bluuebunny/crossref_metadata_2025 huggingface dataset:
Sedimentary record of changes in the condition of Lake Washington
Authors: Edmondson W. T.
Published: April 2010

Variations with depth in properties of the sediment of Lake Washington are compared with known conditions in the lake. Annual changes of deposition form pairs of cryptic layers, dominated respectively by diatoms and mineral particles, that are revealed by X‐radiography. A period of eutrophication is recorded by sediment rich in phosphorus. Two later peaks of P can be attributed to deposition of eroded material during floods. The relative importance of diatom species changed in coordination with changes in nutrition and the presence of Oscillatoria which can suppress some species of centric diatoms by antibiosis. Experiments confirm that selective feeding by oligochetes can result in nonrandom transport of different components of sediment. Sporadic, brief outbursts of rare species of diatoms give precise dating and opportunity for measuring bioturbation under fully natural conditions by repeated sampling. Precise data on vertical distribution of diatoms are given by overlapping scanning electron micrographs of dried cores.
Spatial and temporal variation of natural bacterioplankton assemblages studied by total genomic DNA cross‐hybridization
Authors: Lee SangHoon , Fuhrman Jed A.
Published: April 2010

Variations of the species compositions of marine bacterial communities are poorly understood, largely due to the general lack of cultivability of these organisms. With DNA hybridization, which uses total DNA directly extracted from natural bacteria and thus avoids growing pure cultures, we compared bacterioplankton assemblages from the oligotrophic Pacific Ocean (depths: 25, 100, 500, 1,000 m), the Caribbean Sea (<20 m), and Long Island Sound (LIS; <1 m). Comparisons were across depths, within depth, and across the three sampling locations. Temporal variations were studied with summer LIS samples taken a year apart. Deep Pacific samples (500 and 1,000 m) showed 30–90% similarity to each other, but differed from (similarities ≤5%) photic‐zone (25 and 100 m) samples. The photic‐zone samples showed only 15–45% similarity to each other. The 25‐m samples were the most variable within depth (similarities >50%). The three ocean‐basin samples each had unique community DNA (similarities <16%). The LIS community changed as much within 2 weeks as between successive summers (similarities down to 40–50%); however, the similarities (seven samples in this and a previous study) were never <30%, suggesting a consistent subcommunity. We conclude that the total genomic DNAs of the bacterial communities varied significantly over time and space due to the different constituents of those communities, probably reflecting environmental factors.
Annual study of bacterioplankton community dynamics
Authors: Wikner J. , Hagström Å.
Published: April 2010

Bacterial growth, abundance, and grazing were measured simultaneously during a full seasonal cycle in a temperate brackish water estuary, covering diel and seasonal variability. Growth of bacteria was balanced by bacterivory on an annual basis, and observed net change in bacterial numbers matched the net change calculated by a simple Lotka‐Volterra equation lacking immigration or emigration terms. Bacterial growth was dependent on water temperature below 6°C, but other factors dominated at higher temperatures. The community clearance rate of the bacterivores was stringently regufated at 0.6 d‒1, showing a linear functional response within the range of natural bacterial abundances recorded. Furthermore, bacterivores showed a threshold at 7 × 105 bacteria ml‒1 when grazing ceased, suggesting that pelagic bacteria have a numerical refuge promoting coexistence with bacterivores in aquatic environments. The observed lack of timing between bacterial growth and grazing in spring allowed accumulation of bacterial cells, but grazing exceeded growth in winter. We inferred that the specific growth rate of the bacterial community and the community clearance rate of bacterivores together determined change in and abundance of bacterioplankton in the waters examined.
Evidence that molybdenum‐dependent nitrogen fixation is not limited by high sulfate concentrations in marine environments
Authors: Paulsen Denise M. , Paerl Hans W. , Bishop Paul E.
Published: April 2010

Nitrogen availability frequently controls phytoplankton growth in marine environments. It would seem that N2 fixing microorganisms would have a selective advantage in these environments, but N2 fixation appears to be limited in most marine waters. Previous studies have focused on deficiencies of inorganic nutrients such as P, Fe, and especially Mo as constraints on N2 fixation. It was proposed that a high SO42‒: MoO42‒ ratio interferes with cellular MoO42‒ uptake and in turn results in insufficient quantities for incorporation into the N2‐reducing enzyme complex nitrogenase. In the present study, in situ bioassays demonstrate that Mo is not the limiting nutrient for N2 fixation by marine assemblages. Instead, enrichments of glucose or mannitol were found to initiate or increase N2 fixation in these assemblages. We also show that diazotrophic growth rates of an Azotobacter vinelandii strain containing a single Mo‐dependent nitrogenase are not inhibited at SO42‒: MoO42‒ ratios up to 8 times higher than those calculated for seawater. From these results we propose that widespread limitation of N2 fixation in marine environments is due to deficiencies in organic matter and appropriate microhabitats rather than Mo.
The importance of zooplankton‐protozoan trophic couplings in Lake Michigan
Authors: Carrick Hunter J. , Fahnenstiel Gary L. , Stoermer Eugene F. , Wetzel Robert G.
Published: April 2010

The importance of the zooplankton‐protozoan trophic coupling was determined experimentally by measured changes in protozoan growth rates with increasing zooplankton biomass. In five of six experiments conducted in Lake Michigan, a significant inverse relationship between protozoan growth and zooplankton biomass was observed (avg r2 = 70%). Zooplankton clearance rates on protozoan assemblages [range, 1.0–6.2 ml (µg dry wt)‒1 d‒1] were comparable to those previously measured for phytoplankton which suggested that protozoa are important prey for zooplankton. Clearance rates on individual protozoan taxa [0–15.6 ml (µg dry wt)‒1 d‒1] were size‐dependent. Rates were greatest for taxa <20 µm in size (mainly nanoflagellates and small ciliates). In contrast to findings for phytoplankton, no evidence emerged for grazer resistance nor growth enhancement by planktonic protozoa in response to grazing. The high flux rates for macrozooplankton on heterotrophic nanoflagellates observed in all experiments (0.2–6.0 µg C liter‒1 d‒1) provided evidence that a large fraction of picoplankton C may be directly transferred to higher trophic levels via a picoplankton‐flagellate‐zooplankton coupling.
Changes in epilithon and epiphyton associated with experimental acidification of a lake to pH 5
Authors: Turner Michael A. , Howell E. Todd , Summerby Martha , Hesslein Raymond H. , Findlay David L. , Jackson Michael B.
Published: April 2010

The algal taxonomy and community metabolism of epilithon and epiphyton in a lake experimentally acidified to pH 5 were compared with those in a nearby neutral lake to interpret the effect of acidification on periphyton. Acidification altered the algal community structure. Acidified periphyton had fewer filamentous cyanobacteria, whereas green algae (especially Mougeotia) were relatively more abundant. Periphytic metabolism also differed substantially. Rates of dark respiration were higher and compensation irradiances were greater in all acidified benthic communities. Photosynthesis was C limited and enhanced by experimentally increasing turbulence to simulate rates of water movement in the shallow littoral zone. These findings are consistent with the hypothesis that the filamentous green algae of acid lakes can take up CO2 faster than the adnate algae usually dominant in neutral lakes, thus (partially) overcoming the C limitation found in acidified lakes.
Bacterial 5'‐nucleotidase activity in estuarine and coastal marine waters: Characterization of enzyme activity
Authors: Ammerman James W. , Azam Farooq
Published: April 2010

We measured 5′‐nucleotidase by following the hydrolysis of ATP and measured alkaline phosphatase by conventional fluorometric techniques. 5′‐Nucleotidase (5PN) was found in all estuarine and coastal marine waters where measurements were made, regardless of the degree of eutrophication or phosphate concentrations. Its activity was usually concentrated in the bacterial size fraction. 5PN was competitively inhibited only by 5′‐nucleotides and was distinguishable from alkaline phosphatase by both this substrate specificity and the lack of inhibition by low concentrations of orthophosphate. The percent of uptake of orthophosphate regenerated by 5PN was inversely related to the ambient phosphate concentration.
Bacterial 5′‐nucleotidase activity in estuarineand coastal marine waters: Role in phosphorus regeneration
Authors: Ammerman James W. , Azam Farooq
Published: April 2010

5′‐Nucleotidase (5PN) activity was measured with [γ‐32P]ATP, and related measurements were made by conventional techniques. Our results suggest that 5PN activity was more closely correlated with high algal and bacterial biomass and growth rates (eutrophic environments) than with phosphate depletion. 5PN was also potentially important in phosphate regeneration, even when dissolved nucleotide concentrations of a few nanomolar were assumed. If nuclease hydrolysis of dissolved nucleic acids also contributes to the dissolved nucleotide pool, then phosphate regeneration by 5PN activity would be significantly greater. In the high‐phosphate environments studied, most of the phosphate regenerated by 5PN was not taken up immediately.
Massive fluxes of rhizosolenid diatoms: A common occurrence?
Authors: Sancetta Constance , Villareal Tracy , Falkowski Paul
Published: April 2010

The potential nonlinearities in the relationship between vertical flux of material to the deep sea and rates of production in the surface water include the possibility that stochastic events are responsible for a large proportion of export below the euphotic zone. It has been suggested that large diatoms might play a role in such export production. We summarize data sets referring specifically to the rhizosolenid diatoms, including several not previously published, and show that mass sinking of rhizosolenids may be a common occurrence.
The abundance and composition of freshwater picocyanobacteria in relation to light penetration
Authors: Pick F. R.
Published: April 2010

The abundance and composition of picocyanobacterial (PC) assemblages were measured in 38 lakes of varying trophic state and dissolved inorganic C concentrations. Light attenuation provided the best prediction of PC abundance, explaining half of the variation in summer abundance. Phycoerythrin‐containing PC were particularly abundant (> l05 cells ml‒1) in oligotrophic to mesotrophic hard‐water lakes, while nonphycoerythrin types were generally found in eutrophic and colored lakes. The percentage of phycoerythrin‐containing PC declined significantly with increasing light attenuation among lakes and within experimental enclosures of one lake where light attenuation was altered by nutrient additions and food‐web manipulations. The relationship may be the consequence of changes in spectral quality as lakes become nutrient enriched or colored by humic material.
Fluorescent microparticles: A new way of visualizing sedimentation and larval settlement
Authors: Lindegarth Mats , Jonsson Per R. , André Carl
Published: April 2010

Methods for preparing fluorescently labeled microparticles and bivalve larvae (Cerastoderma edule) are presented. The labeling is cheap, easy, and allows production of great quantities of fluorescent microparticles and larvae. Fluorescent visualization can be used as a tool to analyze hydrodynamical processes in the benthic boundary layer and to directly observe behavioral patterns in settling larvae.
The formation of large marine snow and its sustained residence in surface waters
Authors: Riebesell Ulf
Published: April 2010

The formation of large marine snow macroflocs and stringers was monitored at a fixed station in the southern North Sea. During an 18‐month investigation, large marine snow flocs occurred in the water column on nine occasions for periods lasting between 5 and 16 d. Their formation coincided with both high phytoplankton biomass and low windspeeds. Retention of marine snow in the surface layer was related to slow sinking, neutral buoyancy, and rising of the large flocs. Applying a specially developed instrument showed buoyancy to be caused by gas bubbles incorporated in the flocs. Marine snow flotation coincided with periods of oxygen supersaturation in the water column, suggesting that oxygen production could be responsible for gas bubble formation within the flocs. Disappearance of the large marine snow flocs from the surface layer coincided with drastic increases in windspeed, indicating that enhanced wind‐induced turbulent mixing in the surface layer could have resulted in the breakup of these flocs. Formation and disappearance of marine snow had a marked influence on the light regime in the water.
Effect of coagulation on nutrient and light limitation of an algal bloom
Authors: Jackson George A. , Lochmann Steve E.
Published: April 2010

Coagulation is the formation of large particles from multiple collisions of smaller ones. Because larger particles fall faster than smaller ones, coagulation can be important in accelerating the export of organic matter from the ocean’s surface to the deep sea and has the potential to limit phytoplankton populations. We have developed a model of an algal bloom that includes nutrient and light limitation of algal growth rate and coagulation of single algal cells. The results show two effects of coagulation on the growth model. Loss of dividing cells to coagulating particles can occur when algal cells are growing at a fairly constant rate, placing a cap on the concentrations that algae can achieve. The second effect is enhancement of vertical particle flux from the surface mixed layer in aggregates. This enhanced transport moves algal biomass from the surface mixed layer over shorter periods at rates far greater than those associated with settling of single cells. For example, half the material associated with a bloom of 2‐µm‐radius algae, which would take 350 d to settle out as isolated cells, took 42 d as aggregates. Aggregation was not limited to the large algae, although the rate was slower for the smaller ones. Coagulation was enhanced by higher initial nutrient concentrations, deeper mixed layers, and higher shear rates. Vertical transport associated with aggregation has the potential to be an important mechanism for removing biological material from eutrophic regions.
Experimental tests for particle size‐dependent bioturbation in the deep ocean
Authors: Wheatcroft Robert A.
Published: April 2010

The potential for particle size‐dependent bioturbation rates was experimentally tested at 1,240 m in the Santa Catalina Basin (eastern Pacific). Spherical glass bead tracers in five size classes (8–16, 17–31, 32–62, 63–125, and 126–420 µm) were spread over the sediment surface and tube cored 997 d later. Downcore concentrations of glass beads were enumerated in each of the five size categories and Page’s L‐test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer. In all cores the null hypothesis was rejected; finer tracers penetrated deeper into the sediment. In two of the three cores, vertical biodiffusivities were computed from concentration profiles of downcore tracers. These also showed size dependence, with biodiffusivities ranging from 1 cm2 yr‒1 for the 8–16‐µm fraction to 0.1 cm2 yr‒1 for the 125–420‐µm size class. These data demonstrate that vertical bioturbation rates are particle size‐dependent in Santa Catalina Basin. The likely cause is preferential ingestion and downward transport of fine particles by deposit feeders.
Wind‐induced hydrodynamic control of the phytoplankton biomass in a lagoon ecosystem
Authors: Millet Bertrand , Cecchi Philippe
Published: April 2010

To provide a closer insight into the relationship between wind‐induced hydrodynamic motion and the biological dynamics of shallow bodies of water, an alternating conditional expectation (ACE) algorithm has been used to examine the nonlinear relationship between the phytoplankton biomass in the Thau lagoon (southern France) and wind intensity. Chlorophyll content (mg m‒3), periodically sampled at diff.erent stations, was used as the dependent variable, and windspeeds (m s‒3) averaged over both short and long intervals preceding each sampling day, were used as predictor variables. Results showed a dome‐shaped relationship between chlorophyll content and mean windspeed. The optimum value of ∼4.0 m s‒1 was strongly associated with an alternation between the dominant hydrodynamic processes involved, i.e. the beneficial effect of vertical turbulent diffusion, and the detrimental influence of horizontal advective dispersion. Spatiotemporal development of this nonlinear relationship is proposed, based on environmental thresholds, i.e. a depth of <4 m, and a wind‐stress memory of 1–4, 5–8, and 9–13 d. An environmental optimum for phytoplankton enhancement within these time‐space limits is found.
An extremely low‐light adapted phototrophic sulfur bacterium from the Black Sea
Authors: Overmann Jörg , Cypionka Heribert , Pfennig Norbert
Published: April 2010

Five strains of a brown phototrophic sulfur bacterium (Chlorobium phaeobacteroides) were isolated from the chemocline of the Black Sea (80‐m depth). All contain bacteriochlorophyll e as the main photosynthetic pigment. The strains revealed extreme low‐light adaptation of growth compared to 12 other green and purple sulfur bacterial strains. At very low light intensities (<4 µEinst m‒2 s‒1), the Black Sea strain MN 1 oxidized sulfide faster than the type strain 2430; the latter reached three times higher oxidation rates at light saturation. Low‐light adaptation is achieved by an increase of light‐harvesting pigments (175% compared to the type strain) and a very low maintenance energy requirement. The efficiency of energy transfer (59%) within light‐harvesting structures (chlorosomes) is comparable in other green sulfur bacteria and, therefore, appears to be limited by the molecular organization of the chlorosomes. From data in the literature, a light transmission of 0.0005% of surface irradiance was calculated for the chemocline of the Black Sea. Extrapolation of our laboratory data revealed that anoxygenic photosynthesis could account for 4% of total sulfide oxidation under average light conditions in situ and for 13% at maximal surface irradiance in summer.
Patterns in phytoplankton community structure in Florida lakes
Authors: Duarte Carlos M. , Agustí Susana , Canjield Daniel E.
Published: April 2010

We demonstrate, based on examination of phytoplankton communities from 165 lakes located throughout Florida, the existence of smooth gradients of change in phytoplankton community structure with increasing lake trophic status. This change involves a gradation from a tendency toward the dominance of green algae in oligotrophic lakes to dominance of cyanobacteria in eutrophic and hypereutrophic lakes, with a peak in diatom abundance in mesotrophic lakes. The mean biomass of the dominant genera within these groups was not related to the biomass of the communities where they occurred; instead, it was strongly related to their size, the (geometric) mean biomass of the genera increasing as the 0.74 power of their cell volume.
Phosphorus limitation of primary production in Florida Bay: Evidence from C:N:P ratios of the dominant seagrass Thalassia testudinum
Authors: Fourqurean James W. , Zieman Joseph C. , Powell George V. N.
Published: April 2010

Florida Bay is a shallow, seagrass‐dominated embayment on the southern tip of Florida. Variation of C, N, and P content of leaves of Thalassia testudinum was measured on two spatial scales: locally (10–100 m) in relation to a point source of nutrients associated with a bird colony in eastern Florida Bay and regionally (10– 100 km) across all of the bay. Locally, the P content of leaves decreased from a high of 0.16% P (wt/wt) 30 m from the nutrient source to a low of 0.08% 120 m from the source; the C and N content (34.9 and 2.1%) was independent of distance from the nutrient source. Due to variations in P content, C : P and N : P, but not C : N, varied locally. Regionally, P content varied greatly, from 0.05 to 0.20%; C (29.4–39.5%) and N (1.7–2.7%) showed considerably less variation. Variation in C : P and N : P across the bay encompassed a range nearly as great as reported for all seagrasses around the world combined; C : N showed little variation. Local variation around the nutrient point source indicated that C : P and N : P were indicators of P availability, and trend analysis of the regional spatial variation in C : P and N : P showed that P availability was greatest in northwest, and least in eastern, Florida Bay. This pattern mirrored abundance of seagrasses and productivity in the bay. T. testudinum from the bay appears to be P limited and N saturated, even in the sparsest seagrass communities.
Sea ice: A cast technique to examine and analyze brine pockets and channel structure
Authors: Weissenberger Jiirgen , Dieckmann Gerhard , Gradinger Rolf , Spindler Michael
Published: April 2010

A casting technique was developed to examine the internal structure of sea ice using scanning electron microscopy. After removal of brine by centrifugation at in situ temperatures, water‐soluble resin is deployed to penetrate drained brine channels of sea ice. The resin is subsequently polymerized under UV light at about ‒12°C. Freeze‐drying eliminates the ice by sublimation, and the hardened casts can be mounted for microscopical analysis. Casts can be used to determine volume and extent of habitable space in different types of sea ice. The extracted brine is available for further studies of sea‐ice organisms.
The importance of dissolved organic phosphorus to phosphorus uptake by limnetic plankton
Authors: Bentzen E. , Taylor W. D. , Millard E. S.
Published: April 2010

The substrate [α‐32P]ATP was used to represent the available fraction of the dissolved phosphomonoester (PME) pool and to measure its rate of assimilation by freshwater plankton in systems of low phosphorus availability. We compared [32P]ATP uptake to inorganic 32PO43‒ uptake. The upper bounds to the pool sizes of PO43‒ and PME were estimated with Rigler bioassays, and these values, together with the uptake constants at ambient substrate concentrations, permit comparison of the uptake of organic and inorganic P by limnetic plankton. Affinity of the plankton for both substrates was high, and the estimated flux rates from both pools were similar, demonstrating that PME contributes significantly to total P uptake. We tested the hypothesis that algae >1 µm preferentially assimilate P from PME but observed that the 0.2–1‐µm size fraction dominates uptake of P from either source at ambient concentrations. The specific flux of P from PME into the 1–12‐µm size fraction was often as high as that into the 0.2–1‐µm fraction, but plankton >12 µm typically incorporate <5% of the P from either source.
Uptake of dissolved inorganic and organic bphosphorus compounds by phytoplankton and bacterioplankton
Authors: Cotner, James B. , Wetzel Robert G.
Published: April 2010

Potential sources of dissolved P to phytoplankton and bacterioplankton were examined in a small meso‐eutrophic lake. Kinetic analyses of whole lake water on three dates demonstrated that the maximal rate (Vmax) for phosphate uptake was highest (5.2 nM min‒1) in spring. On all dates, size fractionation of plankton and kinetic analyses of uptake indicated that most (>50%) uptake of phosphate was by phytoplankton at Vmax and by bacteria at ambient concentrations. Isotope dilution assays, with either unlabeled phosphate or various dissolved organic P (DOP) compounds, demonstrated that phosphate was the preferred substrate for uptake into both algae and bacteria. Phytoplankton had greater capacity for uptake of P from both phosphate and DOP than bacterioplankton. We concluded that phytoplankton use both phosphate and DOP, particularly at high substrate concentrations, and that bacterial utilization of P may be limited by the availability of organic C or other nutrients.
Possibility of N or P limitation for planktonic cladocerans: An experimental test
Authors: Urabe Jotaro , Watanabe Yasunori
Published: April 2010

Threshold food N : C or P : C ratios, below which net production is N or P limited, were calculated for two cladocerans, Daphnia galeata and Bosmina longirostris, based on the N and P contents of body tissue and the C balance between ingestion and net production rates under experimental conditions with various food concentrations from 0.05 to 2.50 mg C liter‒1. With changing food concentration, the threshold N : C and P : C ratios for D. galeata changed in weight ratio from 0.039 to 0.077 and 0.0067 to 0.0120, respectively, with the lowest value at the high food concentration. Changes in threshold ratios for B. longirostris, however, were small and mean values were 0.085 and 0.0080 for the N : C and P : C ratios. As a result, the threshold N : C ratio for D. galeata was lower than for B. longirostris at high food concentrations, while the P : C ratio for B. longirostris was lower than for D. galeata at lower food concentrations. Although the threshold elemental ratios calculated here are theoretically minimum estimates, they were higher than the lower end of the sestonic elemental ratios in some lakes, suggesting that it is not unusual for these cladocerans to be N or P limited at certain periods of the year. Sestonic elemental ratios may have potential importance in determining the community structure of zooplankton.
Effects of water velocity on phosphate uptake in coral reef‐hat communities
Authors: Atkinson M. J. , Bilger R. W.
Published: April 2010

To determine a Stanton number (Stm, a dimensionless number giving the ratio of uptake rate to the rate of advection of the substance past the uptake surface) for a reef‐flat community without the effects of wave surge, we placed communities of reef organisms in the bottom of a flume, 9.3 m long and 0.35 m wide. Water was pumped over the experimental communities at 13 different surface flow velocities, ranging between 2.3 and 58 cm s‒1. Rate of phosphate (P) uptake at each velocity was measured by raising the ambient P concentration to ∼2 µM and measuring the rate of decrease in P concentration. Stm for P uptake in the flume was significantly greater than estimates of Stm derived from engineering studies of mass and heat transfer. This result confirms the finding of anomalously high mass transfer based on field data. Rates of P uptake increased as water velocity increased. The log of the first‐order rate coefficient for P uptake was directly proportional to the log of velocity with a slope of ∼0.76. These results indicate that the rate of P uptake into reef benthos is controlled by diffusive boundary layers near the surfaces of organisms and that the surface geometry is such that improved transfer in comparison with engineering surfaces is obtained.
RICE: Early diagenesis of protein: A seasonal study
Authors: Mayer Lawrence M. , Rice Donald L.
Published: April 2010

The diagenetic behavior of proteins, defined as large polypeptides, was examined over a 2‐yr period at a mudflat site subject to intense bioturbation. Protein concentrations in the surface sediment correlated well with deposition of algal detritus from the water column. Cellular biomass made up a significant, though likely not a major, component of protein in the sediments; likewise, changes in biomass could not account for the bulk of protein losses downcore. These protein losses made up most of the total acid‐hydrolyzable amino acid losses and about a quarter of the total N losses. Loss rates of protein are proportional within cores to previously reported estimates of extracellular proteolytic activity at this site, though with variation among sampling times. The combination of high organic matter input and rapid bioadvection allows detection of changing kinetics of decomposition during very early stages of diagenesis, analogous to those observed in algal decay experiments. Specific decay rates, similar to first‐order decay constants, ranged from 0.2 to 8 yr‒1 for protein, total organic C and N, and pheophytin in the labile fraction of organic matter found in the top few centimeters. This labile fraction, which is dominated by nonprotein forms of N, is lost with progressively lower specific decay rates downcore. Various lines of evidence—such as ammonification experiments and low C : N ratios of the remineralized material— suggest that these changing kinetics are at least partially due to replacement of algal detritus by more slowly decaying products of microbial resynthesis rather than simply to varying lability of fractions of the original algal detritus.
Factors regulating periphytic algal biomass
Authors: Hansson Lars-Anders
Published: April 2010

To assess the principal factors regulating periphytic algal communities, I conducted a field study along a productivity gradient of Swedish and Antarctic lakes ranging from extremely low productivity meltwater to highly productive lakes. Because the Antarctic lakes lack fish, as well as molluscs and insect larvae, the data set provides considerable variation in food web composition, offering a rare opportunity to evaluate the importance of these factors in determining the biomass of periphytic algae. Among the possible factors investigated, water temperature, substrate characteristics, and food web composition seem to be of minor importance. Instead, there was a curvlinear relationship between the biomass of sediment‐associated periphytic algae and lake productivity, suggesting a shift from nutrient limitation to light limitation caused by phytoplankton. A temporal study in the littoral zone of one of the lakes included in the spatial study showed that the temporal variation in periphyton biomass within the lake was low compared to the variation between lakes. The temporal study also strengthened suggestions from the spatial study by pointing to nutrient availability as a major factor determining periphytic algal biomass.
Lipids and life‐cycle strategy of a hypolimnetic copepod in Lake Michigan
Authors: Vanderploeg Henry A. , Gardner Wayne S. , Parrish Christopher C. , Liebig James R. , Cavaletto Joann F.
Published: April 2010

Concentration and composition of lipids varied seasonally in adult female Diaptomus sicilis, a hypolimnetic suspension‐feeding calanoid copepod, in Lake Michigan. Triacylglycerol (TG) was the predominant storage lipid; its level remained high (33–40% of dry wt) from June through January. During the period of reproduction from February through May, TG dropped steeply to a low of 9%. The abrupt increase in TG concentration from May to June was probably caused by the recruitment of nonreproducing adult females. Throughout summer and fall ovaries remained unripe. Feeding experiments at satiating food concentrations at 6° and 20°C suggest that low temperature and the hypolimnion was a major reason that ovaries did not ripen. Stored TG served as a potential buffer to starvation, although starvation conditions did not occur. By remaining in the hypolimnion rather than in the epilimnion, D. sicilis is assured a relatively stable supply of algae, low metabolic rate, and escape from predation. These advantages may have to be weighed against a reproductive bottleneck of low temperature.
The pigments of Prochlorococcus marinus: The presence of divinylchlorophyll a and b in a marine procaryote
Authors: Ralf Goericke , Repeta Daniel J.
Published: April 2010

The pigments of the recently isolated marine prochlorophyte Prochlorococcus marinus were characterized by modern chromatographic and spectroscopic analysis. The major photosynthetic pigment is 8‐desethyl, 8‐vinyl chlorophyll a. Accessory pigments are 8‐desethyl, 8‐vinyl chlorophyll b, zeaxanthin, α‐carotene, an unknown carotenoid, and possibly Mg 3,8 divinyl‐pheoporphyrin a5. Chl a is not present in this organism. P. marinus is the first wild‐type oxygenic phototroph that does not have Chl a as its major photosynthetic pigment and it is the only procaryote ∊‐cyclic carotenoids (α‐carotene). P. marinus demonstrates a range of biosynthetic abilities that will necessitate a re‐evaluation of the evolution of chlorophyll and carotenoid biosynthesis in pro‐ and eucaryotic phototrophs.
Light absorption by cyanobacteria: Implications of the colonial growth form
Authors: Agusti Susana , Phlips Edward J.
Published: April 2010

We assessed differences in the light absorption characteristics of nine species of cyanobacteria, colonial and single‐celled, and four species of eucaryotic phytoplankton species. The results indicated that the positive scaling of light absorption by both single cells and cyanobacteria colonies to their size and Chl a content is similar to that of eucaryotic algae, but the large differences in the extent of pigment packaging within single‐celled cyanobacteria (i.e. ci) were unrelated to their size. Cyanobacteria colonies, in contrast, could avoid increased self‐shading with increasing size by reducing their internal pigment concentration as colony size increased, as do eucaryotic cells. The results indicated that cyanobacteria colonies act as distinct optical units, rather than as the sum of their component cells. The ability of many cyanobacteria species to develop colonies may help explain their ability to develop nuisance blooms.
Induction of barite mineralization in the Asiatic clam Corbicula fluminea
Authors: Fritz Lowell W. , Ferrence Gregory , Jacobsen Timothy R.
Published: April 2010

Barite crystals were formed on the inner shell surface in 1 week by specimens of Corbicula fluminea exposed to dissolved Ba concentrations of 140–559 µg liter‒1. Prevalences of barite crystals increased directly with initial Ba concentrations over the course of a 28‐d experiment. Barite crystals were not observed on the shell exteriors of any clams analyzed. Results suggest that Ba was concentrated by C. fluminea and periodically purged from the soft tissues into the extrapallial fluids, where it heterogeneously coprecipitated with aragonite on the inner shell surface.
An immunoprobe to measure Rubisco concentrations and maximal photosynthetic rates of individual phytoplankton cells
Authors: Orellana Mhica V. , Perry Mary Jane
Published: April 2010

The cross‐reactivity of an immunological probe to the key photosynthetic enzyme Rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase) was characterized as part of a larger effort to determine maximal photosynthetic rates of individual phytoplankton cells. Polyclonal antiserum was produced against purified Rubisco from the marine diatom Chaetoceros gracilis. The results of western immunoblotting demonstrated that the antiserum reacted positively with Rubisco from 38 species of algae and higher plants and failed to react with only three species of dinoflagellates and one prochlorophyte species. However, the binding affinity or the strength of the cross‐reaction for the polyclonal antiserum with purified Rubisco varied among species. The antiserum was then affinity purified against spinach Rubisco and its binding affinity for purified Rubisco determined by ELISA. Two taxonomic groupings resulted: one with high‐binding affinity (these species included chrysophytes, bacillariophytes, prymnesiophytes, and chlorophytes) and the other with low‐binding affinity (dinophytes and cyanophytes). Rubisco concentration per cell and light‐saturated rates of photosynthesis were highly correlated for cultures of the diatom Thalassiosira weissflogii. These results indicate that affinity‐purified antiserum can be rigorously characterized for use in quantifying Rubisco concentration and for assessing the maximal photosynthetic potential of individual phytoplankton cells.
Clay turbidity: Regulation of phytoplankton production in a large, nutrient‐rich tropical lake
Authors: Lind Owen T. , Doyle Robert , Vodopich Darrell S. , Trotter Bruce G. , Limon J. Gualberto , Dcivalos‐Lind Laura
Published: April 2010

Data from five sampling stations for 23 dates in 1 yr show that annual phytoplankton production in Lake Chapala is low (80 g C m−2) and governed by high inorganic turbidity. In the most turbid region of the lake, Secchi transparency averaged 0.2 m and the vertical light (PAR) attenuation coefficient (η″) averaged 9.7 m−1; in the least turbid region, Secchi transparency averaged 0.7 m (η″ averaged 2.3 m−1).

Phytoplankton at the shallowest and most turbid station were most productive per unit volume, while the least turbid station, with a deep circulating water column, had the lowest volume‐based production. There was a considerable rainy vs. dry season difference in water transparency and in production. The lake became less turbid during the rainy season due to increased depth and lessened sediment resuspension. The annual lakewide production C.V. was 34% with the greatest day‐to‐day variation during the rainy season.

Phytoplankton Chl a averaged 5.4 mg m−3 of the mixed water column for all regions. Chl a at the shallowest and most turbid station averaged almost twice that of the other stations. Chl a increased through the rainy season (as transparency and inorganic N content increased). Variation in inorganic N accounted for the greatest variation in Chl a at each region.
Benthic oxygen fluxes on the Washington shelf and slope: A comparison of in situ microelectrode and chamber flux measurements
Authors: Archer David , Devol Allan
Published: April 2010

Benthic oxygen fluxes calculated from in situ microclectrode profiles are compared with benthic flux chamber O2 uptake measurements on a transect of eight stations across the continental shelf and three stations on the slope of Washington State. Station depths ranged from 40 to 630 m and bottom‐water oxygen concentrations were 127–38 µM. The fluxes measured by the two methods were similar on the slope, but on the shelf, the chamber flux exceeded the microelectrode flux by as much as a factor of 3–4. We attribute this difference to pore‐water irrigation, a process which apparently accounts for the oxidation of a significant amount of organic C in the continental shelf sediments. Combining our diffusive flux data with other data demonstrates clearly that the bottom‐water oxygen concentration must play some significant role in determining the sedimentary oxygen consumption rate. Numerical simulation of the microelectrode O2 profiles suggests that roughly half the diffusive O2 flux must be consumed within ∼ 1 mm of the sediment surface. If this conclusion is correct, then the magnitude of the diffusive flux depends both on the bottom‐water oxygen concentration and on the supply rate of labile C to the sediment surface.
Daphnia galeata mendotae as a cryptic species complex with interspecific hybrids
Authors: Taylor Derek J. , Hebert Paul D. N.
Published: April 2010

Daphnia galeata mendotae has been recognized as possessing the greatest morphological variation among North American Daphnia species. Prior work has suggested that this variation is a consequence of phenotypic plasticity. Using allozyme markers, we tested this hypothesis by examining the association between genotype and morphology in 22 populations of D. galeata from lakes in Indiana. Analyses indicated a genetic basis for the phenotypic variability, as two different species and their F1 hybrids were detected. The parent species were D. galeata mendotae sensu stricto and a helmeted form of Daphnia rosea. F, hybrids were detected in 17 of 22 lakes and were dominant in 10. Backcross and F2 individuals were rare, however, suggesting that introgression is limited by the existence of reproductive isolating mechanisms.
Influence of phosphorus storage on the uptake of cadmium by the marine alga Macrocystis pyrifera
Authors: Walsh Russell S. , Hunter Keith A.
Published: April 2010

Seasonal changes in the concentrations of Cd and phosphate (P) in the macroalga Macrocystis pyrifera have been studied in Otago Harbour, a shallow marine embayment. Both components showed the same seasonal cycle, with concentration maxima during the austral winter (June–July) and summer periods (December–February) when growth of M. pyrifera was minimal. During these periods, cells contained significant quantities of electron‐dense polyphosphate bodies (PPBs). Culture experiments showed that Cd uptake from seawater media was greatly enhanced when PPBs were induced to form. With 0.44 µmol Cd kg−1 in the medium, cultures forming PPBs contained 40–50 times as much Cd in excess of controls as those grown at the same Cd concentration in which PPBs were not formed. With 44 µmol kg−1 in the medium, PPB‐forming cultures took up about twice as much Cd as those not forming PPBs. The incorporation of Cd into cellular PPBs may be an important mechanism for the uptake of this element even at natural Cd concentrations.
Utilization of deposited and suspended particulate matter by benthic “interface” feeders
Authors: Taghon Gary L. , Greene Ron R.
Published: April 2010

The polychaetes Boccardia pugettensis and Pseudopolydora kempi japonica, like many invertebrates, switch from deposit feeding to passive suspension feeding as the flux of suspended particles increases. We tested the hypothesis that this behavior is energetically profitable because suspended particles have greater food value. In laboratory experiments, animals were restricted to deposit feeding, restricted to suspension feeding, or allowed to do both. Suspended particles had greater mass‐specific concentrations of total organic matter, organic C, labile protein, N, and Chl a. Both species fed at significantly reduced volumetric rates when suspension feeding, but the suspension feeding rate of Pseudopolydora (only 19% of the deposit‐feeding rate) was more depressed than that of Boccardia (45–75% of deposit‐feeding rate). Pseudopolydora’s growth rate was lower when suspension feeding (0.3–0.8% AFDW d−1) relative to deposit feeding (2.8–3.8% AFDW d−1). In contrast, Boccardia grew as well or better when suspension feeding (2.7−7.6% AFDW d−1) relative to deposit feeding (2.2−5.0% AFDW d−1). Despite similar morphologies and behaviors, we found unexpected differences in the abilities of these species to utilize particulate organic matter under varying boundary‐layer conditions.
Relationships between cell volume and the carbon and nitrogen content of marine photosynthetic nanoplankton
Authors: Verity Peter G. , Robertson Charles Y. , Tronzo Craig R. , Andrews Melinda G. , Nelson James R. , Sieracki Michael E.
Published: April 2010

Unialgal cultures were used to investigate relationships between cell volume and the carbon and nitrogen content of nondiatomaceous marine nanophytoplankton. Cell dimensions were determined by image‐analyzed epifluorescence microscopy and particulate C and N by high‐temperature dry combustion. Volumes were calculated by direct integration with published algorithms (biovolume), but could be estimated equally well from linear dimensions as prolate spheres. Preservation with 0.5% glutaraldehyde reduced cell volumes 29% on average. Correlations were highly significant between biovolume of preserved cells and C and N contents. Nonlinear regression models appeared most appropriate because smaller cells contained more C and N per unit volume than did larger cells. Suggested general C densities for estimating cell C from preserved volume were 0.36 pg µm−3 for 101 µm3 cells, 0.24 pg µm−3 for 102 µm3 cells, and 0.16 pg C µm−3 for 103 µm3 cells. Previous regression models substantially underestimated the C densities of nanophytoplankton of 101–103 µm3. The explanation for these differences includes the method of determining mean population volumes, the use of preservatives, and the occurrence of significant vacuolar volume in larger phytoplankton.
Development of a sequential extraction method for different forms of phosphorus in marine sediments
Authors: Ruttenberg Kathleen C.
Published: April 2010

A sequential extraction method (SEDEX) has been developed to separately quantify five sedimentary P reservoirs: loosely sorbed P; ferric iron‐bound P; authigenic carbonate fluorapatite + biogenic apatite + CaCO3‐associated P; detrital apatite P; and organic P. The SEDEX method successfully separates two of the main categories of authigenic phosphate phases called upon most often as sedimentary sinks for diagenetically mobilized P: ferric oxyhydroxide‐associated P and authigenic carbonate fluorapatite (CFAP). It offers a means for separating authigenic CFAP from detrital apatite of igneous or metamorphic origin. The importance of this distinction is that CFAP represents an oceanic sink for reactive P, whereas detrital apatite does not. In addition, a means for reversing secondary adsorption of P onto residual solid surfaces during extraction has been developed.

Extensive standardization of the SEDEX method for application to marine sediments has been performed with analogs for naturally occurring phosphatic phases.
Carbon and nitrogen sources of planktonic bacteria in Lake Constance studied by the composition and isotope dilution of intracellular amino acids
Authors: Simon Meinhard , Rosenstock Bernd
Published: April 2010

We investigated the physiological response of planktonic bacteria to varying C and N sources in mesotrophic Lake Constance (Bodensee) by studying the amino acid composition and the isotope dilution (ID) of [3H] amino acids in the intracellular pool. Bacteria predominantly utilized amino acids for growth from the phytoplankton spring bloom in May until August. During this period the amino acid composition of the pool was rather similar to the composition of dissolved free amino acids (DFAA) in the water. Serine always was the dominant DFAA and also dominated the intracellular pool from May to August. From January until April, however, the intracellular pool was dominated by glutamate, suggesting that during this period the bacterioplankton utilized NH4+ as a major source of N. During the spring bloom and in June, the ID of the most abundant amino acids was 1 (no dilution) to 4. Glutamate, however, exhibited a much higher ID (10–47), suggesting that NH4+ was utilized by the bacterioplankton during these months. In August, however, ID of all amino acids was high and was not reduced by increasing the concentration of DFAA, indicating that the bacteria in this period predominantly utilized dissolved combined amino acids. The ID of leucine when added at saturating concentration (30 nM) was 1.5–3. Incorporation rates of [3H]DFAA as a fraction of bacterial production were consistent with the results of ID measurements.