Showing papers in "Hydrobiologia in 1988"
TL;DR: In this paper, the principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed and new results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water.
Abstract: In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO3 precipitation to phosphorus retention in calcareous lakes.
622 citations
TL;DR: In this paper, a review of the literature on invertebrate drift in running waters is presented, emphasizing papers published during the last 10-15 years, focusing on the last decade and a half.
Abstract: This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.
619 citations
TL;DR: Salinity-induced stability and shallow water favor blooms in the boundary waters of both oceans, which may be of greater importance in the Atlantic because of the proportionally greater area of continental shelf there.
Abstract: At least nine species of Calanidae occupy the area of interest, four in the Atlantic and five in the Pacific. All store wax esters and probably can undergo diapause. Latitudinally overlapping or onshore — offshore associations of two or more species occur in both oceans. Interzonals, with reduced mouth parts in the adult female, are endemic to the Pacific subarctic gyre where their life cycles are completed in one year. Presumably its nearly closed circulation and environmental stability have favored the evolution of endemic species well adapted to those conditions. Lack of ice- and/or salinity-induced stability also limits blooms there. The sub-arctic Atlantic contains several smaller oceanographic features, open to both arctic and Atlantic influences and populated by species of different origins, arctic species can behave as interzonals but may also require two or more years to complete their life cycles. Females may need to feed one year to reproduce the next and therefore they retain functional mouthparts. In some places in the North Atlantic, blooms may start in the sub-ice zone and seed the remaining euphotic zone. There the earliest stages of some the Calanus species can develop close to the ice, using primarily ice algae as food, while the remaining stages are adapted to utilize brief periods of intense primary production in the water column. Salinity-induced stability and shallow water favor blooms in the boundary waters of both oceans, which may be of greater importance in the Atlantic because of the proportionally greater area of continental shelf there. In both oceans the smaller species of Calanidae can produce up to three generations per year.
498 citations
TL;DR: It is advocated that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.
Abstract: Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.
305 citations
TL;DR: The role of wax esters in the life history of calanoids is illustrated with particular reference to a comparison of Calanus finmarchicus and Metridia longa in Balsfjord, northern Norway.
Abstract: Calanus species, particularly those in high latitudes, can accumulate large oil reserves consisting predominantly of wax esters. These wax esters consist predominantly of 16:0, 20:1 (n−9) and 22:1 (n−11) fatty alcohols, mainly formed de novo by the animals from non-lipid dietary precursors, esterified with various fatty acids that are often polyunsaturated fatty acids and largely of dietary, phytoplanktonic origin. Wax ester formation is maximal in copepodite stages IV and V. The lipids are elaborated not primarily for buoyancy regulation but as a source of metabolic energy during overwintering, particularly for reproduction. Large quantities of wax esters are utilised for gonadal development when stage V copepodites mature to females. Development of stage V copepodites to males is not accompanied by wax ester utilisation but males consume large amounts of these lipids in physical activity during reproduction. The role of wax esters in the life history of calanoids is illustrated with particular reference to a comparison of Calanus finmarchicus and Metridia longa in Balsfjord, northern Norway.
288 citations
TL;DR: In this article, a review of the recent literature on the bioavailability of different forms of P in freshwater systems is reviewed, which is defined as the sum of immediately available P and the P that can be transformed into an available form by naturally occurring processes.
Abstract: The recent literature on the bioavailability of different forms of P in freshwater systems is reviewed. Bioavailable P is defined as the sum of immediately available P and the P that can be transformed into an available form by naturally occurring processes. Methods used to estimate the bioavailable P pool, which vary between studies largely depending on the time perspective applied, are critically evaluated. Most studies on particulate P aim to determine the potentially available P pool. Potential bioavailability of particulate P is normally analysed in bioassays with algal yield determinations and the available P fraction is characterized from interpretations of results of sequential chemical extractions. NaOH-extractable P is in most studies the most algal-available P fraction. For soil samples and tributary water particulate matter, NaOH-P has often been found to be equal to algal extractable P. In other studies depletions of NaOH-P have accounted for the algal P uptake, but only a minor proportion of the fraction has been utilized. Organic P in lake water particulate matter and bed sediments of eutrophic lakes can also be algal-available to a significant extent.
