摘要:

SUMMARY.1. The sedimentary distribution of chlorophylls, carotenoids and their breakdown products following the winter‐spring bloom of the dinoflagellatePeridinium gatunensein Lake Kinneret was determined both spatially and vertically within the sediments, using high‐pressure liquid chromatography (HPLC).2. All four stations (epilimnic, oxic St. J (depth = 8m) and D (12m) and hypolimnic, anoxic St. F (21 m) A (41 m) were characterized by the presence of chlorophylla(chl‐a) chl‐b, chl‐c, phaeophytinsa(ph'tin‐a) andb, phaeophorbidea(ph'bide‐a) and lutein, fucoxanthin, diatoxanthin and β‐carotene together with spectrally similar, but HPLC‐resolved, breakdown products in the surface sediments. The central deep station A (41 m), which is seasonally anoxic, trapped and preserved significantly more pigments (e.g. chl‐a= 16.35 μg g−1organic matter) than the more erosive, oxic littoral stations (chl‐a= 1.10 and 0.76μg g−lOM at St. D and J, respectively).3. Whereas it was possible to ascribe the presence of lutein and chl‐bto inputs of green algae and higher plants from the catchment, and fucoxanthin and chl‐c1,c2to winter diatom blooms (e.g.Melosira granulata), there was a remarkable absence of peridinin and dinoxanthin from sediments, despite the dominance of dinoflagellates in the phytobiomass. This is consistent with the well‐known oxic lability of this epoxy carotenoid in aquatic systems, and indicates efficient breakdown of this dinoflagellate organic matter in the water column, prior to sedimentation.4. Although pigment concentrations all decreased with depths within sediments, lutein and β‐carotene were selectively preserved compared to chl‐a and fucoxanthin which, at 40m depth at St. A, decrease

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00503.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Growth and reproduction were measured forDaphnia pulex(Leydig) fedScenedesmus obliquus(Turp.) Kutz. grown with nitrogen‐sufficient and nitrogen‐deficient media. The incorporation of carbon into the body ofD. pulexwas traced using14C‐labelled algae and biochemical fractionation.2.Scenedesmuscultured on N‐defkient media allocated more carbon to lipid and less to protein than when cultured on N‐sufficient media.3. In a short‐term feeding experiment,Daphniaaccumulated more lipid when fed N‐deficient algal cells high in lipid content than when fed algae grown on N‐sufficient media that were lower in lipid.4. Animals grew faster and produced larger broods when fed algae grown on an N‐sufficient medium over an 8‐day period. Daphnids fed N‐deficient algae had higher quantities of body lipid, suggesting it was not a lack of energy which limited their growth and reproduction.5.Daphniafed algae grown on N‐deficient media allocated more lipid to eggs, and their offspring lived longer unde

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00504.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Glycogen, poly‐beta‐hydroxyalkanoate (PHA) and electron transport system (ETS) activity levels were monitored seasonally in light‐ and dark‐grown biofilms from a North Wales river.2. A spring peak was evident in glycogen, PHA and ETS activity levels per cm2and per cell, with the exception of PHA per cell, which peaked in the winter.3. There was a seasonal shift in the type of storage product found, perhaps reflecting seasonal changes in carbon sources.4. The light‐grown spring biofilm yielded the greatest amount of bio‐film storage products per cm2. This should be taken into account during caloric studies of river biofilms as a food source for grazing invertebrates.5. A model is presented of factors influencing storage product deposition in river biofilms. The thickness and cell packing of river biofilms should be noted in future studies. Storage product deposition can occur deep within thick biofilms, irrespective of the river wate

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00505.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The relationship between toxicant‐induced changes in the feeding behaviour of the cladoceran,Daphnia catawba(Coker), and subsequent effects at population and community levels were experimentally addressed.2. We adapted a method for measuring the thoracic appendage beat rate of individuals (termed the TAR and positively correlated with daphnid feeding rate) after exposure to toxicant at known levels, for use as a behavioural bioassay for low levels of aquatic toxicants. The TAR declined significantly with an increase in both sublethal and lethal levels of the surfactant, sodium dodecyl sulphate (SDS).3. We also measured population level effects (i.e. rates of reproduction, survival, andR0), and found that reductions in these values occurred at the same concentrations as the effects on individual behaviour.4. In most cases, the changes in feeding behaviour occurred more rapidly (≤30h) than changes in population parameters (days to weeks).5. We conclude that toxicant‐induced changes in individual feeding behaviour can provide a quicker estimate of effects on individuals and of potential community effects (i.e. effects on their prey populations) than measurements of population parameters. In addition, due to its sensitivity at low levels of toxicants, the behavioural bioassay may be particularly helpful in identifying effects of sublethal levels of aquatic pollu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00506.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. In laboratory experiments, 9.7–25.7% of dissolved organic carbon (DOC) in groundwater (at concentrations of 18.7–24.8 mg 1‐−1) was immobilized after perfusion through 8‐cm‐deep (22‐cm‐diameter) cores of stony stream‐bed substratum.2. This represented immobilization rates of 7.1–23.5 mg m−2h−1or, extrapolated across the year, potential immobilization rates within the stream bed of 62.2–205.9g m−2yr−1. Actual rates in the entire stream bed were probably higher because perfusion through the experimental cores did not reduce groundwater DOC concentrations to levels measured in the adjacent stream.3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.4. Selective enrichments of amino acids in groundwater (up to 20‐fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream‐bed cores probably did not reflect net reductions in dissolved free, low‐molecular‐weight material, with higher molecular weight, more ‘refractory’ material being immobilized instead.5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00507.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The carbon balance of the small cladoceran,Bosmina longirostris, was examined at four food concentrations (0,05, 0.10, 0.25, 2.50mg C 1‐−1) based on long‐term growth experiments.2. At birth,B. longirostrisallocated about 60% of assimilation to body growth at all food concentrations. However, allocation to body growth decreased with age and was less than 5% after the fourth instar at the lowest food concentration. The proportion allocated to reproduction increased with increasing food concentration, but was relatively constant among different adult instars.3. Assimilation rate increased with increasing food concentration and increasing body size: the mean rate from birth to 15 days was 6.6 times higher at the highest food concentration than at the lowest food concentration. However, with decreasing food concentration and increasing body size, a higher proportion of the assimilated carbon was lost as respiration. As a result, the net production rate reached a plateau at intermediate body size and was 9.1 times higher at the highest food concentration than at the lowest food concentration.4. Comparison with previous studies revealed thatB. longirostrisis more efficient thanDaphniawith regard to carbon production, especially at low food conditions, if the death rate is negli

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00508.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Crest size and body size was measured inDaphnia carinataKing sampled from field enclosures in which environmental conditions and notonectid predator (Anisops HyperionKirkaldy) levels had been manipulated, and from control treatments which had predator levels and other environmental factors equivalent to those in the natural environment.2. Individuals ofD. carinatadeveloped larger crests in treatments with predators than in treatments without predators.3. The environmentally manipulated treatment was considered to have lower levels of food but was also likely to have undergone other changes in physicochemistry and resource variability that may have affected crest size. The effect of the manipulation cannot be confirmed, therefore, as the result of variation in food levels. Animals in the treatments considered to have lower amounts of food had smaller crests than in the control treatment irrespective of whether predators were present. The effects of environmental manipulation and predators were additive.4. Enclosures without predators, but in which water from the natural, predator‐rich, environment was exchanged through the enclosure walls, showed no evidence of a chemical induction effect. Chemical induction effects may have been countered by a reduced food supply resulting from the higherD. carinatapopulation densities that developed in these enclosures.5. This work provides a second example of an alteration of the morphological response of daphnid prey to predators by environmental factors, probably food, and suggests this phenomenon may be general in cladoceran species displaying predator‐induced changes in morphol

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00509.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Two experiments with plankton communities from Storrs Pond (NH), one conducted in the laboratory and one in field enclosures, assessed the impact of different cladocerans on rotifers and ciliated protozoa.2. The smallest cladoceran,Bosmina longirostris, did not depress rotifer or ciliate growth rates while the intermediate sized dadoceran,Daphnia galeata mendotae, reduced ciliate growth rates in the enclosure experiment but had only a marginal effect in the jar experiment.D. galeata mendotaehad no effect on any of the rotifers in either experiment.3. In both experiments the largest cladoceran,Daphniapulex, depressed the growth rates of ciliates and those rotifers known to be vulnerable to interference competition.Polyarthra vulgaris, previously shown to be resistant to cladoceran interference, was the only rotifer unaffected byD. pulexin the field experiment but was depressed by the much higher densities of this cladoceran in the laboratory experiment.4. Cladocerans did not affect phytoplankton or bacterioplankton abundance in either experiment. Therefore the mechanism most likely to be responsible for the suppressive effect of cladocerans on rotifers and ciliates in these experiments is direct mechanical interference or predation, rather than exploitative competition.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00510.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The effects of two different invertebrate grazer guilds on the periphytic algal community were studied in a marsh pond in Manitoba, Canada over one entire open‐water season.2. Microcrustaceans (cladocerans, copepods, ostracods), which were numerically dominant in the unperturbed grazer community, effectively reduced the periphytic algal biomass to a persistent, depauperate residual assemblage throughout the season.3. The perturbed grazer community, enclosed and treated with ro‐tenone, was composed primarily of chironomids and oligochaetes. This community permitted a more diverse algal community to develop except when grazer numbers peaked.4. When grazer numbers in the perturbed community were at a maximum, the algal assemblage appeared to be ‘overgrazed’. Algal biomass was reduced below the minimum characteristic of the unperturbed community.5. There was an inverse relationship between algal biomass and grazer numbers in both perturbed and unperturbed communities, but variation in degree of response was much greater in the perturbed system than in the unpertur

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00511.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.2. Laboratory experiments were performed on dried leaves ofSalixsp. andNerium oleander.3. During the first month under the experimental conditions,Melanopsis praemorsa, Physa acula(Gastropoda) andHydropsyche maroccana(Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.4. The weight lost by willow leaves inoculated with the fungiAlatospora acuminata, Anguillospora longissima, Lemonniera aquaticaandTetracladium marchalianumincreased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest withLemonnieraand smallest withTetracladium.5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was byMelanopsisfeeding on leaves conditioned byLemonniera, in which case assimilation percentage by the gastropod was as high as 75%.6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00512.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY