bluuebunny/crossref_metadata_2025 huggingface dataset:
Variable egg development of Dinocras spp. (Plecoptera, Perlidae) and the stonefly seed bank theory
Authors: ZWICK PETER
Published: November 2003

1. Temperature dependence of egg development of Dinocras cephalotes (Curtis) (three German and one Norwegian population) and Slovenian D. megacephala (Klapálek) was studied under a constant 14 : 10 light : dark photoperiod and constant temperature ranges of 4–24 °C and 4–18 °C, respectively. D. cephalotes was also incubated under seasonal field conditions; natural daylength and fluctuating temperatures had no modifying effect.

2. Both species have very similar lower threshold temperatures (4 and 3.5 °C, respectively), thermal demand for development (c. 600 degree days) and high dependence of mean incubation period on temperature (exponents of regressions near 1.5). Present data on D. cephalotes agree with the literature on British and Norwegian material of the same species.

3. Development occurs only at cue temperatures above the lower threshold. Cue temperatures range from 6 °C (some D. megacephala) to 14 °C (some D. cephalotes) and vary strongly within and between egg masses of D. cephalotes. Variation is not random, but seems to be genetically determined.

4. The variable temperature response renders study of effects of particular experimental regimes, and comparisons between local populations, difficult.

5. A latitudinal gradient in cue temperatures for development from 6 °C at c. 46 °N to 12 or even 14 °C at c. 61 °N seems to reflect reduced diversity at high latitudes.

6. Average success of spontaneous hatching exceeded 90% between 12 and 20 °C, but declined towards higher and lower temperatures.

7. Unhatched eggs were not dead but in parapause; development at other, higher or lower, temperatures was induced. Spontaneous plus induced hatching success approached 90%. Developing eggs rarely died; most dead eggs were apparently unfertilized.

8. Dormant plecopteran eggs are proposed to form a seed bank in stream bed sediments. Highly successful development after up to 220 days of dormancy was ascertained in Dinocras, and survival for up to 3 years is reported for other Perloidea.

9. Only systellognathan egg morphology provides options for long dormancy; the other plecopteran superfamilies, notably Nemouroidea, follow different strategies.
Acid‐induced acute toxicity of aluminium to three species of filter feeding caddis larvae (Trichoptera, Arctopsychidae and Hydropsychidae)
Authors: VUORI K.‐M.
Published: November 2003

1. Arctopsyche ladogensis, Hydropsyche angustipennis and Hydropsyche siltalai larvae were exposed to nominal aluminium concentrations of 0, 625, 1250, 2500 and 5000 μg Al l–1 at pH 5.0 for 96 h. Larvae reared at pH 6.4 and without any aluminium treatment were used as controls. Morphological abnormalities in the anal papillae of the larvae were used as the response variable in estimating the median effective concentrations (EC50) of aluminium.

2. No morphological abnormalities were observed in the control larvae. Only a few individuals of A. ladogensis had darkened anal papillae at pH 5.0 without additional aluminium treatment, whereas increasing aluminium concentrations significantly increased the number of individuals in all species displaying darkening and reduction of the papillae.

3. A. ladogensis appeared to be the most sensitive species to increasing aluminium concentrations, as reflected by the significantly lower mean EC50 value for this species compared with those of H. siltalai and H. angustipennis. H. angustipennis larvae were the most tolerant to aluminium.

4. The results indicate that interspecific differences in sensitivity to aluminium may be a key factor influencing the guild structure of filter feeding caddis flies in acidified streams. The results also imply that toxic effects of aluminium on filter feeding caddis larvae occur due to the impairment of normal osmoregulation processes via damage to the ion‐regulatory organs.
Gemmules of sponges from a warm lake
Authors: ILAN MICHA , DEMBO GAL , GASITH AVITAL
Published: November 2003

1. Two types of gemmules were found, each in a different species of sponge, from the warm monomictic Lake Kinneret: (i) clustered gemmules, sharing the pneumatic layer of the gemmular capsule and resembling gemmules of Eunapius; (ii) gemmules that develop non‐synchronously, containing amphidisc spicules within the gemmular capsule and resembling those of Ephydatia. Algal cells were not detected within either type of gemmule although they exist in the developed sponges.

