bluuebunny/crossref_metadata_2025 huggingface dataset:
Size structure and the production/respiration balance in a coastal plankton community
Authors: Smith Erik M. , Kemp Michael W.
Published: June 2010

The quantitative significance of contributions by the picoplankton (,3 mm) to gross primary production (P) and community respiration (R) was investigated seasonally in the plankton community of Chesapeake Bay. Rates of P and R for the total plankton community, integrated over the euphotic zone, ranged from 119‐709 mmol O2 m−2 d−1 and 41‐325 mmol O2 m−2 d−1, respectively. Rates of P and R within the picoplankton community tended to covary with those of the total plankton community, although the strengths of the two relationships were markedly different. The mean proportion of total community R accounted for by the picoplankton averaged 54%, with the two rates being highly correlated. In contrast, the relative contribution of picoplankton to total P was highly variable, ranging from 1 to 77%, with fluctuations in picoplankton production rates explaining only 29% of the variability in total P. Although P and R exhibited a significant positive relationship over the entire data set, individual P: R ratios varied substantially, ranging from 0.95 to 4.73. Seasonal variations in P: R ratios for the picoplankton were out of phase with those of the total community. When the total plankton community was most autotrophic (P: R > 1), the picoplankton P: R was net heterotrophic (P: R < 1), and as total plankton P: R ratios decreased toward balanced metabolism (P: R = 1), picoplankton P: R ratios increased to become net autotrophic. Seasonal and spatial variations in the contributions of picoplankton P and R to total rates had a strong effect on the P: R ratio of the plankton community as a whole. There was a pronounced inverse relationship between the P: R ratio of the total plankton community and the proportion of P attributable to the picoplankton, such that high net autotrophy occurred only when P was dominated by the larger size fractions. These findings indicate an important linkage between the size distribution of the primary producers and the overall balance of P and R in the plankton community, which in turn regulates the potential for organic matter export.
Effect of phosphorus limitation on elemental composition and stable carbon isotope fractionation in a marine diatom growing under different CO2 concentrations
Authors: Gervais Frank , Riebesell Ulf
Published: June 2010

Blooms of the marine diatom Skeletonema costatum were initiated in closed‐system batch cultures with P‐deficient medium under two different initial concentrations of dissolved molecular CO2([CO2,aq]: 20.6 and 4.5 µmol L−1). Algal C: N: P ratios strongly increased with decreasing P concentration. In the exponential growth phase, C: N ratios were 1.3 mol mol−1 higher in the low relative to the high [CO2,aq] treatment. There was no [CO2,aq] effect on C: N: P ratios during P‐limited growth. Carbon isotope fractionation (Âɛp ) was 2–3‰ higher in the high [CO2,aq] treatment. With growth rate decreasing due to P limitation, ep increased in both [CO2,aq] treatments by 2ߝ3‰ despite decreasing [CO2,aq]. Under these conditions the effect of decreasing growth rate on isotope fractionation strongly dominated over that of declining CO2 availability. When extrapolated to the natural environment, these results imply that systematic changes in algal growth, as occurring during the course of phytoplankton blooms, may affect algal isotope fractionation. These results severely complicate the interpretation of carbon isotope measurements in suspended and sedimentary organic matter.
Rapid estimation of in situ growth rates of Caridina nilotica (Crustacea: Decapoda) inLake Victoria: Description and pilot application of a simple, field‐compatible technique
Authors: Hart Rob C.
Published: June 2010

A simple rapid approach to estimating in situ growth rates of Caridina nilotica (Roux), a small shrimp that plays a pivotal role in Lake Victoria's food web, is described. The approach, potentially applicable to many arthropods, is based on moulting intervals (MI) and per moult size increments (PMI) determined during brief experimental confinements. Physiological justification of its reliability as a measure of in situ rates is given. Caridina moults at night. Feral animals collected shortly (≤2 h) before dusk were sorted into one of five arbitrary size classes and held around 27°C overnight without food. MI, the inverse proportion of a batch moulting overnight, increased from 2 d in small shrimps (carapace length [CL] ≤1.8 mm) to >9 d in larger animals (CL ≥4.3 mm)‐a value comparable to egg development time (10.3 d) at the corresponding temperature. PMI was measured from differences in CL of postecdysal shrimps (CLi‐1) and corresponding cast exuviae (CLi). In absolute terms, PMI, surprisingly, was constant (0.284 ± 0.027 mm moult−1) over the size range of shrimps tested, although relative growth (PMI as a percentage of CLi) declined with size. Growth trajectories modeled with regressions fitted to the data (MI = 1.573 x CL0.999 and CLi‐1 = 0.284 + 0.977 x CLi) show that C. nilotica grows significantly faster (by at least 20%) in L. Victoria than previously estimated (Ignatow et al.), with corresponding implications to other evaluations of lake productivity. Prospective refinements and future uses for this simple technique are outlined.
Not all eukaryotic algae can replace zinc with cobalt: Chaetoceros calcitrans (Bacillariophyceae) versus Emiliania huxleyi (Prymnesiophyceae)
Authors: Timmermans Klaas R. , Snoek Josje , Gerringa Loes J. A. , Zondervan Ingrid , de Baar Hein J. W.
Published: June 2010

Zinc and cobalt are essential trace metals for phytoplankton growth and can substitute for each other metabolically in some eukaryotic algal species, especially in some marine diatoms and coccolithophorids. In the present study, it is reported that in the marine diatom Chaetoceros calcitrans, Co cannot replace Zn: in contrast, Co substitution of Zn was found in Emiliania huxleyi. It is concluded that Co can substitute for Zn but that the phenomenon is species/genera‐specific. Differing ability to substitute Zn with Co can be regarded as an additional factor affecting phytoplankton biomass and/ or species composition.
Significant drop of fertilization of Acropora corals in 1999: An after‐effect of heavy coral bleaching?
Authors: Omori Makoto , Fukami Hironobu , Kobinata Hisao , Hatta Masayuki
Published: June 2010

In June 1999, after devastating coral bleaching in 1998, laboratory fertilization of Acropora nasuta, one of the most abundant reef‐building corals in Okinawa, Japan, decreased significantly from usual rates (>94%) to an average of 42% at a sperm concentration of 107 ml−1. Similar decreases were observed in four other mass‐spawning acroporid corals. We also found a decrease in sperm motility in the laboratory. A series of experiments to determine the effects of sperm concentration on fertilization rates revealed that sperm of 107 ml−1 was needed to obtain a rate >80%. Sperm concentration in surface seawater during mass spawning was highest within 1.0 h of spawning but decreased sharply thereafter. These results suggest that gamete dilution plays an important role in limiting the fertilization of coral eggs in the sea. As successful fertilization appears to have been much lower in 1999, we suspect that production of new coral recruits was also reduced greatly. Current and future sea‐temperature increases thus pose a severe potential threat to coral reefs by increasing the frequency of coral bleaching and consequently leading to further declines of coral recruitment and hence, reef corals.
Dynamic bacterial and viral response to an algal bloom at subzero temperatures
Authors: Yager Patricia L. , Connelly Tara L. , Mortazavi Behzad , Wommack K. Eric , Bano Nasreen , Bauer James E. , Opsahl Stephen , Hollibaugh James T.
Published: June 2010

New evidence suggests that cold‐loving (psychrophilic) bacteria may be a dynamic component of the episodic bloom events of high‐latitude ecosystems. Here we report the results of an unusually early springtime study of pelagic microbial activity in the coastal Alaskan Arctic. Heterotrophic bacterioplankton clearly responded to an algal bloom by doubling cell size, increasing the fraction of actively respiring cells (up to an unprecedented 84% metabolically active using redox dye CTC), shifting substrate‐uptake capabilities from kinetic parameters better adapted to lower substrate concentrations to those more suited for higher concentrations, and more than doubling cell abundance. Community composition (determined by polymerase chain reaction/DGGE and nucleotide sequence analysis) also shifted over the bloom. Results support, for the first time with modern molecular methods, previous culture‐based observations of bacterial community succession during Arctic algal blooms and confirm that previously observed variability in pelagic microbial activity can be linked to changes in community structure. During early bloom stages, virioplankton and bacterial abundance were comparable, suggesting that mortality due to phage infection was low at that time. The virus‐to‐bacteria ratio (VBR) increased 10‐fold at the height of the bloom, however, suggesting an increased potential for bacterioplankton mortality resulting from viral infection. The peak in VBR coincided with observed shifts in both microbial activity and community structure. These early‐season data suggest that substrate and virioplankton interactions may control the active microbial carbon cycling of this region.
Baltic Sea nitrogen fixation estimated from the summer increase in upper mixed layer total nitrogen
Authors: Larsson Ulf , Hajdu Susanna , Walve Jakob , Elmgren Ragnar
Published: June 2010

We estimated nitrogen fixation from the increase in total nitrogen (N2 gas excluded) in the upper 20 m during the summer biomass increase of heterocystous filamentous cyanobacteria at the off‐shore Landsort Deep station (BY31, 5 yr) and at 10 more stations in all major basins of the Baltic Sea proper. Estimated fixation rates were 2.3–5.9 mmol N m−2 d−1, within the range of reported direct measurements. Estimated total fixation in the Baltic Sea proper, 180–430 Gg N yr 21 taking nitrogen settling loss and atmospheric deposition into account, was sufficient to sustain 30–90% of the June‐August pelagic net community production. Filamentous cyanobacteria (mostly Aphanizomenon sp.) had low C: N and C: P ratios in spring 1998, indicating internal storage of both N and P. From early June, when their biomass growth started, ratios rose gradually to the biomass peak in August and early September, when the C: N ratio (6.5 mol/mol) was close to the Redfield ratio, but the C: P ratio reached 420, almost four times Redfield. The C: N ratio of the peak biomass was 1.5 times that in spring, and the C: P ratio was 13 times higher. The high C: P ratio indicates a smaller P demand by filamentous diazotrophs than expected from Redfield ratios. Only a few percent of the P mineralized daily is needed for filamentous cyanobacterial growth in summer. Filamentous cyanobacteria incorporated 16–41 mmol N m−2 into biomass (C : N 5 6.2) at BY31 in summer 1998. This was less than the estimated nitrogen fixation, suggesting fixed N leaks from growing diazotrophs.
Sources and composition of high‐molecular‐weight dissolved organic carbon in a southern Louisiana tidal stream (Bayou Trepagnier)
Authors: Engelhaupt Erika , Bianchi Thomas S.
Published: June 2010

The composition and cycling of high‐molecular‐weight dissolved organic carbon (HMW‐DOC) were examined in a tidal stream (Bayou Trepagnier) with seasonally high DOC concentrations (1.0–5.6 mM). 13C nuclear magnetic resonance (13C NMR) was used to examine the bulk chemical composition of natural HMW‐DOC from two field sites over 1.5 yr. The HMW‐DOC at both sites was dominated by aliphatic (41%), carbohydrate (33%), and carboxyl (16%) carbon, with relatively low aromatic carbon abundance (10%). A comparison of 13C NMR signatures of bayou HMW‐DOC and leachate HMW‐DOC collected from leaf litter and soils revealed that plant litter leachate appears to be a more important source of HMW‐DOM than soil. Dominant sources of HMW‐DOC were likely allochthonous inputs of terrestrial plant litter with periodic inputs of soil organic matter during flooding events. The low aromaticity of bayou HMW‐DOC may reflect the influence of low‐oxygen conditions, which inhibit the decomposition of particulate aromatic macromolecules such as lignin and humic material to HMW‐DOC. Lignin‐phenol biomarker concentrations (del6, in mg/100 mg OC) were much lower in HMW‐DOC (1.2) than in plant (5.2) and soil (6.8) organic matter, indicating that a significant fraction of this highly aromatic material was not degraded to HMW‐DOC. Finally, this study demonstrated that lignin and other compounds from terrestrially derived organic matter in sediments and adjacent soils are not a significant source of more soluble moieties that enter the HMW‐DOC pool of the bayou.
Evaluation of the utility of chemotaxonomic pigments as a surrogate for particulate DMSP
Authors: Belviso S. , Claustre H. , Marty J-C.
Published: June 2010

High‐performance liquid chromatography (HPLC) analysis of accessory pigments, which provides a detailed description of a phytoplankton assemblage over the whole size range, was combined with size fractionation of particulate di‐methylsulfoniopropionate (DMSPp) to assess the origin of DMSPp in the sea. More than 200 surface‐water samples were collected over contrasting regions of the ocean. Concentrations of DMSPp ranged between 6 and 190 nM. The size fraction <10 mm accounted for 65 ± 16% (1 sigma) of DMSPp on average. Concentrations of DMSPp in this size fraction were strongly linearly correlated (r2 = 0.84, n = 189, P < 0.0001) with the sum of concentrations of Hex‐fuco (prymnesiophytes) and But‐fuco (chrysophytes‐pelagophytes), after excluding 17 samples from the Ligurian Sea (Northwestern Mediterranean Sea) taken during the spring and summer seasons of 1993 and 1994. These samples were unusual because of their high DMSP content. Concentrations of Hex‐fuco + But‐fuco ap­pear much better surrogates for DMSPp than for DMS. In the size fraction >10 mm, DMSPp was better correlated with peridinin (dinoflagellates) than fucoxanthin (diatoms) concentrations, but peridinin explained at most 25% of the variability in microplanktonic DMSP. Nearly peridinin‐free (<0.01 mg m−3) surface waters of the Ligurian Sea during spring and summer contained >15 nM of DMSPp in the size fraction >10 mm, i.e., 44 ± 15% of total DMSPp. Thus, the particulate material exhibited considerably more DMSP than expected from the levels of accessory pigments in the Ligurian Sea during the spring and summer seasons of 1993 and 1994. We suggest that this excess of DMSPp was contributed by heterotrophic nano‐ and microorganisms.
Detecting food search in Daphnia in the field
Authors: Jensen Knut Helge , Larsson Petter , Högstedt Göran
Published: June 2010

