摘要:

SUMMARY.In the laboratory,Asellus aquaticusdevoured intact green leaves from growing shoots of the aquatic macrophyteElodea canadensis. In four collections ofA. aquaticusonElodeain a lake (Windermere),c. 20% of the specimens contained in their guts fragments of greenElodealeaves; this material and pieces of oak (Quercus) were identified from characteristic leaf hairs. Some specimens had also eaten the filamentous algaOedogonium. Fluorescence microscopy is a useful aid for screening invertebrates that may have eaten living plant tissues.ImmatureA. aquaticus, with an initial mean body length ofc. 3 mm, wet weightc. 1 mg, were grown through sexual maturity over a 49‐day period at 15°C in a series of twenty‐two experiments (six to twelve isolated specimens in each experiment) comparing growth rates on different foods, including instances where no food was given. Animals were fed on a variety of items collected from the littoral of Windermere, plus some laboratory cultures of algae and bacteria. The highest mean specific growth rate (5.8% day−1) was obtained on youngElodealeaves mechanically shaken to remove epiphytes. Other diets yielding fast growth rates (3.7–5.3% day−1) were young growing leaves ofElodeawith few epiphytes and older green and brown living leaves covered with a thick growth of epiphytic algae, epiphytic algae removed fromElodea, plastic imitationElodeaimmersed in the lake until covered with attached algae, epilithic algae on stones,Oedogonium, and decaying oak leaves. Slower growth (1.3–2.2% day−1) and poorer survival was obtained on the following: a pure culture of the bacteriumSphaerotilus natans; cultured bacteria from lakewater; the filamentous algaeCladophoraandStigeocloniumboth with and without epiphytes; faecal matter fromAsellus; freshly killedAsellus; lake sediment. Some growth (mean = 0.7% day−1) and 50% survival for 21 days occurred in ‘starved’ animals kept in filtered, sterilized lakewater. Better survival and slightly faster growth (1.0–1.5% day−1) occurred in ‘starved’ animals kept in filtered and unfiltered lakewater.Growth ofA. aquaticuswas also experimentally determined from birth in animals fed on young greenElodealeaves and on decaying oak leaves. On both diets, growth was curvilinear and approximately exponential from birth to sexual maturity reached atc. 2mg wet weight in 46–60 days at 15°C. In older specimens the relative growth rate gradually fell over a period of 50 days, representing a more linear phase o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01473.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Regular sampling of larval and pupal simuliids in the River Stour (Dorset) showed thatSimulium austeniproduces a single generation of larvae per year, pupating in late April‐early May. The species is abundant in the middle and lower reaches of the Stour and its larger tributaries, but in nearby rivers of comparable size it is rare or absent, Unlike these other rivers, the Stour supports a true phytoplankton dominated by small centric diatoms (Stephanodiscus hantzschii). Peak concentrations of particulate chlorophyll‐α sometimes correspond with the growth period ofS. austenilarvae. The distribution ofS. austenirelative to that of phytoplankton is discussed and the importances of suspended bacteria and water chemistry are briefly consid

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01474.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.A lightweight, free‐flushing water and plankton sampler constructed of readily available, inexpensive material is described. Easily interchangeable tubes of varying volumes allow sampling flexibility. The sampler is activated by a messenger and is shut by two plastic funnels. For analyses in highly stratified waters, the sampler can be adjusted into the horizontal position. Several samplers may be tripped in series. The sampler has proved a versatile and reliable instrument in ecological studies.The tripping mechanism may also be used to release reversing thermometers and closing net

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01475.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Epilithic algae in a small softwater stream in the English Lake District were studied using a direct counting epifluorescence technique. A small trickling filter sewage treatment plant discharged into the stream and cattle grazed in fields adjoining the upper reaches. Both increased the inorganic nitrogen and phosphorus concentrations in the stream but the effect of the cattle was of a more intermittent nature.Cocconeis placentulawas the dominant diatom but large numbers of encrusting green, blue‐green and red algae also occurred in samples from the middle reach, which was heavily shaded by trees in summer. Although it was possible to demonstrate the effect of the sewage effluent on the rate of colonization of clean surfaces placed in the stream, it was only during periods of stable water flow that this was reflected in the standing crop of algae on the stones. TheCocconeiscounts below the sewage outfall tended to be highest in the autumn whereas those of the other diatoms were highest in the spring. The results were, however, extremely variable and apart from the effect of the nutrient inputs, theCocconeisstanding crops were largely related to the rate of water flow. Counts decreased and the variability between and within stones increased as higher rainfall and flow caused instability and scouring of the stones. A similar decrease in standing crop and high variability occurred in conditions of very low water flow but this could not be explaine

