bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective foraging by the crayfish Orconectes virilis and its impact on macroinvertebrates
Authors: HANSON JOHN MARK , CHAMBERS PATRICIA A. , PREPAS ELLIE E.
Published: May 2006

SUMMARY. 1. The impact of crayfish predation on the abundance of macroinvertebrates was examined under semi‐natural conditions. Female (Experiment 1) or male (Experiment 2) crayfish (Orconectes virilis) were held for 5 weeks in twelve small pools (4.67 m2 surface area) at biomasses of 0. 5, 10 or 18 g m−2 (live weight). The pools were stocked with known densities of macroinvertebrates.

2. Crayfish significantly affected the abundance of macroinvertebrates in the pools. Differences in the effects of crayfish on macroinvertebrates were related to crayfish sex, the presence of age‐0 crayfish, and the species of macroinvertebrate.

3. The abundance of snails (Stagnicola elodes and Physa gyrina) was greatly reduced, in comparison with controls, by biomass of female crayfish ≥10 g m−2 and by biomasses of male crayfish ≥5 g m−2. The total density of non‐molluscan invertebrates was inversely correlated with the biomass of female crayfish but the total biomass of non‐molluscan invertebrates did not differ between treatments. This is consistent with our observation that small invertebrates (<2 mg wet weight) were less numerous, and large amphipods (32–64 mg) were more numerous, in pools stocked with female crayfish. In contrast, male crayfish had little apparent effect on the abundance of non‐molluscan invertebrates.

4. Age‐0 crayfish hatched at the end of Experiment 1 and were present in each pool at the start of Experiment 2. Surprisingly, male crayfish preyed little on age‐0 crayfish. At the end of Experiment 2, the densities of age‐0 crayfish varied between six and 116 individuals m−2 and there was a strong inverse correlation between the mean biomass and density of age‐0 crayfish recovered from the pools. This suggests age‐0 crayfish were food limited in the pools and may explain the dominance of oligochaetes (which largely escape predation by burrowing) in the invertebrate community at the end of Experiment 2.

5. These results indicate that even relatively low densities of crayfish could greatly affect the abundance of macroinvertebrates in lakes. The introduction of crayfish into lakes (most lakes in Alberta currently have no crayfish) could substantially affect abundance and species composition of the macroinvertebrate community and, ultimately, the fish populations.
Germination requirements and seed banks of some nymphaeid macrophytes: Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze
Authors: SMITS ANTONIUS J. M. , VAN AVESAATH PIM H. , VAN DER VELDE GERARD
Published: May 2006

SUMMARY.

 Germination experiments demonstrated that the innate dormancy of the seeds of Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze could be overcome by a cold treatment. Light stimulated the germination of the three species. Hypoxic conditions stimulated the germination of Nymphaea alba and Nuphar lutea seeds but the seeds of Nymphoides peltata did not germinate under these conditions.

 Experimental seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata were laid out in three water bodies, varying in pH and alkalinity. Germination patterns indicated that Nymphaea alba and Nuphar lutea produce transient seed banks, but that Nymphoides peliata produces a persistent seed bank. Sampling of natural seed banks and subsequent germination tests were in concordance with the results of the seed bank experiment.

 The experimental above‐ground seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata showed similar germination patterns in the three selected water bodies, despite the differences in pH and alkalinity between them. However, the distribution of Nymphoides peliata is restricted to well‐buffered waters, so that its absence from soft and acid water bodies must be due to post‐germination mechanisms and/or processes.

 In aquatic systems where Nymphoides peltata co‐exists with the other nymphaeid species studied, it is largely restricted to a bell between the helophytes and the vegetation at deeper sites. The deeper sites were dominated by Nuphar lutea and Nymphaea alba. Germination requirements and seedling emergence from buried seeds of Nymphaea alba, Nuphar lutea and Nymphoides peliata play an important role in the establishment of the zonation pattern of these nymphaeid macrophytes.
Concomitant diel vertical migration of a predatory leech and its amphipod prey
Authors: BLINN DEAN W. , DAVIES RONALD W.
Published: May 2006

SUMMARY.

 The concomitant diet vertical migrations of the predaceous leechErpobdella montezumaand its pelagic amphipod prey(Hyalella montezuma)were monitored for 1 year in Montezuma Well, Arizona, U.S.A.

 High densities ofH. montezumaoccurred in the subsurface strata of the water column during the day, but a substantial portion of the population migrated into the surface 1 m at sunset.E. montezumaremained in the lower water strata during the day, but migrated vertically after sunset to exploit the high densities ofH. montezumanear the surface. Densities ofE. montezumaprogressively increased in the upper strata of the water column after sunset as light energy fell below 1 μEin m−2s−1.

 It is suggested that the synchronized nocturnal migrations of the predatorE. montezumain relation to its preyH. montezuma, increases the foraging efficiency of the leech in the highly predictable environment of Montezuma Well.
Growth and maturation of a North American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study
Authors: ANDERSON GARY , HSU SHEAU‐YU
Published: May 2006

SUMMARY.

 We evaluated survival, growth and time to maturation of the fairy shrimp, Streptocephalus seali Ryder, in the laboratory at various combinations of temperature and water hardness.

 Both independent factors affected survival and growth of S. seali. Multiple regression analysis and response surface modelling predict that after 4 days, over 80% survival is obtained at temperatures from 14 to 28°C and water hardnesses from 60 to 130 mg CaCO3 1‐−1.

 Growth rates of larvae were often maximum at physicochemical conditions other than those which had promoted maximum rates of survival. For example, after 12 days mean total body length was almost 12 mm in larvae which had been maintained at 34°C (80 mg CaCO3 1‐−1): the maximum survival rate had been obtained at 19°C. Total length was directly correlated with temperature at the lowest hardness tested, but not at the other two hardnesses (100 and 120 mg CaCO3 1‐−1). At the latter water hardnesses, total length was significantly less at 34°C than at 32°C on all three sampling occasions (4, 8 and 12 days post‐hatch).

 Similarly, developmental stage of larvae correlated well with temperature but larvae reared at 34°C did not develop more quickly than those reared at 32°C. After 12 days, most larvae at the two highest temperature treatments had developed at least to Stage 14 and many were nearly mature; at 17°C most larvae were still at Stage 10.

 During our study of maturation rate of females we noted that egg production was initiated after completion of fourteen or fifteen moults. Mean time to maturation at 27°C (17.3±2.8 days) exceeded that at 32°C (12.3±2.6days). The minimum time to maturation of a shrimp was 9 days at 32°C.
Chironomid biomass determination from larval shape
Authors: NOLTE ULRIKE
Published: May 2006

SUMMARY.

 Ash‐free dry weights and dry weights of each larval instar were determined for nine chironomid taxa using unpreserved material. Larval weight (wμg) was related to body length measurements (l mm) by the equation In w= In a+b In l.

 For a given taxon. the constants In a and b were dependent on larval size and shape, respectively: b was found to increase with larval length, while taxa with characteristically stout larvae yielded higher values for In a.

 Comparison of measurements of freshly‐killed chironomid larvae with measurements taken after preservation in 70% ethanol showed no change in body shape due to preservation. Length measurements from larvae preserved in this way are therefore suitable for use in the calculation of larval biomass when the relationship to the unpreserved weight is known.

 Maximum larval lengths and mean body proportions (length: width ratios) are reported for thirty‐two chironomid taxa.
Macroinvertebrate distribution and production on the floodplains of two lowland headwater streams
Authors: GLADDEN JAMES E. , SMOCK LEONARD A.
Published: May 2006

SUMMARY.

 Spatial and temporal distribution, abundance and production of the floodplain macroinvertebrate communities of two low‐gradient headwater streams in Virginia, U.S.A., were studied over 1 year.

 Spatial and temporal distribution patterns of invertebrates were affected by inundation patterns. Numbers, biomass and production were higher in low than high floodplain areas and on a floodplain continuously inundated over 9 months compared with a floodplain completely flooded only occasionally during storms.

 The predominant species in terms of numbers and production on both floodplains was the harpacticoid copepod Attheyella illinoisensis Forbes. Other species with relatively high production were the sphaeriid clam Pisidium sp., the leptophlebiid mayfly Leptophlebia sp., the isopod Caecidotea racovitzai (Williams), and the chironomids Paratendipes sp. and Polypedilum spp.

 Annual invertebrate production (dry weight) on the floodplain continuously inundated over 9 months was 6.1 g m−2; production on the periodically inundated floodplain was 1.7 g m−2. Collector‐gatherers accounted for 58–61%, and predators 19–25%, of the production.

 Annual invertebrate production on the floodplains, calculated on the basis of a linear metre of channel length, was 84–490 gm−1, or about one to two orders of magnitude greater than probable production in the channels, suggesting the significance of floodplain invertebrates to stream system trophic dynamics.
Zooplankton in Rainbow Bay, a Carolina bay pond: population dynamics in a temporary habitat
Authors: TAYLOR BARBARA E. , MAHONEY DIANE L.
Published: May 2006

SUMMARY.

 Rainbow Bay is a temporary freshwater pond in South Carolina, U.S.A., that typically fills in winter and dries in spring or summer. We studied population dynamics of zooplankton in 1984 and 1985 when it held water for 282 and 57 days, respectively. The zooplankton were diverse, including one species of calanoid copepod, nine or more cyclopoid copepods, nineteen or more cladocerans, and twelve or more rotifers. The community was initially dominated by the copepods Diaptomus stagnalis and Acanthocyclops vernalis or Diacyclops haueri, later by cyclopoids and cladocerans including Daphnia laevis and Simocephalus spp.

