The macroinvertebrate community was studied in 3 reaches along a north-Iberian stream that differ in the amount and nature of food resources. Regardless of shading and water quality, both invertebrate density and biomass were higher at the 2 downstream sites than at the headwater site. The taxonomic composition and functional organization of the faunal assemblages showed clear differences among sites: shredders and gatherers dominated the headwater site, and scrapers or gatherers, depending on the degree of shading and organic pollution, dominated the downtream sites. Macroinvertebrates responded roughly to intersite differences in food resources, but poor relationships between temporal dynamics of shredder or scraper abundance and that of their food were found. Likewise, no clear effect of floods on invertebrate density and biomass was observed.

The short-term stimulation of production, due to marine-derived nutrients (MDN) from spawning salmon, is well documented for certain trophic levels in stream communities (e.g., algae and insect biomass). The effect of these nutrients on the stream ecosystem as a whole, however, remains unclear especially later in the year. Trichopterans have been shown to feed on salmon and other fish carcasses and there is evidence for greater growth rates in the presence of salmon tissue. To address the question of long-term MDN subsidy on trichopterans, we investigated the growth of three limnephilid caddisflies in the spring in the Harris River on Prince of Wales Island, Southeast Alaska. The Harris River has a natural waterfall barrier to salmon and receives large runs of pink (O. gorbuscha) and chum (O. keta) salmon each fall. We selected two shredding caddisflies (Onocosmoecus unicolor) and (Psychoglypha spp.) and one facultative scraper, (Dicosmoecus atripes) for our study. We had two objectives : 1) compare the spring growth of larval caddisflies in a stream section that receives a large autumn run of salmon with their growth in a stream section that is blocked from receiving salmon (due to an impassable waterfall), and 2) compare the growth of shredders with that of a facultative scraper when provided either leaves or biofilm on rocks as food.

Insects were placed in growth boxes in May 2001 with either conditioned alder leaves or stream rocks as food sources. The boxes were placed along with temperature loggers in both the salmon (below the waterfall) and non-salmon (above the waterfall) reaches. The boxes were removed 40 days later. In-stream samples were taken of each caddisfly initially and at the end of the experiment to establish in-stream growth versus growth in the boxes. All larvae were coaxed from their cases, measured for total wet length, dried and weighed. Only D. atripes and Psychoglypha spp. were growing during our experiment and both showed very high relative growth rates in the Harris River. Psychoglypha spp. and O. unicolor were both significantly larger in the leaf boxes and D. atripes was significantly larger in the rock boxes. Both D. atripes and Psychoglypha spp. had significantly greater relative growth rates between food types (on biofilm on rocks and leaves respectively). These results support the notion that D. atripes are most likely facultative scrapers at least in their first year of growth. None of these caddisflies showed differences in their final mean weights or relative growth rates between stream sections, suggesting no effect of MDN on their spring growth in the Harris River. Further research on caddisfly communities in the fall and winter will help clarify if MDN has an influence on the abundance and life history of these species closer to the salmon run. This study questions the long-term influence of MDN on stream communities, particularly those populations that do most of their production in the spring, months after salmon carcasses are no longer visible.

The fish diversity of the Slovak segment of the Danube (representing the transitional zone from the rhithron to the potamon) was under the control of the inland delta which existed in this region until 1992. Seventy-six species were recorded in the studied river section: 61 species were native, 11 were exotic, 5 or 7 were invaders from the lower sections of the Danube, 3 species (and one form) became extinct, and 7 species were not detected during the past 20 years. The increasing pollution until 1985 decreased the fish species richness, but the improvement of water quality thereafter rose their number. However, the construction of the Gabcíkovo River Barrage System put in operation in October 1992 started to change substantially fish species richness and quantity, and fish catch. The formerly functional inland delta controlled by the pulsating discharge disappeared, and was changed to an artificial system of isolated or only marginally connected habitats. The upstream fish migration was stopped by the Gabcíkovo dam and weirs in Cunovo. Therefore, the fish fauna of the side arms lost contact with fish of the main channel and of the bypass canal downstream. The loss of spawning habitats had fatal effects, especially for the wild carp and the pike, which number rapidly decreased. In general, the number of fish species, their density, and fish catch decreased significantly. To improve the situation, it is proposed: 1) to restore the bilateral connection between the main channel and the side arms, 2) to ensure fish migration between the main channel and the side arms, and 3) to simulate the original flooding of the floodplain.

