Equivalent Spherical Diameter Research Articles

Temperature-induced microbubbles within natural marine samples may inflate small-particle counts in a Coulter Counter

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 450:275-280 (2012) - DOI: https://doi.org/10.3354/meps09513 NOTE Temperature-induced microbubbles within natural marine samples may inflate small-particle counts in a Coulter Counter Edward J. Rice, Caterina Panzeca, Gillian M. Stewart* The School of Earth and Environmental Sciences, Queens College, City University of New York (CUNY), Flushing, New York 11367, USA *Corresponding author. Email: gstewart@qc.cuny.edu ABSTRACT: The Coulter Counter, a common instrument used to enumerate phytoplankton, may over-estimate counts of particles <2.5 µm in equivalent spherical diameter (ESD) by an order of magnitude when samples are run at temperatures cooler than ambient laboratory conditions. This phenomenon is likely due to microbubbles generated as a colder sample warms. Evidence for this mechanism derives from the observation that increasing the relative fraction of organic-rich coastal water in warming samples results in increased amplification of small-particle counts due to the stabilization of microbubbles. Count amplification can be eliminated by ensuring there is no temperature difference between the diluent and the sample. Failing to correct for this error confounds analysis of marine phytoplankton size spectra, complicating a broad range of experiments from those measuring productivity to those used to develop ecosystem-based models. KEY WORDS: Coulter Counter · Microbubbles · Temperature · Particle size · Picoplankton Full text in pdf format PreviousNextCite this article as: Rice EJ, Panzeca C, Stewart GM (2012) Temperature-induced microbubbles within natural marine samples may inflate small-particle counts in a Coulter Counter. Mar Ecol Prog Ser 450:275-280. https://doi.org/10.3354/meps09513 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 450. Online publication date: March 29, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Seed-Induced, Structure Directing Agent-Free Crystallization of Sub-Micrometer Zeolite ZSM-5: A Population Balance Analysis

Crystallization of sub-micrometer sized zeolite ZSM-5 from a TPA-free (TPA = tetrapropyl ammonium) reaction mixture 1.0Al2O3/100SiO2/28Na2O/4000H2O, seeded with silicalite-1 seed crystals of two different sizes (260 and 690 nm), was analyzed by population balance methodology. Changes in crystal size distributions and fractions of the newly formed crystalline phase (ZSM-5) were measured and compared with the calculated (simulated) data. For the crystalline end products having D ≥ 0.5 μm (D is the equivalent spherical diameter as measured by a laser-light scattering method), a small disagreement between measured and simulated crystal size distributions is observed and explained by the formation of a small proportion of crystal aggregates at the end of the crystallization process. However, an almost perfect correlation between measured and simulated kinetics of crystallization shows that the formation of aggregates do not considerably influence the growth rate of zeolite ZSM-5 on silicalite-1 seed crystals. ...

Interannual and latitudinal changes in zooplankton abundance, biomass and size composition along a central North Pacific transect during summer: analyses with an Optical Plankton Counter

To evaluate zooplankton interannual and latitudinal changes, Optical Plankton Counter analyses were made on preserved net zooplankton samples collected by NORPAC net from 0-150 m at 35°N-51°N stations along 180° in the central North Pacific during early-mid June 1981-2000. The mean numerical abundance of total zoo- plankton for the 20 years varied latitudinally from 19,200 to 84,300 ind. m -2 but the differences between the three oceanic domains were not significant. However, highly significant latitudinal changes were observed in the mean zooplankton biomass, which ranged from 1.44 to 13.2 mg dry mass m -2 with higher values in the Transitional Do- main (TR) than in the Subarctic and Subtropical Domains. The high biomass in the TR was caused by the dominance of large-sized zooplankton with equivalent spherical diameters (ESD) of 2-4 mm, regarded to consist mainly of Neo- calanus spp. C5. Both the slope and intercept of the Normalized Biomass Size Spectrum also showed significant lati- tudinal changes with a moderate slope and low intercept in the TR due to the dominance of large zooplankton with 2-4 mm ESD in biomass. In contrast to these large latitudinal changes, only limited interannual variations were ob- served for zooplankton abundance and biomass in the central North Pacific during the study period.

レーザー式プランクトンカウンター（Laser Optical Plankton Counter, LOPC）による動物プランクトン群集に対する種別計測に関する検討

動物プランクトンの種別分布量を把握するため，曳航型レーザー式プランクトンカウンター（LOPC）のデータ解析法を検討した。2007 年 4 月昼間に北海道噴火湾の 12 点においてリングネットに装着した LOPC を鉛直曳航した。採集物のカイアシ類と端脚類の体サイズは一部重複したが，LOPC の検出粒子のサイズ組成は種別湿重量組成と同様の変化傾向を示した。LOPC を用いた種別計測のためには，動物プランクトンの種ごとの検出粒子の計測特性を明らかにする必要があると考えられた。

Grain size distribution and age population of detrital zircons from the Changjiang (Yangtze) River system, China

This study investigated the correlation of the size of detrital zircons with their age populations in a fluvial environment. From 31 floodplain sediments that were isolated from the mainstream and ten major tributaries of the Changjiang River, 3526 detrital zircon grains were selected for size examination, and 1358 were chosen for U–Pb age measurements. The Equivalent Spherical Diameter (ESD) of most zircon grains falls within the range of 32–250μm, and the dominant size is 63–125μm. Small-sized zircons with ESDs of <63μm are found in higher proportions in the mid-lower mainstream than in the upper reaches. An overall decrease in the average ESD size of detrital zircons towards the mid-lower reaches reflects the hydraulic sorting effect of different river flow regimes along this river. Overall, the age populations of zircons between the different tributaries and mainstream are similar, and several age groups correspond well with major tectonic–magmatic events that happened in the river basin. This study confirms the notion that younger zircons have coarser and more variable sizes than the older zircons, indicating the potential influence of hydrodynamic fractionation on zircon size and ages. The problem of grain-size bias on age-data acquisition and interpretation of detrital zircons from large rivers is not negligible and deserves more attention when using zircon geochronology to decipher sediment provenance and tectonic evolution. Although the zircons with an ESD of 63–125μm dominate the Changjiang sediment and have similar age populations as the bulk zircons, whether this narrow-sized window can accurately represent the bulk zircon geochronology of the weathered and heterogeneous rocks in the large catchment awaits additional investigations.

Inferring phytoplankton carbon and eco-physiological rates from diel cycles of spectral particulate beam-attenuation coefficient

Abstract. The diurnal fluctuations in solar irradiance impose a fundamental frequency on ocean biogeochemistry. Observations of the ocean carbon cycle at these frequencies are rare, but could be considerably expanded by measuring and interpreting the inherent optical properties. A method is presented to analyze diel cycles in particulate beam-attenuation coefficient (cp) measured at multiple wavelengths. The method is based on fitting observations with a size-structured population model coupled to an optical model to infer the particle size distribution and physiologically relevant parameters of the cells responsible for the measured diel cycle in cp. Results show that the information related to size and contained in the spectral data can be exploited to independently estimate growth and loss rates during the day and night. In addition, the model can characterize the population of particles affecting the diel variability in cp. Application of this method to spectral cp measured at a station in the oligotrophic Mediterranean Sea suggests that most of the observed variations in cp can be ascribed to a synchronized population of cells with an equivalent spherical diameter around 4.6±1.5 μm. The inferred carbon biomass of these cells was about 5.2–6.0 mg m−3 and accounted for approximately 10% of the total particulate organic carbon. If successfully validated, this method may improve our in situ estimates of primary productivity.

Dense winter bloom of the dinoflagellate Heterocapsa triquetra below the thick surface ice of brackish Lake Shihwa, Korea

SUMMARYWe investigated the seasonal abundance of the dinoflagellate Heterocapsa triquetra (Ehrenberg) F. Stein, as well as the relevant in situ environmental factors, in brackish Lake Shihwa, Korea. We also examined the growth rates and morphological characteristics of the species in laboratory cultures. In the field, the population densities of H. triquetra remained at low levels from late spring to early summer, and then completely disappeared from August to November 2007. Interestingly, a dense bloom of H. triquetra appeared below the ice surface on 17 January 2008; identities of the cells were confirmed by rDNA sequence comparisons. The second peak reached a density of 672 × 103 cells L−1 on 28 March 2008, at a water temperature of 9.1°C. Laboratory experiments showed that growth rates of H. triquetra increased with incremental temperature increases within the range of 10 and 20°C. The highest growth rate reached by H. triquetra was 0.62 d−1 at 20°C with a salinity of 30. Above 25°C, the dinoflagellate was unable to grow between salinities of 10 and 15, and reached only relatively low growth rates (&lt;0.12 d−1) under other salinity conditions. However, under continuous cultures at 5°C and 8°C, H. triquetra cells retained its growth capability for more than 12 days, implying that H. triquetra can survive and grows even at very low temperatures. The equivalent spherical diameter (ESD) of H. triquetra did not change markedly between 10 and 25°C, but the equivalent spherical diameter was significantly different at 5°C. The cell volume buildup of H. triquetra at low temperatures is one of the important survival strategies to overcome the harsh environmental conditions. These characteristics make H. triquetra a consistently dominant dinoflagellate in Lake Shihwa during the cold winter season.

Feeding by the Newly Described, Nematocyst‐Bearing Heterotrophic Dinoflagellate Gyrodiniellum shiwhaense

We explored the feeding ecology of the newly described, nematocyst-bearing heterotrophic dinoflagellate Gyrodiniellum shiwhaense (GenBank accession number=FR720082). Using several different types of microscopes and high-resolution video-microscopy, we investigated feeding behavior and types of prey species that G. shiwhaense feeds upon. Additionally, we measured its growth and ingestion rates on its optimal algal prey, the cryptophyte Teleaulax sp. and the dinoflagellate Amphidinium carterae, as a function of prey concentration. These rates were measured for other edible prey at single prey concentrations at which the growth and ingestion rates of G. shiwhaense were saturated. After anchoring the prey with a tow filament, G. shiwhaense fed using a peduncle, ingesting small algal species with equivalent spherical diameters (ESDs) of <13 μm. However, it did not feed on larger algal species that had ESDs≥13 μm or the small diatom Skeletonema costatum. The specific growth rates for G. shiwhaense feeding upon Teleaulax sp. and A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 180-430 ng C/ml. The maximum specific growth rate of G. shiwhaense on Teleaulax sp. and A. carterae were 1.05 and 0.82/d, respectively. However, Heterosigma akashiwo did not support positive growth of G. shiwhaense. The maximum ingestion rates of G. shiwhaense on Teleaulax sp. and A. carterae were 0.35 and 0.54 ng C/grazer/d, respectively. The calculated grazing coefficients attributable to G. shiwhaense on co-occurring cryptophytes and Amphidinium spp. were 0.01-1.87/d and 0.08-2.60/d, respectively. Our results suggest that G. shiwhaense can have a considerable grazing impact on algal populations.

Size-Dependent Bandgap of Nanogoethite

Rod-shaped goethite nanoparticles with average particle sizes (equivalent spherical diameters) of between ∼9 and 38 nm were synthesized via reaction of ferric nitrate with potassium/sodium hydroxide in aqueous solutions. We deconvoluted the UV–vis spectra into individual absorption bands for each of the nanogoethite samples and determined the particle size dependence for each band. As the particle size decreases, the charge transfer band is slightly red-shifted, whereas five other bands, including the electron pair transition that determines the absorption edge, are blue-shifted. Spectra were also used to determine bandgap energies as a function of particle size via Tauc–Mott plots. Over different photon energy ranges, nanogoethite appears to exhibit direct bandgap (2.5–3.1 eV) and indirect bandgap (1.6–2.1 eV) behaviors. The bandgap widens as particle size decreases, an effect that can be described by the Kayanuma equation, from which the reduced mass of an exciton in nanogoethite was found to be ∼3–4% the mass of a rest electron. The existence of an indirect bandgap at relatively lower energy as compared to the direct bandgap and altered redox properties due to shifts and opening of the bandgap as particle size decreases may partially explain size-dependent chemical and photochemical reactivity of goethite.

Flow cytometric studies of platelet responses to shear stress in whole blood

The objective of this work was to evaluate quantitatively the effects of flow on platelet reactions using a flow cytometric technique. Whole blood was exposed to well defined, laminar shear stress in a cone-and-plate viscometer in the absence of added agonists. Blood specimens were fixed with formaldehyde and incubated with two monoclonal antibodies. Antibody 6D1, specific for platelet membrane glycoprotein Ib (GPIb), was used to identify and enumerate platelets and platelet aggregates on the basis of their characteristic forward scatter and 6D1-FITC fluorescence profiles. Anti-CD62 antibody, specific for the granule membrane protein-140 (GMP-140), was used to measure platelet activation. Results showed platelet aggregation increasing with increasing shear stress with marked increase in this response for a pathophysiological stress level of 140 dyn/cm 2 and higher. This stress level also was the apparent threshold for formation of large platelet aggregates (“large” refers to particles larger than 10 μm in equivalent sphere diameter). These platelet responses to shear stress were insensitive to aspirin, but strongly inhibited by agents that elevate platelet cyclic adenosine monophosphate (cAMP) levels. Moreover, pre-incubation of whole blood with monoclonal antibodies that inhibit von Willebrand factor binding to GPIb or von Willebrand factor and fibrinogen binding to GPIIb/IIIa inhibited platelet aggregation. Aggregation induced by shear at 37° C was less in extent than at 23° C. At physiological shear stresses, whole blood was more susceptible to shear-induced platelet aggregation than platelet-rich plasma. This study reaffirms that flow cytometric methods have several important advantages in studies of shear effects on platelets, and extends the methodology to whole blood unaltered by cell separation methods.

A study on the synthesis of (Ba,Ca)(Ti,Zr)O 3 nano powders using Pechini polymeric precursor method

Pechini polymeric precursor method was successfully used to synthesize (Ba 0.95Ca 0.05)(Ti 0.85Zr 0.15)O 3 nano powders. The results of TG/DTA, XRD and IR analyses showed that by heating the precursor between 490 °C and 580 °C, an intermediate phase with possible composition of (Ba,Ca) 2(Ti,Zr) 2O 5CO 3 was formed. Between 580 °C and 700 °C, the intermediate phase transformed to a crystalline solid solution by de-carbonation reaction. The transformation completed at 700 °C. Nano-sized powders with equivalent sphere diameters about 72 nm were obtained by calcination of the precursor at 700 °C for 4 h. The ceramics sintered at 1300 °C for 2 h can reach about 95% theoretical density and the peak dielectric constant is 15,000 at 70 °C.

Planktonic ciliates as a food source for the scyphozoan Aurelia aurita (s.l.): Feeding activity and assimilation of the polyp stage

To clarify the value of planktonic ciliates as a prey source for the moon jellyfish (Aurelia aurita), feeding rates of the polyp stage on Favella ehrenbergii, Strombidium sp., and Myrionecta rubra were quantified in laboratory experiments. The feeding responses on ciliates were compared with those on phytoplankton with similar equivalent spherical diameters (ESDs) by observation of the feeding behavior. The assimilation of ciliates ingested by A. aurita was examined by providing the ciliate Strombidinopsis jeokjo, labeled with nitrogen stable isotope (15N), to the polyps. A. aurita polyps fed on all species of ciliates. Feeding rates of A. aurita polyps as a function of ciliate concentration were fitted to a rectangular hyperbolic equation, and the maximum feeding rate was ca. 32cellsind−1h−1 (0.33μgCind−1h−1) for all ciliate species. The maximum feeding rate on M. rubra was significantly lower than those on the other ciliate genera, which is probably caused by the smaller cell size and distinctive motility of this species. Feeding incidences, defined by the movement of polyp tentacles, rarely occurred on nanophytoplankton with ESDs of ca. 20μm, and the feeding incidence on microphytoplankton with ESDs of ca. 30μm was significantly lower than that on a ciliate with a similar ESD, implying that phytoplankton is not an essential prey for mature A. aurita polyps. After polyps fed on 15N-labeled ciliates, the average nitrogen stable isotope ratio of polyps in the experimental treatments was significantly higher than that in the control, indicating that the polyps were able to assimilate nutrients from the captured ciliates. These results indicate that planktonic ciliates, a main component of microzooplankton and a frequently encountered energy source, likely serve as available food items for A. aurita polyps.

Group sweeping: Feeding activity and filtration rate in the tubiculous amphipod Haploops nirae (Kaim-Malka, 1976)

Haploops nirae is a gregarious tubiculous amphipod that uses its two pairs of antennae to filter particles from the water column. Recent sonar mappings of Haploops seabeds revealed that thousands of hectares of soft-bottom muddy sediments in South Brittany coastal ecosystems are now colonized by this amphipod. The present study investigates (1) the structure of the feeding organs and the mechanisms involved in particle capture, (2) the effect of environmental parameters (current velocity, turbidity and food concentration) on the feeding activity of H. nirae, quantified by the percentage of active individuals, the frequency of antennae beats and the number and duration of feeding events and (3) the retention efficiency and clearance rate of H. nirae individuals, so extrapolation to colonized areas and grazing impact of this species can be estimated. Staining techniques and scanning electron microscopy revealed that Haploops antennae have a more complex structure than congeneric Ampelisca species, involving long setae bearing short setules and that mucus is involved in particle capture. An increase in current velocity seemed to have very little effect on feeding activity but unexpectedly slightly increased the frequency of antennae beats. However, an increase in both organic and inorganic matter both exponentially increased the number of filtering individuals and showed that Haploops are well adapted to feed in turbid conditions: the total time individuals spent filtering remained constant while inorganic particulate matter increased from 10.7 to 85.6 mg·L − 1 . Using a flow-through system, evaluation of retention efficiency showed that only particles larger than 20 μm equivalent spherical diameter were 100% retained by feeding structures, which corresponds to the mean distance between two setules. Clearance rate was estimated at 14.6 ± 0.4 mL·h − 1 .ind − 1 or standardized to 25.2 ± 0.7 L·h − 1 ·g − 1 dry weight. Those values are discussed in light of values obtained in other suspension-feeding species and also extrapolated to the whole Haploops community. We estimated that Haploops have the capacity to filter the entire water column in 4–5 days and a volume of water equivalent to the whole bay in 29–30 days. This study provides evidence that changes in the spatial extent of Haploops communities may have serious impacts within coastal ecosystem they have colonized.

TU-C-BRB-02: Personalized Assessment of KV-CBCT Doses in Image Guided Radiotherapy of Pediatric Cancer Patients

Purpose: To develop an empirical method for estimation of doses to critical structures of children undergoing kV‐CBCT imaging for image‐guidedradiotherapy. Methods: Forty pediatric patients were retrospectively assorted into four groups by gender and scanned sites with approval of IRB. Critical structures in CTimages were delineated on Eclipse treatment planning system and were subsequently packaged into patient CT phantoms for Monte Carlo simulations. A benchmarked EGS4 Monte Carlo code was used to calculate 3D dose distributions produced by High‐quality head and Pelvic protocols that were pre‐defined by manufacturer. The ratios of irradiated volume over longitudinal length (V/L) and the equivalent sphere diameters (ESDs) were calculated by Eclipse. In accordance with the scanned region, either occipital‐frontal circumferences (OFCs) or hip circumferences (HIPs) were calculated by DICOMan software. Regression was performed with SigmaPlot software suite where average standard errors of estimate (SEEs) were compared to evaluate the accuracy of regression and reliability of various parameters. Results: For both sexes, mean doses of all critical structures were observed to decrease linearly with the increase of all physical parameters including age, weight, V/L, ESD, OFC, and HIP. As suggested by smaller standard errors of estimates, OFC and weight are recommended for head dose estimation while ESD and weight are more appropriate for pelvic/abdominal dose regression. Unique empirical functions for the estimation of doses to critical organs for male or female patients are presented which make a personalized dose assessment readily feasible. Conclusions: Using Monte Carlo simulations in a population of 40 selected children, kV‐CBCT doses were found highly correlated with body sizes of children. Considering uneven body development levels among children of same age, OFC and weight are recommended primarily for dose estimation in head, while weight and ESD are preferred for pelvic dose assessment. This work was partially supported by National Basic Research Subject (973) of China (No.2011CB707701), China Scholarship Council (No. 2010601107), and Joint Research Foundation of Beijing Education Committee, China (No. JD100010607)

Optical imaging of mesopelagic particles indicates deep carbon flux beneath a natural iron‐fertilized bloom in the Southern Ocean

We recorded vertical profiles of size distributions of particles (ranging from 0.052 to several mm in equivalent spherical diameter) in the natural iron‐fertilized bloom southeast of Kerguelen Island (Southern Ocean) and in surrounding high‐nutrient, low‐chlorophyll (HNLC) waters with an Under Water Video Profiler during the Kerguelen Ocean and Plateau Compared Study cruise (Jan–Feb 2005). Total particle numerical abundance and total particle volume (TPV) in the 0–200‐m layer were respectively 3‐fold and 20‐fold higher in the bloom, and integrated TPV was correlated to integrated chlorophyll concentration. The difference persisted well into the ocean interior with a 10‐fold higher TPV at 400‐m depth beneath the natural iron‐fertilized bloom. Below 400 m, increases in TPV values at the bloom stations reflect the suspension of bottom sediments. Bloom waters had a greater proportion of large particles from the surface to 400 m and also exhibited an increase of this proportion with depth compared to HNLC waters. Multiple visits to the bloom reference Sta. A3, suggest preferential removal of large particles as the bloom declined. Comparing our particle abundance size spectra with those observed previously in polyacrylamide gel‐filled sediment traps allows us to estimate mesopelagic particle sinking rates. These results suggest that particles sink faster in the HNLC waters than beneath the bloom. The fact that sinking speeds were not a simple monotonic function of particle size and varied spatially highlights the need to go beyond parameterizations of sinking rate as a function of size alone.

Trophic interactions of pelagic crustaceans in Comau Fjord (Chile): their role in the food web structure

Grazing experiments were used to study the trophic interactions among plankton components in a stratified fjord of southern Chile. A strong pycnocline (7–10 m) separating the low-salinity layer from the deeper, high-salinity, marine layer, affected the composition, abundance and distribution of phytoplankton and zooplankton every season. Nanoflagellates averaging 59% were consistently the main components of the plankton biomass in both layers. The microphytoplankton contribution was always higher within the marine layer. Cladocerans and some small copepods showed a vertical gradient with greater abundances in the low-salinity layer, whereas medium-large copepods and euphausiids were more abundant below the pycnocline. Podon leuckarti averaged an ingestion rate of 3.1 µg C ind.−1 day−1, consisting mostly of particles from the nanoplankton size spectrum. Given significant clearance on ciliates and athecate dinoflagellates plus high ingestion rates of heterotrophic nanoflagellates it seems that this species selects for microzooplankton and that heterotrophic components are important in their diet. Calanus australis ingested 15 µg C ind.−1 day−1 on average, covering a wide spectrum of prey sizes (5–65 µm equivalent spherical diameter) and diversity, with active selection for ciliates. The average ingestion rate for Euphausia vallentini was 78.7 µg C ind.−1 day−1, including wide variety of prey sizes but no apparent selectivity. The potential grazing impact (11%) on primary productivity, together with high abundances, feeding selectivity on nanoplankton and production of unconsolidated fecal material indicate that cladocerans could have a double positive feedback effect on the microbial loop, thereby having an important impact by modifying the composition and structure of the planktonic community in Comau Fjord in spring-summer.

Does the study of microzooplankton community size structure effectively define their dynamics? Investigation in the Bay of Biscay (France)

Studies of microzooplankton dynamics based on the analysis of community taxonomic composition are very time-consuming and manpower demanding. Recent developments in automatic plankton counting technology offer a new way to consider plankton dynamics with straightforward analysis of community size structures. The present study aimed to determine if cell size is a good descriptor of microzooplankton dynamics. The dynamics of the microzooplankton community of the Bay of Biscay (France) at three sites and during four sampling periods was analyzed using three different classification criteria: taxonomy, body size (ng C cell 21 ) and equivalent spherical diameter (ESD, mm). A Mantel test revealed that there was no difference in the characteristics of microzooplankton dynamics when studying either community size structure or taxonomic composition. Moreover, a BIO-ENV analysis confirmed that the biotic and abiotic factors selected for affecting microzooplankton community dynamics were the same among the three classification types. Considering these results, it is argued that microplankton dynamics is well defined by the study of the community size structure. While focusing on microzooplankton size structure seems promising, homogenizing the size descriptor used among studies would be needed in order to make worldwide data comparisons and ESD/biovolume should be favored.

Mixotrophy in the Newly Described Phototrophic Dinoflagellate Woloszynskia cincta from Western Korean Waters: Feeding Mechanism, Prey Species and Effect of Prey Concentration

Woloszynskia species are dinoflagellates in the order Suessiales inhabiting marine or freshwater environments; their ecophysiology has not been well investigated, in particular, their trophic modes have yet to be elucidated. Previous studies have reported that all Woloszynskia species are photosynthetic, although their mixotrophic abilities have not been explored. We isolated a dinoflagellate from coastal waters in western Korea and established clonal cultures of this dinoflagellate. On the basis of morphology and analyses of the small/large subunit rRNA gene (GenBank accession number=FR690459), we identified this dinoflagellate as Woloszynskia cincta. We further established that this dinoflagellate is a mixotrophic species. We found that W. cincta fed on algal prey using a peduncle. Among the diverse prey provided, W. cincta ingested those algal species that had equivalent spherical diameters (ESDs) ≤12.6 μm, exceptions being the diatom Skeletonema costatum and the dinoflagellate Prorocentrum minimum. However, W. cincta did not feed on larger algal species that had ESDs≥15 μm. The specific growth rates for W. cincta increased continuously with increasing mean prey concentration before saturating at a concentration of ca. 134 ng C/ml (1,340 cells/ml) when Heterosigma akashiwo was used as food. The maximum specific growth rate (i.e. mixotrophic growth) of W. cincta feeding on H. akashiwo was 0.499 d(-1) at 20 °C under illumination of 20 μE/m(2) /s on a 14:10 h light-dark cycle, whereas its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was 0.040 d(-1). The maximum ingestion and clearance rates of W. cincta feeding on H. akashiwo were 0.49 ng C/grazer/d (4.9 cells/grazer/d) and 1.9 μl/grazer/h, respectively. The calculated grazing coefficients for W. cincta on co-occurring H. akashiwo were up to 1.1 d(-1). The results of the present study suggest that grazing by W. cincta can have a potentially considerable impact on prey algal populations.

Particle size distributions in the upper 100 m water column and their implications for animal feeding in the plankton

We deployed autonomous particle-sensing SOLOPC floats more than eight times during five cruises, amassing almost 400 profiles of particle size ( d > 90 μ m ) and abundance between the ocean surface and 100 m. The profiles consistently had subsurface maxima in particle volume. The median (by volume) equivalent spherical diameter for the particle distribution was 0.4–0.8 mm and increased with depth in a manner similar to that observed in coagulation simulations. There was a sharp cutoff at the bottom of the high particle concentration region. Estimation of particle fluxes made using the size distributions show an increasing downward movement through the particle field above the sharp particle cutoff. The increase of particle flux with depth through the euphotic zone implies a partial spatial separation of production and consumption. The sharp drop in particle volume and flux implies that the base of the particle-rich zone is a region of active particle consumption, possibly by zooplankton flux feeding. Our data show greater concentrations of zooplankton-type particles relative to marine snow-type particles below the particle maximum. Such behavior could explain why zooplankton are frequently observed at and immediately below the particle maximum rather than the productivity maximum and suggests an important role for flux feeding in carbon and nutrient cycling at the base of the particle maximum. This implies that zooplankton act as gatekeepers for the movement of organic matter to the mesopelagic. The ability of the SOLOPC to sample hourly with high resolution in the upper 100 m of the ocean provides a powerful complement for the study of particles where it has been difficult to use sediment traps.

Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 419:57-69 (2010) - DOI: https://doi.org/10.3354/meps08840 Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study M. L. Pedrotti1,*, F. Peters2, S. Beauvais1, M. Vidal3, J. Egge4, A. Jacobsen4, C. Marrasé2 1Marine Microbial Ecology Group, Laboratoire d’Océanographie de Villefranche, CNRS-UMR 7093, BP 28, 06234 Villefranche-sur-mer, France 2Institut de Ciències del Mar, CMIMA (CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalunya, Spain 3Departament d’Ecology, Universitat de Barcelona, Barcelona, Spain 4Department of Fisheries and Marine Biology, University of Bergen, HIB, 5020 Bergen, Norway *Email: pedrotti@obs-vlfr.fr ABSTRACT: The production of transparent exopolymer particles (TEP) in response to several environmental variables was studied in 2 mesocosm experiments. The first (Expt 1) examined a gradient of 4 nutrient levels; the second (Expt 2) examined different conditions of silicate availability and zooplankton presence. Tanks were separated in 2 series, one subjected to turbulence and the other not influenced by turbulence. In tanks with nutrient addition, TEP were rapidly formed, with net apparent production rates closely linked to chl a growth rates, suggesting that phytoplankton cells were actively exuding TEP precursors. High nutrient availability increased the absolute concentration of TEP; however, the relative quantity of TEP produced was found to be lower, as TEP concentration per unit of phytoplankton biomass was inversely related to the initial nitrate dose. In Expt 1, an increase in TEP volume (3 to 48 µm equivalent spherical diameter) with nutrient dose was observed; in Expt 2, both silicate addition and turbulence enhanced TEP production and favored aggregation to larger TEP (>48 µm). The presence of zooplankton lowered TEP concentration and changed the size distribution of TEP, presumably by grazing on TEP or phytoplankton. For lower nutrient concentrations, the ratio of particulate organic carbon (POC) to particulate organic nitrogen (PON) followed the Redfield ratio. At higher nutrient conditions, when nutrients were exhausted during the post-bloom, a decoupling of carbon and nitrogen dynamics occurred and was correlated to TEP formation, with a large flow of carbon channeled toward the TEP pool in turbulent tanks. TEP accounted for an increase in POC concentration of 50% in high-nutrient and turbulent conditions. The study of TEP dynamics is crucial to understanding the biogeochemical response of the aquatic system to forcing variables such as nutrient availability and turbulence intensity. KEY WORDS: Transparent exopolymer particles · TEP production · Phytoplankton · Particulate organic carbon · POC · Turbulence · Nutrients · Mesocosms Full text in pdf format PreviousNextCite this article as: Pedrotti ML, Peters F, Beauvais S, Vidal M, Egge J, Jacobsen A, Marrasé C (2010) Effects of nutrients and turbulence on the production of transparent exopolymer particles: a mesocosm study. Mar Ecol Prog Ser 419:57-69. https://doi.org/10.3354/meps08840 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 419. Online publication date: November 30, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.