ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01625.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe 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 egg

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01626.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryA battery‐operated self‐balancing thermistor temperature indicator is described, producing a D.C. voltage output, 1 V or less, to a recorder or moving coil me

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01627.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThis paper describes a deck‐mounted pumping system developed for collecting discrete, sequential plankton and water samples while also providing a continuous record of sampling depth, water temperature, turbidity and in vivo chlorophyll. It includes some results obtained with the equipment during a study of factors influencing the horizontal distribution of crustacean plankton in the lake Windermer

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01628.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryA 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−1wind, 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 t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01629.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryFluctuations 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−3respectively. 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

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01630.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummarySamples taken from Lake Mutanda in 1975 indicate that the specific composition of the zooplankton has changed from that in 1962. This change is very similar to that which occurred in Lake Bunyonyi sometime between 1931 and 1962. The most important aspect of the change is the disappearance of three species of Daphnia, together with Ceriodaphnia reticulata, Metadiaptomus aethiopicus, and Caridina nilotica. The 1975 samples indicate lower standing crops of zooplankton in all three lakes, and lower ratios of nauplii to copepodids than in 1962. The possibility of these changes being attributable to human activities is discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01631.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryField and laboratory evidence is presented to demonstrate that colonization of a new impoundment by the early invader, Chronomus plumosus L., is strongly influenced by sediment, the depth of which affects both larval abundance and tube shape. Larvae avoid areas with little sediment, such as eroded or newly inundated shores. In laboratory experiments, larvae constructed horizontal tubes in sediments between 3 and 10 mm depth, but in deeper sediments (11–30 mm) most of the larval tubes were vertically orientated. Of these about 70% were U‐shaped and the remainder J‐shaped. Larval abundance was positively correlated with sediment depth in the range 0

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01632.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe 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 ra

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01633.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

SummaryThe abundance of Ceriodaphnia reticulata (Jurine) in Lake Kinneret is restricted every year to the period March to June with a peak in May. The most constant parameter accompanying the peak is temperature with a range of 20–22° C. An attempt was made to clarify whether the estival high average temperatures observed in the epilimnion of this lake (27–28° C) could explain the decrease of the Ceriodaphnia population.Three physiological parameters: food intake, ammonia excretion and respiration rates, were measured experimentally at three temperatures (15, 22 and 27° C). The dry weight of individuals of the winter and summer populations were measured, and the percentages of egg‐bearing females in the populations were calculated.It was found that temperature increase accelerates the rates of ammonia excretion and food ingestion. The acceleration was greater in the lower temperature range (15–22° C) than in the higher one (22–27° C). Conversely, the enhancing of respiration rate is higher in the upper temperature range. The resulting deficit of energy at high temperatures causes a reduction in body size and a significant diminution of egg production, which leads to a progressive decline of

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1976.tb01634.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY