bluuebunny/crossref_metadata_2025 huggingface dataset:
Local genetic adaptation to grazing pressure of the green alga Desmodesmus armatus in a strongly connected pond system
Authors: Vanormelingen Pieter , Vyverman Wim , De Bock Dries , Van der Gucht Katleen , Meester Luc De
Published: January 2011

Dispersal potentially homogenizes genetic variation among populations and thus may prevent local genetic adaptation. If selection gradients are strong and the selection response efficient, however, local genetic adaptation may persist in the face of high dispersal rates. We compared grazing‐resistance traits among populations of the green microalga Desmodesmus armatus, which inhabit ponds that are ecologically different but part of a strongly interconnected pond system. Desmodesmus clones were isolated from a clear‐water and a turbid pond. For 16 clones from an internal transcribed spacer 2 clade with low sequence variation (1.3%) corresponding morphologically to D. armatus, coenobial dimensions and the average number of cells per coenobium, in both the absence and the presence of water conditioned by their main grazer, the waterflea Daphnia, were determined. Clones from the clear‐water pond had four‐celled coenobia with a higher greatest axial linear dimension and an increased average number of cells per coenobium in response to Daphnia kairomone, contrary to clones from the turbid pond. Unexpectedly, they were also characterized by a lower average number of cells per coenobium. No differences among populations were detected for cell length. Genetic variation was present in both populations for all traits, except for the response to kairomone. Continuous dispersal through overflows and rivulets in this pond system is thus incapable of preventing strong among‐population genetic differentiation for ecological relevant traits, testifying both to the capacity of phytoplankton populations to adapt to local conditions and to the importance of grazing as a structuring factor in natural phytoplankton populations.
Effects of environmental conditions on the seasonal distribution of phytoplankton biomass in the North Sea
Authors: Llope M. , Chan K.-S. , Ciannelli L. , Reid P. C. , Stige L. C. , Stenseth N. C.
Published: January 2011

We study the spatial and seasonal variability of phytoplankton biomass (as phytoplankton color) in relation to the environmental conditions in the North Sea using data from the Continuous Plankton Recorder survey. By using only environmental fields and location as predictor variables we developed a nonparametric model (generalized additive model) to empirically explore how key environmental factors modulate the spatio‐temporal patterns of the seasonal cycle of algal biomass as well as how these relate to the ~1988 North Sea regime shift. Solar radiation, as manifest through changes of sea surface temperature (SST), was a key factor not only in the seasonal cycle but also as a driver of the shift. The pronounced increase in SST and in wind speed after the 1980s resulted in an extension of the season favorable for phytoplankton growth. Nutrients appeared to be unimportant as explanatory variables for the observed spatio‐temporal pattern, implying that they were not generally limiting factors. Under the new climatic regime the carrying capacity of the whole system has been increased and the southern North Sea, where the environmental changes have been more pronounced, reached a new maximum.
Distribution and chromatic adaptation of phytoplankton within a shelf sea thermocline
Authors: Hickman Anna E. , Holligan Patrick M. , Moore C. Mark , Sharples Jonathan , Krivtsov Vladimir , Palmer Matthew R.
Published: January 2011

Observations of vertical gradients in phytoplankton community structure were made through the water column of the seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton community composition were routinely observed within the thermocline. The cell abundance maxima for Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima. Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales formixing between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The observed vertical gradients in community structure could therefore result from selection and niche partitioning of phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process.
Latitudinal distribution of diazotrophs and their nitrogen fixation in the tropical and subtropical western North Pacific
Authors: Kitajima Satoshi , Furuya Ken , Hashihama Fuminori , Takeda Shigenobu , Kanda Jota
Published: January 2011

Latitudinal distribution of diazotrophs and their nitrogen (N2) fixation activity were investigated in the western North Pacific in winter (Nov to Dec 2004) and summer (May to Jun 2005) along meridional transects from 37°N to the equator. N2 fixation activity in whole seawater and seawater passed through a 10‐µm filter was assayed by acetylene reduction. The whole‐water N2 fixation was markedly elevated in winter throughout the study area compared to that in summer, probably due to the increased upward supply of phosphate as a result of deeper mixed layer in winter. During both periods a distinct latitudinal variation was observed in N2 fixation of the whole‐water samples at the surface; further, higher activity was observed between the Kuroshio Extension and the salinity front in the North Equatorial Current than in the neighboring areas. The elevated N2 fixation was primarily ascribed to ≪10‐µm diazotrophs during both seasons. Flow cytometry conducted in summer revealed that distribution of nanoplanktonic cyanobacteria was closely correlated with that of N2 fixation activity in the ≪10‐µm fraction, indicating that nanoplanktonic cyanobacteria were the major diazotrophs in that area. In contrast, microplanktonic diazotrophs, Trichodesmium spp. and Richelia intracellularis exhibited different latitudinal distributions from that of nanoplanktonic cyanobacteria, with maximum numerical abundance of R. intracellularis around 8°N and 30°N, and that of Trichodesmium spp. at 26.5°N. Few microplanktonic diazotrophs occurred in the winter. The distribution of the diazotrophs and their N2 fixation activity may be controlled by the supply of phosphate and aeolian dust deposition.
Carbon acquisition by Trichodesmium: the effect of pCO2 and diurnal changes
Authors: Kranz Sven A. , Dieter Sültemeyer , Richter Klaus-Uwe , Rost Björn
Published: January 2011

We investigated carbon acquisition by the N2‐fixing cyanobacterium Trichodesmium IMS101 in response to CO2 levels of 15.1, 37.5, and 101.3 Pa (equivalent to 150, 370, and 1000 ppm). In these acclimations, growth rates as well as cellular C and N contents were measured. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, and CO2 and HCO3‐ fluxes were measured using membrane inlet mass spectrometry and the 14C disequilibrium technique. While no differences in growth rates were observed, elevated CO2 levels caused higher C and N quotas and stimulated photosynthesis and N2 fixation. Minimal extracellular CA (eCA) activity was observed, indicating a minor role in carbon acquisition. Rates of CO2 uptake were small relative to total inorganic carbon (Ci) fixation, whereas HCO{3 contributed more than 90% and varied only slightly over the light period and between CO2 treatments. The low eCA activity and preference for HCO3‐ were verified by the 14C disequilibrium technique. Regarding apparent affinities, half‐saturation concentrations (K1/2) for photosynthetic O2 evolution and HCO3‐ uptake changed markedly over the day and with CO2 concentration. Leakage (CO2 efflux : Ci uptake) showed pronounced diurnal changes. Our findings do not support a direct CO2 effect on the carboxylation efficiency of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RubisCO) but point to a shift in resource allocation among photosynthesis, carbon acquisition, and N2 fixation under elevated CO2 levels. The observed increase in photosynthesis and N2 fixation could have potential biogeochemical implications, as it may stimulate productivity in N‐limited oligotrophic regions and thus provide a negative feedback in rising atmospheric CO2 levels.
Reduction of dimethylsulfoxide to dimethylsulfide by marine phytoplankton
Authors: Spiese Christopher E. , Kieber David J. , Nomura Christopher T. , Kiene Ronald P.
Published: January 2011

Dimethylsulfoxide (DMSO) is an abundant but poorly understood methylated sulfur compound in the marine environment. One potentially significant loss pathway for DMSO is through its biological reduction to dimethylsulfide (DMS), which has been documented in a number of organisms, most notably bacteria. Here we present the first detailed study of DMSO reduction by several marine phytoplankton in axenic cultures. Reduction of DMSO was observed in four algal classes, with in vivo reduction rates ranging from 0.006 to 1.5 µmol [L cell volume]‐1 s‐1 at 1.0 mmol L‐1 DMSO. Corresponding turnover times for measured intracellular DMSO pools varied from hours to days. Michaelis‐Menton kinetic parameters were estimated for Isochrysis galbana, Thalassiosira pseudonana, and Amphidinium carterae. The half‐saturation constant (Km) and maximal rate (Vmax) for DMSO reduction ranged between 0.96 and 2.7 mmol [L cell volume]‐1 and 17‐118 nmol [L cell volume]‐1 s‐1, respectively. Our results suggest that DMSO reduction is a universal activity in marine phytoplankton, even in algae with no detectable dimethylsulfoniopropionate (DMSP). Although reduction of DMSO by marine eukaryotes may not contribute significantly to removal of DMSO from the dissolved phase, this reduction is likely to be a major source of DMS in species lacking detectable DMSP lyase activity. The ability of marine phytoplankton to reduce DMSO to DMS should allow algae to cycle these compounds as part of an antioxidant system.
No limit? The multiphasic uptake of silicic acid by benthic diatoms
Authors: Leynaert Aude , Longphuirt Sorcha Ní , Claquin Pascal , Chauvaud Laurent , Ragueneau Olivier
Published: January 2011

Silicic‐acid uptake kinetics for a field population of benthic diatoms were examined using a radioisotope tracer over a concentration range of 0‐300 µmol L‐1. The microphytobenthos half saturation constant (54 µmol L‐1) and specific uptake rates (0.096 h‐1) for silicic acid were well above those usually found in the pelagic environment. Silicic‐acid kinetics were hyperbolic only at low concentrations (≪60 µmol L‐1). At higher concentrations, a second mechanism that did not suggest saturation was activated. Many benthic diatoms are motile and migrate vertically in the upper few centimeters of sediment where there are strong gradients of nutrient concentrations. The multiphasic uptake may allow them to take maximum advantage of the high silicic‐acid concentrations found at depth.
Production of nitrogen gas via anammox and denitrification in intact sediment cores along a continental shelf to slope transect in the North Atlantic
Authors: Trimmer Mark , Nicholls Joanna Claire
Published: January 2011

We measured the production of N2 gas from anammox and denitrification simultaneously in intact sediment cores at six sites along a transect of the continental shelf (50 m) and deeper slope (2000 m) in the North Atlantic. Maximum rates of total N2 production were measured on the shelf and were largely due to denitrification, with anammox contributing, on average, 33% of this production. On the continental slope, the production of N2 gas decreased but the proportion due to anammox reached a maximum of 65%. This change in both amount and dominant pathway of N2 production could be explained largely by the concentration of organic carbon at each site. With increasing carbon the total production of N2 increased rapidly while the response of anammox was not significant. On the continental slope, total N2 production fell below 2 µmol N m‐2 h‐1 and anammox was strongly related (r = 0.95) to denitrification but the relative magnitude of anammox to denitrification (1.65 : 1) suggested that anammox could not be fuelled by NO2‐ from denitrification alone. On the shelf, however, where total N2 production was predominantly greater than 2 µmol N m‐2 h‐1, no relationship between anammox and denitrification was found and anammox remained constant at 1.4 µmol N m‐2 h‐1. Despite the constancy and greater availability of NO3‐ and lower temperatures on the continental slope, the significance of anammox to the total production of N2 appears primarily controlled by the overall rate of N2 production.
The optical characterization of chromophoric dissolved organic matter using wavelength distribution of absorption spectral slopes
Authors: Loiselle Steven A. , Bracchini Luca , Dattilo Arduino M. , Ricci Maso , Tognazzi Antonio , Cózar Andres , Rossi Claudio
Published: January 2011

We use a new approach to characterize the absorption characteristics of chromophoric dissolved organic matter (CDOM) in standard solutions and in several tropical lake ecosystems (Lake Victoria, Lake Tanganyika, Laguna Ibera). Compared with the common methods where a single slope of CDOM absorption spectrum is determined over a broad spectral region, we estimate the variations in spectral slope as a function of wavelength from 200 to 700 nm. Hence, our results show a distribution of spectral slope, referred to as the spectral slope curve, Sλ, which was used to identify similarities between lakes and standard solutions as well as to show the wavelength intervals in which photodegradation modifies spectral slope. In contrast to the plethora of wavelength intervals and ratios presented in the CDOM literature, a comparison of spectral slope curves between ecosystems provides a potentially important tool to examine the characteristics of CDOM in a consistent manner.
Basin scale distribution of chromophoric dissolved organic matter in the Pacific Ocean
Authors: Yamashita Youhei , Tanoue Eiichiro
Published: January 2011

Chromophoric dissolved organic matter (CDOM) was surveyed along the 160°W transect from the equatorial to the subarctic Pacific. CDOM characteristics were evaluated through the measurement of fluorescence intensity at 320 nm excitation and 420 nm emission and of absorption coefficient (a) at 320 nm, both indicative of marine humic‐like CDOM. In the surface layer (~200 m), different levels but similar optical characteristics of CDOM were found among the oceanic regions studied. In the mesopelagic (200‐1000 m) and abyssal layers (1000 m‐bottom), levels of fluorescence intensities were linearly correlated to those of absorption coefficients, with a similar slope between these layers. However, the intercept of the linear relationship between the two optical parameters was significantly lower for the mesopelagic layer than for the abyssal layer. Differences between intercepts were consistent with the transport of optically distinct CDOM to the mesopelagic layer through the formation of the North Pacific intermediate water (NPIW). At wavelengths shorter than 300 nm, the absorption coefficients of CDOM in the surface layer systematically deviated from the natural logarithmic relationships between absorption coefficients and wavelengths in the 320‐350 nm range. This class of CDOM, estimated using absorption coefficient at 275 nm, was defined as surface‐specific CDOM and may be derived from biocomponents. Surface‐specific CDOM was higher in the relatively young mode water than in old NPIW, suggesting that this class of CDOM is semi‐labile.
Evidence for geochemical control of iron by humic substances in seawater
Authors: Laglera Luis M. , van den Berg Constant M. G.
Published: January 2011

A new method, based on the direct detection of iron‐humic substance (HS) species by cathodic stripping voltammetry (CSV), is used to determine the iron binding capacity and complex stability of fulvic acid (FA), humic acid (HA), and the natural HS in the seawater. The FA binds 16.7 ± 2.0 nmol iron (Fe) (mg FA)−1, whereas the HA and the marine HS bind 32 ± 2.2 nmol Fe (mg FA)‐1. The complex stabilities are (log K’Fe’HS values) 10.6 for FA and 11.1 for HA and coastal HS. Measurements of coastal waters (Irish Sea) show that the HS occur in a widespread fashion, the HS concentration decreasing with increasing salinity and occurring at levels of 400 (at salinity 30) to 70 (at salinity 34) µg L−1. A sample from the deep Pacific was found to contain 36 µg HS L−1, amounting to 4% of the dissolved organic matter. Comparative measurement of the total iron complexing capacity by CSV with competitive ligand exchange showed that the natural HS can account for the entire ligand concentration in the shallow coastal and deep ocean waters tested. Measurements of the iron solubility showed that FA added to seawater and the HS in coastal waters maintain iron in solution at a level just below the iron binding capacity. The preliminary data for the open ocean indicate that the same may be true for HS in deep ocean waters. The data are consistent with a mechanism by which iron is transported from land to sea, associated with land‐derived HS.
Downwelling and deep‐water bottom currents as food supply mechanisms to the cold‐water coral Lophelia pertusa (Scleractinia) at the Mingulay Reef Complex
Authors: Davies Andrew J. , Duineveld, Gerard C. A. , Lavaleye, Marc S. S. , Bergman, Magda J. N. , van Haren Hans , Roberts J. Murray
Published: January 2011

In 2006 and 2007, multiple deployments of current meters and optical sensors on landers and moorings were made in the first detailed in situ study of the particle supply to the coral community in the Mingulay Reef complex in the Sea of Hebrides at 140‐m water depth. Two distinct and predictable supply mechanisms were resolved. One mechanism consisted of the rapid downwelling of surface water caused by hydraulic control of tidal flow that transports particles from the surface to the corals in less than an hour. The rapid downwelling was recorded on the reef top as a pulse of warm, fluorescent, and relatively clear water at the onset of the flood and ebb tides. The pulse was strongest after flood tide and lasted for up to 3 h. The second mechanism consisted of advection onto the reef of deep bottom water with a high suspended matter load. This advection occurred during peak tides and was combined with topographical current acceleration on the reef top, enhancing delivery of particles to the corals.
The effect of groundwater advection on salinity in pore waters of permeable sediments
Authors: Rapaglia John P. , Bokuniewicz Henry J.
Published: January 2011

Measurements of the upward advection and pore‐water profiles of salinity were made at three coastal settings (the Venice Lagoon, Italy; Jamaica Bay, New York; and Mattituck, New York). Coincident measurements of seepage rates using vented benthic chambers and profiles of salinity in pore water collected with a piezometer are used to quantify the coefficient of dispersive mixing. Three mathematical methods were used to quantify this coefficient: a simple, linearized salt balance and two analytical solutions to the steady‐state, one‐dimensional, advection‐diffusion equation in either a slab or a semi‐infinite medium. The majority of dispersive mixing coefficients in fine‐ to medium‐grained silty sand were calculated to be between 0.04 and 0.8 m2 d‐1. In some cases, the dispersive mixing seemed to involve small‐scale preferred pathways for vertical transport, such as would be the case for bioirrigation, gravitational convection, or salt fingering.
Nitrate removal in stream ecosystems measured by 15N addition experiments: Total uptake
Authors: Hall Robert O. , Tank Jennifer L. , Sobota Daniel J. , Mulholland Patrick J. , O'Brien Jonathan M. , Dodds Walter K. , Webster Jackson R. , Valett H. Maurice , Poole Geoffrey C. , Peterson Bruce J. , Meyer Judy L. , McDowell William H. , Johnson Sherri L. , Hamilton Stephen K. , Grimm Nancy B. , Gregory Stanley V. , Dahm Clifford N. , Cooper Lee W. , Ashkenas Linda R. , Thomas Suzanne M. , Sheibley Richard W. , Potter Jody D. , Niederlehner B. R. , Johnson Laura T. , Helton Ashley M. , Crenshaw Chelsea M. , Burgin Amy J. , Bernot Melody J. , Beaulieu Jake J. , Arangob Clay P.
Published: January 2011

We measured uptake length of 15NO3− in 72 streams in eight regions across the United States and Puerto Rico to develop quantitative predictive models on controls of NO3− uptake length. As part of the Lotic Intersite Nitrogen eXperiment II project, we chose nine streams in each region corresponding to natural (reference), suburban‐urban, and agricultural land uses. Study streams spanned a range of human land use to maximize variation in NO3− concentration, geomorphology, and metabolism. We tested a causal model predicting controls on NO3− uptake length using structural equation modeling. The model included concomitant measurements of ecosystem metabolism, hydraulic parameters, and nitrogen concentration. We compared this structural equation model to multiple regression models which included additional biotic, catchment, and riparian variables. The structural equation model explained 79% of the variation in log uptake length (SWtot). Uptake length increased with specific discharge (Q/w) and increasing NO3− concentrations, showing a loss in removal efficiency in streams with high NO3− concentration. Uptake lengths shortened with increasing gross primary production, suggesting autotrophic assimilation dominated NO3− removal. The fraction of catchment area as agriculture and suburban‐urban land use weakly predicted NO3− uptake in bivariate regression, and did improve prediction in a set of multiple regression models. Adding land use to the structural equation model showed that land use indirectly affected NO3− uptake lengths via directly increasing both gross primary production and NO3− concentration. Gross primary production shortened SWtot, while increasing NO3− lengthened SWtot resulting in no net effect of land use on NO3− removal.
Nitrate removal in stream ecosystems measured by 15N addition experiments: Denitrification
Authors: Mulholland Patrick J. , Hall Robert O. , Sobota Daniel J. , Dodds Walter K. , Findlay Stuart E. G. , Grimm Nancy B. , Hamilton Stephen K. , McDowell William H. , O'Brien Jonathan M. , Tank Jennifer L. , Ashkenas Linda R. , Cooper Lee W. , Dahm Clifford N. , Gregory Stanley V. , Johnson Sherri L. , Meyer Judy L. , Peterson Bruce J. , Poole Geoffrey C. , Valett H. Maurice , Webster Jackson R. , Arango Clay P. , Beaulieu Jake J. , Bernot Melody J. , Burgin Amy J. , Crenshaw Chelsea L. , Helton Ashley M. , Johnson Laura T. , Niederlehner B. R. , Potter Jody D. , Sheibley Richard W. , Thomasn Suzanne M.
Published: January 2011

We measured denitrification rates using a field 15NO3− tracer‐addition approach in a large, cross‐site study of nitrate uptake in reference, agricultural, and suburban‐urban streams. We measured denitrification rates in 49 of 72 streams studied. Uptake length due to denitrification (SWdenn) ranged from 89 m to 184 km (median of 9050 m) and there were no significant differences among regions or land‐use categories, likely because of the wide range of conditions within each region and land use. N2 production rates far exceeded N2O production rates in all streams. The fraction of total NO3− removal from water due to denitrification ranged from 0.5% to 100% among streams (median of 16%), and was related to NH4+ concentration and ecosystem respiration rate (ER). Multivariate approaches showed that the most important factors controlling SWden were specific discharge (discharge / width) and NO3− concentration (positive effects), and ER and transient storage zones (negative effects). The relationship between areal denitrification rate (Uden) and NO3− concentration indicated a partial saturation effect. A power function with an exponent of 0.5 described this relationship better than a Michaelis‐Menten equation. Although Uden increased with increasing NO3− concentration, the efficiency of NO3− removal from water via denitrification declined, resulting in a smaller proportion of streamwater NO3− load removed over a given length of stream. Regional differences in stream denitrification rates were small relative to the proximate factors of NO3− concentration and ecosystem respiration rate, and land use was an important but indirect control on denitrification in streams, primarily via its effect on NO3− concentration.
Organic matter diagenesis and bacterial contributions to detrital carbon and nitrogen in the Amazon River system
Authors: Tremblay Luc , Benner Ronald
Published: January 2011

Amino sugars and amino acids, including the bacterial biomarkers muramic acid and D‐amino acids, were measured to investigate the diagenetic alterations of and microbial contributions to detrital organic matter in the Amazon River system. Three size fractions of detrital material were analyzed: coarse and fine particulate organic matter (CPOM and FPOM), and ultrafiltered dissolved organic matter (UDOM). CPOM was depleted in amino sugars and had high percentages of total N as amino acids (32‐37%), consistent with relatively fresh plant debris being a major source of CPOM. FPOM had the highest percentages of total C as amino acids (5‐8%), and its composition appeared to be influenced by the preferential sorption of N‐containing molecules. UDOM had the highest percentages of total N as amino sugars (up to 2.3%) indicating the relatively important contributions from microorganisms. A consistent trend of increasing proportions of D‐amino acids among detrital size fractions, CPOM < FPOM < UDOM, suggests this parameter is a useful diagenetic indicator. About 4‐17% of the C and 17‐37% of the N in FPOM and CPOM were of bacterial origin based on D‐alanine and D‐glutamic acid yields. Similar bacterial contributions to UDOM were evident from the biomarker data, but they were not quantified due to insufficient information about representative yields of source biomarkers. Relationships between biomarker N and total N suggest that microbial activity influences the N content of detrital material. Bacterial contributions to detrital material were primarily as cellular remnants rather than living cells.
Benthic biogeochemical cycling, nutrient stoichiometry, and carbon and nitrogen mass balances in a eutrophic freshwater bay
Authors: Klump J. Val , Fitzgerald Sharon A. , Waplesa James T.
Published: January 2011

Green Bay, while representing only ~7% of the surface area and ~1.4% of the volume of Lake Michigan, contains one‐third of the watershed of the lake, and receives approximately one‐third of the total nutrient loading to the Lake Michigan basin, largely from the Fox River at the southern end of the bay. With a history of eutrophic conditions dating back nearly a century, the southern portion of the bay behaves as an efficient nutrient and sediment trap, sequestering much of the annual carbon and nitrogen input within sediments accumulating at up to 1 cm per year. Depositional fluxes of organic matter varied from ~0.1 mol C m22 yr21 to >10 mol C m−2 yr−1 and were both fairly uniform in stoichiometric composition and relatively labile. Estimates of benthic recycling derived from pore‐water concentration gradients, whole‐sediment incubation experiments, and deposition‐burial models of early diagenesis yielded an estimated 40% of the carbon and 50% of the nitrogen recycled back into the overlying water. Remineralization was relatively rapid with ~50% of the carbon remineralized within ~15 yr of deposition, and a mean residence time for metabolizable carbon and nitrogen in the sediments of 20 yr. On average, organic carbon regeneration occurred as 75% CO2, 15% CH4, and 10% dissolved organic carbon (DOC). Carbon and nitrogen budgets for the southern bay were based upon direct measurements of inputs and burial and upon estimates of export and production derived stoichiometrically from a coupled phosphorus budget. Loadings of organic carbon from rivers were ~3.7 mol m−2 yr−1, 80% in the form of DOC and 20% as particulate organic carbon. These inputs were lost through export to northern Green Bay and Lake Michigan (39%), through sediment burial (26%), and net CO2 release to the atmosphere (35%). Total carbon input, including new production, was 4.54 mol m−2 yr−1, equivalent to ~10% of the gross annual primary production. Nitrogen budget terms were less well quantified, with nitrogen export ~54% of total inputs and burial ~24%, leaving an unquantified residual loss term in the nitrogen budget of ~22%.
Increased supply of ambient nitrogen has minimal effect on salt marsh bacterial production
Authors: Bowen J. L. , Crump B. C. , Deegan L. A. , Hobbiec J. E.
Published: January 2011

We examined the role of chronic low‐level nutrient enrichment on the productivity of heterotrophic marsh bacteria via a marsh fertilization experiment in which we mimicked the conditions of widespread coastal eutrophication by enriching entire salt marshes to approximately 15 × background nutrient concentrations. We measured the uptake of tritiated leucine, as a proxy for bacterial production, in both low and high marsh habitats in four salt marshes, two of which were enriched with nutrients. We hypothesized that adding nitrogen in these detritus‐rich systems would directly stimulate bacterial decomposition of marsh peat. Contrary to our expectations, we found no response to added nutrients in high marsh habitats, where there is a significant supply of organic matter from marsh vegetation. Bacterial production did increase in the low marsh habitats, where fertilization increased the standing stock of benthic chlorophyll. Fertilization did not directly increase bacterial production by providing added nutrients that could be used to decompose organic matter derived from nutrient‐poor marsh grasses. Rather, bacterial productivity was indirectly stimulated by the concomitant increase in labile benthic microalgae in low marsh habitats. Decomposition of salt marshes may therefore have a greater resilience to the threat of chronic eutrophication than has been previously recognized.
Nitrogen cycling in a deep ocean margin sediment (Sagami Bay, Japan)
Authors: Glud Ronnie N. , Thamdrup Bo , Stahl Henrik , Wenzhoefer Frank , Glud Anni , Nomaki Hidetaka , Oguri Kazumasa , Revsbech Niels Peter , Kitazato Hiroshi
Published: January 2011

On the basis of in situ NO3−1 microprofiles and chamber incubations complemented by laboratory‐based assessments of anammox and denitrification we evaluate the nitrogen turnover of an ocean margin sediment at 1450‐m water depth. In situ NO3−1 profiles horizontally separated by 12 mm reflected highly variable NO3−1 penetration depths, NO3−1 consumption rates, and nitrification. On average the turnover time of the pore‐water NO3−1 pool was ~0.2 d. Net release of NH4+ during mineralization (0.95 mmol m−2 d−1) sustained a net efflux of ammonia (53%), nitrification (24%), and anammox activity (23%). The sediment had a relatively high in situ net influx of NO3−1 (1.44 mmol m−2 d−1) that balanced the N2 production as assessed by onboard tracer experiments. N2 production was attributed to prokaryotic denitrification (59%), anammox (37%), and foraminifera‐based denitrification (4%). Anammox thereby represented an important nutrient sink, but the N2 production was dominated by denitrification. Despite the fact that NO3−1 stored inside foraminifera represented ~80% of the total benthic NO3−1 pool, the slow intracellular NO3−1 turnover that, on average, sustained foraminifera metabolism for 12‐52 d, contributed only to a minor extent to the overall N2 production. The microbial activity in the surface sediment is a net nutrient sink of ~1.1 mmol N m−2 d−1, which aligns with many studies performed in coastal and shelf environments. Continental margin areas can act as significant N sinks and play an important role in regional N budgets.
Diurnal variations of surface seawater pCO2 in contrasting coastal environments
Authors: Dai Minhan , Lu Zhongming , Zhai Weidong , Chen Baoshan , Cao Zhimian , Zhou Kuanbo , Cai Wei‐Jun , Chenc Chen‐Tung Arthur
Published: January 2011

We examined diurnal variations of surface seawater pCO2 (partial pressure of CO2) in a suite of coastal marine environmental systems in the vicinity of the South China Sea (SCS) from inshore and nearshore settings in Xiamen Bay, Shenhu Bay, and the southwestern Taiwan Strait, to offshore sites in the basin and on the slope of the northern South China Sea as well as in a coral reef system at Xisha Islands in the middle of the SCS. There were significant diurnal changes of surface pCO2, ranging from 1.0 Pa to 1.6 Pa (10‐16 µatm) in the offshore and oligotrophic sites, ~4.1 Pa in the Taiwan Strait, 5.1‐15.2 Pa in Xiamen Bay and Shenhu Bay, to as high as 60.8 Pa in the coral reef system at Xisha Islands. Processes that modulate these pCO2 diurnal variations were temperature, tide or current, and biological controls. Temperature was a major driver of the pCO2 diurnal variability in the oligotrophic regions, while tidal effects were important in the nearshore. In the coral reef system, biological metabolism dominated variability. Diurnal variability could have a potentially important implication on the estimate of air‐sea CO2 fluxes, which may result in an uncertainty of ±0.48‐0.77 mmol C m−2 d−1 for the offshore sites in the SCS. Such uncertainties were larger in nearshore settings.
The regulation of calcium in Daphnia magna reared in different calcium environments
Authors: Tan Qiao‐Guo , Wang Wen‐Xiong
Published: January 2011

The specific content, dissolved uptake rate, dietary assimilation efficiency (AE), and efflux rate constant (ke) of calcium (Ca) were quantified in juvenile (4‐d) and adult (10‐d) Daphnia magna cultured in low (0.5 mg L−1)‐ and high (50 mg L−1)‐Ca environments using a radiotracer technique. Daphnids raised in the high‐Ca environment had higher Ca contents than did those raised in the low‐Ca environment, and juvenile daphnids had higher Ca contents than adults. Uptake from solution was the dominant source (97‐100%) of Ca for daphnids. The maximum influx rate (Jmax) was higher in juvenile daphnids (3.24‐4.10 mg g dry weight [wt]−1 h−1) than in adults (1.51‐1.62 mg g dry wt−1 h−1), while the influx rates were comparable in different Ca environments. The half‐saturation concentration (Km) was 2.51‐5.58 mg L−1. The AEs of Ca declined exponentially with increases in food concentrations, and lower AE was observed in the higher Ca environment. The ke of Ca (0.83‐1.98 d−1) was the highest among the elements whose ke had been quantified in D. magna, and it was 1.8‐2.4 times higher in the high‐Ca environment. Excretion into water was the dominant route (60‐85%) of Ca release from daphnids; another 15‐40% of Ca was lost as molts. The regulation of Ca in daphnids is mainly accomplished through adjusting their efflux but not their influx of Ca; their regulation ability is very limited, which may lead to a poor performance in daphnids in Ca‐deficient water.
Effects of the Bythotrephes invasion on native predatory invertebrates
Authors: Foster Sophie E. , * Gary Sprule
Published: January 2011

We explore the effects of the invasive predatory cladoceran Bythotrephes longimanus on the abundances and seasonal zooplankton consumption by the native predatory invertebrates Leptodora kindtii, Chaoborus spp., and Mysis relicta in inland lakes of Ontario. In lakes with Bythotrephes, the seasonal consumption by all invertebrate predators combined ranged from 2.39 to 13.50 g m−2 and was 300% higher than in lakes without the invader. This was due to Bythotrephes because there was no invasion effect on Chaoborus or Mysis consumption, while it actually decreased Leptodora consumption. Leptodora and Chaoborus abundances were lower in invaded lakes, but only Leptodora abundance was negatively correlated with Bythotrephes abundance. There was no effect of Bythotrephes on Mysis abundance. Bythotrephes consume more zooplankton than most other predatory invertebrates, including copepods, and often consume more zooplankton than planktivorous fish. The large increase in predatory invertebrate abundance and consumption due to Bythotrephes means that substantial portions of zooplankton production are probably being diverted from other consumers, such as juvenile and planktivorous fish, and that the role of predatory invertebrates in the pelagia of inland lakes has been intensified by the arrival of Bythotrephes.
Staying alive: The post‐consumption fate of parasite spores and its implications for disease dynamics
Authors: Duffy Meghan A.
Published: January 2011

Studies on the effects of selective predation by fish on disease dynamics in Daphnia generally assume that consumption by fish means the death of the parasite. I use a combination of feeding trials and infection assays to test this assumption using the host Daphnia dentifera and its common, virulent yeast parasite, Metschnikowia bicuspidata. Approximately 50% of Metschnikowia spores consumed by bluegill sunfish were released in fecal pellets. These spores remained infective to D. dentifera. Therefore, consumption of infected hosts by fish is not necessarily a dead end for the parasite, and in some cases, fish predation may actually help fuel epidemics in natural populations.
Enhanced viral production and infection of bacterioplankton during an iron‐induced phytoplankton bloom in the Southern Ocean
Authors: Weinbauer Markus G. , Arrieta Jesus‐Maria , Griebler Christian , Herndlb Gerhard J.
Published: January 2011

We followed the viral response to Fe‐enrichment over 3 weeks during the second iron‐enrichment experiment (EisenEx) in the Southern Ocean. Although viral abundance increased in a rather constant way during the course of the experiment inside the patch, the production of bacterial viruses and the fraction of infected cells in bacterioplankton exhibited pronounced maxima on days 7 and 21. In contrast, these parameters remained fairly constant outside the Fe‐fertilized patch. Viral production was also stimulated directly after the Fe‐enrichment. Within the Fe‐replete patch, viral abundance and production was on average 2‐ and 3‐fold, respectively, higher than outside the patch. On average 40% of the bacteria contained viruses in a lytic stage inside the Fe‐replete patch compared to 21% outside the patch. About 11‐12% of the bacteria contained a viral genome inducible with mitomycin C in both inside and outside the patch. Randomly amplified polymorphic desoxyribonucleic acid polymerase chain reaction analysis suggested the development of a specific viral community in the patch. Although short‐term stimulation of viral production was likely due to increased bacterial activity, the long‐term stimulation was likely also influenced by an increased encounter rate between bacterial viruses and hosts. Viral lysis was responsible for most of the bacterioplankton mortality in the patch. Overall, most of the bacterial carbon production entered the detrital or dissolved organic matter pool via the viral shunt in the patch.
Biological consumption of dimethylsulfide (DMS) and its importance in DMS dynamics in the Ross Sea, Antarctica
Authors: Valle Daniela A. del , Kieber David J. , Toole Dierdre A. , Brinkley Jordan , Kienea Ronald P.
Published: January 2011

We studied the biological consumption of dimethylsulfide (DMS) and its role in controlling DMS concentrations in the Ross Sea, Antarctica, during the spring (Nov) and summer (Jan) of 2005. Surface DMS concentrations, measured with a technique that minimized DMS release from Phaeocystis antarctica, increased rapidly in the spring from 0.3 nmol L−1 to 67.7 nmol L−1, paralleling increases in chlorophyll a and bacterial biomass production. Biological DMS consumption (BDMSC) rates were low (0.02 nmol L−1 d−1) at the start of the bloom, but increased to 8.8 nmol L−1 d−1 at the peak of the bloom. Rate constants for BDMSC (kbc) remained relatively low throughout the spring (0.05‐0.21 d−1) and this slow biological turnover contributed to the buildup of DMS during the early bloom. DMS concentrations in the summer (3.2‐16.8 nmol L−1) were much lower than peak springtime concentrations, partly due to the higher BDMSC rate constants (0.22‐0.98 d−1; i.e., faster biological turnover) in the summer. Kinetic analysis suggested that BDMSC rates were nearly saturated at ambient DMS concentrations in the spring but not in summer. BDMSC was mostly carried out in the size fractions ≪1 µm and ≫8 µm, except in the early spring when the ≪1‐µm fraction (likely free‐living bacteria) dominated BDMSC. BDMSC was the main removal pathway for DMS in the surface mixed layer during both the spring and summer, except during the prebloom, when photolysis dominated. BDMSC exerts a major control on DMS concentrations in the Ross Sea throughout the Phaeocystis antarctica bloom.
Connecting recruitment of Antarctic krill and sea ice
Authors: Wiedenmann John , Cresswell Katherine A. , Mangel Marc
Published: January 2011