 Laboratory experiments with sediments from the dry pond support the inference from field data that time of emergence from resting stages was a proximate cause of the initial succession of species. The experiments also showed that eggs of the calanoid copepod, Diaptomus stagnalis, were inhibited from hatching in early November, but became ready to hatch by late November. A similar inhibition was not observed for cladocerans or cyclopoid copepods.

 Food limitation appeared to influence population dynamics following emergence. For the cladocerans Daphnia laevis and Simocephalus spp., great reductions in size‐specific fecundity occurred 1 month (1985) or 3 months (1984) after the pond filled and were associated with disappearance of the rotifer Conochilus hippocrepis. The cladocerans produced ephippia when their fecundities declined. Reproduction of Diaptomus occurred before cladoceran fecundities decreased in 1984, but during their decline in 1985. Broods of Diaptomus were smaller in 1985.

 The impact of invertebrate predators was probably greater than that of vertebrate predators, but neither was sufficient to prevent over‐exploitation of food resources. Prey consumption rates by salamander larvae were estimated from diets and population densities of the larvae in 1984 (Taylor et al., 1988). Their impact on the zooplankton was low in February, increased in March and April as the larvae grew, and then
Measurement of lift and drag forces in the m N range experienced by benthic arthropods at flow velocities below 1.2 m s−1
Authors: WEISSENBERGER J. , SPATZ H.‐Ch , EMANNS A. , SCHWOERBEL J.
Published: May 2006

SUMMARY.
1. A flow tank was constructed which generates homogeneous and stable flow of water up lo velocities of 1.2 m s−1.

2 A sensitive, two‐component balance with its platform inserted in the bottom of the flume allowed the measurement of drag and lift forces in the mN range.

3 The drag forces experienced by several benthic arthropods, which cling to the roughened surface of the platform, are proportional to the square of the flow velocity.

4 Large biological variations in lift forces, leading even to negative lifts in some cases, are indications of special adaptations of the animals to counter the danger of being swept away from their support.
The importance of acid episodes in determining faunal distributions in Welsh streams
Authors: WEATHERLEY N. S. , ORMEROD S. J.
Published: May 2006

SUMMARY.
1. In regional studies of surface‐water acidification, annual means of chemical variables are often used to describe differences and change. Outputs from hydrochemical models are often in the form of mean values, which are used in biological models, and these, in turn, are usually derived from responses to mean conditions. Thus, biological forecasts are constrained to ignore the possible effects of the short‐term variations in water chemistry which characterize acid streams. This approach requires appraisal.

2. Here, regional Welsh data and daily records from a smaller number of streams were used to investigate the estimation of pH parameters. Variations in aluminium concentration in relation to pH were also assessed. Empirical relationships between invertebrate assemblages, fish populations, mean stream chemistry and measures of fluctuation in pH and aluminium concentration were explored.

3. In general, pH or Al variability and mean pH or Al in Welsh streams were closely related, so that the biological influences of episodes could not easily be separated from those of chronic conditions. Mean pH and mean aluminium concentration were the most effective pH and aluminium statistics used in multivariate models of trout density, which were not improved by including other pH or aluminium variables. For models of invertebrate assemblages based on mean pH or mean aluminium, the inclusion of variables related to episodicity (e.g. pH minimum, aluminium maximum) gave moderate increases in precision.

4. This analysis indicates that it is reasonable to use means of stream chemical variables in biological models of acidification. Consideration of chemical variability could give improvements in some cases, but at the expense of increased model complexity and effort in parameter selection. Nevertheless, we emphasize the need for accurate calibration of both biological and hydrochemical models.
The effect of aquatic plant chemistry and morphology on feeding selectivity by the crayfish, Orconectes virilis
Authors: CHAMBERS PATRICIA A. , HANSON JOHN M. , PREPAS ELLIE E.
Published: May 2006

SUMMARY.
1. Feeding preference trials conducted with male and female crayfish (Orconectes virilis) showed that out of ten submersed aquatic plant species, Chara sp. and Lemna trisulca were the preferred food sources, followed by Myriophyllum exalbescens or Utricularia vulgaris.

2. Analysis of plant fibre, alkaloid, total phosphorus, total and available nitrogen, and organic content showed that crayfish feeding preferences were not related (P>0.5) to plant fibre or alkaloid content but were negatively correlated (P<0.05) with plant nutrient content such that species of low nutritional value (Chara and Lemna) were consistently preferred.

3. Despite this preference for low nutrient food, daily intake rates by crayfish for phosphorus, nitrogen and organic matter were greatest when feeding on Lemna or Chara due to the large quantity consumed.

