摘要:

SUMMARY1. This study examines the distribution ofAnabaena affinisfilament lengths under natural conditions as a function of depth and season, and in the laboratory as a function of growth phase. BecauseAnabaena affinisis only toxic when consumed, both its filament length and position in the water column are important determinants of its potential impact on zooplankton populations.2. Star Lake (Norwich, Vermont, U.S.A.), a natural, eutrophic pond, remained thermally stratified throughout theAnabaenabloom. Filament number and length differed significantly with both sampling date and water depth. Most filaments occurred at 0.5 m, particularly at the height of the bloom. Throughout the entire water column average filament length decreased from approximately 0.53 mm in May to 0.14 mm in July. The shortest filaments occurred at the 2.5 m depth. Filament length distributions (combined for all depths) for 29 May, 12 June and 3 July, corresponding to the beginning, middle and end of the bloom, respectively, differed significantly among the three dates. These patterns most likely reflect variable growth conditions, both during the season and in the water column.3. In the laboratory,Anabaenafilament length was affected by medium composition and growth phase. Filaments were significantly longer when grown in MBL than in ASM medium. Also, the average length ofAnabaenafilaments grown in MBL changed significantly as cultures aged; by day 13 filament length (2.01 ± 0.38 mm, mean ± SD) was twice that on day 0 (0.97 ± 0.71 mm). As cell concentration continued to increase, mean filament length gradually decreas

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Invertebrate stream drift was sampled bimonthly in the Acheron River, Victoria, Australia, over a period of 18 months. Replicated hourly samples were collected over a 25‐h period on each sampling date. A total of 194 taxa were identified in the drift. However, total drift density was dominated by few taxa.2. Some evidence was obtained for a seasonal pattern in drift: this was most pronounced in relative abundances of individual taxa and the composition of the drift, rather than in total drift densities. Most of the commonly collected taxa reflected the seasonal pattern of total drift. However, some of the common taxa did not.3. A small number of taxa showed behavioral drift, with a nocturnal increase in drift densities. One species of ‘Baetis’ drifted in high densities over short periods of time around dusk and dawn. It did not drift in higher densities during the night than during the day. The results emphasize the need for drift studies to be more rigorously designed than is typically the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The seasonal development of crustacean zooplankton, heterotrophic nanoflagellates (HNF) and bacteria was examined in Grosser Binnensee, a shallow, eutrophic lake in northern Germany. The grazing impact ofDaphniaon bacteria and nanoflagellates was estimated from field data on population abundances and from clearance rates obtained in laboratory experiments.2. The seasonal succession of zooplankton showed distinct peaks ofDaphnia magna, cyclopopid copepods,Bosmina longirostrisandDaphnia galeataandD. hynlina. The population dynamics ofDapfiniahad the strongest impact on all sestonic components.Daphnia maximacoincided with clearwater phases, and were negatively correlated with particulate organic carbon (POC), HNF and phytoplankton. Bacterial abundance was only slightly affected although daphnids were at times more important as bacterial consumers than HNF, as estimated from measured bacterial clearance rates. Other crustaceans (copepods,Bosmina) were probably of minor importance as grazers of bacteria and nanoplankton.3. HNF abundance varied from 550 ml−1to more than 30000 ml−1. HNF appeared to be suppressed by daphnids and reached highest densities when copepods dominated the metazooplankton. The variation in HNF abundance was not reflected in the concentration of heterotrophic bacteria, which fluctuated rather irregularly between 5 and 20 ± 106ml−1. Long filamentous bacteria which were probably resistant to protozoan grazing, however, appeared parallel to the development of HNF. These bacterial cells, although small in number, could comprise more than 30% of the total bacterial b

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. We offeredScenedesmus obliquusin five densities, from 0.5 to 8 ± 106cells ml−1, to the rotiferAnuraeopsis fissa. Growth rates (r) during the exponential phase (first 7 days) were significantly and positively related to food density. Thervalues (mean ± SD) varied between 0.454 ± 0.067 and 0,856 ± 0.090, from the lowest to the highest food concentration, respectively. Population growth went through a phase of exponential increase which lasted from 7 to 10 days before a plateau and, in some cases, a decrease occurred.2. There was a linear relation between food density and rotifer plateau density. At the highest food density, a peak abundance (mean ± SD) of 2312 ± 226 individuals ml−1was reached, while at the lowest food density there was no identifiable single peak but a plateau, at a density of 361 ± 62 ind. ml−1.3. The egg ratio decreased with increasing population density. The ratio of loose eggs to eggs attached to females indicated that more eggs became detached at higher food densities.4. As in many other rotifer species studied so far, population density ofA. fissawas less stable at higher algal food concentrations. Numerically,A. fissacould be grown at twice the density achieved

