bluuebunny/crossref_metadata_2025 huggingface dataset:
Diazotrophic unicellular cyanobacteria in the northwestern Mediterranean Sea: A seasonal cycle
Authors: Le Moal Morgane , Biegala Isabelle C.
Published: January 2011

Unicellular diazotrophic cyanobacteria (UCYN2‐Fix lineage) were detected using whole‐cell hybridization of specific Nitro821 oligonucleotide probe at the coastal and oligotrophic station SOMLIT off Marseilles (France). This station was sampled monthly, for a year and a half (June 2006‐November 2007). The UCYN2‐Fix community was dominated at 99.9% by picoplankters (0.7‐1.5 µm) mainly as free living in the 0.2‐3‐µm size fraction. They were present all the year long with a mean density of 4.6 cell mL−1, except in summer 2006, when concentrations reached 1.9 x 103 cell mL−1 and 5.3 x 103 cell mL−1 in June and July, respectively. During this bloom, picoplanktonic UCYN2‐Fix represented 10.7% of the picocyanobacterial community. The larger size fractions (3‐10 µm and >10 µm) were also dominated (98.9%) by picoplanktonic UCYN2‐Fix cells, associated with inert particles, or dinoflagellates. However, hardly any nanoplanktonic UCYN2‐Fix were detected (0–0.12 cell mL−1), and Trichodesmium sp. was observed only once in summer at low concentration (0.03 trichome mL−1). We hypothesize that a combination of abiotic parameters, such as elevated temperature, absence of nitrate, presence of phosphate, and an exceptionally high urban pollution event, explain the large bloom of potentially diazotrophic picocyanobacteria. Further studies are needed to confirm the identity of these small cells and their role in nitrogen cycle and marine productivity, especially since some effects of climate change (e.g., increased surface warming and upper‐water‐column stratification) may increase their importance in a near future.
Peptide hydrolysis and the uptake of dipeptides by phytoplankton
Authors: Mulholland Margaret R. , Lee Cindy
Published: January 2011

Rates of peptide hydrolysis (using the fluorescent substrate, lucifer yellow anhydride‐labeled tetra‐alanine) and dipeptide uptake (using dually labeled, 15N and 13C, dialanine) were measured in phytoplankton cultures and in natural populations during algal blooms dominated by one or two taxa. During most sampling events, both peptide hydrolysis and dipeptide uptake were greatest in the size fraction containing the dominant phytoplankter, suggesting that phytoplankton contribute substantially to or may even dominate observed extracellular peptide hydrolysis and dipeptide uptake in the environment. These are the first data suggesting that dipeptides may be taken up directly by phytoplankton and this may represent a previously unaccounted‐for nitrogen source in aquatic systems. Like many other processes in phytoplankton, peptide hydrolysis appears sensitive to the diel light cycle and the nutrient environment, with rates varying depending on the dominant N source, but with no clear pattern. Uptake of dialanine, the dominant product of the hydrolysis of the peptide tetra‐alanine, also varied depending on the dominant taxa and the nutrient regime. Most of the time, it appeared that low production of dialanine by tetra‐alanine hydrolysis limited the uptake of the dipeptide. Close coupling between peptide hydrolysis and dipeptide uptake may also help explain the absence of correlations between rates of peptide hydrolysis and the concentration and composition of the free amino acid pool.
Effect of Saharan dust inputs on bacterial activity and community composition in Mediterranean lakes and reservoirs
Authors: Reche Isabel , Ortega-Retuerta Eva , Romera Otilia , Villena Elvira Pulido , Baquero Rafael Morales , Casamayor Emilio O.
Published: January 2011

We assessed the effects of Saharan dust inputs of particulate matter (PM), total phosphorus (TP), total nitrogen, and water soluble organic carbon (WSOC) on bacterial abundance (BA) in two alpine lakes and two reservoirs in the Mediterranean region. We also experimentally assessed the effects of dust inputs on bacterial activity and community composition and explored the presence of airborne bacteria. We found synchronous BA dynamics at least in one of the study years for each corresponding pair of ecosystems, suggesting an external control. The link between BA dynamics and inputs of PM, WSOC, or TP occurred only in those ecosystems with severe P‐limitation and low dissolved organic carbon. The response was most intense in the most P‐limited ecosystem. Dust addition had a significant positive effect on bacterial growth and abundance, but not on richness, diversity, or composition of the indigenous bacterial assemblages. We also obtained experimental evidence that some airborne bacteria could develop in oligotrophic waters by observing the growth of gamma‐proteobacteria, a group poorly represented in natural aquatic environments.
The effect of temperature on the coupling between phosphorus and growth in lacustrine bacterioplankton communities
Authors: Hall Edward K. , Dzialowski Andrew R. , Stoxen Samuel M. , Cotner James B.
Published: January 2011

Phosphorus (P) routinely limits microbial growth in freshwater ecosystems. The growth rate hypothesis (GRH) relates growth to biomass P content mechanistically through changes in ribosomal ribonucleic acid (rRNA). Although the GRH has been shown in cultured bacteria, less well understood is how GRH relationships are affected by interactions with environmental parameters such as temperature. To address this, we evaluated the relationship between bacterial biomass P, RNA: deoxyribonucleic acid (DNA) ratio, and growth rate in 47 northern temperate lakes. Although RNA:DNA ratio was positively correlated with bacterial biomass P : carbon (C), we found no correlation between growth rate and RNA:DNA or between growth rate and biomass P : C. There was, however, a significant effect of temperature on biomass P : C. We investigated the effect of temperature more directly using filter‐separated bacterial communities from two lakes during two seasons while experimentally manipulating temperature and resources. For the summer communities, bacterial production (BP) and biomass P were positively correlated, and the slope of that relationship increased with increasing temperature. In winter communities, BP and biomass P were again positively correlated; however, the slope of that relationship decreased with increasing temperature. The slope of the relationship between BP and biomass P is a metric of nutrient use efficiency and was strongly influenced by temperature. More importantly, bacterioplankton demonstrated seasonal acclimation or adaptation to in situ temperature, suggesting that studies evaluating multiple communities in time and space fail to find a clear relationship between temperature and bacterial metabolism because bacterial communities are locally adapted to in situ temperature.
Quantification of point‐source groundwater discharges to the ocean from the shoreline of the Big Island, Hawaii
Authors: Peterson Richard N. , Burnett William C. , Glenn Craig R. , Johnson Adam G.
Published: January 2011

Aerial thermal infrared imaging has revealed that submarine groundwater discharge (SGD) along the western coast of the Big Island of Hawaii is often focused as point‐source discharges that create buoyant groundwater plumes that mix into the coastal ocean. We quantified the SGD fluxes associated with several plumes using natural geochemical tracers. Offshore transects of 222Rn and 224Ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes, indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area. Using a series of simultaneous mass balance equations for water, salt, and radon, we determined the groundwater fluxes of six plumes near Kona, Hawaii. The average SGD fluxes ranged from 1100 m3 d−1 to 12,000 m3 d−1 of total (fresh + saline) SGD. The fresh (meteoric) groundwater equivalents for the same flows, modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition, ranged from 630 m3 d−1 to 8600 m3 d−1. These fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh SGD rates in this region.
Oxygen depletion in lake hypolimnia
Authors: Rippey Brian , McSorley Catherine
Published: January 2011

The Livingstone and Imboden (1996) model for the oxygen depletion rate in lake hypolimnia was evaluated with field results in 32 lakes. The volumetric oxygen consumption rate (JV) was strongly related to lake trophic state, as represented by the growing season mean chlorophyll a (Chl a) and annual mean total phosphorus concentration, and might reach a maximum of 0.23‐0.24 g O2 m−3 d−1 in eutrophic lakes. The areal oxygen consumption rate (JA) was not related to trophic state and was lower than the value estimated by the sediment core method, particularly in eutrophic lakes; the mean was 0.0816 6 0.0150 g O2 m−2 whole sediment d−1. We modified the model and it was used to confirm that the field JA, the average for the hypolimnion for the deoxygenation period, is influenced by JV and the range of sediment area to water volume ratio, α(Z) (Z is water depth), in the hypolimnion, as well as the oxygen consumption rate in whole sediment (R). It was suggested that this is the reason for the difference between field and sediment core JA values. The R in 10 lakes varied from 7 to 460 g O2 m−3 whole sediment d−1. Overall, the Livingstone and Imboden model with constant JA and with a JV value derived from an empirical relationship with either measure of trophic state was considered to be a suitable condensed model for oxygen depletion in lake hypolimnia.
Decadal diagenetic effects on δ13C and δ15N studied in varved lake sediment
Authors: Gälman Veronika , Rydberg Johan , Bigler Christian
Published: January 2011

To assess the long‐term (27 yr) effects of sediment aging on stable carbon and nitrogen isotope values (δ13C and δ15N), we used a collection of eight freeze cores of annually laminated (varved) lake sediment collected from 1979 to 2007 in Nylandssjon (northern Sweden). Previous research has shown that 20‐23% of carbon and 35% of nitrogen is lost in 27 yr. Material from specific years was compared in the cores, e.g., δ13C and δ15N of the surface varve of the 1979 core was followed in cores retrieved in 1980, 1989, 1993, 2002, 2004, and 2006. δ13C increased by 0.4‐1.5% during the first 5 yr. After this initial increase, only minor fluctuations were recorded. There is a good correlation between the magnitude in δ13C changes and the initial carbon and nitrogen concentrations, indicating that the initial sediment composition is important for the 13C fractionation. δ15N gradually decreased by 0.3‐0.7% over the entire 27‐yr period. The lack of correlation with the initial sediment composition and the gradual decrease in δ15N indicates a microbial control on δ15N change. The diagenetic changes in the stable isotope values that occur in Nylandssjon are small, but of the same magnitude as the down‐core variation in the varves deposited 1950‐2006. Diagenetic effects should be considered when δ13C and δ15N are used to study organic matter sources or paleoproductivity, especially when dealing with recent trends or small changes. Based on our findings, diagenetic effects for δ13C are observed during the first 5‐10 yr, whereas no delimitation can be recommended for δ15N.
Natural isotopic composition of carbon (δ13C) correlates with colony size in the planktonic cyanobacterium Gloeotrichia echinulata
Authors: Vuorio Kristiina , Meili Markus , Sarvala Jouko
Published: January 2011

To assess variability in carbon isotope signatures (δ13C) between and within populations under natural conditions, with a particular emphasis on colony size, we repeatedly collected planktonic colonies of a freshwater cyanobacterium Gloeotrichia echinulata in two lakes, Pyhäjärvi (southwest Finland) and Erken (southeast Sweden). Despite substantial differences in the average δ13C signature of Gloeotrichia between lakes (‐6.9% in Pyhäjärvi and ‐20.7% in Erken), a similar, systematic increase in δ13C with colony size was observed in both lakes (of 2—3% in Pyhäjärvi and 3—5% in Erken). This suggests declining isotope fractionation with increasing colony size, probably related to diffusion limitation of carbon availability. Temporal variation explained a minor fraction of total subsample variability (range δ13C ~4% in Pyhäjärvi and ~6% in Erken). Isotopic 13C fractionation in Gloeotrichia was likely affected both by carbon source and by colony size.
Inferred level of calcification decreases along an increasing temperature gradient in a Mediterranean endemic coral
Authors: Goffredo Stefano , Caroselli Erik , Mattioli Guido , Pignotti Elettra , Dubinsky Zvy , Zaccantia Francesco
Published: January 2011

The correlation between solar radiation and sea surface temperature (SST) and growth was assessed along a latitudinal gradient. Extension rate and skeletal density were both correlated with calcification rate, indicating that calcium carbonate deposition was allocated evenly between skeletal density and linear extension. Unlike most studies on other tropical and temperate corals, in which calcification was positively correlated with solar radiation and SST, in the present study calcification was not correlated with solar radiation, whereas it was negatively correlated with SST. We hypothesize that photosynthesis of the symbiotic algae of Balanophyllia europaea is inhibited at high temperatures, consequently causing an inhibition of calcification. The regressions between calcification and SST predicted that the calcification of B. europaea would be depressed at 20.5–21.0°C mean annual SST. The scenarios of the Intergovernmental Panel on Climate Change conclude that by 2100, SST will exceed this physiological threshold for most of the populations considered in this study. This study comprises the first field investigation of the relationships between environmental parameters and calcification of a Mediterranean coral and highlights the risks of losing Mediterranean marine biodiversity over the course of future decades.
Intense benthic grazing of phytoplankton in a coral reef
Authors: Genin Amatzia , Monismith Stephen G. , Reidenbach Matthew A. , Yahel Gitai , Koseff Jeffrey R.
Published: January 2011

Grazing on phytoplankton by a section of the fringing coral reef in Eilat, the Gulf of Aqaba, Red Sea, was studied using the control‐volume approach, a direct, nonintrusive technique common in engineering studies. Concentrations of chlorophyll a were measured using four vertical arrays of pumps, 10 pumps on each, that defined an imaginary box (i.e., the control volume), extending from the bed to surface, overlying a section of the sloping fore‐reef >100 m2 in size. Concurrent velocity measurements were made at the center of the box using a vertical array of acoustic current meters. Together, the concentration and velocity measurements allowed us to compute phytoplankton fluxes in and out of the control volume. While phytoplankton patchiness and other turbulent variations in concentration introduced significant variability, mass balances of fluxes into and out of the box indicate a flow‐dependent grazing rate of approximately 10 m d−1 to 20 m d−1. This value was larger than, but not statistically different from, values derived from an "a priori estimate" (calculated based on the density and feeding rates of benthic grazers) and an estimate computed from the observed near‐bed gradient of Chl a. Phytoplankton grazing is a principal pathway through which allochthonous nutrients are imported to the reef community from the flowing water.
Hydrodynamic control of phytoplankton loss to the benthos in an estuarine environment
Authors: Jones Nicole L. , Thompson Janet K. , Arrigo Kevin R. , Monismith Stephen G.
Published: January 2011

Field experiments were undertaken to measure the influence of hydrodynamics on the removal of phytoplankton by benthic grazers in Suisun Slough, North San Francisco Bay. Chlorophyll a concentration boundary layers were found over beds inhabited by the active suspension feeders Corbula amurensis and Corophium alienense and the passive suspension feeders Marenzellaria viridis and Laonome sp. Benthic losses of phytoplankton were estimated via both the control volume and the vertical flux approach, in which chlorophyll a concentration was used as a proxy for phytoplankton biomass. The rate of phytoplankton loss to the bed was positively correlated to the bed shear stress. The maximum rate of phytoplankton loss to the bed was five times larger than estimated by laboratory‐derived pumping rates for the active suspension feeders. Reasons for this discrepancy are explored including a physical mechanism whereby phytoplankton is entrained in a near‐bed fluff layer where aggregation is mediated by the presence of mucus produced by the infaunal community.
Using spatial statistics to infer scales of demographic connectivity between populations of the blue mussel, Mytilus spp
Authors: Smith Geneviève K. , Guichard FrÉdÉric , Petrović Filip , McKindsey Christopher W.
Published: January 2011

