bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacterivory by deposit‐feeding mayfly larvae (Stenonema spp.)
Authors: EDWARDS RICK T. , MEYER JUDY L.
Published: May 2006

SUMMARY.

 The importance of bacteria in the diet of deposit‐feeding mayflies (Stenonema spp.) from the Ogeecnee River, a sixth order low‐gradient blackwater river in Georgia, U.S.A., was determined. Stenonema are abundant and productive on snags in biackwater rivers in the southeastern Coastal Plain of the U.S.A. Bacteria are abundant in the seston in this river, and are a potentially important food source.

 Naturally occurring seston was fed to Stenonema larvae after bacterial DNA in the seston was labelled with methyl‐[3H]thymidine. Larval respiration measurements and growth rate estimations were used to compare the amount of bacterial carbon assimilated and retained in larval tissue to the carbon requirements of the larvae.

 Stenonema larvae incorporated 8.7×107±1.3×107 bacteria larva−1 h−1 This was equivalent to 93±6% of their daily growth, and 47±3% of their total daily carbon needs. Larger larvae incorporated more bacterial biomass, but mass specific incorporation was not related to size. Ingestion of bacteria while eating seston accumulated on snags appears to be an important component of the diet of Stenonema larvae in these rivers.
Growth and development of larval northern cricket frogs (Acris crepitans) in relation to phytoplankton abundance
Authors: JOHNSON LAURA M.
Published: May 2006

SUMMARY.
1. Tadpoles of Acris crepitans were collected from two ponds in central Illinois, Depth, water temperature, distance from shore and water samples were taken at each sample site. The potential for food limitation and non‐random habitat selection were examined.

2. Algal densities from water samples averaged over 1.0× 106 cells ml−1 in Scott's pond hut only 4.6×103 cells ml−1 in Vic's pond.

3. Guts of tadpoles from Scott's pond contained more algal cells than did guts of tadpoles from Vic's pond. Tadpoles from Scott's pond were consistently larger and more advanced in development than tadpoles collected from Vic's pond at the same lime. Therefore, tadpoles of Scott's pond were able to utilize the higher algal densities whereas tadpoles of Vic's pond may be food‐limited, causing reduced growth and development.

4. Canonical discriminant analysis was used to test whether sites with different numbers of tadpoles could be distinguished based on environmental variables. Canonical function I was primarily a measure of water depth at a sample site. This function was significant in Scott's pond only. Sites containing one or more tadpoles were not easily distinguished from each other, but were found in consistently shallower water than sites where no tadpoles were found.
Phenology and the influence of meteorological parameters on the catching success of light‐trapping for Trichoptera
Authors: WARINGER J. A.
Published: May 2006

SUMMARY.
1. Adult Trichoptera were caught for 1 year (February 1989‐March 1990) on the banks of the Danube at Bad Deutsch Altenburg, Lower Austria, using a Jermy‐type light trap. The blacklight tube of the trap was in operation all night, and the samples were taken at daily intervals. From a total of 33,465 specimens caught, the most abundant species were Psychomyia pusilla Fabr. (Psychomyidae), the three hydropsychids Hydropsyche pellucidula Curtis. Hydropsyche bulgaromanorum Mal. and Hydropsyche contubernalis McL., and the leptocerid Ceraclea dissimilis Steph.

2. The total catch included fifty‐three of the 284 Austrian species from thirteen families. One female of the parthenogenetic Apatania muliebris McL. was the second specimen ever collected in Austria.

3. The phenology of seventeen species was studied in detail, all of them summer species. Two types of flying seasons were observed: short flight periods of 3 months or less (seven species) and prolonged periods lasting 4–7 months (ten species).

4. In nine species the sex ratio was significantly different from 1:1.

5. The influence of precipitation, wind speed and night air temperature (maximum, mean and minimum) on catching success was tested. Only the effect of air temperature was significant with maximum night air temperature having a highly significant (P<0,001) correlation with flight activity. No specimens were caught at maximum temperatures below 6.8°C, and catching success was highest on warmest nights.
Suspended clay reduces Daphnia feeding rate
Authors: KIRK KEVIN L.
Published: May 2006

SUMMARY.
1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1‐−1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×103 cells ml−1), but by only 27% at high algal concentrations (20×103 cells ml−1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate.

2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles.

3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.
Effect of food concentration on the carbon balance of Bosmina longirostris (Crustacea: Cladocera)
Authors: URABE JOTARO
Published: May 2006

SUMMARY.
1. The carbon balance of the small cladoceran, Bosmina longirostris, was examined at four food concentrations (0,05, 0.10, 0.25, 2.50mg C 1‐−1) based on long‐term growth experiments.

2. At birth, B. longirostris allocated about 60% of assimilation to body growth at all food concentrations. However, allocation to body growth decreased with age and was less than 5% after the fourth instar at the lowest food concentration. The proportion allocated to reproduction increased with increasing food concentration, but was relatively constant among different adult instars.

3. Assimilation rate increased with increasing food concentration and increasing body size: the mean rate from birth to 15 days was 6.6 times higher at the highest food concentration than at the lowest food concentration. However, with decreasing food concentration and increasing body size, a higher proportion of the assimilated carbon was lost as respiration. As a result, the net production rate reached a plateau at intermediate body size and was 9.1 times higher at the highest food concentration than at the lowest food concentration.

4. Comparison with previous studies revealed that B. longirostris is more efficient than Daphnia with regard to carbon production, especially at low food conditions, if the death rate is negligible.
Biogeochemistry of billabong sediments. I. The effect of macrophytes
Authors: BOON PAUL I. , SORRELL BRIAN K.
Published: May 2006

SUMMARY.

We examined the effects of an emergent macrophyte (Eleocharis sphacelataR. Br., Cyperaceae) and a submerged macrophyte (Vallisneria giganteaGraeb., Hydrocharitaceae) on the biogeochemistry of the sediments of a billabong in south‐eastern Australia.

Sediments from anE. sphacelatabed had significantly lower concentrations of exchangeable phosphorus than did sediments from a nearby bare area or aV. giganteabed, but neither macrophyte had a measureable effect on their sediment's exchangeable ammonium content.

The redox potential in the upper 10cm ofE. sphacelatasediments was about 100 mV higher than that of bare sediments, or of sediments colonized byV. gigantea.

There were few consistent differences between vegetated and bare sediments in terms of the activity of extracellular enzymes, such as α‐amylase, protease, β‐dglucosidase, lipase or alkaline phosphatase. Rates of alkaline phosphatase activity (235–306μmol (g dry wt)−1day−1) were markedly higher than those commonly reported for sediments or soils.

Rates of gas release were higher from bare sediments (21–93 ml m−2h−1) than fromE. sphacelataorV. giganteasediments (17–23 and 21‐24ml m−2h−1, respectively). Gas bubbles consisted mainly of methane (26–66%) and nitrogen (15–68%). Rates of methane ebullition varied from 5 to 60ml m−2h−1.

In‐vitromethanogenesis was most rapid in samples of the upper flocculent sediment. Methanogenesis was slower inV. giganteasediments than in bare area orE. sphacelatasediments, but was markedly accelerated by additions of acetate and/or H2/CO2in all sites.

Profiles of total extractable fatty acids and phospholipid fatty acids demonstrated that material derived from higher plants dominated the sediment organic matter in all sites. Bacteria were also a significant component of sediment organic matter, as fatty acids for which bacteria can be assumed the sole source accounted for 18–30% of total fatty acid content. Biomarkers for sulphate‐reducing bacteria (Desulfobacterspp.) were detected, and for type II methanotrophic bacteria.
Photosynthetic characteristics of Myriophyllum spicatum and six submersed aquatic macrophyte species native to Lake George, New York
Authors: MADSEN J.D. , HARTLEB C.F. , BOYLEN C.W.
Published: May 2006

SUMMARY.

The macrophyte community of Lake George, New York is diverse, composing of forty‐eight submersed species representing a wide range of habitats, depth ranges and life‐history strategies. The photosynthetic rates of seven representative submersed aquatic macrophytes were determined in laboratory studies using measurements of short‐term changes in oxygen concentration at eight light intensities from 0 to 1000 μmol m−2 s−1 at 20°C. The species examined were: Elodea canadensis, Myriophyllum spicatum, Potamogeton amplifolius, P. gramineus, P. praelongus, P. robbinsii, and Vallisneria americana.

Comparisons of maximum net photosynthesis, Michaelis–Menten Vmax and Km for photosynthesis versus irradiance, and dark respiration rates correlated with changes in community composition and species distribution with depth.

In particular, Myriophyllum spicatum exhibited a high photosynthetic rate (Vmax) and high light requirement (both in compensation point and higher half‐saturation constant (Km) indicative of a high light‐adapted species. In contrast, the native species exhibited shade‐tolerant characteristics.

Simple daily carbon balance models indicate that M. spicatum has a higher positive carbon balance near the surface than the native species, but carbon balance decreased more rapidly with decreased light. All species showed greatly reduced carbon balances under a simulated M. spicatum canopy, indicating that native species might not survive. Myriopyllum spicatum leaves would experience self‐shading and eventual sloughing.
Effects of subacute doses of iron (Fe) on Leptophlebia marginata (Insecta: Ephemeroptera)
Authors: GERHARDT A.
Published: May 2006

1. The objective of this paper was to reveal the toxicity of Fe3+ and Fe24 at pH 4.5 and 7 on larvae of the mayfly Leptophlebia marginata, by examining survival, motility, gill ventilation, moulting and feeding in experiments.

2. Fe2+ was the dominant metal species at pH 4.5, and Fe3+ at pH 7. Precipitation of Fe occurred only at pH 4.5, where Fe‐precipitarions were observed on the thorax and the gills of the larvae.

3. Both feeding activity and motility of the animals decreased at pH 4.5 and 10, 20 or 50mg1‐−1 Fetot. After a short period of normal feeding, the animals stopped feeding for approximately 2 weeks and did not start to feed again until the end of the experiment. They were constipated. Survival was >95% in all treatments, except at pH 4.5 and 50 mg Fetot. In this group, about 20% of the animals died after having been constipated for 2 weeks.
Allochthonous coarse particulate organic material in forest and pasture reaches of two south‐eastern Australian streams
Authors: CAMPBELL IAN C. , JAMES KIM R. , HART BARRY T. , DEVEREAUX ANNE
Published: May 2006

1. Terrestrial plant litter entering two forest and two pasture sites on upland streams in south‐eastern Australia was measured over a 2‐year period using traps suspended above the streams. Laterally transported terrestrial plant litter was also determined in one stream, but found to be only 10% of the total.

2. Litter accession to traps suspended above the stream was significantly lower at both forested sites than was litter fall in the adjacent riparian vegetation.

3. Litter input was high (600–700g DW m−2yr−1) and seasonal, with 30–50% of the annual total entering the stream during December—February (summer). However, seasonality was not as great as that recorded in Northern Hemisphere deciduous forest streams.

4. Leaves comprised the largest litter component, but represented a relatively smaller proportion of the litter than is usually the case in Northern Hemisphere deciduous forest streams; in contrast bark was a relatively large proportion of the litter.

5. At the sites flowing through pasture, litter accession was about two orders of magnitude lower than at the forested sites.
Impact of storm‐flow on electron transport system activity in river biofilms
Authors: BLENKINSOPP S.A. , LOCK M.A.
Published: May 2006

1. The effect of storm‐flow on light‐ and dark‐grown biofilms from a North Wales river was monitored using electron transport system (ETS) activity and epifluorescence cell counts.

2. Artificial substrata were colonized in the river, exposed to ambient‐flow (60 cms−1) or storm‐flow (235 cms−1 with suspended sediment addition) for 12h in a laboratory flow tank, and returned to the river to monitor the recovery period.

3. Total cell densities decreased in both the light‐ and dark‐grown biofilms as a result of storm‐flow. In addition, storm‐flow ETS activity per cell increased significantly in the light‐grown samples (2.7 times) but did not increase significantly in the dark‐grown samples (1.6 times).

5. Within 48 h, storm‐flow total cell densities and ETS activity levels had returned to ambient‐flow levels in both light‐ and dark‐grown biofilms.

6. Within each light regime, despite their different histories, both ambient and storm‐flow samples responded the same to daily changes in the river environment, including a second disruption by natural causes, for the remainder of the 24‐day experiment.
A weighted—averaging regression and calibration model for inferring total phosphorus concentration from diatoms in British Columbia (Canada) lakes
Authors: HALL ROLAND I. , SMOL JOHN P.
Published: May 2006

1. The relationship between surficial sediment diatom taxa (Bacillariophyceae) and measured limnological variables in forty‐six British Columbia lakes was explored using canonical correspondence analysis (CCA). Lake‐water total phosphorus concentration (TP), maximum lake depth, conductivity, and calcium concentration each accounted for independent and statistically significant directions of variation in the distribution of diatom taxa.

2. Weighted‐averaging (WA) models were developed to infer lake‐water TP from the relative abundances of 131 diatom taxa in the surficial sediments of thirty‐seven lakes. WA regression and calibration with classical deshrinking provided the best model for TP reconstructions.

3. Our quantitative inference model has two major advantages over existing multiple linear‐regression models: (i) inferences are based on the responses of individual taxa to TP, and do not involve grouping the taxa into a small number of ecological categories; and (ii) the model assumes that diatoms respond to TP in a unimodal, rather than a linear, fashion.

4. The WA model can now be used to infer past lake‐water TP, within the range 5–28νgr1−1, from diatoms preserved in the sediments of British Columbia lakes. The model can provide quantitative estimates of the onset, rate, and magnitude of lake eutrophication in response to natural processes and human disturbances.
Decline of charophytes during eutrophication: comparison with angiosperms
Authors: BLINDOW IRMGARD
Published: May 2006

1. Charophytes have disappeared from several enriched lakes in Scania (southern Sweden) since the 1940s. Poor light conditions, rather than a toxic effect of phosphorus or negative impact of fish, are the most probable reason for this decline.

2. Small species of charophytes (shoot diameter 0.5–1.0 mm), which are able to form dense, low mats, still occur in eutrophic lakes with high phosphorus concentrations, but are restricted to areas of shallow water. In contrast, large species (shoot diameter

1–4 mm) have totally disappeared from the most turbid lakes. I suggest that these species are unable to grow in very shallow water because of damage by ice and wave action.

3. Maximum depth distribution (ze) and Secchi depth (D) were measured in Scanian lakes for both charophytes and angiosperms and combined with data obtained from Chambers & Kalff (1985). According to the combined data, zc and D are closely correlated with each other for both angiosperms and charophytes.

4. The zc of charophytes is higher than zc of angiosperms in clear lakes but lower in turbid lakes. Higher zc of angiosperms in the most turbid lakes is explained by special adaptations of these species to poor light availability (shoot elongation, canopy formation, rapid growth during spring).
The reproductive success of the dipper Cinclus cinclus in relation to the acidity of streams in south‐west Scotland
Authors: VICKERY JULIET
Published: May 2006

1. The breeding success of dippers Cinclus cinclus was assessed in south‐west Scotland over 3 years and related to the acidity of the streams along which they bred.

2. At sites of high acidity, clutch and brood sizes were significantly smaller than those at sites of lower acidity.

3. Egg weight and the incidence of second clutches increased significantly with pH, but there was no evidence to suggest an effect of acidity on hatching success.

4. The rate at which food was delivered to individual nestlings was significantly lower at acidic than non‐acidic sites. Nestling weights and survival were lower at more acidic sites.

5. Reduced brood sizes, low nestling survival and the low incidence of second brooding attempts resulted in a significant reduction in total productivity (number of fledglings produced, per pair, per year) at acidic compared with non‐acidic streams.

6. It is suggested that pH‐related differences in the invertebrate fauna of streams result in low prey availability for dippers on acidic streams, leading to reduced productivity.
Clarification of the criteria used to identify near‐bed flow regimes
Authors: YOUNG W.J.
Published: May 2006

1. Extensive measurements of near‐bed flow velocity were made over a reconstructed section of a cobble‐bed stream using a laser‐Doppler velocimeter. Based on these measurements descriptions of the near‐bed flow structure and flow conditions within benthic habitats are made.

2. The near‐bed flow classification system of Davis & Barmuta (1989) is discussed, and the threshold criteria of the system are shown to be incorrect. The correct criteria are stated and discussed in the context of two‐dimensional uniform bed roughness.

3. The improved classification system is used to classify the laboratory near‐bed flow regime, and this classification is compared to the flow types depicted in near‐bed flow structure diagrams. This comparison highlights the importance of accurately assessing stream‐bed roughness parameters to obtain accurate and useful near‐bed flow classifications.

4. The potential limnological applications of near‐bed flow regime classifications are discussed, with improved benthic invertebrate sampling procedures being given as the likely major benefit.
The behavioural responses of juvenile signal crayfish Pacifastacus leniusculus to stimuli from perch and eels
Authors: BLAKE M.A. , HART P.J.B.
Published: May 2006

Experiments were designed to determine the relative importance of chemical and visual stimuli in eliciting predator avoidance behaviour in juvenile freshwater crayfish Pacifastacus leniusculus (Dana).

 Crayfish placed in visual and/or chemical contact with one of two predators exhibited marked avoidance behaviour, spending less time walking and climbing and more time within shelters.

 The combined effects of both visual and chemical stimuli increased crayfish shelter use and reduced walking and climbing activity to a greater degree than either stimulus when presented alone.

 Crayfish exhibited avoidance behaviour in response to chemical stimuli during periods of light and darkness. Visual detection of predators elicited avoidance behaviour during the day.

 It is suggested that the behavioural response of P. leniusculus to chemical stimuli reduces the likelihood of being detected by visual predators, and that chemical stimuli lower the response threshold for avoidance behaviour in crayfish reacting to visual stimuli. The adaptiviry of using chemical cues to detect predators is emphasized.
The changing ecosystem of a shallow, brackish lake, Hickling Broad, Norfolk, U.K. II. Long‐term trends in water chemistry and ecology and their implications for restoration of the lake
Authors: BALES MICHAEL , MOSS BRIAN , PHILLIPS GEOFFREY , IRVINE KENNETH , STANSFIELD JULIA
Published: May 2006

Hickling Broad underwent major changes from a clear water, charophyte‐dominated state in the decades previous to 1970 to a turbid, phytoplankton‐dominated state by the mid 1970s. These changes were complexly linked with increasing eutrophication by black‐headed gulls and increased salinity due to agricultural changes in the catchment.

 At the turn of the 1970s, the lake began to change again and during the 1980s a submerged plant community, of tall, vigorously growing species (e.g. Myriophyllum spicatum, Patamogeton pectinatus) had recovered, despite a major reduction in the roosting gull population, no change in salinity, and only small reductions in phytoplankton biomass and total phosphorus concentration.

 Recovery of the plants may be linked to grazing of periphyton on them by an increased population of a mysid Neomysis integer which had been suppressed by toxicity from an alga, Prymnesium parvum formerly stimulated by the ingress of gull guano.

 A cladoceran community present in the clear‐water phase has not recovered and may be suppressed by continued high salinities. Further restoration of the lake requires displacement of the large phytoplankton biomass and this might best be contemplated by land use changes leading to lowered salinity and predicted recovery of grazing Cladocera.

 Models are given which summarize the likely workings of the system in the early twentieth century, the mid‐twentieth century, the 1970s and the late 1980s.
Biofilm development and extracellular enzyme activities on wood in billabongs of south‐eastern Australia
Authors: SCHOLZ OLIVER , BOON PAUL I.
Published: May 2006

The accrual of organic matter, chlorophyll a and bacteria, and the activities of various extracellular enzymes were studied during biofilm formation on River Red Gum (Eucalyptus camaldulensis) wood submerged in two temperate Australian billabongs for 24 weeks over summer and winter of 1989–90.

 Peak organic matter content of the biofilm ranged from 0.7 to 3.3mg AFDW cm−2, chlorophyll a content from 1.3 to 4. 2μg cm−2 and bacterial abundance from 18 × 106 to 94 × 106 cells cm−2. Most variation in organic matter content, chlorophyll a content and bacterial abundance in the biofilms couid be attributed to the duration of immersion (28–48% of variation) and to the interaction between site and submergence period (11–12%). Differences between sites and between seasons were less important in explaining total variation.

 Alkaline phosphatase, aminopeptidase and [3‐D‐glucosidase activities, determined per unit substratum surface area, were up to 138 ± 26 nmol cm−2h−1, 113 ± 1 nmol cm−2h−1 and 9.3 ± 2.2 nmol cm−2h−1, respectively. Activities of these three enzymes determined per unit organic biomass were up to 203 ± 25, 157 ± 13, and 16 ± 2.1 nmol mg1 AFDW h−1 respectively. Enzyme activities expressed on an area‐ or biomass‐specific basis responded differently to the effects of season, site and duration of substratum exposure.

 Few consistent relationships could be established between the activity of a given enzyme system and the activity of other enzymes, nor with the various biomass parameters, such as total organic matter content, chlorophyll a content or bacterial abundance.

 We suggest that submerged wood of the River Red Gum is an important site for biofilm development in lentic systems in south‐eastern Australia, and thus as a food resource for grazing invertebrates and for transformations of various nutrients and organic matter.
Decomposition and macroinvertebrate colonization of aquatic and terrestrial leaf material in alkaline and acid still water
Authors: KOK C.J. , VAN DER VELDE G.
Published: May 2006

Decomposition of the leaves of Nymphaea alba L. and Betula pubescens Ehrh. was studied in two ponds of contrasting pH, buffering capacity and trophic level. Rates of carbon loss, concentrations of nitrogen, protein and phenolics and colonization of the leaf material by macroinvertebrates were studied.

 Decomposition of B. pubescens leaves was slower than that of N. alba in both ponds. Protein and phenolic concentrations were higher in the decomposing N. alba material, whereas no significant difference was found for nitrogen concentrations.

 Decomposition of both species was slower in the acid water. The effect of acid water on decomposition rate was similar for both species. Both nitrogen and protein concentrations of N. alba remained higher under acid conditions, whereas no effect of study site was observed on the protein and nitrogen concentrations in B. pubescens litter. The concentration of phenolic compounds was higher in N. alba litter from the acid pond; no such difference was observed for B. pubescens litter. The high concentrations of phenolic compounds in N. alba litter from the acid pond probably induced chemical immobilization (tanning reaction), yielding high concentrations of nitrogen and protein in the litter.

 Diversity of the detritivorous macroinvertebrate fauna on the litter of both species was extremely low in the acid pond, while a relatively high diversity occurred in the alkaline water. Exclusion of large macrofauna inhibited decomposition in the alkaline water, while there was no comparable influence in the acid water.

 The effects of low pH on the decomposition of both terrestrial and aquatic macrophyte litter appeared to be caused by interactive effects of low pH on the microbial decomposition, on the detritivorous macroinvertebrates and, in the case of N. alba, on the resource quality of the detritus.
Gastric evacuation rates of adult and larval alpine newts (Triturus alpestris) under laboratory and field conditions
Authors: SCHABETSBERGER R.
Published: May 2006

1. The fits of exponential, square root, surface‐dependent and power exponential polynomials to gastric evacuation curves in alpine newts were compared. Both the more complex power exponential function and the exponential model provided good descriptions of gastric evacuation in adult and larval alpine newts.

2. Gastric evacuation rates of adult female and male alpine newts did not differ significantly. Temperature‐dependent gastric evacuation rates were strongly affected by the composition of the meals eaten in the natural habitat. The time for total gastric evacuation in adults was generally longer than reported for teleost fishes and was within the range reported for some elasmobranchs.

3. Gastric evacuation rates of newt larvae were low compared to fish larvae. Time for total emptying of the stomach increased exponentially with increasing body dry weight of larvae.
Light‐limited growth and photosynthetic characteristics of two planktonic desmid species
Authors: COESEL PETER F.M. , WARDENAAR KLAASJAN
Published: May 2006

1.Staurastrum chaetoceras, originating from a eutrophic environment, andCosmarium abbreviatumvar.planctonicum, from an oligo‐mesotrophic one, were grown at 20°C in continuous‐flow culture under varied light conditions.

2. Maximum growth rate inS. chaetoceraswas approximately 50% higher than inC. abbreviatum, corresponding to a higher photosynthetic capacity.

3. Higher dry weight values and dark respiration rates inC. abbreviatum(compared withS. chaetoceras) support the suggestion from growth‐irradiance curves thatC. abbreviatumhas to invest a greater part of its photosynthetic energy in the construction and maintenance of specific cell components.

4. The differences in growth and photosynthetic parameters might be related to the presence of a copious mucilaginous cell envelope inC. abbreviatum; such an envelope is lacking inS. chaetoceras.

5. The possible ecological significance of these species‐specific differences is discussed.
A comparison of Acroneuria lycorias (Plecoptera) production and growth in northern Michigan hard‐ and soft‐water streams
Authors: EGGERT SUSAN L. , BURTON THOMAS M.
Published: May 2006

1. Density, biomass, production and growth of a predaceous stonefly, Acroneuria lycorias, were compared between fourth‐order hard‐ and soft‐water streams in Michigan's upper peninsula, U.S.A.

2. Mean densities, estimated from Hess samples, were higher (100 ± 17 individuals m−2) at the hard‐water site than at the soft‐water site (40 ± 9 ind. m−2). Mean dry weight biomass was 4.9 times greater at the hard‐water site.

3. Mean annual production, calculated using the size frequency method, was 5.0 times greater at the hard‐water site (2.18 ± 0.44 g dry weight m−2yr−1) than at the soft‐water site (0.43 ± 0.02g dry weight m−2yr−1). Annual production/mean biomass ratios were similar between sites.

4. Monthly growth rates of naturally occurring nymphs of paired cohorts were similar in both streams. Individual growth rates were similar for nymphs reared in artificial streams at high and low water hardnesses with unlimited food and space.

5. Stonefly production and growth rates were influenced more by indirect physical, biological, or habitat factors than by streamwater cation concentrations.
Periphyton responses to a hydraulic gradient in a regulated river in New Zealand
Authors: BIGGS BARRY J.F. , HICKEY CHRISTOPHER W.
Published: May 2006

1. Periphyton species composition, chlorophyll a concentration, organic matter biomass, and metabolic activity were analysed at a site in a regulated river with low nutrient concentrations to investigate population and community level responses to a spatial gradient in hydraulic conditions. The communities were dominated by diatoms over the full hydraulic range [0.1–0.5m depth, 0.1–1.5ms−1 velocity, and 0.01–1.5 Froude number (Fr)] with Cymbella kappii, Synedra ulna, and Gomphoneis herculeana having the highest relative biovolumes.

2. Unexpectedly, Cymbella kappii and Synedra ulna were abundant or co‐dominant at all levels of velocity and Fr. Gomphoneis herculeana was most abundant within the mid‐velocity range (velocity = 0.8–1.2ms−1).

3. The physiognomy of the communities changed with a change in hydraulic conditions. There was progressively more diatom mucilage as velocity and Fr increased which resulted in a macroscopic change from relatively thin films (1–2mm) at low velocities and Fr (in pool habitats), to thick (approximately 10mm) mats at higher velocities and Fr (in riffle habitats). Associated with this, ash‐free dry mass (APDM) increased strongly, but chlorophyll a concentration did not, resulting in a decrease in % chlorophyll a over the gradient.

4. The results of experiments conducted in an in situ benthic chamber showed no significant differences in gross primary production between two communities of different biomass, but indicated a slightly decreasing trend with increasing velocity (0.14 to 0.38 ms−1). In contrast, community respiration increased greatly with mat biomass and also as a function of increased water velocity. The combined AFDM, chlorophyll a and metabolic results indicated that the zone of photosynthesis was maintained at the surface of the mats, with variable amounts of mucilage being secreted below, depending on hydraulic conditions.

5. The diatom community had considerable physiognomic plasticity through the accumulation of mucilage. It is suggested that this high mucilage secretion may be an active feedback mechanism to help ameliorate environmental stress. If so, present theory on velocity control of periphytic algal development in streams, which is essentially based on passive responses, needs expanding. It is concluded that the response of periphyton to spatial differences in habitat hydraulics in streams is highly complex and it may be difficult to define clear hydraulic habitat preference curves for periphyton communities in nutrient‐poor streams.
Effects of benthivorous bream (Abramis brama) and carp (Cyprinus carpio) on sediment resuspension and concentrations of nutrients and chlorophyll a
Authors: BREUKELAAR ANDRÉ W. , LAMMENS EDDY H.R.R. , BRETELER JAN G.P. KLEIN , TÁTRAI ISTVAN
Published: May 2006

1. The effect of benthivorous bream and carp on sediment resuspension and the concentrations of nutrients and chlorophyll a were studied in sixteen experimental ponds (mean depth 1m, mean area 0.1 ha, sandy clay/clay sediment), stocked with bream or carp at densities varying from 0 to 500 kg ha−1. Planktivorous perch (Perca fluviatilis L.) were added to some ponds to suppress zooplankton.

2. Suspended sediment concentrations increased linearly with biomass of benthivorous fish. Bream caused an increase of 46 g sediment m−2 day−1 per 100kg bream ha−1 and a reduction of 0.38m−1 in reciprocal Secchi disc depth, corresponding to an increase in the extinction coefficient of 0.34m−1.

3. No relationship was found between size of fish and amount of resuspension, but the effect of bream was twice as great as that of carp. Benthivorous feeding was reduced in May because alternative food (zooplankton) was available.

4. Assuming a linear relationship, chlorophyll a level increased by 9.0 μgI−1, total P by 0.03mgl−1 and Kjeldahl‐N by 0.48mgl−1 per 100kg bream ha−1. Silicate, chlorophyll a, total P and total N were all positively correlated with fish biomass, but orthophosphate showed no correlation.
Hydraulic parameters and benthic invertebrate distributions in two gravel‐bed New Zealand rivers
Authors: QUINN JOHN M. , HICKEY CHRISTOPHER W.
Published: May 2006

1. Benthic invertebrates were sampled over a matrix of about eighty combinations of mean velocity (10–150cms−1) and depth (10–150cm) in two rivers that differed in substrate size variability. Vertical velocity profiles were measured at each sample site and substratum roughness was measured and estimated from percentage cover by stone size classes. The influence of depth on periphyton biomass was also measured.

2. The hydraulic and substrate data were used to investigate the correlations between conventional (mean velocity, depth, substrate size) and complex hydraulic variables (Froude number, shear velocity, and water column and boundary Reynolds number) that were either calculated from direct measurements or inferred from mean velocity, depth, kinematic viscosity and substrate roughness. The ecological relevance of these hydraulic variables was investigated by comparing their degree of correlation with invertebrate densities and community metrics.

3. The invertebrate variables had similar correlations with mean velocity and the complex near‐bed hydraulic variables in the river with uniform cobble substrates. In the river with diverse substrates, however, average correlations with Froude number, and inferred shear velocity and boundary Reynolds number were 25–45% higher than with velocity. Of all the individual hydraulic parameters, the boundary Reynolds number, calculated from simple measures, was most strongly correlated with benthic invertebrate distributions and taxa richness. However, invertebrate distributions were more strongly correlated with predictions of multiple regression models, incorporating substrate size, depth and mean velocity, than with any single hydraulic variable.

4. Hydraulic influences on food availability and oxygen concentration in the benthos are likely mechanisms affecting the hydraulic preferences of several taxa. Lower periphyton biomass with depth, partly attributable to light attenuation, appeared to have a non‐hydraulic influence on a collector‐browser species.
Microhabitat as a determinant of diversity: stream invertebrates colonizing leaf packs
Authors: DOBSON MIKE
Published: May 2006

1. Macroinvertebrate colonization of artificial leaf packs of differing palatability to detritivores was measured in a low‐order stream.

2. The most palatable leaf types—alder and young beech—were colonized mainly by detritivores and consumed rapidly, so that species diversity on the substrate remained low. In the case of the less palatable old beech and paper ‘leaves’, however, colonization was slower but species diversity approached that of the surrounding benthos.

3. After 1 week, species diversity in paper ‘leaf packs was equivalent to that of the benthos, but species composition was dissimilar.

4. I argue that species diversity of a patch of stream bed may be inversely related to the abundance or palatability of a given food resource, and that this relationship is maintained by the instability of the stream bed habitat, precluding a long‐term community response to increased food availability. It may be, however, that the dispersal abilities of many aquatic insects allow a rapid response to the creation of novel habitats.
Laboratory studies on the population dynamics of Anuraeopsis fissa (Rotifera) in relation to food density
Authors: DUMONT HENRI J. , SARMA S.S.S. , ALI A. JAWAHAR
Published: May 2006

1. We offered Scenedesmus obliquus in five densities, from 0.5 to 8 ± 106 cells ml−1, to the rotifer Anuraeopsis fissa. Growth rates (r) during the exponential phase (first 7 days) were significantly and positively related to food density. The r values (mean ± SD) varied between 0.454 ± 0.067 and 0,856 ± 0.090, from the lowest to the highest food concentration, respectively. Population growth went through a phase of exponential increase which lasted from 7 to 10 days before a plateau and, in some cases, a decrease occurred.

2. There was a linear relation between food density and rotifer plateau density. At the highest food density, a peak abundance (mean ± SD) of 2312 ± 226 individuals ml−1 was reached, while at the lowest food density there was no identifiable single peak but a plateau, at a density of 361 ± 62 ind. ml−1.

3. The egg ratio decreased with increasing population density. The ratio of loose eggs to eggs attached to females indicated that more eggs became detached at higher food densities.

4. As in many other rotifer species studied so far, population density of A. fissa was less stable at higher algal food concentrations. Numerically, A. fissa could be grown at twice the density achieved in Brachionus.
Comparison of phosphorus deficiency indices during a spring phytoplankton bloom in a eutrophic reservoir
Authors: VRBA JAROSLAV , ÁLEK VOJTĚCH VYHN , HEJZLAR JOSEF , NEDOMA JIŘÍ
Published: May 2006

1. Phosphorus limitation was studied along the eutrophic, canyon‐type Římov reservoir (Czech Republic) during a spring phytoplankton bloom. Concentration of soluble reactive phosphorus (SRP), C:P molar ratio in seston, extracellular alkaline phosphatase activity (APA), and P limitation (bioassay) were used as indices for phosphorus deficiency in the phytoplankton.

2. SRP, C:P, APA, and P limitation indicated a moderate P deficiency in the downstream, but not upper, part of the reservoir.

3. Significant correlations between these parameters were found in the downstream part. Chlorophyll a concentration correlated with APA and P limitation in the upper part.

4. APA was significantly enhanced in the phosphorus‐deficient phytoplankton. However, APA was apparently not related to total biomass or species composition of the phytoplankton.

5. Generally, APA was closely correlated with pH in the reservoir. However, extracellular alkaline phosphatases, with a pH optimum above 9.0, were induced and active only during the phytoplankton bloom, whereas low background activity of extracellular phosphatases was found at low chlorophyll a concentrations (winter, clear‐water phase).
Death, detritus, and energy flow in aquatic ecosystems
Authors: WETZEL ROBERT G.
Published: May 2006

1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels.

2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non‐pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels.

3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels.

4. Non‐predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal‐orientated relationships to the integrated, process‐driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mechanisms.
Distribution and abundance of blackflies (Diptera: Simuliidae) in relation to impoundments in the Buffalo River, eastern Cape, South Africa
Authors: PALMER ROBERT , O'KEEFFE JAY
Published: May 2006

1. The abundance of blackfly species along the length (140 km) of the multiply impounded Buffalo River, eastern Cape, South Africa, was studied between 1986 and 1988.

2. Twenty‐three species of blackflies were recorded, most of which (95%) were usually found 5–10 km from the source.

3. Impoundments favoured five lower‐reach (pest) blackfly species at the expense of two upper‐reach (non‐pest) species. Impoundments have therefore shifted the distribution of blackfly species ‘upstream’, and have increased the distribution of pest blackflies.

4. The smallest impoundment, situated in the Upper Foothill Stony Run Zone, had the greatest effect on blackfly distribution.

5. There was no typical filter‐feeding guild below impoundments. Possible reasons for this included the discharge of toxic algae from impoundments, the lack of compensatory releases, the sudden drying of impoundment tailwaters and the paucity of natural lakes in southern Africa which precludes a pre‐adapted ‘outlet’ fauna.
Use of fluorescently labelled algae to measure the clearance rate of the rotifer Keratella cochlearis
Authors: TELESH IRENA V. , OOMS‐WILMS ANJA L. , GULATI RAMESH D.
Published: May 2006

1. Fluorescently labelled algae (FLA) were used to measure clearance rates of the rotifer Keratella cochlearis. The freshwater algae Chlorella vulgaris and Stichococcus bacillaris were labelled with a fluorescent dye, 5‐(4,6‐dichlorotriazin‐2‐yl) aminofluorescein (DTAF), following a modified staining procedure.

2. Keratella cochlearis ingested both algal species. Clearance rates on tracer foods varied between 2.4 and 6.9 μl ind−1 h−1, which are comparable with those determined using other techniques.

3. The main drawback of the FLA technique was that only a little more than one‐third of the total amount of algal cells of both C, vulgaris and S. bacillaris were well stained with the dye (DTAF), despite the use of a higher concentration of dye and a longer staining period than recommended in the literature.

4. The FLA method can be successfully applied in grazing studies involving size selection and competition for food among zooplankton. The method complements existing techniques for measuring the clearance and ingestion rates of filter‐feeders.
The parabolic pattern of animal growth: determination of equation parameters and their temperature dependencies
Authors: OSTROVSKY ILIA
Published: May 2006

1. Parabolic (power) growth is characteristic of many aquatic poikilothermic animals for certain stages of their development. The parabolic pattern describing growth in weight (or length) under constant ambient conditions can be expressed in the following general form:
image
where Y is growth rate (or specific growth rate), X is animal size, and Ω and τ are coefficients. The constancy of ambient conditions is of cardinal importance in determining τ. The problem of maintaining a constant level of nutrition can be reliably solved only by the presence of food in excess of demand. Data satisfying these requirements have demonstrated that τ does not depend on factors such as temperature, and can be assumed to be independent of ambient conditions. In the growth rate‐weight equation, τ ranges between 0.5 and 0.85 for animals representing a variety of taxonomic groups.

2. The coefficient Ω. is affected by ambient conditions (e. g. temperature, amount of food). Its value reflects the ‘level’ of the growth rate‐size relationship under given conditions. For a specific time period, Ω can be computed from the following formula:
image

where X1 and X2 are the animal sizes (weights, lengths) at time t1 and t2, the beginning and end of the time period. The calculated value of Ω corresponds to the average intensity of the ambient factor (F) affecting the growth during the period between the two observations. If the values of the Ω are calculated for wide range of the factor, the relationship between the Ω. and F, Ω=f(F), can be determined. The function can be then incorporated into the parabolic equation of growth, as

image

3. Dependence of the development rate (1/D, where D is time interval needed to complete a given stage) on temperature (T), and dependence of Ω on T, are both described by sigmoid‐shape curves. The broad intermediate part of these curves, a range to which animals are adapted in nature, can be approximated by straight line functions. For two groups, pan‐size sockeye salmon (Oncorhynchus nerka) and different species of chironomid larvae, it was shown that an equation combining parabolic growth and linear temperature patterns describes accurately the variability observed in growth rates under experimental and natural conditions.
Substance budgets of an upland catchment: the significance of atmospheric phosphorus inputs
Authors: GIBSON C.E. , WU Y. , PINKERTON D.
Published: May 2006

1. Precipitation inputs and outflow stream outputs are presented for 1993 in an upland lake and catchment system on the Antrim Plateau, Northern Ireland.

2. Phosphorus, potassium, chloride and possibly sulphate behaved conservatively inputs were approximately balanced by outputs. Combined nitrogen outputs were very much less than inputs, whereas there was a net export of calcium, magnesium, sodium and silica from the catchment.

3. Precipitation phosphorus inputs (22 kg P km−2yr−1) are compared with literature data and are shown to be near the median value.

4. The phosphorus budget is discussed in relation to the fact that there are few oligotrophic lakes in Northern Ireland. It is suggested this is due to the rainfall inputs, low phosphorus retention by the catchment and rapid flushing rates in the lakes.