bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective Transfer Phenomenon in Friction Couples Lubricated with Base Oils
Authors: Kotnarowski Andrzej
Published: June 2010

The paper deals with generation of selective transfer phenomenon in couples consisting of frictionally-mating elements made of steel and lubricated with oils modified by addition of metal micro- and nanoparticles. Presented results demonstrate the possibility of generation of selective transfer phenomenon in this kind of tribological systems.
Dysphagia in Stroke: A New Solution
Authors: Langdon Claire , Blacker David
Published: June 2010

Dysphagia is extremely common following stroke, affecting 13%–94% of acute stroke sufferers. It is associated with respiratory complications, increased risk of aspiration pneumonia, nutritional compromise and dehydration, and detracts from quality of life. While many stroke survivors experience a rapid return to normal swallowing function, this does not always happen. Current dysphagia treatment in Australia focuses upon prevention of aspiration via diet and fluid modifications, compensatory manoeuvres and positional changes, and exercises to rehabilitate paretic muscles. This article discusses a newer adjunctive treatment modality, neuromuscular electrical stimulation (NMES), and reviews the available literature on its efficacy as a therapy for dysphagia with particular emphasis on its use as a treatment for dysphagia in stroke. There is a good theoretical basis to support the use of NMES as an adjunctive therapy in dysphagia and there would appear to be a great need for further well-designed studies to accurately determine the safety and efficacy of this technique.
Influence of stream size on ammonium and suspended particulate nitrogen processing
Authors: Wollheim Wilfred M. , Peterson Bruce J. , Deegan Linda A. , Hobbie John E. , Hooker Beth , Bowden William B. , Edwardson Kenneth J. , Arscott David B. , Hershey Anne E. , Finlay Jacques
Published: June 2010

We used 15NH4 tracer additions to determine travel distances of ammonium (NH4 ) and suspended particulate organic nitrogen (SPON) in six streams ranging from second to fifth order located within a single watershed on the North Slope of Alaska. Based on the distribution of 15N stored in stream bottom compartments (primary producers or grazers), we estimated NH4 travel lengths. We used a two‐compartment model to estimate the travel length of SPON based on the distribution of source 15N on the stream bottom and SPO 15N in the water column. Both NH4 and SPON travel lengths (Sw and Sp, respectively) increased with discharge primarily due to changes in depth and velocity. Variation in the vertical mass transfer coefficient (vf) of both NH4 and SPON did occur among the streams but was not related to stream size and was relatively small compared to the change in physical characteristics. Thus, in the Kuparuk watershed, physical gradients outweighed biological or chemical changes as controls on NH4 and SPON travel length. The one exception was the Kuparuk fertilized reach, where phosphorus fertilization greatly increased biological activity and NH4 processing compared to unaltered streams. Longitudinal gradients in major biological driving variables such as litter inputs, debris dams, and shading are absent in the Arctic, perhaps explaining the relatively uniform NH4 ‐ vf. Watersheds in other biomes may show differing degrees of physical versus biological/chemical controls. A conceptual model is presented for comparing the relative strength of these controls among different watersheds. Strong relationships between discharge and travel length should greatly aid development of watershed models of nutrient dynamics.
Photosynthesis and photoprotection in symbiotic corals
Authors: Gorbunov Maxim Y. , Kolber Zbigniew S. , Lesser Michael P. , Falkowski Paul G.
Published: June 2010

In zooxanthellate corals, excess excitation energy can be dissipated as heat (nonphotochemical quenching), thereby providing protection against oxidative damage by supraoptimal light in shallow reefs. To identify and quantify the photoprotective mechanisms, we studied the diel variability of chlorophyll fluorescence yields and photosynthetic parameters in situ in corals, using moored and SCUBA‐based fast‐repetition‐rate fluorometers. The results reveal that nonphotochemical quenching is triggered prior to saturation of photosynthetic electron transport by down‐regulation of the reaction centers of Photosystem II (PSII). This process dissipates up to 80% of the excitation energy. On a sunny day in shallow waters, the daily integrated flux of photons absorbed, and subsequently dissipated as heat, is ~4 times that used for photosynthesis. Fluorescence quenching is further accompanied by a slight reduction in the functional absorption cross section for PSII that results from thermal dissipation of excitation energy in the light‐harvesting antennae. These two processes are highly dynamic and adjust to irradiance changes on timescales consistent with the passage of clouds across the sky. Under supraoptimal irradiance, however, up to 30% of PSII reaction centers become photoinhibited, and these are repaired only after several hours of low irradiance. In shallow corals, between 10% and 20% of the reactions centers are chronically photoinhibited and appear to remain permanently nonfunctional throughout the year. Our results establish, for the first time, the suite of biophysical mechanisms that optimize photosynthesis while simultaneously providing photoprotection in symbiotic corals in situ.
Net ecosystem production of dissolved organic carbon in a coastal upwelling system: the Ría de Vigo, Iberian margin of the North Atlantic
Authors: Álvarez‐Salgado X. A. , Gago J. , Míguez B. M. , Pérez F. F.
Published: June 2010