From laboratory experiments, it has been suggested that visually guided feeding, chemical and mechanical perception of increased ingestion rate (including perception of hunger and satiation), and odors associated with algae help Daphnia in tracking food gradients. To test the ability of Daphnia to find food in the field, suspended yeast, suspended clay, or control water was pumped into a localized point in the littoral zone of Lake Myravann (Bergen, Norway). Daphnia longispina and Daphnia pulex, the most numerous zooplankton species in the experimental area, aggregated in areas of yeast input but not when adding suspended clay or control water. Thus, Daphnia is able to evaluate the patches both quantitatively and qualitatively, possibly through perception of increased ingestion rate and odor, while light scattering is indicated to be unimportant. This is the first experiment to demonstrate that Daphnia is able to find patches of food under natural conditions.
Effects of photosynthesis on the accumulation of Mn and Fe by Phaeocystis colonies
Authors: Schoemann V. , Wollast R. , Chou L. , Lancelot C.
Published: June 2010

The significance of Mn and Fe accumulation by Phaeocystis colonies and its control by photosynthesis were investigated by performing incubation assays with radiotracers (54Mn, 59Fe and 14C). Experiments were conducted on pure cultures of Phaeocystis globosa and on natural communities collected during a P. pouchetii bloom in the Balsfjord (subarctic Norwegian fjord) and a P. globosa bloom in the Southern Bight of the North Sea. Results indicate significant accumulation of Mn and Fe in the cultured colonies, as previously shown for Mn. Most of the Mn and Fe accumulation occurred in the mucilaginous matrix of the colonies, and the intracellular assimilation represented only ~10% of the total uptake of these trace elements. These experiments demonstrated that photosynthesis largely governed the uptake of Mn by the colonies but only slightly affected the accumulation of Fe. The positive linear relationships observed for the Balsfjord samples between the Mn uptake and the C fixation in the light suggests photosynthetic control of dissolved Mn removal to the Phaeocystis colonies. As had been predicted in earlier studies, the increase in pH and dissolved oxygen observed around and inside the colonies during the photosynthetic activity of the cells could significantly decrease Mn solubility and enhance Mn oxidation rate. However, these changes would not affect significantly the precipitation of Fe according to the thermodynamic considerations. In the highly turbid waters of the North Sea, the removal of Mn and Fe is increased by both inorganic and organic suspended particles, with no significant effect of photosynthesis on the overall uptake.
Anatomy of turbulence in thermally stratified lakes
Authors: Etemad-Shahidi Amir , Imberger Jörg
Published: June 2010

Turbulence within the thermocline of two thermally stratified lakes—Lake Biwa, Japan, and Lake Kinneret, Israel—was investigated using a portable flux profiler. This instrument provided high‐resolution profiles of temperature, conductivity, and two components of velocity within a measuring volume of approximately 8 mm3. Each data profile was segmented into statistically stationary segments. A range of properties of the turbulence, including direct estimates of the vertical mass flux, were then calculated for each segment. It was found that turbulence in the thermocline was generally patchy, but within a patch, dissipation levels were relatively high. The turbulent motions were found to be fine grained with small Thorpe scales and a large skewness of the distribution of the displacement scale. This is distinct to that found in the ocean, where shear instability produces large overturns. The measurement showed that the net vertical mass flux in the thermocline was negligible and less than that predicted by Osborn (1980). This is explained by noting that the net buoyancy flux consisted of two opposing parts—a down‐gradient irreversible flux due to turbulent mixing and an up‐gradient reversible flux due to restratification—that often cancel each other within a segment. The low measured net buoyancy flux within the interior of the lakes suggested that other processes, such as gravitational adjustments and benthic boundary layer processes, should be responsible for the basin‐averaged vertical transport in these lakes.
Variation in cellular nutrient status within a population of Dinophysis norvegica (Dinophyceae) growing in situ: Singleߚcell elemental analysis by use of a nuclear microprobe
Authors: Gisselson1 LarsߚÅke , Granéli Edna , Pallon Jan
Published: June 2010

Elemental analysis (C, N, and P) of single cells of Dinophysis norvegica collected from the Baltic Sea was performed by use of a nuclear microprobe (NMP). For each cell, elemental maps were created and the cellular C, N, and P content was obtained. Concentrates of D. norvegica cells were collected simultaneously for measurement of particulate C, N, and P content by traditional methods for comparison. The traditional measurements of C, N, and P yielded 2.2–2.5 times higher values per cell than the ones obtained by the NMP method. Nevertheless, the averages for the elemental ratios were very similar for the traditional measurements and NMP. All the analyzed cells were deficient in both N and P, compared with the Redfield ratio. The data show that cellular nutrient status, especially cell quotas of N, can vary considerably within a population of one algal species growing under the same environmental conditions in situ.
Morphological and chemical variability of colloids in the Almeria‐Oran Front in the eastern Alboran Sea (SW Mediterranean Sea)
Authors: Grout H. , Sempere R. , Thill A. , Calafat A. , Prieur L. , Canals M.
Published: June 2010

Across the different water types (Mediterranean, Frontal, and Atlantic waters) in the AlmeriaߞOran Front (Eastern Alboran Sea, SW Mediterranean Sea), we determined organic carbon in the particulate (60–0.2 µm), colloidal (0.2 µm–1,000 Da) and dissolved (<1,000 Da) fractions. The morphological and chemical variability of colloids was studied by means of analytical electron microscopy. Particulate and colloidal organic fractions accounted for 6 to 9% and 1 to 12%, respectively, of the total organic carbon. Visual examination of colloids revealed three morphologically and chemically differentiated morphotypes (globules, aggregates of rounded entities, and spherulitic aggregates) whose distribution, abundance, and chemical composition vary with the depth and between water types. Globules dominated 5 m deep at all stations; always contained Ca, P, S, and Cl; and were marked by the presence of other elements such as Si, Fe, or Mg depending on the water type. By contrast, at 40 m deep, Mediterranean, Frontal, and Atlantic waters were characterized by different morphotypes: FeߚPߚenriched aggregates of rounded entities in Mediterranean waters; globules with variable abundances of Si, Fe, Ca, P, S and Cl in Frontal waters; and Mgߚrich spherulitic aggregates in Atlantic waters. These morphological and chemical differences in colloids across the front raise questions about their origin, their aggregation, and the availability of elements for biological activity.
Upwelling and the condition and diet of juvenile rockfish: A study using 14C, 13C, and 15N natural abundances
Authors: Rau Greg H. , Ralston Stephen , Southon John R. , Chavez Francisco P.
Published: June 2010

Juvenile Sebastes jordani individuals sampled in late spring 1995, 1996, and 1997 near Monterey Bay, California, were analyzed for Δ14C, Δ13C, and Δ15N. As anticipated, a strong negative correlation was found between mean annual juvenile rockfish Δ14C and the preceding 3‐month average Bakun upwelling index for this region. The sensitivity of this isotopic response by juvenile rockfish to upwelling variations was similar to that previously observed in surface‐water inorganic carbon in nearby Half Moon Bay (Robinson 1981). This indicates that the Δ14C of surface‐dwelling marine fish can be used as a measure of fish feeding in freshly upwelled 14C‐depleted water. However, we found no correlation between this parameter and fish somatic condition as measured by deviations in the regressions of individual fish (1) weight on length, (2) otolith size on fish length, or (3) total lipid content on dry weight. This questions the role upwelling plays in affecting juvenile rockfish condition. Also unrelated to fish condition were fish Δ13C and Δ15N, implying that the condition of juvenile S. jordani is unaffected by variation in the consumption of specific, isotopically discernible food resources.
Grazer—resource interactions in the plankton: Are all daphniids alike
Authors: Tessier Alan J. , Bizina Elena V. , Geedey Kevin C.
Published: June 2010

Daphniids have long been considered to be uniquely effective grazers in the planktonic food web of lakes, but whether all daphniid species are equivalent in this functional role is less clear. In particular, a common belief that large‐bodied daphniids are more capable than smaller daphniids at controlling phytoplankton abundance has received limited testing. Using whole water column enclosures in a mesotrophic lake, we compared the ability of four common planktonic daphniids (Ceriodaphnia reticulata, Daphnia ambigua, Daphnia mendotae, and Daphnia pulicaria) to exploit a natural assemblage of phytoplankton. We established replicated monocultures of each daphniid species and allowed their populations to reach a carrying capacity determined by resources. We then compared the effects of each daphniid species on phytoplankton biomass, size structure, taxonomic composition and C:N: P stoichiometry. Populations of all four daphniids stabilized at very low birth and death rates, with larger species having a lower density but a higher biomass than smaller species. The seston C: P molar ratio was driven to equally high values (>300) in all treatments; however, daphniid effects on phytoplankton abundance and composition were quite different. The two smaller daphniids were less effective at depressing phytoplankton populations than were the two larger daphniids. This difference was associated with the persistence of a diverse assemblage of digestionresistant green algae in the Ceriodaphnia and D. ambigua treatments but their elimination from the D. mendotae and D. pulicaria treatments. Several lines of evidence, including growth bioassays, that have used juveniles of a clone of D. pulex‐pulicaria, suggest that body size was not an adequate explanation for these differences in daphniid species effects on phytoplankton.
Small‐scale oxygen fluxes and remineralization in sinking aggregates
Authors: Ploug Helle
Published: June 2010

