Le peuplement des Harpacticides du milieu hyporhéique du ruisseau de Lachein (Pyrénées) a été étudié pendant un an sur un site de 75 m2. 21 espèces dont 9 stygobies ont été recensées. Ce peuplement est caractérisé par sa stabilité dans le temps puisqu'aucune variation saisonnière importante n'a pu être mise en évidence entre les sept séries de prélèvements réalisées. En revanche, ce peuplement présente une forte hétérogénéité spatiale : quatre groupements ont été reconnus dont la répartition se superpose aux différentes unités physiographiques définies par les écoulements de surface : bancs de graviers, chenal, zone d'eau morte. Les bancs de graviers constituent le milieu de vie préférentiel des Harpacticides: à cet endroit, les formes hypogées dominent les espèces épigées qui sont repoussées à la périphérie des bancs. Les conditions hydrodynamiques au sein du milieu hyporhéique permettent d'expliquer ce type de distribution. En effet, ce sont les zones où la perméabilité est la plus élevée qui abritent les populations les plus abondantes et les plus riches en espèces. Toutefois, ces zones ont une diversité spécifique plus faible en raison des phénomènes de compétition inter-spécifique.

Nitrogen dynamics were investigated in the top centimeters of bottom sediment in three different geomorphologic units(riffles, sand bars, pools) and along two contrasted reaches (nitrogen-rich, nitrogen-poor) of a rural stream. Some predictionsof links between geomorphology and processes were verified: (i) hydrological exchanges and nitrification were lower in poolsthan in riffles and bars, whereas (ii) ammonification and denitrification were higher in pools. Studies of denitrification potentialin six other reaches of three N-rich streams support these conclusions and demonstrate that pools are spots of high microbialactivity in streams.

The biomass and the biochemical composition of periphyton were studied during one year in three streams of Réunion Island. The results revealed that nutritional conditions for fish development were most favourable during the dry season. The nutritive value of periphyton was highest in the Marsouins and Mât streams and remained the lowest in the Roches stream. Food availability was strongly affected by high flow, particularly during the exceptional hydrological events of February 1998 (cyclonic high flows). Study of seasonal variations of morphophysiological characteristics and biochemical composition (lipids, proteins) of the grazer gobiidae Sicyopterus lagocephalus showed that inspite of unfavourable nutritional conditions caused by hydrological disturbances, fish continue their reproduction which coincides with the summer high flow period. The significant depletion of lipid reserves which express a deterioration in animal condition is influenced by flooding period. At this time of gonad development involving an additional energy investment, fish were not able to recover a stable nutritional state after the complete achievement of the reproduction cycle. Except during this period, there is a weak participation of the reproductive physiological processes in the seasonal changes of somatic composition of this fish.

The intensification of agriculture has drastically modified the structure of rural landscapes, changing field size, destructinghedgerow networks, and increasing nutrients and fine sediments fluxes to rivers. To evaluate the effects of these disturbances atthe catchment scale, we studied the surface and interstitial water chemistry and the invertebrate assemblages in three differenthabitats: the vegetation, the benthic, and the interstitial. Six headwater streams ranging from undisturbed to disturbed forests(wind-fallen area) and from traditional agriculture to intensive farming areas were studied. Differences between forested andagricultural streams lie in changes in water chemistry, in habitat quality, and in the composition of the assemblages with littlereduction in species richness. The forested streams were only disturbed by large-scale modifications of their catchments (i.e.wind-fallen area along the stream), which made the invertebrate assemblages similar to those of agricultural streams, even ifwater characteristics were not modified. In contrast, large scale modifications of landscape structure near the agricultural streams(hedgerow removal) had little effect on the fauna, but the destruction of the riparian strip (with direct access of the cattle to theriver) profoundly affected the system with drastic modifications of in-stream habitat quality and invertebrate assemblagecomposition. The effects of these disturbances differed according to the habitat considered, with increasing differences betweenassemblages from the interstitial, to the benthic, and to the vegetation habitats. Finally, groups of organisms based on bioecologicaltraits appeared as efficient tools for the evaluation of catchment disturbances, at least for the benthic and thevegetation fauna.

The aim of this work was to evaluate the potential of aquatic macrophytes as biological indicators of the environmental conditionsof rivers in north-eastern Spain. To this end, twenty five river basins were studied to assess the species composition andabundance of macrophytes, and to examine their relation with different geographic, morphometric, mineralization, and trophicstatus parameters. Of the twenty six macrophyte species found, five appeared to be useful as biological indicators of the environmentalconditions of the rivers. L. minor was a good indicator of high mineralization (i.e., conductivity and Cl-) and high trophicstate (especially, N-NO2 -). C. stagnalis was a good indicator of high P-PO4 3- concentrations. P. crispus, P. polygonifolius,and R. penicillatus seemed to be useful indicators of high N-NO3 - concentration. We conclude that, in our study area, aquaticmacrophytes can indeed be used as biological indicators of the environmental conditions of rivers.

We investigated the diel vertical distribution patterns of microcrustacean zooplankton (Cladocera, Copepoda) in a shallow pond (max. depth: 70 cm) of the Öreg-turján peatland (Ócsa, Central Hungary) during three 24-h periods in July (19–20th), August (17–18th) and September (11–12th) 2011. Environmental variables showed remarkable vertical stratification. Oxygen concentration was close to zero in the entire water column from night until sunrise, while the lower strata (from 20 cm below the surface) were close to anoxic during all three diel cycles. It proved to be the main determinant of the vertical distribution of microcrustaceans. Accordingly, the highest proportion of individuals was present in the surface layer. Chlorophyll-a concentration and phytoplankton biomass were inversely distributed compared to zooplankton. Microcrustaceans (mainly Daphnia curvirostris) migrated to the middle layer only in August, which could be explained by a trade-off between food resources, dissolved oxygen (DO) and competition with littoral zooplankters. The diurnal density patterns of microcrustaceans suggested horizontal migration into the aquatic macrophytes during night, which could be a strategy to avoid Chaoborus predation. Our results show that strong vertical gradients of abiotic and biotic factors occur even in such shallow waterbodies. Among them, DO can maintain constant vertical aggregation of zooplankters by limiting their occurrence to the surface layers.

A partir d'échantillons de vandoises capturés par pêche à l'électricité de 1971 à 1976, les principales caractéristiques de la population de l'Ourthe ont été décrites et analysées : structure par âge (longévité maximale : 15 ans), variations de l'abondance des classes d'âge 1958-1972, taux annuel de mortalité (M = 38 %), taux de croissance en longueur (21 cm à 5 ans pour les deux sexes réunis), sex ratio mâles/femelles : 1,04), âge de la maturité sexuelle (3-4 ans et 16 cm), fécondité absolue individuelle en fonction de la taille et de l'âge, cycle saisonnier de la condition et du développement des gonades, relations poids-longueur, période de ponte. La dynamique (croissance pondérale, survie, fécondité et production somatique) d'une cohorte type de vandoises est établie. Des estimations sont proposées pour la biomasse du peuplement (6,3 kg/ha), la production somatique (2,3 kg/ha/an), le potentiel reproducteur (35 ovules/m2) et l'exploitation par la pêche (2,0 kg/ha/an). La discussion traite de la démographie de la vandoise dans quelques rivières européennes.

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju, a potentially toxic bloom forming cyanobacteria(Nostocales), was recorded in the River Seine in August 2001. The cyanobacterium was previously observed in some French ponds but this is the first report of this reputedly tropical species in a river in France.

We studied the morphology of two ‘flesh-eating’ Chydoridae Anchistropus emarginatus Sars, 1862 and Pseudochydorus globosus (Baird, 1830), using populations from Belgium, with particular attention to the structure of the trunk limbs. Both genera belong in subfamily Chydorinae, and both have morphological adaptations with implications for the interpretation of limb morphology in the subfamily. Anchistropus has a large number of specific characters, many of which directly relate to the animal’s habit of feeding on Hydra. In Pseudochydorus globosus, specializations are less numerous. A redescription of both species is offered, with an aim at allowing future comparisons with populations outside the Palaearctic, where cryptic species are expected to occur.

Patterns of leaf colonization by Chironomidae were compared on three leaf substrates differing in rate of processing and palatability for detritivores. Each leaf species was colonized by a similar number of taxa, with Orthocladiinae and Tanytarsini comprising the dominant groups. However, the chironomid assemblage, categorized by functional feeding groups, differed greatly between the three leaf types. Black cherry leaves supported a much higher proportion of shredders (e.g. Brillia flavifrons) than either red maple or American beech packs. In contrast, beech and maple leaf packs were colonized by distinctly higher proportions of gathering-collectors (e.g. Corynoneura spp., Parametriocnemus sp., Stilocladius spp., Constempellina spp., Micropsectra spp.). Overall, the cherry packs supported a significantly higher shredder and gathering-collector biomass per g leaf pack than either the maple or beech leaves. We conclude that (1) shredders were preferentially associated with cherry leaf packs due to its higher palatability compared to the maple and beech leaves, and (2) similar colonization patterns exhibited by gathering-collectors on all three leaf species were the result of a supply of similar-quality fine detritus.

The larvae of these three mites are described for the first time.

1. - Aturus scaber Kramer.

Females of this species lay one, very large egg at a time, suggesting a suppression of the larval stage and direct development to nymph. This expectation has been refuted and the larvae bred in the laboratory. Further information on the life-history is lacking but a parasatic stage is indicated.

2 . - Piona uncata Koenike.

The complete life-history of this mite is described. In the specimens studied the main host was Chironomus plumosus L. Work by Stout shows that this species has an alternative direct development. The larvae are similar except in size to those of P. coccinea Koch.

3. - Protzia eximia Protz.

Eggs are found throughout the winter and laboratory tests show that hatching is dependant on temperature. The larvae resemble those of Panisopsis species, and run actively on the water film. They are able to jump 2 cm from the surface and use this ability to gain a place on their hosts, an unidentified Trichopteran and the fly, Weidemannia bistigmata Curtis. There are probably two generations a year.

An up-to-date table gives hosts for 150 species and references for this information.

Three species of Isoperla occur in Fennoscandia. The most common is I. grammatica, although it has not been recordedabove the subalpine vegetation belt. I. difformis has a similar distribution, but is less common. I. obscura occurs mainlyat high latitudes and altitudes, although it is also abundant in large rivers.Eggs were reared at temperatures of 4, 8, 12, 16, 20 and 24° C. I. difformis did not hatch at 4° C. I. grammatica at 4and 8° C while I. obscura did not hatch at 16° C and above. Egg mortality was high in I. difformis at 24° C. Incubationperiod decreased with increase in temperature and varied between 28 and 68 days in I. grammatica and between 15 and83 days in I. difformis. For I. grammatica and I. difformis, the relationship between the egg incubation period and thewater temperature was linear on logarithmic scales. For I. obscura, no such relationship was found and the mean incubation period at all temperatures was 305 ± 57 (S.D.) days. Explanations are presented to explain these differences in egg incubation characteristics.

Microcystis blooms occur worldwide in eutrophic lakes. Microcystins (MCs) including microcystin-LR (MC-LR) released by Microcystis have adverse effects on aquatic organisms such as rotifers. To detect population growth and reproductive responses, the rotifer Brachionus calyciflorus was exposed to MC-LR at eight concentrations ranging from 0 to 200 μg.L−1 under different temperature (20, 25 and 30°C), and population growth rate (r), ovigerous females/non-ovigerous females (OF/NOF) ratio, mictic females/amictic females (MF/AF) ratio, mictic rate (MR), and 7-d resting egg (7-d RE) production were investigated. The results showed that higher temperatures stimulate the population growth of B. calyciflorus. B. calyciflorus showed high tolerance to MC-LR at concentrations lower than 200 μg.L−1 under different temperatures. Compared to the control, MC-LR at all concentrations increased the r (P<0.05), but decreased the OF/NOF and the MR of the rotifers at 30°C (P<0.01). A clear dose–response relationship existed between the r, the OF/NOF, and the MR of B. calyciflorus and MC-LR concentration at 30°C, respectively. These sensitive parameters could be used to monitor the ecological effects of low concentrations of MC-LR in natural water bodies at the high temperature.

An analysis of the morphology and the prey consumed by two carnivorous species of bladderworts (Utricularia gibba and U. sp.2) from a pond (Annie pond) in the heart of the Kaw swamp (French Guiana) has allowed a comparison of the preferential prey of: 1) a single species over two different periods (the end of the rainy season and the beginning of the dry season during an oligotrophic phase); and 2) the two coexistent species within a single period (the beginning of the dry season, during a temporary mesotrophic phase). Among the immediately adjacent planktonic and periphytic animals, and despite their low prevalence relative to smaller organisms such as Gastrotricha and Rotifera, cladocerans and copepods (particularly large individuals) appeared to be strongly predated. The differing organization and size-class distributions of the traps, as well as the extent of epiphytic colonization, had a probable defining effect on the alimentary regime of the two species of Utricularia. These more or less adaptive characteristics allowed the bladderworts to take advantage of the distinct preferences of various potential prey in terms of nutrition behaviour and habitat so to limit the feeding competition between the two sympatric species. The impact of this selective zooplankton predation by bladderworts on the trophic organization and the ecological functions of this pond are also addressed.

The genus Labiobaetis recently has been reported from Madagascar by Lugo-Ortiz and McCafferty (1997). The two described species were only known from the nymphal stage. Examination of material from more than 800 samples in Madagascar allows descriptions of six new species: Labiobaetis longicercus, L. dambrensis, L. nigrocercus, L. vulgaris, L. punctatus and L. gilliesi. They can be distinguished easily by the shape of the second segment of the labial palp, the shape of the second segment of the maxillary palp, the setation of the labrum, the number of gills, the presence or absence of hindwings and coloration of the abdomen. At present, the imagoes of only five of the eight species are known. They can be identified by the presence or absence of hindwings, coloration of the wings, shape of the sclerotized process between gonopods and shape of the third segment of the gonopods. As all the species assigned to Labiobaetis were recently reassigned to Pseudocloeon, the status and validity of the genera Labiobaetis and Pseudocloeon are discussed.

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.

Les limites de survie indéfinie à température constante se sont montrées les suivantes : 12 à 14° C pour C. alpina, 16 à 17° C pour P, felina, 23 à 24° C pour P. nigra. Les trois Planaires sont néanmoins capables de résister à des températures bien plus élevées pendant un petit nombre de jours.

Using the epilithic diatoms as indicators of environmental conditions, 10 lakes in the High Tatra Mountains were characterised with regard to their stage of acidification. The diatom communities were diverse; 210 taxa were found, including 27 species of north and alpine preference. On the basis of cluster analysis, two groups of lakes were distinguished. The first group included shallow, moderately acidified lakes (Dlugi and Zmarzly Gasienicowy lakes), where acidophilous organisms prevailed, with Achnanthes marginulata being the most numerous. The structure of the diatom community in Dlugi lake was stable over 4 years of observations and did not show any progress in acidification. The second group included mostly very deep, non-acidified lakes where circumneutral organisms prevailed, and among them Achnanthes minutissima was dominant in most cases. The diatom community structures mostly confirmed the status of the lakes studied as judged from their water chemistry.

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.