bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for the role of methane‐derived carbon in a free‐flowing, lowland river food web
Authors: Trimmer Mark , Hildrew Alan G. , Jackson Michelle C. , Pretty James L. , Grey Jonathan
Published: January 2011

We measured the δ13C values of dominant primary consumers and their potential food sources in a groundwater‐fed lowland river. The δ13C of most consumers, such as Gammarus and Simulium, reflected that of the dominant forms of photosynthetic production, whereas the cased larvae of two caddis flies (Agapetus and Silo) were consistently 13C depleted (mean δ13C: ‐41.2% and ‐40.4%, respectively) throughout the year. The river water was supersaturated (approximately 50 times atmospheric) with methane, reflecting both supersaturation in the groundwater and local production in fine sediments. We measured appreciable rates of methane oxidation, relative to water only controls, in the biofilms on gravel, on the caddis fly cases, and on the bottom of larger rocks. In addition, there was a marked difference in the ratio of methane‐oxidizing potential to chlorophyll across those substrata. This ratio was below detection in the biofilm (i.e., no methane oxidation) on the tops of rocks, greater on the bottom of rocks, and maximal for the gravels and the caddis cases. If the caddis larvae acquire most of their carbon by grazing the tops of such rocks (where they are normally found), then they must acquire their depleted δ13C values by occasionally grazing biofilm where the ratio of methane oxidation to chlorophyll was much greater, and the most likely candidate is from their own or conspecific cases. Grazing methane‐oxidizing bacteria could provide the caddis larvae with up to 30% of their carbon, which could represent a true subsidy from an ancient groundwater source.
Variability of biological production in low wind‐forced regional upwelling systems: A case study off southeastern Australia
Authors: Nieblas Anne-Elise , Sloyan Bernadette M. , Hobday Alistair J. , Coleman Richard , Richardsone Anthony J.
Published: January 2011

Temporal variability of upwelling activity and primary production is examined for a southeastern Australian upwelling system off the Bonney Coast (36.5°S‐38.5°S, 138°E‐142°E). Three indices of upwelling activity and primary production are developed based on alongshore wind stress, upwelling plume area (anomalous sea surface temperature), and primary productivity of the upwelling plume (approximated using anomalous chlorophyll a concentration). The majority of the upwelling activity occurs during the austral summer upwelling season from November to March. Interannual variability in the wind forcing for this region shows marginal correspondence to El Nino‐Southern Oscillation variability. Intraseasonal variability followed four distinct phases within the upwelling season of "onset," "sustained," "quiescent," and "downwelling" periods. The Bonney Upwelling is a predictable regional system with temporal variability of its physical forcing that is similar to larger, more intensely studied coastal wind‐driven upwelling systems. However, we find that the Bonney Coast is a low wind‐forced upwelling region compared to other upwelling systems. Simple linear quantitative models developed between upwelling activity predictors (wind and upwelling plume area) and the biological response (chlorophyll a) explain 40‐50% of the seasonal variability of approximated phytoplankton productivity along the Bonney Coast. As primary productivity in a low‐wind system is not affected by the deleterious effects of turbulence and advection, these simple models are able to predict chlorophyll variability in the Bonney region. Models developed in this study provide a method of assessing the effect of decadal or longer variability of chlorophyll concentration in low wind‐forcing upwelling systems at regional and global scales.
Regional variation in oceanographic conditions influences intertidal fish assemblage structure
Authors: Ritter Amy F.
Published: January 2011

I investigated the relationship between regional variation in habitat and oceanographic conditions and the population and assemblage structure of intertidal fishes (the sculpins Clinocottus globiceps, Clinocottus recalvus, and Oligocottus snyderi) throughout the spring and summer in 2001, 2002, and 2003. The assemblage structure of intertidal sculpins varied markedly with distance from an upwelling center: warmer sites in the northern Monterey Bay that were furthest from upwelling activity were dominated by C. recalvus, whereas cooler sites north of the bay closest to upwelling activity were dominated by O. snyderi and C. globiceps. Interestingly, species were spatially distributed according to temperature differences as would be predicted by the geographic distributions and temperature sensitivity of each species: C. recalvus is a more southerly species tolerant of warmer temperatures, whereas O. snyderi and C. globiceps have more northerly geographic distributions and are relatively less tolerant of warmer water conditions. Regional variation in adult and juvenile assemblage structure reflected differences in recruitment rates among species, suggesting that regional differences in assemblage structure of these intertidal fishes are influenced greatly by pre‐recruitment processes. In addition, possible limited larval exchange between the two regions — due to a combination of unique larval behavior of intertidal sculpins and the persistence of an upwelling front that acts as a barrier to larval dispersal — may serve to reinforce these patterns. The spatial differences in the assemblage structure of intertidal sculpins within this region are caused by a combined influence of variation in oceanographic conditions affecting both larval and benthic phases.
Simulation of multiannual thermal profiles in deep Lake Geneva: A comparison of one‐dimensional lake models
Authors: Perroud Marjorie , Goyette Stéphane , Martynov Andrey , Beniston Martin , Annevillec Orlane
Published: January 2011

In this study, we report on the ability of four one‐dimensional lake models to simulate the water temperature profiles of Lake Geneva, the largest water body in Western Europe, over a 10‐yr period from 1996 to 2005, using lake models driven by a common atmospheric forcing. These lake models have already demonstrated their capability of reproducing the temperature distribution in smaller lakes and include one eddy‐diffusive lake model, the Hostetler model; a Lagrangian model, the one‐dimensional Dynamic Reservoir Simulation Model "DYRESM" a к ‐ ε turbulence model, "SIMSTRAT"; and one based on the concept of self‐similarity (assumed shape) of the temperature‐depth curve, the Freshwater Lake model "FLake." Only DYRESM and SIMSTRAT reproduce the variability of the water temperature profiles and seasonal thermocline satisfactorily. In layers in which thermocline variability is greatest, the temperature root mean square error is ≪2°C and 3°C (at the time of highest stratification) for these models, respectively. It is possible to apply certain one‐dimensional lake models that simulate the behavior of temperature to investigate the potential future warming of the water column in Lake Geneva. Importantly, the metalimnion boundary is successfully modeled, which represents an encouraging step toward demonstrating the feasibility of coupling biogeochemical modules, such as, for example, a phytoplanktonic model, to assess the possible biological responses within lakes to climate change.
Physiology, growth, and development of larval krill Euphausia superba in autumn and winter in the Lazarev Sea, Antarctica
Authors: Meyer Bettina , Fuentes Veronica , Guerra Citlali , Schmidt Katrin , Atkinson Angus , Spahic Susanne , Cisewski Boris , Freier Ulrich , Olariaga Alejandro , Bathmanna Ulrich
Published: January 2011

The physiological condition of larval Antarctic krill was investigated during austral autumn 2004 and winter 2006 in the Lazarev Sea. The condition of larvae was quantified in both seasons by determining their body length (BL), dry weight (DW), elemental and biochemical composition, stomach content analysis, and rates of metabolism and growth. Overall the larvae in autumn were in better condition under the ice than in open water, and for those under the ice, condition decreased from autumn to winter. Thus, growth rates of furcilia larvae in open water in autumn were similar to winter values under the ice (mean, 0.008 mm d−1), whereas autumn underice values were higher (0.015 mm d−1). Equivalent larval stages in winter had up to 30% shorter BL and 70% lower DW than in autumn. Mean respiration rates of winter larvae were 43% lower than of autumn larvae. However, their ammonium excretion rates doubled in winter from 0.03 to 0.06 µg NH4 DW−1 h−1, resulting in mean O:N ratios of 46 in autumn and 15 in winter. Thus, differing metabolic substrates were used between autumn and winter, which supports a degree of flexibility for overwintering of larval krill. The larvae were eating small copepods (Oithona spp.) and protozoans, as well as autotrophic food under the ice. The interplay between under‐ice topography, apparent current speed under sea ice, and the swimming ability of larval krill is probably critical to whether larval krill can maintain position and exploit suitable feeding areas under the ice.
Role of dispersal in shaping communities of ciliates and heterotrophic flagellates within riverine biofilms
Authors: Wey Jennifer K. , Norf Helge , Arndt Hartmut , Weitere Markus
Published: January 2011

We tested the role of immigration from the plankton on the structure of local surface‐associated communities of ciliates and heterotrophic flagellates (HF) in flow cells fed with fresh riverine water (Rhine, Germany). By applying size fractionation, we reduced the immigration potential of HF from the plankton in mature, pregrown biofilms by 93%, and observed no significant effects on the abundance and taxonomic composition of HF. Compared with a treatment with natural plankton density, a 100% reduction in the number of planktonic cells flowing over mature biofilms resulted in a reduced total abundance of ciliates, although only slight effects on the relative composition of present morphospecies were detectable. When starting with sterile flow cells, we found an initial linear increase in HF abundance proportional to their planktonic abundance; additionally supplemented planktonic bacteria showed that this initial colonization rate was resource independent. The initial phase was followed by an exponential increase, which was also independent from the resource level and strongest when initial colonization was low. In contrast to the early succession stages, the final abundances reached were independent of the plankton abundance but strongly dependent upon the local resource level. Immigration is an important factor controlling the initial substrate colonization and early growth, and ciliate and HF communities in biofilms become increasingly independent of immigration with maturation, being then controlled by local factors such as resources.
Control of phosphate uptake by zooxanthellae and host cells in the scleractinian coral Stylophora pistillata
Authors: Godinot C. , Ferrier-Pagés C. , Grover R.
Published: January 2011

Depletion experiments were used to assess the uptake rates of phosphate by the tropical coral Stylophora pistillata and its symbiotic zooxanthellae under different conditions. Our results showed the presence of active phosphate carriers both in the animal and the algal fractions, since uptake kinetics followed uniphasic saturation curves in both compartments (Michaelis‐Menten shape). Transporters in the animal and the algae presented different affinities for phosphate, with higher half‐saturation constants for the animal compartment than for the isolated zooxanthellae (K = 1.08 ± 0.42 vs. 0.57 ± 0.18 µmol L−1). The velocity of phosphate absorption increased in the light, suggesting a relationship with the photosynthetic activity of the zooxanthellae. A correlation was found between phosphate uptake rates and the organic or inorganic feeding history of the corals; rates were indeed 4.6 times higher in 8‐week starved than in fed corals and depended on the repletion status of phosphorus stocks within the symbionts. We report evidence showing that zooxanthellae act as a sink of phosphate within the symbiosis.
Salt marshes and eutrophication: An unsustainable outcome
Authors: Turner R. Eugene , Howes Brian L. , Teal John M. , Milan Charles S. , Swenson Erick M. , Tonerb Dale D. Goehringer‐
Published: January 2011

Most plant production by emergent coastal marshes occurs belowground. This belowground production adds to the accumulation of organic matter sustaining salt marshes as sea level rises, thus preventing excessive flooding, eventual plant death, and habitat loss. The ubiquitous nutrient enrichment of coastal salt marshes stimulating aboveground plant growth may result in higher rates of inorganic matter accumulation that compensates for marsh flooding caused by sea level rise. Results from several short‐term experiments, however, demonstrate that root and rhizome biomass and carbon accumulation is reduced with nutrient enrichment, suggesting that eutrophication of coastal waters may not be a compensatory counterbalance to the effects of global sea level rise on salt marshes. We show that the net effects of 36 yr of nutrient enrichment in replicated field experiments do not lead to higher organic or inorganic accumulation. Enrichment reduces organic matter belowground and may result in a significant loss in marsh elevation equivalent to about half the average global sea level rise rates. Sustaining and restoring coastal emergent marshes is more likely if they receive less, not more, nutrient loading.
Anaerobic ammonium oxidation in deep‐sea sediments off the Washington margin
Authors: Engström Pia , Penton C. Ryan , Devola Allan H.
Published: January 2011

The significance of anaerobic ammonium oxidation (anammox) for nitrogen removal in deep continental margin sediments was studied with 15N amendments to suboxic sediments collected from 2800‐3100‐m water depth at eight sites in the Cascadia Basin (eastern North Pacific Ocean). Consistent with earlier data from deep continental margin sediments, pore‐water distributions of inorganic N indicated NH4+ removal from suboxic zone sediments, likely due to reaction with nitrate. Anammox rates estimated from suboxic sediment incubations with 15N‐labled substrates ranged between 0.065 and 1.7 nmol N mL−1 h−1 (wet sediment), which suggested that anammox was responsible for the observed NH4+ removal. Anammox and denitrification rates derived from NH4+ and NO{3 pore‐water profiles were 32‐82 µmol N m−2 d−1 and 50‐110 µmol N m−2 d−1, respectively. The average contribution of anammox to total N2 production was 40% (15N‐amended sediment incubations) to 42% (flux from pore‐water inorganic N), which does not support earlier reports that suggested that the relative importance of anammox increased with water depth and thereby should dominate over denitrification at depths greater than 1000 m.
Iodine assimilation by marine diatoms and other phytoplankton in nitrate‐replete conditions
Authors: de laCuesta John L. , Manley Steven L.
Published: January 2011

Several marine phytoplankton species, primarily diatoms, were examined for the accumulation of iodide (10 species) and iodate (9 species) using radioactive iodine‐125 in f/2 artificial seawater, a nitrate‐enriched medium. Iodide accumulation (net uptake) rates were variable, and diatoms exhibited the highest rates. Emiliania huxleyi and Synechococcus sp. did not accumulate iodide. Accumulation rates ranged from 0 to 1.7 fmol cell−1 d−1. The diatom Porosira glacialis accumulated the greatest amount of iodide and was used to determine efflux rates of iodide. Iodide efflux was characterized by two distinct phases of iodide release: an initial rapid release rate of 10 amol cell−1 min−1 from the free space and a subsequent cellular release rate of 0.13 amol cell−1 min−1, which corresponds to a daily cellular release rate of 0.19 fmol cell−1 d−1. Accumulation of iodate ranged from 0 to 19 amol cell−1 d−1, with P. glacialis displaying the highest rate. Emiliania, Synechococcus, and Chaetoceros did not show significant iodate accumulation. Iodide is the preferred chemical species of iodine for uptake under nitrate‐replete conditions: iodide accumulation rates ranged from 3 to 90 times larger than those for iodate for the species studied. If the iodate accumulated is tightly coupled to its reduction to iodide, the accumulation rates suggest that phytoplankton‐mediated iodate reduction is not environmentally significant. If diatoms can reduce iodate to iodide, their overall contribution to surface‐water iodide, while living, would be further reduced because of their ability to reassimilate released iodide.
Interdecadal variation in seawater d13C and d18O recorded in fish otoliths
Authors: Schloesser Ryan W. , Rooker Jay R. , Louchuoarn Patrick , Neilson John D. , Secord David H.
Published: January 2011

Stable carbon (Δ13C) and oxygen (Δ18O) in the otolith cores of Atlantic bluefin tuna (Thunnus thynnus) vary temporally, with changes that quantitatively follow interdecadal variation in atmospheric and oceanic reservoirs. Both carbon and oxygen isotopic signatures vary significantly by year of birth over the range investigated (1947‐2006), with Δ13C decreasing and Δ18O increasing (‐2.56 × 10−2‰ and 4.3 × 10−3‰ yr−1, respectively). The rate of change in otolith Δ13C was similar to reported rates of atmospheric Δ13C depletion, attributed to deforestation and the burning of fossil fuels (referred to as the Suess effect), suggesting a close link between atmospheric and oceanic carbon pools. Increases in otolith Δ18O were evident but less pronounced, with observed variation possibly attributable to changing salinity in the Atlantic Ocean. Otolith cores of bluefin tuna effectively track interdecadal trends and record past seawater Δ13C and Δ18O.
Behavioral enhancement of onshore transport by postlarval Caribbean spiny lobster (Panulirus argus)
Authors: Goldsteina Jason S. , Butler Mark J.
Published: January 2011

We conducted a series of laboratory experiments to examine the orientation, settlement, and metamorphosis of Caribbean spiny lobster (Panulirus argus) pueruli (postlarvae) in response to cues characteristic of their nursery in back‐reef tropical lagoons. Our results suggest that pueruli were attracted to coastal water sources and the metabolites of red macroalgae (Laurencia spp.) when compared with oceanic water and artificial seawater treatments. Pueruli were not attracted to waterborne cues from sea grass, were repelled by hypersaline or hyposaline water, and discerned coastal cues from water collected as far as 30 km offshore from the reef. We also conducted experiments to examine the settlement behavior of pueruli in response to different substrates and hydrostatic pressures. Pueruli only settled at pressures equivalent to depths ≪5 m, which is where most settlement occurs in the field; settlement behavior was further enhanced by the presence of red macroalgae. Coastal water or artificial seawater containing red macroalgae metabolites hastened puerulus development and molting to the benthic juvenile stage by 20‐30% compared with those exposed to artificial seawater. Collectively, our results demonstrate that spiny lobster pueruli use chemical and pressure cues during onshore transport and selection of settlement habitat, highlighting the important role of behavioral responses to physical cues in the recruitment of this species.
Growth at the edge of the niche: An experimental study of the harmful alga Prymnesium parvum
Authors: Baker Jason W. , Grover James P. , Ramachandrannair Ratheesh , Black Cody , Valenti Theodore W. , Brooks Bryan W. , Roelkec Daniel L.
Published: January 2011

The haptophyte Prymnesium parvum forms harmful blooms toxic to fish in coastal and inland waters. Its growth in relation to niche factors is poorly characterized for the low salinities found in the inland waters in which P. parvum blooms have occurred. The specific growth rate of P. parvum as a function of temperature and salinity was determined in nutrient‐sufficient cultures with low salinity. Additionally, phosphorus‐limited growth was determined at low salinity and temperatures at or below 20°C. In nutrient‐sufficient cultures, decreasing salinity from 4 g L−1 to 0.5 g L−1 reduced the growth rate of P. parvum. The estimated optimal temperature for growth decreased with decreasing salinity from about 27uC at salinities above 10 g L−1, to about 24°C at 4 g L−1, to about 22°C at 0.5 g L−1. In phosphorus‐limited experiments, the half‐saturation concentration for growth was less than 0.02 µmol L−1 under most conditions. The phosphorus‐saturated growth rate was 0.84 d21 at 4 g L−1 salinity and 20°C, and it was reduced at lower salinities and temperatures. The salinity‐temperature interaction found here weakens the negative effect of low temperature on growth at low salinity and might partially explain why blooms of P. parvum occur in the winter months in inland waters of the southwestern United States. However, the relatively slow growth of P. parvum at low temperature and salinity suggests that additional factors should be examined, such as reduced effects of competitors, pathogens, and grazers during winter.
Photodissolution and other photochemical changes upon irradiation of algal detritus
Authors: Mayer Lawrence M. , Schick Linda L. , Hardy Kathleen R. , Estapa Margaret L.
Published: January 2011

Several recent lines of literature point toward strong photoreactivity of phytoplanktonic detritus. We examined effects of irradiation of algal membrane fragments in various stages of decay, with emphasis on transfer of materials from solid to dissolved phase (photodissolution). After simulated solar irradiation for 24 h, up to several tens of percent of particulate organic matter converted to photodissolved organic matter (PDOM). Prior microbial decay enhanced PDOM production. PDOM had initially high C:N ratios, which decreased with irradiation time. Dissolved organic nitrogen dominated nitrogen photodissolution, followed by minor photoammonification and negligible nitrite plus nitrate production. Chromophoric particulate organic matter bleached at visible wavelengths and underwent dissolution, creation, and bleaching at ultraviolet (UV) wavelengths, resulting in net loss of color in particulates and net gain of largely UV‐absorbing PDOM that also exhibited humic‐type fluorescence. Solid phase proteinaceous material became less accessible to proteases after microbial decay but regained this accessibility upon irradiation. Irradiation under anoxic conditions roughly halved production of PDOM, including chromophores and humic fluorophores. Oxygen enhancement of these reactions, along with production of peroxides, implies a strong role for photosensitization. Pigments, unsaturated lipids, and tryptophan emerged as likely sources of reactive oxygen species. Lipid peroxides appeared as a reactive intermediate product. If these reactions in the ocean scale to pigment loss as found in our experiments, at least 5‐15% of particulate organic matter could undergo photodissolution before settling in some planktonic environments. This photodissolution would enhance remineralization by photic zone microbial communities and thus upper ocean elemental recycling.
Zinc isotope composition of settling particles as a proxy for biogeochemical processes in lakes: Insights from the eutrophic Lake Greifen, Switzerland
Authors: Peel Kate , Weiss Dominik , Siggc Laura
Published: January 2011