Net ecosystem production (NEP) rates of dissolved organic carbon (DOC) are estimated in a coastal upwelling system. The study site is a large coastal inlet (2.76 km3) in the northern boundary (42–43°N) of the eastern North Atlantic upwelling system. The two‐dimensional circulation pattern in the system is governed by an offshore Ekman transport quite variable in magnitude and direction. A mass balance of the short‐timescale (2–4 d) changes in measured DOC profiles is performed to obtain the NEP rates. Microbial oxidation of imported labile DOC (8% of total DOC, recycling time t < 5 d) at a maximum net rate of −37 mmol C m−2 d−1 occurred during a downwelling episode in the middle of the highly productive spring period. On the contrary, extensive export of labile DOC (<15% of total DOC, t < 7 days) produced at net rates >42 mmol C m‐2 d‐1 took place during an upwelling episode in July, the middle of the upwelling season. This rate represents ~20% of the net primary production, demonstrating in the field the relative importance of horizontal offshore transport of labile DOC to the export of new production in upwelling systems. An autumn wind relaxation period results in dramatic changes in DOC standing stocks (69 mmol C L‐1) caused by a conspicuous time segregation between sustained net phytoplankton production of labile DOC (+15 mmol C m‐2 d‐1, 11 d) and subsequent rapid bacterial degradation (−63 mmol C m‐2 d‐1, 3 d). Net horizontal export during this period was prevented by reduced offshore Ekman transport values, indicating that net DOC production is not always synonymous with net export. Finally, during the winter period, the large wind‐driven net DOC horizontal exchange rates affected mainly the DOC standing stocks of no bioreactive materials in the system, whereas bacterial oxidation rates during this period reduced to less than −0.14 mmol C m‐2 d‐1.
Observations of a hydrothermal plume in a karstic lake
Authors: Colomer Jordi , Serra Teresa , Piera Jaume , Roget Elena , Casamitjana Xavier
Published: June 2010

A hydrothermal plume with vertical and horizontal length scales of ~18 and ~300 m, respectively, develops in a karstic lake. The plume is generated at the bottom of a basin that contains sediment in suspension, which is at a higher temperature than the water immediately above (the hypolimnion of the lake). The rising convective plume entrains colder hypolimnetic water and develops upward, until it reaches the base of the seasonal thermocline, carrying an important amount of sediment particles from the bottom, which are used as tracers to describe the spatial distribution of the plume. At the level of neutral buoyancy, the plume spreads laterally, as a horizontal baroclinic intrusion.
Fine‐scale measurement of diffusivity in a microbial mat with nuclear magnetic resonance imaging
Authors: Wieland Andrea , de Beer Dirk , Damgaard Lars R. , Kühl Michael , van Dusschoten Dagmar , Van As Henk
Published: June 2010

Noninvasive 1H‐nuclear magnetic resonance (NMR) imaging was used to investigate the diffusive properties of microbial mats in two dimensions. Pulsed field gradient NMR was used to acquire images of the H2O diffusion coefficient, Ds, and multiecho imaging NMR was used to obtain images of the water density in two structurally different microbial mats sampled from Solar Lake (Egypt). We found a pronounced lateral and vertical variability of both water density and water diffusion coefficient, correlated with the laminated and heterogeneous distribution of microbial cells and exopolymers within the mats. The average water density varied from 0.5 to 0.9, whereas the average water diffusion coefficient ranged from 0.4 to 0.9 relative to the values obtained in the stagnant water above the mat samples. The apparent water diffusivities estimated from NMR imaging compared well to apparent O2 diffusivities measured with a diffusivity microsensor. Analysis of measured O2 concentration profiles with a diffusion‐reaction model showed that both the magnitude of calculated rates and the depth distribution of calculated O2 consumption/production zones changed when the observed variations of diffusivity were taken into account. With NMR imaging, diffusivity can be determined at high spatial resolution, which can resolve inherent lateral and vertical heterogeneities found in most natural benthic systems.
Stoichiometry of nitrogen and carbon utilization in cultured populations of Trichodesmium IMS101: Implications for growth
Authors: Mulholland Margaret R. , Capone Douglas G.
Published: June 2010

Rates of particulate organic carbon (POC) and particulate organic nitrogen (PON) accumulation, N2 and CO2 fixation, and NH4+ uptake were measured in cultures of Trichodesmium IMS101 growing on an artificial culture medium without added N substrates. Cultures exhibited a doubling time of about 4 d based on the accumulation of PON, POC, chlorophyll a, and cell number. Cell‐specific rates of N2 and CO2 fixation were highest during midday and during the initial stages of the growth cycle. Up to midlog phase, integrated estimates of CO2 fixation (based on short‐term 13CO2 uptake) closely tracked increases in POC. However, after day 8, estimates of C accumulation based on CO2 fixation exceeded observed POC increases. Within the error of the measurements, N2 fixation estimates (based on C2H2 reduction) also closely tracked, and could largely account for, PON increases over most of the experiment. N demand based on CO2 fixation also followed PON increases during early to midlog phase but diverged during late exponential phase and thereafter by greater than 100%. Estimates of short‐term C fixation rates during and after late exponential phase overestimate net growth of Trichodesmium IMS101, whereas estimates of N2 fixation rates approximated net growth. These observations may partially explain the disparity of estimates of growth in field populations based on 14CO2 fixation compared to N2 fixation. Ammonium accumulated in the culture medium during the experiment, and rates of NH4+ uptake were high throughout the day and over the whole growth cycle. Rates of NH4+ uptake generally exceeded N2 fixation. The turnover of N was therefore much greater than the net accumulation of N in biomass and implies a concurrent high rate of NH4+ release.
The role of DON and the effect of N: P ratios on occurrence of cyanobacterial blooms: Implications from the outgrowth of Aphanizomenon in Lake Kinneret
Authors: Berman Tom
Published: June 2010

Supply (or loading) ratios of biologically available nitrogen and phosphorus, N: P, have often been suggested as the major determinants for the presence or absence of N2 fixing cyanobacteria in aquatic environments. Increasing evidence that some components of the dissolved organic nitrogen (DON) pool can play an active role in supplying N nutrition either directly or indirectly to phytoplankton implies that this source of N must be considered in any attempt to apply the N: P resource ratio approach to predict or explain phytoplankton population composition. For example, the unprecedented bloom of Aphanizomenon ovalisporum that occurred in Lake Kinneret from mid‐September through October 1994 derived most of the N required for growth directly or indirectly from DON rather than from N2‐fixation. This would suggest that factors other than apparent low N: P ratios were important in causing the outgrowth of the cyanobacteria. The present analysis of the Aphanizomenon bloom in Lake Kinneret emphasizes (1) the need to include the DON pool as a potential source of available N for planktonic microbiota; (2) at least for some cyanobacteria, the presence of heterocysts does not necessarily imply active nitrogen fixation; and (3) the development of diazotrophic cyanobacterial blooms in nature is generally due to a multiplicity of environmental factors.
Seasonal changes in the importance of the source of organic matter to the diet of zooplankton in Loch Ness, as indicated by stable isotope analysis
Authors: Grey Jonathan , Jones Roger I. , Sleep Darren
Published: June 2010

Seasonal variations in the stable isotope composition (d13C and d15C) of crustacean zooplankton and their putative food sources in oligotrophic Loch Ness were recorded during 1998. Bulk particulate organic matter (POM) showed d13C values consistent with a terrestrial plant origin from the catchment and exhibited little seasonal variation, whereas POM d15 was more variable, probably due to associated microbial action. In contrast, phytoplankton d13C was relatively light and showed some seasonal variation, but d15 values were more constant. The isotopic signatures of both POM and phytoplankton remained sufficiently distinct from each other throughout the period of study to allow their relative contributions to zooplankton diet to be assessed. Zooplankton isotopic signatures shifted seasonally, reflecting a dietary switch from a reliance on allochthonous carbon derived from POM during winter and early spring to heavy dependence on algal production during summer. Annually, crustacean zooplankton in Loch Ness derive approximately 40% of their body carbon from allochthonous sources, likely mediated via microbial links. Separate determination of isotope ratios for the main zooplankton species allowed a more detailed trophic investigation. The most abundant zooplankton species in the loch, Eudiaptomus gracilis, incorporated appreciable allochthonous carbon even during the peak of phytoplankton productivity. By contrast, Daphnia hyalina grew mainly in late summer and autumn and derived almost 100% body carbon from algal sources. This study is the first to quantify such a seasonal switch in zooplankton dependence between allochthonous and autochthonous sources of organic matter in a large lake.
Quantifying groundwater discharge through fringing wetlands to estuaries: Seasonal variability, methods comparison, and implications for wetland‐estuary exchange
Authors: Tobias Craig R. , Harvey Judson W. , Anderson Iris C.
Published: June 2010

Because groundwater discharge along coastal shorelines is often concentrated in zones inhabited by fringing wetlands, accurately estimating discharge is essential for understanding its effect on the function and maintenance of these ecosystems. Most previous estimates of groundwater discharge to coastal wetlands have been temporally limited and have used only a single approach to estimate discharge. Furthermore, groundwater input has not been considered as a major mechanism controlling pore‐water flushing. We estimated seasonally varying groundwater discharge into a fringing estuarine wetland using three independent methods (Darcy's Law, salt balance, and Br− tracer). Seasonal patterns of discharge predicted by both Darcy's Law and the salt balance yielded similar seasonal patterns with discharge maxima and minima in spring and early fall, respectively. They differed, however, in the estimated magnitude of discharge by two‐ to fourfold in spring and by 10‐fold in fall. Darcy estimates of mean discharge ranged between —8.0 and 80 L m−2 d−1, whereas the salt balance predicted groundwater discharge of 0.6 to 22 L m−2 d−1. Results from the Br− tracer experiment estimated discharge at 16 L m−2 d−1, or nearly equal to the salt balance estimate at that time. Based upon the tracer test, pore‐water conductivity profiles, and error estimates for the Darcy and salt balance approaches, we concluded that the salt balance provided a more certain estimate of groundwater discharge at high flow (spring). In contrast, the Darcy method provided a more reliable estimate during low flow (fall). Groundwater flushing of pore water in the spring exported solutes to the estuary at rates similar to tidally driven surface exchange seen in previous studies. Based on pore‐water turnover times, the groundwater‐driven flux of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and NH4+ to the estuary was 11.9, 1.6, and 1.3 g C or g N m−2 wetland for the 90 d encompassing peak spring discharge. Groundwater‐induced flushing of the wetland subsurface therefore represents an important mechanism by which narrow fringing marshes may seasonally relieve salt stress and export material to adjacent water masses.
Chemosensory guidance cues in a turbulent chemical odor plume
Authors: Webster D. R. , Weissburg M. J.
Published: June 2010

