bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
Population structure, life histories and abundance of copepods in Tjeukemeer, the Netherlands
Authors: VIJVERBERG J. 
Published: May 2006

SUMMARY. The copepod zooplankton of Tjeukemeer was sampled at weekly intervals for 3 years (1969–1971), and ten species were recorded. Five species contributed more than 99% of all individuals collected. Acanthocyclops robustus is the most abundant species (66%), followed by Mesocyclops leuckarti (13%), Cyclops vicinus (11%), Eurytemora affinis (9%) and Diacyclops bicuspidatus (1%).The ecology of the A. robustus population in Tjeukemeer differs from other A. robustus populations in that it dominates the open water zone. This is an additional argument for a taxonomic revision of the A. vernalis‐robustus complex.Seasonal periodicity in abundance of each species was very similar in 3 successive years.All cyclopoid species went into diapause, A. robustus and M. leuckarti during winter, D. bicuspidatus and C. v. vicinus during summer. Most species diapause in a particular copepodite stage.The seasonal variation in the population structure, the fecundity and the sex ratio are described. Both population structure and sex ratio were influenced by diapause and size‐dependent mortality. The fecundity was more influenced by the water temperature and the age structure of the female population than by food situation or size of the females.
Selective feeding and its effect on polymorphism and sexuality in the rotifer Asplanchna sieboldi
Authors: GILBERT JOHN J. 
Published: May 2006

SUMMARY.
Campanulate females of A. sieboldi (clone 12C1) attack Asplanchna brightwelli and A. girodi much more readily than either the alga Volvox aureus or the rotifer Brachionus calyciflorus. Pre‐feeding campanulates on B. calyciflorus prior to testing does not appreciably affect their response to this prey. Discrimination during feeding occurs immediately after the campanulate's corona contacts a potential food organism and is probably mediated by chemoreceptors. Once a food organism is attacked, the probabilities of it being captured and subsequently swallowed are high and similar for each of the four organisms tested.Since food organisms other than Asplanchna. such as V. aureus and B. calyciflorus, induce campanulates in this clone to produce cruciform, and thus frequently sexual, females in succeeding generations, a tendency of these campanulates to select congeneric prey would favour the maintenance of the campanulate morphotype and thus the continuation of parthenogenetic reproduction in the ensuing population.
Effect of temperature on the hatching time of eggs of Ephemerella ignita (Poda) (Ephemeroptera:Ephemerellidae)
Authors: ELLIOTT J. M. 
Published: May 2006

SUMMARY.
Eggs of Ephemerella ignita (Poda) were kept at eight constant temperatures (range 5.9–19.8°C) in the laboratory. Over 85% of the eggs hatched in the temperature range 10.0–14.2°C but the percentage decreased markedly to 39% at 5.9°C and 42% at 19.8°C. Hatching time (days after oviposition) decreased with increasing water temperature over the range 5.9–14.2°C and the relationship between the two variables was well described by a hyperbola. Therefore, the time taken for development was expressed in units of degree‐days above a threshold temperature. Mean values (with 95%CL) were 552 (534–573) degree‐days above 4.25°C for 10% of the eggs hatched, 862 (725–1064) degree‐days above 3.57°C for 50% hatched and 1383 (1294–1486) degree‐days above 3.14°C for 90% hatched. These values can be used to predict hatching times at temperatures below 14.68°C for 10% hatched, 14.54°C for 50% hatched and 14.45°C for 90% hatched. At higher temperatures, the hatching time and the number of degree‐days required for development both increased with increasing temperature. Equations were developed to estimate the number of degree‐days required for development at these higher temperatures.Eggs were also placed in the Wilfin Beck, a small stony stream in the English Lake District. Maximum and minimum water temperatures were recorded in each week and the summation of degree‐days was used to predict the dates on which 10%, 50% and 90% of the eggs should have hatched. There was good agreement between these estimates and the actual hatching times. Only 10–15% of the eggs hatched between October and late February with most of the eggs hatching in March, April and May. Nymphs hatching in October and November probably did not survive the winter.
Trace elements in the Upper Fly River, Papua New Guinea
Authors: BOYDEN C. R. , BROWN B. E. , LAMB K. P. , DRUCKER R. F. , TUFT S. J. 
Published: May 2006

