bluuebunny/crossref_metadata_2025 huggingface dataset:
Host tree architecture mediates the effect of predators on herbivore survival
Authors: RIIHIMÄKI JANNE , VEHVILÄINEN HARRI , KAITANIEMI PEKKA , KORICHEVA JULIA
Published: May 2006

Abstract1. Vegetation structural complexity is an important factor influencing ecological interactions between different trophic levels. In order to investigate relationships between the architecture of trees, the presence of arthropod predators, and survival and parasitism of the autumnal mothEpirrita autumnataBorkhausen, two sets of experiments were conducted.

2. In one experiment, the architectural complexity of mountain birch was manipulated to separate the effects of plant structure and age. In the other experiment the trees were left intact, but chosen to represent varying degrees of natural complexity. Young autumnal moth larvae were placed on the trees and their survival was monitored during the larval period.

3. The larvae survived longer in more complex trees if predation by ants was prevented with a glue ring, whereas in control trees smaller canopy size improved survival times in one experiment. The density of ants observed in the trees was not affected by canopy size but spider density was higher on smaller trees. The effect of canopy structure on larval parasitism was weak; larger canopy size decreased parasitism only in one year. Until the fourth instar the larvae travelled shorter distances in trees with reduced branchiness than in trees with reduced foliage or control treatments. Canopy structure manipulation by pruning did not alter the quality of leaves as food for larvae.

4. The effect of canopy structure on herbivore survival may depend on natural enemy abundance and foraging strategy. In complex canopies herbivores are probably better able to escape predation by ambushing spiders but not by actively searching ants.
Temporal trends in phenology of the honey bee Apis mellifera (L.) and the small white Pieris rapae (L.) in the Iberian Peninsula (1952–2004)
Authors: GORDO OSCAR , SANZ JUAN JOSÉ
Published: May 2006

Abstract 1. The first adult appearance of two insect species, the honey bee Apis mellifera (L.) and the small white Pieris rapae (L.), was examined between 1952 and 2004 in Spain.

2. After factoring out the variability resulting from the broad geographical and topographical range of the 798 sampling localities, multiple regression models were used to detect temporal trends in phenology.

3. The best models were repeated, including spring temperature as the explanatory variable to examine the effects of climate on appearance phenology.

4. Both species showed similar temporal trends, delaying their appearance phenology until the mid‐1970s and advancing it since that time.

5. The appearance times for both species were negatively related to mean temperature between February and April, with both species appearing earlier in years with warmer springs.

6. The strong dependence of appearance dates on temperature indicates that climatic fluctuations are primarily responsible for the inter‐annual variability in spring appearance phenology of both species, and consequently account for the observed long‐term trends.

7. This study demonstrates that insect phenology is an accurate and sensitive bioindicator of climate change.
The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi
Authors: HELLAWELL J. M.
Published: May 2006

(1) Analysis of data from samples of chub taken at monthly intervals from two tributaries of the Herefordshire Wye revealed an annual cycle of scale growth with the formation ofa check during May or June. The frequency distributions of ages deter‐mined from scale checks and the length‐frequency distributions showed close simi‐larities. It was concluded that age determinations based on an examination of the scales were valid, provided care was taken in the identification ofthe first scale cheek. The maximum age observed was 15 years.

(2) Examination ofthe population structure revealed an overall sex ratio close to unity but there was a significant increase in the proportion of females in the 11 + and older age groups. Dominant year‐classes were observed. The strongest was 1959, which was attributed to exceptionally warm, dry, sunny weather during the period May‐September.

(3) Female chub grew more rapidly and attained greater ultimate size than the males. Changes in the pattern of growth during the life‐span were attributed to the attainment of sexual maturity, especially in the females. The length‐weight relation‐ships of the sexes diflFered slightly but were almost identical for the same sex in the two rivers studied. Seasonal variations in the growth‐rate were followed. Most rapid growth occurred after check formation in May or June and continued until September.
The biology of Oligochaeta from Dorset chalk streams
Authors: LADLE M.
Published: May 2006

Fewer species and more individuals of Tubificidae were present in the soft sediments of a polluted ditch than in the relatively unpolluted Bere Stream.

Changes in width frequency of natural populations of Tubifex tubifex and Limno‐drilus hoffmeisteri throughout the year were similar at both the sites investigated.

In laboratory experiments larger populations of Tubifex tubifex developed in fine sediments than coarse. By means of a width‐dry‐weight relationship it was possible to estimate the weight of the experimental populations.
Maximum and actual field feeding‐rates in larvae of the damselfly Pyrrhosoma nymphula (Sulzer) (Odonata: Zygoptera)
Authors: LAWTON J. H.
Published: May 2006

The paper presents information on factors influencing maximum feeding‐rates (measured in the laboratory) in larvae of the damselfly Pyrrhosoma nymphula, and compares estimates of feeding rates in the field with maximum feeding‐rates for larvae of the same size at the same temperature.

Maximum feeding‐rates in Pyrrhosoma larvae of different sizes were measured at 4, 5, 10 and 15°C. At low temperatures (4–5°C) maximum feeding‐rate was depressed more than predicted either from the effects of temperature on the gut‐clearance time of larvae or their respiratory rate. Maximum feeding‐rate declined steadily throughout metamorphosis in the final instar and stopped completely prior to emergence of the adult.

Feeding‐rates in the field were calculated from ‘balanced’ energy equations, i.e. from the sum of larval growth, respiration and the production of faeces and exuviae. Feeding rates in the field were always much less than maximum feeding‐rates for the same size of larva at the same temperature, and at the most were never more than 70% of the latter; they were closer to the maximum in summer than in winter, when they fell as low as 20% of the maximum.

The relevance of these findings to studies on the efficiency with which carnivores utilize energy in the field, and the importance of Odonata larvae as predators in aquatic ecosystems is discussed.
Spectral intensity in some Scottish freshwater lochs
Authors: SPENCE D. H. N. , CAMPBELL R. M. , CHRYSTAL J.
Published: May 2006

In the course of investigations on the ecology of submerged aquatic macrophytes a narrow‐bandwidth spectroradiometer has been used to measure underwater spectral intensity (390–750 nm) in a series of lochs approaching the extremes in optical and chemical properties of Scottish fresh waters. Cosine response and immersion‐effect properties of the collector were determined in the laboratory with a colUmated hght source. Diffuse attenuation coefficients, Ee, ranged from 0·55 in Loch Croispol, a calcareous loch, to 2·9 in Loch Leven, a lowland eutrophic loch. Underwater spectral intensity (1 m) relative to subsurface values show a proportional increase in short‐wave radiation in the blue‐green water of Loch Croispol, while the converse is true of the peaty brown water of Loch Uanagan. Attenuation coefficients were derived over 25 nm wavebands in Lochs Croispol, Leven and Uanagan. The water in the latter two lochs is optically similar although Leven is rich in phytopiankton and has an extinction peak at 675 nm. Uanagan represents the brown‐water type of loch most common in Scotland. Loch Croispol has attenuation coefficients for shorter wave‐lengths at least ten times lower than the other two lochs and only approaches their values at 750 nm. Croispol resembles Crater Lake, Oregon. The colour range at the maximum colonizable depths by rooted macrophytes of brown (Uanagan 4 m) to blue‐green (Croispol 6 m) water is equivalent to 196·0 and 230·6 kJ/Einstein (48·2 and 55·6 kcal/Einstein). Red/far‐red ratios even in plankton‐rich water (Leven) were at least three times the value for sunlight (1·3) and within the total photic zone reached three‐figure proportions. Possible implications for light‐sensitive seeds of aquatic species and for morphogenesis and zonation are discussed.
Molecule‐size distribution of soluble hiunic compounds from different natural waters
Authors: DE HAAN H.
Published: May 2006

It this study the use of Sephadex G‐25, Sephadex LH‐20 and CPG‐10‐75 for the separation of soluble humic compoutids frotn fresh water is tested.

It is shown by Sephadex G‐25 gel filtration that differences in molecule‐size distribution of soluble humic compounds in one lake at different titnes and between lakes can be predicted by E250 and E365 measurements.
Further studies on the occurrence of freshwater Microturbellaria in the British Isles
Authors: YOUNG JOHNSTONE O.
Published: May 2006

Macrostomwn johni sp. nov. from Llyn Cwellyn, N. Wales is described. The species has been recorded from the vegetational littoral in December and February only. The main distinguishing criterion is the penis stylet which consists of a funnel, about 80‐98 μm in length in slightly squashed specimens, curved in two planes and with a sub‐terminal distal opening, the distal end is blunt and cowl (hood) shaped. Other features include the presence of sensory hairs and rhabdoids all over the body, ‘Haft‐papillen’, and eyes. Rhammite tracks are weakly developed. The testes are elongate and the ovaries are compact, though slightly indented, and smaller than the testes. A very short ductus intervesicularis is present. The vagina is short. A ‘Verschlussap‐parat’ is present but poorly developed.
The use of acetone and methanol in the estimation of chlorophyll in the presence of phaeophytin
Authors: MARKER A. F. H.
Published: May 2006

(1)Where grinding or maceration of plant tissue is impractical, immersion in methanol should be used.

(2)The adaption to aqueous methanol of existing techniqus for distinguishing chlorophyll and phaeophytin in aqueous acetone was studied in detail. In methanol the spectra of both phaeophytin a and b were found to be pH sensitive. A method developed involving changes in absorbance at 665 nm is less precise than similar methods using acetone.

(3)The spectra of phaeophytin b in methanol at different pH levels are anomalous. Changes in absorbance between 440 and 410 nm cannot be used for the estimation of phaeophytin.

(4)Plant pigments can be transferred from methanol to aqueous acetone without degradation of chlorophyll. Modified standard techniques may then be used to measure chlorophyll a and phaeophytin a content.
A Lever‐Operated Ekman Grab
Authors: SLACK H. D.
Published: May 2006

A new type of Ekman Grab is described in which the need for a messenger weight is eliminated, improving its operation under non‐static conditions.
The biology of Simocephalus acutirostratus King (Cladocera: Daphnidae)‐laboratory studies of life span, instar duration, egg production, growth and stages in embryonic development
Authors: MURUGAN N. , SIVARAMAKRISHNAN K. G.
Published: May 2006

The life cycle of the cladoceran Simocephalus acutirostratus has been studied in the laboratory with reference to its total life span, duration of instars, egg production and growth. It has four pre‐adult and eighteen adult instars and produces about 248 eggs during a mean life span of 44 days within a temperature range of 28°C‐30°C. Egg production was found to be bimodal, with a sharp decline towards the end of the life cycle. The present results are compared and discussed with those of other tropical and temperate daphnids. It has been shown that while this species resembles most other daphnids (D. middendorffiana, D. pulex, D. carinata) in the growth pattern of pre‐adult instars, it resembles the temperate D. pulex in having a relatively long life span, relatively high egg production and slow rate of growth.

While studies on embryonic development of S. acutirostratus resemble the growth stages of the temperate Daphnia magna, there are differences in the total period of development between the two species. In the latter aspect, however, the present species closely resembles other tropical daphnids.
The seasonal periodicity of planktonic diatoms in a shallow eutrophic lake
Authors: REYNOLDS C. S.
Published: May 2006

The seasonal periodicity of four species of planktonic diatoms in a small eutrophic lake in the Shropshire‐Cheshire Plain, England, is examined. Diatoms typically dominate the spring increase; a second period of growth follows in the summer months. The growth phases are considered in relation to environmental factors in the mere. Of these, light levels appear to be critical in determining the onset of growth and the size of the population maxima, whilst stratification and turbulence play a leading role in the vertical distribution of the algae, and hence, of the growth conditions to which they are exposed. The thermocline is believed to provide a reservoir of diatoms in summer, maintaining them in a position where they are able to gain maximum advantage from increased wind‐induced turbulence. Relative specific differences in growth requirements and in behaviour under varying physical conditions are important in determining which species dominate. Dominance may be modified by the effect of attacks by fungal parasites. It is also shown that, generally, nutrients are present in relative abundance, and only rarely does their availability become a limiting factor. Tt is concluded that diatom growth in this lake is typically subject to physical rather than chemical control.
The reproductive biology of the leech Helobdella stagnalis (L.) in Utah Lake, Utah
Authors: TILLMAN DAVID L. , BARNES JAMES R.
Published: May 2006

The reproductive biology of the glossiphoniid leech Helobdella stagnalis in Utah Lake, Utah was studied for an 18‐month period from June 1970 to December 1971. In this lake it was found that the overwintering adult leeches produce two broods of young in May and June. Evidence is presented to support the idea that the same individual can produce two broods. Two complete cycles of gametogenesis also take place. Continuous water temperatures were recorded at the study site to correlate with reproductive activity. Gametogenesis appears to be temperature dependent with the first generation of sperm taking 4 months to be produced in the fall and winter months while the second generation of sperm is produced in 6 weeks during the spring. Egg production follows a similar pattem.
A preliminary check‐list of the phytoplankton of the Oshun River, Nigeria
Authors: EGBORGE AUSTIN B. M.
Published: May 2006

During hydrobiological investigations on the River Oshun, plankton samples were taken with a hand net of fine mesh for 14 months (May 1968‐June 1969). Thirty‐seven of the sixty species of algae identified have not been previously recorded in Nigeria. The qualitative character of the Oshun algae indicates the dominating nature of the floods in mixing bottom‐living and rock‐dwelling algae with the few euplanktonic species.
The occurrence of benthos deep in the substratum of a stream
Authors: DUDLEY WILLIAMS D. , HYNES H. B. N.
Published: May 2006

The vertical distribution of the benthic fauna of the Speed River, Ontario, was studied over a 13‐month period from October 1970 to October 1971. Various physical and chemical parameters of this interstitial environment were also measured.

Several new techniques for sampling the interstitial environment of rivers wert devised. These methods and their relative efficiencies are considered.

The validity of the terms ‘hyporheal’ and ‘hyporheic’ are discussed and the term ‘hyporheos’ is offered to replace the former.

A brief resume of interstitial sampling methods is given with comments on their limitations for sampling deep heterogeneous substrates.

Chemical parameters are thought to be more important in the control and distribution ofthe fauna than physical parameters.

It is suggested that many larvae of stream‐dwelling chironomids have over‐wintering stages when they penetrate deep into the substrate to: (a) actively feed on the trapped organic detritus; (b) follow an optimum temperature for development.

It is suggested that the shape of an organism determines its success as a hypo‐rheic form and examples are given.

The numbers of animals oecurring in the sub‐benthic populations are shown to be very large indeed. For the Speed River, estimates of between 184,760 and 797,960 animals/m^ are made for different times of the year. Dry weight biomass is estimated o t vary between 30 9 g and 253‐2 g/m^ throughout the year.

Sub‐benthic or hyporheic populations are shown to exist in at least three other Canadian rivers. Some ofthe animals found are shown to be common to two or more of these rivers.

The inefficiencies of many conventional benthic samplers in sampling the total biomass of certain streams with hyporheic populations is discussed.
Effects of the herbicide paraquat on the ecology of a reservoir
Authors: BROOKER M. P. , EDWARDS R. W.
Published: May 2006

Toxicity experiments indicated that changes in the fauna following the use of paraquat for weed control were likely to be indirect effects caused by the death and destruction of angiosperms. Generally, invertebrates living amongst the emergent vegetation in the margins of the reservoir and on the sediments were unaffected though the density of the benthic ostracod Cypridopsis vidua increased rapidly after the death of angiosperms. Of the planktonic invertebrates, those which were generally closely associated with the macrophytes were eliminated or survived at lower densities. Many of the invertebrates intimately associated with the angiosperms (e.g. Lepidoptera, Tricho‐ptera. Gastropoda) were lost completely or colonized the replacement growth of Chara globularis at reduced densities: these effects were extended to the year after treatment. A few species colonizing Chara were able to establish densities comparable with those found on the angiosperms in the pre‐herbicide period but in some cases the time of peak density was delayed.

Data from fish gut analyses indicated that there was a change in the diet of the eel following the death of the angiosperms and that this was largely a reflection of the loss, or reduction in density, of many invertebrates associated with the angiosperms.
Observations on some predators of stream‐dwelling triclads
Authors: WRIGHT JOHN F.
Published: May 2006

A serological technique was used to demonstrate that one species of trichopteran and three species of plecopteran nymphs were feeding on stream‐dwelling triclads. Observations on streams in Caernarvonshire, North Wales, suggested that, in general, these predators were not typical members of the fauna at springheads, where triclads were frequently abundant. In contrast, further downstream the presence of predators was considered to be one of a number of factors which contributed to lower population densities of triclads. However, two small stony streams were encountered where the plecopteran predator Dinocras cephalotes occurred in close proximity to stream‐dwelling triclads from the springhead downwards. In one, both predators and prey were found at all stations but highest triclad numbers were recorded where predators were few. In the second stream the population density of the predator was higher, and here, triclads were very scarce on the undersides of stones and were almost entirely confined o t patches of moss. It appears that the predators may be both limiting the micro‐distribution of the triclad and also perhaps feeding selectively on larger individuals since mature triclads were rare, except at the springhead.
Studies on Plover Cove Reservoir, Hong Kong
Authors: TAI Y. C. , HODGKISS I. J.
Published: May 2006

The four periphytic communities established in Plover Cove Reservoir (the epiphyton, epihthon, epipelon and epipsammon) were investigated between November, 1970 and December, 1971. A rich flora of diatoms was found to dominate all four peri‐phytic communities, and, for this reason, assessment of diatom numbers was used to monitor each community during this survey.

The standing crop of each community, measured by cell counts and by chlorophyll a determinations, showed distinct seasonal patterns. Except for the epipsammon, each community displayed a maximum growth in winter, a moderate spring and autumn growth period and a low summer growth. The episammic flora stood apart from the other attached floras in that it exhibited a prolonged maximum growth period in summer.

Relatively small numbers of species were found to form the main bulk of all four communities (the so‐called ‘constant forms’) and these belonged predominantly to the pennate genera Achnanthes, Fragilaria, Nitzschia and Synedra.
Seasonal variation in the catching power of traps used for perch, Perca fluviatilis L.
Authors: CRAIG J. F.
Published: May 2006

The number of perch caught weekly in traps set in Slapton Ley, Devon has been considered. Five traps were laid in each of six regions during 1970 and 1971. The numbers caught in each region were averaged for eight lifts during 8 weeks and the logarithms of these numbers calculated. The figures obtained showed marked seasonal trends in the catch of the traps and these trends were consistent when both years were compared. If single traps were considered there was marked variability at one time which was attributed to differences in habitat. However, the combined data from each region did give a good comparison of the density of perch between regions.
Chemistry and vegetation of highly acidic streams
Authors: HARGREAVES J. W. , LLOYD E. J. H. , WHITTON B. A.
Published: May 2006

An account is given of the water chemistry and photosynthetic flora of waters in England with a pH value of 3.0 or less. Of the fifteen sites found, thirteen were associated with coal‐mining, one with a barytes mine and one was an industrial effluent. Flowing waters predominated, but in some cases pools in direct contact with the streams were also present. All waters carried high levels of heavy metals and silicate, and most carried moderately high levels of phosphate and combined inorganic nitrogen. The total flora consisted of twenty‐four algae, two mosses and two flowering plants. Of these, three algae and one flowering plant were found in pools only. Euglena mutabilis was both the most widespread species, and often also the most abundant. The number of species present in a reach showed a positive correlation with pH during late summer, and a negative correlation with total acidity in winter. Only four of the algal species found in England are certainly included in the U.S.A. literature. Some, but not all, the apparent differences between the two floras are very probably due simply to taxonomic problems.
The distribution and diel vertical migration of Pseudodiaptomus hessei (Mrázek) (Calanoida: Copepoda) in a subtropical lake in southern Africa
Authors: HART R. C. , ALLANSON B. R.
Published: May 2006

The vertical distribution and diel migratory behaviour of Pseudodiaptomus hessei in a freshwater lake is described. All stages showed a pronounced diel migration.

During daylight naupliar and copepodite instars were almost exclusively benthic in shallow areas (<10m). Copepodite V and adult stages were predominantly benthic even at 40 m. The diurnal vertical distribution pattern implies age‐related differences in photosensitivity and a possible depth‐regulatory mechanism, based on the existence of differential photosensitivity, is offered to account for day‐depth control.

