We describe here the limnological characteristics of the Santillana Reservoir (Spain) and study the phytoplankton distributionduring a typical growing season (July to November). The reservoir is a eutrophic stratified waterbody in central part of Spain,in which the average phytoplankton biomass in summer is higher than 20 µg chlorophyll a 1-1. Maximum phytoplankton biomassin 1999 occurred between the end of summer and the beginning of autumn (September-October). Cyanobacteria, that weregenerally prevalent in phytoplankton community, clearly dominated during the peak of phytoplankton biomass. Microcystiswesenbergii was dominant amongst the cyanobacteria and represented almost 100 % of the biomass at the time of maximumphytoplankton value. The importance of environmental variables triggering cyanobacterial bloom events is discussed. Ourresults indicate that neither temperature nor N/P ratio are related to the bloom development. However, high nutrient concentration(ammonium in particular) and stability of the watercolumn seems to coincide with the maximum abundance of Microcystis wesenbergii.

We studied the rotifer fauna of one of the most pristine peat-swamps in the Southern Thai province of Narathiwas, To Daengpeat swamp. The samples yielded a total of sixty-seven rotifer species. Of these, three -Keratella mixta (Oparina-Charitonova),Lecane enowi Segers & Mertens and Monommata dentata Wulfert- are new to the Oriental region and the Thai fauna, one,Keratella taksinensis n. sp., is new to science. The fauna consists mainly of cosmopolitan (sensu lato) species, complementedby some Paleotropical and endemic taxa, and is dominated by littoral-benthonic taxa, especially Lecane and, to a lesser extent,Lepadella.

Seasonal samples of zooplankton were taken during 1997-1999 at fifteen stations in the Salado River basin, and analysed inorder to study the rotifer fauna. Spatio-temporal changes in the rotifer plankton composition were examined in the main channeland its tributaries. The majority of species found are tolerant of a wide range of pH, whereas others prefer neutral to alkalinevalues. The total rotifer plankton density increased downstream from the headwaters to the middle sector of the river. Theassociated shallow lakes and tributaries were an important source of species. Variations in density and number of species wereshown to be associated with conductivity, and species tolerant of high conductivity conditions were especially prevalent (upper7,000 µS cm-1). Rotifer density was influenced by hydrological conditions, which promoted maximum values during low waterperiods and in the high water condition promoted the incorporation of species from shallow lakes connected with the river duringflood events. The species associations found are related to such water parameters as conductivity and nutrient availability andto the presence of ponds and shallow, waterlogged depressions connected in varying extent to the main channel.

In the present paper Candonopsis murchisoni n. sp., C. dani n. sp., C. williami n. sp., C. kimberleyi n. sp., and C. westaustraliensisn. sp., are described, while C. tenuis (Brady, 1886) is redescribed. All species have been collected in the subterraneanwaters of Western Australia. The new species are easily distinguishable from the existing world species in details of the carapace,walking leg, cleaning leg, furca and hemipenis. Because of new features found, revised diagnosis and a key to the worldspecies are provided. Some species, previously described in the genus Candonopsis Vavra, 1891, are considered as incertaesedis, while others are removed from this genus, which now contains 25 species. Finally, the authors propose the elevation ofthe subgenera Caribecandona Broodbakker, 1983 and Cubacandona Broodbakker, 1983 to the generic level.

Two greenhouses were operated as emergence traps in a stream in southwestern Lower Austria from 1984 to 1989 at a distanceof 28 m from each other. The stream bed under the traps was covered by a metal sheet alternately for one year, thus preventingemergence under the trap with covered bottom so that insects caught in this trap must have come from outside. Theresults have shown that insects from outside constitute a high but un quantifiable proportion of the total catch. In many instancesthere were more insects in the trap with a covered stream bed than in the open one. Therefore the emergence trap method is notadequate for quantitative surface-related studies, including secondary production.

Pour caractériser l'état d'un écosystème aquatique contaminé par des toxiques il est nécessaire de développer des méthodesd'évaluation des impacts écotoxicologiques, basées à la fois sur l'étude de réponses physiologiques et sur la structure des communautésvivant dans cet écosystème. La méthode PICT (Pollution-Induced Community Tolerance) proposée par Blanck et al.(1988), répond à ces deux critères. Elle est fondée sur l'hypothèse qu'une communauté biologique naturelle est constituée dedifférents «composants» ayant des sensibilités variables vis-à-vis d'un toxique donné. Ainsi, suite à une exposition à un toxique,les organismes les plus sensibles ne sont plus concurrentiels et sont remplacés par des organismes plus tolérants. La communautérésultante présente alors une tolérance vis-à-vis du toxique, supérieure à celle observée pour une communauté semblablemais n'ayant pas connu de pression de sélection par ce toxique. Cette différence de réponse peut donner une indication sur l'étatde pollution des milieux dans lesquels ont été échantillonnées différentes communautés. Le choix du test physiologique pourévaluer la tolérance de la communauté est fondamental car la réponse dépend d'une part, du mode d'action du toxique et d'autrepart, des mécanismes à l'origine de la tolérance de la communauté. Il existe peu d'outils de bioévaluation des milieux naturelssoumis à des contaminations toxiques, et cette méthode mérite donc d'être développée. Des travaux appliquant la méthode PICTà des communautés variées et dans divers milieux, permettraient de valider la méthode et de résoudre certains problèmes, quantà la détection de la tolérance. Le développement de méthodologies nouvelles pour caractériser la structure et la tolérance descommunautés étudiées est fondamental pour progresser dans nos connaissances sur le risque écotoxicologique.