Many freshwater algae are parasitized by aquatic fungi belonging to the Chytridiales Order. The top-down effects of parasitism result in individual losses within algal populations. We present data on the parasitism of the diatom Asterionella formosa Hassall by chytrids, occurring in response to hydrodynamic disturbances and the architecture of the algal host on the landscape scale. Among a series of nine reservoirs, the observed pattern of parasitism depends on the levels of hydrodynamic disturbance: the rate of parasitism is higher at intermediate disturbance levels. A. formosa cells are not randomly parasitized. Whatever the disturbance levels, fungi were found to mostly parasitize cell clusters forming non-stellate colonies.

The mid Tafna wadi (N-W Algeria) is exposed to several man induced disturbances including urban, industrial, and agricultural effluents, and alteration of the natural flow regime. The recent installation of a reservoir upstream of the study area has strongly modified the flow regime by extending the period of low water level, and this stream section is only occasionally fed by water releases. Investigations on the hyporheos and benthos of this stream have allowed the comparison of densities, taxa richness and diversity, during three hydrological periods (natural high water, low flow and reservoir water releases), with the aim to highlight effects of the reservoir management on downstream hydrosystems. Species richness and abundance of stygobite crustaceans were low in the hyporheos. Surface water Crustaceans represented 53% of the overall fauna, with Cyclopoidae composing 50% of the Crustaceans. The dominance of the Cyclopoidae was also observed in the hyporheos. Daphniidae were more abundant (37%) in the benthic habitat than in the hyporheic zone. The alternation of high and low discharges appeared to affect the hyporheos more than the benthic communities. The stability concept of the hyporheic habitat does not fit with our results showing a great range of spatial (mosaic habitat) and temporal changes according to the flow regime.

While the impacts of groundwater contamination on interstitial invertebrate communities are well studied, very few work have examined other potential disturbance resulting from agricultural practices. In the present study, the interstitial crustacean fauna was studied in an alluvial aquifer characterized by intensive cereal irrigation, to test the influence of groundwater extraction on the assemblage characteristics (abundance, diversity, persistence, species distribution patterns). Micro- and macrocrustaceans were sampled at 4 seasons in 15 wells with contrasted groundwater use (cereal irrigation / domestic use / no groundwater use) scattered over a 250 km2 alluvial floodplain. The aquifer harbored diverse assemblages dominated numerically and specifically by cyclopoids. Total abundance, diversity expressed using species richness or Shannon index, overall persistence in species composition did not vary between stations whether micro- or macrocrustaceans were considered. Yet, marked differences in the cyclopoids assemblages composition were found in relation to groundwater utilization. Disturbed irrigation wells were dominated by epigean species, while hypogean species were mainly found in less impacted domestic wells. In contrast, amphipods/isopods did not exhibit particular assemblages composition between irrigation, domestic or abandoned wells. The differential responses between micro- / macrocrustaceans, epigean / hypogean species emphasized that levels of disturbance are strongly taxondependent. At the scale of the aquifer, these results suggest that groundwater extraction resulting from intensive irrigation has to be considered as a potential disturbance for the interstitial communities.

The spatial and temporal distribution patterns of benthic macroinvertebrates were studied in an intermittent river in Algeria (Chelif wadi, North Africa), by using the self-organizing map (SOM), an unsupervised artificial neural network. The samples were collected monthly at 8 sampling sites (630 to 20 m above sea level) and community variation was analysed in space and time. Overall, the study sites showed a very poor macroinvertebrate fauna: more than 60% of samples contained less than 11 species, and 99% had less than 30 species. Furthermore, most species displayed very low abundance: 66% of the species were represented by less than 20 individuals (abundance). Among the identified taxa, Chironomidae was the dominant taxon at all sampling sites except at the most upstream site (630 m a.s.l.) where it was replaced by Coleoptera. Concerning monthly changes, the species richness was very low in August and October. Through the learning process of the SOM, samples were classified into four clusters by the SOM, and the classification was mainly related to the location of the sampling sites. Benthic macroinvertebrates were divided into four classes, which revealed the influence of pollution on their longitudinal distribution in this stream. According to the distribution gradients of the environmental variables on the SOM map, their influence on the classification of the sampling sites could be assessed effectively.

We report the results of a study carried out in 2002 on the main limnological characteristics and on the ostracod communities of 16 wetlands of the Parco Oglio Sud (Northern Italy). Physical and hydrochemical variables were measured and ostracod samples were collected in different seasons (April, June, August, and October). Most of the considered sites were characterised by high concentrations of nitrogenous compounds due to washing out from cultivated areas, intermittent river flooding and internal recycling. Observed differences in macrophyte communities were consistent with trophic status of waters, with pleustonic forms dominating most degraded areas. Both morphology of valves (by scanning electron microscopy) and anatomy of soft parts were analysed for ostracod species identification. Nineteen ostracod species in five families were found. Two species, Candona weltneri and Pseudocandona compressa, are new records for Italy. Cypria ophthalmica was collected from all sampling sites; other relatively common species were Cypridopsis vidua, Cyclocypris ovum, and Candona weltneri. No clear seasonality was observed in community structure; highest species diversity occurred in June in most of the studied wetlands. The maximum number of species per site was seven, and a maximum of six species was found in a single sample. Ostracod occurrence in relation to environmental factors was examined using Canonical correspondence analysis (CCA). Total alkalinity and pH were the most important variables structuring the species assemblages. The ostracod fauna found in this area was compared to the known distribution of recent non-marine ostracods in Italy, and the validity of published checklists is discussed.

Thirty-six chrysophycean stomatocysts are reported from the dystrophic Staw Toporowy Nizni lake in the Tatra National Park, Poland. Of these, 7 morphotypes are new to science, 10 are new to Europe, and 13 are new to Poland. SEM micrographs and data on distribution are provided for each stomatocyst. Synonimizations of two stomatocysts are proposed: stomatocyst 58 Hansen 2001 with stomatocyst 117 Zeeb et al. 1990, and stomatocyst 91 Hansen 2001 with stomatocyst 239 Duff et al. 1995. The number of chrysophycean stomatocysts recorded from Poland is currently estimated to comprise 65 extant morphotypes.

The first list of Trichoptera from lakes Vico and Bolsena is reported. It is the result of research carried out in 1955 and 19711979 in lake Vico, and in 1957 and 1959-1990 in lake Bolsena. The distribution of caddisflies around the littoral zone depends on the environmental characteristics of the microhabitats. Overall, 16 species from 7 families were collected, 8 of which were found in both lakes, whereas 5 were only collected in Lake Vico, and 3 only occurred in Lake Bolsena. Hydroptila aegyptia and Ecnomus tenellus were the most abundant species in Vico, Tinodes waeneri and T. maclachlani in Bolsena. The trophic categories of the larvae and their gregarines were identified.

The diagnostic features of the African species of the monotypic subfamily Diplodontinae K. Viets, 1936 are discussed. D. chutteri K.O.Viets, 1980 obviously represents the outgroup of all remaining species. D. scapularis Dugés, 1834 and D. semiperforatus Walter, 1925, both in Africa restricted to the palaearctic part, are sister species characterized by synapomorphic character states in the genital field and shape of palps and legs. Diplodontus schaubi gracilirostris Lundblad, 1942 is elevated to species rank. Two species from Madagascar are described as new to science, with morphological characteristics and a habitat preference so far unknown in this genus. Obviously, they have evolved particular adaptations under long term stable conditions in isolated rain forests of N and E Madagascar. A new diagnosis is proposed for the subfamily Diplodontinae K.Viets, 1936.

Five water mite species of the genus Torrenticola Piersig (Acari: Hydrachnidia, Torrenticolidae) are reported from Iran. T. disabatinola and T. persica are described as new to science; first description are given of the female of T. saboorii Pesic & Asadi, 2002; new records are given for T. nana Di Sabatino & Gerecke, 2003, and T. cf. jasminae Bader, 1988.

The larvae of Allogamus gibraltaricus González & Ruiz, 2001 and A. mortoni (Navás, 1907), two endemic species of the Iberian Peninsula, are described for the first time and compared with other known Iberian species. A key to the larvae of genus Allogamus including all Iberian species is given.