Nocturnal vertical distribution, studied approximately fortnightly during 1970–71, showed no clear seasonal variation. Variations in pattern, most obvious in adult instars, correlated with prevalent lunar conditions. Nocturnal or midnight sinking was evident, particularly in post‐naupliar stages.

Dusk rise and dawn descent were performed at very low light intensities and paralleled changes in light penetration. Dawn descent was less rapid than the dusk rise. An ephemeral dawn rise was sometimes observed but was not a consistent feature of all stages. An endogenous rhythm of locomotor activity was recorded under laboratory conditions. Activity was low during daylight, increased sharply at dusk and then decreased through the night to reach daytime levels at dawn. The stimulus provided by changes in light intensity and/or endogenous activity changes can account for the dusk and dawn movements of P. hessei but a definitive identification of the direct migratory stimulus is not possible. Attention is called to a closer examination of the role of endogenous activity rhythms in vertical migratory behaviour.

The possible adaptive value of vertical migration to P. hessei is examined briefly.
A hand‐operated in situ water sampler
Authors: ABDULLAH M. I. , TENNANT R. H.
Published: May 2006

A hand‐operated water sampler designed specifically for dissolved gas studies in lakes, lagoons and other shallow water is described.
Planktonic diatoms and silica in Loch Leven, Kinross, Scotland: a one month silica budget
Authors: BAILEY‐WATTS A. E.
Published: May 2006

Diatom populations and silica concentrations were monitored at frequent intervals in the shallow, eutrophic Loch Leven over a 27‐day period (October 1972) and the influences of the inflows, outflow and the sediment were assessed. Changes in dissolved and particulate silica are accounted for by incorporating the results into a silica budget.

During this period processes affecting silica within the loch were more important than those outside. The incorporation of diatom frustules into the sediments and the release of dissolved silica from the sediments appeared to be of particular importance. Evidence suggests that dissolution of the frustules of some planktonic diatom species was also important.
A quantitative study of the invertebrate fauna of the River Tees below Cow Green Reservoir
Authors: ARMITAGE PATRICK D.
Published: May 2006

Monthly samples were taken in the River Tees below Cow Green dam from four sites differing in flow conditions, by means of trays containing stones from the river, which were immersed for a period of 1 month. Information on the distribution, abundance and biomass of the benthos of the River Tees is given with additional data on the life‐histories of some of the more common species, during the period May 1971 to May 1972.

Of the seventy‐two taxa found, fourteen made up 95% of the total numbers. Hydra, Polycentropodidae, and the molluscs Limnaea peregra and Ancylus fluviatilis were the most abundant animals in the slower‐flowing water (10–26 cm s−1) and Simuliidae, Orthocladiinae, and Baetis rhodani dominate the riffle (50–75 cm s−1) fauna numerically. Some organisms, Nais spp., Caenis rivulorum and Baetis scambus favoured intermediate flows of 20–60 cm s−1. The slowest‐flowing water contained the largest number of taxa and the site with the fastest flow supported the least. A mean monthly weight per square metre of 14·56 g (95% limits from 7 to 31) was calculated using data from all four sites.

The frequency distribution of nymphal size‐classes is given for B. scambus, C. rivulorum, Ephemerella ignita, and Brachycentrus subnubilus, and the association of certain nymphal size‐classes with a particular site is analysed.

The composition and distribution of the fauna is discussed. It is suggested that the relative richness of the fauna in terms of biomass is attributable to the organic enrichment of the river following the building of the Cow Green dam. The regulation of the flow has allowed the dense growth of algae and mosses, and the development of large molluscan populations, and the reservoir itself provides a rich source of food, particularly zooplankton and phytoplankton, for the river benthos.
The chemical composition and energy contents of copepods and cladocerans in relation to their size
Authors: VIJVERBERG J. , TH. FRANK H.
Published: May 2006

The chemical composition and energy contents of four different species of cladocerans, one species of a calenoid copepod, and mixed samples of four species of cyclopoid copepods were quantitatively determined.

The relative chemical composition, expressed as a percentage of the total organic matter (excluding chitin) of each of the different species analysed, were very similar. The mean relative composition for all species was 71·2% protein, 9·5% carbohydrates, 19·3% lipids, 16·5% total nitrogen and 2·1% total phosphate–phosphorus. A substantial amount of the total nitrogen was found to be non‐protein nitrogen (mean of 23·3% of total nitrogen). The calorific value was calculated from the estimated amounts of proteins, carbohydrates and lipids using conversion factors. The relationship between the calculated organic matter and the chemical oxygen demand (COD) was found to be constant and did not vary much for the different species. The ratio of total organic matter to COD has a mean value of 0·51. Calorific values ranged from 5847 to 6353 cal/g total organic matter.

The amounts of chemical substances or energy contents per individual Copepoda or Cladocera were calculated. Regression lines together with their correlation coefficients have been computed to describe the relationship between the amount of chemical constituents and energy contents per individual, and the length of the individual. The results are extensively compared with those given in the literature and differences are discussed.
Actinomycetes in lake muds: dormant spores or metabolically active mycelium?
Authors: JOHNSTON D. W. , CROSS T.
Published: May 2006

Homogenization and ultrasonication experiments on samples of lake muds indicated that Micromonospora strains were present as a mixture of mycelium and spores. In contrast, strains of streptomycetes and nocardioforms appeared to be in the form of arthrospores or fragmentation spores respectively.

Micromonospora strains originally isolated from lakes were able to grow in both native and enriched muds incubated in the laboratory. Numbers of streptomycetes and nocardioforms did not increase in these muds and are presumed to be relatively inactive in this habitat.

We postulate that Micromonospora strains have an active role in the lacustrine environment as well as in soil.
The distribution of cellulase in freshwater invertebrates of different feeding habits
Authors: MONK D. C.
Published: May 2006

Twenty‐six species of freshwater invertebrates were assayed in vitro for cellulase activity. A soluble cellulose derivative and crystalline cellulose powder were weakly hydrolysed by gut extracts from several insects, and more strongly hydrolysed by extracts from molluscs and crustaceans. There was no correlation between the occurrence of cellulase and the abundance of cellulose in the diet.
The light‐climate of Loch Leven, a shallow Scottish lake, in relation to primary production by phytoplankton
Authors: BINDLOSS MARGARET E.
Published: May 2006

Seasonal changes in incident irradiance and underwater light penetration at Loch Leven from 1968 to 1971 are discussed in relation to the photosynthetic behaviour and crop density of phytoplankton.

Light extinction was highest in the blue and lowest in the orange spectral regions, a pattern typical of other turbid waters. Euphotic depth varied between 1·2 and 7·4 m and was on average c. three times the Secchi disc transparency. Underwater light extinction depended chiefly on phytoplankton crop density (estimated as chlorophyll a). Despite the shallowness and wind‐exposed situation of the loch there was no evidence of appreciable light extinction due to sediment disturbance. Possible causes of variability in the relationship between the minimum vertical extinction coefficient (k min) and the concentration of chlorophyll a are discussed.

The value of ks, the increment in kmin per unit increment in algal concentration, was estimated from field data as 0·0086 In units per mg chl a/m2 and from laboratory spectroradiometer data as 0·0079 In units per mg chl a/m2. These ks values imply theoretical upper limits for the amount of chlorophyll a in the euphotic zone (Σn max) of 430 and 468 mg chl a/m2, respectively. Observed euphotic chlorophyll a contents (Σn) were sometimes close to these upper limits.

Typical photosynthesis/depth profiles are described. Profile area is shown to be related to the logarithm of the ratio between surface‐penetrating irradiance (Io') and the irradiance (Ik) defining the onset of light‐saturation of photosynthesis. Standardized profiles, plotted on a common scale of ‘optical depth’, are used to illustrate the relatively minor influence of variations in Io' and Ik on hourly rates of photosynthesis per unit area.

The saturation parameter (Ik) generally increased as photosynthetic capacity (Pmax) increased; the temperature‐dependence of Ik is explained by the temperature‐dependence of the enzyme‐controlled (dark) reactions of photosynthesis, which control Pmax.

A spring peak in the ratio between surface penetrating irradiance (Io') and Ik is interpreted as a result of a lag in the seasonal increase in water temperature with increase in surface irradiance.

The gradient (K') of the linear light‐limited region of the photosynthesis‐irradiance curve showed little variation and had an average value of 0·31 mg O2/mg chl a.h per 1 W/m2 (PAR).

Interactions between mixed depth, underwater light extinction and phytoplankton productivity are discussed; comparisons are made with other shallow, optically deep lakes.
In defence of average cohorts
Authors: BENKE ARTHUR C. , WAIDE JACK B.
Published: May 2006

SUMMARY. Hynes & Coleman (1968) proposed a method for estimating benthic secondary production for use with populations in which cohorts cannot be distinguished and for use with unidentified benthos. Hamilton (1969) corrected and refined the method, emphasizing the concept of the average cohort. Zwick (1975) recently suggested the method should not be used since: (1) too many conditions need to be filled for use with unidentified material, and (2) it is strongly dependent on growth patterns. This paper shows that Zwick misinterpreted the concept of the average cohort, and his apparent invalidation of the method due to dependence on growth patterns is erroneous.
A study on diapause of zooplankton in a tropical river ‐ The Blue Nile
Authors: el MOGHRABY A. I.
Published: May 2006

SUMMARY. The zooplankton of the Blue Nile overcomes the adverse conditions of the flood by entering into a state of diapause. Resting stages were found in the river bottom, flowing water and rain pools. They were blown to different localities by wind and can withstand long periods of desiccation. Some species of zooplankton go into diapause more than once a year, notably during their seasonal peaks of abundance. Release from diapause occurred in the temperature range 20–30°C and was facilitated by longer photoperiods and decreased concentrations of suspended silt. Various species of zooplankton were induced in facultative diapause when stored in complete darkness.
Increased sensitivity in the measurement of ATP in freshwater samples with a comment on the adverse effect of membrane filtration
Authors: JONES J. G. , SIMON B. M.
Published: May 2006

SUMMARY. Increased sensitivity in the determination of ATP in fresh water and sediment samples was achieved by incorporating protein, EDTA and extra luciferin in the reconstruction of the firefly lantern preparation. Maximum recovery was only obtained when samples were extracted in actively boiling Tris buffer. The method was sufficiently sensitive for the determination of ATP in 1 ml water samples injected directly into the boiling buffer. Concentration of water samples on membrane filters, even volumes as small as 1 ml, caused a significant drop in the ATP recovered. This was thought to be due, at least in part, to cell lysis and the concentration of interfering detrital material on the membrane. Further interference was observed when sediment samples were analysed. This was only partly overcome by dilution of the sample and the importance of the inclusion of internal standards (bacterial cultures) is emphasized.
Effect of food type on the acute and chronic toxicity of copper to Daphnia magna
Authors: WINNER ROBERT W. , KEELING THEODORE , YEAGER ROBERT , FARRELL MICHAEL P.
Published: May 2006

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin‐enriched algae were less sensitive to a chronic copper stress than animals fed a trout‐granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r, the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal‐fed animals, 0.12 for animals reared on trout‐granules). In contrast to chronic toxicity, 72 h LC50 values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.
Distribution of the brine shrimps Parartemia zietziana Sayce and Artemia salina (L.) along a salinity and oxygen gradient in a South Australian saltfield
Authors: MITCHELL B. D. , GEDDES M. C.
Published: May 2006

SUMMARY. The seasonal distribution of Parartemia zietziana and Artemia salina was studied in a South Australian saltfield. P. zietziana occurred alone at salinities from 112 to 214%‰ and A. salina occurred alone at salinities above 285%‰; the two species overlapped in the range 214 to 285%‰. Respiration experiments indicated that A. salina had a lower ‘critical’ oxygen concentration than P. zietziana, apparently due to the presence of haemoglobin in A. salina. This may result in an adaptive advantage at high salinity and low dissolved oxygen.
Geometric mean shape of the shell in lacustrine and riverine limpets,Ancylus fluviatilisMüller
Authors: SUTCLIFFE D. W. , DURRANT P. M.
Published: May 2006

SUMMARY.Geometric mean (GM) shell shape in populations of limpets from three rivers was compared with that of populations from two lakes in England. The GM ratio of width on length was 0.78 in both river and lake limpets, but they respectively had GM ratios of 0.55 and 0.47 for height on width. The difference was compared statistically by prediction of mean values for height and width using linear logarithmic regressions. Shell height was significantly different (P0.05) in river limpets, which were about 20% taller than lake limpets at shell widths of 5.0–6.0 mm. The relationship between shell height and width or length was allometric in limpets from two rivers and isometric in a lake population. Similar results and conclusions were obtained using the GM regression (Teissier, 1948; Ricker, 1973) and the ordinary predictive regression.
The temporal and spatial distribution of the valves of the diatom Rhoicosphenia curvata in the River Wey
Authors: MOSS M. O.
Published: May 2006

SUMMARY. During a study of the seasonal changes in the diatom flora of the River Wey, Surrey, it was found that valves of Rhoicosphenia curvata (Kütz.) Grunow were usually present in samples collected in the stretch of the river between Tilford and Guildford but not in any significant numbers either upstream or downstream of this region. More detailed study showed that a tributary, the Farnham Wey, was the source of this particular diatom and that downstream of the confluence of these rivers the numbers steadily decreased. Valves of Rhoicosphenia curvata were most numerous in suspension in the river during the summer months, although the living organism is an epiphyte growing and dividing vigorously during the early spring and even in late winter. It is suggested that dead cells and detached valves are released into the river, from its tributary, during the summer, there being no evidence that this organism can actively divide or survive as a member of the river plankton. The valves form a convenient marker for the mixing of two distinct bodies of water.
Some observations on the use of the in vivo fluorescence technique to determine chlorophyll‐a in natural populations and cultures of freshwater phytoplankton
Authors: HEANEY S. I.
Published: May 2006

SUMMARY.
The variation in the ratio (R) between cellular fluorescence of chlorophyll‐a and unit extractable chlorophyll‐a was examined with natural populations of phytoplankton and unialgal cultures. Photo‐inhibition of in vivo fluorescence was observed al high values of irradiance with natural populations and in algal cultures, except with blue‐green algae. If samples were dark‐adapted (< 6 W m−2) before measurements were made, changes of fluorescence due to photo‐inhibition could be minimized. Measurements of in vivo fluorescence with dark‐adapted samples of phytoplankton, dominated by species showing large values of R, gave significant correlations (P< 0.001) with determinations of chlorophyll‐a concentration over periods of several weeks.

The values for R for blue‐green algae were appreciably lower than for other algal groups. This, and their lack of photo‐inhibition effects at high irradiance values, are attributed to the association of most of chlorophyll‐a with photosystem I which fluoresces weakly compared to chlorophyll‐a in photosystem II. The significance of these findings for ecological studies is discussed.
The distribution of some freshwater planktonic bacteria in two stratified eutrophic lakes
Authors: JONES J. G.
Published: May 2006

SUMMARY.
Changes in bacterial populations and certain physical and chemical variables in Esthwaite Water between June and September 1975 were studied and compared with results obtained from 1972 to 1974 in the hypolimnia of Blelham Tarn and the Lund tubes. The counts of total bacteria ranged between 1 and 7 × 106ml−1 and were highest in the anoxic hypolimnion. The bacterial genera examined in more detail constituted only a small percentage of this count and included Ochrobium (104ml−1), Naumanniella (103ml−1), Leptothrix (102ml−1), Planctomyces (103ml−1), and Metallogenium (102ml−1). The iron bacteria appear to grow best in the oxycline where there was not only sufficient oxygen for aerobic growth but also a plentiful supply of reduced iron. Planctomyces numbers increased as the thermocline became depressed in September. The results from Blelham Tarn might be interpreted as further evidence of growth by iron bacteria in the absence of dissolved oxygen, but other explanations are possible. Examination of the results by multiple regression analysis showed that it was possible to explain a significant proportion of the bacterial variation (with the notable exception of the Planctomyces counts) in spite of considerable intercorrelation of the regressor variables.
Effects of temperature on gut‐loading and gut‐clearing times of the burrowing mayfly, Hexagenia limbata
Authors: ZIMMERMAN MELVIN C. , WISSING THOMAS E.
Published: May 2006

SUMMARY.
The effect of temperature on gut‐loading times, gut‐clearing times, and the calculated ingestion rates, egestion rates, and consumption indices of the deposit‐feeding burrowing mayfly, Hexagenia limbata, were investigated in laboratory experiments. Rates of movement of two natural sediments of differing colour through the digestive tract were monitored to quantify feeding intensity when ambient water temperatures approached 5, 10, 15, 20, and 25°C.

At each temperature, gut‐loading times (GLT) and gut‐clearing times (GCT) increased as nymph length increased. Mean GLT and GCT values decreased as temperature increased from 5 to 20°C but were longer at 25°C than at 20°C. Relationships between GLT, GCT, and length of nymphs and temperature were best described by multiple regression equations. No diel variation in gutclearing times was observed. Low water temperatures resulted in lower ingestion and egestion rates and consumption indices. At most temperatures nymphs ingested over 100% of their dry body weights per day.
Sexual swarms in Daphnia magna, a cyclic parthenogen
Authors: YOUNG J. P. W.
Published: May 2006

SUMMARY.
Dense swarms were observed in a population of Daphnia magna (Crustacea: Cladocera). The swarms appeared during a sexual period in which females were abundant but males were rare. Each swarm contained several males and large numbers of ‘imminently sexual’ females, a class of females that was rare except in the swarms. This implies that both sexes respond to attractant stimuli, and that the female response occurs only during a brief critical phase in the ovarian cycle.
The food of adult copepods from Lake Kainji, Nigeria
Authors: CLARKE N. V.
Published: May 2006

SUMMARY.
Gut contents of adult copepods from Lake Kainji were analysed. The calanoid copepod Tropodiaptomus banforanus was exclusively herbivorous with Melosira and Peridinium forming a large proportion of the diet. Of the cyclopoid copepods, Mesocyclops leuckarti was mainly carnivorous while the smaller Thermocyclops neglectus was mainly herbivorous. Experiments with Diplocystis (Microcystis) showed that it was not ingested by these three copepod species even after starvation and possible explanations for the results are discussed.
The distribution and growth of coarse fish in gravel‐pit lakes in south‐east England
Authors: GEE ALUN S.
Published: May 2006

SUMMARY.
Age and growth rates of the coarse fish of thirty‐nine gravel‐pit lakes in south‐east England are compared. Species composition was very variable, the commonest species being roach (Rutilus rutilus), bream (Abramis brama), tench (Tinca tinca), perch (Perca fluviatilis) and pike (Esox lucius). Two main kinds of fish community were identifiable from the survey: (1) those consisting of a mixture of cyprinids, usually roach and bream; and (2) those in which cyprinids were rare or absent and the fish community was composed of perch and pike. The majority of the lakes fell into the first category. Comparison of growth curves derived by back‐calculation showed that, in all species, variation occurred from lake to lake and from year to year. The majority of gravel‐pit lake fishes had ‘medium’ growth rates when compared with published data by other workers on different waters. Seasonal growth of roach infected with plerocercoids of Ligula intestinalis was observed at monthly intervals. Annulus formation on the scales of these fish occurred at the onset of growth in May. The heavy Ligula burden in 89% of these fish had not caused the formation of any additional or false rings.
Benthic diatom distribution and grazing by Sarotherodon mossambicus in Lake Sibaya, South Africa
Authors: BOWEN STEPHEN H.
Published: May 2006

SUMMARY.
Distributions of benthic diatoms and benthic floc in Lake Sibaya were examined to determine if preferential grazing by juvenile Sarotherodon mossambicus on benthic detrital aggregate in shallow water maximized diatom concentrations in the diet of the fish. Between 0.1 and 12.0 m depth, the range of diatom densities was 1–60 × 104 cells cm−2 with high but extremely variable densities above 3 m and consistently low densities at greater depths. Light intensity and burial by wave action appear to be primary factors affecting diatom abundance, but the effect of unidentified factors causing local patchiness is also evident. Substrate stabilization by diatoms was observed between 0.3 and 1.8 m depth. Weight of benthic detrital aggregate generally increased with depth such that diatom concentrations were variable above 3 m but were extremely low in benthic detrital aggregate at greater depths. Comparison of diatom concentrations in fish stomachs and benthic detrital aggregate shows that within the shallow waters, fish do not selectively graze those areas richest in diatoms.