The characteristics of chemical odor plumes released into a turbulent open channel flow are evaluated in the context of chemical plume tracking. The objective is to assess the availability and usefulness of chemosensory cues to animals, such as benthic crustaceans, attempting to orient in the plume. Releasing fluorescent dye into the fully developed turbulent boundary layer of a large laboratory‐scale flume created turbulent odor plumes. Flow visualization of odor fields created with varying release velocity, release distance from the bed, and nozzle diameter indicated that chemosensory cues in plumes depend on the release characteristics as well as the ambient flow conditions. Thus, to understand animal behavior, it is important to quantify the plume release properties and characteristics. We chose to quantify concentration fields for the case of isokinetic release using the planar laser‐induced fluorescence technique. These measurements indicate that the time‐averaged concentration converges far too slowly to be useful to a foraging animal. Similarly, resolving the rise slope of a concentration burst requires sampling rates unattainable by animals, and the spatial variation of rise slope is too mild to follow without lengthy sampling periods. In addition, only mild variation with distance from the source is observed in the concentration burst magnitude and duration. Thus, the time‐averaged concentration, rise slope, and burst shape all appear to have limited usefulness for plume orientation for animals known to orient effectively to these types of odor sources.
Use of amino acid composition to investigate settling and resuspension of a spring bloom in the southern Skagerrak
Authors: Petersson Mona , Floderus Sören
Published: June 2010

Short‐term changes in amino acid composition of near‐bed particulate flux were studied at an upper shelf location in the southern Skagerrak, 55 m deep. Sediment trap samples were collected with a 3‐d sampling interval from late April to late June 1992. A high settling rate (85 g m−2 d−1) was intercepted in May, coinciding with high shear velocity and settling of fresh phytoplankton. During the peak in the settling rate, a decrease in the mole percentage of glycine was noticed. At the end of June, smaller peaks of high flux corresponded to periods of increased shear velocity; during this time, the amino acid composition did not change. A Q‐mode factor analysis on the amino acid variation of collected particles showed a relation between certain samples consisting of fresh phytoplankton material. If organic carbon is compared to the shear velocity, the related phytoplankton samples had a positive correlation, whereas the more degraded samples had a negative correlation. The observed patterns suggest a coupling between food web dynamics and particle composition on the one hand and availability of benthic fluff at the sediment surface on the other. The length of the period affected by fresh material could be sorted out by using the amino acid composition and be made comparable to samples influenced by more degraded material.
A test of the ashߚfree dry weight technique on the developmental stages of Patiriellaspp. (Echinodermata: Asteroidea)
Authors: Moreno Guillermo , Selvakumaraswamy Paulina , Byrne Maria , HoeghߚGuldberg Ove
Published: June 2010

Determination of the ashߚfree dry weight (AFDW) of marine specimens requires samples to be rinsed, soaked, and centrifuged. Problems associated with this technique were examined with the developmental stages of seastar species (Patiriella) with different modes of development. The influence of three rinsing solutions (ammonium formate [AF], filtered seawater [FSW], and reverse osmosis water [RO]) was assessed. The hypothesis that the AFDW technique is a measure of organic material was addressed by drying inorganic salts. Developmental stages of Patiriella calcar rinsed in FSW were twice as heavy as those rinsed in RO or AF, indicating that samples should be rinsed in RO or AF before weighing. Soaking treatments had a significant effect on the AFDW of samples of P. calcar (planktonic developer), indicating that the rinsing period should be brief. Zygotes of Patiriella regularis (planktonic developer) were significantly heavier than ova or gastrulae, regardless of treatment. In contrast, there were no significant differences in the AFDW of any stages or treatments of Patiriella exigua (benthic developer). This may be due to the presence of a modified fertilization envelope, which protects these benthic embryos. Inorganic salts with water of crystallization and FSW lost 20–75% and 14% of their dry weight, respectively, after ashing. We propose that salt ions may retain water, which does not evaporate during drying but is lost during ashing, resulting in the overestimation of sample AFDW. If a similar process occurs in the developmental stages of marine invertebrates, changes in the intracellular ionic composition through development may result in inaccurate estimates of biomass.
Iron fertilization and the Trichodesmiumresponse on the West Florida shelf
Authors: Lenes Jason M. , Darrow Brian P. , Cattrall Christopher , Heil Cynthia A. , Callahan Michael , Vargo Gabriel A. , Byrne Robert H. , Prospero Joseph M. , Bates David E. , Fanning Kent A. , Walsh John J.
Published: June 2010

Prior laboratory studies of Trichodesmium have shown a high iron requirement that is consistent with the biochemical demand for iron in the enzyme nitrogenase. Summer delivery of iron, in the form of Saharan dust, may provide an explanation for Trichodesmium blooms observed in offshore waters of the West Florida shelf over the last 50 yr. During ecology and oceanography of harmful algal blooms (ECOHAB) field studies, background iron levels (0.1–0.5 nmol kg−1) were found at the surface during periods of minimal dust delivery (May 2000 and October 1999). In contrast, total dissolved iron concentrations on the order of ∼16 nmol kg−1 were measured at the West Florida shelfߚbreak after a July 1999 Saharan dust event that was identified by advanced very high resolution radiometer (AVHRR) imagery, groundߚbased radiometers, air mass analysis, and aerosol samples (dust and nonߚseaߚsalt nitrate) collected throughout South Florida. The Trichodesmium response following this July dust event was a 100–fold increase over background biomass, reaching a surface stock of ∼20 colonies L−1. Surface dissolved concentrations of both inorganic and organic phosphorus decreased below detectable limits during this bloom. Dissolved organic nitrogen concentrations associated with the bloom (15–20 µM) were 3–4–fold greater than background and much larger than ambient NO3− concentrations (<0.5 µmol kg−1). If all dissolved organic nitrogen (DON) is converted to urea and ammonium, this organic nitrogen could have supported the red tide of >20 µg chl L−1 of the toxic dinoflagellate, Gymnodinium breve, found along the West Florida coast during October 1999.
Physiological constraints on bromoform (CHBr3) production by Ulva lactuca (Chlorophyta)
Authors: Manley Steven L. , Barbero Pebble E.
Published: June 2010

Physiological factors affecting bromoform (CHBr3) production by Ulva lactuca were investigated using metabolic inhibitors and presumed substrates of bromoperoxidase (BrPO). The metabolic inhibitors were used at a verified physiologically active concentration. Bromoform production was nearly tripled in the light (376 ± 92 pg cm−2 h−1) compared to the dark (114 ± 70 pg cm−2 h−1), was inhibited in the light in the presence of the photosynthetic inhibitor DCMU, and was inhibited in the dark in the presence of mitochondrial respiratory inhibitor rotenone. Removal of H2O2 from seawater (treatment with catalase) decreased CHBr3 production in the light and dark. Addition of H2O2 to incubations at either 1.0 mM or 100 µM significantly decreased CHBr3 production in the light and inhibited photosynthesis. In the dark, CHBr3 production was decreased and respiration inhibited in the presence of 1 mM H2O2; CHBr3 production was enhanced and respiration was not affected in the presence of 100 µM H2O2. Removal of dissolved organic matter (DOM) from seawater decreased CHBr3 production, as did the addition of alternative BrPO substrates. These results suggest the presence of an extracellular and intracellular BrPO that protects the alga from both internally produced and externally present H2O2. The results show that H2O2 produced as a result of photosynthetic and respiratory electron transport, presumably by superoxide dismutase, is available to BrPO for bromination, and that the bromination of an unidentified metabolite (presumably Βߚketo acids) and a component of DOM leads to the production of volatile polybromomethanes.
Toxic effects of Heterosigma akashiwo do not appear to be mediated by hydrogen peroxide
Authors: Twiner Michael J. , Dixon S. Jeffrey , Trick Charles G.
Published: June 2010

The ichthyotoxic red tide organism Heterosigma akashiwo (Raphidophyceae) has been associated with fish kill events within the aquaculture industry for many years. The precise toxicological mechanism involved in these fish kills is unclear; however, much research attention has focused on the production of reactive oxygen species (ROS) by these toxic algae. In this study, we investigated the production of hydrogen peroxide (H2O2) by isolates of H. akashiwo and the nontoxic chlorophyte Tetraselmis apiculata. Subsequently, we tested those concentrations of H2O2 on vertebrate cell lines and the invertebrate Artemia salina (brine shrimp) to investigate mortality. Net production rates for the H. akashiwo isolates ranged from 0.46 to 7.89 pmol H2O2 min−1 (104 cells)−1 while obtaining maximum concentrations between 0.14 and 0.91 µM H2O2. Conversely, T. apiculata produced only 0.03 pmol H2O2 min±1 (104 cells with a maximum level on 0.04 µM. However, toxic effects on UMRߚ106 and HEKߚ293 cells were only induced by acute and protracted exposure to concentrations of H2O2 >= 0.1 mM. Additionally, significant mortality of A. salina in the presence or absence of ferric and ferrous iron was induced by H2O2 levels >= 1 mM. Iron is a redox metal that reduces H2O2 to hydroxy radicals. These data collectively indicate that production of H2O2 by multiple isolates of H. akashiwo is orders of magnitude less than that required for mortality of either the vertebrate cell lines or the invertebrate A. salina. Other nonichthyotoxic roles for extracellular ROS are proposed.
The distribution of estuarine and oceanic water masses on the southern shore of O'ahu, Hawai'i: Ecological and coastal management implications, and novel methodology
Authors: Parnell P. Ed
Published: June 2010