The isotope composition of zinc (Zn) was determined in settling particles collected monthly over a year in the hypolimnion of the eutrophic Lake Greifen (Switzerland) in order to explore the potential of this novel isotope system as a proxy for biogeochemical processes in aqueous environments. Significant variation in Δ66ZnJMC3‐0749L of 0.9‰(where Δ66ZnJMC3‐0749L 5 [{66Zn : 64Zn}sample/{66Zn : 64Zn}JMC3‐0749L ‐ 1] x 1000) was found throughout the seasonal cycle of productivity. The most negative Δ66ZnJMC3‐0749L values (down to ‐0.66‰ ± 0.08‰) were observed during the productive summer period from June to September, when the Zn in the settling particles was predominantly associated with organic material, and when Zn concentrations in the epilimnion were lowest. This observation is likely explained with preferential uptake of the light Zn isotopes during algal growth. During the other months, the Zn in the sediment traps showed higher Δ66Zn values, reflecting increasing contributions of anthropogenic or lithogenic components. The average isotopic signature of the settling particles during the autumn‐winter‐spring period (≪‐0.2‰ for Δ66ZnJMC3‐0749L) was somewhat lower than typical for anthropogenic and natural sources, and this possibly reflects the effect of the preferential adsorption of lighter dissolved Zn isotopes onto the settling particles. We suggest that Rayleigh fractionation plays a minor role in controlling the isotopic composition of the settling particles in the lake. Our work demonstrates the presence of an obvious seasonal cycle in Δ66Zn, and this suggests that Zn isotopes can be employed to study nutrient utilization and other biogeochemical processes in lakes and other aquatic environments.
Modeling the duration of intermittent ice cover on a lake for climate‐change studies
Authors: Livingstonea David M. , Adrianb Rita
Published: January 2011

A generalized empirical approach to the problem of the prediction of intermittent lake ice cover for climate‐change studies is presented and applied to historical ice data from Muggelsee, a shallow lake in northern Germany that experiences either no ice cover, intermittent ice cover, or continuous ice cover, depending on the severity of the winter. The approach presented allows the total duration of ice cover in any winter to be estimated in terms of an air‐temperature probability function. Advantages over traditional empirical methods based on the mean air temperature during a fixed period or on the computed number of negative degree‐days are: (1) it is valid for both continuous and intermittent ice cover; (2) it is not necessary to specify a fixed time period for integration in advance; (3) the results emerge in time units, allowing them to be directly compared with the measured duration of ice cover without prior calibration; and (4) it is based on statistical properties of the ambient air temperature that are routinely forecast by climate models, making it easy to apply predictively. Regional climate model forecasts for northern Germany imply that for Muggelsee, the percentage of ice‐free winters will increase from ≪2% to over 60% by the end of the current century.
Effects of climate on organic carbon and the ratio of planktonic to benthic primary producers in a subarctic lake during the past 45 years
Authors: Rosén Peter , Cunningham Laura , Vonk Jorien , Karlssona Jan
Published: January 2011

The effects of climatic variables on lake‐water total organic carbon (TOC) concentrations and benthic and pelagic primary producers during the past 45 yr were assessed using the sediment records of two subarctic lakes, one with mires and one without mires connected to the lake. The lake with a mire showed large and synchronous changes in the planktonic to benthic (P : B) ratio of diatoms and concentrations of TOC inferred from nearinfrared spectroscopy. During periods of warm temperatures, high precipitation, and long ice‐free conditions, we inferred high TOC in the lake, and the diatom community was dominated by planktonic species. The stable carbon isotopic (Δ13C) values of sediment organic matter were negatively correlated with inferred TOC concentration and P :B ratio. We suggest that the changes in TOC and P : B ratio were a result of changing climate, permafrost degradation, and related changes in the catchment. Terrestrial organic matter, by its strong effect on the penetration of light through the lake water, possibly affected the habitats available for benthic photosynthesis and thus the Δ13C of the sediment organic matter. The large changes in recent times may also be because of unusually long ice‐free periods, warmer temperatures, and other associated limnological changes. The lake with no mire next to the lake showed only minor changes in lake‐water TOC during the same period and P :B ratio remained almost constant until the past 5 yr, when the P :B ratio increased rapidly. The observed changes in P :B ratio within this lake may be because of complex interactions of several climate‐related variables.
Ecological, landscape, and climatic regulation of sediment geochemistry in North American sockeye salmon nursery lakes: Insights for paleoecological salmon investigations
Authors: Selbie Daniel T. , Finney Bruce P. , Barto David , Bunting Lynda , Chen Guangjie , Leavitt Peter R. , MacIsaac Erland A. , Schindler Daniel E. , Shapley Mark D. , Gregory-Eavesa Irene
Published: January 2011

We used multiple linear regressions across a Northeast Pacific region 56‐lake set to examine the influence of sockeye salmon spawner densities and limnological, climatic, and watershed characteristics on sediment stable nitrogen isotope (δ15N) and C:N signatures, geochemical proxies used in paleolimnological reconstructions of prehistoric salmon abundances. Across all sites (n = 56), sedimentary C:N was primarily related to variables reflecting allochthonous organic matter and nutrient fluxes, with 67= of the variance explained by watershed vegetation type, watershed area, mean slope, and salmon spawner densities. In a subset of sites with nutrient data (n = 41), 63= of variance in C:N was explained by precipitation and watershed vegetation type. Sediment δ15N was most strongly related to salmon spawner densities, but C:N and watershed area : lake area ratios explained significant residual variance (total 55=). In sites with nutrient data, salmon spawner densities, vegetation type, and spring nitrate explained 62= of the variance in d15N. Sediment C:N and δ15N values exhibited distinct interregional variation, typically varying inversely. Regional d15N‐salmon density relationships (regression slopes) varied strongly with total annual precipitation (r2 = 0.89, p = 0.016, n = 5), suggesting watershed organic matter and nutrient loading vary predictably in relation to regional biogeoclimatic conditions. Our findings demonstrate that paleolimnological analyses are useful for quantitative reconstruction of past salmon densities; however, inferences regarding past salmon populations must consider the factors regulating influxes of nitrogen from watershed sources.
Carbon sequestration and stoichiometry of motile and nonmotile green algae
Authors: Striebel Maren , Bartholmé Silvia , Zernecke Rebekka , Steinlein Christina , Haupt Florian , Diehl Sebastian , Stibor Herwig
Published: January 2011

Actively motile, flagellated phytoplankton taxa often exploit vertical gradients in the availability of light and nutrients. The ability to move actively usually goes along with low investment in structural carbon components and should entail costs in terms of increased energy expenditure. This should be reflected in higher metabolic rates and higher light requirements for growth and, consequently, in lower light‐dependent specific production rates, carrying capacities, and carbon‐to‐phosphorus (C : P) ratios (during phosphorus limitation) of flagellated compared to nonmotile taxa. Laboratory experiments with four flagellated and five nonmotile species of green algae, performed over a light gradient, corroborated these expectations. Parameter fits to short‐term production‐irradiance measurements suggest that flagellated taxa had higher respiration rates and higher light requirements for growth than nonmotile taxa. Accordingly, both short‐term photosynthetic rates and longer‐term (14 d) biomass accrual were lower for flagellated than for nonmotile taxa. While most of the variance in algal C: P ratios was explained by species‐specific effects, there was also a tendency for algal C: P ratios to be lower in flagellated that in nonmotile taxa. Collectively, these results point at significant costs of motility, which may explain why flagellated taxa are often outcompeted by nonmotile taxa in turbulently mixed environments, where active motility is of little use.
Phosphorus release with carbonate dissolution coupled to sulfide oxidation in Florida Bay seagrass sediments
Authors: Jensen Henning S. , Nielsen Ole I. , Koch Marguerite S. , de Vicentea Inmaculada
Published: January 2011

We hypothesized that CaCO3 dissolution, coupled to sulfide oxidation, is an important mechanism by which solid‐phase inorganic P (iP) becomes available to seagrass in tropical carbonate sediments. To examine this supposition, we measured field sulfate reduction rates and simulated the acidity (10‐50 µmol H2SO4 cm−3 sediment) generated by subsequent sulfide oxidation from high (western) and low (eastern) total P (TP) sediments in Florida Bay. Dissolution experiments were conducted using sediment slurries at field pH (pore‐water pH ~6.5‐7.5). While CaCO3 dissolution (maximum 1.3% of sediment dry weight) was evidenced at all sites by leaching of Ca2+ into slurries, at three of the four sites PO43‐ was primarily recovered in the sediment exchangeable pools and at a lower P : Ca ratio than observed in source sediments. In contrast, no PO43‐ was recovered from an eastern bay site with the lowest TP and finest‐grained sediments, suggesting that PO43‐ was either tightly adsorbed or incorporated into the carbonate matrix post‐acidification. The potential for tight PO43‐ resorption by sediment from the low‐TP site was also supported by the rapid rate of isotopic exchange of 33PO43‐ into the sediment matrix. These adsorptive and incorporation processes may explain the low PO43‐ in pore waters in the eastern vs. western regions of Florida Bay, even upon dissolution of carbonates. Carbonate dissolution coupled to sulfide oxidation could potentially provide 1.8 and 23.5 µmol iP m−2 d−1 at eastern and western bay sites, respectively, meeting 5% of eastern and 29% of western bay seagrass (Thalassia testudinum) P requirements.
Diel vertical migration of the deep‐water jellyfish Periphylla periphylla simulated as individual responses to absolute light intensity
Authors: Dupont Nicolas , Klevjer T. A. , Kaartvedt S. , Aksnesa D. L.
Published: January 2011

We evaluate the hypothesis that the vertical migration of Periphylla periphylla is governed by its sensitivity to light intensity. By applying an individual‐based model where random walk is combined with assumed individual responses to light, we compare the predicted vertical distributions with acoustical observations. Important features of the observed P. periphylla distributions can be explained by a simple proximate light response where individual P. periphylla avoids light above a certain threshold but also has a preference for very low light intensities. In addition to accounting for the observed synchronous diel vertical migration phenomenon in P. periphylla, this simple mechanism also accounts for simultaneous asynchronous vertical migrations observed for part of the population.
Pockmarks: Refuges for marine benthic biodiversity
Authors: Webb Karen E. , Barnes David K. A. , Plankea Sverre
Published: January 2011

Pockmarks are one of the most obvious and abundant structural features of the North Sea seabed, yet their influence on fauna is virtually unknown. We report the distribution of benthic megafaunal assemblages in and around four "pockmark complexes" in the North Sea to determine the structure of megafaunal communities inside pockmarks and whether these ubiquitous topographical features acted as refuges against trawling and other disturbances. The study focuses on the large central pockmarks in each of the pockmark complexes. These large pockmarks had depths of around 10 m and diameters of 160‐235 m. Remotely operated vehicle video transects showed that megafauna increased in abundance, species richness, and diversity from outside (background seabed) toward the center of the pockmarks. The number of taxa present in the center of pockmarks was approximately double those of similar surrounding areas, and the centers had almost an order of magnitude more individuals than outside. Carbonate rocks were found in the centers of all the pockmarks and may be indicative of their formation (past methane seeps). These rocks also provide novel habitat to fauna: a complex hard substrate for colonization and shelter in an otherwise homogeneous soft sediment environment. Habitat enrichment and morphological protection are suggested to be the main reasons for the increased faunal abundance and species richness. Indeed, despite fishing data showing the area to be intensively disturbed, large slow‐growing (old) and vulnerable species, such as gorgonian corals, were found in the center of the pockmarks. Pockmarks may offer important refuges from trawling activity.
Nocturnal light and lunar cycle effects on diel migration of micronekton
Authors: Benoit-Bird Kelly J. , Au Whitlow W. L. , Wisdoma Daniel W.
Published: January 2011

The roles of nocturnal light and lunar phase in the diel migration of micronekton from a nearshore scattering layer were examined. Migration patterns were measured over six complete lunar cycles using moored upward‐looking echosounders while nocturnal surface irradiance was recorded. We hypothesized that animals would remain at a constant isolume at night despite changes in nocturnal illumination between nights. The scattering layer migrated closer to the surface during dark nights than during well‐lit ones. However, this movement was not enough to compensate for observed changes in light, and at night animals often remained at light levels higher than they experience at depth during the day. Light and lunar cycle were not completely coupled, allowing separation of the light and lunar phases. Contrary to the initial hypothesis, lunar phase accounted for substantially more of the variability in layer migration than surface irradiance, showing strong effects on the scattering layer’s depth and animal density within the layer. Changes in layer depth and animal density were amplified a small amount by variations in light level but were minimized by the seafloor in shallow areas. The horizontal component of the scattering layer’s migration was also affected by lunar phase, with animals remaining further offshore in deeper waters during nights near and during the full moon, even when these were not the nights with the highest light levels. These results suggest that moonlight may be a cue for an endogenous lunar rhythm in the process of diel migration rather than a direct cause.
Simultaneous determination of in situ vertical transitions of color, pore‐water metals, and visualization of infaunal activity in marine sediments
Authors: Teal Lorna R. , Parker Ruth , Fones Gary , Solana Martin
Published: January 2011

The vertical color transition from brown to gray‐green in marine sediments is linked to the Fe redox boundary and is commonly used as a proxy for biogeochemical state. We combine time‐lapse sediment profile imaging with diffusive gradient thin (DGT) gels to obtain simultaneous in situ measurements of sediment color profiles, porewater Fe and Mn profiles, and qualitative estimates of faunal activity at the Oyster Ground and North Dogger (North Sea). Analysis of Fe and Mn profiles using generalized additive modeling reveals that high variability between profiles within the sites makes it difficult to determine any intersite differences in trace metal behavior. At the Oyster Ground, the depth of sediment color transition (4.78 ± 0.76 cm) was not significantly different from the Fe redox boundary (7.67 ± 4.04 cm). At the North Dogger, there was a significant discrepancy between the depth of the sediment color transition (2.86 6 0.78 cm) and the Fe redox boundary (10.17 ± 1.04 cm), which most likely results from high sulfate reduction rates at the North Dogger, leading to complexation of reduced iron to a form not available to the DGT technique. The differences in the coupling of sediment color and the Fe redox boundary between stations is likely to be related to variations in recent infaunal bioturbation activity, rather than variations in sediment source or fundamental differences in bulk sediment chemistry. Our results highlight the importance of the infaunal community in mediating Fe and Mn cycles, which are key pathways in the degradation of organic matter, and suggest that descriptions of bulk chemistry alone may be insufficient to understand the dynamics of biogeochemical cycling.
Microbially induced flocculation of allochthonous dissolved organic carbon in lakes
Authors: Wachenfeldt Eddie von , Bastviken David , Tranvika Lars J.
Published: January 2011

The flocculation of allochthonous dissolved organic carbon (DOC) in lakes was investigated in a series of laboratory experiments. Flocculation was enhanced by increased temperatures, and addition of glucose increased the flocculation further. A change in pH within the range of 3.3 to 7.3 resulted in decreased flocculation with increasing deviation from the original pH. Flocculation was similar under oxic and anoxic conditions. For all treatments (i.e., temperature and glucose, pH, and O2 regime), flocculation was positively correlated to bacterial respiration. However, bacterial biomass made up a negligible fraction of the formed flocs, suggesting that the formation of detrital particles was a result of bacterial activity, but there was no significant contribution of bacteria to the mass of the particles formed. In all experiments, both the concentration of DOC and concentration of colored dissolved organic matter (CDOM) decreased concomitantly with flocculation, suggesting that CDOM is the precursor of the flocs. Bacteria mediate a translocation of DOC in the water column into particles prone to gravitational settling.
Flow inside a coral colony measured using magnetic resonance velocimetry
Authors: Chang Sandy , Elkins Chris , Alley Marcus , Eaton John , Monismitha Stephen
Published: January 2011

The velocity field within scale models of branching coral Stylophora pistillata colonies was measured using magnetic resonance velocimetry (MRV). The models were based on digital representations of real coral skeletons derived using X‐ray computed tomography (CT) and constructed using rapid‐prototype manufacturing. Two morphologies of S. pistillata from the Red Sea grown in different flow regimes were used. To simplify visualization of the data, velocities were parsed into a series of spherical shells, giving the velocity distributions as functions of distance from coral center for both morphologies. The low‐flow morphology distributed flow velocity relatively evenly throughout the interior. In contrast, the high‐flow morphology showed a wider range of velocities with regions of flow channeling and flow stagnation.
The cold‐water coral community as hotspot of carbon cycling on continental margins: A food‐web analysis from Rockall Bank (northeast Atlantic)
Authors: Oevelen Dick van , Duineveld Gerard , Lavaleye Marc , Mienis Furu , Soetaert Karline , Heip Carlo H. R.
Published: January 2011

We present a quantitative food‐web analysis of the cold‐water coral community, i.e., the assembly of living corals, dead coral branches and sediment beneath, associated with the reef‐building Lophelia pertusa on the giant carbonate mounds at ~800‐m depth at Rockall Bank. Carbon flows, 140 flows among 20 biotic and abiotic compartments, were reconstructed using linear inverse modeling by merging data on biomass, on‐board respiration, δ15N values, and literature constraints on assimilation and growth efficiencies. The carbon flux to the coral community was 75.1 mmol C m−2 d−1 and was partitioned among (phyto)detritus (81%) and zooplankton (19%). Carbon ingestion by the living coral was only 9% of the carbon ingestion by the whole community and was portioned among (phyto)detritus (72%) and zooplankton (28%). Carbon cycling in the community was dominated by suspension‐ and filter‐feeding macrofauna associated with dead coral branches. Sediment traps mounted on a bottom lander trapped 0.77 mmol C m−2 d−1 (annual average), which is almost two orders of magnitude lower than total carbon ingestion (75.1) and respiration (57.3 mmol C m−2 d−1) by the coral community. This discrepancy is explained in two ways: the coral community intercepts organic matter that would otherwise not settle on the seafloor, and through their action as ecosystem engineers, the increased turbulence generated by the coral framework and organic‐matter depletion in the boundary layer augment the influx to the coral community. A comparison of macrofaunal biomass and respiration data with soft sediments reveals that coral communities are hot spots of biomass and carbon cycling along continental margins.
Crossed induction of sex in sympatric congeneric rotifer populations
Authors: García-Roger Eduardo M. , Dias Natália , Carmona María José , Serra Manuel
Published: January 2011

The transition from asexual to sexual reproduction in rotifers of the genus Brachionus (Monogononta) is triggered by a chemical signal produced and released by the rotifers themselves; the signal accumulates in the environment as population density increases. The response to this signal has been hypothesized to be speciesspecific. If not, the timing of sex and final diapausing egg production of a species might not be optimized. In this study, a set of experiments—based on individual and mass culture approaches—was carried out to investigate the differentiation in sex induction signals between sympatric and allopatric congeneric Brachionus populations by analyzing the capability of the medium conditioned by the growth of a population (i.e., medium containing the inducing signal) to induce sex in a different one. We found that populations induce sex in response to medium conditioned by congeneric populations. Results suggest differences among species in their production and responsiveness to sex‐inducing signals, as well as slight differentiation in these signals. The observed lack of strong differentiation between sympatric populations is proposed to have implications in avoidance of competition.
Ocean acidification exacerbates the effect of UV radiation on the calcifying phytoplankter Emiliania huxleyi
Authors: Gao Kunshan , Ruan Zuoxi , Villafañe Virginia E. , Gattuso Jean-Pierre , Helbling E. Walter
Published: January 2011

Increasing atmospheric CO2 concentration affects calcification in most planktonic calcifiers. Both reduced or stimulated calcification under high CO2 have been reported in the widespread coccolithophore Emiliania huxleyi. This might affect the response of cells to photosynthetically active radiation (PAR; 400‐700 nm) and ultraviolet radiation (UVR; 280‐400 nm) by altering the thickness of the coccolith layer. Here we show that in the absence of UVR, the calcification rates in E. huxleyi decrease under lowered pH levels (pHNBS of 7.9 and 7.6; pCO2 of 81 and 178 Pa or 804 and 1759 ppmv, respectively) leading to thinned coccolith layers, whereas photosynthetic carbon fixation was slightly enhanced at pH 7.9 but remained unaffected at pH 7.6. Exposure to UVR (UV‐A 19.5 W m‐2, UV‐B 0.67 W m‐2) in addition to PAR (88.5 W m‐2), however, results in significant inhibition of both photosynthesis and calcification, and these rates are further inhibited with increasing acidification. The combined effects of UVR and seawater acidification resulted in the inhibition of calcification rates by 96% and 99% and that of photosynthesis by 6% and 15%, at pH 7.9 and 7.6, respectively. This differential inhibition of calcification and photosynthesis leads to significant reduction of the ratio of calcification to photosynthesis. Seawater acidification enhanced the transmission of harmful UVR by about 26% through a reduction of the coccolith layer of 31%. Our data indicate that the effect of a high‐CO2 and low‐pH ocean on E. huxleyi (because of reduced calcification associated with changes in the carbonate system) enhances the detrimental effects of UVR on the main pelagic calcifier.