We conducted a large‐scale survey of blue mussel (Mytilus spp.) populations and recruitment along 100 km of the Southern shore of the St. Lawrence Estuary, QuÉbec, Canada. By taking advantage of the residual downstream current of our study system, we used cross‐covariance analysis to test the hypothesis that postrecruitment and larval supply processes result in a positive relationship between local adult abundance and recruitment. We found no evidence of within‐site correlation between adults and recruits. Alternatively, we hypothesized that demographic connectivity between populations would result in a positive covariance between adult abundance and recruitment at downstream sites separated by the average dispersal distance. We observed significant positive cross‐covariance between sites separated by 12‐18 km and 24‐30 km. These results provide the first direct quantification of demographic connectivity between adult production and larval recruitment of Mytilus using simple survey data. The approach developed here measures connectivity over ecological time scales, and thus may be used to monitor temporal fluctuations in dispersal patterns.
Seasonal disturbance to mussel beds: Field test of a mechanistic model predicting wave dislodgment
Authors: Carrington Emily , Moeser Gretchen M. , Dimond James , Mello Joseph J. , Boller Michael L.
Published: January 2011

We report the first field confirmation of a mechanistic model predicting fine‐scale temporal dynamics of wave dislodgment, an important disturbance process structuring many temperate rocky intertidal communities. A biomechanical approach is used to predict the frequency and severity of mussel dislodgment from wave‐swept shores in Rhode Island over a 3‐yr period. Using inputs of wave height and mussel attachment, the model correctly predicts strong dislodgment events during hurricane season (August to October, ~10% monthly loss), a period when large waves coincide with relatively weak mussel attachment. Such a mechanistic approach, incorporating temporal variation in both environmental challenges and physiological tolerances, is necessary to predict patterns of environmental stress; such predictions cannot be made from environmental forecasts alone. In addition to wave dislodgment, we report substantial mussel mortality due to temperature stress (up to 50% monthly loss). These two physical agents, which caused equivalent mussel mortality in our 3‐yr study, are likely to be influenced by future global climate shifts.
An evaluation of iron bioavailability and speciation in western Lake Superior with the use of combined physical, chemical, and biological assessment
Authors: Hassler Christel S. , Havens Sonya M. , Bullerjahn George S. , McKay R. Michael L. , Twissa Michael R.
Published: January 2011

An iron‐dependent cyanobacterial bioreporter (Synechococcus strain KAS101) was used in unison with size‐fractionated iron content (>0.45, <0.45, <0.02 µm), and chemical characterization of iron complexation (C18 resin column) to elucidate the bioavailable forms of iron present in Lake Superior during periods of inverse thermal stratification (May) and strong thermal stratification (September) of the water column. The results provide evidence of organic complexation of iron in Lake Superior waters. Iron in most sampled water was complexed by organic compounds that behaved like fulvic acids, whereas some samples showed evidence for the presence of siderophore‐like compounds. The presence of dissolved organic matter suppressed the cellular luminescence of the bioreporter, indicating an increased iron bioavailability. This effect could result either from the presence of siderophores forming iron complexes that are bioavailable to the bioreporter, or from more indirect effects because of the presence of other organic compounds, such as fulvic acids or polysaccharides. Model ligand additions, iron bioaccumulation, and photo‐oxidation of dissolved organic matter were used to assess the bioavailability of organically complexed iron to the bioreporter. A significant fraction of the iron (40‐100%) was bioavailable to the bioreporter. Iron bioavailability was high enough for the bioreporter not to be iron limited in the water collected from Lake Superior. This measure of bioavailability to picocyanobacteria is relevant because picoplankton accounted for the majority of chlorophyll a in Lake Superior during this study.
Barium and molybdenum records in bivalve shells: Geochemical proxies for phytoplankton dynamics in coastal environments?
Authors: ThÉbault Julien , Chauvaud Laurent , L'Helguen StÉphane , Clavier Jacques , Barats AurÉlie , Jacquet SÉverine , PÉcheyran Christophe , Amouroux David
Published: January 2011

Barium : calcium and molybdenum : calcium ratios were investigated in shells of the tropical scallop Comptopallium radula. Three juvenile specimens were harvested alive in the southwest lagoon of New Caledonia after a 1‐yr hydrological survey. Calcite samples representing a few hours of biomineralization were laser‐ablated along the maximal growth axis and analyzed for Ba and Mo content with an inductively coupled plasma mass spectrometer. Absolute dates of shell precipitation assigned on the basis of periodic formation of shell growth patterns led to the accurate reconstruction of ontogenetic variations of elemental ratios with subweekly resolution. Interindividual variability of Ba : Ca and Mo: Ca time series was low, indicating an environmental control on the incorporation of these elements within shells. Both profiles were characterized by a background level punctuated by sharp peaks. The ingestion of diatoms enriched in Ba (adsorbed on iron oxyhydroxides associated with the frustules) is the most likely cause of the formation of Ba : Ca peaks. Some contribution of diatom‐associated barite is also possible. In every instance, Ba : Ca would possibly be a proxy for the timing and magnitude of diatom blooms. Among all the theories that could be advanced to explain the occurrence of Mo: Ca peaks, the most plausible appears to be the ingestion of phytoplankton cells grown on NO3−, and therefore containing high levels of Mo required for the activity of nitrate reductase. If this is so, then Mo: Ca could be a new proxy for nitrate uptake by phytoplankton in coastal ecosystems, helping to reconstruct the balance between new and regenerated production in paleoenvironments.
Thresholds of gross primary production for the metabolic balance of marine planktonic communities
Authors: Duarte Carlos M. , Regaudie-de-Gioux Aurore
Published: January 2011

The notion that less productive marine planktonic communities tend to be heterotrophic was tested by synthesizing reported estimates of the relationships between the net community production or community respiration and gross primary production (GPP), allowing calculation of the threshold GPP separating less productive, heterotrophic communities from more productive, autotrophic ones. A total of 35 estimates of the threshold GPP were assembled, derived from reports of comparative analyses of individual regions (Mediterranean Sea, Atlantic Ocean, Southern Ocean, Pacific Ocean, and Indian Ocean) and global comparative analyses for open‐ocean and coastal environments, time‐series analyses of changes in planktonic metabolism at individual locations, experimental manipulations in mesocosms, and a semi‐empirical modeling exercise. Planktonic communities of the open ocean and continental shelf showed threshold GPP values ranging 30‐fold, from 0.34 mmol O2 m−3 d−1 to 9.45 mmol O2 m−3 d−1, with those for estuarine and coastal locations reaching 50.60 mmol O2 m−3 d−1. Antarctic and ultra‐oligotrophic ecosystems showed the lowest threshold GPP values (<2.2 mmol O2 m−3 d−1), with a general consistency across approaches for a given ecosystem. Plankton community respiration in the absence of or under low primary production is not negligible and is supported by semi‐labile dissolved organic carbon. The analysis of GPP thresholds suggests that allochthonous organic inputs to the less productive regions of the ocean must be in the order of mmol O2 m−3 d−1, consistent with recent estimates of allochthonous inputs of organic carbon to the ocean.
Climatic forcing of zooplankton dynamics is stronger during low densities of planktivorous fish
Authors: Stige Leif Chr. , Lajus Dmitry L. , Chan Kung-Sik , Dalpadado Padmini , Basedow SÜnnje L. , Berchenko Igor , Stenseth Nils Chr.
Published: January 2011

We analyze interannual variation in zooplankton biomass in the southwestern Barents Sea in spring (May) and summer (June‐July) 1959–1993. Using a threshold modeling approach, we quantify spatial, climatic, and across‐season autoregressive effects under contrasting regimes of low and high densities of planktivorous fish (capelin and herring). Main findings: (1) zooplankton biomass is mainly influenced by capelin feeding, first in the offshore parts of the western Barents Sea in spring and subsequently farther east and north in summer, whereas direct effects of herring are quantitatively less important; (2) effects of climate are stronger during the zooplankton increase phase in spring than in summer and are better predicted using the North Atlantic Oscillation index than using reconstructed sea surface temperature and Atlantic water influx; (3) regional anomalies in zooplankton biomass persist from spring to summer but not from summer to the subsequent spring, indicating that the observed fluctuations have little effect on next year's dynamics; and (4) effects of climatic variation and planktivorous fish interact: climatic (and autoregressive) effects are mainly evident when and where the effect of feeding is weak. Zooplankton dynamics thus appear to be under shifting top‐down and climatic control, the relative importance of the two processes varying spatially, seasonally, and interannually.
Death by dissolution: Sediment saturation state as a mortality factor for juvenile bivalves
Authors: Green Mark A. , Waldbusser George G. , Reilly Shannon L. , Emerson Karla , O'Donnell Scott
Published: January 2011

We show that death by dissolution is an important size‐dependent mortality factor for juvenile bivalves. Utilizing a new experimental design, we were able to replicate saturation states in sediments after values frequently encountered by Mercenaria mercenaria in coastal deposits (Ωaragonite = 0.4 and 0.6). When 0.2‐mm M. mercenaria were reared in sediments at Ωaragonite = 0.4 and 0.6, significant daily losses of living individuals occurred (14.0% and 14.4% d−1, respectively), relative to supersaturated‐control sediments (3.9% d−1). For 0.4‐ mm M. mercenaria, significant mortality occurred under the most undersaturated conditions (Ωaragonite = 0.4, mortality = 9.6% d−1), although mortality at Ωaragonite = 0.6 was not significant (mortality= 2.7% d−1; control‐saturated mortality = 0.2% d−1). For the largest size‐class investigated, 0.6 mm, we show significant mortality for clams under the most undersaturated sediments (Ωaragonite = 0.4, 2.8% d−1). To test if buffered sediments would increase survivorship of juvenile bivalves during periods of recruitment, we manually manipulated sediment saturation state by adding crushed Mya arenaria shell to a mud flat in West Bath, Maine, U.S.A. Although we increased the average sediment saturation state within retrieved cores from Ω = 0.25 ± 0.01 to only 0.53 ± 0.06, numbers of live M. arenaria in buffered sediment increased almost three‐fold in 2 weeks. Buffering muds against the metabolic acids that cause lowered saturation states may represent a potentially important management strategy to decrease dissolution mortality.
Seasonal variation in consumption of benthic bacteria by meio‐ and macrofauna in an intertidal mudflat
Authors: Pascal Pierre-Yves , Dupuy Christine , Richard Pierre , Mallet Clarisse , telet Eric Armynot du Châ , Niquilb Nathalie
Published: January 2011

The trophic fate of benthic bacteria in an intertidal mudflat (Brouage, Marennes‐Oléron, France) was evaluated in situ, and environmental parameters that potentially influence the consumption of bacteria by the most abundant organisms of the meio‐ and macrofauna were identified. Variations in grazing rates were estimated using 15N pre‐enriched bacteria at different temporal and spatial scales on a cross‐shore transect over the mudflat. Grazing incubations were performed in microcosms with freshly collected grazers. Environmental factors varied more by season than by day or sampling station. Bacterial uptake by grazers did not appear to be strongly influenced by abiotic factors and was not linked to bacterial abundance. Algal abundance was negatively correlated with bacterivory in both the nematode community and the foraminifer Ammonia tepida, suggesting that bacteria constitute an alternative resource that is consumed when algae are less abundant. Bacteria were mainly ingested by the mudsnail Hydrobia ulvae and secondarily by nematodes with grazing rates of copepods and A. tepida being considerably lower. The estimated grazing in the upper and middle part of the mudflat represented 7% and 28% of bacterial production, respectively. In the lower mudflat, daily grazing never represented >3% of bacterial production throughout the year. Consequently, grazing appears to be a minor factor in the regulation of bacterial production. Bacterivory did not vary clearly according to season; consequently, the fate of bacteria in this benthic food web is poorly structured by season.
Benthic community structure and spatiotemporal thermal regimes in two upwelling ecosystems: Comparisons between South Africa and Chile
Authors: Wieters Evie A. , Broitman B. R. , Brancha G. M.
Published: January 2011

On the basis of 16‐yr satellite time series (1987–2003) of sea surface temperature (SST) and using univariate and multivariate statistical techniques, we quantified patterns of fluctuation in oceanographic conditions, as well as their spatial structure along the coasts of South Africa and Chile between 29.0° and 34.5°S. Since variations in environmental conditions over multiple timescales are driven by oceanographic‐atmospheric processes modulated by coastal morphology, all of which affect in different ways coastal organisms, we hypothesized that dynamic properties of the environment contribute to characteristic patterns on rocky intertidal biomass structure across upwelling ecosystems. Although long‐term mean temperatures were similar between coasts, the relative importance of annual, semiannual, intraseasonal, and high‐frequency SST fluctuations differed; South Africa is more strongly pulsed over shorter timescales. Similar spatial discontinuities in thermal regimes were observed, with changes at about 32°S. Multivariate summaries of benthic community structure derived from functional group biomasses revealed striking differences between South Africa and Chile, as well as between regions north and south of 32°S within each ecosystem. Between‐continent and regional‐scale differences in community structure were largely unrelated to mean SST, but correlated with the different measures of temporal variance in SST. For all functional groups, as well as aggregate measures of benthic community composition, the weekly to annual SST fluctuations explained large fractions (>35%) of biological variability. Results highlight the importance of quantifying the temporal variance of regimes of hydrographic conditions since multispecies assemblages are expected to respond in different ways to the driving oceanographic processes behind these fluctuations.
Identification of phytodetritus‐degrading microbial communities in sublittoral Gulf of Mexico sands
Authors: Gihring Thomas M. , Humphrys Mike , Mills Heath J. , Huette Markus , Kostka Joel E.
Published: January 2011

We identified microbial taxa that catalyze phytodetritus degradation and denitrification in permeable coastal sediments of the northeast Gulf of Mexico. Stable isotope probing experiments were used to track the assimilation of isotopically labeled substrate into bacterial deoxyribonucleic acid (DNA) and directly link the taxonomic identification of benthic microorganisms with particulate organic matter degradation and denitrification activity. Phytodetritus deposition events were simulated in the laboratory by the addition of 13C‐enriched, heat‐killed Spirulina cells to intact sediment core incubations. Immediate increases in O2 consumption (3‐fold), N2 efflux (16‐fold), and dissolved inorganic nitrogen efflux were observed after phytodetritus addition relative to unamended treatments, suggesting that the benthic microbial community was poised to immediately begin oxidizing deposited organic matter. Analyses of 16S ribosomal ribonucleic acid gene sequences amplified from 13C‐enriched DNA fractions demonstrated that members of the Gammaproteobacteria (Vibrionales and Alteromonadales), Deltaproteobacteria, Actinobacteria, Verrucomicrobia, and Planctomycetes metabolized the phytodetritus amendment. Terminal restriction length polymorphism analyses showed increases in the relative abundance of Gammaproteobacteria, Planctomycetes, and Bacteroidetes with phytodetritus addition. Alphaproteobacteria were identified as metabolically active denitrifiers by phylogenetic analysis of nitrous oxide reductase gene sequences from 13C‐enriched DNA fractions. This study provides the first identification of microorganisms responsible for organic matter degradation in marine sediments by DNA sequence analysis. Microbial assemblages recognized for high‐molecular‐weight organic matter oxidation in the marine water column were important in catalyzing these processes in permeable sediments.
Close coupling between phytoplankton growth and microzooplankton grazing in the western South China Sea
Authors: Chen Bingzhang , Liu Hongbin , Landry Michael R. , DaI Minhan , Huang Bangqin , Sune Jun
Published: January 2011

We conducted 28 dilution experiments during August‐September 2007 to investigate the coupling of growth and microzooplankton grazing rates among ultraphytoplankton populations and the phytoplankton community and their responses to habitat variability (open‐ocean oligotrophy, eddy‐induced upwelling, and the Mekong River plume) in the western South China Sea. At the community level, standing stocks, growth, and grazing rates were strongly and positively correlated, and were related to the higher abundance of larger phytoplankton cells (diatoms) at stations with elevated chlorophyll concentration. Phytoplankton growth rates were highest (>2 d−1) within an eastward offshore jet at 13°N and at a station influenced by the river plume. Among ultraphytoplankton populations, Prochlorococcus dominated the more oceanic and oligotrophic stations characterized by generally lower biomass and phytoplankton community growth, whereas Synechococcus became more important in mesotrophic areas (eddies, offshore jet, and river plume). The shift to Synechococcus dominance reflected, in part, its higher growth rates (0.87 ± 0.45 d−1) compared to Prochlorococcus (0.65 ± 0.29 d−1) or picophytoeukaryotes (0.54 ± 0.50 d−1). However, close coupling of microbial mortality rates via common predators is seen to play a major role in driving the dominance transition as a replacement of Prochlorococcus, rather than an overprinting of its steady‐state standing stock.
Bacterial diversity and morphology in deep ultraoligotrophic Andean lakes: The role of UVR on vertical distribution
Authors: Corno Gianluca , Modenutti Beatriz E. , Callieri Cristiana , Balseiro Esteban G. , Bertoni Roberto , Caravatia Emanuele
Published: January 2011

We investigated the community composition and the relative size‐shape distribution of bacterial assemblages in deep transparent lakes, where bacteria may be affected by harmful ultraviolet radiation (UVR). Summer samples of the euphotic zones of nine ultraoligotrophic lakes located in different drainage basins between 40°27' and 42°49'S in the North Andean Patagonia were analyzed for relative diversity by denaturating gradient gel electrophoresis and the bacterial morphology (free‐living cocci and rods vs. filamentous forms) in relation to environmental factors (UVR, photosynthetically active radiation, temperature, nutrients, nanoflagellates, and ciliate abundances). The overall bacterial community composition was similar in all lakes and over depth in each lake. In contrast, the relative proportion of filaments to total bacterial biovolume was higher in the upper layers, which have higher UVR intensities (305‐340 nm). Lakes with lower Κd305 (diffuse extinction coefficient, 305 nm) showed a greater proportion of filaments. Filament mean length in the upper layers was also significantly greater than at deeper levels. There was a significant correlation between UVR and filament proportion, whereas neither nanopredator abundances (nanoflagellates and ciliates), nor predation pressure, nor resources (dissolved nutrients) could explain the high proportion of filamentation in the near‐surface layers. We propose that UVR plays a decisive role stimulating bacterial filamentation, particularly in lakes with high UVR penetration.
Exceptional mixing events in meromictic Lake Lugano (Switzerland/Italy), studied using environmental tracers
Authors: Holzner C. P , Aeschbach-Hertig W. , Simona M. , Veronesi M. , Imboden D.M. , Kipfer R
Published: January 2011

The deep northern basin of Lake Lugano was permanently stratified over the last 4 decades because of mineralization in response to strong eutrophication. However, two consecutive cold and windy winters (2004‐2005 and 2005–2006) destabilized the water column and led to two exceptionally strong mixing events. The conductivity, temperature, and depth time‐series data from 1995 to 2006 allowed the reconstruction of the evolution of the water body that made deep convective mixing possible. Over the years 1995‐2006, the stability of the water column decreased continuously in winter, reaching a neutral stability at the end of the study period. The Schmidt stability values observed in the winters of 2004–2005 and 2005–2006 were virtually zero. Analyses of helium isotopes, tritium, sulfur hexafluoride, and chlorofluorocarbons in water samples collected immediately after the two mixing events revealed large changes in the tracer concentration profiles and permitted comparisons of the apparent water ages in Lake Lugano with previous measurements. Tracer concentration profiles became more homogeneous and approached atmospheric equilibrium concentrations in the time series. The tracer data, along with changes observed in the physical parameters of the water column, demonstrate the considerable deepwater renewal and gas exchange with the atmosphere that has taken place.
Species specific encystment patterns in three Baltic cold‐water dinoflagellates: The role of multiple cues in resting cyst formation
Authors: Kremp Anke , Rengefors Karin , Montresorc Marina
Published: January 2011

The relationships among cellular nutrient status, environmental conditions (temperature and nutrient availability), and cyst production were studied in batch cultures of three cold‐water dinoflagellates (Scrippsiella hangoei, Gymnodinium corollarium, and Woloszynskia halophila) isolated from the Baltic Sea. We tested the effect of increasing temperature while providing nutrient‐replete conditions as well as the effect of ambient nutrient (N, P) deficiency. The results revealed different encystment cues and patterns in the three species. While depletion of ambient nitrogen and subsequent internal N stress were the primary factors behind cyst production of G. corollarium, higher temperature led to substantial encystment of S. hangoei and W. halophila without a direct link to cellular nutrient physiology. In W. halophila, N limitation induced a transition of the population to small cells presumably representing gametes, but this process was not followed by cyst formation. Phosphorus stress was not directly linked to cyst formation in any of the species. Our data indicate that both reliable token cues (such as temperature) and ultimate causes (for example, nutrient depletion) for encystment are likely involved in the cystformation process. Such duality might provide an explanation for multiple triggers inducing encystment in laboratory settings and the lack of evidence for a direct relationship between nutrient depletion and cyst formation in the field.
Accumulation of prokaryotic remains during organic matter diagenesis in surface sediments off Peru
Authors: Lomstein Bente Aa. , Niggemann Jutta , Jørgensen Bo B. , Langerhuusa Alice T.
Published: January 2011

Bacterial biomarkers (D‐amino acids and muramic acid) were investigated in surface sediments (0–1 cm) at 22 stations in the Peru margin. Concentrations were used to quantitatively estimate the relative importance of peptidoglycan in the preservation of prokaryotic remains during diagenesis. The bacterial imprint in organic matter was also evident from low molar ratios (average of 1.6) of glucosamine and galactosamine. Estimates of the fraction of biomarkers associated with intact peptidoglycan showed that peptidoglycan became a progressively less important component of prokaryotic remains with ongoing diagenesis, whereas other prokaryotic biomolecules increased in importance. The exact nature of these biomolecules remains unknown, but constant ratios between individual D‐amino acids and amino sugars observed in this study provide novel information on their molecular composition. Examination of total hydrolyzable amino acids revealed systematic compositional changes with increasing water depth and age of the sediment, reflecting increased diagenetic alteration of the organic matter. The time scale integrated in the upper 1 cm of the sediment was ca. 2 yr at the shallow sites and up to 20 yr at the deeper stations. The alteration stages of organic matter ranged from coastal and ocean margin sediments at shallow water depth to organic matter as degraded as hemipelagic surface sediments at greater water depths.
UV‐enhanced fish predation and the differential migration of zooplankton to UV radiation and fish
Authors: Leech Dina M. , Boeing Wiebke J. , Cooke Sandra L. , Williamson Craig E. , Torres Lisette
Published: January 2011

The intensity and spectral composition of visible light are known to influence fish predation on zooplankton. However, in clear‐water systems, ultraviolet (UV) radiation (UVR) may also influence fish predation, directly through UV‐enhanced foraging, indirectly through alterations in predator‐prey overlap, or in a combination of the two. Here we test the hypothesis that UVR facilitates fish predation on zooplankton in an oligotrophic lake. Experiments were conducted in 2.2‐m‐long UV‐transparent or UV‐blocking columns suspended in the epilimnion. Zooplankton consumption by young‐of‐the‐year (YOY) largemouth bass (Micropterus salmoides) was compared in the presence and absence of UVR, and the vertical distributions of prey were quantified across light and fish treatments. In addition, a separate experiment was conducted to examine zooplankton vertical responses to UV exposure vs. fish kairomones. Overall, YOY predation on zooplankton was higher in the presence than in the absence of UVR, particularly on diaptomid copepods. This result was only partially explained by zooplankton migratory behaviors, suggesting UV‐enhanced searching capabilities in YOY bass. Furthermore, diaptomids displayed a stronger vertical behavioral response to fish kairomones than to UVR whereas Daphnia exhibited a stronger response to UVR.
Upstream resource abundance determines the food searching behavior of a stream grazer: Effect of microalgal cues
Authors: Katano Izumi , Doi Hideyuki , Oishi Tadashi
Published: January 2011

To maximize their growth, grazers should shift their behavior to balance the cues from predators and periphyton in the field. As a stream grazer seeks periphyton that are heterogeneously distributed, a shift in its behavior on the basis of the intensity of microalgal cues would be beneficial as it would allow the grazer to feed on more periphyton. Using a caddisfly grazer, Glossosoma larvae, we conducted a laboratory channel experiment with upstream experimental plates having four levels of periphyton abundance (control, low, medium, and high), and we recorded the movement behavior of the larvae. As periphyton abundance increased, both larval crawling time and the total crawling distance to the periphyton patch significantly decreased and the directness of the crawling path significantly increased. That is, larvae crawled in various directions as they approached a relatively low‐abundance periphyton patch, whereas they crawled straight to the high‐abundance periphyton patch in a short time. The behavior change was likely due to the detection of some microalgal cue, which should intensify with an increase in upstream periphyton abundance.
Rates of overgrowth by macroalgae and attack by sea anemones are greater for live coral than dead coral under conditions of nutrient enrichment
Authors: Liu Pi-Jen , Lin Shiue-Ming , Fan Tung-Yung , Meng Pei-Jie , Shao Kwang-Tsao , Lina Hsing-Juh
Published: January 2011

A mesocosm experiment was conducted to determine the effects of nutrient enrichment on competitive interactions between a hard coral, a green alga, and a sea anemone. In the low‐nutrient controls, abundances of the green alga, Codium edule, and a sea anemone, Mesactinia genesis, remained low, and they coexisted with the live or dead scleractinian coral, Acropora muricata. Combined nitrogen and phosphorus additions markedly increased the photosynthetic efficiencies of zooxanthellae in A. muricata, the coverage of C. edule, and the asexual reproduction by M. genesis. After 35 d of nutrient addition, C. edule had begun to overgrow live A. muricata, but not dead coral. A. muricata finally died after 105 d, after being totally overgrown by C. edule. Within a few days of contact with live A. muricata, M. genesis was observed for the first time to have induced inflation of modified marginal aggressive organs known as acrorhagi tentacles, which it uses to attack neighboring coral. Nevertheless, M. genesis was not observed to attack C. edule, but moved away from it in the nutrient‐enriched tanks. The hierarchy of competitive superiority under nutrient enrichment was in the order of C. edule > M. genesis > A. muricata. From this experiment, it was evident that nutrient enrichment inhibits corals' ability to compete with sea anemones and algae in Nanwan Bay, southern Taiwan.