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  • 1
    Digitale Medien
    Digitale Medien
    The distribution and diel vertical migration of Pseudodiaptomus hessei (Mrázek) (Calanoida: Copepoda) in a subtropical lake in southern Africa (1976)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 6 (1976), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2427.1976.tb01603.x
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  • 2
    Digitale Medien
    Digitale Medien
    A dissolved oxygen budget model for Lake Erie in summer (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 15 (1985), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: SUMMARY. 〈list xml:id="l1" style="custom"〉1In this paper we extend a vertical mixing model of Lake Erie with an oxygen budget model. The model was tested against data gathered in the summers of 1979 and 1980 with good results, showing that it is capable of simulating vertical distributions of temperature and dissolved oxygen over relatively short time periods.2The results underline the importance of turbulent mixing in distributing oxygen throughout the water column in the Central Basin of the lake. In addition, the results indicate that production and respiration processes dominate the budget under the influence of low wind speeds, while surface fluxes dominate during periods of high wind.3Bottom mixing delays the onset of anoxic conditions at the sediment/water interface by distributing the sediment demand over the 5–6 m depth of the bottom mixed layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2427.1985.tb00242.x
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  • 3
    Digitale Medien
    Digitale Medien
    The fine structure of the periphyton of Chara sp. and Potamogeton natans from Wytham Pond, Oxford, and its significance to the macrophyte-periphyton metabolic model of R. G. Wetzel and H. L. Allen (1973)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 3 (1973), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The fine structure of the periphyton of Chara sp. from Wytham pond, Oxford, is examined using transmission and stereoscan electron microscopy. As a result of this investigation the structural proximity of each periphyte component as required by Wetzel and Allen's metabolic model of macrophyte-periphyton interaction is amply confirmed. The application of stereoscan electron microscopy to a study of feeding in periphyton consumers is also examined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2427.1973.tb00075.x
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  • 4
    Digitale Medien
    Digitale Medien
    The growth of Tilapia mossambica Peters (Pisces: Cichlidae) in Lake Sibaya, South Africa (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 6 (1974), S. 0 
    Details
    ISSN: 1095-8649
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The scales of Tilapia mossambica Peters* from Lake Sibaya show clear rings formed by broken, widely-spaced circuli in the anterior field. In order to determine the rate and time of scale ring formation, the number of circuli in the marginal increment was determined. Five scales from the pectoral region of 2223 fishes caught at regular intervals over two years were examined. When plotted as histograms, the number of circuli in the marginal increment showed a sharp movement to the left in September–October and again in January, indicating that the rings were formed during these months in the majority of fish examined. Pre- and postbreeding feeding migrations, and increases in condition factor, were associated with scale ring formation. Otoliths and opercula were also examined for age determination. Annual length increments were calculated for 450 T. mossambica collected throughout the year, and growth curves plotted. T. mossambica from Sibaya reach maturity after one year at a standard length of about 8 cm in females, and after two years at 10 cm in males. The breeding population had a standard length mode of 11–12 cm in females and 17 cm in males. The maximum final size was about 24 cm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1095-8649.1974.tb05113.x
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  • 5
    Digitale Medien
    Digitale Medien
    The influence of exposure to low temperature on Tilapia mossambica Peters (Cichlidae). (1971)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 3 (1971), S. 0 
    Details
    ISSN: 1095-8649
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: In the cichlid teleost Tilapia mossambica secondary chill coma following exposure to 11° C in freshwater is associated with decreases in plasma osmolarity, sodium and chloride ion concentrations. Fish exposed in seawater diluted to give a NaCl concentration of 5%0 show no signs of coma nor are there decreases in osmolarity or sodium and chloride ion concentrations.It is suggested that the restrictions of T. mossambica to estuaries at the southern end of its distribution in southern Africa relates to the maintenance of near normal sodium and chloride ion concentrations at low temperatures during winter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1095-8649.1971.tb03661.x
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  • 6
    Digitale Medien
    Digitale Medien
    Temperature tolerance of the estuarine prawn Upogebia africana (Anomura, Crustacea) (1971)
    Springer
    Marine biology 11 (1971), S. 337-343 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Continuous temperature measurements were made in a typical South East African estuary. Mean summer (November to March) temperatures were in the range 19° to 24°C, and in winter (June to August) from 13° to 16°C. Large daily temperature fluctuations of 6° to 10°C occurred in summer; these appear to result from tidal movement of cool sea water into the estuary. In winter, temperature fluctuations were much smaller (3° to 5°C). The burrowing prawn Upogebia africana (Obtmann) was found to have an upper lethal temperature of 29°C in both winter and summer. The resistance time of prawns to temperatures above 30°C was much greater in summer than in winter. It was possible to acclimate winter prawns and increase their resistance time to a level comparable to that of summer individuals. A latent period of 40 h occurred before acclimation effects were detectable. Long-term exposure of prawns to high temperatures did not increase their resistance above that of summer prawns. Water at a temperature above this upper lethal temperature is not pumped through the burrows. This avoidance behaviour considerably increases the ability of U. africana to withstand short-lived temperature extremes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00352452
