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.

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 ichthyofauna of the River Minho tidal freshwater wetlands (TFWs) was studied in a semi-enclosed area, between June 2007 and May 2010, to determine temporal patterns of abundance, biomass and species composition. Fish catches, standardized by the number of fyke nets and by the fishing effort, were analysed and related to river flow, water temperature and precipitation. In total, 21 fish species were identified including six non-indigenous species (NIS) which represented 15% of the total captures (yet 43% of the biomass). Regarding ecological guilds, 82% were freshwater species (61% of the biomass) which included all NIS, whereas 13% of the catches were catadromous species (31% biomass) corresponding to eels. Only 4% were estuarine species (1% biomass) and together marine estuarine opportunists and anadromous species accomplished 1% (2 and 6% biomass, respectively). The fish assemblage showed seasonal patterns with a clear distinction between autumn/winter and spring/summer periods. Significant differences in abundance and biomass were also detected between autumn/winter of 2007/2008 and 2008/2009, i.e., inter-annual variations, with the latter period with lower catches yet higher dominance of NIS. Besides, higher water temperature had a significant negative effect on the observed number of species, but a positive effect on the abundance and biomass of NIS. More attention has to be given to TFWs and their role in structuring fish assemblages, because this information is vital for a sound management, conservation and restoration of estuarine areas.

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.

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'action déplétive du cuivre sur les cellules à mucus au niveau des filaments branchiaux chez la Carpe, a été mise en évidence. Cette déplétion est suivie d'une inhibition des cellules mucosécrétrices, levée seulement après un retour aux conditions normales.

Un pompage à gros débit dans le gouffre de la Peyrère, regard sur le karst noyé du système karstique du Baget (Ariège, France), a provoqué une dérive importante des microcrustacés stygobies et, notamment, des Harpacticides de ce secteur. Le site du pompage a été partiellement dépeuplé et, un an plus tard, ne semblait pas avoir retrouvé son équilibre antérieur. Ce pompage a également perturbé le peuplement des Harpacticides du drainage en aval du système sans, toutefois, remettre en cause le peuplement global de ce groupe dans le système.

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.

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.

Lake Vela is a shallow lake facing eutrophication, like many other freshwater reservoirs. A reduction in biodiversity has been observed and cyanobacterial blooms are frequent, occasionally leading to large fish kills. An annual sampling cycle was carried out in the present study, with the aim of understanding the present seasonal variation of Lake Vela’s physico-chemistry and cladoceran assemblage. The present results were compared with those obtained in previous studies. Presently, Lake Vela is facing higher nutrient and Chl a levels than in past years. The cladoceran assemblage is now dominated by small-bodied forms, such as Chydoridae and Bosmina longirostris, except in the spring peak of Daphnia longispina. Still, the seasonal pattern of the cladoceran community is more or less coherent with the general model observed in other temperate lakes. The results also suggest that this was a rather unusual year, with a Daphnia summer peak, probably because of a large fish kill that occurred in late spring.

Two sediment cores from acid lake Store Hovvatn were analysed for chironomid head capsule remains over a sequence spanning from about 1730 A.D. to the late 1970s. Up to 30 taxa were identified from one (0.5 cm) level in the cores. Principal component analysis of taxon relative abundances showed a gradient corresponding more or less to the sediment sample chronology. Redundancy analysis with some chemostratigraphical variables, and with pH values inferred from diatoms, indicated that chironomid community change could be explained as a response to acidification. However, most of the taxa that declined or disappearedup-core are known to occur in acid lakes and pH sensitivity per se does not seem to explain the response of individualspecies. The relative abundance of Orthocladiinae increased up-core and the long term change may be conceived in terms of a retarded productivity or oligotrophication. The most conspicuous change in the chironomid community appears to coincide with decreasing aluminium concentrations in the sediments and may indicate toxic effects from labile aluminium in the water column.

