bluuebunny/crossref_metadata_2025_split huggingface dataset:
Odour‐induced antipredator behaviour of the water flea, Ceriodaphnia reticulata, in varying predator and prey densities
Authors: Seely  , Lutnesky  
Published: March 2003

1. A new marking technique was developed and used to track individual water flea behaviour. A single clone of Ceriodaphnia reticulata exhibited no significant differences in mean depth, mean activity (antennae beats used in swimming), and mean travel (total vertical displacement) for fast‐green dyed and control animals (n = 30, each treatment).2. Individual and group antipredator responses were recorded in three vertebrate predator densities (three odour concentrations of green sunfish Lepomis cyanellus; 0.00, 0.03 and 0.10 fish L–1) and four water flea group sizes (1, 5, 15 and 25), with n = 18 for each of the twelve treatment combinations. Water flea groups were probably mixtures of clones. Differences in behaviour after addition of predator odour showed that increasing predator density increased mean depth of marked individuals and mean proportion of water fleas descending. Additionally, increasing prey density decreased both mean depth of marked individuals and mean proportion of water fleas descending.3. Predator density and prey density had opposing affects on activity and travel for marked individuals. Higher predator density decreased mean activity (antennae beats), yet increased mean travel. Higher prey density increased mean activity, but decreased mean travel. Descending animals altered their swimming pattern by using fewer swimming beats to travel greater vertical distances in the presence of predator odour.
Ingestion and digestion of epilithic algae by larval insects in a heavily grazed montane stream
Authors: Peterson Christopher G. , Vormittag Kara A. , Valett H. Maurice 
Published: March 2003

Summary1. Epilithic algae grown on elevated or non‐elevated ceramic tiles were exposed (to produce assemblages with different grazing histories) in a heavily grazed, montane stream in New Mexico, U.S.A. to Ameletus nymphs (Ephemeroptera) and Ecclisomyia larvae (Trichoptera) and the algal composition in insect faeces was compared to that on the tiles. Differences in grazing and digestion efficiency between grazers were then assessed and also differences in susceptibility to ingestion and digestibility among common algae.2. Ordination of tile and faecal samples, using the relative abundance of common algae, revealed that: (i) algal assemblages on elevated vs. non‐elevated tiles differed only slightly; (ii) the taxonomic composition of algae in faeces of both caddis and mayflies differed substantially from that on the tiles, indicating low grazing efficiency for some algal taxa; and (iii) the algal composition of faeces produced by caddis larvae and mayflies was similar, indicating little difference in grazing efficiency between them. However, some algal taxa were more susceptible to ingestion by caddisfly larvae when occurring on elevated tiles than on non‐elevated tiles, suggesting that previous exposure to caddis grazing influenced assemblage attributes.3. Although Ameletus and Ecclisomyia differed little in grazing efficiency, the percentage of diatoms that were dead after passage through the gut was greatest in the mayfly treatment, suggesting that mayflies digested diatoms more efficiently than the caddis. Analyses of differences in the condition of chloroplasts within diatoms in tile and faecal samples showed that losses of ’live‘ diatom cells (i.e. those containing full chloroplasts) during gut passage through mayflies equalled the increase, in faeces, of ’dead‘ (empty frustules) cells of all common diatoms. In contrast, some diatoms were digested inefficiently by caddis larvae.4. Algae on elevated tiles contained a higher proportion of dead diatoms than those on non‐elevated tiles, possibly because mayflies visited raised tiles more often and, consequently, ingested and defaecated cells at a higher rate in the absence of caddis larvae. Moreover, diatom taxa differed in the percentage of cells that were dead within tile assemblages, with populations of typically grazer‐resistant taxa (e.g. Achnanthidium minutissimum, Planothidium lanceolatum and Cocconeis placentula var. euglypta) containing significantly more dead cells than grazer‐susceptible taxa [e.g. small, chain‐forming Fragilaria (= Staurosirella)]. This result suggests that a trade‐off exists between ingestion vs. digestion resistance of microalgae. Both the ingestion and digestion efficiency of algivorous macroinvertebrates could influence the structure and function of algal assemblages. In heavily grazed systems, where algal cells are probably processed through grazer guts repeatedly, differential resistance to digestion among algae may be particularly important.
Development, maintenance and role of riparian vegetation in the river landscape
Authors: Tabacchi Eric , Correll David L. , Hauer Richard , Pinay Gilles , Planty‐Tabacchi Anne‐Marie , Wissmar Robert C. 
Published: March 2003

Summary1. Riparian structure and function were considered from a longitudinal perspective in order to identify multiscale couplings with adjacent ecosystems and to identify research needs.2. We characterized functional zones (with respect to vegetation development in association with various biogeochemical processes) within geomorphological settings using a delineation based upon erosional, transitional and depositional properties.3. Vegetation dynamics within the riparian corridor are clearly influenced substantially by hydrological disturbance regimes. In turn, we suggest that vegetation productivity and diversity may widely influence riverine biogeochemical processes, especially as related to the consequences of changing redox conditions occurring from upstream to downstream.4. However, surface and groundwater linkages are the predominant controls of landscape connectivity within riparian systems.5. The importance of riparian zones as sources and sinks of matter and energy was examined in context of structural and functional attributes, such as sequestering or cycling of nutrients in sediments, retention of water in vegetation, and retention, diffusion or dispersal of biota.6. The consequences of interactions between different communities (e.g. animals and plants, micro‐organisms and plants) on biogeochemical processes are notably in need of research, especially with respect to control of landscape features. Multiscale approaches, coupling regional and local factors in all three spatial dimensions, are needed in order to understand more synthetically and to model biogeochemical and community processes within the river‐riparian‐upland landscape of catchments.
The effects of biofilms on chemical processes in surficial sediments
Authors: Woodruff S. L. , House W. A. , Callow M. E. , Leadbeater B. S. C. 
Published: March 2003

1. The objectives of the present work were: (a) to evaluate the effects of the development and the presence of a photosynthetically active algal biofilm on chemical fluxes and processes at the sediment–water interface; (b) to measure the effects of the biofilm on chemical concentration gradients in the bulk sediment; and (c) to monitor pH and dissolved oxygen concentration in the biofilm, and through the sediment–water interface using microelectrodes.2. Two experiments were performed over a period of 8 weeks using a recirculating fluvarium channel containing river sediments with an exposed surface of 0.2 m2 and 20 dm3 of overlying solution. The first experiment was in darkness with minimal effects of a photosynthetically active biofilm. The second experiment in natural light produced a complex photosynthetic biofilm involving a succession of diatoms, green algae and cyanobacteria.3. The solution overlying the biofilm was monitored continuously for dissolved calcium, silicon, phosphorus, alkalinity and oxygen, as well as conductivity, temperature and pH. The surface of the sediment was also monitored for biological and physical changes as the biofilm developed. The overlying solution was analysed over a period of 48 h at 2‐h intervals to examine the effects of a well‐developed algal biofilm. At the end of the 48 h, pH and oxygen microelectrodes were used to measure gradients above and through the biofilm, and porewaters were analysed from sediments which had been longitudinally sectioned at a maximum depth resolution of 0.5 mm.4. Biofilm development had a large influence on the composition of the overlying solution and the development of vertical concentration gradients of solutes in the porewater. Once a diatom community was established, the concentration of dissolved silicon was low (< 40 μm), with all the silicon diffusing from the underlying sediment being consumed in the biofilm (≈ 0.026 μmol m−2 s−1 at the end of the experiment).5. The concentrations of calcium, alkalinity and phosphorus in digested sediment increased near the sediment–water interface. X‐ray diffraction analysis showed that calcite was formed at the surface. Estimation of the fluxes of alkalinity and calcium in the overlying solution were consistent with calcite formation during daylight and possible dissolution in darkness. The maximum precipitation flux of calcium was 0.87 μmol m−2 s−1 and the maximum net release flux was 0.89 μmol m−2 s−1.6. The net loss of soluble reactive phosphorus from the overlying solution measured over the intensive sampling period of 48 h is consistent with a coprecipitation mechanism and a surface density of phosphorus included in the lattice of calcite of 0.097 μmol m−2. Processes in the biofilm rather than diffusion from the sediment porewater control chemical fluxes of calcium, alkalinity and phosphorus from the sediment to the overlying water.
Importance of transient storage zones for ammonium and phosphate retention in a sandy‐bottom Mediterranean stream
Authors: Butturini Andrea , Sabater Francesc 
Published: March 2003

