The Asian clam Corbicula fluminea is one of the most invasive species in freshwater aquatic ecosystems. The rapid growth,earlier sexual maturity, short life span, high fecundity and its association with human activities makes C. fluminea anon-indigenous invasive species likely to colonize new environments. This species, originally distributed in Asiatic ecosystems,is now a common inhabitant of American and European freshwater habitats. The present paper reviews the information related tothe life cycle, ecology and potential ecological and economic impacts caused by C. fluminea in the invaded habitats.Furthermore, this paper also proposed future works that may be implemented in order to increase our general knowledge aboutthe ecology of this bivalve.

Organisms belonging to the green algal genera Desmodesmus and Scenedesmus are characterized by a high degree of flexibility allowing them to be true cosmopolitans and to withstand harsh conditions. The environmental conditions determine which phenotypes are being produced and one of the most dangerous situations for the algae is when the organisms are confronted with strong grazing pressure from numerous zooplankton organisms. An overview is given of several aspect of an induced defense in many non-spiny Scenedesmus and some spiny Desmodesmus that may form typical protective eight-celled colonies to avoid mortality from numerous grazers. The morphological response does seem to be linked with a herbivorous zooplankton chemical cue, rather than to a more general animal excretory product. The grazing activity of small sized grazers is reduced, but not of large Daphnia. However, arguments are given why grazing protection of colonial Scenedesmus is probably more efficient under natural than under carbon/light limited laboratory conditions. Finally, a life-history cycle of Desmodesmus and Scenedesmus is presented in which biological aspects such as the anti-grazer response and sexual reproduction are being included.

The green alga Chlamydomonas reinhardtii usually occurs in cultures as single, biflagellated cells. However, C. reinhardtii isknown for its ability to form gelatinous and palmelloid stages that arise as a result of an interaction with its environment.Exponentially growing unicellular C. reinhardtii formed palmelloid colonies rapidly within 25 h when cultured together withtheir enemy the rotifer Brachionus calyciflorus. Consequences of palmelloid formation for population dynamics of both C. reinhardtiiand B. calyciflorus were examined in continuous flow systems. Palmelloids were only formed in a one-stage systemwhere B. calyciflorus grazers and C. reinhardtii prey were cultured together, but not in a two-stage system in which mainly unicellularC. reinhardtii was pumped into a rotifer culture placed in darkness. The rotifer abundance was lower and the algal biomasshigher in the one-stage system compared to the grazing unit of the two-stage system. Inasmuch as palmelloids seemed togive C. reinhardtii cells resistance to grazing, we suggest that at least one of the reasons why C. reinhardtii is capable of formingpalmelloids is to cope with herbivory.

Ten species of molluscs were identified in the freshwater tidal area of the River Minho estuary. Species richness per site rangedfrom 1 to 9. Abundance ranged from 230 to 4130 individuals per m², with an average of 1412 individuals per m2. Corbiculafluminea(Müller, 1774) presented the highest density, corresponding to 88.7 % of the total specimens gathered, followed byPisidium amnicum (Müller, 1774) with 5.8 %. Biomass ranged from 17.0 to 249.6 g AFDW m-2, with an average of 99.8 gAFDW m-2. C. fluminea was the species dominating the total biomass (95.4 %), followed by Bithynia tentaculata (Linnaeus,1758) with 1.6 %. A multivariate analysis revealed a community with two distinct groups : one group almost or exclusivelyrepresented by C. fluminea, and another group with a more diverse assemblage.

Salinity is a serious threat to freshwater ecosystems, particularly those near coastal areas. An increase in salinity producesdrastic changes in community structure of freshwaters, sometimes in an irreversible fashion. Thus, freshwater species must copewith salinity stress in a manner proportional to their degree of tolerance. Bearing this in mind, we studied the acute and chroniceffects of different salinity concentrations in two species of cladocerans: Daphnia magna Straus, a standard test organism, andDaphnia longispina O. F. Müller, an autochthonous species. Salinity experiments were based on successive dilutions of a stocksolution of NaCl in a synthetic medium. The results showed that D. magna is more tolerant than D. longispina, both in acute(EC50 5.9 and 2.9 g/L, respectively) and chronic (EC50 5.0 and 2.2 g/L, correspondingly) exposures. In the chronic exposure,salinity caused a significant reduction in fecundity and a developmental delay (increase in age at first reproduction), as well asa decrease in the growth rate of daphnids. However, these effects were mainly observed at salinity concentrations where mortalityoccurred.

The winter of 2009/2010 was particularly severe in Northern Portugal resulting in higher river flow levels. A study was undertaken to assess the impact of this situation on several populations of freshwater bivalves (e.g., Anodonta anatina, Corbicula fluminea, Margaritifera margaritifera, Potomida littoralis and Unio delphinus) in the catchments of the Rivers Minho, Douro, Tâmega, Tua and Sabor. Massive die-offs occurred for all species in all rivers, resulting in the removal of great numbers and biomass from the riverbed to the adjacent riverbanks, reaching maximum values of 2280 individuals.m−2 and 10 225 g wet weight.m−2, respectively. The invasive Asian clam C. fluminea had both highest density and biomass (however, this invasive bivalve is not dominant in several surveyed sites, and some rivers are still not colonized by this species). Results show that the quantitative and qualitative importance of this carrion transfer to the riverbank should be incorporated in future studies on the assessment of ecosystem function, contributing to a better understanding of the role of freshwater bivalves as resource pulses in adjacent terrestrial habitats. Some of the affected species have conservational importance and these extreme climatic events are predicted to increase in the future. These massive die-off events should be incorporated into management plans and selected restoration measures such as rapid relocation of endangered native mussels back to the riverbed can be easily applied to lessen possible impacts.

A review of present information on the zoogeography of Chironomidae at subfamily and generic levels is given. The known distribution, including some previously unpublished records, of all recognisable genera (307) and subgenera (56) is tabulated according to zoogeographical region. The greatest number of genera is known from the Nearctic (202) followed by the Palaearctic (187), Neotropical (109), Australasian (107), Afrotropical (104) and Oriental (100). The chironomid fauna of each zoogeographical region is discussed and a comparison of the number of known species and percentage representation of each subfamily for each region is given. An account of the distribution and ecology of each of the ten subfamilies is included. To date, some 3 700 species are described representing only 30 % of the estimated world chironomid fauna. The fossil record of the group is briefly discussed and the Chironomidae are estimated to be at least 200 million years old dating back to the Triassic period.

The first part of the paper reviews and criticises drift samplers. The samplers are divided into three broad categories:

1. Samplers without flow-meters (Fig. 1).

2. Samplers with flow-meters (Fig. 2).

3. Tube samplers (Fig. 3) and other more complex samplers.

The second part of the paper considers some problems associated with drift sampling.

As the volume of water flowing through a drift sampler increases, the size of the catch increases. The average relationship between the two variables can be expressed by a regression line (e.g. Fig. 5). A distinction is made between drift rate (the number of invertebrates passing a sampling point in unit time) and drift density (the number of invertebrates per unit volume of water). The relationship between drift rate and drift density is discussed. A summary is given of all the factors which affect drift density.

The sampling efficiency of drift samplers is discussed, and the results of efficiency tests are described. As the performance and sampling efficiency of a drift sampler vary with local stream conditions, they must be thoroughly tested before the start of regular drift sampling.

The study of the diel periodicity in invertebrate drift is discussed. The diel drift pattern greatly varies when different sampling periods are used (Fig. 6).

The following statistical problems are discussed:

1. Temporal and spatial variations in drift rate and drift density, using Poisson series as a statistical model.

2. The estimation of total numbers drifting downstream. Total drift is estimated from drift rate when agreement with a Poisson series is accepted for samples across the stream. Total drift is estimated from drift density when agreement with a Poisson series is rejected, and the catches in a series of nets are proportional to the volumes of water sampled by the nets.

Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their interactions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydrological exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies.

In order to assign 18 mayfly taxa found in streams in the Macaé River basin into Functional Feeding Groups, the anatomy of their feedingapparatus was examined through scanning electron microscopy. Also, habitat preference and field observations of feeding behaviour were madeto assure FFG assignment. Ephemeropteran taxa were classified into five FFGs: Passive Filterers - Hylister plaumanni; Active Filterer -Lachlania boanovae and Campylocia sp.; Brushers - Askola froehlichi, Farrodes carioca, Hagenulopsis spp., Massartela brieni, Miroculis froehlich,Miroculis sp., and Thraulodes spp; Grazers - Cloeodes spp., Americabaetis spp., Camelobaetidius spp.and Baetodes spp.; Scrapers -Leptohyphes pereirae, Leptohyphes spp., Tricorythodes spp. and Tricorythopsis spp. Species of the three best represented mayfly families insouth-east Brazil were assigned to different FFGs (Leptophlebiidae - Brushers; Baetidae - Grazers and Leptohyphidae - Scrapers), with oneexception, Hylister plaumanni (Leptophlebiidae; Active filterers). This information is useful to understand the role of mayflies in stream ecosystems,and to help the development of ecological theories for tropical streams.