Sinking aggregates are the major component of the vertical particulate flux in most regions of the ocean. Controlling factors for aggregate remineralization rates and solute exchange with the surrounding water, however, are poorly quantified because of few empirical data. To study the role of flow and diffusion on aggregate remineralization rates, oxygen distributions were mapped within and around aggregates by use of microelectrodes in a flow field similar to that experienced by sinking aggregates. The oxygen distribution was asymmetrical with a wake of undersaturated water at the rear (downstream) of the aggregates. Oxygen concentrations within the aggregates were >80% of air saturation. The diffusive fluxes of oxygen at the aggregate‐water interface were similar along the equator and at the downstream pole for a wide range of different aggregate sources (field‐sampled diatom aggregates, lab‐made diatom aggregates, aggregates formed from freeze‐thawed diatoms, and zooplankton detritus aggregates) measured at various temperatures. Remineralization rates were reaction limited and, hence, determined by substrate quality and quantity rather than by transport‐limited oxygen supply during sedimentation at ambient oxygen concentrations above ~25 µM.
Role of the oxygen‐deficient zone in transfer of organic carbon to the deep ocean
Authors: Devol Allan H. , Hartnett Hilairy E.
Published: June 2010

Benthic carbon oxidation rates and carbon burial rates have been determined for two contrasting continental margins and their sum has been used as an estimate of carbon rain rate to the sediments. On the Washington State margin, where the water column is oxic, rain rates at 100 m were about 15 to 20 mmoles C m−2 d−1 and they decreased with increasing water depth to values of near 3 mmoles C m−2 d−1 at 1,000 m. The rain rate estimates, CR, were described by a power function, CR = CR100m(z/100)−α, with an attenuation coefficient, α, of 0.93 (CR100m = 16.2, r2 = 0.89). This attenuation rate is similar to numerous others previously reported for various oceanic areas. In contrast, off northwest Mexico, where the water column is oxygen deficient between 180 and 700 m, rain rates at 100 m were considerably less, about 7.5 mmoles C m−2 d−1, but rain rates at 1,000 m were similar to those off Washington. Thus, the attenuation coefficient for the Mexican margin was significantly lower, α = 0.36 (CR100m = 7.4, r2 = 0.77). Off Mexico, the rain rates estimated from sedimentary parameters were corroborated by values determined directly from sediment‐trap deployments. The generally smaller rain rates off Mexico are probably due to the lower primary production, hence lower initial supply. The lower attenuation rate, however, is hypothesized to result from a decreased oxidation rate of the sinking flux within the oxygen‐deficient zone relative to a more typical oxic water column.
The interaction between physical disturbance and organic enrichment: An important element in structuring benthic communities
Authors: Widdicombe Stephen , Austen Melanie C.
Published: June 2010

The interaction between physical disturbance and organic enrichment, with respect to its effect on the diversity and community structure of a macroinfaunal assemblage, has been examined in a benthic mesocosm experiment. The experiment was conducted at the Solbergstrand mesocosm (Norwegian Institute for Water Research) using subtidal sediment collected from Bjørnhordenbukta, a small sheltered bay in Oslofjørd. Ninety‐eight areas of homogenized sediment were subjected to one of seven levels of organic enrichment, combined with one of seven different frequencies of physical disturbance, each replicated once. This structured matrix of physical disturbance and organic enrichment treatments demonstrated the combined effects of these factors to be nonadditive. Diversity was lower than expected when low frequencies of physical disturbance acted in conjunction with high levels of organic enrichment or when high frequencies of physical disturbance were combined with low levels of organic enrichment. Diversity was higher than expected when both disturbance and enrichment were either high or low. The implications of this interaction between physical disturbance and organic enrichment for the application of the dynamic equilibrium model (Huston 1979) to sediment communities are discussed. Multivariate analysis also showed community structure to be significantly affected by physical disturbance, organic enrichment, and interactions between the two. It is concluded that strong interactions between physical disturbance and organic enrichment, coupled with both small‐ and large‐scale variability in these factors, could promote heterogeneity and diversity in benthic infaunal assemblages. However, this remains to be tested in field conditions. Additionally, interactions between physical disturbance and organic enrichment may have important implications for matters of coastal zone management.
Mass balance of heavy metals in New Haven Harbor, Connecticut: Predominance of nonpoint sources
Authors: Rozan Timothy F. , Benoit Gaboury
Published: June 2010

A mass balance was constructed quantifying all known sources and sinks for the metals Ag, Cd, Cu, and Pb in New Haven Harbor, Connecticut, USA. Sources included direct atmospheric deposition, rivers, treated sewage effluent, combined sewer overflows, and permitted industrial discharge. Sinks were burial in sediments, tidal exchange with Long Island Sound, removal in salt marshes, and dredging. All of these fluxes were measured directly, rather than estimated, and uncertainties were quantified. The mass balance closed successfully within the uncertainty of the measurements. Riverine inputs account for most of the total yearly metal flux. Metal concentrations in the river can be approximated as a simple linear function of discharge. Salt marshes remove an amount of metal equivalent to 20%–30% of the flux from the river before it reaches the harbor. Burial in sediments is the major sink for all metals examined, but dredging acts as a substantial short‐circuit of this sink. Tidal exchange appears to be a relatively small term; however, it is also the least well quantified. Sewage treatment plant (STP) effluent and combined sewer overflow discharge are minor contributors to the overall metal balance, except in the case of Ag. Metal concentrations in STP effluent are a linear function of discharge. Atmospheric deposition is of minor importance but is comparable to sewage effluent. Lakes can be used as natural collectors and indicators of atmospherically deposited metals.
Benthic‐pelagic coupling and suspension‐feeding bivalves: Linking site‐specific sediment flux and biodeposition to benthic community structure
Authors: Norkko Alf , Hewitt Judi E. , Thrush Simon F. , Funnell Thrush
Published: June 2010

Suspension‐feeding bivalves play an important role in coastal ecosystems by affecting near‐bed hydrodynamics and, subsequently, rates of biodeposition. We designed a high‐resolution field study to investigate rates of sedimentation and biodeposition around individuals within beds of the large pinnid bivalve, Atrina zelandica, and to link these rates with sediment biogeochemical characteristics and macrofaunal community structure. The study was conducted at three sites arrayed along a gradient of increasing suspended seston concentration, enabling us to assess changes in the strength of the Atrina‐macrofauna interaction with background sedimentation. Sedimentation rates and inputs of organic carbon and nitrogen were higher close to individual Atrina (<=10 cm) compared to further away (>30 cm). Seafloor sediments nearer Atrina were enriched in carbon and nitrogen and had more diverse and abundant macrofaunal assemblages. The strength of this interaction decreased with increasing background sedimentation. Although other mechanisms, both biotic and abiotic, may explain some of these patterns, we have identified variations in macrofaunal community structure that at least partly can be linked to site‐specific sedimentation, at the small scale of single Atrina, nested within the larger landscape scale of Atrina beds, emphasizing Atrina's role in habitat modification, both structurally and functionally.
An in situ instrument for planar O2 optode measurements at benthic interfaces
Authors: Glud Ronnie N. , Tengberg Anders , Kühl Michael , Hall Per O. J. , Klimant Ingo
Published: June 2010

A new in situ instrument for two‐dimensional mapping of oxygen in coastal sediments is presented. The measuring principle is described, and potential mechanical disturbances, solute and particle smearing associated with the measurements, and calibration routines are evaluated. The first in situ measurements obtained in two different benthic communities are presented. In a shallow photosynthetic sediment (1 m of water depth), an extensive horizontal and temporal variation in the O2 distribution caused by benthic photosynthesis and irrigating fauna was resolved. Repetitive planar optode measurements performed along a transect in central Øresund, Denmark (17 m of water depth) revealed a positive correlation between the apparent O2 penetration depths (OP) measured with a lateral distance <5.0 mm, whereas OP measured with a larger horizontal distance (up to 50 m) were not correlated. Consequently, the OP varied in patches with a characteristic size of 5.0 mm. The instrument described is a powerful new tool for in situ characterization of spatiotemporal variations in O2 distributions within benthic communities. The instrument can be adapted for use at full ocean depths, e.g., on deep‐sea landers or remote operating vehicles.
Multiyear increases in dissolved organic matter inventories at Station ALOHA in the North Pacific Subtropical Gyre
Authors: Church Matthew J. , Ducklow Hugh W. , Karl David M.
Published: June 2010

The inventories and dynamics of dissolved organic matter (DOM) in the surface water at Station ALOHA were analyzed from the Hawaii Ocean Time‐series (HOT) data set for the period 1989—1999. Euphotic zone, depthintegrated (0—175 m) concentrations of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were temporally variable. In particular, during the period 1993—1999, concentrations of DOC and DON increased while inventories of DOP remained unchanged. DOC inventories increased by 303 mmol C m−2 yr−1, a value equivalent to approximately 2% of measured primary production (14C method) at this site. DON increased at 11 mmol N m−2 yr−1, resulting in a mean molar DOC:DON ratio of 27.5 for the accumulated DOM. Accumulation of DOC and DON without corresponding accumulation of DOP resulted in changes to the bulk organic C:N: P stoichiometry; bulk DOC:DOP ratios increased 16% and DON:DOP ratios increased by 17%. These results indicate that a small fraction of the annually produced organic matter escaped biological utilization on time scales of months to years. More importantly, the accumulated DOM inventories grew progressively enriched in C and N relative to P. Fundamental changes in the North Pacific Subtropical Gyre (NPSG) habitat appear to have altered microbial processes that regulate organic matter fluxes. Considered together, the long‐term increases in DOC and DON inventories are consistent with previous observations, indicating that a recent reorganization of plankton community dynamics may have altered organic matter cycling in this ecosystem.
Coupled dynamics of dimethylsulfoniopropionate and dimethylsulfide cycling and the microbial food web in surface waters of the North Atlantic
Authors: Simó Rafel , Archer Stephen D. , Pedrós-Alió Carlos , Gilpin Linda , Stelfox-Widdicombe Claire E.
Published: June 2010