SUMMARY.
Measurements were made of calcium, magnesium and eight trace elements (Cu, Zn, Fe, Mn, Ni, Pb, Cd, Co) in waters, sediment and biota at eight sites in the Upper Fly River, Papua New Guinea. Determinations from streams draining an area rich in copper ore showed relatively low values for soluble copper and this was attributed to the small amount of ore exposed to weathering, heavy rainfall and high pH of water associated with the limestone bedrock. More iron was transported in a soluble form down a headwater tributary (Alice River) than in the Fly River but higher iron concentrations were associated with particulate matter in the Fly than in the Alice. The geochemistry of the catchment and the distance from the headwaters were important influences on the amount of particulate iron and its distribution between soluble and particulate forms.Levels of metals in the biota generally reflected the background concentrations of metals encountered at each site. Concentrations of Cu, Cd, and Zn were lower in starved invertebrates compared with unstarved individuals but no consistent changes were observed in Fe or Mn content.
Aspects of the ecology of Prymnesium parvum (Haptophyta) and water chemistry in the Norfolk Broads, England
Authors: HOLDWAY P. A. , WATSON R. A. , MOSS BRIAN 
Published: May 2006

SUMMARY.
Prymnesium parvum, an ichthyotoxic phytoplankter, has been recorded, at times abundantly, in the River Thurne, Norfolk, and its associated Broads. Its occurrence has been apparently more frequent and its population sizes probably larger since the late 1960s than previously and fish mortalities due to it now occur almost annually.The Thurne system is brackish and may have become more so, due to exploitation by drainage pumps, of a saline water table, in recent years. Evidence for this is conflicting, but in any case an increase in salinity is unlikely to have made increased Prymnesium growth more likely. Eutrophication of some Broads in the system is most likely to have increased the populations of Prymnesium since the late 1960s and data are presented on the present water chemistry of the system for comparison with previous records, and on current phytoplankton and Prymnesium crops in different parts of it. P. parvum has been isolated from the system as a unialgal culture and compared in morphology, salinity tolerance and ichthyotoxicity with a strain of P. parvum from Israel. The Broads strain differs slightly in size and pigmentation, but not in salinity tolerance. In culture it produces more ichthyotoxin than the Israeli strain.
The adaptive significance of cyclomorphosis in Daphnia: more possibilities
Authors: HEBERT PAUL D. N. 
Published: May 2006

SUMMARY.Morphological variability inDaphniapopulations has often been uncritically ascribed to phenotypic plasticity. For instance, detailed study revealed that the ‘cyclomorphic species’D. carinatas. l. was a complex of nine species. Several of these species often cohabit and seasonal change in their relative frequencies causes phenotypic cycles which mimic true cyclomorphosis. Intraspecific genetic variation in head shape also seems widespread and is likely to be important in explaining phenotypic changes in many single species populations.The hypothesis that helmet formation inDaphniais primarily related to predator avoidance is not supported by work on theD. carinatagroup. Seasonal trends in species composition can be explained without reference to differential predation. Natality differences exist between species with disparate head size suggesting that helmet formation may have direct effects on fitness. Two possibilities are considered. The length of the anterior adductor muscle is directly correlated with helmet size and such variation may affect swimming efficiency. In addition the laminar design of helmets suggests a role in gas exchange.
Dissolved organic carbon fluxes in the Shetucket River of eastern Connecticut, U.S.A.*
Authors: KLOTZ R. L. , MATSON E. A. 
Published: May 2006