4. We suggest that feeding preferences of O. virilis are not determined by plant chemistry but, rather, relate to ease of handling small, short, bottom‐dwelling plants such as Chara and Lemna as compared with large erect, roseate or floating‐leaved forms. Because crayfish are selective herbivores, their introduction into waters where they do not naturally occur could have a dramatic effect on both the species composition and biomass of submersed plants.
Characterizing individual, population and community effects of sublethal levels of aquatic toxicants: an experimental case study using Daphnia
Authors: JONES MATTHEW , FOLT CAROL , GUARDA SONIA
Published: May 2006

SUMMARY.
1. The relationship between toxicant‐induced changes in the feeding behaviour of the cladoceran, Daphnia catawba (Coker), and subsequent effects at population and community levels were experimentally addressed.

2. We adapted a method for measuring the thoracic appendage beat rate of individuals (termed the TAR and positively correlated with daphnid feeding rate) after exposure to toxicant at known levels, for use as a behavioural bioassay for low levels of aquatic toxicants. The TAR declined significantly with an increase in both sublethal and lethal levels of the surfactant, sodium dodecyl sulphate (SDS).

3. We also measured population level effects (i.e. rates of reproduction, survival, and R0), and found that reductions in these values occurred at the same concentrations as the effects on individual behaviour.

4. In most cases, the changes in feeding behaviour occurred more rapidly (≤30h) than changes in population parameters (days to weeks).

5. We conclude that toxicant‐induced changes in individual feeding behaviour can provide a quicker estimate of effects on individuals and of potential community effects (i.e. effects on their prey populations) than measurements of population parameters. In addition, due to its sensitivity at low levels of toxicants, the behavioural bioassay may be particularly helpful in identifying effects of sublethal levels of aquatic pollutants.
Other environmental factors affect the size of crests developed by Daphnia carinata (Cladocera: Daphniidae) in response to notonectid predators
Authors: BENZIE JOHN A.H.
Published: May 2006

SUMMARY.
1. Crest size and body size was measured in Daphnia carinata King sampled from field enclosures in which environmental conditions and notonectid predator (Anisops Hyperion Kirkaldy) levels had been manipulated, and from control treatments which had predator levels and other environmental factors equivalent to those in the natural environment.

2. Individuals of D. carinata developed larger crests in treatments with predators than in treatments without predators.

3. The environmentally manipulated treatment was considered to have lower levels of food but was also likely to have undergone other changes in physicochemistry and resource variability that may have affected crest size. The effect of the manipulation cannot be confirmed, therefore, as the result of variation in food levels. Animals in the treatments considered to have lower amounts of food had smaller crests than in the control treatment irrespective of whether predators were present. The effects of environmental manipulation and predators were additive.

4. Enclosures without predators, but in which water from the natural, predator‐rich, environment was exchanged through the enclosure walls, showed no evidence of a chemical induction effect. Chemical induction effects may have been countered by a reduced food supply resulting from the higher D. carinata population densities that developed in these enclosures.

5. This work provides a second example of an alteration of the morphological response of daphnid prey to predators by environmental factors, probably food, and suggests this phenomenon may be general in cladoceran species displaying predator‐induced changes in morphology.
The growth of brown trout (Salmo trutta) in mild winters and summer droughts in upland Wales
Authors: WEATHERLEY N.S. , CAMPBELL‐LENDRUM E.W. , ORMEROD S.J.
Published: May 2006

SUMMARY.
1. We compared the observed annual growth of 0‐ and I‐group trout in nine Welsh upland streams, with growth predicted from temperature assuming that this was the only limiting factor.

2. Autumn weights of second year fish were 51–67% of predicted (Gmax) values in 1988, but only 30–40% in 1989 and 1990 when drought occurred. Though initial weights of fry were unknown, simulations suggested that first year growth was also less than Gmax, but with no obvious effect of drought.

3. To evaluate the possible effects of future climate change, we simulated stream temperature regimes 1.5–4.5°C above those of a recent year with temperatures similar to the long‐term average. Growth was set at 60%Gmax for both 0‐ and I‐group, or at 40% for I‐group to represent the effect of drought. As winter temperature increased, time to hatching and emergence decreased, for example by 56 and 49 days respectively for a rise of 3°C. 0‐group growth was slightly enhanced at up to + 3°C but retarded at + 4.5°C. Simulations of I‐group growth suggested that warmer winters could enhance trout growth while warmer summers would only increase growth if there were no adverse effects of drought.

4. We discuss many uncertainties in these simulations, which nevertheless suggest the magnitude of possible effects of climate change.
Effects of phosphorus limitation on the epidemiology of a chytrid phytoplankton parasite
Authors: BRUNING KEES
Published: May 2006

SUMMARY 1. The effect of phosphorus limitation of the diatom Asterionella formosa Hass. on growth, survival and epidemic development of its fungal parasite Rhizophydium planktonicum Canter emend. was estimated, using measurements of production and infectivity of the zoospores of the chytrid grown on host cultures with different phosphorus‐limited growth rates.

2. Phosphorus‐limited host cells were less susceptible to infection with zoospores of the parasite than non‐limited host cells.

3. The sporangia on phosphorus‐limited algae produced substantially less zoospores, but the development time of these sporangia was only slightly reduced.

4. As a result of these effects, Rhizophydium will reach lower growth rates at a given host density, and survival of the parasite will require higher host densities when Asterionella is phosphorus‐limited.

5. The zoospore production remained high enough to enable the parasite to grow faster than the alga at sufficiently high host densities, both at limiting and non‐limiting phosphorus levels.

6. In spite of the reduced growth rate of the parasite, phosphorus limitation of Asterionella was found to facilitate the development of a Rhizophydium epidemic. This was a consequence of the reduced algal growth rate at phosphorus limitation, which makes the host population more easily outgrown by the parasite.

7. Phosphorus limitation of the host could reduce the threshold host density required for the development of an epidemic by a factor of 2.5.
Secondary production of Chironomidae (Diptera) in a north temperate stream
Authors: BERG MARTIN B. , HELLENTHAL RONALD A.
Published: May 2006

SUMMARY 1. Secondary production of chironomids (Diptera: Chironomidae) in a third‐order northern Indiana stream was estimated using species‐specific, and in most cases cohort‐specific, life‐history data from the field.

2. Chironomid life‐history patterns were diverse, ranging from one to four generations per year in addition to asynchronous development. Cohort production intervals (CPI) for all taxa ranged from 56 to 266 days. CPI for cohorts of conspecifics differed up to 3‐fold.

3. Annual secondary production was estimated using the instantaneous growth method or the size—frequency method depending on whether cohorts were distinguishable or not. Total annual chironomid production was 29 700 mg dry mass m−2, which is the highest value reported for chironomids from a north temperate stream.

4. Eighty per cent of the total chironomid production was attributed to five species: Diamesa nivoriunda (33.9%), Cricotopus bicinctus (16.6%), Pagastia sp. (10.2%), C. trifascia (9.7%) and Orthodadius obumbratus (9.6%).

5. The annual P:B ratio ranged from 4.7 to 21.9. Thus, high secondary production was due to high mean annual standing stocks and not to rapid biomass turnover.
Phosphorus retention in streams draining pine and hardwood catchments in the southern Appalachian Mountains
Authors: D'ANGELO D.J. , WEBSTER J.R.
Published: May 2006

SUMMARY.
1. This study was designed to determine how catchment use affects stream phosphorus retention by comparing retention in streams draining three mixed hardwood catchments and three catchments that were planted in white pine in the 1950s.

2. Catchments of similar area and stream discharge were chosen and phosphorus uptake was measured monthly in each catchment along with temperature, discharge, velocity, coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), and microbial respiration associated with FPOM.

3. On an annual basis, average phosphorus retention was not different between streams draining pine and hardwood catchments nor were there significant differences between physical (temperature, velocity and discharge) or biological (CPOM, FPOM and respiration) parameters based on catchment type. However, discharge was more variable in streams draining pine catchments.

4. Because phosphorus uptake was correlated with discharge, phosphorus retention was also more variable in streams draining pine catchments. Storms caused a greater increar.e in discharge and loss of phosphorus in pine streams than in mixed hardwood streams, but discharge returned to baseline more quickly in pine streams.

5. We suggest that discharge regimes and phosphorus dynamics of streams draining pine catchments are less resistant to change but more resilient than streams draining mixed hardwood forests.
The influence of summer/winter conditions of temperature and irradiance on diel oscillations in photosynthesis by Fragilaria crotonensis
Authors: WALLEN D.G.
Published: May 2006

SUMMARY.
1. The common pennate diatom (Bacillaryiophyta) Fragilaria crotonensis Kitton showed strong periodicity in its photosynthesis ‐irradiance (P—I) relationship under summer conditions of high irradiance and temperature which damped progressively throughout the growth phase. Under winter conditions of low irradiance and temperature, weak periodicity was observed.

2. The amplitude of diel oscillations in photosynthesis as a function of irradiance under winter conditions showed only slight variation throughout the growth phase. Under summer conditions, however, amplitudes for both α and Pmax were highest in the early exponential phase, declining progressively during growth.

3. These results indicate that the occurrence of periodicity is dependent, in part, on the growth phase of the cells and, in part, on environmental parameters of irradiance and temperature variations under simulated summer and winter conditions.
Differences in processing dynamics of fresh and dried leaf litter in a stream ecosystem
Authors: GESSNER MARK O.
Published: May 2006

SUMMARY.
1. Although the bulk of litter input to stream ecosystems is in the form of fresh leaves, current understanding of organic matter processing is largely founded on experimental studies made with pre‐dried leaves. This paradox points to the critical need for evaluating to what extent those experiments with dried leaves reflect natural litter decomposition.

2. The mass loss rates, patterns of mass loss, and chemical changes during processing of fresh leaf litter were compared with air‐dried leaf litter in a stream ecosystem.

