Clearance rates of sessile rotifers: in vitro determinations

We measured laboratory clearance rates of 10 rotifer and one unidentified bryozoan species from 3 different lakes using ³²P labeled algae (Chlamydomonas) or yeast (Rhodotorula). Clearance rates for all rotifers fed yeast ranged from < 2.0 to > 260 µl · animal^–1 · h^–1 depending on species. The in vitro clearance rates of two sessile rotifers (Ptygura crystallina and P. pilula) were not significantly different from previously measured in situ rates (Wallace and Starkweather 1983). Clearance rates for 5 rotifers fed algae ranged from < 5.0 to > 90.0 µl · animal^–1 · h^–1. Ptygura beauchampi, P. crystallina, P. pilula, Floscularia conifera, and F. melicerta ingested both cell types but their clearance rates varied substantially among species and between cell types. There was a substantial time-dependent loss of 32P from formalin-fixed animals (Sinantherina socialis) awaiting processing. This loss stabilized at approximately 20 hours and was estimated to be about 40% of the initial ingested label. Clearance rates for the bryozoan fed yeast or algae were highly variable, ranging from < 1.0 to > 3 000 µl · animal^–1 · h^–1.     

In situ clearance rates of planktonic rotifers

The in situ clearance rates of several rotifer species from a small, temperate eutrophic lake were measured using three radioactive tracer cell-types, a bacterium (Aerobacter), a yeast (Rhodoto-rula), and alga (Chlamydomonas). Rates were below 10 µl/anim/h but varied significantly among species. Keratella cochlearis, Kellicottia bostoniensis, and Conochilus dossuarius ingested all three tracer cells but rates varied substantially with tracer cell-type. Polyarthra dolichoptera and P. euryptera ingested only the algal cells. Co-occurring forms of K. cochlearis and species of Polyarthra differed markedly in size and in tracer cell utilization, indicating niche diversification in food resources.     

Larval metamorphosis in sessile rotifers

Postnatal development of six species of sessile rotifers in the families Flosculariidae (Floscularia decora, Lacinularia flosculosa, Limnias ceratophylli, Ptygura crystallina) and Collothecidae (Collotheca ornata, Stephanoceros fimbriatus) was investigated by observing free-swimming and newly settled larvae until they metamorphosed into adults. Three variants of metamorphosis were observed. A hypothetical explanation of changes of the coronal construction of orders Gnesiotrocha and Pseudotrocha is considered.     

On relation to substrate in sessile rotifers

Information on the distribution of 45 sessile rotifers from diverse freshwaters in south and central Sweden was analyzed to reveal possible relationships to their substrates. Almost all of them showed an exclusively periphytic occurrence. The highest number of species was found on Utricularia, but otherwise it was not possible to correlate rotifer presence to any special macrophyte or category of plants (e.g., fine-leaved or floating-leaved species).     

In situ determinations of bacterial selectivity and filtration rates by five cladoceran zooplankters in a hypertrophic subtropical reservoir

Cladoceran in situ feeding rates on natural bacteria labelledwith [methyl-³H] were studied in parallel with feeding ratedeterminations on ¹⁴C-labelled Chlorella in a hypertrophic subtropicalreservoir (Lake Hartbeespoort) through spring and summer (1986/87).Community filtration rates (CFR5) on bacteria and algae weresimilar, but selection for Chlorella (relative to natural bacteria)increased from midsummer in association with declining bacterialdensity and increasing dominance of ‘inedible’ componentsof the natural phytoplankton. Species-specific filtration rates(SSFRs) were determined for Daphnia pulexllongispina, Ceriodaphniareticulata, Diaphanosoma excisum, Bosmina longirostris and Moinamicrura during their respective seasonal occurrence in the studyperiod. SSFRs on algae and bacteria increased with body length(L, mm) in all species apart from Bosmina. Species-specificdifferences in absolute feeding rate (FR, ml animal^–1day^–1), the slope of the FR-L relationship and bacteriaselectivity were evident. The feeding rate of all cladoceranson bacteria is described by the power equation FR 5.231L^1.42FR values on bacteria relative to FR values on algae averaged     

In situ growth rates of marine phytoplankton: approaches to measurement, community and species growth rates

Taxonomic structure and biomass weighting are important determinantsof measurable marine phytoplankton community growth potential.Maximal diel-averaged growth rates of communities appear tofall between 3 and 3.6 doublings day^–1. Mean net growthrates are considerably lower. Ranges of community growth ratesmeasured in tropical, sub-tropical and (summer) temperate ecosystemsare similar. There appears to be a broad dichotomy between thegrowth potential of diatom species as compared to non-diatoms.Doubling rates of small diatoms frequently exceed communitybiomass doubling rates by wide margins. Diel-averaged growthrates of large diatoms, microflagellates and non-motile ultraplanktonpopulations are lower and similar in magnitude to communitygrowth estimates. Maximum growth rates of species measured insitu are in good agreement with maximum growth rates measuredin laboratory cultures. High specific productivity of sub-dominantor rare diatom species or assemblages will be diluted in thelower specific growth rates of microflagellate and non-motileultraplankton assemblages. Specific rates of grazing upon speciesand functional groups remain to be quantified, but stabilityof community size and taxonomic structure implies close linkagebetween growth and mortality rates at the species level overtime intervals of several generations.     

In situ determination of sulfide turnover rates in a meromictic alpine lake

A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.     

In situ growth rates of Sargassum horneri (Fucales,Phaeophyta)1

The relative growth rate of the brown alga Sargassum horneri (Turner) C. Agardh in the sea at Maizuru Bay, Japan, was investigated from summer to winter to examine the impact of declining solar radiation and temperature. The observed change in the growth rate between summer and winter was insignificant, in spite of a major decline in solar radiation and water temperature. The mean relative growth rate was 4.6% per day, equivalent to the daily net photosynthetic production previously reported for this species.     

In situ growth rates of deep-water octocorals determined from 3D photogrammetric reconstructions

Growth rates of deep-water corals provide important information on the recovery potential of these ecosystems, for example from fisheries-induced impacts. Here, we present in situ growth dynamics that are currently largely unknown for deep-water octocorals, calculated by applying a non-destructive method. Videos of a boulder harbouring multiple colonies of Paragorgia arborea and Primnoa resedaeformis in the Northeast Channel Coral Conservation Area at the entrance to the Gulf of Maine at 863 m depth were collected in 2006, 2010 and 2014. Photogrammetric reconstructions of the boulder and the fauna yielded georeferenced 3D models for all sampling years. Repeated measurements of total length and cross-sectional area of the same colonies allowed the observation of growth dynamics. Growth rates of total length of Paragorgia arborea decreased over time with higher rates between 2006 and 2010 than between 2010 and 2014, while growth rates of cross-sectional area remained comparatively constant. A general trend of decreasing growth rates of total length with size of the coral colony was documented. While no growth was observed for the largest colony (165 cm in length) between 2010 and 2014, a colony 50–65 cm in length grew 3.7 cm yr^?1 between 2006 and 2010. Minimum growth rates of 1.6–2.7 cm yr^?1 were estimated for two recruits (<23 cm in 2014) of Primnoa resedaeformis. We successfully extracted biologically meaningful data from photogrammetric models and present the first in situ growth rates for these coral species in the Northwest Atlantic.     

Contribution to the study of african rotifers: rotifers from Mali

In samples collected from different parts of the Republic of Mali (W-Africa), ninety-two taxa of rotifers were identified. Some were present in different forms; 56% were cosmopolitan, 19% thermophilous with a wide distribution, 20% tropicopolitan and 5% cold-stenothermous. These latter species seem to be relicts of palaeoclimatic conditions in Africa.     

In situ study of the effect of oyster biomass on benthic metabolic exchange rates

Oxygen consumption and dissolved nitrogen fluxes at the water-sediment interface of an oyster-bed were measured in situ using transparent enclosures inserted on undisturbed sediment. Experiments were performed in summer, under dark and light conditions, with various densities of the oyster Crassostrea gigas (0–150 animals m ^{– 2}). The influence of oyster biomass on oxygen and ammonia exchange rates was similar in both lighting conditions. Oxygen consumption increased with increasing biomass, though not at the level of prediction for the highest biomasses, suggesting a depressed respiration rate. Ammonia release never matched the rates predicted by adding sediment efflux to oyster excretion, when biomass exceeded 100 g DW m ^{– 2}. The coupling between oxygen consumption and ammonia release (O : N ratio) was thus influenced by oyster biomass. Stabilization of nitrogen release was related to enhanced nitrification in the presence of oyster and/or sediment uptake of ammonia against the molecular gradient. Urea release was erratic but appeared uninfluenced by oyster biomass. Fluxes of oxygen and of each nitrogen compound displayed thus a specific response to modifications of the oyster biomass. Both the organisms and the sediment are involved in regulation processes of metabolic exchange rates at the water-sediment interface.     

In situ oxygen consumption rates of cells in V-79 multicellular spheroids during growth

The rate of consumption of oxygen by V-79 cells in multicellular spheroids was measured as a function of the spheroid diameter. In situ consumption was equal to that of exponentially growing cells for spheroids less than 200 micron in diameter. The rate of oxygen consumption decreased for cells in spheroids between 200 and 400 micron diameter to a value one-fourth the initial, then remained constant with further spheroid growth. Comparison of consumption rates for spheroid-derived cells before and after dissociation from the spheroid structure indicated that the spheroid microenvironment accounted for only 20% of the change in oxygen consumption rate. Cell-cell contact, cell packing, and cell volume were not critical parameters. Plateau-phase cells had a fivefold lower rate of oxygen consumption than exponential cells, and it is postulated that the spheroid quiescent cell population accounts for a large part of the intrinsic alteration in oxygen consumption of cells in spheroids. Some other mechanism must be involved in the regulation of cellular oxygen consumption in V-79 spheroids to account for the remainder of the reduction observed in this system.     

Thermocouple psychrometer for in situ leaf water potential determinations

Summary An in situ thermocouple psychrometer was tested to determine its capability for tracking the changing leaf water potentials of aspen (Populus tremuloides Michx.) under controlled conditions and in the field. The results agreed with theoretical expectations — a sharp decline in leaf water potential during the photoperiods and recovery during the dark periods, each to progressively lower levels during a soil drying cycle. In the field, a mid-day pause in the declining leaf water potentials was noted and attributed to transient stomatal closure. Details of the construction and use of the assembly are given.The authors are plant physiologists, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah 84401, stationed in Logan, Utah, at the Forestry Sciences Laboratory.     

In situ zymography: topographical considerations

In situ gelatin zymography is a simple technique providing valuable information about the cellular and tissue localization of gelatinases. Until recently, the use of this technique has been confined to soft, relatively homogeneous tissue. In this report in situ zymography has been utilized to assess the sub-lamellar location of gelatinases in the hard, semi-keratinized epidermal layer and the adjacent soft connective tissue matrix of the dermis of the equine hoof. We show that alterations in the orientation at which the tissue is dipped and withdrawn from the emulsion cause profound alterations in emulsion thickness. Microscopic variations in the surface topography of frozen tissue sections also influence emulsion thickness making interpretation of the results difficult. Given these results, researchers must be aware of potential variations in zymographic analysis may be influenced by physical tissue parameters in addition to suspected gelatinase activity.     

In situ specific loss and growth rates of purple sulfur bacteria in Lake Cisó

Abstract Growth rates and population dynamics of phototrophic bacteria in Lak Cisó were analysed by measuring bacterial abundances and determining specific rates of growth and loss. Net growth rates were calculated from actual changes in biomass assuming exponential growth. Values ranged between −0.072 and 0.037 per day (d⁻¹) for Chromatium , and between −0.043 and 0.022 d⁻¹ for Amoebobacter . Exponential loss rates through sedimentation, decomposition and washout were determined independently. Values ranged between 0 and 0.025 d⁻¹ in the case of Chromatium and between 0 and 0.015 d⁻¹ in the case of Amoebobacter . Finally, gross growth rates were calculated by adding net growth to losses. Maximal values were 0.063 d⁻¹ for Chromatium and 0.037 d⁻¹ for Amoebobacter . In the case of Chromatium , population growth rates were found to be correlated with the amount of light available per unit of growing biomass. It was concluded that growth of phototrophic bacteria in Lake Cisó was limited by light availability. Altogether, purple sulfur bacteria seemed to maintain a very large biomass with very slow growth, thanks to very slow losses during stratification. During holomixis the situation was more dynamic. Washout of cells and disappearance of algal cells allowed more light to reach the bacteria. Therefore, high growth rates were found towards the end of the winter. A similar pattern repeated itself from year to year. These are the first estimates of in situ growth rates for populations of phototrophic bacteria.     

In situ growth rates and biofilm development of Pseudomonas aeruginosa populations in chronic lung infections

The growth dynamics of bacterial pathogens within infected hosts are a fundamental but poorly understood feature of most infections. We have focused on the in situ distribution and growth characteristics of two prevailing and transmissible Pseudomonas aeruginosa clones that have caused chronic lung infections in cystic fibrosis (CF) patients for more than 20 years. We used fluorescence in situ hybridization (FISH) directly on sputum specimens to examine the spatial distribution of the infecting P. aeruginosa cells. Mucoid variants were present in sputum as cell clusters surrounded by an extracellular matrix, whereas nonmucoid variants were present mainly as dispersed cells. To obtain estimates of the growth rates of P. aeruginosa in CF lungs, we used quantitative FISH to indirectly measure growth rates of bacteria in sputum samples (reflecting the in vivo lung conditions). The concentration of rRNA in bacteria isolated from sputa was measured and correlated with the rRNA contents of the same bacteria growing in vitro at defined rates. The results showed that most cells were actively growing with doubling times of between 100 and 200 min, with some growing even faster. Only a small stationary-phase subpopulation seemed to be present in sputa. This was found for both mucoid and nonmucoid variants despite their different organizations in sputum. The results suggest that the bacterial population may be confronted with selection forces that favor optimized growth activities. This scenario constitutes a new perspective on the adaptation and evolution of P. aeruginosa during chronic infections in CF patients in particular and on long-term infections in general.     

A statistical analysis of flow cytometric determinations of phagocytosis rates.

Uptake of particles by phagocytosing cells is a process that exhibits variability of its rate. This variability is inherent in the mechanism of particle uptake and in the mechanisms that determine the distribution of physiological states within a population of phagocytosing cells. When numbers of particles ingested by cells are determined flow cytometrically an additional measurement variability is superimposed on and interacts with the aforementioned biological variability. In one method of determining population phagocytosis parameters, which involves fitting theoretical equations to experimental time course data on the fractions of cells which have ingested 0, 1, 2, ... particles, the effects of measurement variability are circumvented, although this usually has the cost of not using all the sample data obtained. However, in a second, simpler, method which is based on determining the time course of the number of particles ingested by an average cell, measurement variability is not circumvented and its effects must be considered. An analysis of the combined effects of biological and measurement variability on the results obtained with the simpler method is presented in this paper. Experimental results for phagocytosis of latex microspheres of uniform size and fluorochrome content by populations of the ciliate Tetrahymena pyriformis show that, for this system, measurement variability is entirely negligible in comparison with biological variability. This conclusion might not apply to other systems, however, and situations which might make measurement variability of some significance are mentioned in the paper. The equations given can be used for the analysis of such situations.