250 citations
TL;DR: The energetic demand of microorganisms in natural waters and the flux of energy between microorganisms and metazoans has been evaluated by empirical measurements in nature, in microcosms and mesocosms, and by simulation models, but empirical evidence is mixed.
Abstract: The energetic demand of microorganisms in natural waters and the flux of energy between microorganisms and metazoans has been evaluated by empirical measurements in nature, in microcosms and mesocosms, and by simulation models. Microorganisms in temperate and tropical waters often use half or more of the energy fixed by photosynthesis. Most simulations and some experimental results suggest significant energy transfer to metazoans, but empirical evidence is mixed. Considerations of the range of growth yields of microorganisms and the number of trophic transfers among them indicate major energy losses within microbial food webs. Our ability to verify and quantify these processes is limited by the variability of assimilation efficiency and uncertainty about the structure of microbial food webs. However, even a two-step microbial chain is a major energy sink.
244 citations
TL;DR: The geochemistry, availability and abundance of different forms of phosphorus in soil, water and sediments are reviewed in this article, and the present knowledge of phosphorus pathways in ecosystems and their regulation is discussed.
Abstract: The geochemistry, availability and abundance of different forms of phosphorus in soil, water and sediments are reviewed. The present knowledge of phosphorus pathways in ecosystems and their regulation is discussed.
210 citations
TL;DR: Most Ethiopian lakes are part of closed drainage systems and collectively form an extensive salinity series, here treated comparatively for geographical, chemical and algal characteristics as discussed by the authors, and the principal determinant of a lake's position in the series is the open or closed nature of its individual drainage.
Abstract: Most Ethiopian lakes are parts of closed drainage systems and collectively form an extensive salinity series, here treated comparatively for geographical, chemical and algal characteristics. Chemical data are presented for 28 lakes and numerous inflows, including original analyses for 15 lakes, in which total ionic concentration and electrical conductivity vary over 4 orders of magnitude. The principal determinant of a lake's position in the series is the open or closed nature of its individual drainage. At present there are three major closed systems (Awash R. — Afar drainage, northern rift lakes, southern rift lakes), numerous crater lakes with seepage -in and -out, and two cryptodepressions with marine inputs. Salinity is primarily determined by evaporative concentration, enhanced in lakes associated with past marine influence or recent volcanic activity by readily soluble materials in the catchment, and by some thermal-reflux pathways. However, anomalously dilute closed lakes exist, indicative of other processes of solute loss (e.g. past basin overflow, ‘reverse weathering’, seepage-out).
207 citations
TL;DR: Experimental studies, including laboratory observations of copepod reproductive response to food concentration and incubation techniques for measuring in situ reproductive rates, are important for understanding howCopepod dynamics may filter year-to-year differences in phytoplankton production cycles.
Abstract: It is frequently put forward that variability in fisheries productivity is related to interannual variation in physical processes affecting phytoplankton productivity. Here, alternative views of the role of copepods as an intermediary link in North Atlantic marine food chains are discussed. Following Bainbridge & McKay (1968) and Cushing (1982), a strong link between phytoplankton and fisheries variability is proposed for some fish stocks, like cod and redfish, that spawn in spring in regions where Calanus finmarchicus dominates the plankton. Otherwise, in regions where small copepods and other microzooplankton dominate the prey field productivity for larval fish, a weak link is proposed. Experimental studies, including laboratory observations of copepod reproductive response to food concentration and incubation techniques for measuring in situ reproductive rates, are important for understanding how copepod dynamics may filter year-to-year differences in phytoplankton production cycles.
197 citations
TL;DR: Food size-range for 13 species of Tintinnina and 18 species of Oligotrichina were studied using electronic particle counting and in situ observation of food vacuole contents, showing that natural particles were consumed at rates that varied from 1 to 20 μg C 1 day−1.
Abstract: Food size-range for 13 species of Tintinnina and 18 species of Oligotrichina were studied using electronic particle counting and in situ observation of food vacuole contents. Tintinnids consume nanoplankton in the size range 2–20 μm. Oligotrichous naked ciliates consume particles in the size range 0.5–10 μm. Ciliates smaller than 30 μm take 72% picoplankton and 28% nanoplankton. For ciliates between 30 μm and 50 μm the proportions are reversed (30% pico- and 70% nanoplankton), while the larger ciliates (> 50 μm) take nanoplankton almost exclusively (95% nano- and 5% picoplankton). A seasonal study of total Oligotrichida grazing showed that natural particles were consumed at rates that varied from 1 to 20 μg C 1−1 day−1. This included between 1 and 38% of the bacterioplankton production and 9 to 52% of the nanoplankton production. In the N-W Mediterranean the total ciliate production varied from 0.4 to 8.2 μg C 1−1 day−1.
TL;DR: A comparison of Kenyan reefs of different historical and observed levels of fishing exploitation showed that more exploited reef lagoons had greater sea urchin densities and sizes, fewer and smaller fish and less coral cover.
Abstract: A comparison of Kenyan reefs of different historical and observed levels of fishing exploitation showed that more exploited reef lagoons had greater sea urchin densities and sizes, fewer and smaller fish and less coral cover. In the most exploited lagoon the biomass of the burrowing sea urchin Echinometra mathaei increased five fold during the previous 15 years. An ecological study of the three most common omnivorous sea urchin species inhabiting hard substrate within these reef lagoons (E. mathaei, Diadema savignyi and D. setosum) suggests that they are ecologically separated by predation and avoid predators and competitors by occupying different size burrows or crevices within the lagoon. Predator removal through fishing activities may result in ecological release of the sea urchins and result in competitive exclusion of weaker competitors. The most exploited reef had a nearly monospecific barren of E. mathaei living outside burrows suggesting that E. mathaei may be the top competitor. Its ecological release appears to lead to a decrease in live coral cover, increased substrate bioerosion and eventually a loss of topographic complexity, species diversity, fish biomass and utilizable fisheries productivity. Data from the outer reef edge were more difficult to interpret but may indicate similar patterns. Within this area, physical stresses such as waves and currents may be a greater controlling force in regulating fishing activities and coral reef community structure.
TL;DR: Submerged macrophytes are adversely affected by a large increase in the external phosphorus input to a lake and may be caused by epiphyte shading, phytoplankton shading or deposition of unfavourable sediments.
Abstract: Emergent macrophytes take up their phosphorus exclusively from the sediment. Submerged species obtain phosphorus both from the surrounding water and from the substrate, but under normal pore and lake water phosphorus concentrations, substrate uptake dominates. Release of phosphorus from actively growing macrophytes (both submerged and emergent) is minimal and epiphytes obtain phosphorus mainly from the water. Decaying macrophytes may act as an internal phosphorus source for the lake and add considerable quantities of phosphorus to the water. A large part of the released phosphorus is often retained by the sediments. In perennial macrophytes the amount of phosphorus released from decaying shoots is dependent on the degree of phosphorus conservation within the plant. Macrophyte stands may also be a permanent phosphorus sink due to burial of plant litter. Macrophytes affect the chemical environment (oxygen, pH), which in turn has effects on the phosphorus cycling in lakes. However, the impact of aquatic macrophytes on whole-lake phosphorus cycling is largely unknown. Controlled full- scale harvesting, herbicide or herbivory experiments are almost totally lacking. Emergent macrophytes respond positively to eutrophication, but fertilization experiments have shown that nitrogen rather than phosphorus may be the key element. Submerged macrophytes are adversely affected by a large increase in the external phosphorus input to a lake. This effect may be caused by epiphyte shading, phytoplankton shading or deposition of unfavourable sediments.
TL;DR: Relative coverage of filamentous periphytic algae increased with chlorophyll a (chl a) biomass on natural substrata in 22 northwestern United States and Swedish streams, suggesting that biomass range of 100–150 mg chl a m−2 may represent a critical level for an aesthetic nuisance.
Abstract: Relative coverage of filamentous periphytic algae increased with chlorophyll a (chl a) biomass on natural substrata in 22 northwestern United States and Swedish streams. A biomass range of 100–150 mg chl a m−2 may represent a critical level for an aesthetic nuisance; below those levels, filamentous coverage was less than 20%. Other indices of water quality (dissolved oxygen content and measures of benthic macroinvertebrate diversity) were apparently unaffected by periphytic biomass or filamentous coverage in these streams. Neither was biomass related to limiting nutrient content (soluble reactive phosphorus, SRP), as has been observed in previous experiments using bare rocks in streams and slides in artificial channels. Ambient SRP concentration may not be a useful predicter of periphyton accrual on natural substrates, due to uptake and recycling of P throughout the stream and undetermined losses such as sloughing and grazing.
TL;DR: In this article, the first extraction schemes were designed to quantify discrete chemical or mineralogical compounds and several systematic errors have been detected and the schemes have been modified and simplified accordingly, which makes it necessary to be cautious when comparing results from the literature in this field.
Abstract: Characterization of sediment phosphorus is commonly based on sequential chemical extractions, in which phosphorus is supposed to be selectively removed from different compounds in the sediments The first extraction schemes were designed to quantify discrete chemical or mineralogical compounds As extraction schemes have been tested on different sediments, several systematic errors have been detected and the schemes have been modified and simplified accordingly Other chemical extractions or treatments have attempted to determine phosphorus bound to particles with a certain strength or binding energy, the purpose being to determine the labile, loosely bound, exchangeable, mobile or algal-available fraction of sediment phosphorus All extraction procedures yield operationally defined fractions and cannot be used for identification of discrete phosphorus compounds The many methodological modifications make it necessary to be cautious when comparing results from the literature in this field
TL;DR: The calanoid copepod Calanus sinicus was reared in the laboratory under excess food conditions, and its development and growth rates were measured at various temperatures.
Abstract: The calanoid copepod Calanus sinicus was reared in the laboratory under excess food conditions, and its development and growth rates were measured at various temperatures. Egg development time (DH, days) was dependent on temperature (T °C), and was expressed as DH = 55.3 (T + 0.7)−1.44. Postembryonic development followed the equiproportional rule. The stage duration was short in NI and NII, but compensatingly longer in NIII. Between NIV and CII, it was nearly isochronal, and beyond CII, it tended to increase gradually. The time from egg to adult was expressed as DCVI = 1258 (T + 0.7)−1.44. The specific growth rate was also temperature-dependent and highest from CI to CIII, intermediate from NII to CI and from CIII to CV, and lowest from CV to CVI. The growth rates of C. sinicus are higher than those of co-occurring small copepods such as Paracalanus, Acartia and Microsetella.
TL;DR: These studies suggest that mixotrophy, the trophic utilization of particulate food and dissolved organic matter as well as photosynthetically fixed organic matter, is a balanced process that can be regulated by environmental conditions.
Abstract: Phagotrophy by pigmented flagellates is known from the literature but has recently been rediscovered in the context of microbial food webs. Particle ingestion rates were found to be equivalent for pigmented and nonpigmented microflagellates in both field and laboratory studies. Ingestion rates of the chrysophytes Ochromonas danica, O. minuta, and Poterioochromonas malhamensis, the dinoflagellate Peridinium inconspicuum, and the cryptophytes Cryptomonas ovata and C. erosa were compared with those of two nonpigmented Monas species using 0.57 µm polystyrene beads as a food source. Ingestion rates were 0.31 to 3.17 beads/cell/h and filtration rates were 10−7 to 10−8 ml/cell/h with no detectable difference between pigmented and nonpigmented forms. Ingestion rates in unpigmented Monas species showed a linear increase with increasing particle concentration from 1.9 × 106 to 1.6 × 107 beads/ml.
TL;DR: It is concluded that the relative importance of bacteria and protozoa as nutrient regenerators in the detrital food loop is dependent largely on the overall carbon:nutrient ratio of the bacterial substrate.
Abstract: We have used a model food chain composed of a natural bacterial assemblage, a pennate diatom and a bacterivorous microflagellate to investigate the factors controlling the relative importance of bacteria and protozoa as sources for regenerated nitrogen in plankton communities. In bacterized diatom cultures in which diatom growth was nitrogen-limited, the carbon:nitrogen (C:N) ratio of the bacterial substrate greatly affected which population was responsible for the uptake of nitrogen. When nitrogen was added as NH4+ and the cultures were supplemented with glucose, the bacteria competed successfully with the algae for NH4+ and prevented the growth of algae by rapidly assimilating all NH4+ in the cultures. Bacterivorous protozoa inoculated into these cultures grazed the bacterial population and remineralized NH4+, thus relieving the nitrogen limitation of algal growth and allowing an increase in algal biomass. In contrast, bacteria in cultures supplemented with the amino acid glycine (C:N = 2) were major remineralizers of nitrogen, and the influence of protozoan grazing was minimal. We conclude that the relative importance of bacteria and protozoa as nutrient regenerators in the detrital food loop is dependent largely on the overall carbon:nutrient ratio of the bacterial substrate. The role of bacterivorous protozoa as remineralizers of a growth-limiting nutrient is maximal in situations where the carbon:nutrient ratio of the bacterial substrate is high.
TL;DR: A new sampling approach (Random Point-Abundance Sampling and modified electrofishing) is described for early-life fish ecology that is mobile, effective for all sizes of larvae and 0 + juveniles of most species, quantitative, and applicable to a number of freshwater situations.
Abstract: Horizontal zonation of fish reproduction, a lotic-to-lentic succession similar to that seen with increasing stream order, was evident from the relative abundance of larval and 0 + juvenile fishes in three floodplain spawning and nursery areas (lotic, semi-lotic, lentic) of the Upper Rhone River, France. Although the lotic and lentic ecosystems provided similar estimates of standing crop (0 + juveniles), differences were apparent in the reproductive and trophic guild structure of the YOY taxocoenoses at the three sites. A new sampling approach (Random Point-Abundance Sampling and modified electrofishing) is described for early-life fish ecology. The electrofishing method employed is mobile, effective for all sizes of larvae and 0 + juveniles of most species, quantitative, and applicable to a number of freshwater situations; and the punctual data resulting from this sampling approach are comparable both spatially and temporally.
TL;DR: Major non-polar lipid classes in the sediments included sterols, alcohols, hydrocarbons and an unusual suite of very long-chain unsaturated ketones and esters which have not previously been reported from antarctic environments.
Abstract: The compositions of carotenoids, chlorophylls and lipids at four depths in Ace Lake have been determined as a means of studying the vertical zonation of species in the lake and for comparison with the lipids found in the bottom sediments. The four major species of phytoplankton found in the lake were identified by electron microscopy. The most abundant phytoplankter was Pyramimonas gelidicola McFadden (Chlorophyta, Prasinophyceae) which occurred in greatest numbers at 10 m, the base of the oxylimnion. The pigments and lipids at this depth were mainly derived from this alga. At 11 m (the top of the anoxylimnion) only traces of lipids and pigments attributable to P. gelidicola were found, indicating only limited settling of algal cells through to the anoxylimnion, at least in summer. The pigments at 11 m were dominated by bacteriochlorophylls c derived from green photosynthetic bacteria Chlorobium spp. These pigments were also abundant at 23 m suggesting the presence of intact bacterial cells which had settled out from higher in the water column. Major non-polar lipid classes in the sediments included sterols, alcohols, hydrocarbons and an unusual suite of very long-chain unsaturated ketones and esters which have not previously been reported from antarctic environments. Several novel compounds, not found previously in either sediments or organisms, are reported. These include tri- and tetra-unsaturated straight-chain C39 methyl ketones and C40 ethyl ketones and the methyl ester of a tetra-unsaturated straight-chain C36 fatty acid. The distributions of lipids in the sediment were markedly different from those in the water column indicating extensive bacterial degradation and recycling of labile lipids.
TL;DR: There is growing evidence that animals, predators and herbivores, directly or indirectly can control biomass of primary producers and internal cycling of phosphorus.
Abstract: Aquatic animals directly influence the cycling of phosphorus in lakes through feeding and excretion Traditionally, animals (zooplankton, benthic invertebrates and fish) have been assigned only minor roles in the process of freshwater phosphorus cycling They were regarded as consumers without much regulating influence Today there is growing evidence that animals, predators and herbivores, directly or indirectly can control biomass of primary producers and internal cycling of phosphorus
TL;DR: Improved methods for measuring bacterial growth and mortality and studies of the nonpredatory mechanisms of bacterial mortality are required to resolve the paradox of neither predation by metazoans nor protists balances rates of bacterial growth.
Abstract: Knowledge of the rates of bacterial mortality, particularly predatory mortality, is important in determining the fate of bacterial production. Communities of planktonic bacteria have specific growth rates on the order of 1 d−1, but there is relatively little variation in bacterial abundance, implying that growth and mortality are closely coupled. A review of the mechanisms of bacterial mortality suggests that predation and parasitism are the most likely factors balancing the rapid rates of bacterial growth on daily time-scales. Experiments done in two-stage continuous cultures partially support this notion. At bacterial growth rates of 1 d−1, predatory mortality was on the order of 1.5–2 d−1 and nonpredatory mortality was undetectable. On the other hand, a review of existing field studies indicates that neither predation by metazoans nor protists balances rates of bacterial growth. Improved methods for measuring bacterial growth and mortality and studies of the nonpredatory mechanisms of bacterial mortality are required to resolve this paradox.
TL;DR: The surface area of river-worn cobbles can be estimated from linear regression equations of area on a two-dimensional term of the form (xy + yz + zx) where x, y, and z are either the axial dimensions or axial perimeters of stones Dimension measurements are made with calipers and perimeters are measured with a tape measure or a mapping wheel as discussed by the authors.
Abstract: The surface area of stones can be quickly, accurately, and precisely estimated from linear regression equations of area on a two-dimensional term of the form (xy + yz + zx) where x, y, and z are either the axial dimensions or the axial perimeters of stones Dimension measurements are made with calipers, and perimeters are measured with a tape measure or a mapping wheel The best fit slopes for the equations are determined from a representative sample of stones whose surface areas are measured by mapping Estimates of surface areas of river-worn cobbles by these methods had mean percentage absolute errors of about 4%, considerably better than other methods examined
TL;DR: There is an apparent connection between the appearance of Gonyostomum and acidification, but it seems not to be the low pH per se that is the cause, but rather interlinked factors.
Abstract: During the last 20–30 years the flagellate Gonyostomum semen has become more abundant in lakes, especially small humic lakes, in Scandinavia. Mass development of the alga has been reported from areas affected by anthropogenic acid deposition, and reports from bathers of health problems are becoming frequent. Although there is an apparent connection between the appearance of Gonyostomum and acidification, it seems not to be the low pH per se that is the cause, but rather interlinked factors. The present tendency towards a wider distribution of the alga in non-humic lakes, emphasizes the importance of a better understanding of small humic lakes.
