular analysis (16S rRNA gene and cpcBA-IGS region) the dominant group of picocyanobacteria belonged to the Cyanobium gracile cluster (group A) of the picophytoplankton clade in April. Members of two other picocyanobacterial groups (group B and C) were also detected.

Plant litter breakdown, an important process for energy and matter flows in freshwater ecosystems, has been extensively studied except in the karst (and calcite depositing) habitats. The aim of this paper was to answer three questions regarding the breakdown of leaf litter in calcite depositing environment: (i) Does leaf decomposition hinder calcite deposition and vice versa?; (ii) What role do other environmental factors play?; and (iii) How long does leaf litter persist in these habitats? Leaves of beech (Fagus sylvatica) and butterbur (Petasites hybridus) were exposed for 8 weeks in 8 microhabitats: 2 calcite deposition rates × 2 flow velocities × 2 seasons. A linear model was better at predicting leaf litter persistence but only for the period after the extreme loss of leaf mass occurring during the initial leaching of highly hydrosoluble compounds in the first week (11.6% of beech and 54.2% of butterbur regardless of the studied environmental factors). Higher flow velocity and calcite deposition rates stimulated the breakdown of both leaf species. During summer, breakdown was accelerated for butterbur leaves only. Since breakdown rates of both litter types were faster at high calcite depositing sites, it can be concluded that the breakdown process is not hindered by calcite deposition in general. The amount of deposited calcite per gram of leaf litter increased linearly over time (after the first week of exposure) on both leaf species. More calcite was deposited on the fast-decomposing butterbur leaves than on beech leaves.

Aerobic anoxygenic phototrophic (AAP) bacteria are widely distributed in marine and freshwater ecosystems. The aims of this study were to investigate the diversity and abundance of AAP bacteria in cyanobacterial bloom-forming eutrophic lakes and to study the association of AAP bacteria with the bloom-forming cyanobacteria. Analysis of pufM gene (the light-reaction center gene) clone libraries indicated that in eutrophic lakes (Lake Taihu and Lake Chaohu, China) with cyanobacterium Microcystis blooms, the AAP bacteria were related to members of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. In Lake Taihu and Lake Chaohu, Alphaproteobacteria accounted for 81.5% and 75.0% of Microcystis-associated AAP bacteria, respectively, and 84.6% and 72.5% of free-living AAP bacteria, respectively. The predominance of Alphaproteobacteria in the two lakes was different from the previously reported predominance of Betaproteobacteria in freshwater lakes. Quantitative real-time PCR analysis indicated that in Lake Taihu and Lake Chaohu, AAP bacteria represented an important part of the bacterial community associated with Microcystis, and the abundance of Microcystis-associated AAP bacteria (18.3% and 11.7%, respectively) was higher than that of free-living AAP bacteria (5.1% and 7.9%, respectively). The abundance of AAP bacteria in the two bloom-forming lakes was higher than the previously reported level in other eutrophic freshwater bodies.

Studies in tropical streams are relatively few, and one of the still-unresolved methodological issues is sample size. Adequate sample size for temperate streams cannot be extrapolated for tropical sites, because of the differences in species richness and the proportions of rare species. We evaluated reliable sample size for estimation of resemblance among samples of macroinvertebrate assemblages inhabiting riffles of tropical streams, using the autosimilarity approach. Sample sizes were much larger than those currently employed in tropical studies. Sampling units consisted of individuals associated with single stones (15–20 cm). Evaluations employed the Bray-Curtis index for abundance data and the equivalent Sorensen index for presence-absence data. Autosimilarity curves were constructed using both sampling units and individuals. The estimation of resemblance among samples was strongly dependent upon sample size at reduced sampling effort, particularly for the Bray-Curtis index. For the same sampling effort, fixed counts of individuals obtained randomly from sampling units gave better estimations of resemblance, and their similarity curves tended to stabilize earlier than those using sampling units. A minimum of 9–15 sampling units (stones) or 150–850 individuals is necessary for adequate estimations of resemblance using presence-absence data, and 13–18 sampling units or 750–1550 individuals are required for relative abundance data in tropical streams.

Colonization of incubated wood samples by invertebrates and biofilm was compared between a lowland and an upland stream over a 15 month period. Invertebrate densities increased during the first weeks of incubation and then decreased to rather stable densities during the remaining investigation period in both streams. Within the first incubation weeks invertebrate numbers were significantly higher in the lowland stream. Higher dissolved nutrient concentrations and water temperatures accelerated initial epixylic biofilm development in the lowland stream. Lowest invertebrate numbers on incubated branches in the lowland stream coincided with increased discharge. Extreme low flows in the upland stream resulted in lowest invertebrate numbers on incubated wood during the study. Temporal patterns of biofilm and invertebrates indicated some interactions, but statistical significance was low, which might be caused by the variety of interacting effects. Additionally, invertebrate assemblages of in-stream wood samples were collected from four lowland and four upland streams to examine differences of epixylic invertebrate assemblages between the two stream types. Invertebrate densities were significantly higher on submerged wood from lowland streams than wood from upland streams. However, no clear differences in invertebrate assemblages found between the stream types. The study results show that introduced wood in lowland and upland streams is rapidly colonized by aquatic invertebrates and provided an attachment site for biofilms. Invertebrate numbers during the first two months of incubation significantly overestimate the invertebrate numbers found on resident in-stream wood in lowland and upland streams. Analyses of taxonomic composition of wood-inhabiting invertebrate assemblages from natural wood from lowland and upland streams revealed that each stream displayed a rather specific epixylic fauna.

Resource availability influences the flow of energy through food webs, thus affecting biomass and trophic structure of consumer communities. To assess the effect of availability of allochthonous (leaf litter) and autochthonous (periphyton) resources on the trophic structure of macroinvertebrates, we sampled monthly for a year two sites (upstream forested, downstream open canopy) of Challhuaco, a low order mountain stream in the Patagonian Andes. Leaf litter and periphyton dynamics showed the expected pattern, peaking in autumn and spring, respectively. Temporal variations of shredders and scrapers were synchronized, with the logic delay, with resource abundance. Although leaf litter mass was similar at both stream reaches, shredders were more abundant at the forest site. Periphyton biomass was higher at the forest, while scrapers were more abundant at the open site. The patterns of resource and consumer abundance, and community functional structure were mostly explained by the interaction of abiotic factors and trophic relationships.

Though much is known about freshwater snail ecology, their circadian rhythms remain poorly investigated. Well-fed, stress-free, mid-size adults of six species common in central Italian lakes were exposed to natural sunlight and photoperiod, and their activity status was recorded at 3-h intervals during a 9-d indoor experiment. All species exhibited evident diurnal habits despite high individual variability, with midday-to-early-afternoon activity peaks. Activity was correlated with diel light conditions but not with short-term changes in albedo. The prosobranch Bithynia (=Codiella) leachii and the pulmonates Physa (=Physella) acuta and Planorbis planorbis were the most active species and exhibited the longest-lasting response to daytime food addition. The prosobranch Valvata piscinalis exhibited long periods retracted in its shell with the operculum shut, and the remaining taxa (the pulmonates Galba (=Lymnaea) truncatula and Radix (=Lymnaea) auricularia) exhibited an intermediate degree of activity. P. acuta was the most active species at night and exhibited the quicker response to nighttime food addition. Alertedness to (diurnal) predators may be highest for the highly active P. acuta and P. planorbis, whose antipredator defenses are mainly behavioral. Diel activity patterns and other ecological characteristics suggest that P. acuta may be favored in food-rich habitats, while V. piscinalis may not be able to fully exploit food resources, especially if in limiting quantities. All snail species – and P. acuta in particular – may stimulate periphyton metabolism while keeping its biomass low by grazing mainly during the time of maximum photosynthesis.

This study investigates a phytophylous community of Chironomidae larvae on the submerged plant species Myriophyllum spicatum L. in a eutrophic lake (Lake Sakadaš, Danube floodplain area in Croatia) during summer 2004. This macrophyte species appeared for the first time in the lake in 2004, lasted approximately three months and was considered as a temporary habitat. The chironomid community was very abundant in the stands of this macrophyte species, which developed at three sites. The recorded species belong to three subfamilies: Chironominae (Chironomini and Tanytarsini), Orthocladiinae and Tanypodinae. Species composition varied in time, though Orthocladiinae with their representative Cricotopus sylvestris gr. dominated throughout the entire sampling period, accounting for approx. 60% of the total community. However, the presence of this species group experienced a marked drop to only 10% in September when Chironomini larvulae and Paratanytarsus sp. prevailed. Furthermore, the share of Endochironomus albipennis (Meigen 1830) in relation to other species was also consistently higher. NMDS ordination and cluster analysis separated three main colonization periods based on larval abundance. RDA analysis indicated the influence of environmental variables, especially Secchi depth, macrophyte dry weight, depth and water temperature, on chironomid community structure.

Daphnia longispina (O. F. Müller 1785) and Daphnia cucullata (G. O. Sars 1862), despite coexisting in similar densities in the lake, showed different demographic cycles. To search the causes of such variances between the two Daphnia, selected population parameters (density, body proportions, reproductive output) were correlated with the density of five dominant and potentially competitive species of Cladocera. The same parameters were estimated in relation to predation pressure of vertebrates (planktivorous fish) and invertebrates (Leptodora kindtii (Focke 1844)). The obtained results show that competition had no apparent impact on life-histories of Daphnia. Different strategies of the two Daphnia resulted from the uneven effect of invertebrate and vertebrate predators. D. longispina that was affected by planktivorous fish and Leptodora kindtii invested in reproduction and carried big egg-clutches. D. cucullata, which was insignificantly influenced by fish, displayed low reproductive output but changed their body proportions in the process of cyclomorphosis when occurring with L. kindtii. Other life-history trade-offs altered during the year, in accordance with the intensity of predation pressure.

Complete inventories of the fauna at a given place, for a specific community or geographical area are often exceedingly hard to get. In recent years a number of estimation techniques have emerged that can be used to extrapolate from these samples to the true number of species in an area. These estimation models are based on different mathematical approaches and can be classified as either species accumulation curves or nonparametric estimators (Brose et al., 2003, Ecology, 84, 2364–2377). In this paper, we have tested the performance of some of the richness estimators on nineteen mountain ponds in Castilla y León (Spain) in order to provide guidance on their potential use in future researches. We collected benthic macroinvertebrate of these ponds from the littoral zone with a pond net by kicking and sweeping. Ten-second samples were collected in each pond up to a total time of 3 to 5 minutes per pond, depending on the pond size. In addition, two of the ponds, were sampled in 2004, 2006 and 2007 providing a three-year time series. The results of this study showed that Jackknife 2 was the best of the evaluated methods based on all chosen criteria and also performed well across all studied ponds. Jackknife 1, Chao 1 and Chao 2 also presented good results and they were inferior to Jackknife 2 mainly because of the requirement for larger sub-sample sizes.

Largemouth bass, Micropterus salmoides, have inhabited Lake Biwa in central Japan for over three decades as top predators. Lake Biwa consists of two basins – a large, deep north basin and a small, shallow south basin. Since the mid 1990s, vegetation and bluegill sunfish, Lepomis macrochirus, have thrived in the lake – especially in the south basin. Because dense vegetation can mediate the predator-prey relationship between largemouth bass and bluegill, the largemouth bass in the south basin are assumed to be under less favorable conditions than those in the north basin. The length-weight relationship of the largemouth bass in the two basins differed; the body weights of largemouth bass in the north basin significantly exceeded those in the south basin. Moreover, largemouth bass in the south basin appeared to have significantly larger gapes than those in the north basin. Such fish in the south basin were likely selected during and after the ontogenetic diet shift stage, probably because they are capable of handling bluegill more efficiently than those with normal-sized gapes.

