bluuebunny/crossref_metadata_2025 huggingface dataset:
Temporal variability of phytoplankton community structure based on pigment analysis
Authors: Letelier R. M. , Bidigare R. R. , Hebel D. V. , Ondrusek M. , Winn C. D. , Karl D. M.
Published: May 2010

Algal chlorophyll and carotenoid distributions were measured periodically in the euphotic zone of Sta. ALOHA (22°45'N, 158°00'W) between February 1989 and October 1991 to document the variability in phytoplankton abundance and composition. The annual mean depth‐integrated (0–200 db) concentration of Chl a displayed significant interannual variability. Seasonal patterns in Chl a concentration were found to be depth‐dependent. Elevated Chl a in the mixed layer is the result of photoadaptation as the mixed layer deepens in winter. Increases in Chl a at the deep chlorophyll maximum layer (DCML) in spring are explained by increased nutrient availability caused by a deepening of the DCML relative to the σθ = 24.25 density surface.

An algorithm based on the ratios of Chl a to diagnostic pigments present in specific algal taxa was used to estimate the contribution to total Chl a by the major algal groups represented within the DCML. Results indicate the presence of a phytoplankton community at the DCML with the following mean composition: Prochlorococcus spp. (39%), cyanobacteria (24%), prymnesiophytes (22%),and chrysophytes (13%). No single taxon is responsible for the springtime increase in Chl a observed in this habitat. Results from size fractionation and normal‐phase high performance liquid chromatography confirm that Prochlorococcus spp. are the principal contributors of Chl a to the DCML.
Anoxic and oxic degradation of 14C‐labeled chloropigments and a 14C‐labeled diatom in Long Island Sound sediments
Authors: Sun Ming-Yi , Lee Cindy , Aller Robert C.
Published: May 2010

Anoxic and oxic degradation pathways of sedimentary chloropigments were examined by spiking marine sediment with14C‐labeled algal cells and purified chloropigments from the diatom Skeletonema costatum. These experiments suggest that Chl a degrades through multiple pathways. Under oxic conditions, most bulk sedimentary Chl a degraded to various colorless compounds and only a minor fraction degraded to pheophytin a; added 14C‐labeled Chl a also degraded quickly, but 30–40% of this Chl a was converted to pheophytin a. Under anoxic conditions, only a small fraction of bulk Chl a degraded, but added 14C‐labeled Chl a continuously degraded and ~30–40% of it was converted to pheophytin a. Pheophytin a is relatively stable under anoxic conditions but degrades under oxic conditions, thus it is a potential end product of chloropigment degradation in anoxic environments.

Degradation pathways are likely dependent on the relative proportion of unassociated Chl a to chlorophyll complexes present in the sediment. Only unassociated Chl a appears to be available for anoxic decomposition. Under oxic conditions, some colorless products were further degraded and solubilized; none of the 14C label added as purified pigments was lost under anoxic conditions during the 1‐month incubation. About 80% of the acetone‐extractable 14C in labeled cells was lost in 1 month from sediments under oxic conditions and ~30% under anoxic conditions.
Dissolved organic carbon concentrations in marine pore waters determined by high‐temperature oxidation
Authors: Martin William R. , McCorkle Daniel C.
Published: May 2010

We have developed sampling methods and an analytical system to determine the concentration of dissolved organic C (DOC) in marine pore waters. Our analytical approach is a modification of recently developed high‐temperature, Pt‐catalyzed oxidation methods; it uses chromatographic trapping of the DOC‐derived CO2, followed by reduction to CH4 and flame ionization detection. Sampling experiments with nearshore sediments indicate that pore‐water separation by whole‐core squeezing causes artificially elevated DOC concentrations, while pore‐water recovery by sectioning and centrifugation does not appear to introduce DOC artifacts. Results from a set of northwestern Atlantic continental slope cores suggest that net DOC production accounts for > 50% of the organic C that is recycled at the sediment‐water interface.
Consequences of riverine flooding for seston and theperiphyton of floating meadows in an Amazon floodplain lake
Authors: Engle Diana L. , Melack John M.
Published: May 2010

Algal biomass and the chemical composition of seston and floating meadow periphyton were measured in an Amazon floodplain lake during a period of channelized river inflow and a period of overbank flow. During both periods, sedimentation of riverine particulates and loss of dissolved nutrients created strong spatial chemical gradients from the river onto the floodplain which were stable for months at a time. The molar : P of dissolved inorganic nutrients supplied by river water was very low (NO3− + NH4+ : SRP < 5) and decreased further as water entered the floodplain. Initial loss of sediment in surface waters increased the organic content of seston and periphyton and decreased the C : N of seston within 2 km of the river. More gradual loss of finer P‐rich particles caused 2−4‐fold increases in N : P and C : P ratios inside the floodplain. During channelized river inflow, epiphytic algal biomass peaked where inorganic turbidity was high (>50 mg liter−1) and phytoplankton biomass was low. Later in the year, overbank flow elevated dissolved nutrient levels inside the lake and disrupted thermal stratification. This transition from lentic to lotic conditions coincided with the seasonal high for epiphytic algal biomass and the seasonal low for phytoplankton biomass. Overall, epiphytic algal biomass was 4–10 times higher than phytoplankton biomass on a per unit area basis. In situ bag experiments revealed that inorganic turbidity regulates the ability of attached algae to utilize nutrients supplied by river water. Epiphytic algal biomass decreased after contact with undiluted river water. Epiphytic algal biomass increased 5‐fold in river water diluted by 90%.
The role of planktonic bacteria in phosphorus cycling in lakes ‐ Sink and link
Authors: Vadstein Olav , Olsen Yngvar , Reinertsen Helge , Jensen Arne
Published: May 2010

Due to their high P content (~10 times

that of the algae), the bacteria in Lake Nesjøvatn were responsible for 80% of the net uptake of this element in summer. Thus, the heterotrophic bacteria acted as a sink and competed for inorganic phosphate with the algae, but the bacteria were unable to achieve physiological P saturation. Heterotrophic flagellates feeding on P‐rich bacteria regenerated two‐thirds of the P released by grazers. Therefore the role of bacteria is not as mineralizers but as net consumers of phosphate, and, because of their high requirement for P, they are a key factor in regulating the P flux in lakes. The main importance of bacteria in regeneration of P is as P‐rich food particles.
DAPI direct counting underestimates bacterial abundances and average cell size compared to AO direct counting
Authors: Suzuki Marcelino T. , Sherr Evelyn B. , Sherr Barry F.
Published: May 2010

We compared estimates of bacterial abundance and of average bacterial cell size based on direct counts of bacterioplankton cells stained with acridine orange (AO) or 4'‐6‐diamidino‐2‐phenylidole (DAPI). Estimates of numbers ml−1 of bacteria stained with DAPI were on average 70% (range 57–82%) of bacterial counts made with AO as the stain. Cell volumes estimated from DAPI‐stained cells were even less, on average 59% (range 34–80%) of those determined from measurement of AO‐stained cells. The combination of lower DAPI values for both cell numbers and cell volumes resulted in overall underestimation of total bacterial biovolume liter−1. DAPI‐determined total biovolumes ranged from 25 to 61% of biovolume values obtained via counts and measurements of AO‐stained cells in the two data sets. These results can be ascribed to the differential staining of cell components by DAPI and AO. We recommend that DAPI staining be used with caution for estimating bacterial standing stock parameters.
Effect of UV‐B radiation and humic substances on growth and motility of Gyrodinium aureolum
Authors: Nielsen Tom , Ekelund Nils G.A.
Published: May 2010

We investigated the effect of ultraviolet‐B radiation (280–320 nm) on the growth and motility of the marine dinoflagellate Gyrodinium aureolum in the presence of humic substances. The specific growth rate after 7 d of the UV‐BBE (biologically effective radiation) exposure (2.15 kJ m−2 d−1) decreased by 92% compared to the control. The growth rate for UV‐B treated cells increased by 18, 26, and 10% when cells were cultured in medium enriched with humic substances (1.7, 4.2, and 8.3 mg liter−1). However, the growth rate was lower at the highest humic substance than at the two lower concentrations. When humic substances were used as a filter to shade the organisms from UV‐B radiation without substantial changes in the amount of white light, instead of being added to the medium, the growth rate increased with the concentration of humic substances. UV‐B radiation had little or no effect on the motility of G. aureolum, whether humic substances were added or not. Phototactic orientation of the UV‐B‐treated cells was significantly weaker than the control to actinic white light (400–700 nm, 47 m−2). The presence of humic substances during treatment with UV‐B radiation reduced the inhibition of the positive phototaxis in G. aureolum.
Microbially mediated cobalt oxidation in seawater revealed by radiotracer experiments
Authors: Lee Byeong‐Gweon , Fisher Nicholas S.
Published: May 2010

The influence of microbial activity on Co and Mn oxidation in decomposing diatom cultures was determined with radiotracer techniques. Adding a consortium of microorganisms collected from coastal seawater (0.2–3‐µm size fraction) to the cultures increased particulate Co formation rates at 18°C by an order of magnitude (to 3.8% d−1) and particulate Mn formation rates 3‐fold (to 7.9% d−1) over rates in cultures without added microorganisms. The rates of both particulate Co and Mn formation increased with incubation temperature (Q10 = 2.5–2.9 for Co and 1.3–1.8 for Mn; T = 4–18°C) and were faster in the dark than in the light. Ascorbic acid (used as a reducing agent) rinses of particulate Co and Mn indicated that these particles were primarily formed by the oxidation of Co(II) and Mn(II) to metal oxides. By manipulating Mn: Co ratios we showed that formation of particulate Co is directly mediated by microbial activity rather than Co adsorption to or oxidation by Mn oxides. The results help explain the scavenged‐type profile exhibited by Co in the water column and the high Kds of Co in marine sediments.
Egg viability in the copepod Temora stylifera
Authors: Ianora Adrianna , Poulet Serge A.
Published: May 2010

Estimates of production rate and viability of eggs are reported for Temora stylifera collected in the Bay of Naples (Italy). Complementary observations on rates of fecal pellet and spermatophore production and female longevity were also conducted during the incubations. In situ egg viability was highly variable during the 2 yr of observation, with mean monthly values of <80% of total egg production. Under experimental food‐saturated conditions, the nature and hatching success of eggs were modified depending on type of food. With a dinoflagellate diet (Prorocentrum minimum), the responses of copepods were characterized by maximum production of viable eggs, high female longevity in the presence or absence of males, and low rates of fecal pellet production. The opposite was true with a diatom diet (Thalassiosira rotula), except fecal pellets were produced at a higher rate, showing indirectly that this algae was neither properly assimilated nor transformed into production. Total and mean daily egg production were more or less the same with the two diets, indicating that under poorer food conditions copepods can maximize total egg production but not viability.
Turbulence and planktonic nitrogen fixation: A mesocosm experiment
Authors: Howurth Robert W. , Butler Thomas , Lunde Katharine , Swaney Dennis , Chu Chia Ren
Published: May 2010

Heterocystic species of N‐fixing cyanobacteria are rare in the plankton of most estuaries and coastal seas, and rates of N fixation tend to be concomitantly low in the water columns of these systems. High turbulence in estuaries and coastal seas is commonly cited as a factor excluding planktonic, heterocystic cyanobacteria. We investigated the effects of turbulence in a 7‐week‐long mesocosm experiment. Reciprocating grids generated turbulence in 3.0‐m3 tanks containing water and plankton from Oneida Lake. Four mesocosms received a high level of turbulence (mean values of 0.2 and 0.7 mW kg−1 as determined by two different methods); such turbulence is much higher than has been observed in lakes and is at the upper end of that found in estuaries strongly influenced by tides. Four other tanks received levels of turbulence that were higher yet (mean estimates of 1.8 and 3.8 mW kg−1 from the two methods); this higher level of turbulence probably exceeds that found in coastal waters except in areas influenced by surf or in shallow estuaries with very significant tides. Heterocystic, planktonic cyanobacteria bloomed and fixed N in all eight mesocosms, and turbulence had no significant effect on N fixation. Rates were quite high, indicating no major deleterious effect of even extremely high turbulence on this process. The turbulence in our mesocosms was great enough to have prevented the formation of anoxic microzones on the surface of cyanobacterial cells. Thus, our results indicate that such microzones are not essential for high rates of planktonic N fixation by heterocystic cyanobacteria and that the relative absence of N fixation by these organisms in coastal seas is not due to a lower probability of such microzones developing in marine systems than in freshwaters.
Variability of shoreline erosion and accretion within a beach compartment of Flathead Lake, Montana
Authors: Lorang Mark S. , Stanford Jack A.
Published: May 2010

We measured shoreline reconfiguration and variability in shoreline retreat in Flathead Lake, which is a large glacial lake regulated by a hydroelectric dam at its natural outlet. Wave‐induced erosion rates ranged from 0.5 to 2.5 m yr −1 at the northshore study site where fetch, and hence wave energy, was maximal. Shoreline retreat was not solely related to storm intensity or volumetric changes in nearshore bars. Three erosive processes were involved in the measured variability of shoreline retreat: undercutting, endstripping, and overwash. Wave scour on an exposed bank caused undercutting and endstripping, while overwash resulted when water was forced over the top of the shoreline. Shoreline morphology and vegetation determined the type of erosion process and the rate of shoreline retreat. Shoreline retreat was offset by localized and dramatic accretion caused by sediment entrapment by drift logs bordering the shoreline. The eroding shoreline and nearshore bed were sediment sources for the accretion. Drift logs naturally protected the shoreline from direct wave attack and stimulated sediment accretion, providing new recruitment area for riparian vegetation.
New procedure for determining reactive Fe(III) and Fe(II) minerals in sediments
Authors: Wallmann Klaus , Hennies Kristof , König Iris , Petersen Wilhelm , Knauth Hans-Diethard
Published: May 2010

Sediments from the River Elbe estuary and incubated sediments were extracted with 1 N HCl for 24 h at room temperature. The extracted ferric and ferrous iron was determined with DC and AC polarography. Acid‐volatile sulfide was determined from H2S trapped in aqueous zinc acetate solution. Analysis of sediment samples and extraction residues with Mössbauer spectroscopy demonstrated that the Fe oxidation state was conserved during extraction and polarographic determination, siderite and vivianite were completely dissolved, and Fe(II) in chlorite was partially extracted with HCl. Incubation experiments showed that extractable Fe was almost completely oxidized to Fe(III) at the oxic sediment surface and reduced to Fe(II) in deeper anoxic layers within a few weeks. Reactive Fe(III), i.e. that fraction of Fe which was reducible on the time scale of the incubation experiment, was completely extracted with HCl.
Chlorophyll a concentrations in the North Pacific: Does a latitudinal gradient exist?
Authors: Dickson Mary-Lynn , Wheeler Patricia A.
Published: May 2010

Chlorophyll a concentrations were measured as a function of depth from 28 to 48°N along 152°W in March 1991 with Whatman GF/F and 0.2‐µm Nuclepore filters. Surface Chl a concentrations measured with 0.2‐µm Nuclepore filters were up to fourfold higher than those measured with Whatman GF/F filters. The largest difference between the two filter types was found in subtropical waters, where picoplankton were a major constituent of the phytoplankton assemblage. Chl a concentrations integrated from 0 to 175 m showed a threefold increase (9–26 mg Chl a m−22) between 28 and 48°N when Whatman GF/F filters were used. However, integrated Chl a concentrations based on measurements with 0.2‐µm Nuclepore filters were nearly constant (25–31 mg Chl a m−2) over the transect. These results lead us to question the existence of previously reported latitudinal gradients in integrated Chl a concentrations in the North Pacific Ocean.
Planktivore effects on zooplankton epibiont communities: Epibiont pigmentation effects
Authors: Willey Ruth L. , Willey Robert B. , Threlkeld Stephen T.
Published: May 2010

We observed the development of epibiont communities on freshwater crustacean zooplankton from 12 July–31 August 1991 in three ponds: one with planktivorous fish, a second with planktivorous larval salamanders, and a third with planktivorous fish added midway through the sampling period. Prevalence, on zooplankton, of pigmented euglenoid epibionts (Colacium vesiculosum), alone and with unpigmented peritrich ciliates (Vorticella campanula and Epistylis sp.), was significantly reduced by the addition of planktivorous fish in the third pond, while the prevalence of peritrich ciliates alone was not. Neither of the ponds with unaltered planktivore regimes showed a similar pattern of change in prevalence of pigmented and unpigmented epibionts on zooplankton. The relative loss of pigmented euglenoid epibionts, after planktivore addition, suggests that epibiont color or contrast may increase the susceptibility of their substrate organisms to planktivores.
Production of microbial organic aggregates from macrophyte‐derived dissolved organic material
Authors: Alber Merryl , Valiela Ivan
Published: May 2010

Organic aggregates were produced in the laboratory by bubbling dissolved organic material derived from five species of coastal macrophytes. The weight of aggregates produced after bubbling was significantly related to the amount of DOC (dissolved organic C) initially present. An average of 19% of the initial DOC was converted to aggregates, 23% remained in solution, and the remaining 58% was mineralized to CO2. The C : N ratios of aggregates did not vary between species or runs and ranged from 4 to 12. Microscopic examination of aggregates showed that they contained large numbers of rod‐shaped bacteria. The data were interpreted to suggest that aggregates are composed of live and dead bacteria, other microbes, and extracellular material. The ingestion of aggregates of this type by consumers is a potentially important route for the flow of labile organic C in marine systems.
Radiotracer study ofphosphorus uptake by plankton and redistribution in the water column of a small humic lake
Authors: Salonen Kalevi , Jones Roger I. , De Haan Henk , James Mark
Published: May 2010

The movement of P in the plankton of a humic lake was studied in late July within a 2‐m‐diameter tube. The tube enclosed water from the surface to below the epilimnion with the steep vertical stratification of the lake undisturbed. [32P]orthophosphate was mixed into the epilimnion of the enclosure and its fate followed for 2 weeks. In the epilimnion ∼85% of all the P in organisms was in Daphnia longispina, which comprised almost all the zooplankton biomass. The respective proportions for bacterioplankton and phytoplankton were ∼12 and 3%. Early in the experiment when the temperature of the epilimnion was ∼20°C, the turnover rate of phosphate was of the order of 3 h. By the first sampling, 3 h after the experiment began, bacteria showed the highest affinity for phosphate, but with this coarse time resolution, the pattern of 32P incorporation into phytoplankton appeared similar. The specific radioactivity in D. longispina equaled that in the bacterial and algal fractions after only 2 d, implying rapid and direct foodchain linkage between these P pools. An explanation for such rapid transfer of P may be that D. longispina consumes food with a high concentration of P, such as bacteria. At the end of the experiment, the specific radioactivity of the dissolved P pool was considerably lower than that of the other fractions, indicating only slow exchange between part of the dissolved P pool and the plankton.
Experimental dissolution of diatom silica in concentrated salt solutions and implications for paleoenvironmental reconstruction
Authors: Barker Philip , Fontes Jean‐Charles , Gasse FranÇoise
Published: May 2010

Two diatom frustule dissolution experiments (DE1 and DE2) were performed on material from Lakes Geneva and Nantua, SE France. In DE1, the dissolution of diatom silica from sediments was measured over a 92‐d period at room temperature in six 3 M salt solutions (NaCl, Na2CO3 KNO3 CaCl2, LiNO3, MgCl2), in 0.6 M NaCl, and in distilled water. As expected, dissolution was greatest in Na2CO3 where high pH leads to ionic dissociation. A similar process was also apparent in solutions of KNO3 and LiNO3 which were only slightly alkaline. In contrast, weakly acid solutions of MgCl2 and CaCl2 produced less dissolution than distilled water. Between 0.6 and 3 M NaCl, silica solubility appeared to reach an undetermined optimum which could correspond to minimum values of ion activity coefficients. In a second experiment (DE2), the dissolution of living diatoms from Lake Geneva was monitored over 46 d in 3 M solutions of Na2CO3 and NaCl and in distilled water. The results were not in accordance with the expected theoretical levels predicted by Pitzer’s equations when applied to silica solubility in concentrated solutions. Clear interspecific differences in diatom dissolution rates occurred in both experiments. The gross valve surface area: volume ratio was found to be a useful first‐order approximation of a particular diatom species’ propensity to dissolve. Only minor differences in diatom assemblage composition were observed in NaCl solutions over the experimental period whereas major changes were caused by Na2CO3 solutions.
Comparison and evaluation of different techniques for measuring absorption efficiency in suspension feeders
Authors: Navarro J. M. , Thompson R. J.
Published: May 2010

We compared several methods for measuring absorption efficiency (AE) in marine invertebrates using the horse mussel Modiolus modiolus. All were based on the principle of comparing the digestion of organic material relative to an unabsorbed tracer substance but varied in the nature of the absorbable fraction and the inert, nonabsorbed marker. For mussels feeding on natural seston, estimates of AE were slightly higher when silicate was used instead of ash (the marker commonly used in the Conover ratio method), except when the proportion of silicate in the food was very low. When mussels were fed cultured algae, estimates of AE were lower and less reproducible with either ash or silicate as the nonabsorbable fraction. The use of carbon or total chloropigments instead of organic content (weight loss on ignition) as the absorbable component in Conover’s equation gave acceptable values for AE. Differences between mean values from the various techniques were significant, but small, owing to the high precision of the measurements. The Conover ratio procedure is convenient for determining the AE of suspension feeders when the food source is natural seston, and the method provides reproducible values, but variance is greater when the inorganic content of the food is low, as in cultured algae.
Responses of estuarine phytoplankton to exogenous glucose: Stimulation versus inhibition of photosynthesis and respiration
Authors: Lewitus Alan J. , Kana Todd M.
Published: May 2010

The effects of glucose on pigmentation, photosynthesis, and respiration were examined in diverse phytoplankton types isolated from a subestuary of Chesapeake Bay and acclimated to an irradiance limiting for growth. Two algal responses to glucose uptake, heretofore rarely reported, were commonly observed. Glucose enhanced pigmentation in three of six species examined and increased gross photosynthesis in four of these species. The stimulation of photosynthesis by glucose was accompanied by an increase in gross respiration, suggesting that glucose was respired by these species. The results indicate that in some phytoplankton species light limitation on photosynthesis can be at least partially relieved by respiration of exogenous organic substrates.
Increasing the sensitivity of a FACScan flow cytometer to study oceanic picoplankton
Authors: Dusenberry Jeflrey A. , Frankel Sheila L.
Published: May 2010

Existing limitations on the sensitivity

of commercially available flow cytometers do not permit the detection of extremely dim picoplankton cells, particularly Prochlorococcus marinus in near‐surface oligotrophic ocean waters. This problem was overcome by making some simple modifications to a FACScan (Becton Dickinson) flow cytometer to increase its sensitivity by about fivefold. The fluorescence and side scatter sensitivity was increased by replacing the existing focusing lens and beam‐steering mirror with a 3× expansion telescope and a slightly shorter focusing lens, resulting in a smaller laser spot size at the interrogation point. Forward scatter sensitivity was increased by replacing the existing photodiode with a photomultiplier tube, which has a background noise level about an order of magnitude lower. The fluorescence sensitivity of the modified instrument, measured with a quantitative fluorescence microbead standards kit, is 74 molecules of equivalent soluble fluorochrome for fluorescein. The instrument can now detect extremely dim P. marinus from open‐ocean surface waters.
Why does the relationship between sinking flux and planktonic primary production differ between lakes and oceans?
Authors: Baines Stephen B. , Pace Michael L. , Karl David M.
Published: May 2010

The fraction of primary production lost to sinking (the export ratio) increases with productivity in the ocean and decreases slightly with productivity in lakes. To explore why this distinction exists, we compared marine and freshwater regressions relating chlorophyll concentrations in the euphotic zone to each of the three variables that define the export ratio: primary productivity, carbon sinking fluxes, and euphotic zone depth. Chlorophyll was found to predict these three variables well (r2 = 0.54–0.90) in both lakes and the ocean. The differences between the marine and freshwater export ratio—productivity relationships stem primarily from a discrepancy in the primary productivity—Chl relationships. On average, a >10‐fold difference in Chl‐specific productivity exists between the most oligotrophic lakes (Chl = 0.2 mg−3) and oceanic regions with similar Chl concentrations. This difference disappears at higher concentrations of Chl because primary productivity: Chl ratios increase with productivity in lakes. In addition, carbon sinking rates average 2–3‐fold higher in the oceans than in lakes with similar concentrations of Chl. The trends of marine and freshwater export ratio‐production can be qualitatively reproduced with Chl‐based predictions of euphotic zone primary productivity, depth, and carbon sinking losses from regressions. Marine and freshwater ecosystems may differ systematically in the efficiency of nutrient recycling processes in the water column and in the nature of settling material.
Nutrient dynamics and turnover rates of phosphate and sulfate in Lake Victoria, East Africa
Authors: Lehman John T. , Branstrator Dorm K.
Published: May 2010

The dominant process removing sulfate from the water of Lake Victoria is biological uptake by plankton >1 µm in size. Uptake of sulfate in the water column is substantially greater than uptake at the sediment surface. Despite low ambient concentrations (3–4 µM), rates of uptake of sulfate by phytoplankton do not increase when additional sulfate is added to the water, and ambient concentrations are adequate to support maximum uptake rates. Uptake rates for phosphate are similarly near‐maximal in offshore waters. Furthermore, experimental addition of sulfate or phosphate fails to increase biomass production over control levels, but addition of N alone or in combination with P and S does increase algal biomass. Although sulfate concentrations in Lake Victoria are lower than values reported for any large lake worldwide, our results indicate that sulfate behaves as a nonlimiting nutrient in Lake Victoria and that it does not limit the primary productivity of the lake.
Comparative demography and population dynamics of two coexisting copepods in a Venezuelan floodplain lake
Authors: Twombly Saran
Published: May 2010

I used an inverse matrix projection model to estimate vital rates (growth, survival, and reproduction) for two coexisting copepod species in a Venezuelan floodplain lake as a first step in identifying the ultimate environmental factors that determine distribution and abundance of a species. Zooplankton were sampled four times a week from June through December 1984, and the resulting abundance data were used together with the estimation technique to extract time series of vital rates over a 6‐month period. There were marked temporal differences in population maxima of each species. Abundance of Diaptomus negrensis fluctuated with changes in recruitment and mortality of stages NV, NVI, CIII, and CIV. Peak abundance of D. negrensis coincided with a peak in the abundance of the invertebrate predator Chaoborus sp. In contrast, population size of Oithona amazonica was unrelated to recruitment but directly related to survival of the youngest copepodite stages, which was poor until October when abundance of Chaoborus declined. These demographic analyses target the stages most susceptible to environmental (selection) pressures, providing a basis for understanding the evolution of life‐history strategies, and suggest the hypothesis (as yet untested) that prolonged coexistence is facilitated between species whose abundance is determined by different demographic (and thus environmental) factors.
A current‐activated sediment trap
Authors: Hargrave B. , Siddall G. , Steeves G. , Awalt G.
Published: May 2010

A current‐activated sediment trap is described that collects particles based on preselected current speed and direction criteria. The collector incorporates a steep‐walled funnel, a motor‐driven carousel with sample cups, an absolute optical shaft encoder, and an acoustic current meter. A field trial of the trap was carried out in a shallow marine embayment over 3 d where it correctly positioned cups in response to tidal changes in current speed and direction. Particle organic content and sedimentation rates calculated over hourly intervals were similar to measurements with a standard sequential sampling trap over several hours when the two traps were deployed simultaneously.
Variable retention of diatoms on screens during size separations
Authors: Logan Bruce E. , Passow Uta , Alldredge Alice L.
Published: May 2010

Particles smaller than filter mesh pores can collide and stick to mesh fibers, biasing size separations based only on pore diameter. The removal of flocculating diatoms (Chaetoceros gracilis, Nitzschia angularis) was greater than removal of a nonfloc‐forming species (Thalassiosira weissflogii) even after including the effects of cell size. Over a 5‐d period an average of 1.4% of cells of N. angularis were removed by 230‐µm pore‐diameter screens; on day 6, 7.5% of cells were removed as cells began to flocculate. The percentage of C. gracilis removed continually increased from 0.4 to 28% during the same period, while the removal of T. weissflogii was constant at 0.19% over a 10‐d period. Prior to the onset of flocculation, sticking coefficients (rate of cell attachment to mesh fibers/rate striking fibers) were 0.05 for T. weissflogii, 0.26 for N. angularis, and 0.73 for C. gracilis. Size separations will therefore tend to concentrate more flocculent species of phytoplankton into size fractions much larger than cell diameters.
The size ratio between planktonic predators and their prey
Authors: Hansen Benni , Bjornsen Peter Koefoed , Hansen Per Juel
Published: May 2010

Size selectivity spectra of 28 planktonic predators from 18 studies in the literature are compared. The linear size ratio between predators and their optimal prey is 1 : 1 for a dinoflagellate, 3 : 1 for other flagellates, 8 : 1 for ciliates, 18 : 1 for rotifers and copepods, and ∼50: 1 for cladocerans and meroplankton larvae. These size ratios seem consistent within groups, and their validity is supported by quantitative information from the literature. However, a difference between filter feeders and raptorial‐interception feeders, preferring relatively smaller and larger prey respectively, is evident across the taxonomic groups. A classification of planktonic predators into functional groups is therefore crucial for the construction of models of pelagic food webs.
Effects of the concentrations of toxic Microcystis aeruginosa and an alternative food on the survival of Daphnia pulex
Authors: Reinikainen Marko , Ketola Matti , Walls Mari
Published: May 2010

We investigated the effect of the cyanobacterium Microcystis aeruginosa (strain PCC7820) on the survival of juvenile and adult Daphnia pulex (Cladocera) in different food concentrations (the green alga Scenedesmus obtusiusculus). M. aeruginosa reduced survival in D. pulex. The peptide toxin microcystin‐LR is present in this strain of M. aeruginosa. The toxic effect decreased with increasing concentrations of S. obtusiusculus. Juvenile D. pulex generally died faster than adults at high concentrations of cyanobacteria. However, juvenile D. pulex did better than adults at the lowest concentration of S. obtusiusculus.
Marine calcification as a source of carbon dioxide: Positive feedback of increasing atmospheric CO2
Authors: Frankignoulle Michel , Canon Christine , Gattuso Jean‐Pierre
Published: May 2010

Calcification is a well‐recognized source of CO2 to the surrounding water and thus a potential source of atmospheric CO2 due to chemical equilibria involving the CO2 species. The released CO2: precipitated carbonate ratio (Ψ) has recently been estimated to be 0.6 in seawater (taking into account the buffering capacity of the latter). We report an analytical expression enabling the computation of this ratio. Calculations show that the amount of CO2 that must be released to equilibrate seawater increases with increasing partial pressure of CO2 in seawater (pCO2), which results from human impact on atmospheric CO2. We show that at 15°C Ψ increased from 0.55 during the time of glaciation to 0.67 at present and would increase to 0.84 for a pCO2 of 1,000 µatm. Doubling the preindustrial pCO2 value results in a total CO2 source of ∼5 Gt C (taking into account the described buffering effect).
Dissolved humic substances of vascular plant origin in a coastal marine environment
Authors: Moran Mary Ann , Hodson Robert E.
Published: May 2010

Bacterial decomposition of vascular plant detritus in coastal wetlands results in the conversion of particulate organic matter to dissolved form and causes the release of humic substances into the bulk dissolved organic carbon (DOC) pool. We found that 34% of the DOC accumulating during degradation of salt marsh grass (Spartina alterniflora) from coastal wetlands of the southeastern U.S. fits the definition of humic substances and that lignin is the primary source of the dissolved humic substances (66% of the total). Although marine bacterioplankton used the lignin‐rich humic substances more slowly and less efficiently than other components of the DOC pool, a significant fraction (24%) of these substances was mineralized within 7 weeks. Concentrations of vascular plant biomarkers (lignin phenols) indicate that 11–75% of the dissolved humic substances on the southeastern U.S. continental shelf is from vascular plant‐dominated environments. Calculations indicate that about half this material is contributed by the coastal salt marshes and half by river export. Vascular plant influence was lower in the bulk DOC pool (2–38%), indicating that terrestrially derived material is harbored preferentially in the humic substances subcomponent of marine DOC.
Sulfate reduction and diffusion in sediments of Little Rock Lake, Wisconsin
Authors: Urban N. R. , Brezonik P. L. , Baker L. A. , Sherman L. A.
Published: May 2010

Rates of sulfate diffusion and reduction were measured in sediments of Little Rock Lake, an oligotrophic, soft‐water lake in northern Wisconsin. Laboratory measurements of kinetics of sulfate reduction found half‐saturation constants (20–30 µmol liter−1) and Q10 values (2.6) similar to values reported in the literature. Sulfate reduction under in situ conditions in sediment cores was limited by sulfate and followed similar uptake kinetics as in laboratory experiments. Some variation in kinetic parameters was evident as a function of location in the lake. No seasonal variation was observed in sulfate reduction rates in the lake sediments, and littoral and pelagic sites exhibited similar rates. Rates of sulfate reduction were much higher than fluxes of sulfate calculated from pore‐water profiles. Pore‐water profiles also indicated little difference in diffusive fluxes among pelagic and littoral sites and among seasons. The discrepancy between diffusive fluxes and sulfate reduction rates is ascribed to high rates of oxidation of reduced sulfur. Nonlinear rates of sulfate reduction and calculated turnover times of sediment sulfide pools support the hypothesis that sulfide oxidation occurs nearly as rapidly as sulfate reduction.
In situ chemical inhibition of benthic diatom growth affects recruitment of competing, permanent and temporary meiofauna
Authors: Hentschel Brian T. , Jumars Peter A.
Published: May 2010

To reduce the supply of a potentially limiting food for meiobenthos, we developed a new method to inhibit benthic diatom growth by perfusing pore waters with herbicide diffusing from a buried gel. Placing the gel in a bottom‐sealed chamber constrained the chemical gradient to the vertical dimension so that concentrations in overlying pore waters could be predicted from a one‐dimensional diffusion model. Our goal was to determine whether the meiofaunal oligochaete Amphichaeta leydigii and juveniles of the polychaete Hobsonia florida, whose adults deposit feed, share benthic diatoms as a limiting resource during recruitment. We verified that gels containing the herbicide DCMU inhibited microalgal growth in the laboratory. The field DCMU manipulation also significantly reduced diatom abundance relative to control gels.

The recruiting H. florida population was divided at median size into two classes. Development of feeding tentacles begins at that size—suggesting that size classes differ in feeding mode. Smaller juveniles showed no significant response to the treatment, while larger juveniles and oligochaetes both had significantly reduced abundances in DCMU patches. No other dominant meiofauna showed significant responses to the treatment. Calculated concentrations of DCMU in surficial sediments were ∼0.01–0.1× those that cause lethal or sublethal effects on animals, and nontarget invertebrates showed no significant effects—implying that A. leydigii and H. florida abundances varied because of the effect of DCMU on diatoms rather than as a direct response to the chemical itself. This evidence of a shared resource suggests food limitation as a competitive bottleneck between the meiofaunal oligochaete and recruiting H. florida juveniles and a critical stage in the life history of the deposit‐feeding polychaete.
Single‐cell RNA content of natural marine planktonic bacteria measured by hybridization with multiple 16S rRNA‐targeted fluorescent probes
Authors: Lee SangHoon , Kemp Paul F.
Published: May 2010

Despite the potential of cellular RNA as a tool for the study of bacterial activities in natural environments, cellular RNA has rarely been measured because of methodological limitations. In a previous study, we quantitatively analyzed single‐cell RNA content with multiple 16S rRNA‐targeted fluorescent probes. In the present study, we explore the potential of this approach with 12 samples of natural planktonic bacteria collected from coastal water over a 6‐month period (late winter to summer). We measured fluorescence from single cells hybridized with multiple probes, cellular DNA and RNA by ethidium bromide (EtBr) fluorometry, and [3H]thymidine (TdR) incorporation rates. Fluorescence of the probe‐hybridized cells was highly correlated to cellular RNA determined by EtBr fluorometry. Winter and summer samples showed different patterns of fluorescence‐frequency distribution. Temperature had a large positive effect on TdR incorporation rates, but there was a negative correlation with cellular RNA content; only the samples taken at elevated summer temperatures showed a positive relationship between TdR incorporation and cellular RNA content. We estimated that the RNA content of the cells not visibly labeled with five probes was <0.3 fg.
Do symbiotic dinoflagellates secrete lipid droplets?
Authors: Leonard Muscatine , Gates Ruth D. , Ingrid LaFontaine
Published: May 2010

We investigated the claim that symbiotic dinoflagellates from corals and sea anemones release lipid droplets in vitro. Putative lipid droplet secretion in vitro is taken as evidence for lipid translocation from algae to host in hospite in symbiotic cnidarians. We confirmed that symbiotic algae isolated from the tropical sea anemone Condylactis gigantea exhibited surface “blebs” and attached droplets. The surface entities stained positively with the DNA‐specific fluorochrome Hoechst 33258 and with the chromosome stain lacto‐aceto‐orcein, but not with the lipid lysochrome Sudan Black B. In contrast, bona fide lipid droplets isolated from C. gigantea gonad stained positively with Sudan Black B. The data support the interpretation that droplets attached to isolated symbiotic dinoflagellates are host cell nuclei and are consistent with ultrastructural data published elsewhere.
The importance of Prochlorococcus to community structure in the central North Pacific Ocean
Authors: Campbell Lisa , Nolla H. A. , Vaulot Daniel
Published: May 2010

Assessments of plankton community structure in the oligotrophic oceans based solely on microscopy may overstate the importance of heterotrophic bacterial biomass. Using flow cytometry to distinguish heterotrophic bacteria from the photosynthetic procaryotes Prochlorococcus spp., we found that Prochlorococcus contributed 31% of total bacterial counts in the upper 100 m at station ALOHA (22°45′N, 158°W). In terms of carbon, procaryotic biomass was the largest component (≥ 80%) of the microbial community, but almost half of this was photosynthetic biomass contributed by Prochlorococcus. Overall, the total 200‐m integrated photosynthetic biomass exceeded heterotrophic bacterial biomass (55 vs. 45%). We suggest that the relative proportion of photosynthetic to heterotrophic bacterial biomass varies among oligotrophic regions of the ocean and that dominance by heterotrophic bacteria is not typical.
Biogeochemical control of phosphorus cycling and primary production in Lake Michigan
Authors: Brooks Arthur S. , Edgington David N.
Published: May 2010

A 3‐yr study in Lake Michigan has shown a 27 mmol P m−2 increase in the mass of total P (TP) in the water during spring when the lake is mixed from surface to sediment. This value is an order of magnitude greater than the annual P input from external sources. TP changed in concert with increases in chlorophyll a and organic N and decreases in nitrate and soluble Si. The concentration of soluble reactive PO43− (SRP) remained relatively constant throughout the study. We hypothesize that the SRP concentration is maintained by a chemical equilibrium with calcium‐phosphate species. The increased mass of TP arises from the sequestering of P by algae which displaces the chemical equilibrium and allows more P to be released to the water from the sediments. Solar irradiance and the duration of mixing determine the magnitude of the spring bloom and the demand for P that must be supplied through the flux of P from the sediments to the overlying water.
Phenotypic plasticity of the filter screens in Daphnia: Adaptation to a low‐food environment
Authors: Lampert Winfried
Published: May 2010

Daphnia can enlarge the area of the screens on its filtering limbs in response to low concentrations of food. Seven species of Daphnia had larger filter screens when grown at low levels of food compared to animals of the same size raised at high levels of food. The increase in screen area varied between 19 and 83% among species. Larger filter screens resulted in higher filtering and feeding rates. Threshold food concentrations for growth, calculated from the carbon budget for different Daphnia species, were biased when adaptation of the filter screens was ignored. Daphnids used for measuring assimilation rates are usually cultured at high levels of food and thus have small filter screens. If filter‐screen enlargement is taken into consideration in estimating assimilation rates, thresholds come close to the realistic values measured in long‐term growth experiments. Filter‐screen adaptability is considered a response to varying nutritional conditions in the pelagic zone.
Estimating carbon, nitrogen, protein, and chlorophyll a from volume in marine phytoplankton
Authors: Montagnes David J. S. , Berges John A. , Harrison Paul J. , Taylor F. J. R.
Published: May 2010

The size of 30 small (2–60 µm) phytoplankton species was examined with a microscope and a Coulter Counter before and after fixation. Acid Lugol’s iodine caused cells to shrink immediately. The shrinkage effect was constant for concentrations of 1–10% Lugol’s iodine (in seawater). For optically measured cells fixed in 2% Lugol’s iodine, volume of live cells = 1.33 × (volume of fixed cells). Coulter Counter and optically measured volumes did not agree. For live cells, optical cell volume = 1.24–2.04 × (Coulter Counter determined volume); this difference is likely due to inaccurate volume measurements of non‐spherical cells by the Coulter Counter and by inaccurate microscopy resulting from optical distortions (errors of <0.5 µm in cell dimensions). Cell quota estimates were presented following the relation y = axb, where x = optically measured cell volume (µm3), y = any cell constituent (pg cell−1), and a and b are constants. The constants a and b were 0.109 and 0.991 for carbon, 0.0172 and 1.023 for nitrogen, 0.043 and 1.058 for protein, and 0.00428 and 0.917 for Chl a. Our relation of carbon to volume differs from other literature values, in which there is no consensus. Our data can be used to determine carbon, nitrogen, protein, and Chl a estimates from field material that has been fixed with Lugol’s iodine, observed live, optically measured, or Coulter Counter measured; however, the variability in published data suggests that any of these estimates will have a large potential error.