TL;DR: In this article, the dependence of lake trophic state on external phosphorus loading is modeled by two general types: empirical, steady state models derived from statistical treatment of data from large numbers of lakes, and theoretical, dynamic models based on more or less detailed mathematical descriptions of kinetics of nutrient and population dynamics.
Abstract: Models describing the dependence of lake trophic state on external phosphorus loading are of two general types: empirical, steady state models derived from statistical treatment of data from large numbers of lakes, and theoretical, dynamic models based on more or less detailed mathematical descriptions of kinetics of nutrient and population dynamics.
TL;DR: In this article, four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control).
Abstract: Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.
TL;DR: Measurements of bacterial and bacterivore abundance, concentrated on comparisons between seasons, on diel cycles and on spatial variations, have been used to evaluate mechanisms controlling bacterial populations and provide the best insight into what controls populations of bacteria in the sea.
Abstract: A variety of methods have been used to estimate the degree of control exercised upon marine bacterioplankton by grazing organisms. These include filtration or dilution of samples to reduce grazers, the use of specific inhibitors to prevent growth or grazing, and the use of artificial particles or radio-labelled bacteria as tracers for the natural bacterioplankton. Each of these techniques has drawbacks which may lead to under- or overestimates of grazing. In addition, they tell us little about which organisms are doing the grazing or the degree to which viruses or lytic bacteria compete with grazers for bacterial production.
TL;DR: Roughly estimated nucleus numbers in single adult females of C. finmarchicus, glacialis and hyperboreus were similar at 72 000, 85 000, and 96 000 respectively, suggesting that, given similar nucleus numbers, there is nucleotypic control of whole-organism characteristics.
Abstract: Data on embryonic and larval development times (D) of Calanus species are analysed using Bělehradek’s temperature (T) function, D = a (T - α) b , with b = −2.05 as in previous studies. Among these species, α for embryonic duration varies directly with temperatures in their geographical ranges and a is related to egg diameter. Using α and b from embryonic durations, the fitted values of α for older stages are related to body sizes. Roughly estimated nucleus numbers in single adult females of C. finmarchicus, glacialis and hyperboreus were similar at 72 000, 85 000, and 96 000 respectively. Genome sizes (2C) of adult females are ca. 13 pg DNA in C. finmarchicus and pacificus, ca. 17 pg in C. sinicus, ca. 21 pg in C. helgolandicus and marshallae, and ca. 25 pg in C. glacialis and hyperboreus. These correspond roughly to body sizes and temperature-corrected development rates, quite precisely so in the sibling pair C. finmarchicus and C. glacialis, suggesting that, given similar nucleus numbers, there is nucleotypic control of whole-organism characteristics.
TL;DR: Future considerations of carbon-energy flows within pelagic food webs should include internal, biotic feedback controls, in addition to abiotic forcing functions, in the regulation of these flows.
Abstract: Future considerations of carbon-energy flows within pelagic food webs should include internal, biotic feedback controls, in addition to abiotic forcing functions, in the regulation of these flows. Over the past two decades, research on microbial communities of pelagic ecosystems has yielded data suggestive of cybernetic-like regulation operating within these communities. As presently conceived, phagotrophic protozoa have a pivotal role in such regulation as a consequence of their rapid growth, grazing, and nutrient regenerative capabilities. Feedback controls within microbial food webs may have significant effects on distal portions of pelagic ecosystems, including the fate of organic detritus and metazoan production.
TL;DR: Bacterial uptake of inorganic phosphate (closely investigated in Escherichia coli) is maintained by two different uptake systems which are Pi-repressible and used in situations of phosphorus deficiency and Pit system, which is constitutive.
Abstract: Bacterial uptake of inorganic phosphate (closely investigated in Escherichia coli) is maintained by two different uptake systems. One (Pst system) is Pi-repressible and used in situations of phosphorus deficiency. The other system (Pit system) is constitutive. The Pit system also takes part in the phosphate exchange process where orthophosphate is continuously exchanged between the cell and the surrounding medium.