Cyanobacteria are a worldwide group of photosynthetic prokaryotes that can cause nuisance blooms in eutrophic waters. It is generally accepted that their resting cells, akinetes, play an important role in the dispersal, recruitment, initiation of blooms and survival under unfavourable conditions, therefore information on the germination, distribution and abundance of akinetes in natural sediments is essential for understanding the ecology and bloom dynamics of N2-fixing cyanobacteria. The present study describes the effect of irradiance on the germination and subsequent growth of N2-fixing filamentous cyanobacteria developed from natural akinete stock in sediment of Lake Balaton (Hungary) with varying phosphorous supply. The research focuses on the invasive Cylindrospermopsis raciborskii and Aphanizomenon flos-aquae the most abundant species of this lake. In the experiments, the germination of ten filamentous N2-fixing cyanobacteria species was observed. The species assemblages of the germinated cyanobacteria populations showed strong light and phosphorus dependence. Anabaena and Anabaenopsis species became dominant in phosphorous-rich conditions, while in phosphorus-deficient environments Aphanizomenon species and C. raciborskii dominated. Among the germinated filaments we have detected Anabaenopsis cunningtonii and Anabaena compacta, which have not been observed in Lake Balaton previously. Our results suggest that among the filamentous heterocytic cyanobacteria of this shallow lake the invasive C. raciborskii was the best competitor when phosphorus supply and irradiance were low.

The prediction of the composition and structure of fish communities in reservoirs is essential in the management of the fisheries,an activity fundamental in emerging countries where human riverine populations depend on freshwater fish for their animalprotein supply. The transformation of the river in a reservoir constitutes an environmental filter for the riverine fish specieswhich, before anything else, must find food resources in the reservoir for their individual maintenance. After the closure of Petit-Saut Dam in 1994, fish were sampled by gillnets in the Sinnamary River in the period 1994-2000 and in the Petit-Saut Reservoirbetween 1998 and 2000. The stomach contents of the main species were analysed for 6 main food items. Analyses of similaritywere conducted in order to compare river and reservoir diets of individual species on one hand and the trophic structure offish assemblages on the other. Twelve species out of 23 analysed showed significant modifications in their feeding habits. Thechanges affected species from every feeding guild as established from the river stomach contents data. As a consequence thetrophic structure was deeply modified in the reservoir. The abundance of piscivores and herbivores decreased while the relativeimportance of omnivores and invertivores increased. There was a general tendency for species to increase their food niche breath.The ability of species to modify their feeding habits is shown to be of fundamental importance for the trophic organizationof the fish community in the Petit-Saut Reservoir.

To determine the relationship between biofilm characteristics and organic nutrient content, we investigated the development of hyporheic biofilms on artificial substrata (glass slides) in the early phase of bacterial colonization (one week) in contrasting river habitats with significantly different concentrations of dissolved organic carbon (DOC) and biodegradable and refractory DOC (BDOC and RDOC). Results suggest that the quality of DOC (i.e. BDOC versus RDOC content) controlled electron -transport system (ETS)-active bacterial abundances early in colonization, while DOC concentrations limit biofilm development onlyin the latter phase of colonization.

The lichen flora of freshwater habitats in the Italian Alps is reviewed: 20 genera and 43 species are known, of which crustoselichens with sexual reproduction prevail. Freshwater lichen richness is highest near the treeline on siliceous substrata in exposedand well-lit sites. The importance of several ecological factors on freshwater lichen distribution and ecology is discussed.

The effect of substrate texture on colonization by stream macroinvertebrates was studied in a mountain stream. Experimental patches made of natural substrate, with two levels of cobble and gravel texture (rough and smooth), were subjected to two colonization periods (two hours and one week) within a riffle. Cobble texture affected the number of individuals and taxa colonizing substrate patches, although these relationships depended on time of colonization and some local environmental factors. Texture influence was different for different taxa, and only affected the scraper functional feeding group after one week of colonization, probably in relation to the development of an epilithic layer. These results suggest a significant effect of the surface texture of substrate on colonization by macroinvertebrates, although the effect is complex and needs more careful examination.

Particulate organic matter (POM), dissolved organic matter (DOM), bacteria and cladoceran were sampled seasonally atZhihugang Estuary and Lake Center in Taihu Lake. The δ13C of the four organic matter fractions showed consistent temporalvariation, with heaviest values in summer and lower at other times of the year. The cladoceran δ13C showed a significantcorrelation with that of POM, reflecting a heavy dietary dependence on POM during the study period. The bacteria becameenriched in 13C compared with that of DOM throughout the sampling dates, although no significant relationship was foundbetween the two fractions. δ13C values of POM, cladoceran and bacteria were all negative significantly correlated with oxidationand reduction potential (ORP), and specific conductivity (SpCond). As for δ15N, the seasonal pattern of food web componentswas variable. The POM δ15N signature exhibited the most enriched isotope ratios during the summer months when dissolvedinorganic nitrogen (DIN) nutrients were at their lowest concentrations. The consumption of DIN in summer can explain in partthe progressive accumulation of heavy nitrogen isotopes during this period. Spatially, δ13C and δ15N of the food web componentswere all slightly depleted at Estuary than that at Lake Center during the study period, possibly due to large allochthonous inputsat Zhihugang Estuary. Relatively wide ranges of stable isotopic values from both sites suggest that seasonality should beconsidered when attempting to establish food web structures in a eutrophic lake.

The description of new taxa of small minnow mayflies (Insecta : Ephemeroptera : Baetidae) includes the following. Cryptonymphacopiosa n. gen. and n.sp., from Brazil, is distinguished by long, robust, pilose setae on the medial margin of the prosthecae; apically narrow glossae and paraglossae ; absence of hindwingpads ; and long, basally narrow gill 1. Rivudiva n. gen., includingR. minantenna n.sp., from Brazil, and R. trichobasis n.sp., from Brazil and Paraguay, is distinguished by a broad linguaand relatively narrow superlinguae ; broad glossae with a distomedial row of long, robust, falcate, simple setae ; and tarsal clawswith minute denticles arranged in an ellipse. Spiritiops silvudus n.gen. and n. sp., from Brazil and French Guyana, is distinguishedby a long, robust, pilose seta arising from the medial margin of the right prostheca and tarsal claws with two rows of denticlesand lateral long, fine, simple seta. Varipes lasiobrachius n. gen. and n. sp., from Colombia and Ecuador, is distinguished bythe reduced right prostheca and U-shape arrangement of denticles on the tarsal claws. Zelusia principalis n. gen. and n. sp., fromBrazil and Colombia, is distinguished by a medially raised labrum, bifid right prostheca, and long, slender maxillary palps.

South American species of small minnow mayflies (Insecta : Ephemeroptera : Baetidae) that have been previously placed in Baetis Leach or Pseudocloeon Klapálek are revised. Species that resided in Baetis are shown to include Camelobaetidius alcyoneus, n. comb., C. coveloae, n. comb., C. dryops, n. comb., C. tantillus, n. comb., Cloeodes nocturnus, n. comb., C. stelzneri, n. comb., Fallceon inops, n. comb., F. murphyae, n. comb., F. yaro, n. comb., Moribaetis aneto, n. comb., M. comes, n. comb., and M. socius, n. comb. Species that resided in Pseudocloeon are shown to include Americabaetis albinervis, n. comb., A. bridarolli, n. comb., A. bruchi, n. comb., A. jorgenseni, n. comb., A. oldendorffi, n. comb., A. peterseni, n. comb., A. weiseri, n. comb., Cloeodes turbinops, n. comb., and C. venezuelensis, n. comb. The bases of the revisions are discussed under each species. The presence of Fallceon and Moribaetis in South America is confirmed for the first time.

Knowledge on ecological impacts of forestry practices on aquatic ecosystems relies almost exclusively on data from large-scale forest harvesting, often involving clearfelling of whole stream catchments. To determine effects associated with less intensive and widespread forest management, we examined the responses of headwater streams to small-scale forest harvesting, including riparian zones adjacent to study reaches but corresponding to less than 5% of the catchment areas. Stream reaches running through recently (2–4 years) harvested forest patches were paired with and compared with adjacent reaches bordered by mature broadleaf forest. We determined abiotic stream characteristics, invertebrate community structures and abundances, trout size and population densities, and leaf litter breakdown rates in each of these pairs. Harvested reaches were found to have different channel cross-section morphology and greater invertebrate abundances in leaf packs than mature forest reaches. Shifts in the abundance of common invertebrate predators were also attributed to riparian forest harvesting. Litter breakdown rates and brown trout densities did not show any significant difference between harvested and mature forest reaches across the four site pairs, possibly because of nonlinear responses to post-harvest riparian canopy openness. Managers must be aware that small-scale forest harvesting in stream riparian areas is not without consequences for aquatic ecosystems. Whether natural riparian forest openings, such as caused by tree death and blow-down, have similar effects on stream ecosystems is an important question to address if we are to confirm the usefulness of small-scale forestry and improve forest and stream management schemes.