Organisms belonging to the green algal genera Desmodesmus and Scenedesmus are characterized by a high degree of flexibility allowing them to be true cosmopolitans and to withstand harsh conditions. The environmental conditions determine which phenotypes are being produced and one of the most dangerous situations for the algae is when the organisms are confronted with strong grazing pressure from numerous zooplankton organisms. An overview is given of several aspect of an induced defense in many non-spiny Scenedesmus and some spiny Desmodesmus that may form typical protective eight-celled colonies to avoid mortality from numerous grazers. The morphological response does seem to be linked with a herbivorous zooplankton chemical cue, rather than to a more general animal excretory product. The grazing activity of small sized grazers is reduced, but not of large Daphnia. However, arguments are given why grazing protection of colonial Scenedesmus is probably more efficient under natural than under carbon/light limited laboratory conditions. Finally, a life-history cycle of Desmodesmus and Scenedesmus is presented in which biological aspects such as the anti-grazer response and sexual reproduction are being included.

Corbicula fluminea populations were sampled annually from 1997 to 2000 at the beginning of the autumn, i.e. at the end of the reproduction period, at 14 sites along the Saône and Rhône rivers. Recruitment in the upper reach of these rivers was generally high. Conversely, the observation of other sectors revealed generally low or no production of juveniles, missing cohorts and major year to year variations in population structure. Nevertheless, no dramatic fall in population density was observed during the surveyed four years. This suggests that the longevity of the Corbicula populations of the Saône and Rhône rivers is ensured to a great extent by the drifting of individuals from the upper course of these rivers and their tributaries. Two possible causes are put forward to explain the low recruitment observed : low production of phytoplankton that prevents adults from constituting sufficient energy reserves to ensure the full development of larvae, and/or toxic contamination, which inhibits the development of phytoplankton and it is lethal for pediveligers.

A long-term study (1985-1999) conducted at backwater and tailwater sites of a large reservoir located in the middle course of the 808 km long Warta River (Poland), showed that not only obligatory riverine species suffer from the effect of the dam. Facultative riverine eel, burbot, wels and pike considerably decreased in number and standing crop, including their apparent absence in some years following the damming. Nevertheless, median densities of perch and roach, two generalists thriving in European regulated rivers, increased from tens and hundreds, respectively, to thousands per hectare. Significant increases in density were also recorded for other four species: zander, ruffe, bream and silver bream. Thus, the reaction of facultative riverine fish, often supposed to be resistant to aquatic habitat deterioration, is diverse with respect to impoundment. Apart from the migratory eel, which have not been caught at the backwater site for the last 8 years, all the remaining significant temporal changes were recorded at the tailwater site. Out of habitat flexibility coefficients relating to refuge, feeding and spawning, only the latter considerably differed between the successful and unsuccessful species after impoundment, which testifies to the critical role of spawning flexibility in a human-modified environment.

Tropical island streams worldwide are being threatened by existing or proposed dams and diversions. Numerous streams of the Hawaiian Islands have diversions that remove freshwater for human use; however, little research has addressed diversion effects on aquatic insect communities in tropical streams. We studied the effect of water removal by a stream diversion on density and biomass of two introduced Trichoptera, Cheumatopsyche analis (Banks) (Hydropsychidae) and Hydroptila potosina (Buenoa-Soria) (Hydroptilidae), in Iao Stream, Maui, Hawaii, from April-August 2000. Both species seem to have multivoltine life cycles. Pooled Trichoptera (both species) biomass was significantly greater above the diversion (178.3 mg.m-2 and 112.9 mg.m-2 for upstream and downstream, respectively). For each individual species the mean total instar biomass was significantly reduced below the diversion (38 % and 54 % reduction for C. analis and H. potosina, respectively). Both species had greater densities above the diversion; however, individual larval mass of H. potosina instars, but not C. analis instars, was significantly lower below the diversion. Our results suggest that reduced habitat quality, due to lowered stream flow, limits density of both species below the diversion, whereas lowered food quantity and quality may differentially affect H. potosina biomass through reduced body sizes. These data suggest that water removal not only reduces habitat quality, but significantly lowers the community biomass of these introduced Trichoptera species, affecting the trophic energetics of stream reaches downstream of a diversion in Hawaii. Similar changes to macroinvertebrate communities would be expected below dams and diversions of streams in other tropical regions.