We develop an age‐structured model for two krill populations near the Antarctic Peninsula and estimate the relative recruitment events that reproduce observed trends in krill abundance and age structure. Estimates of recruitment in both regions show a nonlinear relationship between recruitment and sea ice area in the combined Bellingshausen and Amundsen Seas from the previous winter and spring, with large recruitment events occurring over a narrow range of ice area, and minimal recruitment otherwise. This finding may allow for an adaptive approach in which future catch limits are adjusted based on predictions of biomass. This result also suggests that the ecosystem may change dramatically once average ice area drops below the recruitment threshold.
Release of reactive bromine and iodine from diatoms and its possible role in halogen transfer in polar and tropical oceans
Authors: Hill Valerie L. , Manley Steven L.
Published: January 2011

An in situ incubation assay measuring the bromination and iodination of phenol red was developed to detect the release of reactive bromine and iodine (primarily hypobromous acid [HOBr] and hypoiodous acid [HOI], respectively) from a putative extracellular bromoperoxidase of marine diatoms. Six of 11 species showed significant release compared to controls. Polar species were particularly active, releasing 0.6–180 fmol HOBr cell−1 h−1 (0.04–1.8 µmol HOBr [mg total chlorophyll]−1 h−1; at the seawater bromide concentration, 840 µmol L−1) and 1.9–271 fmol HOI cell−1 h−1 (0.02–2.7 µmol HOI [mg total chlorophyll]21 h−1, at 100 µmol L−1 iodide). Porosira glacialis consistently showed the highest rates of release. Several temperate diatoms, including Achnanthes cf longipes, known to have a bromide‐sensitive peroxidase involved in stalk formation, and warmwater species also showed the ability to release reactive bromine and iodine. This release was influenced by light, temperature, bromide (and iodide) concentration, H2O2 concentration, and pH. The rate of HOBr release by polar diatoms was much greater than bromoform emissions measured by others from laboratory cultures and seaice algae in the field. This indicates that most of the HOBr released may react with dissolved organic matter (DOM) to form nonvolatile bromine organics. Some fraction of diatom‐produced HOBr and HOI may also form volatile Br2 and I2, which could transfer to the polar troposphere. The reaction of diatom‐released reactive bromine and iodine with seawater DOM may represent the major mechanism in the formation of oceanic polybromo‐ and polyiodo‐methanes.
Growth and photoregulation dynamics of the picoeukaryote Pelagomonas calceolata in fluctuating light
Authors: Dimier CÉline , Brunet Christophe , Geider Richard , Raven John
Published: January 2011

Growth, photosynthesis, and photoacclimation properties of batch cultures of Pelagomonas calceolata (Pelagophyceae) were compared for 1 week under three different fluctuating light regimes with the same total daily amount of light. Treatments consisted of a sinusoidal diurnal light cycle or a high‐frequency fluctuating light simulating two different regimes of vertical mixing (highly fluctuating light [HFL] or fluctuating light [FL]). Three to five samples were taken every day for analysis of pigments, absorption spectrum, variable fluorescence, nonphotochemical quenching (NPQ), electron transport rate vs. light curves, and cell concentration. Pelagomonas achieved the same growth rate during the exponential growth phase under all three light conditions, revealing a high degree of acclimation to light and also suggesting that the daily light dose is the main factor regulating growth and division. Photophysiological adjustments occurred in the cells in response to the three light regimes. Pelagomonas seems to adopt the n‐type photoacclimation in HFL, whereas the σ;‐type photoacclimation is applied in FL. The cells rapidly trigger photoprotective mechanisms such as the xanthophyll cycle and NPQ, even though these do not appear to be able to fully prevent photoinhibition. The enhanced costs for maintenance and repair associated with HFL may have limited the allocation of energy to growth, thus explaining the shorter duration of the exponential growth phase in this regime with respect to the two others.
The origin of methylmercury in open Mediterranean waters
Authors: Cossa Daniel , Averty Bernard , Pirrone Nicola
Published: January 2011

We present high‐resolution vertical profiles of methylated mercury (MeHgT = monomethylmercury + dimethylmercury) concentrations in the water column of the open and marginal areas of the Mediterranean Sea. MeHgT concentrations ranged from <0.015 pmol L−1 to 0.430 pmol L−1 (n = 130), with maximal concentrations occurring within the maxima of oxygen consumption. Within the most biologically active zone (0‐600 m), the MeHgT vertical profiles exhibited a nutrient‐like pattern. The MeHgT vs. phosphate relationships were highly significant (p < 0.001), whichever the station. We argue that most of the MeHgT in the water column originates from in situ methylation of inorganic HgII associated with the regeneration of the organic matter. The demethylation of MeHgT as water ages seems responsible for the MeHgT distribution in deep waters. The influences of the methylmercury inputs from the atmosphere, rivers, and coastal or abyssal sediments appear to be locally restricted.