bluuebunny/crossref_metadata_2025 huggingface dataset:
Silicon depletions in some Norfolk rivers
Authors: EDWARDS A. M. C.
Published: May 2006

Water samples collected weekly from the rivers Yare, Tud, Wensum and Tas in Norfolk, England, displayed marked depletions in the spring and summer of the concentration of dissolved silicon. These were unconnected with any hydrological event and were assumed to be due to the assimilation of silicon by diatoms. Equilibrium concentrations were maintained in the Yare and Tud during the weeks prior to and following the spring bloom. It was estimated that 35 Mg (51%) of the predicted load were removed from the Yare during the 11 weeks of this depletion and 6‐0 Mg (45%) from the Tud. The lowest observed concentration (0‐4 mg/l) occurred during the first week in May when over 90% of the silicon had been removed. However, the maximum amount of removal and hence maximum diatom productivity occurred earlier at a time of higher water discharge. A similar pattern was observed in the Yare during the spring of 1971. Two small blooms occurred later in the summer of 1970 in the Yare and Tud. It was estimated that 15% ofthe Yare's dissolved silicon load of 263 Mg was in the assimilated form and 12‐5%of the Tud's output of 56‐6 Mg. The weathering of silicate minerals was probably the source of almost all the silicon and the outputs represented a silicon erosion rate of 1‐15 Mg/km2/year for the Yare and 0‐77 Mg/kmVyear for the Tud.
Studies on energy transformation in the freshwater snail Pila globosa
Authors: VIVEKANANDAN E. , HANIFFA M. A. , PANDIAN T. J. , RAGHURAMAN R.
Published: May 2006

The effects of eleven chosen feeding levels ranging from 0 to 198 mg damp dry (plant) Ceratophyllum/g live snail/day on the absorption, conversion and metabolism of the snail Pila globosa (of 1 ‐9 g body weight) have been studied. Absorption rates increased from 3‐0 to 21‐0 mg dry food/g live snail/day in snails fed 3‐4‐28‐8 mg dry food/g live snail/day. In these snails, absorption efficiency decreased from 87.5 to 73.0%. Conversion rates increased from 0‐3 mg/g/day for snails receiving 23‐4 mg/g/day to 2‐7 mg/g/day for those fed maximum amounts, and the efficiency (K2) also increased from 1‐9% to 130%. When compared to other gastropods, Pila globosa appears to be a poor convertor. During 30 days' starvation, the test individuals lost 4.4 mg dry body substance/g/day i.e. the maintenance cost was 14‐7 cal/g live snail/day. The SDA increased by four times for those feeding on maximum rations in comparison to those receiving about 5 mg/g/day, i.e. the energy cost for converting food was increased four times.
Effect of a fulvic acid fraction on the growth of aPseudomonasfrom Tjeukemeer (The Netherlands)
Authors: DE HAAN H.
Published: May 2006

In this paper the effect of a fulvic acid fraction on the growth of a Pseudomonas sp. from fresh water is reported. The presence of fulvic acid in the culture medium caused an increase in the cell yield and in the cell yield per μl O2taken up by the Pseudomonas. The observed stimulating effect has been explained in terms of co‐metabolism of fulvic acid by the Pseudomonas.
The metazoan fauna of a sewage‐carrying wadi, Nahal Soreq (Judean Hills, Israel)
Authors: BROMLEY H. J. , POR F. D.
Published: May 2006

(1) An analysis of the metazoan fauna of Nahal Soreq was made at several sampling stations from October 1970 to August 1971. Relative abundance of each species or group of species was estimated by semi‐quantitative sampling, and population structures are given here in the form of percentage tables. (2) A succession of three zones, indicating three degrees of pollution, were recognized: a ‘Nematode zone’ in the most polluted waters, a ‘Chironomus zone’, where purification has progressed a little, and a ‘Proasellus (and ostracod) zone’, where purification is nearing completion. (3) These zones of indicator organisms roughly correspond to three zones classified in a ‘Saprobien System’ manner: a polysaprobic zone (Nematode zone), a mesosaprobic zone (Chironomus zone), and an oligosaprobic zone (Proasellus zone). A state of complete purification or recovery is not reached, and the purification process is stopped in the oligosaprobic condition by the disappearance of the stream underground. The other invertebrates characterizing these three zones are given. (4) A comparison is made of the saprobic zones and their corresponding fauna with findings reported elsewhere‐‐‐Europe, North America and South Africa. The successional changes are generally similar to European findings with some notable absentees, and there are also some similarities with polluted South African streams. (5) Seasonal changes in species composition and the position of these species along the stream are discussed. There are small changes which appear to be a result of life cycle habits in some air‐breathing dipterans and a slight change in the position of chironomids downstream, which is correlated with the winter rain floods. (6) The faunal types and numbers occurring downstream are compared with the increase in algal species diversity, dissolved oxygen and coli bacterial counts. It is suggested that the degree of pollution is the primary factor in the establishment and population build‐up of any particular species, but that presence of suitable substrates, availability of food and presence of predators play a larger part where the water is cleaner.
Reactions of some caddis larvae (Trichoptera) to different types of substrate in an experimental stream *
Authors: HIGLER L. W. G.
Published: May 2006

In laboratory experiments with full‐grown larvae of three Trichoptera species (Limnephilus rhombicus, Potamophylax rotundipennis and Sericostoma pedemontanum) in an artificial stream, four types of bottom material were provided in combination with various currents. Only L. rhombicus reacted to low current speed (9 cm/sec), moving downstream when a bottom current was present. L. rhombicus and P. rotundipennis showed a distinct preference for pebbles over sand and for coarse pebbles over crushed brick. S. pedemontanum burrowed under pebbles or stones. L. rhombicus showed a distinct tendency to climb onto the dividing gauze or vertical sticks. All three species preferred shaded parts of the experimental stream to the illuminated parts.

The results are related to field observations. Limnephilus rhombicus occurs in stagnant and slow‐running waters. Potamophylax rotundipennis is restricted to rather fast‐running streams with a perpetual flow, while Sericostoma pedemontanum occurs in the same type of stream.
Egg production, development and growth in Moina micrura Kurz (1874) (Cladocera: Moinidae)
Authors: MURUGAN N.
Published: May 2006

Laboratory observations on the egg production, development and growth in the Cladoceran Moina micrura show that this species has a life span of 13 days during which it produces 6M 8 eggs. Two preadult and eleven adult instars were recorded at a temperature range of 28°–30°C. The rate of egg production calculated on a cumulative basis was found to be lower (a = 1.0368) than that of other tropical species. The embryonic stages in Moina micrura closely resembled other cladoceran species, although with a short development period of 24 h. The total life span, growth rate and the total number of eggs produced in Moina micrura have been compared with those of allied tropical, temperate and arctic daphnids. The significance of this relationship to secondary productivity in tropical ecosystems has been discussed.
Changes in the ecology of the Norfolk Broads
Authors: MASON C. F. , BRYANT R.J.
Published: May 2006

The Norfolk Broads have recently shown a marked loss of both floral and faunal diversity. To detect any recent changes and to provide a baseline for future research, twenty‐eight broads were visited in 1972–73. Samples of aquatic flora and benthic fauna were taken and a number of physical parameters were measured.

In the private broads a good inverse correlation between chlorophyll‐a concentration and Secchi disc readings was found, suggesting that phytoplankton was largely responsible for the turbidity of the water. The relationship did not hold for the public broads where erosion and the stirring of sediments by motor launches is intense.

Eleven broads were completely devoid of macrophytes. A macrophyte flora was well developed only in Upton and in the five Thurne broads and in these latter there was evidence of a recent loss in diversity. The sudden loss of formerly abundant species of macrophyte has been recorded frequently from the broads. The benthic fauna was poorly developed in most broads and was dominated by Limnodrilus hoffmeisteri and/or Potamothrix hammoniensis. Valvata piscinalis was the only regularly occurring gastropod in the benthos. Most of those broads with a diverse benthic fauna also had an abundant growth of macrophytes.

Possible reasons for the recent changes in the ecology of the broads are discussed.
Cyclomorphosis in natural populations of Oscillatoria redekei Van Goor
Authors: GIBSON C. E.
Published: May 2006

Evidence is presented of a regular seasonal variation in the filament length of Oscillatoria redekei Van Goor in Lough Neagh. This cycle is not in phase with the seasonal changes of the biomass of the species, but seems to occur in step with the nutrient concentrations. Some possible mechanisms of filament replication are discussed and evidence is presented that mechanical forces are not effective in breaking filaments. The ecological significance of cyclomorphosis in this species is difficult to establish.
Effects of temperature on food ingestion rate and absorption, retention, and equilibrium burden of phosphorus in an aquatic snail, Goniobasis clavaeformis Lea *
Authors: ELWOOD J. W. , GOLDSTEIN R. A.
Published: May 2006

The effects of sublethal temperatures on feeding rates and phosphorus dynamics of a freshwater snail, Goniobasis clavaeformis Lea, were determined and feeding rates were measured at four temperatures. The food source was aufwuchs labelled with radioactive phosphorus. A model was developed to elucidate the results of this type of study. Food ingestion rate increased with increasing temperature up to 14°C and then decreased at temperatures above 14°C. The elimination rate of absorbed phosphorus increased with increasing temperature throughout the entire range of experimental temperatures, 10‐19.3°C. Mean retention times of absorbed phosphorus i n Goniobasis were estimated to be 34, 24, 10, and 6 days at 10, 13.8, 15, and 193°C, respectively. Mean retention time of unabsorbed 32P in the gut of this species as a function of temperature followed the same temperature relationship as that of ingestion rate.

The absorption efficiency of phosphorus was estimated to be constant at about 39% for ail experimental temperatures, although the data suggest that the absorption ePRciency may have been related inversely to the rate of gut clearance or directly to the residence time of food in the gut. The equilibrium body load of phosphorus at each experimental temperature was estimated based on concentrations of stable phosphorus in the food source and the kinetics of 32P in Goniobasis. The equilibrium body burden of phosphorus in Goniobasis increased with increasing temperatures up to a maximum at 11–12°C and then decreased at temperatures above 12°C.
The effect of oxidized material on the vertical distribution of freshwater benthic fauna
Authors: KIRCHNER W. B.
Published: May 2006

The vertical distribution of representatives of the benthic groups: Ostracoda, Nematoda, Oligochaeta, Harpacticoida, Cyclopoida, and Chironomidae was determined. All groups had their highest numbers and biomass in the first 2 cm.

The downward extent of oxidized material affected the distribution by dispersing the biomass more as seen by the deeper occurrence of groups when the oxidized material increased. Both the nematodes and oligochaetes were found to inhabit the first reduced layer when the oxidized material was less than normal.
Ecological studies on algal‐lysing bacteria in fresh waters
Authors: DAFT M. J. , McCORD SUSAN B. , STEWART W.D.P.
Published: May 2006

Algal‐iysing bacteria are present in five lochs, two reservoirs, one sewage works and five alkaline soils whieh were examined. Nine out of thirty‐six isolates have been studied in detail and all are gram‐negative non‐fruiting myxobaeteria. All are aero‐philic, require a neutral or alkaline pH (optimum 7.0–9.0) for good growth, have temperature optima of 28–37°C, require contact with the host for lysis to oecur, and are so similar in morphology and host range that they all appear to be strains of a single genus. They lyse all bloom‐forming Cyanophyeeae on whieh they have been tested, including species of Anabaena, Aphanizomenon, Gloeotrichia, Microcystis and Oscillatoria. Their abundance is usually correlated direetly with the abundance of Cyanophyeeae in eutrophic waters and it is probable that in most ecosystems the algae and the bacteria co‐exist, although if the equilibrium changes markedly as a result of change in environmental conditions situations may arise where the bacteria may play an important role in the lysis of algal blooms. The available evidence suggests, however, that this is likely to be a rare occurrence in natural ecosystems.
Decomposition of aquatic biota and sediment formation: organic compounds in detritus resulting from microbial attack on the alga Ceratium hirundinella
Authors: CRANWELL P. A.
Published: May 2006

To obtain further evidence of the contribution of autochthonous organic matter to lake sediments, the benzene‐methanol extract of the particulate matter remaining after microbial attack upon an alga, Ceratium hirundinella, during laboratory simulation of natural decomposition processes, has been separated into its components. Comparison of each component with corresponding material isolated from the fresh alga facilitates the recognition of unchanged substances and microbial products in the decomposed sample. Certain common features in the occurrence and distribution of n‐alkanes, alkenes, n‐ and branched/cyclic alkanoic acids, alkenoic and hydroxy acids in degraded algal organic matter and in sediments of productive lakes are believed to indicate a contribution of autochthonous material to the sediment.
Planktonic diatoms and some diatom‐silica relations in a shallow eutrophic Scottish loch
Authors: BAILEY‐WATTS A. E.
Published: May 2006

The species composition of planktonic diatom crops in Loch Leven, Kinross, Scotland varied considerably over the years studied (1968–71) with centric forms predominating. Dense populations were often produced and rates of increase and decrease were high.

Relations with dissolved silica did not appear always to be simple; instances occurred during which both diatoms and silica were increasing or decreasing. Moreover, certain rates of increase in dissolved and frustule silica exceeded the rates at which silica flows into the loch even when the inflows appeared to be the only available dissolved silica source.
The substrate bin—a new sampling device for studying diel vertical migratory movements on to and off lake sediments
Authors: HART R. C.
Published: May 2006

The substrate bin, used to study diel migratory movements of the copepod Pseudodiaptomus hessei on to and off bottom interfacial areas is described. It consists essentially of a transparent Perspex box open at its upper end and supported upright within a metal framework. A lid, hinged along one face of the open end of the bin, opens and closes automatically through a simple system of levers as the apparatus is lowered on to or raised off a solid substrate.

The apparatus is lowered on to the lake bed where it opens. Diel movements on to or off the shallow layer of bottom substrate enclosed within the bin can be examined by retrieving bins serially at different times.

Using this apparatus in conjunction with standard net sampling techniques, clear evidence for an alternation of benthic and pelagic phases during diel cycles was obtained. Notwithstanding an apparent oversampling of the benthic component, the magnitude of which cannot be defined precisely, it is concluded that the apparatus provides a simple and reliable method of sampling.
A portable quantum meter‐spectroradiometer for use in aquatic studies
Authors: UPHOFF GARY D. , HERGENRADER GARY L.
Published: May 2006

This paper describes the design, construction and use of a portable battery‐powered, submersible spectroradiometer. The distribution of energy underwater is determined by measuring successively through six sensors fitted with interference filters which partition the underwater spectrum. This system also contains a quantum sensor which detects the photosynthetically active radiation under water. The instruments’ small size and battery operation make it especially useful for studying small lakes or reservoirs from small boats. Measurements taken from Pawnee and Wagontrain, two of the Salt Valley Reservoirs in eastern Nebraska, are given as examples of the use of the instrument.
Factors influencing phytoplankton growth and succession in Farmoor Reservoir
Authors: YOUNGMAN R. E. , JOHNSON D. , FARLEY M. R.
Published: May 2006

Weekly observations were made at the Thames Water Authority's Farmoor reservoir during the development of the spring bloom of phytoplankters from November 1973 to March 1974. Counts were made of the phytoplankters, their fungal parasites and the zooplankters. Analyses were made of those chemical parameters which it was thought might exert an influence on phytoplankton growth. Physical and meteorological measurements were also made.

The development and decline of four phytoplankton populations were observed. The growth of Asterionella formosa Hass. was interrupted in December when 43·5% of the cells were parastiized by Zygorhizidium affluens Canter. Stephanodiscus astraea (Ehr.) Grün. and Stephanodiscus hantzschii Grün. were not similarly affected. All three diatoms were apparently limited finally by silica depletion. The desmid, Closterium peracerosum Gay. became 66% parasitized by an undescribed chytrid and declined rapidly.

Light, turbulence, zooplankton grazing and nutrients other than silica appeared to be unimportant.
Studies on the Ephemeroptera of a Northumbrian river system
Authors: WISE E. J.
Published: May 2006

The River Coquet is a clean, fast flowing, moderately calcareous river. It is young to mature in development and supports a typical torrential fauna. Marked trends in successional replacement along the river course are confined to the scarce species of Ephemeroptera and the absence of longitudinal zonation in the distribution of some common species is related to the topographical characteristics of the system. A distinct successional trend by one species is attributed to its intolerance to the lower temperatures at high altitudes. Major discontinuities in distribution are found between the Ephemeroptera of the main river and certain tributaries. The paucity of certain otherwise abundant species in one region is related to silt deposition resulting from sand and gravel excavation.
The food ofPlanaria torva(Müller) (Turbellaria‐Tricladida), a laboratory and field study
Authors: REYNOLDSON T. B. , SEFTON A. D.
Published: May 2006

The food of Planaria torva was examined in the laboratory by exposing a range of potential prey to the triclad and observing prey mortality. Under these conditions P. torva fed mainly upon tubificid oligochaetes and gastropods. The former activity was regarded as untypical of the field situation and due to limitations of the laboratory habitat.

The food of P. torva was determined in the field by taking monthly samples from October 1967 to May 1969 of a population living in Linlithgow Loch, West Lothian, Scotland. A serological technique was used to examine the gut contents of the field triclads. For reasons explained in the text, the prey organisms tested for serologically were gastropods, oligochaetes (Tubificidae), Asellus and chironomid larvae. Planaria torva fed most extensively on Gastropoda, Asellus was the second main food while Tubificidae and Chironomidae were taken only seasonally and in small numbers. The limited extent of feeding on tubificids supports the laboratory data. Small P. torva gave proportionately fewer positive reactions to the prey antisera than large individuals. This was explained by the fact that small individuals occurred most frequently in the warmer months and took smaller meals; both of these features shorten the detection period of food in the gut and therefore give fewer reactions. The diet of small and large P. torva was similar in the field and showed considerable overlap with that of Dugesia polychroa.

The food of Polycelis tenuis, Dendrocoelum lacteum and Dugesia polychroa in Linlithgow Loch was described on an annual basis and the results confirmed earlier observations.
Body length, size of resting eggs and identification of the ephippia of Ceriodaphnia megalops and Ceriodaphnia pulchella
Authors: BOTTRELL HOWARD H. , NEWSOME T.
Published: May 2006

The ephippia of Ceriodaphnia megalops and Ceriodaphnia pulchella are described. Their ephippia may be identified by their size and shape, supplemented by measurement of the length of the resting egg. The ephippia are shed free in the water and float by means of a special area of gas‐filled tissue. Each ephippium contained one ellipsoid resting egg. The length, width and shape of the resting eggs of both species were investigated, and comparisons made with published data of their parthenogenetic eggs. For both species the volume of a resting egg was virtually the same as the volume of a parthenogenetic egg, but the resting egg was more elongated. The shape of resting eggs was linearly related to egg volume on logarithmic axes in a manner similar to that reported for the parthenogenetic eggs of these two species. The linear relationship between total parthenogenetic egg volume and body length reported for these two species did not apply to their resting eggs.
Wind distribution of the egg masses of Chironomus anthracinus (Zetterstedt) (Diptera: Chironomidae) in a shallow, wind‐exposed lake (Loch Leven, Kinross)
Authors: DAVIES B. R.
Published: May 2006

A mass emergence of Chironomus anthracinus (Zetterstedt) took place at Loch Leven, Kinross, in late May and early June 1971, leading to a large concentration of egg masses. The distribution of egg masses within the lake was determined on 6 June 1971 and the accumulation of egg masses along wind‐exposed shores, under the influence of a 17–23 km h−1 wind, was noted. Oviposition site selection by the weak flying adults appears to have little importance upon the final distribution of larvae within the lake. Temporary planktonic activity of first instar larvae under the influence of wind‐induced water currents is briefly discussed as a dispersal mechanism in the light of observed egg mass accumulation in the lake.
The numbers, biomass and transport downstream of micro‐crustaceans and Hydra from Cow Green Reservoir (Upper Teesdale)
Authors: ARMITAGE PATRICK D. , CAPPER MARTIN H.
Published: May 2006

Fluctuations in numbers and biomass of Copepoda, Cladocera and Hydra drifting out of the Cow Green reservoir via the outflow were investigated during the period August 1972‐November 1973. Cladocera, chiefly Daphnia hyalina var. lacustris Sars and Copepoda, were most abundant between July and September, occurring at mean densities of 1278 and 215 m−3 respectively. Hydra was most abundant between August and October at a mean density of 19 m−3. Winter densities of all groups were low and 98% of the total annual output occurred between July and October. An estimated 150 kg (136 kg of Cladocera, 13kg of Copepoda and 1 kg of Hydra) dry weight was released from the reservoir during the year November 1972‐October 1973. During periods of peak abundance about 1–2% of the total fauna drifting out of the reservoir was found 6·5 km below the dam. The effect of reservoir discharge and flow in tributaries of the Tees on this transport downstream is discussed. It is suggested that the micro‐crustaceans and Hydra, even if not fed upon directly, will have considerable influence on the Tees benthos when they settle out and decompose to produce a nutrient‐rich detritus.
Experimental studies on nymphal growth in Leptophlebia vespertina (L.) (Ephemeroptera)
Authors: BRITTAIN JOHN E.
Published: May 2006

The mayfly, Leptophlebia vespertina (L.) was reared at field temperatures in the laboratory. The egg incubation period was 21–26 days. There were seventeen to nineteen nymphal instars. Growth was generally rapid during the first 3½ months and slow thereafter. This change occurred at the same time in both the laboratory and the field population. Temperature is considered to be the major factor regulating this and other changes in growth rate.
Starvation and the size structure of zooplankton communities*
Authors: THRELKELD STEPHEN T.
Published: May 2006

The survival time of zooplankton under conditions of total starvation is expressed as a function of weight‐specific respiration rate and the fraction of initial (pre‐starvation) body weight which may be lost prior to death. Data from the literature on these two components of survival time are used to formulate a general expression of survivorship of zooplankton at 20°C as a function of body weight: t=2·95 w0·25, where t is in days and w is μg dry weight. Survival time data from the literature on 25 marine and freshwater species are compared to this prediction as are new data on Daphnia pulex Leydig, D. magna Straus and Simocephalus serrulatus (Koch). The effects of age‐specific (non‐starvation) mortality are considered; in particular, older individuals of each of these species survive for shorter periods of time than predicted and an interaction between age‐specific and starvation‐induced mortality is proposed. The effects of total and partial starvation on the size structure of zooplankton communities are discussed.
Temporal and spatial distribution of the dinoflagellate Ceratium hirundinella O.F. Müller within a small productive lake
Authors: HEANEY S. I.
Published: May 2006

The growth of Ceratium hirundinella in Esthwaite Water, a small productive lake, was investigated during 1975; the horizontal distribution of the alga was studied on four occasions over a 3‐week period. Measurements of lake temperature, oxygen concentration, and vertical stratification of Ceratium at close intervals of depth, were also made. Lake population estimates from large samples at many stations were compared with small samples at the regular sampling station. On two occasions the means of these samples were significantly different (P<0·01). On one date, the estimate of Ceratium abundance in the lake from the large sample at many stations was more than twice the value obtained from the sample collected at the regular sampling station. The population of Ceratium was contagiously distributed in all the large samples. On 3 days the horizontal distribution showed an increase in Ceratium numbers towards the windward shore of the lake. Very large accumulations of Ceratium were found in the metalimnion, just above the anaerobic hypolimnion, during late afternoon. Possible mechanisms of horizontal pattern development are considered, based on the measurements of the vertical distribution of Ceratium, and meteorological factors. The ecological consequences for Ceratium of vertical and horizontal movements, and its spatial distribution in the lake, are discussed.
Application of underwater light measurements in nutrient and production studies in shallow rivers
Authors: WONG S. L. , CLARK B. , PAINTER D. S.
Published: May 2006

Due to fluctuations in water turbidity, river depth and total reflection from one river section to another, plant production is poorly correlated to solar radiation incident on the water surface. A relationship was observed between daily relative photosynthesis and photosynthetically available radiation (PAR) at the plant depth for Cladophora, with a correlation coefficient (r) of 0·73. Therefore, the effect of low light levels can be compensated for when evaluating nutrient‐growth relationships for Cladophora in the field.
Feeding rhythmicity in a migratory copepod (Pseudodiaptomus hessei (Mrázek))
Authors: HART R. C.
Published: May 2006

SUMMARY. This paper describes a day/night feeding rhythm in the copepod Pseudodiaptomus hessei in subtropical Lake Sibaya (27°20′ S, 32°40′ E) and examines the origin of this rhythmicity on the basis of field and laboratory observations.

Under natural conditions, adult and late copepodite stages (CIV‐CV) of this copepod were predominantly benthic during daylight and migrated at dusk into pelagic waters in which they remained until dawn. Pronounced changes in feeding activity (based on the proportion of animals which contained food in the gut) were associated with this transition from a benthic to pelagic distribution; feeding activity was low by day and high at night. The younger copepodite stages (CI‐CIII) were less strongly benthic during daylight and showed correspondingly less pronounced diel changes in feeding activity.

Laboratory experiments involving concurrent light/dark and continuous dark regimes showed that batches of adult and CIV—CV stages fed throughout 24 h, although faecal pellet production increased with time under both light regimes. The laboratory observations are interpreted as negating the possibility that diel differences observed in the field arose through an endogenous feeding rhythm. The possibility that food resources in near‐bottom waters was inadequate to support reasonable feeding activity is rejected on several counts. It is concluded that the feeding rhythm in P. hessei arises from an inferred infaunal distribution during daylight which would preclude filter‐feeding activity. The circumstantial evidence supporting this suggestion is given and the suggestion is evaluated.
The effect of catchment geochemistry and geomorphology on the productivity of a tropical African montane lake (Little Connemara Dam No. 3, Rhodesia)
Authors: NDUKU W. K. , ROBARTS RICHARD D.
Published: May 2006

SUMMARY. An extensive limnological study of a tropical African montane lake (Little Connemara Dam No. 3) was undertaken in 1975 to explain the discrepancy between the high nutrient content of the bottom muds and the oligotrophic status of the water column. Little Connemara Dam (No. 3) lies in a small dolerite catchment. The dolerite is strongly jointed allowing considerable water movement and it weathers easily under high rainfall. A number of homes are built in the small catchment.

The results of the study showed that the majority of the nutrients were being flushed into the lake from septic tanks via underground streams. As the dolerite weathers, large amounts of iron and manganese, but little calcium or carbonate, are released. The PO4‐P in the water column is complexed with the Fe and Mn allowing only small concentrations for use by algae. Nitrogen enters the lake mainly as particulate nitrogen but is not significantly converted to soluble combined forms of nitrogen at the low pH values (6.2—6.7) found in the lake. Bioassay experiments indicated that combined forms of nitrogen limited phytoplankton growth.
The life cycle of Trichocorixa verticalis interiores Sailer (Hemiptera, Corixidae) with special reference to diapause
Authors: TONES PATRICIA I.
Published: May 2006

SUMMARY. The life cycle of Trichocorixa verticalis interiores was studied in six Saskatchewan saline lakes. A detailed study of the timing of the stages in the life cycle showed that T. v. interiores has a life cycle which differs from that of all other Corixidae. This species overwinters solely in the egg stage. Females oviposit in the late summer and all adults die in the fall. The eggs, which remain in a pre‐blastokinesis stage of embryonic development until the following spring, are prevented from developing in late summer by diapause which lasts approximately 2 months. Although diapause terminates in October, embryonic development does not occur in cold water during the winter months. Experimental results indicate that exposure to cold is not necessary to break diapause.
Some physical and chemical effects of the Cow Green (Upper Teesdale) impoundment
Authors: CRISP D. T.
Published: May 2006

SUMMARY. The paper describes observations on water temperature and dissolved oxygen in Cow Green reservoir and also changes caused by impoundment to temperature, chemistry, dissolved oxygen and the discharge regime of the River Tees immediately downstream of the dam.

Impoundment and river regulation have considerably smoothed‐out fluctuations in discharge of the Tees and have ehminated the very low and very high discharges which were characteristic of the natural river.

Reservoir water levels show an annual pattern of draw‐down during summer, refilling in autumn and overflow during winter and spring. Tliermal stratification of the reservoir occurs rarely and is generally of short duration. Water temperatures at mid‐reservoir correspond closely to those of water discharged from the reservoir. The temperature regime in the river downstream is modified as follows:

reduction in amplitude of annual temperature fluctuations by 1–2°C,

marked reduction of diel fluctuations, (3) delay of the spring rise in water temperature by 20–50 days and of the autumn fall by 0–20 days. These temperature changes could reduce the annual maintenance ration of a 10 g brown trout (Salmo trutta L.) by about 15% and delay the annual peak of metabolism by about 1 month. The effect upon growth rate of trout would be negligible.

Fluctuations in ionic content at the reservoir inflow are comparatively large and can be related approximately to river discharge. Fluctuations at the outflow are smaller and appear to be largely seasonal. Regulation has not appreciably altered the dissolved oxygen content of the River Tees.
Paleolimnology and trends in the phosphorus and iron budgets of an old man‐made lake, Barton Broad, Norfolk
Authors: OSBORNE P. L. , MOSS BRIAN
Published: May 2006

SUMMARY. Barton Broad, Norfolk is a shallow, eutrophic lake. During the last 30 years submerged macrophytes have declined and phytoplankton numbers have increased. This change is traced through the stratigraphy of a 60‐cm mud core. Diatom frustule counts of 1‐cm sections of the core showed that an epiphyte‐dominated diatom community was replaced by a planktonic community. From chemical analysis and radio‐isotope dating of the core, sedimentation rates and past phosphorus and iron loadings are estimated. Sedimentation rates were between 1.2 mm and 3.1 mm year−1 during the early part of the core but doubled in the 1950s to 5 mm year−1, doubled again in the 1960s and have increased to 12 mm year−1 in the 1970s. Retention of phosphorus in the sediment increased from 0.5 g m−2 year−1 to 18–21 g m−2 year−1 in two steps. A similar trend is shown for iron. The diatom species composition and chemistry of the core sections are correlated with increased nutrient loading and the decline of macrophytes. Contemporary phosphorus and iron budgets are calculated from inflow–outflow data and balanced using sediment retentions estimated from the core data. It is believed a large proportion of phosphorus and iron enters the Broad by movement of sediment along the river bed. A reduction of 25% of the 1975 phosphorus loadings would probably permit re‐establishment of some macrophytes. The present chemistry and algal communities of Barton Broad and the River Ant are described.
Substrate discrimination by larvae of the sessile rotifer Ptygura beauchampi Edmondson
Authors: WALLACE ROBERT LEE
Published: May 2006

SUMMARY. In an acid bog pond, the sessile rotifer Ptygura beauchampi was limited to the trap door areas of one of three distinct prey capturing organs of the carnivorous hydrophyte Utricularia vulgaris; four other co‐occurring congeneric species (U. gibba, inflata var. minor, intermedia, and purpurea) were not colonized. This pattern was not the result of differential capture of larvae by the prey traps. Laboratory settling experiments demonstrated that P. beauchampi larvae select this particular substrate to the exclusion of all others. This selectivity was independent of the presence of captured prey organisms in the traps.

P. beauchampi larvae select younger vestibules (trap door areas) over older ones. Observations of natural populations showed denser colonization of those slightly bigger traps closer to the plant stem. However, no relation was found between vestibular area and adult rotifer density. Selectivity for traps more proximal to the plant system was not demonstrated. In natural populations a distinct distribution of adults within the vestibule was noted. This pattern was statistically different from sites which the larvae colonize in laboratory experiments. Adult distribution is probably a modification of the larval settling pattern by site‐dependent survivorship of adults.

Larval settling experiments showed that larvae select uncolonized vestibules over those previously colonized of approximately equal age. Settling outside the vestibule area was highest on traps closest to the plant stem and was related to the density of adults colonizing the vestibule.

The adaptive significance of larval selection of a particular substrate is discussed.
Control of feeding behaviour and selective cannibalism in the rotifer Asplanchna
Authors: GILBERT JOHN J.
Published: May 2006

SUMMARY. Feeding responses in campanulate females of Asplanchna sieboldi were induced with filtrates of homogenized saccate female clonemates, showing that such behaviour can be triggered entirely by chemical stimuli. The failure of campanulates to attack campanulate clonemates, however, probably cannot be explained by the tissue chemistry of these females – filtered and unfiltered homogenates of campanulates were as active as those of saccates—and appears to be a function of some property limited to the campanulate body surface.

The roles of chemical and physical properties of food items in controlling feeding behaviour in Asplanchna and other rotifers are considered.
Influence of zinc on lotic plants
Authors: SAY P. J. , WHITTON B. A.
Published: May 2006

SUMMARY. The toxicity of zinc to Hormidium rivulare Kütz. in laboratory culture media is decreased by rises in the levels of magnesium, calcium and phosphate, and increased by rises in pH and cadmium. The effects of all these are sufficiently marked that they may be expected to have considerable importance in the field. In contrast, assays with sodium, chloride and sulphate showed no detectable influence of these ions on zinc toxicity.

When applied at higher concentrations, calcium was always more effective than magnesium, but the reverse was sometimes true at lower concentrations. Both magnesium and phosphate were more effective in reducing zinc toxicity with zinc‐tolerant populations than with zinc‐sensitive ones. Cadmium was highly toxic, either alone or in combination with zinc; however, calcium had a proportionately greater effect in reducing cadmium toxicity than zinc toxicity. The toxic effects of zinc and cadmium were synergistic, and it seems probable that the presence of cadmium at levels of 0.01 mgl−1 and above will usually lead to a significant increase in the toxicity of any zinc also present. Cadmium (in the absence of zinc) was 34 times more toxic than zinc to a zinc + cadmium sensitive population, and 15.5 times more toxic to a zinc + cadmium tolerant population. Because of the synergistic response, cadmium had an even greater effect in the presence of zinc.
Sampling and handling procedures for the polarographic measurement of oxygen in hypolimnetic waters
Authors: DAVISON W.
Published: May 2006

SUMMARY. A new method for collecting and handling water samples prior to their polarographic measurement is described. Its usefulness has been demonstrated by testing its ability to exclude oxygen from anoxic hypolimnetic samples. The criterion of detection was 15 μg1−1 of oxygen for the 95% confidence level. Different sampling and different handling procedures were compared, and only one overall method proved to introduce no significant contamination.
The digestion of cellulose and other dietary components, and pH of the gut in the amphipod Gammarus pulex (L.)
Authors: MONK D. C.
Published: May 2006

SUMMARY. Gut extracts from Gammarus pulex hydrolysed native and other cellulose substrates in vitro. Digestive fluid cellulase is probably endogenous as cell‐free fluid mediated cellulose hydrolysis, but no bacteria were isolated from the fluid which produced a detectable extra‐cellular cellulase. There was no apparent digestion of plant cell walls during their passage along the digestive tract, which took about 5–7 h at 10°C. The pH sensitivities of the digestive enzymes and the pH of the various regions of the gut suggest that carbohydrate digestion occurs in the proventriculus, midgut glands and anterior midgut, but protein digestion may be largely limited to the posterior midgut. The pH of the digestive fluid was altered slightly, but significantly, by the consumption of different natural and artificial test diets and by starvation. The most probable reason for the non‐digestion of plant cell‐walls is the lack of necessary enzymes other than cellulase. The role of cellulase may be confined to digesting the many small, non‐cellular particles which are present in the gut.
Feeding habits and diet in two populations of spined loach, Cobitis taenia (L.)
Authors: ROBOTMAM P.W. J.
Published: May 2006

SUMMARY. The feeding habits of Cobitis taenia were studied by means of monthly samples taken over a 2‐year period, October 1972‐October 1974, from two sites, one on the River Great Ouse at Newport Pagnell and the other at some neighbouring gravel pits. Dietury components, seasonal variation in these components, and seasonal and diurnal variation in feeding intensity were examined. The ecological niche of the food items and their size range are discussed, since both these factors appeared important in governing the micro‐habitat of the fish.

The feeding activity followed a seasonal cycle with little or no feeding in the winter and a high level of feeding activity in mid‐summer.

The diet showed a predominance of small food items, such as chydorids. copepods and rhizopods. These items varied in occurrence during the feeding period which appeared to be related to their own abundance, pointing to non‐seleclive feeding by the fish. The small size and benthic habits of the food items, many of which are closely associated with surface layers of mud and weed, indicated a preference by Cobitis taenia (L.) for feeding in this type ot habitat and on this type of food, in contrast to the stone loach. Noemacheilus barbatulus (L.), which is believed to inhabit stony areas and take larger food items.
Investigations on the meiofauna and sediment of the Shatt Al‐Arab near Basrah (Iraq)
Authors: ARLT GÜNTER , SAAD MASSOUD A. H.
Published: May 2006

SUMMARY. Sediment quality and meiofauna distribution were investigated in the Shatt Al‐Arab near Basrah (Iraq). Four stations were fixed in a transect reaching from the eulittoral to the main channel of the river. The sediment was investigated with respect to wet mud density, dry mud density, water content, organic matter, calcareous substances, and allochthonous inorganic materials. There were no major differences between the sediments taken at the different stations. Sediment quality was not a limiting factor for the distribution of meiofauna; important factors were water current, light penetration and temperature. The current has a great influence on sediment structure, the main channel of the river had harder sediment consisting of clay. Because of high turbidity, light can reach the bottom only in shallow water at stations I and II; macrophytes were present only at these two stations. The highest numbers of invertebrates were found at station II (0.5 m depth). As water depth increased, the abundance of meiofauna decreased. Nevertheless, the number of individuals at station I (0.05 m) in the tidal zone was lower than at station II. This fact can be explained by the magnitude of changes of the environmental conditions, especially temperature and insolation. There were very large diurnal temperature fluctuations, fluctuating between 10 and 25°C on a single day. Many meiofauna species cannot tolerate such fluctuations and colonize mainly the deeper reaches of the river, which are continuously covered by water. Stronger currents in the middle of the river prevent the settlement of large numbers of animals in this area.
Food and feeding habits ofMesocyclops leuckarti(Claus) in Lake Kinneret (Israel)*
Authors: GOPHEN MOSHE
Published: May 2006

SUMMARY.The diet and feeding habits of natural and cultured populations ofMesocyclops leuckartiwere studied. Nauplii and copepodid stages I–III are herbivorous. Copepodid stages IV–V and adults preferentially preyed uponCeriodaphniaandDiaphanosomawhereasBosminawas not preyed upon. Rate of predation onCeriodaphniaand newbornArtemianauplii was higher between 15–22°C than between 22–27°C. Under starvation conditions, the survival time for males was shorter than for females.
Field estimates of oxygen consumption for the brine shrimp Parartemia zietziana Sayce (Crustacea: Anostraca) in two salt lakes in Victoria, Australia
Authors: MARCHANT R. , WILLIAMS W. D.
Published: May 2006

SUMMARY. Oxygen consumption of P. zietziana was measured monthly in two saline (>60‰ salinity) lakes from November 1973 to November 1975 with short (<2 h) in situ incubations in BOD bottles. Tests in which oxygen decline was monitored continuously showed that there was no handling effect and respiratory rate was constant down to 1.8–1.9 mg O2 1−1, about 40% of the usual initial concentration. Incubations over 24 h demonstrated no diurnal fluctuations in oxygen consumption. Multiple regression analysis indicated that 90% of the variance in respiratory rate (R in mg O2x10−4h−1 individual−1) was accounted for by changes in salinity (3%; S in ‰), temperature (7%; T in °C) and dry weight (8%; W in mg × 10−3): log R =−1.123+0.0025+0.021 T+ 0.756 log W. From this equation and data on population density, population respiration was calculated: 91864.5 mg O2 m−2 year−1 in Pink Lake and 12367.5 mg O2 m−2year−1 in Lake Cundare.
Macrophytic vegetation of the River Swale, Yorkshire
Authors: HOLMES N. T. H. , WHITTON B. A.
Published: May 2006

SUMMARY. An account is given of the distribution down the River Swale in summer 1976 of 132 species of photosynthetic plants which are recognizable macroscopically. Some environmental data are included. The river may be regarded as falling into three zones, both with regard to its physical features and its type of vegetation. The upper zone has rocky substrata, fast flows and a macrophytic vegetation largely of bryophytes; the middle zone has unconsolidated substrata and the macrophytic vegetation is relatively sparse; the lower zone is silted and the macrophytic vegetation consists largely of angiosperms. The flora of the Swale is compared with that of the Tees, since eventually the former is likely to receive water from the latter as part of a major water transfer scheme. Eleven species of ‘river’ angiosperm which are present in the Tees above the projected abstraction point are absent from the Swale above the inflow point.
Fecundity and reproduction of perch (Perca fluviatilis L.) in Lake Agios Vasilios, Greece
Authors: PAPAGEORGIOU NICOLAOS K.
Published: May 2006

SUMMARY. In Lake Agios Vasilios, male perch become sexually mature during their first year of life whereas females become sexually mature during their second year. The mean absolute fecundity was 8080 eggs; values ranged from 2080 to 28488. The mean relative fecundity was 141 eggs/g body wet weight (ranging from 113 to 201). The absolute increase in weight of gonads is related to the age of the fish. The spawning period is from the middle of March to the beginning of April, at a mean water temperature of 8°C.