The distribution of estuarine and oceanic water masses along the shelf of Mamala Bay, O'ahu, Hawaii, were determined by use of larval supply and recruitment patterns of benthic invertebrate species, stable C and N isotopic compositions of the suspension‐feeding bivalve, Spondylus tenebrosus, turbidity, drifter, and CTD data. The recruitment of different species among estuaries was used to associate larval species with particular estuarine waters. Recruitment patterns of these species along the shelf were then used to infer water‐mass distributions along the shelf. The spatial recruitment pattern of an oceanic lepadomorph barnacle, Conchoderma virgatum, was useful to infer shelf areas exposed to oceanic waters. Water‐mass distributions inferred from the recruitment distribution of these species concurred with spatial patterns of turbidity and stable C and N isotopic compositions of S. tenebrosus, as well as drifter observations. Water‐mass distributions observed in this study also concurred with biological distributional patterns observed in other studies, such as distributions of phytoplankton and zooplankton and the distribution of coral bio‐erosion in the Bay. The ecological implications of this work include further evidence of the physical control of recruitment and biological pattern and the possible control of patch dynamics on the scale of kilometers due to significant recruitment variability at this scale. The prevailing distribution of water masses determined in this study also has important implications for the management of watersheds associated with Mamala Bay.
The effect of emergent vegetation on convective flushing in shallow wetlands: Scaling and experiments
Authors: Oldham C. E. , Sturman J. J.
Published: June 2010

Many wetlands around the world are characterized by shallow water, dense vegetation in the littoral zones, no significant riverine inflow and minimal circulation. Recent research on the hydrodynamics of such wetlands has identified convective circulation as being important for flushing of the littoral zones. To quantify this process, a parameterization of the convective discharge per unit width, which had been previously developed for nonvegetated systems, was extended to include a drag coefficient dependent on Reynolds number and vegetation density. The drag coefficient also included the effect of anisotropic permeability of the vegetation. The effects of relatively dense emergent vegetation (~17% by volume) on convective flushing of shallow wetlands with low‐Reynolds number (~100) flow was then investigated using experiments in a laboratory convection tank (0.5 by 2 by 0.1 m) and in a wetland mesocosm (5 by 15 by 1 m). Bottom convective currents of ~1‐10 mm s21 were measured in both the laboratory and the mesocosm. These currents resulted in the shallow, vegetated regions of the mesocosm being flushed in 4 h. The discharge per unit width (m2 s‐1) predicted by the developed parameterization compared favorably (R2 = 0.7) with the discharge per unit width measured in both the laboratory and the mesocosm. The short timescales of convective flushing, even in the presence of reasonably dense vegetation, indicate the likely significance of this mechanism in sheltered wetlands.
Responses of Zn assimilation by coastal plankton to macronutrients
Authors: Wang Wen-Xiong , Dei Robert C. H. , Xu Yan
Published: June 2010

We examined the Zn uptake in marine diatoms and its transfer to marine copepods under different nutrient‐replete and ‐deplete conditions. Zn uptake, quantified by measurements of both total cellular and intracellular Zn accumulation in two coastal diatoms (Thalassiosira pseudonana and Thalassiosira weissflogii), was greatly dependent on the ambient nitrogen conditions. Semicontinuous culture experiments demonstrated that diatom cells accumulated much less Zn with decreasing ambient nitrate concentration. The calculated Zn uptake rate decreased by 1.8 times in T. pseudonana and 1.5 times in T. weissflogii with a decrease in ambient N concentration from 176 µM to 17.6 µM. N‐starved cells also accumulated much less Zn compared with N‐enriched cells. The uptake rate decreased by 2.5–2.6 times when both diatoms were starved of N for 2 d. The intracellular partitioning of Zn in the diatom T. pseudonana was positively related to the ambient N level within the short‐term exposure period (5 h). P starvation, however, resulted in an increase in Zn accumulation in the diatoms, whereas Si starvation did not significantly affect the rate of Zn uptake in diatoms. The trophic transfer was quantified by measurement of Zn assimilation efficiency in two copepods (Calanus sinicus and Acartia spinicauda) feeding on diatoms with a different N quota. Assimilation generally increased with an increase in the N quota of the diatoms. In one experiment (C. sinicus feeding on diatom T. weissflogii), the influence of different N status in diatoms on Zn assimilation by copepods was statistically significant. In contrast, the elimination rate (physiological turnover rate) was independent of the N quota of the cells. Nitrogen enrichment may lead to an increase in Zn uptake and transfer in marine plankton. Our study therefore suggests that there is considerable interaction between macronutrients and Zn uptake by plankton in aquatic systems.
Atlantic climate governs oceanographic and ecological variability in the Barents Sea
Authors: Ottersen Geir , Stenseth Nils Chr.
Published: June 2010

In the arcto‐boreal Barents Sea, temperature variability is an important source for the pronounced year‐to‐year fluctuations in fish recruitment. Sea temperature is closely linked to the volume flux of the relatively warm Atlantic water masses flowing in from southwest, as well as to regional heat exchange with the atmosphere. We examine the relations between Barents Sea temperature, inflow, and North Atlantic scale climate variability. For the last three decades, large‐scale climate forcing statistically has accounted for 75% of the variability in the barotrophic inflow, whereas the North Atlantic Oscillation and sea temperature combined statistically explain 55% of the variability in cod recruitment. Our results suggest a chain‐of‐events relationship between large‐scale atmospheric variability, Barents Sea oceanography and the ecology of this highly productive region.
Multispectral in situ measurements of organic matter and chlorophyll fluorescence in seawater: Documenting the intrusion of the Mississippi River plume in the West Florida Shelf
Authors: Del Castillo Carlos E. , Coble Paula G. , Conmy Robyn N. , Müller‐Karger Frank E. , Vanderbloemen Lisa , Vargo Gabriel A.
Published: June 2010

We performed multispectral, in situ fluorescence measurements of detrital colored organic matter (COM) and chlorophyll a (Chl a) in surface waters of the West Florida Shelf using the Wet Labs spectral absorption and fluorescence instrument (SAFIre). Continuous underway measurements allowed simultaneous mapping of the dispersal pattern of riverine organic material and Chl a on the shelf. We used two fluorescence emission ratios to differentiate between riverine and marine COM. The data showed unusually high concentrations of COM offshore. These were attributed to an offshore extension of the Mississippi River plume. Comparisons between in situ Chl a concentrations measured with the SAFIre and Chl a values obtained from the sea‐viewing wide field‐of‐view sensor (SeaWiFS) satellite data using OC4 and MODIS algorithms showed that, although both algorithms overestimated Chl a, MODIS performed better than OC4, particularly in areas with high COM concentrations. Analysis of the relationship between Chl a and COM concentrations within the study area showed regional variability probably caused by differences in river source.
High chemoautotrophic primary production in Lake Kinneret, Israel: A neglected link in the carbon cycle of the lake
Authors: Hadas Ora , Pinkas Riki , Erez Jonathan
Published: June 2010

Intensive chemosynthetic microbial activity fueled by H2S oxidation with dissolved O2 was measured by 14C fixation in the dark and in presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea in Lake Kinneret waters. This process occurred in water collected below the photic zone (20 m) at the chemocline in the late autumn (November—January) and close to the sediment water interface in May when the chemocline starts to form. Averaged depth integrated chemoautotrophic primary production at the chemocline was 16% and 24% of the photosynthetic primary production during May and autumn, respectively. The maximal rates were measured in December 1992, reaching values of >90% of the photosynthetic rate. The δ13C of particulate organic matter at the chemocline ranged between −27‰ and −39‰, the latter being associated with intensive chemosynthesis. These δ13C values support our earlier hypothesis that chemoautotrophic bacteria constitute, directly or indirectly (through the microbial loop), a 13C depleted food source for the zooplankton in the lake during autumn and early winter. Mass and isotopic balance of carbon and H2S suggest that chemosynthetic productivity may constitute 20%–25% of the primary production in Lake Kinneret annually.
Effect of temperature on diatom volume, growth rate, and carbon and nitrogen content: Reconsidering some paradigms
Authors: Montagnes David J. S. , Franklin Montagnes
Published: June 2010

We examined the response of diatoms to naturally experienced temperatures and tested these hypotheses: (1) diatoms follow the rule that organism size decreases with increasing temperature; (2) diatom growth rate follows a Q10‐like response; (3) diatom carbon (C) and nitrogen (N) content per unit volume (V) decrease with increasing size, and changes in temperature affect this relationship; and (4) diatom C:V is the same as that of other phytoplankton. We also present, as predictive equations, relationships between (1) growth rate, temperature, and size; (2) C content and V; and (3) N content and V. Eight diatoms and two flagellates were acclimated for approximately five generations and grown for approximately five more generations at five temperatures (9–25°deg;C) on a 14 : 10 light : dark cycle at ~50 µmol photons m−2 s−1. Growth rate, cell V, and C and N content per cell were measured; relationships between these parameters and temperature were determined. For five diatoms and both flagellates, cell V decreased with increasing temperature; cells decrease by ~4% of their mean V per °C. Growth rate appeared to increase linearly with temperature in all cases. The literature suggests that a linear response is the rule, not the exception. Temperature did not significantly affect C or N per V of diatom species. When all diatoms were considered, both C and N per V decreased with increasing cell size; our data support the argument that diatoms differ from other protists in this respect, but the difference is less pronounced than stated in previous reports.
Variation in δ15N and δ13C trophic fractionation: Implications for aquatic food web studies
Authors: Zanden M. Jake Vander , Rasmussen Joseph B.
Published: June 2010

Use of stable isotope techniques to quantify food web relationships requires a priori estimates of the enrichment or depletion in δ15N and δ13C values between prey and predator (known as trophic fractionation; hereafter Δδ15N and Δδ13C). We conducted a broad‐scale analysis of Δδ15N and Δδ13C from aquatic systems, including three new field estimates. Carnivores had significantly higher Δδ15N values than herbivores. Furthermore, carnivores, invertebrates, and lab‐derived estimates were significantly more variable than their counterparts ( f‐test, p < 0.00001). Δδ13C was higher for carnivores than for herbivores (p = 0.001), while variances did not differ significantly. Excluding herbivores, the average Δδ15N and Δδ13C were 3.4‰ and 0.8‰, respectively. But even with unbiased fractionation estimates, there is variation in isotopic fractionation that contributes to error in quantitative isotope model outputs. We simulated the error variance in δ15N‐based estimates of trophic position and two‐source δ13C diet mixing models, explicitly considering the observed variation in Δδ15N and Δδ13C, along with the other potential error sources. The resultant error in trophic position and mixing model outputs was generally minor, provided that primary consumers were used as baseline indicators for estimating trophic position and that end member d13C values in dietary mixing models were sufficiently distinct.
Microsatellites reveal high population connectivity in eelgrass (Zostera marina) in two contrasting coastal areas
Authors: Reusch Thorsten B. H.
Published: June 2010

Populations of marine angiosperms, or seagrasses, are at the basis of productive ecosystems thriving in shallow coastal areas around the world. Genetic markers allow important inferences on the connectivity of seagrass populations. Here, I compare the fine scale geographic structure in eelgrass (Zostera marina) at a regional scale (2–60 km) among two adjacent coastal areas, the northern Wadden Sea (N = 8), and the southwestern Baltic (N = 5). Plants were genotyped for eight highly polymorphic microsatellite loci displaying a total of 114 alleles. Consistent with their clonal mode of reproduction, populations in the Baltic were genetically less diverse compared to those in the Wadden Sea, suggesting an effective population size that is half compared to the Wadden Sea. Although I expected more gene flow among populations in the Wadden Sea where abundant seeds can be transported by strong tidal currents, no quantitative difference in population differentiation was detectable between both coastal areas. To the contrary, in the atidal Baltic, nonsignificant genetic differentiation (FST < 0.009) was present up to waterway distances of 54 km, compared to only 33 km in the Wadden Sea. Correlations between genetic and geographic distances were weak in both areas, and significant only in the Wadden Sea. I examined as one potential mechanism responsible for high population connectivity whether the genotypic composition of rafting reproductive shoots differed from resident Baltic populations (N = 2) using assignment tests. At one sampling occasion, at least 130 immigrant seeds m−1 shoreline were identified based on their multilocus genotype. The results have implications for coastal management and restoration and suggest that local population history may be less crucial for explaining seagrass distribution than previously suggested.
Small‐scale shear effects on heterocystous cyanobacteria
Authors: Moisander Pia H. , Hench James L. , Kononen Kaisa , Paerl Hans W.
Published: June 2010

Planktonic, filamentous, heterocystous cyanobacteria form blooms in certain nitrogen‐limited ecosystems but are absent or rare in others that seem to have suitable environmental conditions. We tested the hypothesis that small scale shear affects physiological activities and morphology of heterocystous cyanobacteria in high turbulence environments. Using Taylor‐Couette flow to generate small‐scale shear, we conducted one set of experiments on cultures of two strains of Baltic Sea Nodularia and a complementary set of experiments using natural Baltic Sea phytoplankton assemblages. Experiments were run at various shear durations (1–72 h) and levels (2.2–18 s−1), corresponding to energy dissipation rates in the upper mixed layer from moderate to strong winds. The effect of shear on nitrogenase activity (NA), CO2 fixation, pH, dissolved inorganic carbon, and cyanobacterial filament length was tested. Results from the culture experiments showed that shear had a negative effect on NA and CO2 fixation for both Nodularia strains and that filament length decreased for one of them. The lower limit for shear effects on NA and CO2 fixation appeared to be less than 2.2 s−1. Results from the experiments on natural phytoplankton assemblages from the Baltic Sea showed that both CO2 fixation (reflecting cyanobacterial photosynthetic activity) and NA decreased in response to shear. However, shear did not affect CO2 fixation in the ≪2‐µm size fraction. Aphanizomenon and Anabaena filaments fragmented under shear rates (2.2 s−1, 12 h) that did not affect Nodularia filament length. These results suggest that small‐scale shear imposes a control on cyanobacterial activity and morphology and that this control appears to be genus and species specific.
Grazing rates of bacterivorous protists inhabiting diverse marine planktonic microenvironments
Authors: Artolozaga Itxaso , Valcárcel María , Ayo Begoña , Latatu Ainhoa , Iriberri Juan
Published: June 2010

Bacterivory on aggregates and bulk seawater by three nanoflagellates and a microciliate was investigated. A new approach to measure bacterivory on the attached bacterial community is proposed. Macroaggregates containing attached fluorescently labeled bacteria (FLB) were obtained by adding labeled planktonic bacteria to rolling tanks filled with natural seawater, and they were used to measure protistan grazing rates on the bacteria attached to aggregates. Protistan grazing on free‐suspended bacteria was measured according to the monodispersed FLB uptake technique. The four protists showed low grazing rates when feeding on free‐suspended bacteria at the low densities usually found in seawater. Surprisingly, the analyzed protists also showed low grazing rates when feeding on aggregates despite the very high bacterial densities inhabiting them. The analysis of the influence of prey density on bacterial grazing rates suggests that feeding on bacteria attached to aggregates involves a relevant additional effort when compared to feeding on free‐suspended bacteria. The paradox between these results and the very high abundance of protistan communities usually found in aggregates is discussed attending to the view of aggregates as biological reactors. Therefore, marine macroaggregates can be considered as microniches able to support the maintenance of a protistan community without food limitation, as well as to attract protistan colonizers by generating a water layer enriched in organic matter and bacteria.