In this study we documented the instar densities and life cycle of Telmatogeton torrenticola Terry (Chironomidae : Telmatogetoninae) from Kinihapai Stream, Maui, Hawaii. Greatest larval densities of this midge are found on substrates of high velocity, shallow flows of cascades, and splash zones of waterfalls, with lower densities in riffles. In the summer of 1994 we compared the effects of two microhabitats (termed optimal and suboptimal) on inter-instar density and relative abundance. In a second year (1995), we evaluated the effect of long-term reduced stream flow on these variables only in optimal microhabitats. A significant reduction in stream flow from 1994 to 1995 was correlated with a similar reduction in larval densities that precluded larval colonization of suboptimal habitats in 1995, thereby preventing sampling in this microhabitat during that summer. Depth of optimal habitats of 1995 were significantly shallower than both habitats of 1994, with suboptimal habitats of 1994 the deepest. Total larval density was significantly higher in 1994 optimal habitats, while 1994 suboptimal and 1995 optimal habitats were statistically similar. Individual instar densities showed variable differences among habitats and years, with the first three instars always highest in 1994 optimal habitats. All instars and pupae were collected on most sampling dates in both years ; however, pupae were only collected on a two dates in suboptimal habitats of 1994. Based on larval size frequency histograms, T. torrenticola has a multivoltine, asynchronous life cycle, with continuous reproduction, which is variable among microhabitats characterized by different flow velocity and depth, and between years of differing stream discharge. Reduced stream flow during the summer of 1995 had effects of reducing densities and changing life cycle features similar to those found in 1994 (a year of higher stream flow) suboptimal habitats.

Decomposition of dry and fresh willow leaves and the dynamics of invertebrates during this decomposition were followed in upstream and downstream Oued Zegzel, Eastern Morocco. A seasonal comparison of the two studied sites stressed the importance of the structure of the benthic fauna in the process of decomposition. The rate of decomposition was faster in summer, following an increase in the biomass of invertebrates. It was slower in winter, when abundances of Chironomidae reached their maxima. The decomposition of willow leaves was faster upstream, where invertebrates biomass was greater. The artificial drying of leaves before their immersion had a positive effect on the activity of invertebrates. Whereas Melanopsis praemorsa preferred the dry leaves during the four seasons in upstream Zegzel, the preference of Hydropsyche maroccana for the fresh leaves in the downstream station changed according to the season. The seasonal variation of leaves quality seems to especially influence invertebrate colonisation, and thereafter the decomposition process in downstream Zegzel.

The aim of our paper was to study the space and time variations of phosphorus contents in the sediment, water and tissue of aquatic plants. Tissue Total Phosphorus of six aquatic plants (Callitriche platycarpa, C. hamulata, C. obtusangula, Elodea nuttallii, E. canadensis and Ranunculus peltatus) was analysed alongside the sediment Total Phosphorus (TP) and Soluble Reactive Phosphorus concentrations (SRP) in water, at the same site. Twelve sites were selected, and, samples were collected to test the seasonal and the annual patterns of phosphorus variation in 3 compartments. Streams ranged from oligotrophic to eutrophic waters. The sediments varied from mesotrophic to eutrophic states. A highly significant site effect was shown for water and for sediment. Water SRP varied with time (season, year), whereas no significant time effect was established for the sediment TP. Tissue TP varied according to year and season in Callitriche platycarpa, C. hamulata and E. nuttallii. The tissue phosphorus storage depended on the trophic level of sediment and water and varied according to species. The rank order of tissue TP content was C. obtusangula > R. peltatus ≥ E. nuttallii ≥ E. canadensis > C. platycarpa > C. hamulata. Removal of aquatic plants biomass with its accumulated phosphorus could be an alternative technique to other eutrophication control strategies. Further work is needed to improve our knowledge to estimate the ecological risk of harvesting on biodiversity and on ecosystem function.

The biomass and the biochemical composition of periphyton were studied during one year in three streams of Réunion Island. The results revealed that nutritional conditions for fish development were most favourable during the dry season. The nutritive value of periphyton was highest in the Marsouins and Mât streams and remained the lowest in the Roches stream. Food availability was strongly affected by high flow, particularly during the exceptional hydrological events of February 1998 (cyclonic high flows). Study of seasonal variations of morphophysiological characteristics and biochemical composition (lipids, proteins) of the grazer gobiidae Sicyopterus lagocephalus showed that inspite of unfavourable nutritional conditions caused by hydrological disturbances, fish continue their reproduction which coincides with the summer high flow period. The significant depletion of lipid reserves which express a deterioration in animal condition is influenced by flooding period. At this time of gonad development involving an additional energy investment, fish were not able to recover a stable nutritional state after the complete achievement of the reproduction cycle. Except during this period, there is a weak participation of the reproductive physiological processes in the seasonal changes of somatic composition of this fish.

The effect of substrate texture on colonization by stream macroinvertebrates was studied in a mountain stream. Experimental patches made of natural substrate, with two levels of cobble and gravel texture (rough and smooth), were subjected to two colonization periods (two hours and one week) within a riffle. Cobble texture affected the number of individuals and taxa colonizing substrate patches, although these relationships depended on time of colonization and some local environmental factors. Texture influence was different for different taxa, and only affected the scraper functional feeding group after one week of colonization, probably in relation to the development of an epilithic layer. These results suggest a significant effect of the surface texture of substrate on colonization by macroinvertebrates, although the effect is complex and needs more careful examination.

This paper describes spatio-temporal variability of the basic ice condition parameters, relationships between selected lakes in terms of those parameters, and frequency of fast (ice cover) and floating ice. Attention is also paid to morphology and topography of ice cover in lakes Jamno, Bukowo, Gardno, and Łebsko during 1960/61-1999/2000. Based on data archived at the Institute of Meteorology and Water Management, the following ice parameters were analysed: date of the first ice appearance; date of the first ice cover formation, date of disintegration of the last ice cover, date of disappearance of the last ice, ice season duration, number of days with ice, number of days with ice cover, ice conditions continuity, and maximum ice thickness in winter. Lakes Jamno and Bukowo, located in the western part of the Polish coast, are characterised by milder ice conditions, compared to the more eastward lakes (the Gardno and the Łebsko). Ice parameters were found to correlate closely, with statistical significance exceeding α = 0.01 and correlation coefficients usually higher than 0.90, between individual lakes, particularly the neighbouring ones. The highest frequencies of fast and floating ice, 70-75 % and about 10 %, respectively (altogether more than 80 %), were recorded in the last pentade of January. Fast ice (ice cover), accounting for 80 % of all the ice types, was found to dominate in the lakes studied; fast ice domination is typical of small and shallow water bodies. Ice cover is formed as a result of uniform increase in ice rind thickness. After the fast ice has decayed, an ice field pushed by the wind may form ice piles rising to a few metres above the water surface. At the beginning of the ice season, the piled ice appears most often on the western and northern shores, while at the end of the season it tends to stay on the eastern shores. The processes, associated with the presence of piled ice on the shore, are destructive not only for the shore, but also for constructions deployed within the ice range. The ice piles also affect transport and accumulation of sediment, mainly in the shore zone.

Field investigations on 12 populations of Omphiscola glabra were carried out in central France over a 5-year period to determine the ability of the species to aestivate in its habitats when summer drying occurred. In the department of Haute-Vienne, spring-born snails aestivated with their apertures applied to the surface of a substratum and most of them were located on the banks of ditches. With the return of wet conditions, the survival of these snails was low. In the department of Indre, most springborn snails aestivated by burrowing into the marl and were distributed over the whole surface area of their habitats. Higher survivals were noted for these O. glabra after aestivation. Despite a significant difference in the frequencies of buried lymnaeids, the position of snails with a natural infection with F. hepatica in their dried habitats was similar to that found for uninfected ones. The variations found in the aestivation of O. glabra might be explained by the dominant substratum (granite gravel and scarce mud in Haute-Vienne, or a thick layer of marl in Indre) and the plant cover on ditch bottoms.

This study investigated major pigment patterns of 8 cyanoprokaryota, 2 rhodophytes and 2 cryptomonads isolated from freshwater ecosystems. Analysis was done by means of HPLC. The method, historically adapted to marine phytoplankton, was modified to accommodate limnic algae. Quantitative results obtained in this study can be used for phytoplankton quantification techniques based on pigment patterns. Compared to marine strains, the studied freshwater cyanoprokaryote strains reveal a more complex pigment pattern, including myxoxanthophyll, canthaxanthin and echinenone. Cryptophyta possess the two acetylenic class-specific marker compounds allo- and monadoxanthin, crocoxanthin was not detectable. Rhodophytes show a simple pigment pattern similar to marine species. Previous reports as to the existence of chlorophyll-d could not be confirmed (historical reports probably refer to an artefact of preparation). Besides methodological considerations, the phenomenon of complementary chromatic adaptation is discussed briefly.

Using cluster analysis, ecological profiles of the species, and the (Diamesinae + Orthocladiinae) / Chironominae ratios, prealpine rivers were classified by their chironomid communities based on 338 species: (1) summer-cold mountain rivers (Isar, Salzach, Inn/Mühldorf), (2) summer-warm moraine-stretches (Würm, Alz/moraine rupture, Amper, Altmühl), (3) the summerwarm lowland river Upper Alz (lake outlet and the stretch to Altenmarkt village), (4) the lower section of the river Inn regulated by dams, which is dominated by a littoral community. The river Upper Alz is faunistically differentiated along it’s course. Classification of river stretches is predominantly explained by rhithral and eurytope species. Potamal and littoral species had no effect on classification. The results suggest that water temperature is the most important factor of the chironomid-based river classification, which is in harmony with studies by Rossaro (1992) and Lindegaard & Brodersen (1995). Locally, other morphological parameters as reach slope and substrate may be important factors as well. However, further data are needed to clarify their role in species distribution.

The fifth instar larva of Plectrocnemia laetabilis McLachlan, 1880 is described for the first time, and the main taxonomic characters are figured. The larvae of P. laetabilis are very similar to those of P. conspersa (Curtis, 1834), but they are easily distinguishable by some characters of the frontoclypeal apotome, labrum and abdominal segment IX. Additionally, some notes on distribution and ecological preferences are included.

In karst sink-holes within the environs of Czajków, and in an old fishpond within the Skorocice gypsum valley, 24 taxa of euglenophytes, comprising Euglena (10), Phacus (9), Lepocinclis (2), and Trachelomonas (3) were found. Four of them, Phacus elegans Pochmann, Ph. arnoldii Swirenko var. ovatus Popova, Ph. plicatus Conrad, and Ph. curvicauda Swir. var. robusta Allorge & Lefèvre, are new for the Polish flora, and rarely reported worldwide.

Major pigment patterns of 18 chlorophyceae, 7 charales, 4 euglenophyta, and 2 dinophyta isolated from freshwater ecosystems, were investigated by means of HPLC. In this study, quantitative results are presented, too, which are capable for phytoplankton quantification techniques based on pigment patterns. Chlorophyceae revealed a pattern similar to that of higher plants, but in some strains, loroxanthin as well as α-carotene were present. In charophytes, except for vegetative specimens of Chara tomentosa, γ-carotene was detected in antheridia only. Among investigated freshwater euglenophytes diadinoxanthin was the major carotenoid, with neoxanthin and ß-carotene present in minor amounts. Besides chlorophylls-a and -c, dinophytes contained high quantities of peridinin, whereas fucoxanthin was absent. An unknown component eluting just before violaxanthin showed a spectrum reminding of peridinin.

Using the epilithic diatoms as indicators of environmental conditions, 10 lakes in the High Tatra Mountains were characterised with regard to their stage of acidification. The diatom communities were diverse; 210 taxa were found, including 27 species of north and alpine preference. On the basis of cluster analysis, two groups of lakes were distinguished. The first group included shallow, moderately acidified lakes (Dlugi and Zmarzly Gasienicowy lakes), where acidophilous organisms prevailed, with Achnanthes marginulata being the most numerous. The structure of the diatom community in Dlugi lake was stable over 4 years of observations and did not show any progress in acidification. The second group included mostly very deep, non-acidified lakes where circumneutral organisms prevailed, and among them Achnanthes minutissima was dominant in most cases. The diatom community structures mostly confirmed the status of the lakes studied as judged from their water chemistry.