Cross-transplantations of Omphiscola glabra between two French departments (Haute-Vienne and Indre) were carried out to study snail settlement in these new sites during six years and to determine if this snail species was well adapted to its local parasites (Fasciola hepatica and Paramphistomum daubneyi). Local snails placed in new sites for each department were used as controls. In Indre furrows, the number of adults per population and the area of each habitat peaked on the third year post-introduction. Similar findings were also noted in the Haute-Vienne furrows occupied by local snails but peaks were only observed on the fourth year. In contrast, in Haute-Vienne sites populated by introduced snails, there was a progressive decrease in snail abundance and habitat area from the second year. The local O. glabra transplanted in Haute-Vienne kept their same degree de susceptibility to F. hepatica and P. daubneyi, thus demonstrating a good adaptation of these snails to their parasites. In other groups of transplanted snails, the first natural infections were only noted from the second or third year post-introduction and their prevalence progressively increased over time. Local adaptation of these latter snails to parasites would be more progressive in time and would stretch over several snail generations.

Potamogeton perfoliatus readily adopts different morphological forms, and is therefore especially suitable for investigating variations of aquatic plants' morphology according to different environmental conditions. This paper discusses the morphological diversity of P. perfoliatus at different sites in Lake Balaton, where it occurs as one of the dominant species. We measured 11 morphological variables which were analyzed statistically within the environmental gradients present in the Lake (gradients in trophic condition, water depth and in wave exposure). We found morphological differences between the plants growing on the southern shallow shore which is more exposed to waves and those growing on the northern, deeper and sheltered shore as well as differences along the trophic and the water depth gradient. On the northern shore plants were significantly longer, their internodes were longer and their leaves were relatively thinner (greater Standard Leaf Area). Plants were larger in the more nutrient rich western basins of the Lake and also showed morphological changes along the water depth gradient. The different degrees of wave exposure probably interact partly with trophic differences due to lake morphology. However, we proved that modifications in plant morphology, of which some might be adaptive and therefore of importance in a changing environment, do occur in the common, submerged macrophyte P. perfoliatus in Lake Balaton.

Three new freshwater ameirid species were discovered in the Western Australian subterranean habitats and described in this paper. They all proved to belong to the genus Nitocrellopsis Galassi, De Laurentiis & Dole-Olivier, 1999, representing the first record of this genus in Australia. Nitocrellopsis operculata sp. nov. was collected in 2003 in the Pilbara region, during the Pilbara Regional Survey, led by the Western Australian Department of Environment and Conservation (DEC). It can be distinguished from all other congeners by the reduced armature of the antennal exopod, which is an autapomorphic feature. Also, no other species of Nitocrellopsis has cuticular windows on prosomal or urosomal somites, or six elements on the third exopodal segment of the second leg. Nitocrellopsis halsei sp. nov. and N. pinderi sp. nov. are sister-species, collected in 2007 in the neighbouring Yilgarn region, by the private environmental consulting company Bennelongia Pty Ltd. Numerous morphological similarities include somite ornamentation, armature patterns of the swimming legs and the fifth leg, as well as the shape and armature of the antennula, antenna and almost all mouth appendages, while the main differences between the two are observed in the body size and habitus appearance, caudal rami shape and size, presence/absence of large lateral pores on the fourth pedigerous somite, number of spinules on the anal operculum, number of setae on the madibular endopod, and shape of the exopod of the fifth leg. Although they differ from any other congener by a combination of characters, no significant autapomorphic features were observed. In order to find a more natural allocation of these three species, a cladistic analysis is performed on all current members of Nitocrellopsis and three outgroup taxa, based on 45 morphological characters. The resulting cladogram shows that the ingroup is well defined by at least four synapomorphies, but the Australian species from the two regions are only remotely related to each other, showing the importance of looking at small-scale patterns when inferring Gondwanan biogeography. Three sister-species pairs are recognized in the genus and a key to all 12 members is provided.