bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosynthetic use of inorganic carbon among primary and secondary water plants in streams
Authors: SAND‐JENSEN KAJ , PEDERSEN MORTEN FOLDAGER , NIELSEN SØREN LAURENTIUS
Published: May 2006

1. We analysed photosynthetic rates and inorganic carbon use of thirty‐five vascular macrophyte species collected submerged in eight nutrient‐ and CO2‐rich Danish lowland streams. The species were classified in four groups as mainly terrestrial, homophyllous and heterophyllous amphibious and truly submerged. These groups represent plant species differently adapted to life in water.

2. Photosynthetic rates measured in water increased in the gradual transition from mainly terrestrial, through amphibious to truly submerged species. Species normally in contact with air adapted to submergence by increasing the photosynthetic rate at limiting CO2. Photosynthetic rates of submerged parts of heterophyllous amphibious species were close to those of submerged species. Submerged species with thin or finely dissected leaves had the highest photosynthetic rates, probably because of low diffusional resistance to uptake of nutrients and gases.

3. In contrast to submerged species, terrestrial and amphibious species were unable to use HCO3−. Extensive oversaturation with CO2 in the streams allows, however, many amphibious species to photosynthesize well under water, based on CO2‐use alone. Amphibious CO2‐users, with very few structural adaptations to life under water, can therefore be as dominant in the submerged vegetation of lowland streams as HCO3−‐using water plants. Moreover, the streams provide open space for colonization from the dense vegetation ashore.

4. Among the 1265 Danish herbaceous species no less than seventy‐five terrestrial species occasionally grow submerged, forty‐five species are amphibious, and fifty‐one are true water plants. These numbers suggest that adaptation to permanent or temporary submergence is an ongoing process involving many species and that the land‐water interface does not represent as difficult a barrier as often believed.
Long‐ and short‐term dynamics of submerged macrophytes in two shallow eutrophk lakes
Authors: BLINDOW IRMGARD
Published: May 2006

1. Periods with clear water and abundant submerged vegetation have alternated with periods of turbid water and sparse vegetation during recent decades in Lake Tåkern and Lake Krankesjön, two shallow, calcium‐rich, moderately eutrophic lakes in southern Sweden, Between 1983 and 1991, submerged vegetation (predominant species: Chara tomentosa, Nitellopsis obtusa, Myriophyllum spicatum) covered about 50% of the open lake area in Lake Tåkern. In Lake Krankesjön, submerged vegetation was sparse during 1983–84, but increased continuously in the following years and covered about 50% of the open lake area by 1990 and 1991. Potamogeton pectinatus was the first species to expand in Lake Krankesjön, but was later replaced by C. tomentosa.

2. During 1983–84, turbidity was high in Lake Krankesjön, which indicated that submerged macrophytes were light‐limited. During 1986–91, there was a negative correlation between the areal coverage of charophytes and angiosperms, indicating that competition for space had become an important limiting factor. The same negative correlation was found in Lake Tåkern for 1983–91.

3. Charophytes had much higher biomass per unit area than angiosperms in both lakes and reduced water movement considerably. This was probably one reason for the increase of water transparency in Lake Krankesjön during the spatial expansion of these plants. Charophytes also stored large amounts of phosphorus and nitrogen, Charophytes are probably superior competitors for both space and nutrients and thus have competitive advantage over angiosperms in this lake type.

4. In Lake Krankesjön, both P. pectinatus and C. tomentosa were negatively affected by high water level during the growing period. Total disappearance of submerged vegetation occurred in both lakes after catastrophic events (dry‐out during summer or mechanical damage by ice) caused by extremely low water level. Changes in water level are thus one of the most important reasons for among‐year fluctuations in areal coverage of submerged macrophytes in these lakes.
Effects of suspended clay on Daphnia body growth and fitness
Authors: KIRK KEVIN L.
Published: May 2006

1. Suspended sediments often reduce the abundance, fitness, and feeding rates of planktonic cladocerans. This paper examines the effect of suspended clay particles on the body growth and life‐history parameters of Daphnia ambigua. Cohorts were exposed to zero or 50mgl−1 suspended clay (particle size <2μm). Individuals exposed to clay had significantly lower body lengths at a given age than individuals in the control cohort. Parameters for the von Bertalanffy body growth equation were calculated for each individual; the asymptotic maximum body length (lmax) was reduced, but the growth rate constant (k) was unaffected, by the presence of suspended clay. Body length at reproductive maturity was lower in the presence of suspended clay; this may be an adaptive response and is similar to the response of cladocerans to limiting food concentrations.

2. Age‐specific survivorship and fecundity were both reduced, and the ages of maturity and first reproduction were both increased, in the presence of suspended clay. The overall effect of these demographic changes was a 70% decline in the net reproductive rate (Ro), a measure of fitness.

3. Suspended clay affected the relationship between body length and fecundity. Animals of a given length produced fewer eggs in the presence of suspended clay. In addition, there was a significant interaction in the effects of body length and clay on brood size: the slope of the regression line of brood size as a function of body length was lower in the presence of clay. This interaction has also been observed in limiting food concentrations, and may be caused by reductions in body length at maturity in low food or high clay environments.

