bluuebunny/crossref_metadata_2025 huggingface dataset:
The cocoon and hatchling of Nais variabilis (Naididae: Oligochaeta)
Authors: LOCHHEAD G. , LEARNER M. A.
Published: May 2006

SUMMARY. 1. The cocoon of Nais variabilis is ovoid with an average length of 527.6±8.4 μm (95% CL) and an average breadth of 378.1±9.9 μm. The cocoon wall is about 7 μm thick and the average volume of the cocoon cavity is 0.035±0.002 mm3. Most cocoons contain one ovum; only single‐ovum cocoons developed.

2. Cocoons hatch in about 80 days at room temperature (average 20°C. range 17–23°C). Hatchlings emerged posterior end first and were, on hatching, about one‐third the adult live length of 8.5±10.3 mm.

3. It is estimated that adult Nais variabilis are unlikely to produce more than an average of ten cocoons each. Adults ceased asexual budding on becoming nature and died shortly after the completion of cocoon production. There was a brief co‐existence of generations.
A preliminary classification of running‐water sites in Great Britain based on macro‐invertebrate species and the prediction of community type using environmental data
Authors: WRIGHT J. F , MOSS D. , ARMITAGE P. D. , FURSE M. T.
Published: May 2006

SUMMARY. 1. Macro‐invertebrate species lists were obtained for 268 sites on forty‐one river systems throughout Great Britain by qualitative sampling in spring, summer and autumn. Information on twenty‐eight environmental variables was also collated for each site. The sites were ordinated on the basis of their species content using detrended correspondence analysis (DCA) and classified by two‐way indicator species analysis (TWINSPAN). Correlation coefficients between ordination scores and single environmental variables indicated that Axis 1 distinguished between types of rivers and Axis 2 reflected variation along the length of rivers. A preliminary classification of sites into sixteen groups has been proposed, together with a key which allows new sites to be classified. Information on the species and environmental features which characterize each group is also presented.

2. Multiple discriminant analysis (MDA) was employed to predict the group membership of the 268 sites using the twenty‐eight environmental variables. 76.1% of sites were classified correctly. An independent assessment of predictive ability using forty test sites yielded a 50% success rate. Predictive ability was higher for the classification presented in this paper than in fifteen additional classifications produced using data from single seasons and/or different taxonomic treatments.

3. TWINSPAN and MDA were found to be useful approaches to the classification of running‐water sites by their macro‐invertebrate fauna and the prediction of community type (as indicated by the occurrence of species in the sites comprising the group) using environmental variables. Extension of the scope of the classification, coupled with the use of additional environmental variables to increase predictive ability, is now in progress.
Effects of copper on species composition of periphyton in a Sierra Nevada, California, stream
Authors: LELAND HARRY V. , CARTER JAMES L.
Published: May 2006

SUMMARY. 1. Changes in species composition of the periphyton of an oligotrophic. Sierra Nevada stream continuously dosed for 1 year at three concentrations of copper (2.5, 5 and 10 μg 1−1 CuT; approximately 12, 25 and 50 ng 1−1 Cu2+) were determined.

2. The numerically most abundant taxa were Bacillariophyceae (Achnanthes minutissima, Cocconeis placentula, Cymbella microcephala, C. sinuata, Fragilaria conslruens, F. crotonensis. Navicula spp., Synedra acus and S. rumpens), and the Cyanophyta Lyngbya spp., a co‐dominant during spring and summer.

3. Population densities of Lyngbya spp. were markedly reduced at all test concentrations of copper. Population densities of the principal Chlorophyta (Spirogyra spp. and Cladophora spp.) and the diatom Amphipleura pellucida were reduced at 5 μg 1−1 CUT. Of the twenty‐two most abundant taxa, sixteen were reduced in abundance by continuous exposure to 10 μg 1−1 CuT.

4. There was no commensurate reduction in standing crop (total number of individuals of all taxa). Achnanthes minutissima, a co‐dominant in the control, was the primary replacement species. Other taxa that were more abundant at 5 μg1−1 CuT than in the control were Ceratoneis arcus, Cocconeis placentula, Navicula spp. and Synedra rumpens. Only A. minutissima and Calothrix spp. were more abundant at 10 μg 1−1 than in the control.

5. Three resemblance measures (Canberra metric, Bray‐Curtis and Dice) and diversity (Brillouin's) were evaluated for detecting differences in species composition among experimental stream sections. The Canberra metric, an index sensitive to proportional rather than absolute differences, was the most informative of these indices.
The macroinvertebrates and fish of a Colorado stream during a period of fluctuating discharge
Authors: CANTON STEVEN P. , CLINE LEO D. , SHORT ROBERTA. , WARD JAMES V.
Published: May 2006

SUMMARY. 1. During a 2‐year study of the fish and macroinvertebrates of a third‐order montane stream, a severe drought in the first year resulted in a temporary cessation of surface flow. Flow was continuous during the second year.

2. Some taxa (e.g. Ophiogomphus severus) exhibited higher density during the drought year, others declined in abundance during low flow (e.g. Baetis spp.), whereas a few (e.g. Tricorythodes minutus) appeared unaffected. Total macroinvertebrate density decreased by 50% during the low flow year compared to the normal flow year. Mayflies were most severely affected, but also exhibited the most dramatic recovery.

3. The collector‐gatherer functional feeding group was abundant only during the normal flow year, whereas shredders and predators exhibited increased relative abundance during low flow.

4. Fish populations were severely reduced in the low flow year. However, fishes rapidly invaded the area following resumption of normal flow.
Adaptive head coloration in case‐making caddis larvae
Authors: OTTO C.
Published: May 2006

SUMMARY. 1. In daylight conditions brown trout preferably attacked head capsules with a contrasting colour pattern compared to those which were more uniformly coloured. This preference was reversed under reduced illumination. It is argued that striped head capsules are cryptic to predators at low light intensities.

2. In caddis larvae contrasting head patterns are found mainly in lentic species, whilst the heads of lotic larvae are usually more uniformly coloured. Lentic species dwell in conditions of more diffuse illumination than lotic one, and each category thus achieves high crypsis with respect to head capsule coloration.

3. Lentic molannid and phryganeid larvae often dwell at considerable depths, and these species also have the most sharply defined head patterns. These species are predatory and, besides being cryptic to larger predators, may also be cryptic to their prey.

4. Intraspecific variation in head capsule coloration in relation to habitat type is also discussed.
Cellulolytic decomposition in streams of contrasting pH and its relationship with invertebrate community structure
Authors: HILDREW ALAN G. , TOWNSEND COLIN R. , FRANCIS JEANETTE , FINCH KAREN
Published: May 2006

SUMMARY. 1. Ceilulolytic decomposition, measured by loss of tensile strength in strips of cellulose test cloth, was estimated in thirty‐four stream sites in experiments in summer, autumn and winter.

2. The results of multiple regression analyses showed that strength loss was most closely related to temperature in summer, when the model accounted for only 38% of the variation, and to stream pH in autumn and winter, when the models accounted for 52% and 75% of the variation, respectively.

3. The relationship between decomposition rate and the structure of invertebrate communities in streams of dissimilar pH is discussed. We argue that a very rapid rate of decomposition of coarse particulate organic matter may profit consumers of fine particulate organic matter at the expense of coarse particle shredders.
Cadmium in freshwaters: concentrations and chemistry
Authors: LAXEN DUNCAN P. H.
Published: May 2006

SUMMARY. 1. Concentrations of cadmium are reported for twenty largely unpolluted freshwaters in north‐western England. They range from 15 to 117 ng l−1 total Cd in the rivers and streams and from 18to51 ng l−1 in the lakes, lying on the low side of values reported in the literature. The care required to obtain reliable data is stressed.

2. A comparison is made between the fraction of Cd found to be particulate (>0.2 μm) and that which is calculated to be adsorbed on particulate matter. This provides further insight into the speciation of Cd, as well as a test of the application of a simple adsorption model to the prediction of the observed speciation.

3.The adsorption model is found to be a poor predictor of the measured fraction of particulate Cd. Possible reasons for this are explored and the potentially important role of slow desorption kinetics is emphasized.
Sinking rates of planktonic diatoms in an unstratified lake: a comparison of field and laboratory observations
Authors: GIBSON C. E.
Published: May 2006

SUMMARY. 1. Natural population sinking rates were calculated by fitting an exponential regression to 6 years’observations on declining crops of Melosira italica subarctica O. Müll. and Stephanodiscus astraea (Ehr.) Grun.

2. Losses were described by an exponential model which yielded still water sinking rates of 0.86 md−1 for M. italica and 0.45md−1 for S. astraea.

3. Laboratory measurements of the sinking rate of natural populations showed that the rate increased abruptly from less than 0.2 m d−1 in growing populations to 0.4 m d−1 after silica depletion.

4. The measured sinking rate of S. astraea agreed well with that observed in the field. Where as populations of M. italica appeared to sink more quickly in the lake than could be accounted for by laboratory observations.
The stable carbon isotope ratios of fish and their invertebrate prey in four New Zealand rivers
Authors: ROUNICK J. S. , HICKS B. J.
Published: May 2006

SUMMARY.

Sources of carbon utilized by invertebrates and fish in four New Zealand streams were investigated using stable carbon isotope analysis. Complementary analyses were made to determine σ13C alteration (fractionation) by fish reared on a known food and to examine the distribution of 13C/12C ratios in different tissues.

σ13C values of hatchery‐reared rainbow trout (white muscle tissue) were 13C‐enriched compared with their food (trout pellets) by an average of 1.7%0. σ13C values of different organs and tissues never differed by more than 1.8%o in any fish species; white muscle always had an intermediate value.

σ13C values of invertebrates ranged from‐28.4 to –20.4%o– At the more open sites invertebrates were 13C‐depleted, reflecting some use of algal carbon. However, invertebrates from the most heavily shaded stream site were unusually enriched in 13C. An undetected carbon source of terrestrial origin, perhaps 13C‐enriched dissolved organic carbon in groundwater, may have been contributing indirectly to invertebrate biomass carbon.

σ13C values for fish were not closely linked to aquatic invertebrate ratios; instead, at all sites their carbon was isotopically similar to terrestrial organic carbon. The reasons for this apparent anomaly are unclear.
The denitrification capacity of sediment from a hypereutrophic lake
Authors: KASPAR HEINRICH F.
Published: May 2006

SUMMARY.

In sediment from Wintergreen Lake, Michigan, denitrification was not detectable by the acetylene inhibition method at in situ nitrate concentrations. When nitrate was added to sediment slurries, denitrification capacities up to 18.8μg N g‐1 h‐1 were measured. The denitrification capacities decreased with increasing sediment depth and distance from shore.

The high denitrification capacities in these sediments which under natural conditions had no supply of nitrate and oxygen suggested that denitrifies with alternative mechanisms for anaerobic energy conversion were present. Nitrous oxide was a significant portion of the N‐gas produced immediately after the nitrate addition. Small amounts (4–5% of the total N‐gas production) of nitric oxide accumulated in the early phase of nitrate reduction. Presumably after depletion of nitrate and nitrite both N2O and NO were further reduced to N2.

About 70%r of the added nitrate was denitrified, and the remainder was assumed to have been reduced to ammonium.
Life history and ecological role of the xylophagous aquatic beetle,Lara avaraLeConte (Dryopoidea: Elmidae)
Authors: STEEDMAN R. J. , ANDERSON N. H.
Published: May 2006

SUMMARY.

This study documents the life history of the xylophagous elmid beetle,Lara avara, and estimates its contribution to wood degradation in Oregon streams. The life cycle was found to be 4 to 6 or more years long, with all but 2–3 months of that spent in the larval stage.

Larvae grow through seven instars, taking about 1 year for instars 1–3, and from 3 to 5 or more years for instars 4–7.

Last‐instar larvae leave the water to pupate. Adults live approximately 3 weeks and occur from May to August. The eggs are deposited on submerged wood.

Larvae probably obtain their nutrition by absorbing substances liberated into decaying wood by microbial activity. They do not produce their own cellulase, nor do they have a symbiotic gut flora similar to that of xylophagous cranefly (Tipulidae) larvae.

Faecal production byL. avaralarvae averaged 13% dry body wt d‐1. This yields an estimate of faecal production of 1.6 g m‐2y‐1in Oregon Coast Range streams (about 0.3% y‐1of wood standing crop).
A choice chamber experiment on the selection of algae as food and substrata by Nais elinguis (Oligochaeta: Naididae)
Authors: BOWKER D. W. , WAREHAM M. T. , LEARNER M. A.
Published: May 2006

SUMMARY.

A choice chamber experiment was performed in the laboratory to quantify the selection of benthic algae as food and substrata by Nais elinguis.

Most worms actively chose filamentous algae and/or diatoms as substrata whereas unicellular or colonial chiorophycean algae were discriminated against. Diatoms were selected in preference to latex beads but the worms could not discriminate between living filaments and nylon monofilaments. A thigmotactic response to filaments and a chemotactic response to diatoms may be implicated.

The worms ingested unicellular algae at a greater rate than colonial and filamentous algae. The rates at which the algae were ingested were negatively correlated with the lengths of the algae. A filament 200 μm long was the largest item ingested, representing about 63% of the length of the pharynx of the worm.

Ivlev's electlvity indices were positive when the rates at which the algae were ingested exceeded about 20 individuals h‐1. The index was negatively correlated with the lengths of the algae, but the time periods spent by the worms in association with the algae were unrelated to the electivity index.

The data confirmed previous observations on the selection of algae as food and substrata by Nais elinguis in a natural habitat.
The effect of invertebrate and vertebrate predators on the foraging movements of Ischnura elegans larvae (Odonata: Zygoptera)
Authors: HEADS P. A.
Published: May 2006

SUMMARY.

The foraging movements of late instar Ischnura elegans larvae were monitored in laboratory experiments to study the effects of predators on larval feeding behaviour.

Ischnura larvae are sit‐atid‐wait, or ambush, foragers, moving occasionally between perches in search of profitable feeding sites. Larval foraging movements, monitored at different densities of Daphnia prey, increased significantly when prey were absent.

In experiments without prey, larval movement was inhibited by the presence of fish predators, as well as by invertebrate predators (Notonecta glauca), but not by closely related, non‐predatory invertebrates (Corixa punctata) or physical disturbance of the water (intermittent air bubbles).

Further experiments varied Ischnura hunger levels (0–8 days without food) and illumination (light or dark) with and without notonectid predators. Hunger had no consistent effect on penultimate instar behaviour but final instar foraging activity was significantly modified: movements increased after 4 days starvation and decreased again after 8 days. This response was suppressed by the presence of predators. Both larval instars moved significantly less often in the light, even when predators were absent.

These phenotypically flexible predator‐avoidance responses are likely to decrease the risk of predation by both visual and tactile predators. However, predators clearly have an important influence on the feeding niche of Ischnura larvae, and may decrease the overall feeding efficiency, growth rate, and survival of larvae by constraining their movement in search of profitable feeding sites.
Determination of biologically available phosphorus using a radiobioassay technique
Authors: JORDAN C. , DINSMORE P.
Published: May 2006

SUMMARY.

A kinetic approach in which the uptake rate of simultaneous additions of orthophosphate and carrier‐free phosphorus‐ 32 by a standard culture of the green alga Selenastrum capricornutum under near neutral conditions was used to obtain an estimate of the readily available components of the total phosphorus pool in natural freshwater samples.

A comparison was made between the values of the biologically available phosphorus obtained using this radiobioassay technique and those obtained by the soluble reactive phosphorus procedure for thirty‐one freshwater samples. Only about three‐quarters of the phosphorus measured as soluble reactive phosphorus was readily available to algae. The results agreed with those obtained in an earlier study in which an enzymatic procedure was used to determine orthophosphate.

The results of tests carried out on the water samples used in this study were consistent with the conclusion that the presence of a hydrous ferric oxide‐orthophosphale complex in the samples caused the soluble reactive phosphorus value to be greater than the corresponding biologically available phosphorus value.
Correlates of habitat favourability for benthic macroinvertebrates at five stream sites in an Appalachian Mountain drainage basin, U.S.A.
Authors: MILLER CLARK
Published: May 2006

SUMMARY.

Based on monthly samples taken over a 1‐year period, average density (individuals m‐2). average standing biomass and annual production of benthic macroinvertebrates were estimated at five sites within an Appalachian Mountain drainage basin. Two sites were on first order streams and differed from the three second order sites: they were smaller and more shallow and they were depressed in pH and chemical richness.

Patterns of abundance of individual taxa, of higher taxonomic groups and of functional (feeding) groups differed according to whether abundance was measured as density, as standing biomass or as annual production. Standing biomass was chosen as the measure of macroinvertebrate abundance because available evidence indicates that only standing biomass is consistently, positively correlated with survivorship, and thus with habitat favourability.

Two non‐insect taxa (the crayfish Cambarus and the snail Leptoxis carinata) dominated standing biomass at each site. Consequently, differences among sites in total macroinvertebrate standing biomass and differences within and among sites in standing biomass of functional groups were determined by differences in estimated standing biomass of these two taxa. Differences in estimates of crayfish standing biomass were consistent with an explanation based on the availability of refuges created by large substrate particles. The abundance of L. carinata appeared to be controlled primarily by water chemistry and possibly secondarily by predators. A number of insect taxa exhibited patterns of standing biomass consistent with hypotheses based on effects of annual depth‐flow regimes. Hypotheses based on differences in food resource and on competition appeared, in general, to be inconsistent with observed patterns of macroinvertebrate abundance.

Contrary to predictions of the River Continuum Concept, the shredder functional group in the Guys Run drainage and in other temperate woodland streams was found to be a minor part of total macroinvertebrate standing biomass. Further, in a majority of small forested stream sites studied to date, standing biomass of grazers has been determined to be greater than that of shredders.
Periodical citations in aquatic entomology and freshwater benthic biology
Authors: RESH VINCENT H.
Published: May 2006

SUMMARY.

Periodicals cited and frequency of periodical citation were examined for two aquatic entomology textbooks published in 1984 (The Ecology of Aquatic Insects, Resh & Rosenberg, eds.; An Introduction to the Aquatic Insects of North America, Merritt & Cummins, eds.) and a bibliography of freshwater benthic biology [published by the North American Benthological Society (NABS) in 1984]. These results were then compared with periodicals cited in Wetzel's (1983) Limnology textbook and with analyses of literature citations in limnology and entomology.

In the aquatic entomology and benthic biology sources, eighteen‐twenty journals each contained ≥1% of total citations and fourteen‐twenty‐eight journals (3.3–5.3% of all journals cited) contained 50% of total citations; however, over one‐half (51.7–57.8%) of the journals contained only a single citation.

In the limnology sources examined, thirteen‐seventeen journals contained ≥1% of total citations, twenty‐four‐fifty‐nine journals (4.3–17.8% of all journals cited) contained 50% of total citations, and 54.5–58.5% of the journals contained a single citation.

Core lists of journals (≥1% of total citations) in Resh & Rosenberg and NABS closely agreed with core lists used for Aquatic Sciences and Fisheries Abstracts.

Based on analysis of 1684 papers published in seven journals from 1975 to 1984, 48% of papers published on aquatic entomology and freshwater benthic biology topics dealt with descriptive studies of macroinvertebrate life histories of bionomics.
Population dynamics of the freshwater dinoflagellate Ceratium hirundinella in the largest shallow lake of Central Europe, Lake Balaton, Hungary
Authors: PADISÁK JUDIT
Published: May 2006

SUMMARY.

Horizontal distribution, long‐term (1933–82) and short‐term (day‐to‐day) changes in abundance, vertical stratification and circadian rhythm of the freshwater dinoflagellate Ceratium hirtmdinella were studied in Lake Balaton, the largest shallow lake of Central Europe.

The lowest abundance was consistently found in those areas of the lake which had the strongest currents.

The density of C. hirundinella seemed to be, at least in those parts of the lake above the level of fertility considered oligotrophic, insensitive to changes in trophic conditions; only its relative contribution to total biomass decreased with increased enrichment.

During the day the bulk of the population stayed at a level in which the light intensity was between 126 and 440 μE m‐2 s‐1 PAR.
Shredder abundance and leaf breakdown in an Appalachian Mountain stream
Authors: BENFIELD E. F. , WEBSTER J. R.
Published: May 2006

SUMMARY.

Breakdown rates of dogwood (Cornus florida L.), red maple (Acer rubrum L.) and white oak (Quercus alba L.) leaves were investigated at two first‐order and two second‐order sites in an Appalachian Mountain stream.

Leaves exposed in mesh bags were sampled on eight occasions over a 207 day period and breakdown rates were compared using an exponential decay model.

There was a consistent ranking in leaf breakdown rate within each site, i.e. dogwood > red maple > white oak, and all species broke down faster at second‐than at first‐order sites.

Our data suggest that differences in species‐specific leaf breakdown rates were largely a function of shredder abundance on the leaves.
A note on ‘stomaching’ for the quantitative sampling of epiphyton
Authors: BOWKER D. W. , van TEUTEM W. , FRY J. C.
Published: May 2006

SUMMARY. 1. Methods for the quantitative removal of epiphyton from Cladophora glomerata were compared.

2. Stomaching for 3–5 min effected maximum epiphyte release. Agitation for up to 40 min in water or hydroiysing solutions of hydrochloric acid or F.A.A. removed significantly fewer epiphytes.

3. Stomaching is recommended as a new, simple, quick and effective method for quantitative epiphyton sampling.
Temperature, oxygen and heat‐budgets of six small western Irish lakes
Authors: ALLOTT N. A.
Published: May 2006

SUMMARY. 1. Temperature and oxygen were examined in six small western Irish lakes (areas 2–110 ha) in 1981, 1982 and 1984.

2. The four deeper lakes (z̄= 6–11m) stratify stably in the same manner as some well‐known stratifying lakes in Britain. Windiness (due to proximity to the ocean) seems generally to be reflected in the lakes by the presence of a sharp thermo clinic. Considerable variation in the pattern of stratification occurs from year to year.

3. Two shallow lakes (z̄= 4.1 and 2.7m) stratify only in periods of warm, calm weather.

4. Annual heat‐budgets range from 4.1 kcal cm−2 to 13.7 kcal cm−2. There is a strong linear relationship between mean‐depth and annual heat‐budget.

5. Oxygen depletion is severe in the more productive lakes.
A regression technique for the estimation of epiphytic invertebrate populations*
Authors: DOWNING JOHN A.
Published: May 2006

SUMMARY. 1. A regression method is proposed for the estimation of populations of epiphytic invertebrates. Small samples of macrophytes and attached animals are taken by gentle enclosure. Regression analysis is used to relate the number of animals collected to the macrophyte species composition and ibiomass in these small samples. These relationships estimate the number of organisms of each taxon per unit mass of each macrophyte species. Areal population density is estimated by multiplication of macrophyte mass‐specific invertebrate density by standing macrophyte biomass.

2. The regression method yields population density estimates several times greater than the best of current methods for several fauna. Differences are most pronounced for active organisms such as water mites, amphipods, cladocerans, copepods, lepidopterans, ostracods, and trichopterans.

3. Precision levels obtained using the regression method are comparable to other techniques. The regression technique automatically provides estimates of macrophyte species‐specific colonization density and the abundance of organisms swimming among macrophytes in littoral areas.
Periphyton communities in a pristine mountain stream above and below heavy metal mining operations
Authors: DENISEGER J. , AUSTIN A. , LUCEY W. P.
Published: May 2006

SUMMARY. 1. Changes in species composition of the periphyton on introduced substrates were determined in an oligotrophic mountain stream subject to long‐term heavy metal contamination.

2. At the upstream control site, the numerically most abundant taxa were Bacillarioph yta i(Achnanlhes minutissima, Achnanthes microcephala and Achnanthes linearis) as well as, in summer, the Chlorophyta (Mougeotia spp. and Ulothrix subtilissima).

3. At the downstream contaminated site the periphyton community was totally dominated by Bacillariophyta throughout the sampling period. A, minutissima and A, microcephala were co‐dominants during spring. Seasonal succession patterns did not parallel those at the upstream site. Chlorophyta were virtually absent and A. minutissima comprised 94% of the community during summer.

4. Species diversity, species evenness and dissimilarity index were utilized to detect differences in species composition, abundance and number. Slight differences were found in spring samples while summer samples indicated major differences between sampling sites.
Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium
Authors: ROSILLON DOMINIQUE
Published: May 2006

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid‐May to mid‐June. Tiny nymphs occurred from June to late August.

2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day−1), very low from November to February (0.8% wet wt day−1) and high until emergence (2.3% wet wt day−1); short day length seemed to be the major factor reducing growth rate during winter.

3. Mortality was close to zero during winter and 1.4—1.7% day−1during other seasons. Total mortality from egg to adult was 99.6%.

4. The annual production was about 9g wet wt m−2 year−1 and the annual P/B̄ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m−2 day−1) and zero in February.
The flora, fauna and water chemistry of Tagimaucia crater, a tropical highland lake and swamp in Fiji
Authors: SOUTHERN W. , ASH J. , BRODIE J. , RYAN P.
Published: May 2006

SUMMARY. 1. Tagimaucia crater lake and swamp are located at an altitude of 820m in Taveuni, Fiji (lat. 16°S; long. 179°56'W). Rainfall exceeds evaporation in all seasons and residence time for water in the shallow lake (2.5–5.5 m deep) is only 4 days.

2. Dissolved ion concentrations are low (conductivity 14–18μScm−lat 25°C), and the water is slightly acidic (pH 5.0–6.5 at 25°C), Median total phosphorus (0.5 gm−3) and total nitrogen (3.3gm−3) are moderately high and probably represent dissolved and suspended organic matter. Median chlorophyll a concentrations (2.5 mg−3) were low and indicate low phytoplankton productivity.

3. The swamp vegetation is dominated by Lepironia articulate (Retz.) Domin and algae which form floating sedge peat islands, and Pandanus taveuniensis St John and other small trees where alluvium and colluvium are infilling the margins of the crater. The surrounding slopes are forested.

4. The fauna of the lake and swamp are low in both diversity and abundance. The only aquatic vertebrates observed were Anguilla eels and cane toads, Bufo marinus L., and the only bird was the swamp harrier, Circus approximans approximate Peale. A variety of aquatic insects were observed but crustaceans and other invertebrate taxa were scarcely recorded.

5. Although the swamp and lake are otherwise undisturbed, several recently introduced plants and animals have been recorded.
The estimation of crop evacuation rates in Chaoborus larvae (Diptera: Chaoboridae) using natural prey
Authors: GIGUÈRE L. A.
Published: May 2006

SUMMARY. 1. Crop evacuation rates were estimated for the first time in Chaoborus larvae, using natural prey.

2. Fourth instar C. americanus Matheson digested copepods (Diaptomus leptopus S.A. Forbes) 48.7% faster than daphnids (Daphnia rosea Leydig) of similar size; meal size did not significantly affect the instantaneous rate of digestion (IRD) within each prey type. Prey specific IRD has not been reported before for zooplankton.

3. Prey specific differences in IRD require the use of natural prey when digestion experiments are to be used to estimate natural rates of food consumption of animals.
Geochemical aspects of aqueous iron, phosphorus and dissolved organic carbon in the humic Lake Tjeukemeer, The Netherlands
Authors: DE HAAN H. , DE BOER T.
Published: May 2006

SUMMARY. 1. The main source of P, Fe and DOC in the humic Lake Tjeukemeer is superfluous water pumped from surrounding peaty polders. Most particulate P is intracellular but almost all particulate Fe is abiotic.

2. The size and molecular weight of the P, Fe and DOC (mainly fulvic acids (FA)) were determined by ultrafiltration and Sephadex G‐100 gel filtration. Throughout the year most dissolved P and Fe was in colloids >35 nm with apparent molecular weight between 30,000 and 150.000. The bulk of FA occurred in particles <35nm.

3. Calculating the atomic ratios of P, Fe and organic C in the different size classes revealed that Fe‐FA chelates are a minor species of the Fe pool. Less than 10% of the fulvic acids occurred as Fe‐FA chelates.

4. Based on their apparent size and molecular weight, the Fe‐FA chelates are colloidal aggregates, probably with the formula Fen‐1(FA)n.

5. About 50% of the dissolved P had the same size as the Fe‐FA aggregates. These aggregates were only noticeable in winter when humus‐rich polder water was flushed through the lake. During the rest of the year the dissolved Fe and P consisted mainly of acid‐labile inorganic colloids which might have been organically coated.
Resource‐mediated demographic variation during the midsummer succession of a cladoceran community
Authors: THRELKELD STEPHEN T.
Published: May 2006

SUMMARY. 1. The midsummer succession of cladoceran zooplankton in Lake Texoma was examined by demographic characterization of lake populations and a parallel set of life table experiments in which the dominant cladoceran species were raised on naturally occurring lake phytoplankton at lake temperatures. Diaphanosoma leuchtenbergianum occurred throughout the study period (mid June‐mid August 1981) but Daphnia parvula, D. galeata mendotae and Ceriodaphnia lacustris were rarely detected after 15 July.

2. Analyses of size structure and size‐specific fecundity of the cladoceran populations showed that (1) size structure shifted to smaller individuals in mid July, (2) size‐specific fecundity was relatively constant in the smaller size classes and was constant or declined in larger females of each species, and (3) size at maturation did not vary significantly during the study of any population.

3. Individual growth rates of the two Daphnia species and Ceriodaphnia in the life table experiments were significantly lower in mid July when populations were declining and when size structure of each population was more dominated by smaller Individuals. The reduction in individual growth rates was short‐lived in the life table experiments; growth rates returned to pre‐decline levels by the end of July.

4. Two effects of temporary reductions in individual growth rates when size‐specific fecundity and size at maturation are constant are (1) that size structure is temporarily shifted to smaller individuals, and (2) the potential rate of population growth is reduced because of delays in reproduction. Because data on size structure and size‐specific fecundity are commonly used to evaluate the relative effects of predators and resource changes on populations it is noteworthy that erroneous conclusions about the mechanism of population decline may be reached when individual growth rates vary.
Nutrient limitation of Myriophyllum spicatum growth in situ
Authors: ANDERSON M. ROBIN , KALFF JACOB
Published: May 2006

SUMMARY. 1. The hypothesis that the submersed macrophyte biomass in natural weedbeds is nutrient limited was tested in situ by an enrichment experiment.

2. The response of Myriophyllum spicatum was significant and positive for N‐enrichment, resulting in a 30–40% increase in biomass over controls. There was no response to phosphorus or to potassium enrichment.

3. Plant length and number of shoots per rephcate were also significantly increased by nitrogen additions but again showed no response to phosphorus and potassium.

4. Water depth differences were also found to affect the plant responses in some cases.

5. The macrophyte response to fertilization was similar to that recorded for emergent macrophytes and terrestrial crops but much smaller than for phytoplankton.
Spatial and temporal variation in the diet of a predaceous stonefly (Plecoptera: Perlodidae)
Authors: WALDE SANDRA J. , DAVIES RONALD W.
Published: May 2006

SUMMARY. 1. Spatial and temporal variation in the diet of the univoltine predatory stonefly, Kogotus nonus, was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet of Kogotus reflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.

2. The seasonal shift from sole utilization of Orthocladiinae to inclusion of Baetis in the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.

3. Feeding rate on Baetis. as assessed by per capita gut contents, showed a seasonal shift from a positive correlation with Baetis density in winter to a negative relationship with predator density in spring. This suggested that feeding by small Kogotus is a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference.
Relations between suspended bacteria, epiphytic bacteria and submerged vegetation over the spring growing season in a calcareous headstream
Authors: RIMES CARRIE A. , GOULDER R.
Published: May 2006

SUMMARY. 1. Quantitative observations on suspended bacteria, epiphytic bacteria and submerged vegetation, in a calcareous headstream in North Humberside, were made at regular intervals from January to June 1984.

2. Downstream increase in concentration of suspended bacteria was observed along a 135 m richly‐vegetated section but not over a 150 m vegetation‐free section, hence there was measurable drift loss of bacteria only from within the vegetated section.

3. The total number of epiphytic bacteria within the vegetated section was estimated from the density of epiphytic bacteria per unit dry weight of submerged vegetation and the total dry weight of submerged vegetation.

4. The total number of epiphytic baeteria within the vegetated section decreased frtim 2.5 × 1015 in January to 0.8 × l015 March before increasing to 4.7 × 1015 by June. This pattern was related to deerease and subsequent increase in density of epiphytic bacteria per unit dry weight of vegetation. The total dry weight of submerged vegetation inereased throughout the study period.

5. The daily drift loss of bacteria from the vegetated section averaged 53% (range 9–132%) of the total epiphytic bacteria, a loss rate which might reasonably be supported by the epiphyte population.

6. The dimensions and volume of suspended bacteria increased, between the source and the downstream limit of the vegetated section, to resemble those of epiphytic bacteria.

7. The results suggested that released epiphytic bacteria might largely be the source of suspended bacteria in this headstream.
Regulation of damseifly populations: the effects of weed density on larval mortality due to predation
Authors: THOMPSON DAVID J.
Published: May 2006

SUMMARY. 1. The effects of weed detisity oti the predalion of damseifly larvae by Notonecta were investigated iti a laboratory experimetit.

2. In the absence of weeds. Notonecta exhibited a Type 2 functional response, but this changed to a Type 3 response as weed density increased. Consideration is given to the possible significance of these results for the regulation of field populations of damseifly larvae.
Does ionic strength affect the configuration of aquatic humic substances, as indicated by gel filtration?
Authors: DE HAAN H. , JONES R. I. , SALONEN K.
Published: May 2006

SUMMARY. 1. The effect of ionic strength on the configuration of aquatic humic substances was studied by gel filtration and dialysis of water from small. Finnish forest lakes of varying colour.

2. Sephadex gel filtration of water from the most humic lake gave similar elution profiles of UV absorbance and dissolved organic carbon (DOC). Gel filtration of unconcentrated samples from all three lakes under natural conditions of ionic strength (I = 1.7 × 10−4) and pH (5.5–6.0) gave similar fractionation of humic substances, despite their widely differing colour (30–350 mg Pt l−1) and DOC (5–25mg C l−1).

3. Increasing the ionic strength by two orders of magnitude caused considerable retardation on the Sephadex columns of the humic substances, suggesting a decrease in their molecular size and/or shape.

4. Dialysis experiments strongly indicated that ionic strength‐induced changes in the configuration of the aquatic humic substances are indeed real. Hence it is probable that the elution behaviour of aquatic humic substances on Sephadex gels has previously been wrongly attributed to ionic strength‐dependent interactions between the gel and the humic substances.
A laboratory study of predator‐prey interactions of stoneflies and mayflies
Authors: WILLIAMS D. DUDLEY
Published: May 2006

SUMMARY. 1. Reactions of individual predatory stoneflies to contact by individual mayfly prey, and vice versa, were studied in the laboratory using two sets of species, one from a stream in southern Ontario. Canada, and the other from a stream in North Wales.

2. Based largely on information received via their antennae, the stoneflies were capable of distinguishing between conspecifics and mayfly prey and between prey species. A clear preference for certain prey species was evident but less preferred species were made more attractive when damaged or when the stoneflies were very hungry. Detection of conspecifics by stoneflies was confused in the presence of prey or the local smell of prey body fluids and this led to interference during hunting and feeding at high predator densities.

3. Some mayfly species were capable of distinguishing between conspecifics. other mayflies and predators. The cerci were important in intra‐ and interspecific contact encounters between mayflies and were used in a fencing fashion to establish a minimum distance between nymphs. However, the cerci did not appear to play an anti‐predation role as stoneflies captured and ate mayflies with and without cerci in equal numbers.

4. Reactions to conspecifics by the Palaearetie mayflies Rhithrogena semicolorata (Curt.) and Baetis rhodani (Pictet) were similar to those of the ecologically‐equivalent Nearctic species Stenonema vicarium (Walker) and Baetis vagans McDunnough.

5. In encounters between mayflies, intra‐ and interspecific responses were similar. However, the responses of some mayfly species to conspeeifics were modified in the physical presence of a predator or the water from its holding tank. Different mayfly species made specific responses to predaeeous stoneflies. Responses to a herbivorous stonefly were either similar to conspeeific encounters or were intermediate between them and encounters with predators.

6. Experiments to reveal the exact nature of the stonefly stimulus detected by the mayfly nymphs strongly suggested that there were two components to the stimulus. One was physical contact by the predator's antennae, the other was chemical in nature and could be detected only over short distances (up to a few mm). Independently each could elicit a response, but combined their effect appeared to be synergistic.

7. Different mayfly species responded differently to the stonefly Phasganophora capitata (Pictet) and this sequence of sensitivity was mirrored by the predator's choice of prey species—the most sensitive to the predator being the favoured prey and the less sensitive the least favoured. The significance of these findings to optimal foraging theory, as applied to tactile predators, is discussed.
The distances travelled by downstream‐moving trout fry, Salmo trutta, in a Lake District stream
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY. 1. Field experiments were performed in the day and night at six modal water velocities (range 10–52cm s−1), using: (i) newly‐ emerged fry without neutral buoyancy; (ii) older fry in poor condition (weight well below that expected for resident fry); (iii) older fry in good condition (weight similar to that of resident fry); (iv) dead fry.

2. An exponential model described the return rate of fry to the stream bottom; the mean distance travelled downstream varied considerably between the four fry categories, but always increased linearly with increasing water velocity.

3. Results were similar for dead fry and newly‐emerged fry released at night; 50% of the fry returned to the bottom in 10–11 s and nearly all returned in c. 70s, the maximum distance travelled ranging from c. 7 m at 10 cm s−1 to c. 37m at 52cm s−1, Newly‐emerged fry released in the day returned slightly faster (54s for 99% return to bottom).

4. Older fry in poor condition returned to the bottom slightly faster in the day than at night, but took about 2 min and travelled about twice the distance covered by dead fry. Older fry in good condition returned to the bottom at the fastest rate (3–6s for 50% and c. 30s for the rest), and travelled only about half (at night) or a third (in day) of the distance covered by dead fry.

5. The implications of this investigation are discussed and it is concluded that, apart from water velocity, the age and condition of the fry were the two most important factors affecting their downstream movement.
Colonization and ecological development of new streams in Glacier Bay National Park, Alaska
Authors: MILNER ALEXANDER M.
Published: May 2006

SUMMARY 1. Colonization and ecological development of postglacial freshwater communities was investigated in Glacier Bay National Park, south‐eastern Alaska, following the rapid recession of a Neo‐glacial ice sheet within the last 250 years.

2. Environmental variables shown to be most significant in stream development were temperature, flow regime and sedimentation.

3. The Chironomidae (Diptera) were the pioneer invertebrate colonizers of newly emergent streams arising as meltwater from receding ice sheets and displayed a distinct pattern of succession with stream maturity.

4. Ephemeroptera and Plecoptera colonized warmer clearwater streams, but Trichoptera had a minimal role in invertebrate community development.

5. Establishment and production of salmonid fish populations in the new streams related principally to stream flow and sediment characteristics.

6. Future pathways along which the streams may develop is probably dependent on the degree of large organic debris input.

7. Stream development, structure and function are summarized including reference to theories of ecosystem development, ecological succession and community stability.
Relationships between bathymetry, water quality and diatoms in some Hebridean lochs
Authors: FLOWER R. J. , NICHOLSON A. J.
Published: May 2006

SUMMARY 1. Computer methods for mapping and calculating morphometric characteristics are described and applied to seventeen previously unsurveyed South Uist lochs.

2. Deposited sea salt is shown to have a major effect on water quality and the effect varies according to distance from the west coast. Calcium concentrations appear to be determined by dissolution of locally abundant shell debris. Sulphate and particularly nitrate concentrations are influenced significantly by catchment sources.

3. Surface sediment diatom assemblages from all seventeen sites are analysed using multi‐variate methods (Hill, 1979). Assemblages are shown to be clearly distributed along DECORANA axis 1 and are clustered into five groups by TWINSPAN.

4. Correlation analysis of water quality, morphometric characteristics, and DECORANA axes scores indicates that conductivity has the strongest influence on surface sediment diatom assemblage composition whereas morphometric characteristics have no demonstrable effect.