Summary1. The ability of hyporheic sediments to exchange water and retain ammonium and phosphate in the Riera Major stream ,North‐East Spain, under different discharge conditions was measured by conducting short‐term nutrient and chloride additions.2. The mean exchange coefficients from free‐flowing water to the storage zone (k1) and vice versa (k2) were 0.82 × 10–4 s−−1 and 7 × 10−−3 s−−1, respectively. The ratio of storage zone cross‐sectional area to stream cross‐sectional area (AS/A) averaged 2.8 × 10–2 and was negatively correlated with discharge (r = –0.85, d.f. = 13, P < 0.001).3. The percentage of hyporheic zone water which came from surface water varied as a function of discharge and hyporheic depth, ranging between 33% and 95% at 25 cm depth, and between 78% and 100% at 10 cm depth.4. The nutrient retention efficiency in the hyporheic zone at 10 cm depth measured as uptake length (Swh) was less than 3.3 cm for ammonium and 37 cm for phosphate. Higher nutrient retentions were measured in the sediments at 10 cm depth than at 25 cm, indicating that near‐surface sediments were involved more actively in phosphate retention than the deeper hyporheic sediments. The lack of ammonium at any depth of the hyporheic zone showed that ammonium was very rapidly taken up in the surfacial sediments.
AusRivAS: using macroinvertebrates to assess ecological condition of rivers in Western Australia
Authors: Smith M. J. , Kay W. R. , Edward D. H. D. , Papas P. J. , Richardson K. St J. , Simpson J. C. , Pinder A. M. , Cale D. J. , Horwitz P. H. J. , Davis J. A. , Yung F. H. , Norris R. H. , Halse S. A. 
Published: March 2003

Summary1. AusRivAS (Australian River Assessment Scheme) models were developed, using macroinvertebrates as indicators, to assess the ecological condition of rivers in Western Australia as part of an Australia‐wide program. The models were based on data from 188 minimally disturbed reference sites and are similar to RIVPACS models used in Britain. The major habitats in the rivers (macrophyte, channel) were sampled separately and macroinvertebrates collected were identified to family level.2. Laboratory sorting of preserved macroinvertebrate samples recovered about 90% of families present when 150 animals were collected, whereas live picking in the field recovered only 76%.3. Reference sites clustered into five groups on the basis of macroinvertebrate families present. Using seven physical variables, a discriminant function allocated 73% of sites to the correct classification group. A discriminant function based on seven physical and two chemical variables allocated 81% of sites to the correct group. However, when the same reference sites were re‐sampled the following year, the nine variable discriminant function misallocated more sites than the seven variable function, owing to annual fluctuations in water chemistry that were not accompanied by changes in fauna.4. In preliminary testing, the wet season channel model correctly assessed 80% of reference sites as undisturbed in the year subsequent to model building (10% of sites were expected to rate as disturbed because the 10th percentile was used as the threshold for disturbance). Nine sites from an independent data set, all thought to be disturbed, were assessed as such by the model. Results from twenty test sites, chosen because they represented a wide range of ecological condition, were less clear‐cut. In its current state the model reliably distinguishes undisturbed and severely disturbed sites. Subtle impacts are either detected inconsistently or do not affect ecological condition.
The effects of fish on assemblages of amphibians in ponds: a field experiment
Authors: Smith G. R. , Rettig J. E. , Mittelbach G. G. , Valiulis J. L. , Schaack S. R. 
Published: March 2003

1. Bluegill sunfish (Lepomis macrochirus) dominate fish assemblages of small lakes and ponds throughout the eastern United States and may play a major role in structuring aquatic communities. We examined the impact of adult bluegill on amphibian density by stocking bluegill at a range of densities into partitions of an experimental pond in which amphibians were free to colonize.2. Adult bluegill had a major impact on the amphibian assemblage. By the end of the experiment, gray treefrog (Hyla versicolor) tadpoles were nine times less abundant, and red‐spotted newt (Notophthalmus viridescens) adults were three times less abundant in the presence of adult bluegill than in their absence. In contrast, bullfrog (Rana catesbeiana) tadpoles tended to increase in the presence of adult bluegill. Adult bluegill also had a negative effect on the abundance of predaceous aquatic insects.3. There was no indication that interactions among amphibians were significant in determining the above patterns. We suggest that the strong impact of adult bluegill resulted from a combination of direct and indirect effects on amphibian larvae and predaceous aquatic insects.
A new energetics model for brown trout, Salmo trutta
Authors: Elliott J. M. , Hurley M. A. 
Published: March 2003

1. The chief objective of the present study was to develop a functional model for the daily change in the total energy content of a brown trout, Salmo trutta , (equivalent to growth when positive) in relation to the difference between energy intake (energy content of food) and energy losses (metabolism + losses in faeces and excretory products). Energy budgets for individual fish were obtained in earlier experiments with 210 hatchery trout (live weight = 11–270 g) kept at fairly constant temperatures (mean values ranging from 3.6 to 20.4 °C), but without strict control of temperature or oxygen, and in later experiments, with 252 trout (1–300 g) bred from wild parents and kept at five constant temperatures (5, 10, 13, 15 and 18 °C) and 100% oxygen saturation. Each trout was fed a fixed ration of shrimps, Gammarus pulex, the ration level varying between zero and maximum.2. Energy intake (CIN, cal day−−1) was measured directly and expressed as a proportion (p) of the maximum energy intake (C, cal day−−1), the latter being estimated from a model developed earlier. In a new model, energy losses (CQ, cal day−−1) were expressed as a function of temperature, fish weight and ration level. This model was continuous over the 3.6–20.4 °C range, had twelve fitted parameters and was an excellent fit to the data for the 462 trout (P < 0.001, R2 = 0.9970). In an extended model, the weight exponent for energy losses was not assumed equal to that for energy intake, the difference between the two exponents being very small, but significant, with a slight improvement in the fit of the model (R2 increased to 0.9972).3. The limits of model use were discussed. An example of its utility was to elucidate the complex relationships between both positive (growth) and negative daily changes in the total energy content of the trout, and temperature, fish size and variable energy intake. The model has raised several questions for future work, including the effect of increasing energy intake by a change of diet from invertebrates to fish or fish pellets, and a comparison of growth models based on weight or energy changes.
Exploring patterns of population subdivision in the net‐winged midge, Elporia barnardi (Diptera: Blephariceridae), in mountain streams of the south‐western Cape, South Africa
Authors: Wishart  , Hughes  
Published: March 2003

1. The net‐winged midges (Diptera: Blephariceridae) are a highly specialized group whose morphological characteristics and specific habitat requirements suggest a limited potential for dispersal. Levels of genetic variation were examined within streams, between streams in the same range and between mountain ranges in larval populations of Elporia barnardi in the south‐western Cape of South Africa. The aim was to examine the hypothesis that population structure would reflect the poor potential for dispersal.2. Significant deviations from Hardy–Weinberg equilibrium in 17 of the 57 individual comparisons indicate a non‐random mating population. Given the swarming behaviour and life history traits, larvae sampled may reflect the product of limited matings.3. Analysis of population substructuring revealed significant levels of differentiation among geographically proximate populations. Large differences between streams within Table Mountain, similar in magnitude to those between mountain ranges, suggest that movement of individuals out of the stream catchment is rare. Observed FST values are more similar to those of fully aquatic species than other lotic insects with winged adult stages.4. Results suggest that mountain ridges provided effective physical barriers to the dispersal of E. barnardi, with the catchment representing the effective population unit.
Coupling the microbial food web with fish: are bacteria attached to cyanobacteria an important food source for underyearling roach?
Authors: Kamjunke Norbert , Mehner Thomas 
Published: March 2003

1. After observing that juvenile roach fed intensively on cyanobacteria and that cyanobacteria were densely colonized by heterotrophic bacteria, we tested whether the bacteria are used by underyearling roach and the extent to which they contribute to the energy requirements of the fish.2. We radiolabelled attached bacteria in a natural cyanobacterial suspension, fed the fish with these particles, and estimated their assimilation by roach. Biomass of attached bacteria on cyanobacteria increased with the proportion of the cyanobacterium Microcystis in total cyanobacteria. Biomass‐specific thymidine incorporation of attached bacteria was higher than that of free bacteria.3. In feeding experiments, we detected assimilation of bacterial biomass into muscle tissue of underyearling roach. Fish consumed Microcystis to a lesser extent compared with Aphanizomenon but assimilation of attached bacteria was higher when roach fed on Microcystis because of the higher biomass of epibacteria on this cyanobacterium. However, biomass of attached bacteria was too low to be an important food source for underyearling roach.4. We conclude that assimilation of epibacteria from cyanobacteria cannot explain the success of roach in eutrophic lakes.
Effects of logging on macroinvertebrate production in a sand‐bottomed, low‐gradient stream
Authors: Kedzierski Wendy M. , Smock Leonard A. 
Published: March 2003

1. Macroinvertebrate production and macrophyte growth were studied in logged and unlogged sections of a sand‐bottomed, low‐gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had been clear‐cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years.2. A primary difference among the logged and unlogged sections of the stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300‐times greater in the logged than the unlogged section.3. Annual macroinvertebrate production in the sediment was higher in the unlogged section (41 g dry mass m–2) than in the logged section (25 g m–2).4. Annual macroinvertebrate production on Sparganium was higher in the logged section (10 g m–2 of plant surface area) than in the unlogged section (6 g m–2). Annual production associated with Chara, which occurred only in the logged section, was 196 g m–2 of stream bottom covered by this plant.5. Whole‐stream annual macroinvertebrate production, calculated by summing habitat‐specific production that was weighted by habitat availability, was greater in the logged section (103 g m–2) than in the unlogged section (41 g m–2). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section.6. Much of the additional macroinvertebrate production in the logged section was by collector‐filterers living on macrophytes. Production by collector‐gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging.7. Although logging along high‐gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low‐gradient stream.
Effects of an introduced piscivorous fish on native benthic fishes in a coastal river
Authors: White Jason L. , Harvey Bret C. 
Published: March 2003

1. We used field surveys to compare the density and mesohabitat‐scale distribution of the native coastrange sculpin (Cottus aleuticus) and the prickly sculpin (C. asper) in coastal rivers in north‐western California, U.S.A., with and without an introduced piscivorous fish, the Sacramento pikeminnow, Ptychocheilus grandis. We also measured mortality of tethered prickly sculpin in a field experiment including river, habitat type (pools versus riffles) and cover as factors.2. Average sculpin density (C. aleuticus and C. asper combined) in two rivers without pikeminnow was 21 times higher than the average density in two rivers in a drainage with introduced pikeminnow. In riffles, differences in the density of sculpins among rivers could be linked to differences in cover. However, riffles in rivers without pikeminnow had an average sculpin density 77 times higher than rivers with pikeminnow, yet only nine times more cover. In pools, cover availability did not differ among rivers, but the density of sculpins in rivers without pikeminnow was 11 times higher than rivers with pikeminnow.3. In the field experiment, mortality of tethered sculpin varied substantially among treatments and ANOVA indicated a significant River × Habitat × Cover interaction (P < 0.001). Overall, tethered prickly sculpin suffered 40% mortality over 24 h in rivers with pikeminnow and 2% mortality in rivers without pikeminnow, suggesting that predation is the mechanism by which the pikeminnow affects sculpins.4. The apparent reduction in sculpin abundance by introduced pikeminnow has probably significantly altered food webs and nutrient transport processes, and increased the probability of extinction of coastrange and prickly sculpins in the Eel River drainage.