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01476.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.The main groups of animals found in the muddy sediments of Lough Neagh were Chironomidae (Diptera) and Oligochaeta (mainly Tubificidae). At 8 m depth, the average biomass of the main species in these groups was:Chironomus anthracinus, 2.64gm−2;Procladius, 342.8 mgm−2; tubificids (Tubifex, Potamothrix, Aulodrilus, Limnodrilus), 418.7mgm−2. At 25m depthC. anthracinusandProcladiuswere less abundant,C. plumosuswas present and among the tubificidsLimnodrilushad a higher density (up to 50000m−2) often an order of magnitude greater than at 8m. Kinnego Bay, a semi‐enclosed, polluted area of the lough, had fewer chironomids than the open lough, with chieflyC. plumosusandProcladius. Limnodriluswas more abundant than at 8m.Dero obtusa(Naididae) was also present, sometimes in large numbers (31000m−2).The response of this fauna to eutrophication in L. Neagh appears to be a diminution in the number of species present, withC. plumosusgradually replacingC. anthracinusas the dominantChironomus, and tubificids, particularlyLimnodrilus, becoming more abundant, A further stage, shown in Kinnego Bay, hasProcladiusas the most numerous' chironomid. Average total biomass at the three sites was 3.9gm−2at 8m, 13.2gm−2at 25 m in the main lake, 2.8gm−2in Kinnego Bay. At 8m depth,C. anthracinuscontributed 76% of the total biomass, at 25mLimnodriluscontributed 74% andC. anthracinus15%, and in Kinnego Bay,Limnodriluscontributed 40%,C. plumosus28%

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01477.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Unlike previously studied lakes with prolonged winter ice and snow cover, Lake Paajarvi, southern Finland, has a high humus content and consequently differs in both the quantity and quality of light penetration into its waters. Moreover, the range of temperature fluctuation and the degree of development of thermal stratification are greater in Paajarvi, and this increased environmental heterogeneity apparently stimulates diversity in the phytoplankton community, especially in the seasonal succession of species. Differences in the photosynthetic capacity of algae from different depths in the water column were not great. This is attributed to the extremely shallow euphotic zone, algae circulating freely through the steep light gradient and sedimenting rapidly once they pass through the thermocline into the hypolimnion. It is suggested that ‘adaptation’ of phytoplankton to the great seasonal changes in irradiance is achieved largely by successive growths of different species in the community, and that the adaptations and vertical migrations by individual algal species, which have been reported from polar and high alpine lakes, may be of secondary importance in Pääjärvi. The species successions in Pääjärvi produce changes in the pigment content of algae similar to those reported from polar and high alpine lakes, confirming that change in pigmentation is an important mechanism in light adaptation, whether at community or individual level. Algal pigment content was particularly high at the end of the long period of winter ice cover, indicating a degree of adaptation to the prolonged low‐light conditions, which produced the extremely high photosynthetic capacities measured at this time. However, phytoplankton production at any irradiance was primarily determined

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01478.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.An important influence on gross photosynthetic rates per unit area is the success with which phytoplankton competes for the available light with non‐algal suspended material and dissolved organic compounds. Using a range of Irish lakes, with euphotic zones varying between 0.7 and 20 m and with chlorophyll‐α values between 1 and 860 mg m−3, the effect on gross rates of photosynthesis is analysed for changes in the balance between the factors contributing to light attenuation. Net values per unit area are also likely to be modified in well‐mixed systems as the ratio of light to dark regions in the water column are altered with changes in light penetration. Depth gradients in dark respiration are reported for L. Neagh which vary according to previous light history and nutrient stress. Possible cases of restraint on phytoplankton growth are discussed for optically deep si

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01479.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Four methods were used to determine the energy content of somatic tissues ofPerca 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−1for lipid, 5.65 cal mg−1for 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 disc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01480.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY