To test whether leaf litter from eucalyptus plantations affects stream macroinvertebrate communities, we manipulated litterinputs into a small headwater tributary of the Agüera stream (northern Spain) running under mixed deciduous forests. Threecontiguous 50 m long reaches were used: the upstream reach was left as a control (site C), whereas the two downstream siteswere covered by 1 mm mesh nets to avoid natural litter inputs, and twice a month received litter collected at a deciduous forest(site D, mid) or a eucalyptus plantation (site E, downstream). Benthic Surber samples were taken from the three sites before andafter the treatment and density, biomass and structure of the community were compared. Density and biomass of macroinvertebratesdid not differ among sites before the treatment. Total density and biomass of macroinvertebrates increased in all the sitesduring the experimental period but most considerably at the site were deciduous forest inputs were simulated (station D). At theend of the experiment shredders were significantly less abundant at site E (eucalyptus) than at site D (deciduous). In addition,shredder density and biomass per total organic matter amount and per total leaf amount became higher at site D. In conclusion,these results suggest a subtle negative impact of eucalyptus litter on stream macroinvertebrate communities, especially on shredders.

Two-day life cycle tests with the rotifer Brachionus calyciflorus were run to study the nutritional quality effects to rotifers ofScenedesmus pectinatus grown under non-limiting, nitrogen limiting and phosphorus limiting conditions and the feedback of therotifers on the food algae. Under nutrient-limited conditions of its algal food Brachionus production was depressed, animals producedfewer eggs and were smaller sized. Clearance rates of Brachionus offered non-nutrient-limited and nutrient-limited foodwere similar. The number of cells per colony was similar for S. pectinatus under nitrogen limited and phosphorus limited conditionsboth in the absence and presence of Brachionus. Cell volumes of phosphorus limited S. pectinatus were larger than thoseof nitrogen limited cells. The most dramatic response of the food alga S. pectinatus was observed in non-nutrient-limited conditions:a strong size enlargement occurred only in the presence of Brachionus. This was caused by a higher share of eight-celledcolonies and larger individual cell volumes in the presence of rotifers than in their absence. S. pectinatus might gain an advantageof becoming larger in moving out of the feeding window of its enemy, but nutrient limited conditions might undermine theeffectiveness of such reaction.

Animal populations have a certain synchronization between their fluctuations and the environmental factors which have adirect influence on density, sex ratio and recruitment. Trichodactylus borellianus is a common freshwater crab of theTrichodactylidae family, originary from South America. This crab is omnivorous and grazes upon the littoral communities. Thepresent study is the first analysis of the natural distribution and population dynamics of freshwater crabs in La Plata Basin(Argentina) and their relationship with certain abiotic and biotic parameters. It was carried out in three environments (riverinezone of streams and river) of the Paraná River floodplain. Crab populations were sampled monthly from August 2001 to October2002. The mean crab abundance among the study sites was significantly different, being lower in samples from the environmentsurrounding the principal channel of the Paraná River. Crab density showed two peaks: the highest occurred during late winterand early spring, and the lowest during late summer. Males were only more abundant in late winter and spring. In spring, summerand autumn, the population showed a contagious distribution. The population displayed a regular arrangement in winter.From mid-spring to mid-autumn juveniles were very frequent whereas adults predominated the rest of the year. Total crab numberin the stream nearest to the main channel varied according to the level and temperature of the river. In the other sites, locatedfurther from the main channel of the Paraná River, crab numbers and vegetation biomass showed a more similar arrangementwith a higher correlation.

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.

Mediterranean temporary ponds (MTPs) are highly distinctive habitats with intermittent and unstable environmental conditions,inhabited by several rare and endemic plant and animal species. Temporary pond ecosystems have been classified asendangered all over the world; nevertheless, they are disappearing at a high rate, especially in the Mediterranean region. MTPsare a priority habitat under the European Union Habitats Directive and thus appropriate management and conservation effortsshould be applied. Further research is needed in order to better understand the environmental characteristics and ecology of thishabitat which is not always the case in many countries. In this study a range of environmental data were collected from the GreekMTP habitat sites including the altitude, the geology, the representativity, the ecological status and other biological data aimingto assess the environmental status of all known Greek MTPs. Statistical analysis were performed and thematic maps were createdusing a Geographical Information System (GIS). Greek MTP’s were classified according to their characteristics and habitatpressures were identified and further analysed. A comparison between the present environmental status of the MTPs in Greecewith the MTPs in other Mediterranean countries was undertaken and relevant conservation and management measures were proposed.The outcome of this study was that a significant percentage of the MTP habitat sites in Greece are at risk mainly due tohuman activities, such as agricultural pollution, expansion of cropland and water resources over-exploitation. It was concludedthat immediate restoration and conservation actions should be taken so as to prevent further ecological degradation.

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 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.