bluuebunny/crossref_metadata_2025 huggingface dataset:
Zync with Me
Authors: Shamma David A. , Liu Yiming
Published: May 2010

This chapter details a real world case study of a synchronized video-sharing tool, Zync. Zync was integrated into a popular instant messenger program that enables a virtual co-present “watch together” and “on-the-couch” viewing experience. Users can watch videos together in sync with each others, while they chat via text messages. Using logged data from 2,814 users, three types of people who share videos via IM are identified, as well as the different kinds of videos commonly shared and how users shared these videos with their IM friends. The authors follow up on these trends with user studies and interviews, which further explains how and why people are motivated to share videos. Based on their findings, the authors identify and define future design areas for synchronized sharing of video; to help keep people connected through media.
Modeling Cd partitioning in oxic lake sediments and Cd concentrations in the freshwater bivalve Anodonta grandis
Authors: Tessier A. , Couillard Y. , Campbell P. G. C. , Auclair J. C.
Published: May 2010

Cadmium concentrations were measured at 49 littoral sites in 38 lakes distributed over 350,000 km2 in the provinces of Québec and Ontario, both in the abiotic environment (oxic sediments and overlying water, diagenetic iron oxyhydroxide deposits on Teflon collectors) and in the soft tissues of the freshwater bivalve Anodonta grandis collected along a Cd contamination gradient. Concentrations of dissolved Cd above the water‐sediment interface were highly undersaturated with respect to CdCO3(s). The partitioning of Cd between water and surficial oxic sediments is interpreted in terms of sorption of this metal to sedimentary organic matter and Fe oxyhydroxides, by means of surface complexation concepts. Binding intensity values for the sorption of Cd to Fe oxyhydroxides (KFe−Cd) and organic matter (KOM−Cd) are estimated from field data (i.e. Cd concentrations in diagenetic Fe deposits, in the sediments, and in the water). The following empirical relationships between binding intensities and lake pH are found: log KFe−Cd = 0.82 pH − 1.30 (r2 = 0.89) and log KOM−Cd = 0.97 pH − 2.45 (r2 = 0.78). Calculated Cd partitioning with these binding intensities indicates that Cd is bound mainly to organic matter in these sediments.

Linear regression analysis indicates that Cd concentrations in the soft tissues of the bivalves, [Cd(Org)] (µg g−1 dry wt), are related to dissolved Cd concentrations: [Cd(Org)] = 44[Cd2+] + 10 (r2 = 0.81) for [Cd2+] expressed in nmol liter−1. In these lakes, simple normalization of sedimentary extractable Cd with respect to sedimentary Fe oxyhydroxide or organic C concentrations proved inadequate for predicting Cd concentrations in A. grandis. Combining surface complexation concepts with the free‐metal ion model of trace metal‐organism interactions, we show that Cd concentrations in the soft tissues of A. grandis can be predicted with similar success as with the dissolved Cd concentration from water pH and sediment chemistry (total sedimentary Cd, Fe oxyhydroxides, and organic C concentrations).
Simulating bacterial clustering around phytoplankton cells in a turbulent ocean
Authors: Bowen James D. , Stolzenbach Keith D. , Chisholm Sallie W.
Published: May 2010

The hypothesis that bacteria can cluster around phytoplankton cells in the turbulent mixed layer was tested with a model that simulates bacterial chemotaxis toward a neutrally buoyant phytoplankton cell exuding dissolved organic C. The model results indicate that bacteria can attain population densities orders of magnitude above background levels in microzones occupying <0.1% of the fluid volume surrounding each phytoplankton cell. The simulation results indicate that at turbulence intensities expected in the upper mixed layer of the ocean (shear rates of ∼0.15 s−1) bacteria initially approach phytoplankton through random swimming and relative fluid motions. Chemotactic response serves to prolong a bacteria’s stay near the phytoplankter before it is carried away by random swimming and fluid motions. At these shear rates, up to 20% of the chemotactic bacteria population could be clustered around exuding phytoplankton cells, even though individual bacteria stay in a cluster less than a minute. For these conditions the time‐averaged exudate exposure of the bacterial population could be 10 times higher than that of a nonchemotactic population. Exudate exposures in unsteady shearing were found to equal or exceed the corresponding steady shear values. Although unsteady bursts of turbulent mixing in the oceanic surface layer should disperse clusters, intervening calm periods are long enough to allow clusters to reform. The model indicates that bacterial clustering is unlikely to have a significant effect on phytoplankton nutrient uptake or on the fate of bacterial secondary production in the microbial food web.
The chlorophyll‐labeling method: Measuring specific rates of chlorophyll a synthesis in cultures and in the open ocean
Authors: Goericke Ralf , Welschmeyer Nicholas A.
Published: May 2010

We tested the assumptions underlying the Chl‐labeling method of measuring phytoplankton growth rates. The observed 14C‐labeling patterns of Chl a are consistent with the presence of three kinetically important pools, the macrocycle, the phytol sidechain, and at least one precursor pool. The turnover rates of these pools were determined from a kinetic analysis of their labeling patterns. Turnover rates of Chl a or its two subunits were not significantly different from zero. The turnover rate of the precursor of the Chl a macrocycle was a constant multiple of the specific rate of pigment synthesis (µChl). An equation was derived that predicts µChl a from the 14C labeling of Chl a. Rates of 14C incorporation into Chl a and rates of C fixation are severely unbalanced when algal cultures photoadapt. It is likely that µChl a as determined by the Chl‐labeling method equals µC, the specific rate of carbon synthesis, only when growth is balanced. We demonstrated that the growth of natural phytoplankton populations can be severely unbalanced when the algae grow under a natural photocycle or when the algae are subjected to shifts in light intensity; we also observed that Chl a was synthesized in the dark. Thus, with the Chl‐labeling method it is not possible to determine carbon‐based growth rates when algae photoadapt or when the duration of the incubation covers only part of the diel light cycle. Chl‐labeling experiments should therefore be based on 24‐h incubations so that the measurements integrate over the diel photocycle.
Time‐course development of 14C specificactivity of chlorophyll a, carbon, and proteins in algal cultures
Authors: Riemann Bo , Lignell Risto , Laws Edward
Published: May 2010

The 14C labeling of Chl a, C, and protein was followed in eight algal batch cultures and three algal continuous cultures. High pressure liquid chromatography and paper chromatography were applied in purifying Chl a. From methodological investigations, we concluded that time‐course measurements of 14C specific activities for Chl a, C, and protein gave similar results as long as turnover of the inorganic C pool reduced the specific activity of inorganic C by ≲ 30%. In these cases growth rates estimated from labeling of total algal C overestimated net growth rates by ∼ 18%. Chl a C‐specific activities consistently exceeded particulate C specific activities in dense cultures when inorganic C turnover reduced the specific activity of the inorganic C by ≳ 65%. The difference in specific activity was positively correlated with the degree of isotope dilution. When the growth rates based on labeling of Chl a were corrected for isotope dilution, they exceeded growth rates estimated from changes in particulate C by ∼ 12%, the difference presumably reflecting respiratory loss of algal C. However, even when isotope dilution corrections were applied, growth rates estimated from particulate C labeling consistently underestimated net growth rates when the specific activity of the inorganic C declined by >65%. The degree of underestimation was positively correlated with the extent of isotope dilution.
Variations in the specific absorption coefficient for natural phytoplankton assemblages: Impact on estimates of primary production
Authors: Babin Marcel , Therriault Jean‐Claude , Legendre Louis , Condal Alfonso
Published: May 2010

Data collected in the estuary and Gulf of St. Lawrence in summer 1989 and 1990 were analyzed to quantify horizontal variations in the spectral values of the specific absorption coefficient of phytoplankton in different natural environments and to examine the consequences of assuming this specific absorption spectrum as constant when estimating primary production. Absorption spectra of total particles were measured with the glass‐fiber filter technique, and absorption by phytoplankton was estimated numerically. We analyzed 369 spectra to estimate the actual extent of variations in the specific absorption coefficient by phytoplankton at several spatial scales in the St. Lawrence system. The potential impact of these variations on the estimation of primary production was assessed for various ecosystems with a spectral primary production model. This model takes into account chlorophyll variations with depth together with associated variations in attenuance and variations in partitioning of the various absorbing components in going from eutrophic to oligotrophic waters. Using this model, we found that, at large scale (>1,000 km), the relative error in estimating primary production can be as high as 24% in oligotrophic waters when a constant specific absorption spectrum is assumed. Field measurements of primary production support results derived from the model.
Bacterivory in algae: A survival strategy during nutrient limitation
Authors: Nygaard Kari , Tobiesen August
Published: May 2010

Bacterivory in obligate phototrophic algal flagellates may be an important strategy for acquiring nutrients during periods of inorganic nutrient limitation. Several marine algal flagellates were shown to increase bactivory when phosphate was limited. Grazing on bacteria by algal flagellates was found during blooms of Prymnesium parvum in Sandsfjorden, western Norway, in 1989 and Chrysochromulina polylepis on the south and west coast of Norway in 1988. Dissolved phosphate was not detectable in these situations. Algal flagellates may graze bacteria to obtain phosphate, which may permit these algal flagellates to develop blooms when phosphate becomes limited.
Experimental records of the effects of food patchiness and predation on egg production of Acartia tonsa
Authors: Saiz Enric , Tiselius Peter , Jonsson Per R. , Verity Peter , Paffenhöfer Gustav‐Adolf
Published: May 2010

The effects of predation and spatial patchiness in food distribution on egg production of the marine calanoid copepod Acartia tonsa were investigated in the laboratory. A postexperiment egg production method was developed to override the decline in number of copepods due to predation. The copepods were able to remain in food patches about 41–47% of the time, and consequently egg production rates were higher than expected from the average food concentration. Predation by the calanoid copepod Labidocera aestiva tended to increase egg production rates of A. tonsa. The interaction of patchiness and predation resulted in relatively less time spent by A. tonsa in the food patches, probably as a consequence of conflict between hunger level and predation risk.
Theoretical analysis of size distributions determined with screens and filters
Authors: Logan Bruce E.
Published: May 2010

Nets, screens, and filters are used to sieve out particles larger than the pore sizes. However, during separation a significant fraction of particles smaller than the pore diameters will also be removed by collision and adhesion to the mesh fibers. Two filtration models were used to predict the size and mass distributions of particles during size separation. A capillary tube model was used to calculate particle removal by different screens, and a fibrous filter model was used for glass‐fiber filters. The extent of particle removal was modeled assuming a size distribution of 3,100 particles evenly distributed at logarithmic intervals over 31 size classes ranging from 0.1 to 100 µm. As many as 8% of the particles and 50% of the total particle mass could be retained by a 210‐µm (pore diam) mesh even though all particles were <100 µm. This high retention of particles implies that when size distributions are prepared with screens and filters, the mass concentration in smaller size fractions will be considerably underestimated.
Spatial persistence and sediment disturbance of an arenicolid polychaete
Authors: Kruger Clinton D. , Woodin Sarah Ann
Published: May 2010

Field evidence suggests that biogenic sediment movement influences the distribution of infauna but also that biogenic processes account for only a small proportion of total sediment movement. This difference may be due to biogenic additions to the sediment or the mode of biogenic vs. physical deposition or to calculation of the biogenic effect as inappropriately scaled temporal and spatial averages. Spatial persistence of biogenic effects over time would bias such averages. Individuals of the arenicolid polychaete Abarenicola pacifica can be sized and mapped by the diameter and position respectively of their fecal coils. Their spatial distributions show significant clumping. Both individuals of A. pacifica and their biogenically disturbed patches have considerable spatial persistence over time. Individuals remained in the same spatial location for up to 12 d. Over 50% of all patches of biogenic sediment disturbance persisted for at least the 16‐d observation period, and the patches were highly localized. Thus spatial and temporal averages may be inappropriate for determining the importance of biogenic effects, due to nonuniform distribution of individuals and their spatial and temporal persistence.
Limnetic macroscopic organic aggregates (lake snow): Occurrence, characteristics, and microbial dynamics in Lake Constance
Authors: Grossart Hans‐Peter , Simon Meinhard
Published: May 2010

We have studied macroscopic aggregates sampled in situ by SCUBA diving in Lake Constance. Such aggregates are well known from marine environments as marine snow but have not been studied extensively in lakes. In contrast to marine snow, formation of lake snow aggregates is mostly dependent on wind‐induced turbulences. Our results show that abundance, chemical composition, settling velocity, microbial colonization, and bacterial production of lake snow are fairly similar when compared to marine snow. The component particle composition reflects the composition of the plankton community in the bulk water. The mean size of our lake snow aggregates was fairly small (5 mm) although the aggregates were densely colonized by bacteria. The bacterial abundance on aggregates on a per volume basis was ∼108 ml−1, which is 100 × higher than in the bulk water. The turnover of lake snow aggregates on the basis of bacterial protein production and particulate combined amino acids on aggregates usually was between 3 and 30 d. Soluble reactive phosphorus (SRP) concentrations in the matrix water of aggregates were >1,000 times higher than in the surrounding water when its SRP concentrations were close to the detection limit (0.05 µM). These results indicate that lake snow aggregates are important sites for nutrient regeneration with enhanced microbial activity. On the basis of abundance and dry weight, we estimated that lake snow aggregates comprised 20–40% of the detrital particulate organic C. This finding indicates that lake snow is important for the cycling and flux of elements and energy in lakes and needs to be included in the conceptual framework of lacustrine ecosystem studies.
An algal carbon budget for pelagic‐benthic coupling in Lake Michigan
Authors: Fitzgerald Sharon A. , Gardner Wayne S.
Published: May 2010

A budget for algal carbon was constructed to quantify the magnitude and major pathways of pelagic‐benthic coupling at a site in southeastern Lake Michigan. The flux of algal C to the benthos and the rate of carbon burial were estimated from sediment traps and dated sediment cores, respectively. Assimilation and respiration rates of Diporeia sp., an abundant benthic amphipod, and of sediment microheterotrophs were measured in a microcosm study with 14C‐labeled algae (Melosira italica). Melosira (italica and islandica) accounted for 53% of the algal C flux to the sediments. Radionuclide concentrations indicated no net sediment burial of organic C. Of the total C assimilated by Diporeia, 60% was respired, 35% was incorporated into biomass, and 5% was accounted for as soluble dissolved organic compounds. The areal rate of Diporeia respiration (29 nmol C cm−2 d−1) was 23 times greater than that for sediment bacteria (1.3 nmol C cm−2 d−1). Release of radioisotope in the form of dissolved organic compounds was much lower than that incorporated and respired for both Diporeia and sediment bacteria. Of the 61 mmol C m−2 of algal C estimated to be deposited during the spring bloom, Diporeia assimilation accounted for 61%, significantly more than the 2% observed for microbially mediated algal decomposition. These observations support the hypothesis of a strong pelagic‐benthic energy coupling between the spring diatom bloom and Diporeia in Lake Michigan.
Host preference, seasonality, and community interactions of zooplankton epibionts
Authors: Chiavelli Deborah A. , Mills Edward L. , Threlkeld Stephen T.
Published: May 2010

We examined host preference, seasonality, and zooplankton‐epibiont community interactions of three phototrophic epibionts: Colacium calvum, Colacium vesiculosum, and Synedra cyclopum on pelagic crustacean zooplankton over a 4‐yr period in Oneida Lake, New York. The three epibionts were most common from midspring to early summer. Colacium calvum and S. cyclopum preferred Daphnia as a host over all other taxa and C. vesiculosum preferred cyclopoids followed by Daphnia. The prevalence of all three epibionts was directly correlated to the density of Daphnia. and no zooplankton were observed with these epibionts when Daphnia was absent from the zooplankton community. Predation on Daphnia by age‐0 fish indirectly limited the seasonal presence of both Colacium spp. Synedra cyclopum was abundant in years when water transparency and Daphnia pulex abundance were highest, and rare in years when transparency was low and Daphnia galeata was the most abundant Daphnia. Lake nutrient concentrations had no discernible effect on epibiont abundance.
The effect of peritrich ciliates on the production of Acartia hudsonica in Long Island Sound
Authors: Weissman Penny , Lonsdale Darcy J. , Yen Jeannette
Published: May 2010

We studied the effects of attached peritrich ciliates on the fitness of natural populations of Acartia hudsonica (Pinhey) in Stony Brook Harbor, Long Island Sound. Ciliate infection occurred during late spring, and ciliate load (No. ind.−1) was not related to copepod age, stage, or body size. Simulated in situ experiments conducted throughout the period of abundance of A. hudsonica showed that egg production rate (No. d−1) was positively correlated to ambient water temperature, but negatively correlated to ciliate load. Salinity and the concentration of total or >8–10 µm Chl a were not significant in explaining the variation in egg production rate. Egg hatching success (%) was not influenced by the infection status (presence or absence) of the female. Infected nauplii had lower survival rates (d−1) compared to uninfected nauplii, but their developmental rates (molts d−1) were not significantly different.

Significantly slower average sinking rates were found for infected adults compared to uninfected adults. Slower sinking rates for infected copepods may have been due to an increase in surface area which increased drag. Infected adults with slower sinking rates may be more susceptible to predation. Our findings show that peritrich ciliates can play a role in the seasonal decline and future recruitment of A. hudsonica.
The ecology and taxonomy of epizoic diatoms on Cladocera
Authors: Gaiser Evelyn E. , Bachmann Roger W.
Published: May 2010

We examined cladocerans from littoral and pelagic zones of 62 north temperate marshes and lakes during four sampling periods to collect and identify epizoic diatoms and correlate their presence and prevalence to limnological characteristics. Forty‐nine diatom taxa were found on 20 species of Cladocera. Epizoic diatom assemblages on littoral cladocerans were diverse and contained typical epiphytic taxa. However, a single diatom taxon, Synedra cyclopum, comprised 63% of all epizoic diatoms and was most common on large pelagic Daphnia spp. Thirty‐five percent of the study lakes had epizoic diatoms on cladocerans. These spanned a large range of trophic states and geographic regions and differed from lakes without epizoic diatoms by having cladoceran assemblages dominated by Daphnia spp. Prevalences and densities of epizoic diatoms were highest shortly after ice‐out when the lakes were not stratified and temperatures were between 10 and 15°C. The seasonality of epizoic diatoms on Cladocera may result from a combination of temperature and nutrient preference of the diatoms and the temperature‐dependent cladoceran molt rate. Densities averaged 119 cells per carapace in lakes with epizoic diatoms, with patterns of arrangement on the carapace and the relationship of density with prevalence indicating rapid growth of S. cyclopum on cladocerans. Such growth may represent a burden affecting cladoceran life history and behavior.
Experimental methods for measuring the effect of light acclimation on vertical migration by Daphnia in the field
Authors: Leibold Mathew A. , West Colin T.
Published: May 2010

A new method is developed and tested for measuring vertical migration behavior by zooplankton in the field by means of acrylic columns with conical traps. Migration behavior in columns by different species and by different individuals of the same species is similar to migration behavior in the lake. We further show that acclimation to light intensity can be a factor in determining the amplitude of vertical migration in Daphnia pulicaria.
Lack of agreement among models for estimating the photosynthetic parameters
Authors: Frenette Jean‐Jacques , Demers Serge , Legendre Louis , Dodson Julian
Published: May 2010

Comparisons were conducted between estimates of photosynthetic capacity (Pmax) and photosynthetic efficiency (α) calculated with different models of the photosynthesis vs. irradiance curve. Values computed on the same data sets are different according to the models used. Estimates for Pmax with the exponential and hyperbolic tangent models (without a term for photoinhibition) are in good agreement (4% difference). The same comparison for α shows poor agreement (24% difference between the two models). When a parameter for the intercept is added to the two models, the lack of agreement increases to 8% for Pmax and 46% for α. When the mean photosynthetic parameters calculated with the two models are introduced into various published models for calculating primary production, differences in the resulting estimates range between 20 and 133%. Comparing the exponential model with a term for photoinhibition to the hyperbolic tangent model (without a term for photoinhibition) shows a 24% difference in the estimate of α. Equations are given for transforming values calculated with the various models.
Algal photosynthetic activity and its response to meromixis in hypersaline Mono Lake, California
Authors: Jellison Robert , Melack John M.
Published: May 2010

Photosynthetic activity was measured in hypersaline Mono Lake during an 8‐yr period (1983–1990) spanning the onset (1983), persistence (1984–1987), and breakdown of meromixis (1988). Algal biomass in spring and autumn decreased following the onset of meromixis and annual photosynthetic production was reduced (269–462 g C m−2 yr−1; 1984–1986) compared to nonmeromictic conditions (499–641 g C m−2 yr−1; 1989 and 1990). A gradual increase in photosynthetic production occurred even before meromixis ended because of increased vertical flux of ammonium due to deeper mixing and the buildup of ammonium in the monimolimnion. Annual production was greatest in 1988 (1,064 g C m−2 yr−1) when the weakening of chemical stratification and eventual breakdown of meromixis in November resulted in large fluxes of ammonium into the euphotic zone.

Most of the variation in rates of light‐saturated carbon uptake normalized to chlorophyll a (assimilation numbers) was explained by a regression on temperature (60%); measures of the light and nutrient environments accounted for a further 8% of the observed variation. Estimates of ammonium supply due to vertical mixing and Artemia monica excretion indicate nitrogen is most likely to limit photosynthetic production during spring and late autumn when A. monica is absent and algal biomass high. Light is also likely to limit production during these periods based on comparisons of the average mixed‐layer irradiance to the light intensity at which maximum photosynthetic rates were reached. Light limitation was more pronounced under monomictic conditions when algal biomass was higher.
Nutrient limitation and grazing control of the Baltic plankton community during annual succession
Authors: Kivi K. , Kaitala S. , Kuosa H. , Kuparinen J. , Leskinen E. , Lignell R. , Marcussen B. , Tamminen T.
Published: May 2010

Nutrient limitation and grazing control of the planktonic community were studied in the northern Baltic Sea off the SW coast of Finland during the phytoplankton growth season of 1985. In situ experiments based on a 23 factorial design were performed in mesocosm enclosures on 10 occasions. The manipulations used included phosphorus (PO43−) and nitrogen (NH4+) additions and the removal of metazooplankton by 100‐µm prefiltration. In each experiment, the responses of phytoplankton, bacterioplankton, heterotrophic nanoflagellates, and protozooplankton were followed for 2 d. Orthogonal multiple regression analysis was used to reveal which manipulations had statistically significant effects.

Nitrogen was found to be the basic limiting nutrient for phytoplankton throughout the productive season. During early summer, only the combined addition of P and N evoked a clear increase in the growth of phytoplankton. In general, bacterial productivity was not highly affected by the manipulations. In summer the removal of metazooplankton caused a rapid increase in the amount of protozooplankton in the units with 100‐µm prefiltration or prefiltration combined with N addition. In the absence of metazooplankton, the nutrient‐induced increase in primary productivity was channeled to protozooplankton, whose growth in the units where metazooplankton was present was severely limited by food competition or by direct metazooplankton grazing.
Nitrogen vs. phosphorus limitation of algal biomass in shallow coastal lagoons
Authors: Fang Peggy , Zedler Joy B. , Donohoe Regina M.
Published: May 2010

The relative importance of nitrogen and phosphorus limitation in shallow coastal lagoons was tested in replicate microcosms which were inoculated in summer with three algal groups and subjected to four levels of nutrient enrichment in five N: P ratios (20 treatments, n = 4). A subset of 12 treatments was repeated in spring. Algal groups were green macrophytes, phytoplankton, and benthic mats of cyanobacteria with associated epiphytes. Nutrients limited biomass when supply was less than the demand of the total community (supply < 0.270 mg N liter−1 d−1). For the wide range of N and P treatments, N limitation was much more common than P in summer (14 of 20 treatments); differential limitation was not as clear in spring. Although biomass was never directly controlled by P, there were indications that P supply was more important to the cyanobacterial mats, especially in spring. While N directly controlled the biomass of macroalgae, macroalgae controlled the biomass of mats and phytoplankton. From this we hypothesize that macroalgae efficiently sequestered low concentrations of N and outcompeted the other groups. Only when N supply exceeded macroalgal demand was N available to the other groups. The differences among algal groups and the temporal variation in N and P limitation help explain the conflicting evidence for nutrient limitation.
Phylogenetic diversity of aggregate‐attached vs. free‐living marine bacterial assemblages
Authors: DeLong Edward F. , Franks Diana G. , Alldredge Alice L.
Published: May 2010

The phylogenetic diversity of macroaggregate‐attached vs. free‐living marine bacteria, co‐occurring in the same water mass, was compared. Bacterial diversity and phylogenetic identity were inferred by analyzing polymerase chain reaction (PCR) amplified, cloned ribosomal RNA (rRNA) genes. Ribosomal RNA genes from macroaggregate‐associated bacteria were fundamentally different from those of free‐living bacterioplankton. Most rRNA types recovered from the free‐living bacterioplankton were closely related to a phenotypically undescribed α Proteobacteria group, previously detected in surface waters of North Pacific and Atlantic central ocean gyres. The results suggest that members of this phylogenetically distinct, a proteobacterial group are abundant free‐living bacterioplankters in coastal, as well as open‐ocean habitats. In contrast, most macroaggregate‐associated rRNA clones were closely related to Cytophaga, Planctomyces, or γ Proteobacteria, within the domain Bacteria. These data indicate that specific bacterial populations, different from those which predominate in free‐living bacterioplankton, develop on marine phytodetrital aggregates. The inferred properties of attached bacterial assemblages have significant implications for models of microbially mediated transformation of particulate organic material.
Enzymatic activities and metabolic rates of pelagic chaetognaths: Lack of depth‐related declines
Authors: Thuesen Erik V. , Childress James J.
Published: May 2010

Metabolic potentials of 16 species of chaetognaths were estimated by measuring the activities of citrate synthase (CS) and pyruvate kinase (PK) and correlating these activities with oxygen consumption rates measured on the same individuals. Furthermore, CS activities were generally higher than PK activities, suggesting that chaetognaths are aerobically poised in their metabolism. Metabolic rates and enzyme activities were examined with regard to body size and minimum depths of occurrence. There was an overall decline in both oxygen consumption and enzyme activities with body mass in interspecific comparisons. The highest CS and PK activities were measured in individuals of the bathypelagic species Caecosagitta macrocephala. The lowest enzyme activities measured in a southern California chaetognath were in the mesopelagic species Pseudosagitta maxima. The lowest overall PK activity was measured in the antarctic species Pseudosagitta gazellae. In contrast to the rapid declines in metabolic potential with depth that have been observed for pelagic fish and crustaceans, no decline in metabolic rate nor in enzyme activities can be ascribed to depth of occurrence for pelagic chaetognaths. Below depths of several hundred meters, chaetognaths have metabolic rates comparable to those of meso‐ and bathypelagic fish and crustaceans.
Potamocorbula amurensis: Comparison of clearance rates and assimilation efficiencies for phytoplankton and bacterioplankton
Authors: Werner Ingeborg , Hollibaugh James T.
Published: May 2010

This study compared clearance and assimilation of natural bacterioplankton (<1.2 µm) and cultured phytoplankton by an Asian bivalve, Potamocorbula amurensis. The average clearance rate for bacterioplankton was 45 ml h−1 clam−1 and was independent of the size (shell length, wet wt including shell, or dry tissue wt) of the clam. The clearance rate for phytoplankton is given by f = 162 + 166 × WW or f = −40 + 199 × L where f, WW, and L are clearance rate (ml h−1), wet weight including shell (g), and shell length (cm).

Bacteria were readily assimilated by P. amurensis. Gross assimilation was 73% after 49 h compared to 90% for Isochrysis galbana. Net assimilation was 45 and 53% for bacterioplankton and I. galbana, respectively. Bacterial carbon appeared to be respired faster than algal carbon. As seen in other bivalves, feces production increased and assimilation efficiency decreased at higher food concentrations.

At the mean bacterioplankton and phytoplankton standing stocks found in northern San Francisco Bay, bacteria supplied ~13 and 16% of the sum of bacteria and phytoplankton C and N, respectively, consumed by a 1‐cm P. amurensis. We calculate that a 1‐cm clam could double its C biomass in 221 d by feeding on bacterioplankton and in 26 d by feeding on phytoplankton.
Observations of coherent bands of algae in a surface shear layer
Authors: Kenney Bernard C.
Published: May 2010

Shear layers 1–2 cm thick were found immediately below the surface of lakes under “glassy” calm conditions. Driven by very faint breezes, these thin shear layers contained bands of algae aligned with the shear. The bands were being actively generated in the shear layer which was uncoupled from the underlying flow. The neutrally buoyant algae spanned the shear layer vertically within the bands. Virtually no algae were observed in the spaces between bands. The spacing between bands of algae was much smaller in scale than surface slicks and Langmuir circulations previously reported on lakes and oceans. No evidence was found of downwelling beneath the bands nor of an array of counter‐rotating helical vortices with axes aligned with the algal bands. In fact, the surface‐layer flow appeared essentially two dimensional and very different from the underlying flow which was clearly three dimensional and turbulent. Similar shear layers may occur at the surfaces of lakes and oceans under glassy calm conditions but go unnoticed because of the absence of a suitable tracer such as algae.
An effective and safe method for sorting small molluscs from sediment
Authors: Robinson S.M.C. , Chandler R.A.
Published: May 2010

A method is presented which enables infaunal juvenile bivalves to be separated from associated sediment with a combination of elutriation and flotation techniques. Simple elutriation is used to remove less dense organic detritus and a relatively new, nontoxic compound (sodium polytungstate) is used to create a heavy liquid that sorts the bivalves from sediment by relative density. The technique was applicable to 12 species of molluscs of various sizes and was 98–100% effective in separating juvenile Mya arenaria, ranging from 0.5 to 24 mm in shell length, from surrounding sediment.
Aerobactin production by a planktonic marine Vibrio sp
Authors: Haygood Margo G. , Holt Pamela D. , Butler Alison
Published: May 2010

Production of siderophores by marine bacteria could potentially contribute to metal complexation by organic compounds in seawater. Direct isolation of planktonic marine bacteria on siderophore indicator plates showed that siderophore producers are present. The siderophore‐producing organisms that could be detected on this medium were more numerous in the mixed layer than in deeper water at this sampling site. One strain (DS40M5) was characterized and found to be a marine Vibrio sp. A siderophore produced by Vibrio sp. DS40M5 is aerobactin, a compound not previously known from planktonic marine bacteria.
Diel variations in the optical properties of a marine diatom
Authors: Stramski Dariusz , Reynolds Rick A.
Published: May 2010

Diel variations in the optical properties of the marine diatom Thalassiosira p̀seudonana were examined in a nutrient‐replete laboratory culture exposed to a day‐night cycle in natural irradiance which simulated the light regime in upper layers of the euphotic zone (~10 m). Measurements of the beam attenuation coefficient, absorption coefficient, and size distribution of cells in suspension were used to determine optical cross‐sections and refractive index of cells. The optical cross‐sections varied greatly over a diel cycle; the absorption cross‐section (Xa) increased by as much as 35% and the attenuation (σ̄c) and scattering (σ̄b) cross‐sections by 80% between minima near sunrise and maxima near sunset. These changes were associated with significant variations in refractive index and cell size. Diel changes in the imaginary part of the refractive index (n'), driven by variation in intracellular pigment concentration, accounted for 58– 72% of the difference between the daily maxima and minima in σ̄a. Variations in the real part of the refractive index (n) contributed substantially (up to 85%) to the daily range in σ̄c and σ̄b. Increases in cell size were important during the morning, increasing the attenuation cross‐section to a similar extent as the refractive index. Variability in n correlated strongly with changes in intracellular C concentration. The normalization of attenuation and scattering cross‐sections to cellular C content resulted in a threefold reduction in the magnitude of diel variations. If such patterns are general features of planktonic microorganisms in the natural environment, it would suggest that varying particle concentration need not be the only (or even major) factor responsible for diel variability in the bulk optical properties of seawater. As a consequence, estimating particle production rates from diel variability in the beam attenuation coefficient may not be justified in some oceanic situations; however, using this variability to estimate production in terms of particulate organic C may be appropriate.
Photophysiological responses of intertidal benthic microalgal communities to in situ light environments: Methodological considerations
Authors: Pinckney J. , Zingmark R. G.
Published: May 2010

Photosynthesis vs. irradiance (P‐I) curves usually express production in terms of production per unit biomass. However, for benthic microalgal communities, the depth of the sediment photic zone as well as the amount of biomass exposed to light varies as a function of incident irradiance. We examined the photosynthetic responses of intertidal benthic microalgal communities from different light environments with traditional depth‐integrated methods as well as the percent Pmax and fixed‐depth interval methods. P‐I curve parameters (α, Ik, Im) change depending on the method used. With the depth‐integrated biomass‐specific method, microalgae in unshaded mudflats have a higher α (0.261±0.016) than microalgae in shaded tall Spartina habitats (0.161±0.014), suggesting that mudflat microalgae are more shade‐acclimated than tall Spartina microalgae. However, if curves are constructed with measurements obtained at a fixed depth (surface) in the sediment, tall Spartina microalgae exhibit a significantly higher α (0.260±0.020) than mudflat microalgac (0.175±0.006). With the latter method, tall Spartina surface microalgae appear more shade‐acclimated than mudflat surface microalgae. We conclude that the fixed‐depth interval method provides a more realistic representation of the photophysiological responses of benthic microalgal communities.
Inferring the specific conductivity of lake water with scaled chrysophytes
Authors: Siver Peter A.
Published: May 2010

Siliceous scale‐bearing chrysophytes have been used successfully in reconstructing the historical pH of lake water. In addition to pH, the distributions of many taxa of scaled chrysophytes are also significantly correlated with the concentration of dissolved salt. A model (r2 of 0.87), based on scaled chrysophytes, was developed with weighted averaging regression to infer the specific conductivity of lake water. The model was applied downcore in a small soft‐water lake in Connecticut whose inferred pH had remained between 6.2 and 6.5 for the past 170 yr. Despite the relatively stable pH, the inferred specific conductivity had more than tripled since the turn of the century. The rise in the salt level of the lake water correlated with known changes in the watershed, including the building of lakeside cottages and establishment of a surface silica mine.
Metabolism of streamwater dissolved organic carbon in the shallow hyporheic zone
Authors: Findlay Stuart , Strayer David , Goumbala Cheikh , Gould Kim
Published: May 2010

Approximately 50% of streamwater dissolved organic C (DOC) disappeared from interstitial water moving along a hyporheic flowpath below a gravel bar. Concurrent decreases in oxygen and increases in dissolved inorganic C (DIC) indicate metabolism of streamwater‐derived DOC by hyporheic microbes. Loss of 100 µM DOC would account for 24–39% of the oxygen depletion and DIC accumulation. Sediments were incubated with DOC collected from the stream channel and two wells along the flowpath to examine whether streamwater and hyporheic DOC could support growth of sedimentary bacteria. Streamwater and hyporheic DOC collected from the upstream end of the flowpath stimulated higher bacterial growth rates and supported higher biomass than hyporheic DOC collected from the downstream end. The supply of streamwater‐derived DOC is a significant source of C for hyporheic sediment microorganisms, and these organisms are capable of using about half the DOC contained in streamwater.
Use of dissolved combined and free amino acids by planktonic bacteria in Lake Constance
Authors: Rosenstock Bernd , Simon Meinhard
Published: May 2010

We measured the use of dissolved combined (DCAA) and free amino acids (DFAA) by planktonic bacteria during the growing season in Lake Constance (Bodensee). Utilization was estimated from the decrease of DCAA and DFAA concentrations in 1‐µm filtrates and compared to the C demand for the net production of bacterial biomass measured from the increase of bacterial abundance. During the phytoplankton spring bloom and the clear‐water phase, DFAA accounted for 30–48% and DCAA 5–62% of the bacterial C demand. From August until November use of DFAA comprised <5% and DCAA 50– 148% of the bacterial C demand. In aphotic depths, amino acids accounted for a higher fraction of the C demand relative to euphotic depths. From mid‐July until early September use of DCAA exceeded the bacterial C and N demand, leading to release of ammonium. During the spring bloom and the clearwater phase, DFAA + DCAA accounted for <100% of bacterial C demand, suggesting that other substrates were also used. Concentrations and utilization rates of DFAA covaried, whereas maxima of DCAA use followed maxima of DCAA concentration with a time‐lag of several weeks. Measurements of the extracellular isotope dilution of [3H]amino acids indicated that after the diatom bloom, bacterial hydrolysis and use of DCAA were closely coupled and release of DFAA accounted for <7% of the DCAA used. During this time, turnover of the DFAA pool could be explained on the basis of release and utilization. Our results show that DCAA and DFAA are important substrates for the growth of planktonic bacteria in the lake.
Stimulation of the microbial food web in an oligotrophic, slightly acidified lake
Authors: Bell Russell T. , Vrede Katarina , Stensdotter-Blomberg Ulrika , Blomqvist Peter
Published: May 2010

We investigated the relative importance of inorganic nutrients vs. organic C in controlling bacterial production in a clear‐water, slightly acidified lake. We added dissolved organic C (DOC) as glucose (0.5 mg C liter−1) with and without inorganic nutrients (10 µg P liter−1 and 100 µg nitrate‐N liter−1) to 350‐liter enclosures. The treatment with DOC and nutrients in combination stimulated bacterial production (thymidine incorporation) steadily (from 1 to 9 pmol liter−1 h−1) throughout the 3‐week period. Glucose added alone and N+P added alone (at 2 × lake concn) had little effect on bacterial production. The enhancement of bacterial production by glucose with N+P in turn resulted in an increase in chrysophyte biomass, mainly the mixotroph Dinobryon. The enhancement of bacterial production was transferred up to protozoans (ciliates + heliozoans). These results indicate that bacterioplankton are potentially a link for C in this system and that there is a sensitive balance between bacterial limitation by DOC and inorganic nutrients in this oligotrophic lake.
Efficiencies of ingestion and assimilation by an invertebrate predator using C and P dual isotope labeling
Authors: Lehman John T.
Published: May 2010

Daphnia rosea was uniformly labeled with both 14C and 33P, then offered as prey to Bythotrephes cederstroemi Schoedler, a nonindigenous predatory cladoceran which has become established in the Laurentian Great Lakes. Both C and P from the prey were ingested with equal efficiency (58–59%, SE = 2%) by Bythotrephes and retained with equal efficiency over the next 12 h. Feeding behavior by the predator involves a fastidious process of shredding and discard of exoskeletal material and selective ingestion of soft tissue. Most of the ingested matter is consequently digested; assimilation efficiency is 85% (SE = 2%).
Effect of concentrating the virus‐rich 2‐2nm size fraction of seawater on the formation of algal flocs (marine snow)
Authors: Peduzzi Peter , Weinbauer Markus G.
Published: May 2010

Particle aggregates >0.5 mm in diameter (marine snow) are an important component of marine environments. Viruses are now recognized as active members of the marine microbial food web, infecting both planktonic primary producers and bacteria. The effect of adding material from the 2–200‐nm size fraction, concentrated from seawater with ultrafiltration, on the development of phytoplankton biomass and formation of algal flocs was examined. At higher concentrations of material in this size fraction (2.3 times enrichment with virus‐like particles), the buildup of phytoplankton biomass was initially delayed. After 8 d, these enrichments resulted in the formation and persistence of up to 5 times higher numbers of larger aggregates (≥ 1‐mm equivalent spherical diameter) concomitant with even higher phytoplankton biomass. Both the size distribution of algal aggregates and primary production can be affected by material in the size range of 2–200 nm containing large numbers of viruses.
Photobiological studies of Skeletonema costatum adapted to spectrally different light regimes
Authors: Nielsen Marianne V. , Sakshaug Egil
Published: May 2010

Photoadaptational responses to three irradiances for each of five spectral distributions of light were studied in the marine diatom Skeletonema costatum. The C : Chl a ratio increased linearly with increased absorption of light per unit Chl a within the range of irradiances studied. The quantum yield for growth decreased monotonically with increased absorption of light. Our results imply that photoadaptational changes in the C : Chl a ratio and in the maximum quantum yield for growth of S. costatum are simple functions of the number of absorbed photons. Thus, spectrally dependent photoadaptational changes in these parameters can easily be incorporated into mathematical models as simple functions by substituting absorbed light per unit Chl a for ambient irradiance.
Effects of low oxygen waters on Chesapeake Bay zooplankton
Authors: Roman Michael R. , Gauzens Anne L. , Rhinehart W. Kirk , White Jacques R.
Published: May 2010

The bottom waters of the mesohaline portion of Chesapeake Bay become depleted in oxygen in summer. We found that copepods and nauplii were in low abundance or absent from bottom waters when oxygen concentrations were <1 mg O2 liter−1. In contrast, when oxygen concentrations were higher in bottom waters in spring or summer due to episodic mixing events, the highest copepod abundances were often found in bottom waters. Laboratory experiments confirmed that oxygen concentrations <1 mg O2 liter−1 resulted in reduced survival of the copepods Acartia tonsa and Oithona colcarva and inhibited the hatching of A. tonsa eggs. The decrease in Chesapeake Bay copepods in May–June parallels the decline of oxygen in bottom waters. Our field and laboratory data suggest that this decline in copepods could result from reduced recruitment as a consequence of egg mortality in the low‐oxygen bottom waters. In summer this source of mortality would be reduced because warmer water temperatures would allow the eggs to hatch in the upper water column above the low‐oxygen bottom waters.