Invited Lectures.- A commentary on current approaches in the aquatic sciences.- Spatial heterogeneity as a multiscale characteristic of zooplankton community.- One: Invertebrates.- Genetic structure of natural populations of Nitrobacter in an aquatic environment.- Diel changes in the alkaline phosphatase activity of bacteria and phytoplankton in the hyper- eutrophic Villerest reservoir (Roanne, France).- Vertical and seasonal variations of inorganic carbon allocation into macromolecules by phytoplankton population in a brown-colored and a clear-water lake.- The microbial loop in a humic lake: seasonal and vertical variations in the structure of the different communities.- Diel changes in the biochemical composition of the particulate matter coupled with several parameters in the hypereutrophic Villerest reservoir (Roanne, France).- Spatio-temporal distribution of the microphytobenthic biomass in intertidal flats of Tagus Estuary (Portugal).- Heterogeneity of periphyton in French Mediterranean rivers.- Assessment of the bio-indicator capacity of aquatic macrophytes using multivariate analysis.- Time and spatial dynamics of Mediterranean lagoon macrobenthos during an exceptionally prolonged interruption of freshwater inputs.- A comparative study of the zoobenthos of eight land-water interfaces (Lake of Geneva).- The macroinvertebrate communities of streams draining a small granitic catchment exposed to acidic precipitations (Vosges Mountains, northeastern France).- Spatial distribution and temporal variability of some aquatic insects in the Franco-Geneva river, Allondon.- Use and partition of space and resources by two coexisting Rhyacophila species (Trichoptera) in a high mountain stream.- Diel patterns of feeding and vertical migration in daphnids and diaptomids during the clear water phase in Lake Geneva (France).- Modification of migratory behavior of planktonic Crustacea in the presence of a bloom of Microcystis aeruginosa (Cyanobacteria).- Spatial and temporal distribution of the zoobenthos community in a woodland pond (Switzer-land).- Spatial patterns of planktonic microcrustaceans in a small shallow lake.- Space and time distribution of zooplankton in a Mediterranean lagoon (Etang de Berre).- Feeding behavior and migrations in a natural population of the copepod Acartia tonsa.- Two: Vertebrates.- Habitat variability and space utilization by the amphibian communities of the French Upper-Rhne floodplain.- Heterogeneity and typology of fish habitat in the main stream of a Breton coastal river (Elorn-Finistre, France).- Analysis of spatial and temporal organization in a salmonid brook in relation to physical factors and macrophytic vegetation.- Reproduction, condition and food of adult arctic charr (Salvelinus alpinus, L.) in Lake Pavin (Massif Central, France).- Sand smelt (Atherina boyeri) migration within the water system of the Camargue, southern France.- Spatial pattern of size distribution of four fish species on Runion coral reef flats.- Microhabitat requirements for settlement of juveniles sparid fishes on Mediterranean rocky shores.- Spatial and temporal separation of littoral zone fishes of Lake Geneva (Switzerland-France).- Effects of vertical prey distribution on the food-searching behavior of Danube bleak Chalcal-burnus chalcoides mento.- Temporal distribution of perch (Perca fluviatilis L.) in a lake-reservoir (Moselle, France): analysis of catches with vertical gill nets.- Impact of Caulerpa taxifola colonization on the littoral ichthyofauna of North-Western Mediterranean sea: preliminary results.- Ichthyogeographic regions and watershed size in the French river Rhne network.- Three: Methodology.- In situ observation of suspended solid aggregates in rivers.- Multi-scale heterogeneity in a macrobenthic epifauna community.- Examination through a Principal Component Analysis of the phosphorus exchanges between sediments and water in trophically different reservoirs.- 31P-NMR study of natural phytoplankton