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  • 7
    Digitale Medien
    Digitale Medien
    An Estuarine Fauna in a Freshwater Lake in South Africa (1966)
    [s.l.] : Nature Publishing Group
    Nature 209 (1966), S. 532-533 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] A normal freshwater fauna was found, as typified by chironomids, oligochaetes, fresh water pulmonates (Bulinus, Biomphalaria, Lymnaea) and the prosobranch Melanoides, freshwater fish (Clarias), mayflies, Odonata, belostomatids, dybiscids and hydrophyllids. In addition there is a typical estuarine ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/209532a0
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  • 8
    Digitale Medien
    Digitale Medien
    Phosphorus cycling in a dense Potamogeton pectinatus L. Bed (1981)
    Springer
    Oecologia 49 (1981), S. 56-66 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary An analysis of phosphorus concentrations and standing stocks in the various components of a dense Potamogeton pectinatus L. community in a brackish lake showed that the amounts of P per unit area varied in the following order: Sediments 〉 Above ground macrophytes 〉 Detritus 〉 Benthic Invertebrates 〉 Below ground macrophyte tissue 〉 Epiphytic algae 〉 Water soluble P 〉 Water borne particulate P. Seasonal changes in the variability of these stocks are described, and shown to be controlled by the annual growth and decomposition pattern of the Potamogeton. The sediments were suggested as the major source of P for the plant biomass. Studies using 32P tracer showed that of a given input of P to the water, 32% went to large epiphytic algae, 17% to the Potamogeton, 16% to the benthic fauna (mostly filter feeding bivalves), 28% to the sediments (almost all incorporated in the top 1 cm), and the remaining 7% was adsorbed on to, or absorbed by microorganisms associated with detritus. Analysis of 32P uptake curves indicated that of the P absorbed by the Potamogeton, a significant proportion went to the complex adnate periphyton on the leaf surface. We were unable to separate this fraction. Movement of P in the community was shown to be a closed cycle, and any release of P from decaying macrophytes would be rapidly reabsorbed by epiphytic algae. It is unlikely that phosphorus, once cycling in the macrophyte community, would become transferred to the circulation in the open lake.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00376898
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  • 9
    Digitale Medien
    Digitale Medien
    Ecology of the sundays river Part I. Water chemistry (1970)
    Springer
    Hydrobiologia 36 (1970), S. 479-488 
    Details
    ISSN: 1573-5117
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Wasserproben von einer Reihe von Stellen des Sundays Rivers in der Östlichen Kapprovinz, Süd Africa, sind analysiert. Die chemischen Eigenschaften sind bezogen auf der geologischen and geographischen Natur des Sammelgebietes.
    Notizen: Summary Water analyses were done on samples taken at a series of points along the Sundays River in the Eastern Cape, South Africa. The chemical characteristics of the water were then correlated with the geological and geographical nature of the catchment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00039801
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  • 10
    Digitale Medien
    Digitale Medien
    Ecology of the Sundays River Part II. Osmoregulation in some Mayfly nymphs (Ephemeroptera : Baetidae) (1970)
    Springer
    Hydrobiologia 36 (1970), S. 489-503 
    Details
    ISSN: 1573-5117
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung 1. Die Nymphen der Eintagsfliege Cloeon crassi sind imstande eine Lösung von einer 10.500 ppm hohen Konzentration fester Stoffe zu ertragen. 2. Kleine Nymphen sind empfindlicher gegen hohe Konzentrationen solcher Lüsungen als gro\e. 3. In Toleranzversuchen mit C. crassi wurde kein Unterschied zwischen mit Meerwasser zubereiteten Media and Media von gleicher ionischer Zusammensetzung, wie das Wasser vom Sundays River, festgestellt. 4. Messungen der Haemolymph-Gefrierpunkt-Depression zeigen da\ C. crassi je nach der Konzentration des Mediums zu Hyperund Hyporegulierungen fahig ist. 5. Haemolymph der Nymphen der Eintagsfliege C. africanum in Sü\wasser ist von gleicher osmotischer Konzentration wie C. crassi; es wurde jedoch keine Andeutung irgendeiner Hyporegulationsfähigkeit in anderen Media gefunden. 6. Nymphen der Eintagsfliege Centroptilum excisum sind unfähig eine Lösung von einer Konzentration höher als 7.000 ppm fester Stoffe zu ertragen. 7. Diese Ergebnisse sind mit Bezug auf die Verbreitung der drei Arten im Gebiet des Sundays River diskutiert.
    Notizen: Summary 1. Nymphs of the mayfly Cloeon crassi can tolerate total dissolved solids concentration up to 10,500 ppm; these results agree with field observation. 2. Juvenile nymphs are more sensitive than adults to high concentration of dissolved solids. 3. No difference was detected in tolerance experiments on C. crassi between media made up with sea water or media of the same ionic composition as Sundays River water. 4. Measurements of haemolymph freezing point depression indicate that C. crassi can both hyper-regulate and hypo-regulate, depending upon the concentration of the media. 5. Haemolymph of nymphs of C. africanum in freshwater have the same osmotic concentration as that of C. crassi but no indication of any hyporegulatory ability was found in other media. 6. Nymphs of Centroptilum excisum cannot tolerate concentrations of total dissolved solids greater than 7,000 ppm. 7. The results are discussed in relation to the distribution of the three species in the Sundays River.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00039802
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