2. Sponges began producing gemmules in the lake with the onset of lake drawdown and ceased when lake level was minimal. The gemmules hatched when the lake level began to rise.

3. Under experimental conditions gemmules hatched between 13 and 35 °C. Germination was optimal at 20–25 °C. Chilling of young gemmules prior to incubation at 25 °C improved germination rate.

4. The percentage of germinating dry gemmules diminished 4–6 months after their collection from the lake. None germinated after 10 months. Submerged gemmules maintained high viability with ageing (up to 100% germination 18 months after collection). Desiccation influenced gemmule viability over time, by both decreasing the percentage of germinating gemmules and increasing the lag time before onset of germination.

5. Gemmules kept in the dark germinated significantly less than those illuminated for 12 h day
Atyid shrimps (Decapoda: Atyidae) influence the spatial heterogeneity of algal communities over different scales in tropical montane streams, Puerto Rico
Authors: PRINGLE CATHERINE
Published: November 2003

1. Atyid (Decapoda: Atyidae) shrimps influence the distribution of algal communities over different scales in tropical montane streams of Puerto Rico. Within pools of an atyid‐dominated stream, atyid shrimps enhanced patchiness in algal communities along the depth gradient. Algal bands occurred in shallow pool margins where atyids did not forage (< 3 cm below water surface), with significantly greater standing crop, taxon richness, and structural complexity than deeper areas. In deeper water, atyids reduced small‐scale patchiness in algal community composition and maintained a low‐growing understorey turf dominated by sessile diatoms (Bacillariophyta) and, sometimes, closely cropped, filamentous blue‐greens (Cyanophyta).

2. Among pools of the atyid‐dominated stream, atyids interacted with light to determine algal patchiness between stream margins and deeper areas. In sunny pools, algal standing crop was 140‐fold greater in pool margins than in deeper areas where atyids foraged. In shaded pools, however, standing crop in pool margins was only 5‐fold greater than in deeper areas. Effects of light on algal standing crop were greater outside atyid foraging areas than within, indicating that shrimp grazing overrides the positive effects of light.

3. In contrast to the atyid‐dominated stream, algal communities in an atyid‐poor stream were characterized by a high biomass of loosely attached epipelic diatoms and no depth zonation. Interstream rock and shrimp transplant experiments indicated that atyids significantly reduced algal standing crop and altered community composition on rocks from atyid‐poor streams within 24 h. Results support the hypothesis that atyid shrimps play a major role in determining observed interstream differences in algal communities.
Changes in phosphorus and nitrogen cycling following food web manipulations in a shallow Dutch lake
Authors: VAN DER MOLEN DIEDERIK , BOERS PAUL
Published: November 2003

1. The flow of phosphorus and nitrogen through the food web of the shallow, eutrophic lake Wolderwijd was analysed for 2 different years before and for 1 year after food web manipulation.

2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.

3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.

4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column.
Interspecific competition and habitat selection by the riverine dragonfly Onychogomphus uncatus
Authors: SUHLING FRANK
Published: November 2003

1. Substratum selection by the burrowing larvae of the dragonfly Onychogomphus uncatus was examined in an artificial laboratory stream at different larval densities and in the presence of one of three other dragonfly species.

2. The larvae of O. uncatus, as well as those of the other species, clearly preferred gravelly sand substratum rather than gravel or stone.

3. At low larval density (71.4 m–2) in the stream, 83% of the O. uncatus were found in gravelly sand. An increase of larval abundance in the stream to 202.4 specimens m–2 resulted in greater density in all substrata, but this increase was proportionally lowest in gravelly sand.

4. The presence of a second species had various effects on the microdistribution of O. uncatus. In the presence of Gomphus simillimus or Cordulegaster boltoniiimmaculifrons the distribution of O. uncatus changed significantly; their density increased in the normally less preferred substrata. This effect is interpreted as asymmetric interspecific interference. The presence of a third species, Onychogomphus forcipatus unguiculatus, had no effects.
Temperature‐mediated dynamics of planktonic food chains: the effect of an invertebrate carnivore
Authors: BEISNER BEATRIX , MCCAULEY EDAWRD , WRONA FREDERICK
Published: November 2003

1. This study involves an examination of two‐ and three‐trophic‐level food chains at two temperatures (18 and 25 °C) in order to determine how the addition of a carnivore to a predator–prey system can alter the dynamics of populations and how this effect may be temperature mediated. The system consisted of phytoplankton, Daphnia pulex and the flatworm Mesostoma ehrenbergii.

2. Although the plant–herbivore system is inherently unstable at 25 °C, the addition of the carnivore led to a further destabilization of the Daphnia–algal dynamics at the higher temperature. No destabilization effect of the carnivore was noted at 18 °C. At the lower temperature, all populations persisted and the carnivore induced changes only in the age structure of the Daphnia populations rather than in overall biomass.

3. The differential effects of the carnivore at two temperatures can be attributed to shifts in the life history, physiological rates and the reproductive strategy employed by Mesostoma.

4. Previous theoretical work has predicted that the addition of a third trophic level to an unstable predator–prey system should stabilize dynamics. Our results indicate that the effect of a carnivore on plant–herbivore dynamics can be significantly affected by ambient temperature.
Recolonization by benthic invertebrates after experimental disturbance in a Swiss prealpine river
Authors: MATTHAEI CHRISTOPH , UEHLINGER URS , MEYER ELISABETH , FRUTIGER ANDREAS
Published: November 2003

1. Although the crucial point of disturbance experiments in streams is the extent to which they can simulate an actual spate, this aspect has been widely neglected in the design of such studies. Similarly, the influence of the specific hydrological disturbance regime of a stream on its benthic community has received much theoretical attention in recent years, but hypotheses have rarely been tested in the field.

2. Our field experiment compared the structure of the benthic invertebrate community in the prealpine River Necker in north‐eastern Switzerland with predictions of the patch dynamics concept about the faunal composition of frequently disturbed streams. We also compared the resistance and resilience of the invertebrates between two sites in the River Necker. A similar substratum composition at both sites, but higher shear stress values both at baseflow and bankfull discharge at site 2, implied a higher disturbance frequency at the latter site. Five patches of stream bed of ≈ 9 m2 were disturbed by kicking and raking at each site, while five similar areas served as controls. From each plot, six Surber samples were taken: the first immediately after the disturbance, and the following five 1, 3, 6, 10 and 30 days later.

3. Resilience of the total benthic invertebrate fauna was high. The total number of individuals recovered to undisturbed densities within 30 days at site 1 and 6 days at site 2. Taxon richness recovered within 3 days. In accordance with theory, taxa with high recolonization rates made up a major percentage of the total number of individuals, especially in disturbed plots. However, this percentage was lower at site 2 in spite of the higher disturbance frequency at this site. Rhithrogena spp., Leuctra spp. and the Simuliidae recovered faster to undisturbed densities at site 2. In contrast, absolute recolonization rates of these taxa were higher at site 1, where total invertebrate densities were more than twice as high as at site 2.

4. Our results suggest that the time since the last disturbance should be considered as an important factor in studies of benthic invertebrate communities in prealpine rivers, because disturbances can alter the community structure. In frequently disturbed streams, very short sampling intervals may be needed to detect differences in taxon‐specific colonization rates. The specific hydrological disturbance regime of such streams is also important, because even within‐stream differences in the resilience of the benthic invertebrate community are possible.
Genetic differentiation in Daphnia obtusa: a continental perspective
Authors: HEBERT PAUL , FINSTON TERRIE
Published: November 2003

1. The restricted scale of most prior studies of genetic diversity in daphniid populations provides limited information on the geographical patterning of gene frequencies. The present study addresses this gap by examining allozymic divergence in populations of the most broadly distributed daphniid in the warm temperate regions of North America, Daphnia obtusa, across its range.

2. Local populations of this species show the gene frequency differentiation typical of other daphniids. In contrast to other daphniids with broad distributions, however, further divergence is apparent at a larger geographical scale, with North American D. obtusa fragmented into three lineages showing largely allopatric distributions. The three lineages are based primarily on allele frequency shifts at three polymorphic loci and are represented by eastern, central and south‐western groupings.

3. Because of this pattern of differentiation, there is no simple monotonic relationship between geographical distance and genetic divergence. Instead, local metapopulations belonging to a specific lineage show little genetic divergence over several thousand km, while marked shifts in gene frequency occur over a few hundred km in regions where different lineages are in contact.
The influence of a river bird, the dipper (Cinclus cinclus), on the behaviour and drift of its invertebrate prey
Authors: JENKINS R.K.B. , ORMEROD S.J.
Published: November 2003

1. We examined the behavioural response of stream macroinvertebrates to real and simulated predatory activity by a river bird, the Eurasian dipper, Cinclus cinclus L.

2. In the field, we assessed whether invertebrate drift changed in response to live dippers in enclosures; we found no effects on the drift of any of the five families for which individual analyses were possible, either because it was infrequent, or involved distances too short to be detected (< 0.5 m).

3. In a laboratory stream, we observed prey during encounters with a model dipper which simulated flight, swimming, bill contact with the prey, and stone turning. Invertebrate families varied in their response. Simuliids and hydropsychid caddis lacked effective escape behaviour, consistent with heavy losses through predation by dippers in the wild. Other families either drifted (Baetidae, Gammaridae) or moved away (Heptageniidae, Ephemerellidae, Leuctridae, Perlidae) from the model dipper, but responded only to bill contact or simulated stone turning. Such delayed responses would not protect individuals directly targeted by foraging dippers and partly explain the lack of detectable effects by dippers on drift in the field.

4. We suggest why invertebrates do not show more marked escape responses to this important predator.
The relationships among three habitat scales and stream benthic invertebrate community structure
Authors: CARTER J.L. , FEND S.V. , KENNELLY S.S.
Published: November 2003

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km2 Yakima River basin in south‐central Washington, U.S.A.

2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).

3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small‐scale physical structure.

4. Multiple discriminant function analyses indicated that segment‐ and reach‐scale variables discriminated among species‐defined groups better than sample‐scale variables.

5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.

6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.
Sediment‐related growth limitation of Elodea nuttallii as indicated by a fertilization experiment
Authors: BEST E.P.H. , WOLTMAN H. , JACOBS FH.H.
Published: November 2003

1. A fertilization experiment was performed to identify the limiting nutrient for the growth of submerged vegetation in ditches of a peat‐grassland system in the Netherlands, in which restoration measures involved ceasing fertilization, exporting nutrients by removal of above‐ground plant mass and large‐scale introduction of calcium‐rich, nutrient‐poor artesian water.

2. Growth of Elodea was significantly enhanced by enrichment with nitrogen alone, and by fertilization with nitrogen in combination with phosphorus, and by nitrogen in combination with phosphorus and potassium.

3. Plant tissue nutrient concentrations increased significantly, for nitrogen by enrichment with nitrogen alone, and with nitrogen in combination with phosphorus and potassium; for phosphorus by enrichment with phosphorus alone and with phosphorus in combination with nitrogen and potassium; tissue concentrations of potassium were not enhanced by any treatment.

4. The elemental ratios of treated plants indicated that nitrogen, rather than phosphorus, was limiting in all treatments, except in those involving nitrogen and NK enrichment (when phosphorus was limiting).

5. The efficiency with which plants used nutrients declined with increased supply of nitrogen and phosphorus, but was unchanged when potassium was increased. Efficiencies were similar to those of other aquatic macrophytes.
Grazing by a native and an exotic crayfish on aquatic macrophytes
Authors: NYSTRÖM PER , STRAND JOHN
Published: November 2003

1. We compared grazing by native noble crayfish (Astacus astacus) and the exotic signal crayfish (Pacifastacus leniusculus) on seedling or well‐established macrophytes.

2. In a pool experiment, seedlings of emergent Scirpuslacustris and floating‐leaved Potamogetonnatans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage.

3. In a preference experiment two submerged macrophytes (Charavulgaris and Elodeacanadensis), and both seedlings and established plants of S. lacustris and P. natans, were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans.

4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures.

5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating‐leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating‐leaved vegetation.
Potential fragmentation and loss of thermal habitats for charrs in the Japanese archipelago due to climatic warming
Authors: NAKANO SHIGERU , KITANO FUMIAKI , MAEKAWA KOJI
Published: November 2003

1. The upper thermal limits of the present distributions of two charr species, Dolly Varden, Salvelinus malma, and white‐spotted charr, S. leucomaenis, in streams of the Japanese archipelago were examined using groundwater temperature as an index of thermal condition. The lower limits of the altitudinal distributions of Dolly Varden and white‐spotted charr were delineated, respectively, by 8 and 16 °C groundwater isotherms.

2. The potential impact of future climatic warming on the geographical distribution, habitat extent and population fragmentation of each species was predicted at both the full archipelago and individual catchment levels.

3. For Dolly Varden, analysis at the full archipelago level indicated a loss of 27.6, 67.2, 79.6 and 89.6% of the current geographical range, respectively, for a 1, 2, 3 and 4 °C increase in mean annual air temperature. The present distribution area of white‐spotted charr would likewise reduce by 4.1, 20.5, 33.8 and 45.6%, respectively.

4. Based on the analyses of three individual catchments, one for Dolly Varden and two for white‐spotted charr, the lower habitat boundaries for the two charr species could be expected to rise increasingly to higher elevations in each catchment as warming proceeded. As a consequence, there would be large reductions in mean habitat area, with increasing habitat fragmentation followed by localized extinctions of the two species.
Patterns in benthic food webs: a role for omnivorous crayfish?
Authors: NYSTRÖM PER , BRÖNMARK CHRISTER , GRANÉLI WILHELM
Published: November 2003

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty‐one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond.

2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance.

3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment‐dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)).

4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte‐associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish.

5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density.

6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.
Tropical acid streams – the chironomid (Diptera) response in northern Australia
Authors: CRANSTON P.S. , COOPER P.D. , HARDWICK R.A. , HUMPHREY C.L. , DOSTINE P.L.
Published: November 2003

1. Chironomidae, sampled by interception of drifting cast pupal exuviae, responded to inputs of acid, heavy metal‐rich waters in a seasonally flowing tropical stream in northern Australia.

2. Responses included gain of distinctive (indicative) taxa, loss of some species typical of pristine conditions, and increase in species richness.

3. Experimental manipulation (upstream diversion) of a mine adit entry showed that these responses were the result of change in water quality.

4. The higher species richness at low pH, which is contrary to temperate studies, may be explained by the large tropical (Australian and south‐east Asian) pool of species tolerant of naturally occurring acidic aquatic habitats.

5. The structure and responses of the exuvial‐assessed chironomid community matched long‐term larval data.
A classification of mixotrophic protists based on their behaviour
Authors: JONES HARRIET
Published: November 2003

1. Mixotrophs are organisms which combine phototrophy and heterotrophy; such nutritional behaviour is widespread among protists. This ability to combine multiple modes of nutrition varies between species and is not related to their taxonomic grouping. A classification of mixotrophic protists, based on their behaviour, is proposed, dividing them into four groups.

2. Group A includes protists whose primary mode of nutrition is heterotrophy and where phototrophy is employed only when prey concentrations limit heterotrophic growth. In groups B, C and D phototrophy is the dominant mode of nutrition. In group B phagotrophy supplements growth when light is limiting, therefore ingestion of prey is inversely proportional to light intensity; in group C phagotrophy provides essential substances for growth and ingestion is proportional to light intensity; and group D includes those who have very low ingestion rates, ingesting prey only, for example, for cell maintenance during prolonged dark periods.

3. This classification is aimed towards predicting the impact of any particular mixotrophic protist on the aquatic food web, and how this impact may vary depending on the environmental conditions. A model representation of the four groups is discussed.
Response of invertebrates to lotic disturbance: is the hyporheic zone a patchy refugium?
Authors: DOLE‐OLIVIER M.‐J. , MARMONIER P. , BEFFY J.‐L
Published: November 2003

1. Natural experiments, in the form of disturbance from spates, were used to study the resistance and resilience of interstitial communities. Investigations were conducted in a by‐passed section of the Rhône River characterized by an artificial hydrology with frequent spates separated by regular minimum discharge of 30 m3 s–1.

2. Three areas of a bar were studied, upwellings at the head of the bar (stations 1 and 2), and downwelling at the tail of the bar (station 3). In the head of the bar the substratum was characterized by stable cobbles, while mobile gravels dominated in the tail of the bar. At each station, samples were derived from four depths (0.5, 1.0, 1.5 and 2.0 m below the surface of the substratum). Fifteen spates occurred during the study period whose peak discharge ranged from 50 to 1640 m3 s–1. Temporal variations of the fauna were studied by comparing the spate effect observed 1 day (resistance), 7 days (resilience) and 17 days after the spate. Within‐class correspondence analysis was used to compare the temporal variability of the fauna within each class {station/depth}.

3. The fauna differed markedly between the three stations, and the relative density of stygobionts (i.e. hypogean fauna) decreased from 55% at station 1 to 4% at station 3. The spatio‐temporal variability increased dramatically from station 1 to station 3.

4. The results suggest that the hyporheic zone acts as a patchy refugium: the stations were more or less active refugial zones, depending on hydrology (upwelling or downwelling), substratum stability and spate amplitude.

5. The downwelling station was the main refugium area for benthic taxa. Important migrations of benthic groups (e.g. Gammarus, Cladocera) or hyporheic taxa (e.g. Cyclopoida and Harpacticoida) were observed deep into the sediment (2 m). Vertical movements of stygobionts (Niphargus, Niphargopsis) were also observed at high amplitude spates. These movements were very important (great numbers of individuals migrated) at low and medium magnitude spates, but were unimportant at high discharge, when the threshold of sediment instability was exceeded. In this case the substratum became mobile and induced drift of benthic organisms.

6. Conversely, in the upwelling stable stations, accumulation was less important (lower number of species and lower densities) but more constant with increasing discharge, suggesting that substratum stability is also a key factor.

7. Generally recovery was rapid at all stations (within 7 days) but no relationships were found between resilience (rate of recovery) and the amplitude of spates.
Spatial pattern, patch dynamics and successional change: chironomid assemblages in a Lake Erie coastal wetland
Authors: BOTTS P.
Published: November 2003

1. Distribution patterns in 1994 and 1995 of chironomid larvae in the sediments of wetlands on Presque Isle, Pennsylvania were used to determine whether relationships exist among species composition and wetland age, position or environmental characteristics. Canonical correspondence analysis was used to relate wetland age, degree of isolation, vegetation abundance and water chemistry to species composition.

2. Of forty‐two chironomid taxa collected, Tanytarsus lugens group, Paratanytarsus sp. and Cladotanytarsus mancus group were the most widespread, but Lauterborniella agrayloides, Stictochironomus sp. and Cryptochironomus sp. were locally abundant in several sampling sites.

3. The canonical ordination based on all site characteristics was statistically significant and accounted for 54.9% of the variance in the species data and 69.5% of the variance in the species–environment relationship. The variables that contributed significantly to the ordination model were macrophyte abundance, conductivity and wetland area.

4. Partial canonical ordination based on environmental conditions with wetland age and position effects as covariables showed that environmental conditions explain a significant proportion of the variance in species composition among sites. Neither wetland age nor position variables explain a significant proportion of the variance in species composition.
Long‐term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation
Authors: ZAGARESE HORACIO , WILLIAMSON CRAIG , VAIL TIMOTHY , OLSEN OLAF , QUEIMALIÑOS CLAUDIA
Published: November 2003

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short‐term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.

2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.

3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa
How much water does a river need?
Authors: RICHTER BRIAN , BAUMGARTNER JEFFREY , WIGINGTON ROBERT , BRAUN DAVID
Published: November 2003

1. This paper introduces a new approach for setting streamflow‐based river ecosystem management targets and this method is called the ‘Range of Variability Approach’ (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.

2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty‐two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA, a range of variation in each of the thirty‐two parameters, e.g. the values at ± 1 standard deviation from the mean or the twenty‐fifth to seventy‐fifth percentile range, are selected as initial flow management targets.

3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long‐term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.
Landscape approaches to the analysis of aquatic ecosystems
Authors: JOHNSON LUCINDA , GAGE STUART
Published: November 2003

1. In the mid‐1970s, Hynes (1975) wrote eloquently about the complex interactions between aquatic and terrestrial systems. Central theories in stream ecology developed thereafter have dealt with the longitudinal flow of energy, materials and organisms in streams, and, with the exception of the flood pulse concept (Junk, Bayley & Sparks, 1989), have largely ignored areas outside the riparian zone. The structure of the upland and activities occurring there play a more important part than previously recognized in regulating community structure and ecosystem processes in streams.

2. These new perspectives are made possible by developments in hierarchy theory, patch dynamics, and the refinement of tools used to quantify spatial and temporal heterogeneity.

3. Geographical information systems (GIS), image processing technology and spatial statistical techniques allow quantitative assessment of lateral, longitudinal and vertical components of the landscape that interact at several spatial and temporal scales to influence streams. When GIS is used in concert with geostatistics, multivariate statistics, or landscape models, complex relationships can be elucidated and predicted.

4. To a certain extent, the tools discussed above have only automated functions that were previously performed manually. This suite of tools has improved the ability of aquatic ecologists to examine relationships and test theories over larger, more heterogeneous regions than were previously possible.

5. At the local, state and federal level, management and regulatory frameworks are currently being re‐evaluated to incorporate this new perspective in resource management and policy decision making.

6. We will discuss current and future trends in technologies and tools used for aquatic ecosystem research, and the use of techniques as they are applied in these regional assessments are also discussed.
Focusing environmental management budgets on non‐linear system responses: potential for significant improvements to freshwater ecosystems
Authors: STATZNER BERNHARD , CAPRA HERVÉ , HIGLER LAMBERTUS , ROUX A.
Published: November 2003

1. The non‐linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non‐linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.

2. Identifying three measures that are currently the focus of large freshwater management budgets (waste‐water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.

3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision‐making strategy will achieve greater environmental improvements for a given total budget.
Influence of ultraviolet‐B radiation on the drift response of stream invertebrates
Authors: KIFFNEY PETER , LITTLE EDWARD , CLEMENTS WILLIAM
Published: November 2003

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet‐B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.

2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid‐day conditions at Fort Collins, Colorado (longitude 105°30′; latitude 40°35′).

3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB‐exposed streams may be a behavioural response and/or a result of injury.

4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.
Sedimentation in a large lake: the importance of fluctuations in water level
Authors: GIBSON C.E. , GUILLOT J.
Published: November 2003

1. A sediment trap study was conducted in the central basin of Lower Lough Erne, Northern Ireland.

2. The material caught was low in organic matter, ash weight was 77% of dry weight on average.

3. Mass deposition of material was shown to be correlated with lake water level. When lake water level fell or rose above the middle range, the amount of material caught by the trap increased markedly. The effect was exaggerated by an unusually dry summer in 1995 which caused abnormally low water levels in the lake.

4. Comparison of Erne data with Windermere shows similar deposition rate of many substances, but the deposition rate of iron is thirteen times higher in Erne than in Windermere, and iron made up 39% of the ash weight in the Erne trap data.

5. Only 17% of the silica removed from the water column during diatom growth was recovered in the trap over the same time period.

