The green alga Chlamydomonas reinhardtii usually occurs in cultures as single, biflagellated cells. However, C. reinhardtii isknown for its ability to form gelatinous and palmelloid stages that arise as a result of an interaction with its environment.Exponentially growing unicellular C. reinhardtii formed palmelloid colonies rapidly within 25 h when cultured together withtheir enemy the rotifer Brachionus calyciflorus. Consequences of palmelloid formation for population dynamics of both C. reinhardtiiand B. calyciflorus were examined in continuous flow systems. Palmelloids were only formed in a one-stage systemwhere B. calyciflorus grazers and C. reinhardtii prey were cultured together, but not in a two-stage system in which mainly unicellularC. reinhardtii was pumped into a rotifer culture placed in darkness. The rotifer abundance was lower and the algal biomasshigher in the one-stage system compared to the grazing unit of the two-stage system. Inasmuch as palmelloids seemed togive C. reinhardtii cells resistance to grazing, we suggest that at least one of the reasons why C. reinhardtii is capable of formingpalmelloids is to cope with herbivory.

The aim of this study was to analyse the digestibility and viability of diatoms following gut passage through Aegla uruguayana.Crabs (n=28) and diatom samples were collected from Las Pencas Stream (Entre Ríos Province, Argentina).Organisms were allowed to graze on the source, then they were placed in aquaria to defecate. Samples of faecal and source materialwere analysed microscopically to quantify 'live', 'dying' and 'dead' diatoms, and inoculated onto Chu 10-infused agar culturesto observe cell viability. Significant differences were found among source and faeces content of 'live' and 'dead' cells(p<0.01). Nevertheless, the percentage of digestion after gut passage was only 11.5 %. Both agar cultures produced colonies thatincreased in cell density over time with significantly higher enhancement in faecal treatment (p<0.05). Evidence of digestionresistance and reproductive stimulation by gut passage could be tested in this experience.

The freshwater scud Echinogammarus stammeri is a very abundant benthic crustacean in riverine systems of northern Italy.The molecular physiology of L-[3H]leucine transport across cell membranes of E. stammeri was investigated. At pH 7.4, thepresence of a NaCl gradient stimulated the leucine transport rate, when compared with KCl gradient. By contrast, alkaline pHstrongly inhibited transport activity. In NaCl medium at acidic pH, leucine uptake displayed a specific activity 2.1-fold lowerthan that measured at neutral pH. Analysis of the uptake as a function of external leucine concentration revealed saturation kinetics.Leucine uptake appeared broadly unspecific and it was much strongly inhibited by the non-polar amino acids phenylalanine,methionine, and BCH, as well as by hydrophobic hydroxyacids. These results revealed important differences with respect toamino acid transport systems described in marine crustaceans. Their relevance in the feeding adaptation of the scud is brieflydiscussed.

In order to assign 18 mayfly taxa found in streams in the Macaé River basin into Functional Feeding Groups, the anatomy of their feedingapparatus was examined through scanning electron microscopy. Also, habitat preference and field observations of feeding behaviour were madeto assure FFG assignment. Ephemeropteran taxa were classified into five FFGs: Passive Filterers - Hylister plaumanni; Active Filterer -Lachlania boanovae and Campylocia sp.; Brushers - Askola froehlichi, Farrodes carioca, Hagenulopsis spp., Massartela brieni, Miroculis froehlich,Miroculis sp., and Thraulodes spp; Grazers - Cloeodes spp., Americabaetis spp., Camelobaetidius spp.and Baetodes spp.; Scrapers -Leptohyphes pereirae, Leptohyphes spp., Tricorythodes spp. and Tricorythopsis spp. Species of the three best represented mayfly families insouth-east Brazil were assigned to different FFGs (Leptophlebiidae - Brushers; Baetidae - Grazers and Leptohyphidae - Scrapers), with oneexception, Hylister plaumanni (Leptophlebiidae; Active filterers). This information is useful to understand the role of mayflies in stream ecosystems,and to help the development of ecological theories for tropical streams.

We studied the effects of a waste water treatment plant on organic matter dynamics in Fosso Bagnatore, a Mediterraneanstream near Rome (Italy). Concentrations of dissolved organic carbon and seston, along with the standing crops of coarse benthicorganic matter and fine benthic organic matter, were monitored monthly during 2002 in two reaches situated upstream anddownstream of a waste water treatment plant effluent. Additionally, we examined two stream functional characteristics: wholestream metabolism, which was measured from diel changes in oxygen concentrations, and nutrient removal, which was studiedby experimental additions of NH4-N, NO3-N and PO4-P. The possible influence of WWTP organic matter alterations on ecosystemfunctioning was addressed by measuring epilithon characteristics (standing crop, C:N:P ratios and chlorophyll a content).The WWTP effluent caused an increase (several-fold) of DOC and seston concentrations, and FBOM standing crop, moreoverit modified their temporal variation. Downstream of the wastewater treatment plant we detected an higher heterotrophic microbialbiomass and a correspondent higher community respiration. The uptake of NH4-N, NO3-N and PO4-P was highly variableprobably as consequence of the high variability of the compartments involved (e.g. DOC, FBOM, community respiration). Weshowed that WWTP effluent altered the organic matter dynamics of this Mediterranean-type headwater stream and that theseeffects were reflected in its ecosystem functioning. Because of the linkage of headwaters to downstream ecosystems and due totheir significant role in landscape and catchment processes, the alterations of organic matter dynamics that we detected at a localscale may have important consequences on a broader scale.

Three new species of the genus Harpagopalpus are described from Madagascar, allowing a redefinition of diagnostic characterstates of the monotypic family Harpagopalpidae, previously known only from Western Africa (two species) and India (onespecies. The separation of the subgenera Harpagopalpus and Harpagopalpellus is supported by new characters. Harpagopalpusoctoporus K.Viets, 1924 and H. tetraporus K.Viets, 1924 are redescribed and a lectotype is designated of H. octoporus. A fourthnew species is described from Cameroon, based on a male specimen erroneously considered to be the female of H. octoporusby K. Viets.

The epikarstic waters of a restricted sector of the Ojo Guareña cave (north Iberian Peninsula) were investigated to characterizethe physico-chemical variation in an annual cycle, to improve the scarce knowledge of the aquatic cave fauna on the IberianPeninsula, to look for distribution patterns of species per habitat along the annual cycle, and to search for the environmentalbasis (either physico- or hydro-geochemical) that could explain species distribution in the epikarst. The habitats studied includedall puddles and gours present in the sector selected making a total of 51 chemical and 42 biological samples for the entirecycle. The waters show no appreciable contaminationand exhibit small chemical variations throughout the year which arepatently affected by external weather conditions. The 53 taxa found belong to ten higher taxonomic groups (Oligochaeta,Turbellaria, Mollusca, Copepoda, Ostracoda, Isopoda, Bathynellacea, Tardigrada, Acarina and Cnidaria), and consist mainly ofcrustacea with a total of 27 species. Fourteen species were stygobionts (belonging to ten genera), nine of which are new to scienceand ten of which are endemic. Cave pools that appeared to be more stable in terms of water volume and mineralization, hada lower pCO2 and were carbonate oversaturated, harboured the greatest number of taxa. It is these pools that can maintain strictlycave dwelling species. Pools with lower levels of mineralization and greater water volume fluctuations had a lower diversityof fauna and in general lacked stygobiotic species.