4. The similarity between the effects of limiting food concentrations and suspended clay on Daphnia body growth, survivorship, fecundity, and brood size makes sense, given previous observations showing that suspended clay reduces the feeding rate of D. ambigua by up to 70% due to mechanical interference with feeding behaviours.
Effects of temperature and body size on radiocaesium retention in brown trout, Salmo trutta
Authors: UGEDAL O. , JONSSON B. , NJÅSTAD O. , NÆUMANN R.
Published: May 2006

1. The elimination rate of radiocaesium in brown trout Salmo trutta L. was determined in the laboratory at four water temperatures (range 4.4–15.6°C). In the experiments three or four homogenous size‐groups of fish (mean weights 23–496 g) were studied at each temperature.

2. The brown trout received acute oral doses of 134Cs and were killed at intervals for radioactivity counting. The retention versus time curves were composed of two distinct exponential components. The long‐lived component was quantitatively the most important for retention of radiocaesium. Elimination rate increased with increasing water temperature and decreased with increasing body weight.

3. The biological half‐life of 134Cs (Tb, days) was related to fresh body weight (W, g) and water temperature (t, °C) by the equation: Tb= 290 ×W°.176× e‐°.106×t. The elimination rate of Cs could be predicted from weight‐specific metabolic rate as given by Elliott's equations for brown trout.
An experimental test of the egg‐ratio method: estimated versus observed death rates
Authors: BRETT MICHAEL T. , MARTIN LISA , KAWECKI TADEUSZ J.
Published: May 2006

1 The accuracy of death‐rate estimates provided by the egg‐ratio method was assessed by directly measuring the real death rates of six large laboratory Daphnia populations for 40 days.

2. Of six models tested the Kawecki iterative model gave the best relationship to real death rates in terms of variance explained, bias, and fit at both 4‐ and 8‐day sampling intervals. Although considered theoretically correct by persons familiar with the mathematics of egg‐ratio models, the Edmondson—Paloheimo model gave slightly worse results in terms of bias and fit.

3. Using raw data, as opposed to smoothed data, gave the best fit between estimated and observed rates for both the Kawecki iterative and Edmondson‐Paloheimo models.

4. Size‐selective predation did not increase error in estimates of the death rate; however, non‐steady‐state dynamics were correlated with error in model estimates.

5. In general, the models gave a relatively good description of real dynamics, but they regularly produced negative death rates, and were grossly wrong for some individual estimates. The present study also gives practical suggestions on application of this technique to field populations.
Extreme cyclomorphosis in Daphnia lumholtzi
Authors: SORENSEN KATHRYN H. , STERNER ROBERT W.
Published: May 2006

1. Daphnia lumholtzi, not previously reported in North America, was found in a small reservoir in East Texas in January, 1991, This species possesses extremely long spines and large fornices; an allometric study was performed to detect any temporal differences in specific growth rates of the spines relative to the body.

2. In nature, mature females attained 1.8mm body length, excluding spines, but when the head and tail spines are included, the total length reached a maximum of 5.6mm.

3. Differences in the growth patterns of the head spine and the tail spine relative to the body existed for D. lumholtzi from January to March 1991. Both the head and the tail spines grew at a faster rate than the body during all 3 months although the rates varied between them. The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars.

4. The head spines grew at a constant allometric rate over time while the tail spine grew faster as the temperature increased. Both varied significantly in length over the 3 months, with animals having the shortest spines in February and the longest in March.
Sensitivity of mayfly nymphs to red light: implications for behavioural ecology
Authors: HEISE BRIAN A.
Published: May 2006

1. Visual sensitivity of the mayflies Stenacron interpunctatum (Say) and Stenonema vicarium (Walker) to red (650 nm) and infra‐red (950 nm) light was tested using a behavioural assay. Nymphs were placed in a runway and sequentially exposed to green light, red light, infra‐red light and no light (control) at one end of the runway. The distance run away from the light, and the number of alarm reactions to the light were recorded.

2. Both species reacted strongly to both red and green light, running significantly greater distances and reacting more frequently to these wavelengths of light than to either infrared light or the control.

3. These results show that unobtrusive observations of mayfly nocturnal behaviour should be made using infra‐red, and not red light, for illumination. Previous studies of aquatic insect nocturnal behaviour may have produced biased results if red light was used.
Simultaneous patterns of temperature, oxygen, zooplankton and fish distribution in Lake Kinneret, Israel
Authors: KALIKHMAN I. , WALLINE P. , GOPHEN M.
Published: May 2006

1. Temperature, oxygen concentration and zooplankton density were measured simultaneously on 25 December 1990 at twenty‐six stations during an acoustic survey of the fish population of Lake Kinneret, Israel. Data from a preliminary acoustic survey were used to establish the optimal distance between transects (4km).

2. The distribution of temperature and oxygen concentration (and their gradients), and zooplankton and fish densities were compared using three‐dimensional plots and correlation analysis. Both fish and zooplankton were concentrated in frontal zones where temperature and oxygen gradients were highest.

3. In the south‐eastern part of the lake, where fish abundance was highest, a minimum of zooplankton density was observed, suggesting that predation by fish reduced zooplankton concentrations.
Complex relations between freshwater macro‐ and meiobenthos: interactions between Chironomus riparius and Chydorus piger
Authors: van de Bund WOUTER J. , DAVIDS C.
Published: May 2006

The potential importance of interactions between macro‐ and meiobenthos in the littoral zone of takes was studied in a series of laboratory experiments with a chironomid and a chydorid.

 In a situation of intraspecific density dependence, Chydorus piger Sars inhibited the growth of Chironomus riparius Meigen, while both second‐ and fourth‐instar C, riparius stimulated the parthenogenetic reproduction of C. piger.

 The meiofaunal chydorids may thus have a structuring effect on macrofaunal chironomid populations by interfering with the early‐instar larvae.

 With macro‐ and meiofaunal species both operating at the primary consumer‐level of the food web, this kind of complex interaction will affect the magnitude of secondary production available to higher trophic levels.
The importance of fluvial hydraulics to fish‐habitat restoration in low‐gradient alluvial streams
Authors: RABENI CHARLES F. , JACOBSON ROBERT B.
Published: May 2006

A major cause of degradation and loss of stream fish is alteration of physical habitat within and adjacent to the channel. We describe a potentially efficient approach to fish restoration based upon the relationship between fluvial hydraulics, geomorphology, and those habitats important to fish.

 The aquatic habitat in a low‐gradient, alluvial stream in the Ozark Plateaus physiographical province was classified according to location in the channel, patterns of water flow, and structures that control flow. The resulting habitat types were ranked in terms of their temporal stability and ability to be manipulated.

 Delineation and quantification of discrete physical spaces in a stream, termed hydraulic habitat units, are shown to be useful in stream restoration programmes if the ecological importance of each habitat unit is known, and if habitats are defined by fluvial dynamics so that restoration is aided by natural forces.

 Examples, using different taxa, are given to illustrate management options.
Role of interaction zones between surface and ground waters in DOC transport and processing: considerations for river restoration
Authors: VERVIER PHILIPPE , DOBSON MIKE , PINAY GILLES
Published: May 2006

A study of dissolved organic carbon (DOC), nitrates and total dissolved phosphorus (TDP) concentrations, conductivity and bacterial numbers was undertaken in subsurface water of the Garonne River (France) under low‐flow conditions. The velocity of subsurface flow through a 300‐m gravel bar, during this study, was less than 43 m day−1. DOC, nitrates and TDP concentrations, conductivity and bacterial numbers fluctuated within the gravel bar with no discernible spatial pattern. Bacterial abundance was correlated with DOC concentration. Results were compared to a previous study of the Stillaguamish River (U.S.A.) (Vervier & Naiman, 1992).

 These studies provide evidence that gravel bars are important in the processing of DOC by bacteria in the subsurface water. Bacterial activity is, in turn, determined by sources of DOC from upstream at high discharge, and by patchy local microhabitats at low discharge.

 Restoration of rivers should incorporate, wherever possible, meanders with associated gravel bars and riffles. These will improve DOC‐processing capacity, in addition to other benefits predicted by the Building Block Model (Petersen, Petersen & Lacoursière, 1992).
Natural rehabilitation of stream fish populations in an Illinois catchment
Authors: BAYLEY P.B. , OSBORNE L.L.
Published: May 2006

An extreme drought in 1988 dried first‐ and second‐order streams in the Salt Fork basin (1190 km2) in east‐central Illinois. This event provided a natural experiment in which the natural rehabilitation of fish populations could be measured in the whole catchment following resumption of stream flows.

 Fish were sampled before, during, and after the drought (1987–1990) throughout the basin (eighty‐eight samples in July‐September) using methods of known efficiency. Analyses of covariance [using log (distance from source) as the covariate] indicated no significant differences (P>0.2) of biomass or species richness between pre‐drought and post‐drought samples from sites desiccated during 1988 or among pre‐drought, drought, and post‐drought years among samples from perennial Streams. Therefore, recovery occurred within 1 year, but there was no indication of increased biomass or species richness in permanent streams resulting from fish moving down or remaining downstream during the drought.

 Fish biomass per unit length of stream segment was modelled as a power function of distance of the segment from the source of each stream to estimate changes in biomass of the whole catchment. Before and subsequent to the drought, 90.0t of fish occupied the total 729km of stream length in the basin, compared with 74.61 in the drought year. Although, the drought affected 80% of total stream length, fish biomass was reduced by only 17% in the drought year because only the lower‐order streams were desiccated and their normal biomass density was lower than in perennial streams.

 In conclusion, it is expected that no expenditure on stocking fish would be necessary in restoration projects on these lower‐order, surface runoff streams, providing that they are connected to permanently flowing streams that contain a full complement of species.
Patterns in metal content of submerged aquatic macrophytes: the role of plant growth form*
Authors: JACKSON LELAND J. , KALFF JACOB
Published: May 2006

Sediments and eleven species of rooted submerged aquatic macrophytes were sampled from twenty‐five lakes in southern Quebec to examine species patterns in metal content.

 Linear regression models relating the content of metals in the macrophytes to their sediments demonstrated that the isoetoid (Eleocharis acicitlaris, Eriacaulon septangulare, Isoetes sp. and Sagittaria graminae) and the non‐isoetoid species had different plant‐sediment relationships. Canopy‐forming (Myriophyllum spicatum, Potamogeton amplifalius, P. crispus and P. perfoliatus) and understory species (Elodea canadensis, P. robbinsii and Vallisneria americana) had similar linear regression model slopes, but the understory species had significantly higher intercepts, indicating higher plant metal contents for a given sediment metal concentration.

 We grouped species by their biomass density (biomass (kg)/height (m)), a measure of the packing of the plant canopy, and averaged values for each metal, thereby producing one model per group. Comparison of the models by analysis of covariance revealed no significant differences in metal content. However, the canopy‐forming species that occurred in monospecific and mixed species stands (M. spicatum and P. amplifolius) had significantly higher metal content for a given sediment metal content when an understory was present.

 These results show that sediment metal content explains the largest proportion of variation in plant metal content across all sites and species. Deviations from what would be predicted by the most general model are not related to large‐scale differences in sediment geochemistry, but to the physical structure of the weedbed within geochemically similar sediments.
The drag coefficient of cased caddis larvae from running waters: experimental determination and ecological applications
Authors: WARINGER J.A.
Published: May 2006

Drag coefficients of cylindrical‐case caddis larvae from running waters were investigated in the laboratory using an artificial stream channel.

 Dead larvae of the limnephilids Allogamus auricollis (first to fifth instars), fifth instars of Potamophylax cingulatus, Chaetapteryx fusca, Drusus monticola, Metanoea rhaetica and fourth instars of the brachycentrid Micrasema minimum, were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to dislodge the larvae ranged from 3.00cms‐1

(A. auricollis, first instar) to 70.50cms‐1 (P. cingulatus). With flow normal to the long axis of the case (lateral position), these speeds ranged from 2.20cms‐1 (M. minimum) to 20.80cms‐1 (P. cingulatus).

 In frontal position, individual Reynolds numbers at the moment of dislodgement ranged from 74 (A. auricollis, first instars) to 14100 (P. cingulatus), and from 14 (M. minimum) to 1143 (P. cingulatus) in lateral position. Regression equations correlating case length, mean case width or fresh weight with Reynolds numbers at the moment of dislodgement (frontal and lateral position) were very highly significant with r20.91.

 For the range of Reynolds numbers given above, the drag coefficient varied between 5.05 (A. auricollis, first instars) and 0.26 (P. cingulatus) in frontal case position and from 2.97 (M. minimum) to 0.69 (C. fusca) in lateral case position. Furthermore, the relationship between Reynolds number and drag coefficient was found to be linear on a In/In scale for both frontal and lateral case position.
Macroinvertebrate functional feeding groups in the middle and lower reaches of the Buffalo River, eastern Cape, South Africa. II. Functional morphology and behaviour
Authors: PALMER CAROLYN , O'KEEFFE JAY , PALMER ANTHONY
Published: May 2006

While it was impossible to assign twelve taxa from the middle and lower reaches of the Buffalo River, eastern Cape, South Africa to functional feeding groups (FFGs) on the basis of their foregut contents alone, we were able to assign these taxa to FFGs, with varying degrees of certainty, on the basis of their mouthpart morphology and feeding behaviour.

 The two Hydropsychidae were identified as passive filterers on the basis of their feeding behaviour. The ultrastructure of the labia and maxillae of the ten Ephemeroptera, and observation of the feeding behaviour of five of these, were used to assign them to FFGs.

 Only mayfly species whose morphology and behaviour were recorded could be positively assigned to the FFGs active or passive filterer, gatherer, brusher, and scraper. The FFG designation described the predominant feeding behaviour, and all observed taxa exhibited a range of feeding activities.

 FFGs are useful descriptive categories which clarify both the nature and distribution of the food eaten, and the role of the organism in the ecosystem. FFGs affect a variety of stream processes, and the role of the FFG concept in understanding stream functions is discussed.
On the evolution of commensalism in the Chironomidae
Authors: TOKESHI MUTSUNORI
Published: May 2006

Commensalism is widespread among the Chironomidae. Animal hosts include the Ephemeroptera, Plecoptera, Trichoptera, Megaloptera, Hemiptera, Odonata, Diptera, Mollusca and fishes. In general, benthic organisms with relatively large body size and intermediate mobility appear to be chosen most frequently as hosts.

 The evolutionary advantage of a commensal mode of life in the Chironomidae is discussed. Better feeding opportunity, increased mobility, protection from disturbance and reduced predation risk are likely to constitute the four aspects of major importance in establishing commensal relations. It is proposed that the Chironomidae have always been under the pressure of both limited mobility and high predation due mainly to their morphological characteristics. Under these circumstances commensalism is considered as a convenient strategy to solve both the mobility and predation problems at the same time. In particular, association with large‐sized hosts is thought to make the chironomid commensal less vulnerable to a variety of freshwater predators which are in general gape limited.

 The evolutionary path to parasitism seems to have been more difficult in the Chironomidae, with fewer taxa being recorded as parasites than commensals. The parasitic mode of life requires that the benefit of feeding directly on the host's bodily resource exceeds the cost incurred in the form of reduced fitness of the host and hence a reduced host population, the situation that a limited number of ectoparasitic chironomid species appear to tolerate.
Reproductive potential and lifetime potential fecundity of the freshwater amphipods Gammarus fossarunt and G. roeseli in Austrian streams and rivers
Authors: PÖCKL MANFRED
Published: May 2006

Fecundity of Gammarus fossarum populations at six stream sites (S1‐S6) and G. roeseli populations at two sites (S5 and S6) was studied monthly during 1985–1988, distinguishing seven morphological stages of embryonic development. Mean survival of G. fossarum eggs was 65% (60–70%) in nature and 60% (57–63%) in the laboratory; egg survival of G. roeseli was 52% (46–58%) in nature and 41% (35–47%) in the laboratory. Regressions of egg numbers per clutch against body wet weight (WWT) decreased significantly for egg developmental stages 2 to 7 (hatching).

 In stream populations, ovigerous females of G. fossarum were absent in October (six sites) and November (five sites); ovigerous G. roeseli were usually absent from October until March.

 Overall mean egg volume (EV) increased significantly from 0,08 ± 0.001 mm3 and 0.075 ± 0.001 mm3 for stage 2 eggs, to 0.174 ± 0.012mm3 and 0.160 ± 0.013 mm3 for stage 6 eggs of G. fossarum and G. roeseli, respectively. The dry weights of stage 2 eggs, stage 6 eggs and neonates (stage 7) were not significantly different, within and between species; mean dry weight was 36 ± 3 μg.

 Egg volumes and fecundity indices (FI, weight‐specific number of eggs per clutch) were not significantly different between the same months of four successive years, so the data were pooled to give a single representative ‘year’. At most sites there were marked seasonal fluctuations in these variables. In both species, mean EV was largest for ‘winter’ eggs in December/January and smallest for ‘summer’ eggs in May, EV decreased during some months of the year when FI increased, and vice versa. Mean reproductive effort (RE = EV × FI) declined from high ‘winter’ values to low ‘summer’ values, and this difference was most marked at sites where the major foodstuff available was seasonally limited (autumn‐shed tree leaves). Overall (‘annual’) mean RE was also lowest at these sites (S3 and S4) but was some 13% greater at sites where nutrients and food were present in the greatest quantifies (S5 and S6). Specific maximum potential body sizes and hence maximum potential fecundities (fifty‐nine eggs for G. fossarum and eighty‐seven eggs for G. roeseli) were attained only at S5 and 56. Mean RE was nearly identical for G. fossarum and G. roeseli from the same sites.

 At experimental temperatures (T) in the range 3.8–20.2°C, females of the same body weight carried significantly different egg numbers per clutch. The relationship between FI and T was described by a second‐order polynomial. The calculated optimum T was 12.1°C for G. fossarum and 16.3°C for G. roeseli. Interspecific differences were highly significant.

 Theoretical lifetime potential fecundity was approximately 194 eggs for G. fossarum
Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH
Authors: GRIFFITH MICHAEL B. , PERRY SUE A.
Published: May 2006

Leaf litter processing rates and macroinvertebrate shredder assemblages in leaf packs were compared in four streams on the Allegheny plateau in the central Appalachian Mountains, U.S.A.; these streams were characterized by different bedrock geology and streamwater pH.

 Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream.

 Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies.

 The differences in processing rates between the more alkaline stream and the neutral streams were not associated with differences in shredder biomass, but appeared to be related to taxonomic differences in the shredder assembiages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.
The effects of trout on epibenthic odonate naiads in stream pools
Authors: WISEMAN S.W. , COOPER S.D. , DUDLEY T.L.
Published: May 2006

In a southern Califomian stream naiads of a lestid damselfly (Archilestes grandis Rambur) were much less abundant, moved less, exhibited fewer conspicuous behaviours, were more likely to occur in refuge areas, and had different diets in pools containing versus pools lacking rainbow trout (Oncorhynchus mykiss Richardson). To determine if trout were responsible for these patterns, we removed trout from some stream pools and added them to pools lacking trout, with unmanipulated trout and troutless pools acting as controls.

 The abundance and emergence of A. grandis were drastically reduced, and the proportion of lestid populations in refuge areas greatly increased, when trout were added to pools; however, the removal of trout had less drastic effects on lestid abundance and distribution, Aeshna walkeri (Kennedy) was also more abundant in pools lacking than in pools containing trout.

 Trout manipulations affected lestid behaviour, with swimming being observed only in troutless pools and movement tending to be greater in pools lacking rather than containing trout.

 One week after manipulations started, the number of prey items per lestid gut was higher in troutless control than in trout addition pools. Ostracods and chironomids were more abundant, and mayflies were less abundant, in the diets of lestids from pools lacking versus containing trout. Comparisons of the environmental abundances of prey taxa and lestid diet composition indicated that lestid selectivities for Caenis were higher, and those for Paraleptophlebia, ostracods, and Eubrianax lower, in trout than in troutless pools.

 Although similar at the beginning of manipulations, head widths of lestids in troutless control pools were greater than those in trout addition pools after 3 weeks.
Factors limiting the distribution of submerged waterplants in the lowland River Vecht (The Netherlands)
Authors: VERMAAT J.E. , DE BRUYNE R.J.
Published: May 2006

The significance of light climate and water movement for the absence of submerged vegetation in the largest part of the River Vecht was investigated at three stations along the river during the summer of 1991.

 The underwater light climate was found to be quite adverse for the development of waterplants due to turbidity and periphyton development. Attenuation coefficients of the water were found to be high: on average 2.6, 2.8 and 3.0 m−1 for the southern, central and northern stations, respectively. In spring most of the light attenuation (90–100%) was due to the water layer; in summer periphyton and water were equally important. The light climate limited the potential occurrence of submerged macrophytes to a zone shallower than 1m. The observed distribution of the waterplants along the river's length, however, could not be explained by the light climate alone. Presence of submerged vegetation is restricted to the southern section of the river where there is relatively little boat traffic.

 Wave action caused by the (mainly recreational) boat traffic was observed to negatively affect plant growth in an in situ experiment with a breakwater. This points to physical damage by wave action caused by passing boats as the main factor determining waterplant distribution. An alternative explanation is the much higher density of houseboats in the northern section. When present, houseboats effectively shade out the zone shallower than 1 m, thus preventing the development of a submerged vegetation.
Long‐term pattern of alternative stable states in two shallow eutrophic lakes
Authors: BLINDOW IRMGARD , ANDERSSON GUNNAR , HARGEBY ANDERS , JOHANSSON STEFAN
Published: May 2006

Lake Tåkern and Lake Krankesjön, two moderately eutrophic, shallow lakes in southern Sweden, have during the past few decades shifted several times between a clear‐water state with abundant submerged vegetation and a turbid state with high phytoplankton densities.

 Between 1985 and 1991, Lake Takern was in a clear state, whereas Lake Krankesjon shifted from a turbid to a clear state. During this shift, the area covered by submerged macrophytes expanded, followed by an increase in water transparency, plant‐associated macroinvertebrates, and piscivorous fish. Nutrient concentrations, phytoplankton biomass and abundance of planktonic cladocerans decreased.

 In both lakes, water level fluctuations were the most common factor causing shifts, affecting submerged macrophytes either through changes in light availability or through catastrophic events such as dry‐out or mechanical damage by ice movement.

 Our data give further support for the existence of two alternative stable states in shallow lakes maintained by self‐stabilizing feedback mechanisms.
Hatching of Daphnia sexual eggs. I. Intraspecific differences in the hatching responses of D. magna eggs
Authors: DE MEESTER LUC , DE JAGER HILDE
Published: May 2006

To test the hypothesis that the variability in hatching response of the sexual eggs of Daphnia has a genetic component, hatching after a standardized decapsulation technique was studied in different D. magna families, resulting from intra‐ as well as interclonal crosses.

 There were significant differences in hatching response between families. Average hatching rates ranged from 0.0% to 81.9%, depending on the family under study.

 Offspring‐on‐parent regressions indicate that the hatching rate‐of sexual eggs is to a large extent determined by the genotype of the mother (maternal inheritance).

 Our results suggest that there is ample generic variation on a microgeographic scale for characteristics related to hatching of sexual eggs in Daphnia.
A seasonal study of phosphorus deficiency in a eutrophic reservoir
Authors: NEDOMA JIŘÍ , PORCALOVA PETRA , KOMÁRKOVÁ JAROSLAVA , VYHNÁLEK VOJTĚCH
Published: May 2006

Seston elemental composition (C, N, P) and the orthophosphate uptake rate constant, k(upt), were measured in the epilimnion of the eutrophic Římov Reservoir in the period March‐August 1989.

 Seasonal series of log C/P, log N/P and log [k(upt)] values were highly correlated (r2 in the range 0.84–0.93), but, based on literature‐derived criteria, k(upt) values indicated stronger P deficiency than did the C/P values.

 The results showed moderate to strong phosphorus deficiency in summer, moderate deficiency at the end of the spring peak of phytoplankton, and no deficiency early in the spring or during the spring clear‐water period.
Estimating the size at maturity in field populations of Daphnia (Cladocera)
Authors: STIBOR HERWIG , LAMPERT WINFRIED
Published: May 2006

Two methods for estimating the average body size at the onset of reproduction were applied to populations of Daphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes of Daphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg‐bearing females is reached.

 The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.

 During one season, D. hyalina exhibited pronounced changes in fecundity, proportion of egg‐bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (clear‐water phase).
Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus in a Danish stream
Authors: JACOBSEN DEAN , SAND‐JENSEN KAJ
Published: May 2006

Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus was studied in a Danish lowland stream during the main growth seasons of summer 1991 and 1992. Young apical leaves escaped consumption probably because of their location and dense packing, but herbivory loss increased linearly with age and exposure time of older leaves. Nitrogen content was relatively high in both young (4.61% DW) and old leaves (3.65% DW) but a food preference experiment showed that young leaves were preferred by the main herbivore, the trichopteran Anabolia nervosa.

 The percentage of standing plant biomass lost to herbivory (the apparent loss) between sampling periods increased from early May to a mid‐June maximum (24.8% in 1991, 4.2% in 1992), and subsequently declined to zero within a month. The averages for the growth seasons were 10.5% in 1991 and 2.0% in 1992. Yet, the proportions of annual plant production harvested by herbivores were low and almost the same (1.3 and 1.8%) because consumption was low when plant production peaked in late summer.

Consumption was almost the same early in the two years, but plant growth dynamics differed markedly and was the main factor determining apparent herbivory loss.

 Despite heavy damage early in the summer, P. Perfoliatus contributed a minor fraction (1–5%) of the trichopteran diet. This fraction appeared to be restricted by the low macrophyte biomass during early summer.

 The results emphasize that apparent herbivory loss does not estimate the harvested proportion of plant production, and that plant growth dynamics should be analysed to attain precise estimates of herbivory rates.
Seasonal size variation in the predatory cladoceran Bythotrephes cederstroemii in Lake Michigan
Authors: BURKHARDT STEFFEN
Published: May 2006

Dry weight, body length and spine length were measured for the exotic cladoceran Bythotrephes cederstroemii collected from offshore and inshore stations in southeastern Lake Michigan. Average dry weight of each developmental stage exhibited seasonal variation by a factor of more than 5.

 Mean dry weight of Bythotrephes was closely correlated with water temperature. Contrary to the inverse relationship between water temperature and body size frequently observed for other invertebrates, the dry weight of Bythotrephes increased at higher ambient temperatures.

 No significant correlation was observed between abundances of major zooplankton taxa and the dry weight of Bythotrephes. An indirect effect of temperature on prey consumption may cause seasonal variation in dry weight of Bythotrephes in Lake Michigan.

 Distances between adjacent pairs of barbs, added to the caudal spine with each moult, are significantly shorter in Bythotrephes which produce resting eggs. Less material investment in the exoskeleton of sexually reproducing females was observed in favour of growth and reproduction.
A photometric technique for the measurement of plant surface area: the adsorption of Brilliant Blue dye on to plant surfaces
Authors: WATALA KATARZYNA B. , WATALA CEZARY
Published: May 2006

1. A new photometric method for determining the surface area of plants, which relies on the adsorption of Coomassie Brilliant Blue G‐250 on the plant surface, is described and compared with other methods.

2. The method was applied to a variety of aquatic plants and found to provide a routine procedure to determine plant surface area.
Distribution, abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River
Authors: STRAYER DAVID L. , HUNTER DEAN C. , SMITH LANE C. , BORG CHRISTOPHER K.
Published: May 2006

1. An extensive series of PONAR grabs was used to determine the distribution and abundance of unionid clams in the freshwater tidal Hudson River.

2. The five species of unionids collected were distributed very unevenly within the river. Mean river‐wide density and biomass of unionids were 8.0m−2 and 6.2 g DM m−2 (shell‐free)., respectively.

3. The environmental variables that we measured (water depth, distance from shore, sediment granulometry and organic content, presence or absence of macrophytes, and the chlorophyll a and particulate organic matter content of the water) explained little of the variation in abundance of unionids.

4. The distributions of the various species of clams did not differ significantly with respect to the environmental variables measured.

5. We estimate that unionids filter a significant amount of water (0.14m3 m−2 day−1, on average) in the Hudson River estuary, roughly equivalent in magnitude to downstream flushing.

6. We project that unionids will serve as a major substratum for the settlement of the zebra mussel (Dreissena polymorpha), which is now invading the estuary. We emphasize that unionids may play important non‐trophic roles in large river ecosystems.
Effects of predation, trout density and discharge on habitat use by brown trout, Salmo trutta, in artificial streams
Authors: GREENBERG LARRY A.
Published: May 2006

1. The effects of predation risk, fish density and discharge on habitat use by juvenile brown trout, Salmo trutta, in four artificial streams were studied. Each stream contained three habitats, riffles, runs and pools, the latter two each being further divided into shallow margins and deeper mid‐regions.

2. The presence of northern pike, Esox Indus, caused trout to decrease use of pool midregions, where pike also occurred, and to increase use of other habitats. Increasing the number of trout caused trout to increase use of pools and the shallow margins of runs. Decreasing discharge reduced the area of the run and pool margins covered by water, thereby reducing use of these areas by trout.

3. Habitat selection indices for the different treatments were calculated. The data indicated that riffles and the mid‐regions of runs were preferred habitats, whereas run margins and pools were inferior habitats used when intraspecific fish densities were high.

4. Despite density‐ and discharge‐dependent habitat use by trout, the number of trout consumed by pike was independent of trout density and discharge.

5. The results reveal the flexibility of habitat use by trout and illustrate the potential danger of applying data on habitat use in one stream to others where habitat availability and bioric interactions may differ.
Factors affecting the distribution and abundance of an unpigmented heterotrophic alga Prototheca richardsi
Authors: WONG ADELINE L.‐C. , BEEBEE TREVOR J.C. , GRIFFITHS RICHARD A.
Published: May 2006

1. Numbers of the contramensal alga Prototheca richardsi were high in spring in two ponds used for breeding by anuran amphibians, but lower at other times of year and undetectable in two ponds not used by anurans.

2. Prototheca richardsi became abundant in the silt of eight experimental ponds which contained tadpoles, but remained undetectable in four otherwise identical ponds lacking tadpoles.

3. Prototheca richardsi numbers in laboratory microcosms remained stable for many days in sterile tap water, but declined with a half‐life of about 6 days in pond water at 20°C.

4. Further studies with microcosms using antibiotics and electron microscopy indicated that mortality of P. richardsi was caused primarily by pathogenic bacteria.
Macrophytes from lakes in the eastern Pyrenees: community composition and ordination in relation to environmental factors
Authors: GACIA ESPERANÇA , BALLESTEROS ENRIC , CAMARERO LLUIS , DELGADO OLGA , PALAU ANTONI , RIERA JOAN LLUIS , CATALAN JORDI
Published: May 2006

1. Thirty‐six species of macrophytes (fourteen flowering plants, two quillworts, sixteen mosses and liverworts, and two algae) were collected in an extensive survey of 116 high mountain lakes in the eastern Pyrenees. Seventy per cent of the lakes showed macrophyte development.

2. The isoetids (Isoetes lacusiris, Isoetes setaceaandSubularia aquatica) were the dominant growth form, although the natopotamidSparganium angusifoliumwas the most widespread species. Potamids (Potamogetonspp.,Ranunculusspp.), the algaNitellagr.opacaand some mosses (Warnstorfia exannulata, Sphagnum denticulatum) were often present.

3. A multivariate ordination analysis (RDA‐redundancy analysis) revealed that water chemistry, altitude and vegetation cover of the catchment, and nutrient availability are major environmental factors associated with macrophyte distribution along the eastern Pyrenean lakes. Isoetids prevailed in softwater oligotrophic lakes, potamids in relatively hardwater oligotrophic lakes, andPotamogeton natansandCallitriche palustrisin small and eutrophic water bodies affected by the presence of cattle.
Particle selection over a broad size range by crustacean zooplankton
Authors: BERN LARS
Published: May 2006

1. Preferences for particles over a broad size range were assessed in four crustacean zooplankton species under field conditions. The particles employed were six spherical algae with diameters of 2, 6, 13, 19, 38 and 61 μm.

2. Diaphanosoma brachyurum and Daphnia cucullata preferred the two smallest particles, Chydorus sphaericus the three smallest and Eudiaptomus gracilis the 19 μm particle.

3. These size preferences agree well with earlier determinations based on seston particles in the same lake, indicating consistent size preferences by these species over a broad size range.
Trophic ecology of red roach (Rutilus arcasii) in a seasonal stream; an example of detritivory as a feeding tactic
Authors: LOBÓN‐CERVIÁ JAVIER , RINCÓN PEDRO A.
Published: May 2006

1. Diel feeding activity and diet of red roach (Rutilus arcasii) were determined on five occasions (February, April, June, August and November 1985) in a seasonal, fluctuating stream subject to severe summer droughts and cold winter floods.

2. Except in June, the two age groups of the population (1 + and >1+) fed mainly on detritus and showed no significant differences either in their feeding intensity or in the relative contribution of the main diet components (detritus, plants and invertebrates).

3. The size, abundance and availability of drifting invertebrates influenced red roach feeding. When drift was scarce or inaccessible, both age groups fed on detritus, plants, or a combination of the two. These niche shifts were a trophic tactic aimed at maintaining feeding when other, more nutritional and energetically valuable foods were scarce.

4. A comparison with other populations suggested that a detritus‐based diet had no major cost in the life history of the red roach. We hypothesize that the highly opportunistic trophic strategy of this Iberian endemic cyprinid is an adaptative response to seasonal Mediterranean streams.
Environmental significance of ice to streamflow in cold regions
Authors: PROWSE T.D.
Published: May 2006

1. The five major hydrologic regimes of cold regions are typically classified as proglacial, wetland, spring‐fed, arctic nival and subarctic nival. Each has a distinctive hydrograph determined by the source and timing of runoff.

2. The hydrologic response of streams in cold regions is influenced significantly by the source and pathways of moisture from the landscape to the stream channel. Snow and ice masses, such as snow cover, permafrost and icings, play principal and unique roles as major moisture sources, and in affecting runoff pathways.

3. Once flow has been routed from the landscape into a channel system, the effects of floating ice begin to control the flow system. Notably, many of the most significant hydrologic events in cold regions, such as floods and low flows, are more the result of in‐channel ice effects than of landscape runoff processes. This has not been adequately recognized in general assessments of cold‐regions water resources.

4. Only recently have the broader environmental effects of river ice been addressed in any concerted fashion. This paper reviews the various stages of ice formation, growth and break‐up, and summarizes the major hydrologic and ecological effects associated with each. Priority research topics are also identified.