6. Trap data are compared with historical data for sediment deposition and the implications of sediment focusing are discussed.
Food selectivity and diel vertical distribution of Chaoborus edulis (Diptera, Chaoboridae) in Lake Malawi
Authors: IRVINE KENNETH
Published: November 2003

1. Diel diet and vertical distribution patterns of the larval instars of Chaoborus edulis were studied in deep water near the central part of Lake Malawi, Africa.

2. First instar larvae contained very little food in their crops and probably depended on reserves from the egg. Second, third and fourth instars fed on zooplankton and were size‐selective in their feeding. The mean size of prey eaten by the three instars was significantly different from each other, with larger instars feeding on larger prey. Smallest available prey was selected against and the upper size of prey was probably constrained by larval gape. Nauplii were not found in any of several thousand larvae examined. Phytoplankton did not form a significant part of the diet.

3. There was a progressive and related increase in diel periodicity in feeding and vertical migrations of successive instar stages. Fourth instars migrated particularly large distances. Such migrations removed them from their zooplankton food supply but avoided predators. A refuge from predators is probably found in or near the permanent zero oxygen boundary, at depths greater than 200 m.
Field experiments on the mobility of benthic invertebrates in a southern English stream
Authors: WINTERBOTTOM JULIE , ORTON STUART , HILDREW ALAN
Published: November 2003

1. In each of twenty‐six week‐long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.

2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.

3. A ‘mobility index’ measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net‐spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.

4. Mobility in a second stonefly (Nemurella pictetii) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.

5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.
Predators can induce swarming behaviour and locomotory responses in Daphnia
Authors: PIJANOWSKA JOANNA , KOWALCZEWSKI ANDRZEJ
Published: November 2003

1. Exposure to chemical cues released by fish induced a tendency to form and maintain aggregations in two Daphnia clones originating from habitats inhabited by fish (and invertebrate predators), while Daphnia from a clone originating from a fishless habitat did not aggregate in response to fish cues.

2. Daphnia from one of the two clones responsive to fish cues, also aggregated in response to chemical cues released by invertebrate predators or to a substance released from homogenized Daphnia.

3. Chemical cues released by predators and the substance released from homogenized conspecifics induced a significant decrease in Daphnia’s swimming speed and an increased readiness to perform a somersaulting escape behaviour, especially in response to light cues.
Nutrient transfer between parafluvial interstitial water and river water: influence of gravel bar heterogeneity
Authors: CLARET CÉCILE , MARMONIER PIERRE , BOISSIER JEAN‐MICHEL , FONTVIEILLE DOMINIQUE , BLANC PAUL
Published: November 2003

1. Nutrient concentrations in interstitial water springs at the downstream ends of two gravel bars in the River Rhône were measured in order to estimate the importance of nutrient inputs [nitrate, dissolved organic carbon (DOC), biodegradable and refractory fractions of DOC] from the parafluvial zone (saturated sediments adjacent to the wetted channel, i.e. interstitial habitats of gravel bars) to the river as well as seasonal variations in these inputs.

2. Compared with surface water, parafluvial water had lower concentrations of DOC (especially the refractory fraction) and generally higher concentrations of nitrate. These differences were at their lowest during winter.

3. The influence of gravel bar geomorphological heterogeneity (grain size and spatial distribution of fine sediments) on parafluvial inputs was studied in terms of nutrient content and biofilm characteristics along transects across the gravel bars.

4. A gravel bar located in a stable area of the river had low transversal heterogeneity and acted as a sink for DOC and as a source of nitrate. The low fine sediment content and the high oxygenation of interstitial water must have enabled aerobic processes such as mineralization of organic matter and nitrification to occur.

5. In contrast, gravel bars located in a degradation zone of the river had a spatially variable structure, acting as a sink for DOC and nitrate because localized accumulation of fine sediment and ensuing hypoxic conditions induced anaerobic processes such as denitrification.

6. This study highlights the important influence of geomorphological heterogeneity in gravel bars for nutrient transformations as well as nutrient exchanges between parafluvial interstitial systems and the adjacent river over a seasonal cycle.