A long-term study (1985-1999) conducted at backwater and tailwater sites of a large reservoir located in the middle course of the 808 km long Warta River (Poland), showed that not only obligatory riverine species suffer from the effect of the dam. Facultative riverine eel, burbot, wels and pike considerably decreased in number and standing crop, including their apparent absence in some years following the damming. Nevertheless, median densities of perch and roach, two generalists thriving in European regulated rivers, increased from tens and hundreds, respectively, to thousands per hectare. Significant increases in density were also recorded for other four species: zander, ruffe, bream and silver bream. Thus, the reaction of facultative riverine fish, often supposed to be resistant to aquatic habitat deterioration, is diverse with respect to impoundment. Apart from the migratory eel, which have not been caught at the backwater site for the last 8 years, all the remaining significant temporal changes were recorded at the tailwater site. Out of habitat flexibility coefficients relating to refuge, feeding and spawning, only the latter considerably differed between the successful and unsuccessful species after impoundment, which testifies to the critical role of spawning flexibility in a human-modified environment.

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.

The distribution of bloom-forming cyanobacteria in eutrophic to hypereutrophic ponds was studied in northern Taiwan in 2009. Eighty-four ponds were sampled in mid-summer, and the relationship between colony size and relative abundance of each cyanobacterial species was analyzed. Anabaena crassa and Cylindrospermopsis raciborskii were the dominant species in terms of frequency of appearance. The colony size of An. crassa increased significantly with its relative abundance. The relative abundance of C. raciborskii was usually below 10%, and its filament length was not correlated with its relative abundance. The colonies of Microcystis aeruginosa normally consisted of several tens of cells. However, when M. aeruginosa exclusively dominated the plankton community, the average number of cells in a colony reached several hundreds. The mean filament length of Planktothricoides raciborskii significantly increased with its relative abundance. The correlations between colony size and relative abundance of the ten cyanobacterial species were significantly positive for three species, insignificantly positive for five species and insignificantly negative for two species. Given the various ecological advantages of large colonies, the results of this study may suggest that the formation of large colonies of some cyanobacterial species is important to their dominance and/or bloom formation.

A key issue in the implementation of the Water Framework Directive is the classification of streams and rivers using biologicalquality parameters and type-specific reference conditions. Four groups of stream types were defined in NE Spain on the basisof 152 diatom samples by means of detrended correspondence analysis and classification techniques. Diatom analysis was restrictedto epilithic taxa, and the sites included gradients ranging from near-natural streams to sites with poor ecological quality.The main gradient shows a clear separation of sites in relation to the degree of human influence: polluted streams (mainly locatedin the lowlands) differ from streams in mountainous areas and in the Pyrenees. A second gradient is related to physiographicalfeatures. Headwater streams can be distinguished by their catchment geology. The type-specific diatom taxa for the streamtypes studied were determined by using indicator species analysis (IndVal). The type-specific taxa from near-natural streams arecoincident with the indicator taxa for high ecological status. Human impact reduced the typological heterogeneity of the diatomcommunity composition. Overall, the diatom communities in NE Spain exhibit a regional distribution pattern that closely correspondswith that observed in river systems elsewhere. Physiographical differences are only evident in undisturbed sites, whilenutrient enrichment and other human disturbances may mask the regional differences in the distribution of diatom communities.

Colonial Microcystis aeruginosa were obtained when the unicellular algae were exposed to flagellate Ochromonas sp. filtrate. To investigate the benefit of this morphological change, flagellates were added into cultures of unicellular and colonial M. aeruginosa, respectively. The clearance rates of flagellates on algae were markedly decreased when they were cultivated with induced colonial M. aeruginosa. This result indicated that colony formation in M. aeruginosa was a predator-induced defense, which could reduce predation risk from flagellate. The increased content of soluble extracellular polysaccharide (sEPS) and bound extracellular polysaccharide (bEPS) may play an important role in adhering M. aeruginosa cells together to form colonies. The decrease of ΦPS II and the increase of sinking rates of induced colonial M. aeruginosa showed that the costs of grazed-induced colony formation in M. aeruginosa may reflect in the photosystem II efficiency, and in the sinking rates.

We investigated the chemical characteristics of the astatic soda pans in the Carpathian Basin based on comprehensive new and archive data. Analysed parameters were salinity and ionic composition. The most frequent type of soda waters was the basic alkaline type (Na-HCO3) that represented more than half of the natural soda pans. Besides 11 subtypes occurred. The second and third most frequent types were the chloride (13%) and sulphate subtypes (11%), with the secondary dominance of these anions. The other subtypes meant <4% of the pans. Magnesium sometimes occurred as a secondary dominant cation beside sodium. Until now, this subtype of soda waters has not been published in any part of the world, because of the general rule of soda lake formation (depending on low levels of magnesium and calcium). We found a regionally constant correction factor [Salinity (mg.L−1)=0.8×El.Cond. (μS.cm−1)] for confidentially estimating salinity from electrical conductivity in these habitats. Salinity varied between sub- (0.5–3 g.L−1) and hypersaline (>50 g.L−1) ranges, with its mean value (∼4 g.L−1) in the hyposaline range (3–20 g.L−1). The basic alkaline type had random geographical distribution, while the other subtypes were restricted to certain regions of the Basin. The high number of subtypes reflects the high chemical diversity of alkaline soda pans in the relatively small territory of the Carpathian Basin.

La croissance de huit espèces d'algues du phytoplancton d'eau douce (6 Chlorophycées, 1 Diatomée, 1 Cyanophycée) a été étudiée en culture. Plusieurs méthodes d'évaluation de la biomasse ont été comparées : poids sec, comptages cellulaires, densité optique, chlorophylle. Selon les espèces, l'extraction de pigments par l'acétone donne des valeurs inférieures de 5 à 50 % par rapport à l'éthanol. S'il n'a a pas de carence en nutriments, une assez bonne approximation du taux de croissance peut être calculée à partir des paramètres acquis par des expériences de photosynthèse (Pmax). Les variations de taille des cellules au cours du cycle de division sont également décrites. Le taux de croissance des huit espèces est décrit en fonction de la température et de la lumière selon un système d'équations inspirées de la formulation de Steele (1965). Les paramètres obtenus permettent de bien modéliser l'évolution d'une culture en tenant compte du phénomène d'ombre propre.

16 composantes physico-chimiques des eaux courantes sont discutées à partir des résultats d'environ 12 000 analyses effectuées de 1960 à 1970 dans les cours d'eau français et de l'examen d'une abondante documentation relative aux travaux européens.

Après l'examen des localisations et des significations de valeurs particulières, des classes sont proposées pour chaque paramètre en tant que repères et bases d'interprétation des analyses chimiques.

This study investigated the relationships of three major aquatic assemblages (diatom, macroinvertebrate, and fish) and environmental variables, including sub-basin, hydrology, land cover, and water quality variables on multiple scales. Samples were collected at 720 sampling sites on the Korean nationwide scale. Geological variables, including altitude and slope, showed a strong positive correlation with proportions of forest in land cover types and cobbles in substrates, while they were negatively correlated with water quality variables, including conductivity and total phosphorus. Considering the concordance of the different assemblages, species richness of fish and macroinvertebrates displayed significant correlation, and diatoms were significantly correlated with fish. However, diatoms did not show significant correlation with macroinvertebrates. Altitude and slope showed significant correlation with all biological variables of the three assemblages. Macroinvertebrates and fish showed positive relations with large substrate sizes. Indices of diatoms and macroinvertebrates well reflected the perturbation of water quality variables. However, fish indices showed a relatively low association with water quality variables, compared with those of diatoms and macroinvertebrates. These patterns were also confirmed by the ordination and prediction of biological indices with environmental variables through the learning process of a self-organizing map as well as random forest. Overall, our study supports the concept of multi-scale habitat filters and functional organization in streams, and is consistent with the recommended use of multiple biological indices with more than one assemblage for the assessment of the biotic integrity of aquatic ecosystems.

Le peuplement des Crustacés du sous-écoulement du ruisseau de Lachein (Pyrénées) a été étudié sur un site de 75 m2 et à une profondeur de 0,60 m.Les écoulements de surface déterminent quatre zones principales, deux bancs de graviers, un chenal et une zone d'eau morte. La porosité (20 à 30 %), plus élevée dans les bancs de graviers que dans le chenal, est également plus forte à l'amont des bancs qu'à l'aval. La granulométrie diffère selon les zones, les bancs de graviers étant caractérisés par une plus forte abondance des éléments mesurant 1 à 8 mm. Les caractéristiques chimiques du sous-écoulement, toujours proches de celles du cours subaérien, évoluent de façon identique à ces dernières au cours des saisons. Les valeurs de l'O2 dissous, proches de la saturation en surface, sont comprises entre 0,02 % et 84,7 % dans le sous-écoulement où leur distribution dépend très directement de la dynamique des écoulements de surface. Les teneurs en matière organique particulaire, comprises entre 4 et 13,6 %, subissent une évolution saisonnière. Les valeurs moyennes les plus basses caractérisent le chenal.Les Crustacés, représentés par 50 espèces et sous-espèces. dont 22 taxons stygobies, montrent une forte similitude faunistique avec ceux colonisant le système karstique du Baget dont le ruisseau de Lachein est issu. Ils sont caractérisés par une organisation stable dans le temps, dominée par les Copépodes et, notamment, par les Harpacticides qui constituent 60 % du peuplement. Leur densité moyenne est de 369 individus/10 l. La répartition spatiale des Malacostracés comme des Harpacticides est très variable, avec des espèces eurytopes (formes épigées) et sténotopes (formes hypogées) ; parmi ces dernières, les unes sont inféodées aux zones les plus oxygénées, d'autres au contraire, sont limitées aux zones les moins oxygénées. Chez les Harpacticides, les densités comme les pourcentages des formes hypogées sont très directement liés aux différentes zones définies par les écoulements de surface.