Microcystis aeruginosa mainly occurs as single cells in laboratory cultures, but in the colonial morph under natural conditions.This phenomenon suggests that some factors may be responsible for the typical occurrence of colonies in lakes. Todemonstrate this possible effect, lake water with abundant or few zooplankton was filtered through a 0.15 µm membrane filter,and used as test water. Microcystis aeruginosa was cultured in BG-11 medium, with or without test water. The results showedthat filtered lake water with abundant zooplankton could induce colony formation in M. aeruginosa, whereas M. aeruginosapopulations in the control and the treatment of filtered lake water with few zooplankton were still strongly dominated by unicellsand paired cells, and no colony was formed. In the treatment of filtered lake water with abundant zooplankton, some coloniesof several, dozens, and sometimes even hundreds of M. aeruginosa cells were formed. The unicells reduced to 53.4±6.5%and the proportion of cells in colonies increased from 0 to 24.5±4.6% of the populations. The mean number of cells per unit ofM. aeruginosa in the treatment of filtered lake water with abundant zooplankton was promoted significantly compared withthose of the control and the treatment of filtrated lake water with few zooplankton. In addition, no significant difference in growthrate was detected between the control and the treatments, regardless to the filtered lake water (i.e. with abundant zooplanktonor with few zooplankton). Thus, we concluded that colony formation in our experiment was probably not associated withthe nutrition difference but with some dissolved substances probably released from abundant zooplankton in the natural lakewater, which may be one of the environmental factors responsible for the colonial form in M. aeruginosa.

Un catalogue de 83 espèces de Chironomides récoltées en Camargue est présenté.

Pour chaque espèce sont indiqués :

- la période d'émergence des imagos ;

- l'abondance relative au sein de la famille et de la sous-famille à partir des piégeages d'imagos ;

- les ouvrages ayant permis la détermination spécifique (Imago, Nymphe, Larve) ;

- la répartition dans le monde ;

- la répartition en France : 10 espèces sont nouvelles pour la Faune de France, 8 le sont pour la Camargue ;

- les observations biologiques et écologiques nouvelles : adaptations aux variations de la chlorosité, aux teneurs en oxygène dissous, résistance à l'assèchement.

Trois espèces ont une répartition circum-méditerranéenne ; trois autres sont également connues de la région éthiopienne.

Sediment and plant-associated macroinvertebrates were sampled in six shallow water bodies along the central part of the coastof Mediterranean Spain. The size of ponds, salinity and hydroperiod were highly variable. Seventy-one taxa were recorded, someof them were endemic or uncommon species, evidencing the important contribution of these ponds to biodiversity. Crustaceansand gastropods of biogeographical interest were found in the most primeval site. Correspondence analysis showed that macroinvertebrateassemblages responded to environmental variables such as salinity, temporality and eutrophication. The brackishwater fauna was dominated by crustaceans, while oligochaeta and insect larvae were abundant in freshwater conditions.Oligochaetes were abundant at localities with high trophic level, whereas localities with semi-permanent waters were dominatedby chironomids. The density of macroinvertebrates was clearly related with trophic state but we did not find significant relationshipsbetween density and salinity or water permanence. For plant associated samples our results showed negative relationshipsbetween species richness and temporality or salinity, contrary to sediment samples, where the Oligochaeta/Chironomidaeratio in sediments and the percentage of sensitive taxa (Ephemeroptera, Odonata, Trichoptera) were useful indices, and weredependent on pond typology. This study emphasizes the broad ecological variety of ponds found in these wetlands and theirimportance for biodiversity. Some ponds act as permanent biodiversity reservoirs in fluctuant marshes with seasonal dryness,calling for more attention on their ecological relevance for management strategies.

Le Riou-Mort draine le bassin houiller de Decazeville, région fortement industrialisée dont il reçoit les eaux usées. La chimie et les algues benthiques ont été étudiées dans 14 stations sur le Riou-Mort et ses affluents ainsi que dans 7 stations sur la rivière Lot. Le Riou-Mort et ses affluents sont sévèrement pollués en aval des principaux centres industriels par les effluents de diverses usines dont une fonderie de zinc. Les principaux polluants sont des solides en suspension, du zinc, du cadmium, du cuivre, de l'acide sulfurique et du manganèse. La rivière Lot transporte des teneurs élevées de zinc et de cadmium en aval du confluent du Riou-Mort ; les teneurs en zinc persistent au moins 40 km vers l'aval. La flore d'algues benthiques change de façon marquée au niveau des sources de pollution. Pour une pollution "modérée" par les métaux lourds, les communautés de l'amont, dominées par Cladophora glomerata, Ulothrix zonata, Vaucheria sp., Melosira varians et Synedra ulna sont remplacées, en aval, par des communautés dominées par Stigeoclonium tenue, Gongrosira incrustans, Gomphonema parvulum et Surirella ovata. Pour une pollution extrême par métaux lourds, aucune espèce d'algue ne subsiste en certaines stations tandis qu'en d'autres, la flore est réduite à deux espèces : Gomphonema parvulum et Achnanthes minutissima. Les effets les plus sévères sur les algues benthiques sont produits par de fortes concentrations en solides en suspension combinées à de fortes teneurs en zinc et en cadmium.

The production estimate for Fontinalis squamosa of 92 gm m-2 was a minimum one assuming an annual branching pattern. Standing crops for the total stream area of bryophytes of 325 gm m-2 for the site at Artigusse and of 92 gm m-2 for the Estaragne tributary were recorded. The area covered was however high in the former and very low in the latter (only 7%). The maximum recorded standing crops were 1 960 gm m-2 for Cratoneuron commutation and 682 gm m-2 for Fontinalis and Fissidens combined.

The splash zone around a small water chute is described.

The relative effects of irradiance and spectral composition on the colonization and development of macroalgal communities were examined in four streams exposed to full sunlight in southern Brazil. A set of solar filters surrounded the artificial substrata to provide various quantitative and qualitative light conditions. In addition to the control, the conditions were full sunlight attenuated by 50, 70 and 90%, blue light (filter transmitting 430–500 nm), green light (500–600 nm) and red light (>600 nm). Macroalgal percent cover was determined three times during the colonization period (15, 39 and 70 days). Significant differences occurred in the mean values for macroalgal community percent cover between treatments at 15 and 39 days, suggesting that early and intermediate stages of the colonization were directly influenced by irradiance. There was an almost complete absence of macroalgae with 90% attentuation, but progressive increases with 70 and 50% attenuation. However, the mean values for macroalgal community percent cover did not differ significantly between color treatments, suggesting that the effects of irradiance on macroalgal colonization were stronger than those of spectral composition at similar intensity. The quantitative responses differed among the taxa.

This study describes the diet composition of 42 rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (90-480 mm TL), capturedin May 1995 in the Urederra River (North of Spain). Rainbow trout of all sizes fed mainly on midge (adults, larvae andpupae), but there were some differences in the feeding habits of small and large fish. We found that as the trout grew larger terrestrialprey became the most important food item. Rainbow trout avoided Leuctridae and showed some preference forEphemeroptera, Diptera larvae and Nemouridae larvae. Native fish predation and exploitation of the same trophic resources inthe Urederra River, could negatively affect native fishes, such as European minnow,Phoxinus phoxinus L., 1758 or brown trout, Salmo trutta L., 1758.

The colonization of periphytic algae in a temperate floodplain was studied in Lake Sakadaš, a part of a fluvial floodplain along the Danube River. An in situ investigation, using artificial substrata, was started after extremely high spring flooding and was carried out during long-lasting summer floods (July–August 2010). The physical and chemical environment was variable and large stands of metaphyton, submersed and floating macrophytes were spread along the lake. The periphyton development was initiated on the first day of exposition and algal abundance increased exponentially till day 27. Directional changes in the relative abundance of algal species, shown by the results of the non-metric multidimensional scaling, indicate a pattern of short-term sequences in algal colonization. The initial attachment of planktonic cyanobacteria and unicellular diatoms (initial phase, days 1–3) to the biofilm matrix was followed by the development of the filamentous chlorophytes, Cladophora glomerata and Oedogonium spp. (intermediate phase, days 6–15) and then by stalk-forming diatoms particularly Gomphonema spp. (late phase, days 18–33). According to the redundancy analyses, water temperature and oscillations of Danube water level that define the flooding pattern had the most significant influence on algal colonization. Flood-induced spreading of metaphyton firstly supported the rapid progress of algal colonization towards a climax community, while later, metaphyton together with macrophytes disrupted algal community by increasing the mechanical injuries, shading and grazing pressure. Consequently, algal abundance and community structure were returned to the intermediate phase of colonization.

The studies of differences in life history and suitability of both water temperatures and trophic levels among rotifer sibling species improve our understanding of speciation, sibling species coexistence and possible niche differentiation over space and time, and consequences for the functioning of ecosystems induced by climate change and eutrophication. We collected Brachionus calyciflorus from Lake Baixiang and Lake Kongque, two tropical shallow lakes, in Xishuangbanna city, Yunnan, China, clonally cultured them in laboratory, and found that the B. calyciflorus complex contains two sibling species named sibling species BNA13 and BNB3 by phylogenetic analysis, and investigated the life-table parameters of the two sibling species BNA13 and BNB3 at four temperatures (16, 20, 24 and 28°C) and four algal densities (0.5, 1.0, 2.0 and 4.0×106 cells.mL−1). The results showed that the responses to increasing temperature and algal density for each of the life-table parameters differed with rotifer sibling species. Sibling species, temperature, algal density and their interactions almost all significantly affected the durations of juvenile period, embryonic development, reproductive period, post-reproductive period, mean lifespan, net reproductive rate, generation time and intrinsic rate of population growth. Sibling species significantly affected the age-specific survivorship. Temperature, algal density and their interaction and the interaction of sibling species and temperature significantly affected the age-specific fecundity. Regardless of the effects of temperature and algal density, the durations of juvenile period, embryonic development, reproductive period, post-reproductive period and mean lifespan, age-specific survivorship, net reproductive rate and generation time of the B. calyciflorus sibling species BNA13 were greater than those of BNB3, but the intrinsic rate of population growth of BNA13 was lower than those of BNB3. This suggests that the two B. calyciflorus sibling species adopted variable life history strategies, low population growth and high survivorship for sibling species BNA13, and high population growth and low survivorship for sibling species BNB3. Both the intrinsic rates of population growth of BNA13 and BNB3 were the highest at 28°C and 4.0×106 cells.mL−1 algal density, indicating that some adaptations of the B. calyciflorus sibling species BNA13 and BNB3 in tropical shallow lakes to water temperatures and trophic levels were similar, and they have the potential for coexistence in single waterbody of higher temperature and higher trophic level.

Aquatic microfungi play a fundamental role in organic matter decomposition in fluvial ecosystems. These micro-organisms degrade leaf recalcitrant compounds like lignin, thereby enhancing the utilization of organic material by the microbial community. The main input of allochthonous organic matter in Mediterranean streams occurs during the autumn. In-stream breakdown processes can be affected by high physical abrasion during flooding but changes in stream water chemistry may also affect decomposition enzymatic activities of stream microorganisms. We measured two ligninolytic activities (phenol oxidase and peroxidase) and a cellulolytic activity (cellobiohydrolase) in leaves, branches, sand and gravel substrata in a reach of a Mediterranean stream. Highest ligninolytic activities were measured in biofilm developed on inorganic substrata (sand and gravel) where also accumulated the highest fungal biomass (ranging from 3.3 x 10-4 to 7.22 mg Ergosterol gAFDM-1) especially in sand substrata. Conversely, cellulolytic activities were significantly higher in biofilm on organic substrata (leaves and branches). Physical and chemical factors, such as discharge and stream water nutrient concentration (Dissolved Inorganic Nitrogen) were affecting enzymatic activities, particularly enhancing the phenol oxidase. Moreover, the chemical composition of the available OM (high cellulose in leaves, high lignin in detritic material) strongly influenced the decomposition activity in each biofilm. A precise description and quantification of the benthic substrata was used to obtain enzymatic activity values in terms of stream reach. Those results showed a temporal pattern in the decomposition activities in the reach, beginning with the decomposition of cellulose (October) followed by lignin compounds (November and December).

Aquatic insects are widely distributed, and are especially diverse and abundant in tropical streams, where they play an important role in the food chain due to their diversity of feeding strategies, and the potential for the transfer of energy between aquatic and terrestrial environments. The intimate relationship found between these insects and environmental variables means that they are often used as bioindicatorss in environmental studies. We tested the hypothesis that the loss of environmental integrity in tropical streams will lead to a loss of species and a decline in the abundance of mayflies (Leptophlebiidae), in addition to a change in species composition, and the dynamics of population. Collect immature leptophlebiids in 18 streams representing different degrees of conservation, in the Brazilian Cerrado. The environmental integrity of the sites was assessed using a Habitat Integrity Index (HII), which generates values of zero (degraded) to one (preserved), based on soil use, the extension and conservation of riparian forest, as well as morphological features of the stream. A total of 4945 immature leptophlebiids were collected and identified as belonging to 16 species or morphospecies. On an average, a reduction of 0.1 in the value of the HII led to the loss of five specimens and one species. The composition of the communities varied systematically along the environmental gradient, with more sensitive species being found only when the index was above a threshold of 0.6. The importance of the riparian vegetation for the aquatic biota, especially its role in the mitigation of impacts from the surrounding matrix, supports the universal conservation of this type of habitat.

The microdistribution and abundance of freshwater gastropods were studied in lower reaches of three streams on Moorea, French Polynesia, during austral spring (AS) and austral fall (AF) 1994-1996. Seven species were examined: Neritina canalis Lamarck, Neritina turrita Gmelin, Clithon spinosa Budgin, Septaria porcellana Linnaeus, Neritina auriculata Lamarck, Melanoides tuberculata Müller, and Thiara granifera Lamarck ; the first five species are in the Neritidae, the latter two in the Thiaridae. Most gastropod species had higher densities during AF 1996 than AS 1995 (p = 0.0001) with higher densities being found in riffle than in pool habitats (p = 0.0001). No relationship between substrate type and either species presence-abundance or shell size was observed. A stepwise multiple regression indicated that velocity, depth, and substrate roughness were determinants of gastropod abundance for some species within these streams. A distinct microhabitat preference for the bottoms of rocks was observed for C. spinosa and N. canalis. The limited range of N. auriculata's occurrence within streams results from its salinity tolerance and response to hydraulic stress.

Les rapports volumétriques entre l'œuf amictique (V0) et la femelle adulte (VA) sont établis et discutés chez 21 populations naturelles ou expérimentales appartenant à 15 espèces.Chez les Rotifères herbivores, la relation allométrique est décrite par l’équation : V0 = 3,62 VA 0,816. L'exposant de celle-ci est très proche de la valeur générale 0,75 reliant l'investissement reproductif à la taille. Une relation intraspécifique similaire est observée chez B. calyciflorus. Le ratio V0/VA est moins variable chez les Asplanchna ovovivipares dont le rapport du poids sec au poids frais (4 %) est notablement inférieur à celui des autres espèces ( > = 10 %).En outre, des relations allométriques similaires ont été calculées entre le volume des œufs de durée et celui des œufs mâles d'une part, et le volume de la mère d'autre part, chez, respectivement, sept et trois des espèces précédentes. Les écarts observés sont interprétés comme le résultat de contraintes sélectives différentes.

Is it possible to link leaf decomposition and associated invertebrates with the typological character of an heterotrophic stream ? This is an important question because it is related the spatial dynamics of the functioning low order streams, in the sense that it considers the use and interactions of allochthonous organic material along the horizontal axis of the stream. In the autumn/winter of two successive years, alder leaf breakdown rates and their nutrient variation (N, P, K) were estimated in a stream with energetically increasing dependence on POM inputs in the upstream direction. The succession of invertebrates colonizing the incubated leaves was observed and related to the characteristics of this organic substrate. Though extremely variable in time, the coefficients of decomposition revealed a spatial gradient in close association with the specific heterotrophic character of the different sites. Invertebrate trophic groups colonizing the leaves exhibited a pattern similar to their typological distribution in the stream : shredders were dominant in the upper stations and they were replaced by collectors in the lower ones. We concluded that a longitudinal pattern of decomposition of exogenous organic materials exists in streams that show a predictable typological shift along this gradient.

Sediment resuspension is an important internal lake process in regulating nutrient cycling and ecosystem structure. Tubificid worms are widely and abundantly distributed in freshwater ecosystems and are able to alter the sediment characteristics. This study was conducted to verify the hypothesis that the alteration of sediments by tubificids may substantially influence the sediment resuspension process. Specifically, we investigated the influence of Limnodrilus hoffmeisteri (Tubificidae) on sediment resuspension using an apparatus designed to simulate the sediment resuspension process in Lake Taihu (China). We examined L. hoffmeisteri according to its density (30 000 ind.m−2) in Lake Taihu and simulated the light (3.2 m.s−1), moderate (5.1 m.s−1) and strong (8.7 m.s−1) wind processes present in Lake Taihu. Tubificids loosened the sediment through their feeding and defecation activities and increased the sediment water content. The appearance of tubificids increased the suspended solids (SS) in a 1.6 m water column under all three wind processes. During the sedimentation process, SS decreased rapidly in both the control and tubificid treatments. The total SS in the water column was significantly increased by tubificids and it changed significantly with time. In addition, the small size particles of the SS in the tubificid treatment were higher than that in the control. So, the appearance of tubificid worms (L. hoffmeisteri) enhanced sediment resuspension and raised the proportion of small size particles in SS.

The rotifer fauna present in Thale-Noi Lake, Pattalang Province, Thailand on the 16th September 1995 is reported. A total of 106 species, the majority of which belong to the genera Lecane (31 %), Lepadella (13 %) and Brachionus (9 %) are recorded. Cephalodella songkhlaensis n.sp. and Trichocerca siamensis n.sp. are described, Lecane calcaria Harring & Myers is redescribed. An additional fourteen rotifer species are recorded for the first time from Thailand. The genera Metadiaschiza Fadeew and Paracephalodella Berzins are synonymized with Cephalodella Bory de St. Vincent.

L'inventaire détaillé des Oligochètes du Léman conduit l'auteur à décrire quelques formes nouvelles et à préciser l'origine du benthon de ce grand lac subalpin peuplé d'éléments allochtones et autochtones.

Des investigations portant sur le genre Diadesmis (Bacillariophycées), observé à l'aide du microscope photonique et du microscope électronique à balayage, ont été réalisées dans différents biotopes des archipels de Crozet et de Kerguelen : lacs, mares temporaires, mousses et sols. Dix espèces ont été recensées. Diadesmis arcuata Heiden, décrite à l'origine dans l'archipel de Kerguelen, est réexaminée et typifiée. Cinq espèces nouvelles pour la science sont décrites : Diadesmis comperei, Diadesmis costei, Diadesmis crozetikerguelensis, Diadesmis langebertalotii et Diadesmis subantarctica. Les espèces appartenant au sous-genre Paradiadesmis ont une structure particulière : les interstries sont constituées de tubes creux quadrangulaires.

Concentrations of a wide range of chemical variables were determined in 206 water samples taken between May 1996 and May 1998 from a set of 25 natural lakes in the French Massif Central. From each lake 6 to 9 samples were collected. Mean and standard deviation of total alkalinity, conductivity, pH, concentrations in K+ , Mg2+ , Ca2+ , Na+ , Cl-, SO2 4 , total phosphorus, nitrate-nitrogen, dissolved silica, chlorophyll a, and water colour were calculated for each lake. These results are briefly compared with those obtained in an earlier study in which chemical analyses were carried out on a reduced set of lakes from the same region. In most lakes and for most elements, concentrations observed in the present study were similar to those observed previously. The seasonal variations of the elements which are most strongly influenced by biological processes were also investigated. Using hierarchical cluster analysis three main lake groups were distinguished : i) alkaline lakes, ii) deep lakes with lowalkalinity and iii) shallow lakes with low alkalinity. The major patterns of variation in the data set were also investigated using principal components analysis (PCA), which confirms that total alkalinity and maximum water depth are the main environmental gradients in this set of lakes. In conclusion, the potential of this data-set for building diatom-based transfer functions to reconstruct past limnological conditions is discussed.

The aim of this paper is to report the colonization process of three headwater rivers of two large trans-national Pacific riverbasins shared by Chile and Argentina, by exotic Chinook salmon (Oncorhynchus tshawytscha). To characterize the populations atthe sites, fish were analyzed in terms of length, weight, age, and stream residency patterns. Fishermen familiar with the area wereinterviewed to establish the seasonal occurrence of fish and to reconstruct the history of the colonization process. Records ofsalmon production in Chile by regions were examined to evaluate the potential origin of fish in coastal net pen aquaculture. Theregularity of spawning runs in our study sites indicates that Chinook salmon have established spawning populations in theserivers. While spawning was verified in all three rivers, only one seems to serve as a holding area for pre-spawning salmon early inspring. The correlation in the historical occurrence of Chinook salmon in the three rivers suggests that they have been colonizedas part of the same introduction event. Moreover, the temporal correlation with the development of ocean net pen production forthis species in the Chiloé region suggests that the fish may originate from escapes from these enterprises. As in all previousreports of exotic Chinook salmon in Patagonia and New Zealand, populations in the three rivers have a combination of streamand ocean ecotypes. We discuss the importance of plasticity in critical life history characteristics for the success of Chinooksalmon in Patagonia, compared to other species of anadromous salmonids.