3. Although overall mass loss rates were similar between treatments (k= 0.0213 day−1 and 0.0206 day−1), fresh leaves lost mass at a constant rate, whereas the decay of dried leaves proceeded in two distinct phases. Soluble organic carbon, phosphorus, and potassium were rapidly leached from dried litter, but were largely retained in fresh material for more than a week. Kinetics of concentrations of cellulose and changes in amounts of lignin remaining per leaf pack revealed further differences in decomposition dynamics between treatments, apparently related, either directly or indirectly, to differences in leaching behaviour.

4. Dynamics of nitrogen and protein contents were similar between treatments, indicating that microbial colonization was not greatly delayed on fresh leaves.

5. It is concluded that the retention of labile carbon and nutrients in fresh leaf litter facilitates their utilization by leaf‐associated micro‐organisms and invertebrates, resulting in an increased importance of biotic processes relative to physical processes such as leaching.

6. At the ecosystem level, retention of carbon and nutrients in streams would be increased, allowing greater overall productivity. Conversely, the availability of labile organic carbon would be reduced in compartments such as the epilithon, fine sediments, and the water column.
Asymmetric resource competition in a filter‐feeding stream insect (Hydropsyche siltalai; Trichoptera)
Authors: ENGLUND GÖRAN
Published: May 2006

SUMMARY.
1. Field experiments in a lake outlet stream were carried out on filter‐feeding larvae of the caddisfly Hydropsyche siltalai Döhler, to assess whether microhabitat quality, establishment and growth rate is affected by position (upstream—downstream) within a dense aggregation of larvae.

2. Artificial substrates holding high‐density aggregations of hydropsychid larvae were used. Marked III‐instar H. siltalai larvae were implanted either in the upstream end or in the downstream end of an aggregation and recovered after 17 days.

3. Larvae recovered from the downstream end of an aggregation were smaller than those that had been implanted in the upstream end.

4. Fewer larvae had settled in the downstream end of aggregations compared to the exposed upstream part.

5. Naturally colonizing H. sitalai larvae were, in contrast to implanted larvae, more numerous behind aggregations. Small (first and second instar) Hydropsyche angustipennis (Curtis) and/or H. pellucidula (Curtis) larvae were more numerous in front of aggregations.

6. Current velocities, measured with a microcurrent velocity meter, and density of drifting prey, were significantly lower behind aggregations of hydropsychid larvae. Food availability decreased by about 50% behind aggregations.
The effect of food on protein content in rotifer and cladoceran species
Authors: GUISANDE C. , TOJA J. , MAZUELOS N.
Published: May 2006

SUMMARY.
1. The protein content of individuals of four species of cladoceran and two species of rotifer in eight ponds was measured over several time periods. The protein content in coarsely filtered water, which includes particulate (less than 31 μm for cladoceran and less than 10μm for rotifers) and dissolved proteins, was also analysed to estimate the amount of food available to the animals.

2. A positive relationship between protein content of individuals and protein in the food was found for all the species. The increase in protein content of the animals was less pronounced when food was more abundant.

3. When food concentration was lower, a greater reduction in protein content was observed in two species of rotifers than in four cladoceran species. Moreover, when comparing among species of Cladocera, the reduction in protein content at low food concentrations was more marked in the small‐bodied than in the large‐bodied species. These results are consistent with the size‐efficiency hypothesis.
Life history, growth and production of Mysis relicta in the large, fiord‐type Lake Mjøsa, Norway
Authors: KJELLBERG GØSTA , HESSEN DAG O. , NILSSEN JENS PETTER
Published: May 2006

SUMMARY.

Biomass, production and life history of Mysis relicta were studied in the large Lake Mjøsa during the years 1976–80. Biomass fluctuations were large, but biomass averaged about 1 g wet wt m−2 or 200 ind. m−2. Cumulative net production during summer ranged from 1.6 to 2.1 g wet wt m−2. Mean population P/B‐ratio was close to 2.

Neither production or biomass of Mysis were correlated with the biomass of phytoplankton or the main Zooplankton prey species (Daphnia and Bosmina), suggesting a predominant ‘top down’ control of Mysis in this lake.

The life cycle was well synchronized with development of food items, but predation pressure also affected life‐history patterns. The proportion of juveniles apparently increased in years with strong fish predation pressure, producing a predominantly 1‐year life‐cycle pattern the following year.

Mysis had a predominant 2‐year life history, but a traction of the population may reproduce after 1 or 3 years. Reproduction occurred exclusively during winter. Even in such a large and stable system, where Mysis has coexisted with its main food items and predators for 8–10 000 years, a flexible life history is maintained and is probably an important buffer against year‐to‐year fluctuations in food and predator abundance.
Dynamics of surface water/groundwater ecotones in a karstic aquifer
Authors: VERVIER Ph. , GIBERT J.
Published: May 2006

SUMMARY.

Interactions between surface waters and groundwaters were analysed by studying degrees of similarity between a surface stream and groundwater in a karstic system.

Exchange of water and solutes (‘abiotic interactions’) and living organisms (‘biotic interactions’) were quantified by characteristic parameters measured at the outlet of the karstic system during hydrological changes across the year as well as during a flood.

The ratio of bicarbonate to calcium described abiotic interactions. In the seasonal study, biotic interactions were estimated from the proportion of epigean organisms in the communities sampled at the outlet. These interactions during the flood were estimated by comparing numbers of Cladocera, epigean organisms, with numbers ofNiphargus virei, hypogean organisms.

The location of the ecotone created by interactions between the surface stream and the karstic system showed marked spatial fluctuations according to the prevailing hydrology. Interactions were strong during high‐water periods whereas they were negligible during low‐water. Similar fluctuations occurred within a few hours during the flood.

Results are compared with those from fluvial systems to discuss the importance of the dynamics of these surface/underground ecotones in the functioning of lotie ecosystems.
Life history and production of the predatory caddisfly Rhyacophila vao Milne in a spring‐fed stream
Authors: DIXON R.W. JAMIESON , WRONA FREDERICK J.
Published: May 2006

1. The predatory caddisfly Rhyacophila vao Milne (Rhyacophilidae) displayed a 2‐year, semivoltine life cycle in a small, spring‐fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2‐year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid‐June to early September.

2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non‐linear growth rate for instars I‐IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day−1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature‐independent at 0.87% dry wt day−1.

3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day−1.

4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non‐linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time‐adjusted annual estimates, although higher ratios were observed for the non‐linear growth phase of Cohort 2. Total cohort production (linear + non‐linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m−2. The corresponding cohort P/B ratio was 5.01 and the adjusted annual P/B, 3.01.

5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m−2; Year 2, 526.9 ± 967.5mg dry wt m−2) as were unadjusted and annual P/B ratios.
Development and composition of the epixylic biofilm in a blackwater river
Authors: COUCH CAROL A. , MEYER JUDY L.
Published: May 2006

1. Comparisons of chlorophyll a, bacterial density, frequencies of dividing cells, ash‐free dry mass (AFDM) and extracellular polysaccharide content were made for biofilm developing on wood (Salix) submerged in replicated stream‐side flumes exposed to either ambient light (light treatment) or covered to exclude light (dark treatment). Biofilm was sampled on days 3, 6, 9 and 14 during experimental periods occurring irrMay, September, November and December.

2. There were no significant differences in bacterial cell densities, frequencies of dividing cells, AFDM or extracellular poiysaccharide content between light and dark treatments. Ash content and bacterial biomass was similar to seston, suggesting the importance of seston as a source of material accumulating in the biofilm.

3. Of total epixylic organic carbon 7.2% was estimated to be extracellular polysaccharide, and 0.8% was bacterial carbon. At least nine times more carbon was contained in extracellular polysaccharide than in bacterial biomass.

4. In the epixylon of the Ogeechee River, bacterial dynamics appear to be controlled by factors other than the availability of algal substrates.
Seasonal migration by larvae of an epiphytic chironomid
Authors: KORNIJÓW RYSZARD
Published: May 2006

1. A clear seasonal alternation of Endochiranomus albipennis larvae between submerged plants and the bottom sediment was observed in the littoral of a deep mesotrophic and a shallow eutrophic lake. The analysis of change in larval density and of occurrence of pupae suggests that larvae migrated from plants to the bottom sediment in early autumn and back to the plants, where they pupate, in spring.

2. Up to 95% of the third and fourth instar larvae overwintered in the bottom sediment in special cocoons. Larvae staying in the sediment without cocoons were also dormant. The timing of cocoon formation was different in the two lakes.

3. Migration may have a significant influence on the seasonal changes in dominance structure and density of epiphytic and benthic faunas.
The ecology of two intermittent streams in Victoria, Australia
Authors: BOULTON A.J. , LAKE P.S.
Published: May 2006

1. We compared aquatic macroinvertebrate assemblage composition within and between habitats (pools and riffles) at four sites on two intermittent streams in Victoria, Australia during a drought year followed by a wetter year to see how different spatial and temporal scales influenced patterns of community structure detected by multivariate techniques of ordination and classification. We also examined the fit between faunal groups and ‘flow phases’ characterized by multivariate analyses of physicochemical variables in an earlier paper.

2. Pools contained more taxa and individuals than riffles. At the more temporary site, there was considerable overlap between the faunal composition of pools and riffles, whereas habitat‐specific assemblages consistently occurred at the more permanent sites. Most taxa were either tolerant, permanent stream forms able to persist in streams that dry briefly, or facultative species that occur in lotic or lentic habitats. Few species appeared specifically adapted to temporary waters.

3. Within habitats, there were some matches between faunal groups and flow phases, especially with the onset of the ‘diminishing flow’ phase, characterized by rising water temperature and conductivity, and declining pH and dissolved oxygen. However, disjunctions among faunal groups were less marked than those between flow phases, and were absent at an intermediate scale when habitats were pooled within sites. At the broadest scale of analysis (within habitats between sites and years), historical events (e.g. whether pools upstream dried completely during the previous summer) apparently influenced community composition as much as site‐specific abiotic differences.
The ecology of two intermittent streams in Victoria, Australia
Authors: BOULTON A.J. , LAKE P.S.
Published: May 2006

1. Temporal changes in species richness, total abundance, and numbers of individuals in seven functional feeding groups were compared between pools and riffles at four sites on two intermittent streams in Victoria sampled during a drought year followed by a wetter year.

2. Species richness increased steadily over time, peaking in the riffles just before flow ceased. Maximum species richness occurred in the pools shortly after flow stopped, implying emigration from the drying riffles. There were two peaks in total numbers, first in autumn when flow commenced and again in late summer as flow diminished. Generalist feeders (collector‐gatherers and collector‐scrapers) were usually abundant throughout the year. Scraper densities rose in late spring‐early summer in conjunction with enhanced periphyton growth, whereas predator numbers steadily increased during the year, peaking in all habitats just before they dried.

3. Several floods in spring significantly reduced species richness and total numbers of individuals but recovery to pre‐flood levels was generally complete within 2 weeks. Although floods had little effect upon succession, as indicated by trajectories in ordination space, the dry period interrupted otherwise cyclical sequences, consistently resulting in arch‐shaped trajectories. Faunal change appeared to be allogenic, driven by the seasonal cycle of environmental phases.

4. A group of early colonists or ‘pioneer’ species was replaced after several weeks by heterogeneous groups of ‘mid‐successional’ taxa responsible for differences in faunal composition between riffles and pools. When flow diminished, these groups were replaced by ‘summer’ species, apparently capable of tolerating deteriorating environmental conditions, and potentially intensifying biotic interactions.

5. We suggest that the cyclical temporal changes in assemblage composition observed in this study represent ‘seasonal periodicity’, whereas recovery after unpredictable disturbances such as floods that temporarily disrupt the cycle fits the definition of ‘succession’. Succession rate is a measure of resilience, recovering to the cyclical trajectory that would exist in the absence of disturbance. ‘Lag effects’ brought about by reduced recruitment during the drought were not evident until the following year, emphasizing the significance of historical events and the need for long‐term studies to describe the ecology of intermittent streams adequately.
Community structure of larval Chironomidae (Diptera) in a backwater area of the River Danube
Authors: SCHMID P.E.
Published: May 2006

1. The larval chironomid community was studied quantitatively in three cross‐sections of an impounded area of the River Danube between July 1985 and July 1986.

2. Sixty‐six species were identified, most of which belonged to the subfamily Orthocladiinae, but species of the tribe Chironomini were numerically dominant.

3. The sections differed distinctly in terms of species number and diversity; a tendency towards increasing species richness and diversity was observed in the upstream sections of the impoundment. Marked fluctuations in these two parameters characterized the area close to the dam; the temporal oscillations in diversity values differed significantly between the sections (ANOVA: P<0.05).

4. Clear differences were found between sampling sites in terms of community resilience, the minimum eigenvalue of the community matrix defined as the rate of return of a disturbed system. Longer return times after ‘disturbances’ could be expected at sites further upstream from the dam.

5. Temporal persistence of species composition was estimated for each section with Kendal's correlation coefficient from 1985 to 1986. Sites further upstream of the dam illustrated a significantly greater temporal species persistence over time and a smaller degree of fluctuation, compared to the dam area (ANOVA: P<0.05). A significant negative relationship was found between overall persistence and cumulative monthly water discharge, at the dam site (P<0.01).

6. Classification of the larval chironomid community gave evidence of generally low spatio‐temporal overlap between species in the impoundment area.
Food, microhabitat, or both? Macroinvertebrate use of leaf accumulations in a montane stream
Authors: RICHARDSON J.S.
Published: May 2006

1. Leaf packs in streams may serve as food and substrate to many macroinvertebrates, but the relative importance of these two functions has not been disentangled. To test the hypothesis that leaf packs are colonized primarily for their food value rather than as microhabitat, the colonization of leaf packs of red alder and of polyester cloth in a natural stream was compared.

2. Species of shredders showed large differences in the colonization of the two types of leaf pack with almost no use of artificial leaf packs. Non‐shredders were also more abundant on natural leaf packs, however, they colonized artificial leaf packs six to eighty times proportionally more than shredders.

3. The effect of different leaf types was virtually eliminated for non‐shredders when the amount of fine parriculate detritus (food for many non‐shredders) trapped in the leaf pack was added to the analysis as a covariate. Therefore, to non‐shredders, leaf types differed only in the retention of fine particulate organic matter.

4. Comparisons of the use of both kinds of leaf packs in riffles versus pools revealed that significantly fewer animals colonized pool leaf packs.

5. These results suggest that food value, and not microhabitat, is the primary determinant of leaf pack use for most shredders and non‐shredders.