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Population dynamics and feeding ecology of adult and larval alpine newts(Triturus alpestris, Laurenti) were investigated in a high‐altitude karts lake to estimate their feeding pressure on the copepodArctodiaptomus alpinuf(Imhof). Estimates of population size for reproducing adults ranged from 666 to 864 individuals in the lake during July and August. Total abundance of larvae before the onset of ice cover varied considerably between 4400 and 25400 individuals in different years.2.Arctodiaptomus alpinuswas an important prey item for adult and larval alpine newts. During the second half of their aquatic period, adult newts moved to deeper water where the copepod reached its highest densities near the sediment. Adults and larvae exhibited no periodic feeding pattern. The feeding rhythm was more synchronized among the larvae than among the adults.3. Daily food consumption, estimated using the Elliott&Persson (1978) model, reached 4–21 mg dry biomass in adults. The daily ration of larvae was about 7% of body dry weight in the temperature range 6‐11°C. Compared to published estimates of daily food consumption in salmonid fishes, the feeding pressure of newts appea

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Lake Kinneret is a warm (13–30°C) monomictic lake. Between January and June a heavy annual bloom of the dinoflagellatePeridinium gatunensedominates phytoplankton biomass (250 g m−2). At the beginning of the summer, degradation and decomposition of thePeridiniumbiomass occurs, serving as a trigger for intense sulphate reduction in the hypolimnion and sediments.2. The rates of sulphate reduction in the sediments varied seasonally from 12 to 1700 nmol SO4.−2reduced cm−3day−1in December and July, respectively. The availability of organic matter and sulphate is high in June after the crash of thePeridiniumbloom and the beginning of stratification and is lowest in December before overturn.3. Sulphate concentrations in the hypolimnion range between 0.52 mM and 0.20 mM during mixing (January‐April) and before overturn (December), respectively. The depletion in sulphate in the hypolimnion is stoichiometrically correlated to the increase in sulphide. The lake is not depleted of sulphate at any time, so the sulphate reduction process in Lake Kinneret is not limited by sulphate concentrations except in the sediments just bef

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Phosphorus limitation was studied along the eutrophic, canyon‐type Římov reservoir (Czech Republic) during a spring phytoplankton bloom. Concentration of soluble reactive phosphorus (SRP), C:P molar ratio in seston, extracellular alkaline phosphatase activity (APA), and P limitation (bioassay) were used as indices for phosphorus deficiency in the phytoplankton.2. SRP, C:P, APA, and P limitation indicated a moderate P deficiency in the downstream, but not upper, part of the reservoir.3. Significant correlations between these parameters were found in the downstream part. Chlorophyllaconcentration correlated with APA and P limitation in the upper part.4. APA was significantly enhanced in the phosphorus‐deficient phytoplankton. However, APA was apparently not related to total biomass or species composition of the phytoplankton.5. Generally, APA was closely correlated with pH in the reservoir. However, extracellular alkaline phosphatases, with a pH optimum above 9.0, were induced and active only during the phytoplankton bloom, whereas low background activity of extracellular phosphatases was found at low chlorophyllaconcentrations (winter, clear‐water

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels.2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non‐pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels.3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels.4. Non‐predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal‐orientated relationships to the integrated, process‐driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mec

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer.2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level.3. There was evidence that the deep‐water community consisting ofChara corallinahad adapted physiologically to low‐light conditions. Net light saturated photosynthesis (CO2exchange) per unit chlorophylla(Chla) was reduced to 1.7 μg C (μg Chla)−1h−1at the lower boundary, half of that recorded at 5 m. The concentration of Chiaper gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chla(g dry wt)−1at 16 m vs. 4 mg Chla(g dry wt)−1at 5 m]. Chlbalso increased with depth and there was no change in the ratio of Chlaand Chlbwith increasing depth. The saturation light intensity (Ik) of the community at the lower boundary was only 78 μmol photons m−2s−1. Photosynthetic parameters (Ikand α) as well as the Chlacontent remained relatively constant throughout the seasonal and short‐term changes in radiation.4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep‐water community would be sensitive to any further changes in unde

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The degree to which fish faunas have been invaded by exotic species is quantified on the basis of river basins.2. Nineteen exotic species are now established in Spanish fresh waters.Alburnus alburnus(L., 1758) is reported here for the first time.3. The native/total fish ratio varies from 0.71 in Galicia, the best preserved fish fauna, to 0.41 in Douro, the most modified fish assemblage. The national average ratio (0.63) is similar to that reported for Portugal (0.65), but higher than that in Italy (0.56) and much lower than that in Greece (0.88).4. Exotic fishes have sometimes become successfully established over wide areas in a short time.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY