bluuebunny/crossref_metadata_2025 huggingface dataset:
Biological and hydrodynamic regulation of the microbial food web in a periodically mixed estuary
Authors: Eldridge Peter M. , Sieracki Michael E.
Published: May 2010

Abundances of chroococcoid cyanobacteria and heterotrophic bacteria in surface waters of the York River subestuary covary with spring‐neap tidally induced changes in the mixed‐layer depth. Abundances of their principal grazers, heterotrophic protists, however, do not oscillate. A simulation model of this system using nonlinear, density‐dependent functions has been developed to replicate cycles observed in the two bacterial abundances and simulate bacterial production and protistan grazing. A Jassby‐Platt equation is used to determine growth rate from the mean mixed‐layer light and empirically derived growth and α parameters. Changes in mixed‐layer depth regulate light availability, thereby controlling cyanobacterial growth rates. The model predicts a close coupling between cyanobacterial growth and grazing during destratified periods when cyanobacterial stocks are low. During stratified periods, when cyanobacteria biomass values are high, the model suggests that grazing is saturated and has little effect on cyanobacterial biomass. Grazing on heterotrophic bacteria is rarely saturated and is only loosely coupled to heterotrophic bacteria production during destratification. The model was tested at several grazer feeding preferences for cyanobacteria or heterotrophic bacteria and reproduced observed microbial biomass values most accurately when there was no initial preference. These model dynamics suggest that the heterotrophic protists fed equally well on both heterotrophic bacteria and cyanobacteria.
The development of pH and pCO2 microelectrodes for studying the carbonate chemistry of pore waters near the sediment‐water interface
Authors: Cai Wei‐Jun , Reimers Clare E.
Published: May 2010

We made stable and rapid‐responding pH and pCO2 microelectrodes. The pH microelectrode has a ∼100‐µm‐diameter half‐sphere bulb tip of pH glass, and the pCO2 sensor has a 200–300‐µm‐diameter silicone‐membrane covered tip. Because the pH microelectrodes have electrical resistances that are >1010 ohms, all electrical connections arc kept scrupulously clean and dry to prevent current leakage during in situ measurements. Suspension effects are negligible when measuring pH in marine sediments.

To demonstrate the performance of the pH and pCO2 microelectrodes, we report in situ microprofiles of pH and pCO2 and contiguous profiles of O2 and the formation factor from coastal sediment in San Diego Bay, California. A sharp pH decrease from 7.90 to 7.15 (seawater scale) and a pCO2 increase from 578 to 3,000 µatm in the top 1 cm of sediment arc interpreted to be primarily the result of HS, Fe2+, and Mn2+ oxidation by O2 rather than metabolic CO2 production. The O2, pH, and pCO2 profiles also reveal that there was photosynthetic activity in the top 2 mm of sediment which caused an O2 maximum and a total dissolved inorganic carbon minimum.
Re‐evaluation of high temperature combustion and chemical oxidation measurements of dissolved organic carbon in seawater
Authors: Sharp Jonathan H. , Benner Ronald , Bennett Lenore , Carlson Craig A. , Dow Rachael , Fitzwater Steve E.
Published: May 2010

Various commercial HTC analyzers are now being used in marine laboratories with inconsistent and less than uniform results. A small intercalibration exercise was held in Bermuda to compare results from several commercial HTC analyzers and the traditional wet chemical oxidation method. The exercise utilized a single low carbon water to determine the instrument blank, and a single set of standards was used for all analyses. Five Sargasso Sea water samples from the surface to 4,000 m and a dried extract of dissolved organic matter from a black‐water river were used as the samples for comparison. Analyses by the four methods agreed within 15%, and the seawater values were similar to previously published values. The results demonstrate the importance of careful instrument blank determination and of accurate determination of the CO2 peak.
A lightweight extruder for accurate sectioning of soft‐bottom lake sediment cores in the field
Authors: Verschuren Dirk
Published: May 2010

A new extrusion device is described for time‐efficient sectioning of high quality cores of soft‐bottom lake sediments, in particular piston cores and core samples that include the undisturbed sediment‐water interface. The instrument is lightweight, versatile, and easy to operate in the field while maintaining maximum accuracy in sectioning a sediment profile in predefined increments.
Daphnia lumholtzi in North America: Another exotic zooplankter
Authors: Havel John E. , Hebert Paul D. N.
Published: May 2010

Daphnia lumholtzi, whose natural distribution is restricted to Australia, southwest Asia, and Africa, has been detected recently at numerous localities in the southern U.S. The present study establishes that D. lumholtzi populations from two of these localities are allozymically distinct from an Australian population but genetically similar to each other, suggesting they share a common origin not from Australia. The inland distribution of D. lumholtzi suggests it was not introduced in ballast water of large ships. One of the first localities known to have D. lumholtzi is also the first North American site where Nile perch were introduced in 1983. If D. lumholtzi was introduced at this time, it has colonized sites across the southern U.S. extremely rapidly, suggesting that it will soon be common in lakes and reservoirs in warm temperate regions of North America.
An experimental model of the solar‐stimulated fluorescence of chromophoric dissolved organic matter
Authors: Vodacek Anthony , Green Sarah A. , Blough Neil V.
Published: May 2010

We present an experimental model of CDOM solar‐stimulated fluorescence. Three‐dimensional fluorescence spectra of natural waters were used to determine the solar‐stimulated emission as a function of depth in the water column. Inclusion of the wavelength‐dependent fluorescence quantum yield provides emission values in absolute units of photons s−1 cm−2 5 nm−1. Attenuation of light in the water column was also modeled, allowing determination of total upwelled emission. The upwelled fluorescence is compared to irradiance reflectance calculated from a semianalytical model. The fluorescence contribution to reflectance in the blue‐green to green region can be as high as 70% for blackwater but is rapidly reduced by the introduction of scattering particles. Except for blackwaters, CDOM fluorescence does not significantly affect irradiance reflectance ratios commonly used in remote‐sensing applications. In water with moderate amounts of CDOM (absorption coefficient at 355 nm ≥0.5 m−1), fluorescence will dominate water Raman scattering as a secondary influence on the light field in the green spectral region.
Five tests of food‐limited growth of larvae in coastal waters by comparisons of rates of development and form of echinoplutei
Authors: Fenaux Lucienne , Strathmann Megumi F. , Strathmann Richard A.
Published: May 2010

Any single method of testing food limitation can be misleading or inconclusive. We therefore used five different tests for food‐limited growth of larvae of a sea urchin from the northwest Mediterranean: 1. In both spring and autumn, larvae given a nearly natural ration of food from daily changes of seawater grew and developed more slowly than larvae with the same water enhanced with a cultured alga. 2. Larvae given a nearly natural ration of food developed more slowly in autumn, when concentrations of chlorophyll a and particles in the plankton were lower, than in spring when these indications of food were higher. 3. Larvae given the enhanced ration grew and developed more rapidly than larvae in presumed cohorts in the plankton. 4. In both spring and autumn, larvae in the field had a food‐limited form (longer arms and delayed formation of the echinus rudiment) in contrast to larvae given an enhanced ration. 5. Larvae in the autumn plankton had a more food‐limited form than larvae in the spring plankton. Results of all five tests indicated food‐limited growth in coastal waters in autumn; three indicated food‐limited growth in spring. The concentrations of natural food were not unusually low. Food‐limited growth suggests that these larvae may commonly feed with maximal or near‐maximal clearance rates. If echinoid larval growth is limited by food under these conditions, it is likely that growth of other larval invertebrates is food limited in many coastal waters.
Migration of large‐scale subaqueous bedforms measured with seagrasses (Cymodocea nodosa) as tracers
Authors: Marbà Núria , Cebrián Just , Enríquez Susana , Duarte Carlos M.
Published: May 2010

The vertical growth of seagrasses in response to burial by migration of bedforms is combined with dating techniques to provide precise and rapid estimates of the migration speed of subaqueous dunes over seagrass patches. Two methods to estimate the time interval between the passage of successive dunes and the motion of single dunes through seagrass patches are described. The second method is more precise. The application of these methods to vegetated (Cymodocea nodosa) subaqueous dunes in the Alfacs Bay (NW Mediterranean) showed that the dunes traveled at an average speed of 13.0±0.6 m yr−1 and demonstrated that the methods can resolve migration speeds from 0.15 to 980 m yr−1 with this particular seagrass species. In areas vegetated with different seagrass species, bedform migration can be estimated over different time scales. The strong coupling between seagrass and sediment dynamics resembles the coupling of vegetation and land dunes.
Nitrogen incorporation into decomposing litter of Spartina alterniflora
Authors: White David S. , Howes Brian L.
Published: May 2010

Litter N dynamics were followed during

decay in aboveground biomass of Spartina alterniflora (Loisel.) in litter bags and a cohort of intact culms. Initial enrichment with 15N allowed partitioning of the total litter N pool into originally incorporated N during plant growth vs. N incorporated from external sources during decay. Both the original 15N and total N pools declined through fall but stabilized in winter. As temperatures increased in spring, the original 15N pool again declined, but the total N pool remained stable due to significant incorporation of N from external sources. By the midpoint in decomposition, 50–65% of the total detrital N pool was from external sources and at least part of the N incorporation was biologically mediated. The apparent incorporation of external N based on 15N techniques in this study is greater than previous estimates based on net N accumulation. We conclude that external N incorporation into decaying S. alterniflora is a potentially much more important mechanism of short‐term N retention in salt‐marsh ecosystems than previously thought.
Locus of methane release and mass‐dependent fractionation from two wetland macrophytes
Authors: Harden Harmon S. , Chanton Jefrey P.
Published: May 2010

Factors responsible for the alteration of CH4 isotopic composition during gas transport by emergent macrophytes were investigated in Pontederia cordata (Pickerelweed) and Sagittaria lancifolia (Bull tongue). Measured rates of CH4 emission from petioles and leaves indicated that the locus of gas release from these plants is the petiole and not the leaf. Methane concentration profiles of gases within petioles further indicated that most CH4 is emitted from the lower portion of the petiole near the waterline. Ethane and propane tracer experiments confirmed mass‐dependent fractionation during gas transport through these plants. After injection with a gas mixture, both plant types emitted ethane 12% faster than propane. Twenty‐five minutes or more after injection, ethane was found to be depleted in gas within petioles relative to the injected gas. The degree of fractionation observed for the 13CH4/12CH4 and ethane/propane pairs was similar to values predicted by kinetic gas theory.
Hydrodynamic impediments to settlement of marine propagules. and adhesive‐filament solutions
Authors: Abelson Avigdor , Weihs Daniel , Loya Yossi
Published: May 2010

“Protruding bodies,” such as kelp stems, seagrasses, filiform algae, artificial reefs, and engineered structures, constitute substrata for proliferation of benthic communities of great ecological and economical importance. Unfortunately, very little is known of hydrodynamic aspects of settlement in such habitats. Based on flow‐tank experiments and theoretical considerations, we discuss hydrodynamic interference with settlement of larvae on protruding‐body habitats. We suggest that larvae may overcome these interferences by producing mucous threads up to 100 body lengths in size. These adhesive threads enable propagules of suspension feeders to settle in environments of high food‐particle flux and low sedimentation rate. The results suggest that hydrodynamic impediments to encounter play a major role in determining the spatial distribution of benthic species on protruding bodies by favoring propagules of species with such adhesive devices.
Accumulation of a pheophorbide a‐like pigment in sediment traps during late stages of a spring bloom: A product of dying algae?
Authors: Head E. J. H. , Hargrave B. T. , Subba Rao D. V.
Published: May 2010

We examined the concentration and composition of pigments in material collected in a sediment trap array that collected samples over 14 sequential 4‐d periods covering a spring bloom which was dominated by diatoms. Pyropheophorbide a, a chlorophyll a derivative known to be produced by copepod grazing, accumulated in traps in similar amounts throughout the bloom period. A second more polar a‐type pheophorbide accumulated only during late stages of the bloom, in amounts comparable with those of chlorophyll a (+ isomers) and higher than those of pyropheophorbide a. This pheophorbide was spectrally and chromatographically very similar to a pheophorbide a‐like pigment that has been attributed elsewhere to dying Phaeocystis. Previously, pheopigments in the water column and in sediment traps have been considered products of zooplankton grazing, but dead or dying phytoplankton may contribute significantly to both pools.
Prediction of planktonic protistan grazing rates
Authors: Peters Francesc
Published: May 2010

Data on planktonic protistan feeding were gathered from the literature and multiple regression statistics used to find a model that would predict ingestion rates over a wide range of biological and environmental conditions. The proposed model (with an R2 = 0.75) includes temperature and cell volumes and concentrations of both prey and predator as explanatory variables. Data from a lotic system departed from the rest of the data set, but marine and lentic systems were indistinguishable. Whether the grazing experiments were done with direct or indirect methods was not important. All continuous variables presented a power relationship with respect to ingestion rate with the exception of temperature, which had an exponential relationship. Prey concentration had a direct effect on ingestion rates, although these did not show the saturation of a typical hyperbolic relationship, most likely due to the nature of the data and the statistical model itself. Larger predator concentrations as well as larger prey cell volumes resulted in decreased ingestion rates.
A method to determine integrated predation in stratified waters
Authors: Massana Ramon , Pedrós‐Alió Carlos
Published: May 2010

Integrated predation (number of prey cells eaten per surface area and time) must be calculated to study the impact of predation in stratified systems where predator and prey populations are not uniformly distributed along the vertical axis. We considered the effect of the vertical distribution of populations and the functional response of the predator in this calculation. We developed seven algorithms which take into account both, one, or neither factor. Two cases of predation in the metalimnion of Lake Cisó (Banyoles, Spain) are used as examples to illustrate the limitations and advantages of the different approaches. In the first example (the rotifer Anuraeopsis fissa feeding on phototrophic purple bacteria) the vertical distribution of populations is very important (the populations were highly segregated), whereas use of the functional response makes very little difference. In the second example (the ciliate Coleps hirtus feeding on Cryptomnonas phaseolus) the situation is reversed: the important factor is use of the functional response (the prey abundance was very high compared to the half saturation constant of ingestion for the predator).
Predation by gelatinous zooplankton and resource limitation as potential controls of Acartia tonsa copepod populations in Chesapeake Bay
Authors: Purcell Jennifer E. , White Jacques R. , Roman Michael R.
Published: May 2010

Gelatinous zooplankton are conspicuous p’redators during summer in Chesapeake Bay. Inverse correlations of the abundances of gelatinous predators and their zooplankton prey have led to speculation that these predators may control their prey populations. We measured predation on copepods by hydromedusae, scyphomedusae, and ctenophores in the mesohaline region of the bay in May–October 1987 and 1988. We simultaneously assessed the possibility of food limitation in Acartia tonsa by measuring its phyto‐ and microzooplankton food resources and rates of adult female egg production. We conclude that A. tonsa populations are not limited by gelatinous zooplankton predation and rarely by food. Other predators (e.g. fish, adult copepods) and environmental limitations (e.g. temperature, hypoxic bottom waters) probably affect A. tonsa abundances in this region.
Seasonal change in activity of abyssal demersal scavenging grenadiers Coryphaenoides (Nematonums) armatus in the eastern North Pacific Ocean
Authors: Priede I. G. , Ragley P. M. , Smith K. L.
Published: May 2010

The responses of the grenadier fish Coryphaenoides (Nematonurus) armatus to bait deployed on the sea floor at station M in the North Pacific Ocean (34°50′N, 123°00′W; 4,100 m deep) in February and October were compared. In February 1990 and 1992, the first fish arrived after an average time of 25 min and stayed an average of 150 min. In October 1991, the respective times were 15 and 98 min. The faster response in October is correlated with a higher mean swimming speed of 0.0692 m s−1 compared with 0.0262 m s−1 in February. Fish activity was elevated in October following seasonal enrichment to the benthos by downward flux of particulate organic matter from the surface. Grenadier abundance was estimated from arrival times as 325 individuals km−2, corresponding to a wet weight biomass of 146 mg m−2 or 10.2 mg C m−2.
The distribution of colloids in the North Atlantic and Southern Oceans
Authors: Wells Mark L. , Goldberg Edward D.
Published: May 2010

The concentrations and size distributions of small (<200 nm) colloids were measured at three stations in the North Atlantic and two stations in the Southern Ocean. The stations were chosen to cover a range of oceanographically distinct regimes, from highly productive nearshore environments to oligotrophic open‐ocean waters. Colloid number concentrations decreased appreciably from the surface to ∼150‐m depth at three of these stations. Concentrations in deep waters of the North Atlantic were high but erratic, suggesting that colloid abundance is regulated by rapid rates of reactions. The colloids were mainly organic and their immediate sources appear to include both autotrophic and heterotrophic activity as well as sediment resuspension. Transmission electron microscope examination of colloid size distributions and morphology indicates that aggregation is the principal removal mechanism for these colloids. Evidence from the cumulative size spectra of small colloids indicates that colloid aggregation is most intense in vertically delineated zones near the surface, around the main thermocline (∼1,000–1,500 m), and in bottom waters. These findings show that the marine colloidal state is abundant but discontinuous in both space and time throughout a wide range of oceanographic environments.
Effects of burrow ventilation on activities of a terebellid polychaete and silicate removal from sediment pore waters
Authors: Marinelli Roberta L.
Published: May 2010

The behavior and activities of a terebellid polychaete, Eupolymnia heterobranchia, in the presence of artificially irrigated tubes and the effects of Eupolymnia and artificial irrigation on silicate removal from sediment pore waters were examined in the laboratory. Eupolymnia built more tubes and longer tubes in sediments containing artificially irrigated tubes relative to unventilated sediments. Moreover, worm tubes were located closer to artificially ventilated tubes than expected by chance. Silicate fluxes were positively related to the dry weight of worms and to the number of tubes in sediments when they consisted of either Eupolymnia tubes or artificially irrigated tubes alone. However when tube types were mixed (Eupolymnia + artificially irrigated tubes), silicate fluxes were lower than in sediments containing artificially ventilated tubes alone. Thus, worm behavior was altered by the presence of artificially irrigated tubes. In addition, interactions between worms and artificially ventilated tubes served to reduce silicate flux relative to sediments containing artificially ventilated tubes only.
Effect of wind on the distribution of phytoplankton cells in lakes revisited
Authors: Webster Ian T. , Hutchinson Paul A.
Published: May 2010

Experimental evidence suggests that winds having speeds >2–3 m s−1 are required to mix floating phytoplankton cells (or colonies) away from the water surface. We consider theoretical, steady state distributions of phytoplankton in a lake caused by turbulence and circulation patterns induced by winds having speeds above this critical level. The model incorporates an eddy diffusivity which varies with position in the water column. It predicts concentration variations in the downwind direction which are more in accord with experiment than a previously presented model having an eddy diffusivity uniform in the vertical. If the windspeed is less than the critical value, then a floating phytoplankton scum is expected to remain on the surface. The horizontal distribution of a phytoplankton population will be very different depending on whether the windspeed is greater or less than the critical speed.
On the distribution of blue‐green algae in lakes: Wind‐tunnel tank experiments
Authors: Hutchinson Paul A. , Webster Ian T.
Published: May 2010

In this study, we demonstrate in the laboratory that the distribution of weakly floating algae in wind‐driven, steady state, two‐dimensional flow in a water body is in accord with theoretical predictions. We confirm the theoretical results that the concentrations of algal colonies of uniform flotation speed should increase exponentially in the downwind direction and that the length scale of this concentration variation should be inversely proportional to the colony flotation speed. We observed accumulation of a surface film at the downwind shore of our tank. This film dampens surface waves, inhibits surface mixing, modifies the nearshore water circulation, traps the algae, and allows the algae to accumulate into mats.
Sites of particle selection determined from observations of individual feeding larvae of the sand dollar Dendraster excentricus
Authors: Appelmans Nicholas
Published: May 2010

To determine where particles that differ in flavor are selected during feeding, I videotaped individual larvae of Dendraster excentricus while they fed from a mixed suspension of polystyrene beads of 10‐ and 20‐µm diameter. A reciprocal treatment design that controlled for the effect of size consisted of flavoring one of the two particle sizes with exudate from an axenic culture of Dunaliella tertiolecta while the other remained unflavored. Analysis of gut contents showed that larvae preferentially ingested flavored particles (ANOVA, F = 17.10, P < 0.001). Analysis of videotaped larvae revealed selection at the ciliated band in two of the four experiments, although these did not always favor flavor. Clearance rate at the ciliated band was significantly higher than at the gut (ANOVA, F = 12.68, P = 0.004), and only 1–5% of particles were lost during transfer from the ciliated band to the mouth. The difference in clearance rate resulted from ejection of particles by the mouth and esophagus (the dominant site of selection) occasionally overriding selection at the ciliated band.
N remineralization in planktonic protozoa
Authors: Ferrier‐Pages C. , Rassoulzadegan F.
Published: May 2010

Ammonium excretion rates of two marine planktonic protozoa (an oligotrichous ciliate, Strombidium sulcatum, and an aplastidic flagellate, Pseudobodo sp.) both isolated from oligotrophic Mediterranean waters were quantified with heat‐killed bacteria as the food source for the protozoans. Ammonium excretion rates ranged from 0.25 to 2 µg N mg DW−1 h−1 for the ciliate and from 2.8 to 8.5 for the phagotrophic flagellate. Maximum excretion rates took place during the early exponential growth phase, suggesting possible covariation of excretion rates with either protozoan body size or their growth rates or metabolic state. Comparison of these excretion and regeneration rates with those obtained in situ for oligotrophic waters (∼0–37 nmol liter−1 h−1) indicates that protozoa may account for >50% of the nutrient recycling in these waters.
Has the importance of photoautotrophic picoplankton been overestimated?
Authors: Fahnenstiel Gary L. , Redalje Donald G. , Lohrenz Steven E.
Published: May 2010

Postincubation differential filtration (PIDF), preincubation differential filtration (PreIDF), and track autoradiography (TA) were compared for estimating cell‐specific and total photoautotrophic picoplankton production. Experiments were performed in Lakes Michigan and Huron and in the Gulf of Mexico. When Synechococcus dominated the photoautotrophic picoplankton community (>70% of total picoplankton abundance), PIDF estimates of cell‐specific and total picoplankton production were ∼3.0 × (range, 2.0–3.8×) higher than TA estimates. PreIDF estimates of cell‐specific and total picoplankton production, however, were only slightly higher than TA estimates (mean, 1.4×; range, 1.4–1.5×). The higher PIDF estimates were attributable to breakage and damage of larger photoautotrophs during postincubation filtration and to retention of this labeled material on the smaller (0.2 µm) pore‐size filter. Results from PIDF experiments must be viewed with caution and previous estimates of picoplankton production, cell‐specific or total, based solely on PIDF may need to be re‐evaluated.
Effects of flow on competitive superiority in scleractinian corals
Authors: Genin Amatzia , Karp Lee , Miroz Aharon
Published: May 2010

An effective attack by a scleractinian coral on a subordinate neighbor typically results in the death of the subordinate’s margin along the intercoral gap. We tested the assumption that spatial variations observed for interactions between a highly “aggressive” coral, Galaxea fascicularis (Linne) and its subordinate neighbors can be partly explained by hydrodynamic conditions. For several months, we used submerged pumps to expose transplanted corals in situ to intermittently enhanced flow. This manipulation rendered aggression by G. fascicularis ineffective. Strong currents deflect the aggressor’s tentacles and possibly enhance the rate of tissue recovery in subordinate corals. Observations of naturally occurring pairs of G. fascicularis and subordinate neighbors indicated that the proportion of cases, in which the subordinate neighbor exhibited damaged margins was significantly lower at sites exposed to strong currents compared with protected reefs. If other aggressive corals are similarly affected by flow, then at nondisturbed reefs, corals using aggressive strategies should have an advantage at sites characterized by weak flow, whereas fast‐growing corals that compete by overtopping their neighbors should be superior at exposed sites. These conclusions agree with observations that the abundance of G. fascicularis and the percentage of unoccupied substratum are lower at the exposed sites.
Abundance and distribution of carbohydrates in the ocean
Authors: Pakulski J. Dean , Benner Ronald
Published: May 2010

Carbohydrate concentrations in depth profiles from the Atlantic and Pacific Oceans, the Gulf of Mexico, and the Gerlache Strait (Antarctica) were determined by MBTH analysis without hydrolysis and after hydrolysis with dilute HCI and concentrated H2SO4. Total carbohydrate (TCHO) concentrations in surface waters varied from 7 to 33 µM C and accounted for 21 ± 7% of the dissolved organic carbon (DOC) measured by high‐temperature combustion. Polysaccharides (PCHO) were the dominant form of carbohydrate in waters above oxygen minima whereas monosaccharides were dominant in the deep ocean. PCHO comprised 71 ± 18% of TCHO and 16 ± 9% of the DOC above oxygen minima at all stations. Hydrolysis‐resistant PCHO comprised 67 ± 30% of the total PCHO. Monosaccharide (MCHO) concentrations averaged 4.3 ± 1.9 µM C and varied little with depth at all stations. The large (5‐fold) decrease in PCHO concentrations between surface waters and oxygen minima suggested that polysaccharides are an active component of the carbon cycle in the upper ocean.
Photosynthesis of Phaeocystis in the Greenland Sea
Authors: Cota Glenn F. , Smith Walker O. , Mitchell B. Greg
Published: May 2010

During the spring bloom in the northern Greenland Sea in 1989, Phaeocystis displayed photosynthetic rates and efficiencies, absorption in the red, and quantum yields approaching predicted theoretical maxima. Average values of these photosynthetic parameters for Phaeocystis were about an order of magnitude higher than those typically observed for natural assemblages of diatoms which often dominate the phytoplankton in polar waters. Phaeocystis populations were exceptionally well acclimated to temperatures near 0°C and all light conditions encountered. With such high photosynthetic rates and quantum yields, Phaeocystis may outcompete other species and play a dominant role in elemental cycles where major blooms are recurrent features. During Phaeocystis blooms, primary productivity in polar regions would be seriously underestimated by models using previously reported averages.
The importance of Daphnia in determining mortality rates of protozoans and rotifers in lakes
Authors: Pace Michael L. , Vaqué Dolors
Published: May 2010

We measured mortality of protozoans and rotifers in three lakes of contrasting zooplankton communities. We also compared protozoan growth in an experiment which controlled Daphnia biomass but varied body size. Mortality was determined as the difference between growth rates over 24 h in containers with and without zooplankton. Growth rates of heterotrophic flagellates and ciliates were high in the presence of a small assemblage of zooplankton and near zero or negative when either Daphnia pulex or Daphnia galeata was the dominant zooplankton species. Growth rates of rotifers were also usually lower in the presence of Daphnia. Mortality rates of heterotrophic flagellates, ciliates, and rotifers were positively related to the mean body size of Daphnia in comparisons among experiments. In an experiment with equal biomasses but different sizes of D. pulex, flagellate growth rates were lower in treatments with large Daphnia. High mortality in zooplankton communities dominated by larger species of Daphnia appears to be important in determining differences in the abundances of protozoans and rotifers among lakes.
Chemical identity and ecological implications of a waterborne, larval settlement cue
Authors: Zimme‐Faust Richard K. , Tamburri Mario N.
Published: May 2010

Planktonic oyster larvae (Crassostrea virginica) respond behaviorally to waterborne chemical cues and rapidly settle on substratum. “Settlement” is defined here as attachment of the larval foot to the substrate. Although a topic of considerable research for the past 50 yr, the identity of these cues remains unresolved. We provide four lines of experimental evidence all pointing to the singular identity of these substances. First, molecular‐weight fractionations of seawater used to bathe adult oysters (with intact biofilms) were bioassayed, indicating the presence of waterborne settlement inducers between 500 and 1,000 Da. The inducers were degraded by proteases but not by carbohydrases or by lipase. Of several proteases we applied, only those cleaving basic amino acids (lysine and arginine) from the C‐terminal and arginase (an enzyme condensing arginine at the C‐terminal to ornithine) eliminated settlement‐inducing activity. Second, trypsin hydrolysates of casein were significantly more effective in causing larval settlement than products of either acid or pronase hydrolysis of this protein. Third, a tri‐peptide having arginine at the C‐terminal, glycyl‐glycyl‐l‐arginine (hereafter referred to as GGR), evoked settlement at a concentration as low as 10−10 M. Dose‐response curves for GGR and for the active fraction (500–1,000 Da) of oyster bath water were essentially identical. Fourth, tests of 21 free amino acids identified only lysine and arginine as settlement cues. Larval settlers were far more sensitive to arginine than lysine but significantly less sensitive to arginine than to peptides with arginine at the C‐terminal.

Our combined results are all consistent in identifying low‐molecular‐weight peptides with arginine at the C‐terminal as the natural, water‐soluble cues inducing oyster settlement.
Chemical weathering of phosphate and germanium in glacial meltwater streams: Effects of subglacial pyrite oxidation
Authors: Chillrud S. N. , Pedrozo F. L. , Temporetti P. F. , Planas H. F. , Froelich P. N.
Published: May 2010

Data from three glacial meltwater streams draining Mt. Tronador in the southern Argentine Andes (72°W, 41°S) show that subglacial pyrite oxidation and the subsequent precipitation of iron oxides strongly influence dissolved phosphate concentrations but do not appear to affect dissolved germanium concentrations. Total‐Fe (TFe) and total‐P (TP) concentrations are high in all three glacial streams, but the ratios of soluble reactive phosphate (SRP) to TP are very different. The Upper Manso Stream that drains the Manso Glacier has relativeiy low SRP (0.01–0.23 µM), representing a small fraction of its TP (0.1–5%). The SRP of the two streams draining smaller side glaciers (0.12–0.69 µM) represents a much larger portion of their TP (20–32%). TFe, dissolved sulfate, and δ34S data suggest that pyrite oxidation is the most likely weathering reaction contributing sulfate to the Upper Manso Stream but not to the two smaller glacial‐fed streams, in which atmospheric inputs can account for all of the sulfate. Dissolved Ge appears to show no preferential sorption relative to dissolved silica, in contrast to the speculation that Ge preferentially sorbs on fresh iron hydroxyoxide surfaces.
The rare earth element geochemistry of Mono Lake water and the importance of carbonate complexing
Authors: Johannesson Kevin H. , Lyons W. Berry
Published: May 2010

Rare earth element (REE) concentrations for the alkaline, saline waters of Mono Lake in eastern California are reported. The total REE concentrations of the lake water ranged from 4,681 to 7,979 pmol kg−1 . Shale‐normalized REE profiles for the lake water indicate that the heavy REEs (HREE) are enriched 20–200 times over the light REEs (LREE) compared to shale.

The speciation of the REEs in Mono Lake was modeled with a combined specific ion interaction and ion‐pairing model which allowed activity coefficients for the major solutes (γM, γX), the REEs (γM), and the REE ion pairs (γMX) to be determined in the high ionic strength lake waters (I = 1.84 m). The speciation model suggests that essentially all the REEs in solution are complexed with carbonate ions and that >99% of each REE is complexed as Ln(CO3)2− species. The carbonate ion concentration of Mono Lake water is 0.27 m. Stability constants for these complexes increase with atomic number; consequently, these complexes are responsible for the HREE enrichments. Activity product calculations for REE phosphate coprecipitates in the high phosphate waters of Mono Lake (i.e. 800–1,000 µmol kg−1) indicate that the lake water is close to saturation with respect to these precipitates and suggest that the coprecipitates may effectively limit the maximum dissolved REE concentrations in the lake.
The radiatively driven natural convection beneath a floating plant layer
Authors: Michael Coates , John Ferris
Published: May 2010

If part of a water body is shaded while an adjacent part is warmed by direct sunlight, contrasting thermal gradients develop. This differential heating generates a surface flow from the illuminated into the shaded portion of the water body. One example of this situation is macrophytes floating on the surface of a small lake. The macrophytes shade the underlying water, and if there is open water adjacent to this shaded region, then differential heating may be expected. We show that the presence of the roots of small floating plants displaces the intrusion downward but does not prevent its formation. Further, we show that relations describing the differential absorption mechanism in the absence of macrophyte roots remain valid with roots present. Using these relationships, we calculate that an intrusion generated by differential heating may contribute significantly to replacement of nutrients taken up by the macrophytes.
Microautoradiography (with combined liquid scintillation) applied to the study of trace metal uptake by suspended particles: Initial results using 63Ni as a tracer
Authors: Barbeau Katherine , Wollast Roland
Published: May 2010

We report the development of a microautoradiographic method for the study of trace metal‐particle interactions in natural waters. This technique, in combination with conventional liquid scintillation counting methods, was applied to surface water samples from the Belgian coastal zone and Scheldt estuary. 63Ni was used as the metallic radiotracer. Ni partitioning in our experimental system was shown to be a primarily abiotic process, driven by passive sorption reactions and limited in extent on a 24‐h time scale by the slow reaction kinetics of Ni. Small particles (< 1 µm) were important as sorption sites, while large particles exhibited variable and particle‐specific scavenging potential.
Genetic differentiation in North American and European populations of the cladoceran Bythotrephes
Authors: Berg David J. , Garton David W.
Published: May 2010

Bythotrephes cederstroemi, a Palearctic cladoceran (Crustacea) zooplankter, has recently invaded all of the Laurentian Great Lakes. We used cellulose acetate gel electrophoresis to examine the genetic structure of these newly founded populations and to compare it to the structure of established European populations of B. cederstroemi and a congener, Bythotrephes longimanus. All populations of Bythotrephes had low intrapopulation genetic variation, with 1–12 multiple‐locus genotypes per population. Genotype frequencies were often different from Hardy‐Weinberg expectations for North American populations, primarily due to heterozygote excesses. Interpopulation variation was low within drainage basins but high among basins. Great Lakes populations were most similar to Finnish populations, while Swedish and German populations formed a separate group. North American populations appear to have been founded from a single European population, probably located in the northeastern Baltic region. Sympatric populations of B. cederstroemi and B. longimanus showed a greater degree of similarity than allopatric conspecifics, leading to the conclusion that these may represent morphologically distinct forms of a single species. Our results indicate that, as with other cladoceran species, restricted gene flow and founder events may be important in determining patterns of geographic variation among populations of Bythotrephes. Genetic variation among populations within drainage basins was lower than across basins, regardless of geographic distance between sites. Thus, river basins act as pathways of dispersal, leading to significant migration between populations within a basin but little migration between basins.
Growth and reproduction of the cladoceran Ceriodaphnia dubia from a forested floodplain swamp
Authors: Anderson David H. , Benke Arthur C.
Published: May 2010

Microcrustaceans are abundant in many freshwater wetlands, including forested floodplain swamps, but little has been done to assess their secondary production and functional role in these systems. Since standard cohort approaches to estimating secondary production are impossible with continuously growing and reproducing microcrustaceans, it is necessary to obtain independent determinations of their growth and reproductive characteristics under environmental conditions encountered in their natural habitat throughout the year. The growth and reproduction of Ceriodaphnia dubia fed natural swamp seston were measured at 10, 15, 20, and 25°C—temperatures which span much of the annual temperature range in southeastern floodplain swamps. Somatic biomass growth rates were as high as 61% d−1. Total growth rates (somatic tissue and egg mass) reached 95% d−1. Both somatic growth rates and total growth rates could be described as functions of individual size and temperature. High egg production, particularly in the larger instars, resulted in individuals maintaining high total growth rates (>20% d−1 at most temperatures) over the lifespan. Lifetime egg production accounted for >50% of biomass produced by individuals at all temperatures and >80% for temperatures ≥20°C. Somatic growth rates for C. dubia fed swamp seston were within the range of literature estimates for other species of Ceriodaphnia under various food conditions.
Modeling phytoplankton patchiness under the influence of wind‐driven currents inlakes
Authors: Verhagen Jan H. G.
Published: May 2010

A model has been developed that describes phytoplankton patchiness under the influence of wind‐induced circulation in lakes. It is shown that especially in large lakes the adjustment of the horizontal phytoplankton distribution to a change in windspeed (in the lower windspeed region) can take several weeks, but the vertical patchiness response is much faster, usually within 1 d. In the model presented here, the phytoplankton cells are allowed to disperse in the horizontal direction by introducing a dispersion coefficient in the wind direction that takes into account some of the effects of mixing by large‐scale currents in the horizontal plane. The model shows that horizontal and vertical patchiness increases with the flotation velocity of the phytoplankton, decreases with windspeed, and decreases with the strength of the horizontal wind‐induced circulation currents compared to the circulation strength in the vertical plane. Model results are in agreement with observations reported in the literature.

With the help of the model results, simulations of surface chlorophyll patterns in lakes can give important information about the general pattern of horizontal wind‐driven circulation.
Observations of the free‐swimming behavior of Acartia tonsa: Effects of food concentration and turbulent water motion
Authors: Saiz Enric
Published: May 2010

The free‐swimming behavior of the calanoid copepod Acartia tonsa is described as a function of food concentration and quantified turbulence.

In still water, Acartia spent most of its time feeding. Time allocated to feeding bouts did not change much as a function of food concentration (from 98% to 81%). Functional response to food was mainly determined by the duration of feeding bouts and the proportion of time spent in them. Lengthy feeding bouts might be involved with the actual capture and ingestion of food, while brief feeding bouts might be involved in the search for an optimum food density and the discrimination of food quality.

Turbulence did not affect the amount of time allocated to feeding bouts but induced a significant shift to bouts of shorter duration at low food concentration. Computed encounter rates were 2.5 times higher in the presence of turbulence and indicated that turbulence intensity might have been enough to increase realized food concentrations to levels comparable to satiation at some of the low food concentrations tested.
Oxygen regulation of nitrification and denitrification in sediments
Authors: Rysgaard Søren , Risgaard‐Petersen Nils , Niels Peter Sloth , Kim Jensen , Lars Peter Nielsen
Published: May 2010

Oxygen regulation of nitrification and denitrification in sediments was investigated with 15N isotope techniques. Sediment cores were incubated in a continuous ftowthrough system in which the O2 concentration was varied in the overlying water while the NO3− concentration was kept constant. Nitrification was stimulated with increasing O2 concentrations in the overlying water from 0 to 100% of atmospheric saturation, whereas only a slight stimulation was observed above 100%. At O2 concentrations below 100% of atmospheric saturation, NO3− from the overlying water was the most important source of N for denitrification, whereas above 100% of atmospheric saturation, NO3− produced by nitrification was the main source of N for denitrification. The converse effects of the O2 levels on the source of NO3− can be explained by applying a simple one‐dimensional model: O2 in the overlying water controls the diffusional distance of NO3− to the anoxic zone of denitrification and consequently the location of NO3− vertically in the sediment as well as the magnitude of the nitrification activity. Our results suggest that in aquatic environments containing low NO3− concentrations in the overlying water (such as coastal waters), higher O2 conditions will stimulate denitrification, while the opposite will occur in systems containing high NO3−concentrations (such as eutrophic lakes and streams).
A field study of metal toxicity and accumulation by benthic invertebrates; implications for the acid‐volatile sulfide (AVS) model
Authors: Hare Landis , Carignan Richard , Huerta‐Diaz Miguel A.
Published: May 2010

The toxicity and accumulation of Cd from sediment by benthic invertebrates was measured along a Cd gradient created in nature. The efficacy of acid‐volatile sulfide (AVS) concentrations in improving the prediction of biological effects in nature is also evaluated for the first time. The Cd concentration of sediments from a shield lake in Québec was adjusted to obtain Cd : AVS ratios of from 0.05 to 10. The sediments were then subjected to in situ colonization by invertebrates over a 1‐yr period. Cd concentrations in pore waters were very low at Cd : AVS molar ratios < 1 but increased markedly at ratios > 1. The results of previously published laboratory bioassays suggest that Cd would not be toxic to invertebrates when the molar ratio of Cd : AVS was <1. The biological effects of contaminated sediment varied greatly among taxa, as determined by both an animal’s sensitivity to Cd and the animal’s behavior. The abundance of only one of the insect taxa present, Chironomus (salinarius gp.) sp., was significantly related to the Cd: AVS molar ratio. For the other taxa present, there was no relationship between either abundances or growth rates and the Cd : AVS molar ratio. The general lack of expected toxicity at the high Cd : AVS molar ratios in our field study can be explained by the differing sensitivities to Cd for the animal species used in the laboratory and in the field and by the relatively low concentrations of Cd in excess of AVS even at the highest Cd : AVS molar ratio.