SUMMARY.
Seasonal changes in dissolved organic carbon (DOC) concentrations were monitored biweekly for 1 year at seven stations in the Shetucket River watershed in eastern Connecticut, U.S.A. Nine monthly diurnal studies revealed 24‐h fluctuations of up to 53% of the seasonal range of 250–2200 μm DOC.Net DOC removal along a 1.9‐km stretch below a secondary sewage treatment plant (activated sludge effluent diluted to a final average volume of 1.4% in the river) ranged from 0 to 1600 and averaged 68 ± 64 mmol m−2 day−1. Removal of DOC further downstream could only be observed during a severe 3‐h October storm when net uptake ranged from 16 to 92 mmol m−2 h−1, using upstream‐downstream techniques. Oxygen respiration could account for about half of the net DOC removal during the October storm.Even though net uptake was somewhat greater than reported in other lotic studies, about 97% of the DOC potentially available to benthic heterotrophs was exported further downstream.
The natural prey of larvae of the damselfly, Ischnura elegans (Odonata: Zygoptera)
Authors: THOMPSON DAVID J. 
Published: May 2006

SUMMARY.
A method for determining the prey of a damselfly larva under natural conditions is described, with its shortcomings.Within the limits of the method, it would appear that Ischnura elegans consumes different prey items in roughly the same proportions as their occurrence in the field.Anomalous results are explained in terms of differences in encounter rates between predator and prey and/or ease with which prey can be handled.
The limnology of Cabora Bassa, Moçambique, during its first year
Authors: BOND W. J. , COE NANCY , JACKSON P. B. N. , ROGERS K. H. 
Published: May 2006

SUMMARY.
Cabora Bassa, a new impoundment in the Middle Zambezi River, was closed in December 1974, filling rapidly to 12m below full supply by May 1975.The lake, with five basins, lies along a west–east axis almost parallel to prevailing south‐easterly winds. Limnological records, from several stations along the lake axis, indicated homoiothermal conditions until September, the hot dry season. From then until records ceased in December, thermoclines and oxyclines were present in the deeper eastern basins. Hydrogen sulphide was recorded in hypolimnial waters towards the end of the year. Open water of the shallow, wind‐ and wave‐swept eastern basins remained oxygenated throughout the year.Water transparency increased fivefold from April to December, increasing too from east to west. pH was alkaline becoming more acid in cool winter months and in bottom waters of stratified basins. Conductivity ranged from 95 to 119 °S cm−1 with higher values in shallow lake margins. Chemical content of surface waters showed little seasonal or spatial variation and was, in general, comparable with pre‐impoundment levels.Duration of the initial ‘productive phase’ will probably be shorter than Kariba due to more rapid lake water exchange but indications are that productivity will be higher in the maturation phase.
Mortality patterns in trout (Salmo trutta and S. gairdneri) exposed to an anionic detergent in relation to concentration and mechanisms of toxic action
Authors: ABEL P. D. 
Published: May 2006

SUMMARY.
Histological and electron microscopical study of the gills of fish poisoned by the anionic detergent sodium lauryl sulphate indicates that the nature of the toxic action changes at a concentration of about 120 mg I−1. Toxicity tests were conducted to determine whether this change could be detected in the test data, using brown trout (Salmo trutta) and rainbow trout (S. gairdneri).Toxicity curves showed no indication of the change in toxic action, but at concentrations of 120 and 130 mg I−1 of sodium lauryl sulphate ‘split’ probit lines occurred, and the lines for 150 mg I−1 consistently differed in slope from other lines.
Comparative estimations of the energy content of fish tissue from bomb calorimetry, wet oxidation and proximate analysis
Authors: CRAIG J. F. , KENLEY M. J. , TALLING J. F. 
Published: May 2006

SUMMARY.
Four methods were used to determine the energy content of somatic tissues of Perca fluviatilis. Two forms of direct calorimetry (both adiabatic and non‐adiabatic) and wet (dichromate) oxidation gave similar results. When energy contents were calculated from proximate analysis using accepted conversion factors (9.45 cal mg−1 for lipid, 5.65 cal mg−1 for protein) results were higher than those from the other methods. The discrepancy was eliminated when a lower, directly determined energy content for the extracted lipid fraction was used.Some historic and technical aspects of the comparison are discussed.