Oceanic dimethylsulfide (DMS), the main natural source of sulfur to the global atmosphere, is suggested to play a key role in the interaction between marine biota and climate. Its biochemical precursor is dimethylsulfoniopropionate (DMSP), a globally distributed, intracellular constituent in marine phytoplankton. During a multidisciplinary Lagrangian experiment in the subpolar North Atlantic, we determined the fluxes of DMSP and DMS through phytoplankton, microzooplankton, and bacterioplankton and compared them with concurrent carbon and sulfur fluxes through primary and secondary productions, grazing, and release and use of dissolved organic matter. We found that DMSP and derivatives contributed most (48–100%) of the sulfur fluxes and 5–15% of the carbon fluxes. Our findings highlight DMSP as a prominent player in pelagic biogeochemical pumps, especially as a major carrier in organic sulfur cycling. Also, our results illustrate the key role played by microzooplankton and heterotrophic bacteria (hence the microbial food web) in controlling the amount of phytoplanktonic DMSP that ultimately vents to the atmosphere in the form of DMS.
Increased sensitivity to ultraviolet radiation in nitrogen‐limited dinoflagellates: Photoprotection and repair
Authors: Litchman Elena , Neale Patrick J. , Banaszak Anastazia T.
Published: June 2010

Nitrogen (N) limitation significantly increased the sensitivity of photosynthesis to inhibition by ultraviolet radiation (UV) in two estuarine dinoflagellates, Akashiwo sanguinea (= Gymnodinium sanguineum) and Gymnodinium (= Gyrodinium) cf. instriatum. Biological weighting functions (BWFs) and the kinetics of photosynthetic response to UV indicated that the main mechanism for the increase in sensitivity was less efficient repair. A decrease in cell size and in the concentration of the photoprotective mycosporine‐like amino acids also elevated sensitivity. The BWFs predict that increased UV‐B due to ozone depletion would cause a more than 1.5‐fold greater additional inhibition of N‐limited compared to nutrient‐sufficient dinoflagellates. The BWFs of the N‐limited cultures are similar to those measured for natural assemblages of phytoplankton in the Chesapeake Bay under low N availability.
Impacts of nutrients and grazing mortality on the abundance of Aureococcus anophagefferens during a New York brown tide bloom
Authors: Gobler Christopher J. , Renaghan Marc J. , Buck Nathaniel J.
Published: June 2010

Although nutrients and grazing both contribute to the formation of harmful algal blooms, research on these events has rarely considered both factors simultaneously. To ascertain the impact of nutrients and grazing on brown tides of Aureococcus anophagefferens, nutrient bioassays were conducted in parallel with dilution‐style microzooplankton grazing experiments during an intense bloom that occurred throughout Great South Bay (GSB), New York, in fall of 1999. During the study, Aureococcus represented between 25 and 85% of phytoplankton biomass and attained peak cell densities > 6 × 105 cells ml−1. Concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in GSB were high (mean = 430 µM and 32 µM, respectively) during the bloom, while dissolved inorganic nitrogen (DIN) levels were low (mean = 2.5 µM). Although the experimental additions of nitrogen (nitrate or urea) typically enhanced the growth rates of the non‐brown tide phytoplankton community, such additions often had no impact on, or decreased, growth rates of Aureococcus relative to unamended control treatments. These observations suggest that growth of non‐brown tide phytoplankton depended on ambient N supply rates, while Aureococcus experienced nutrient replete growth. Dilution experiments indicated that microzooplankton grazing rates on A. anophagefferens were significantly lower than those on other algal populations. This reduced grazing pressure contributed toward higher net growth rates for Aureococcus relative to non‐brown tide phytoplankton. In sum, these results demonstrate that both top‐down (low grazing mortality rates) and bottom‐up (a high DOC/DON, low DIN nutrient regime) factors can contribute to the proliferation of brown tide blooms in New York waters.
Flux of larval fish around Cape Hatteras
Authors: Grothues Thomas M. , Cowen Robert K. , Pietrafesa Leonard J. , Bignami Francesco , Weatherly Georges L. , Flagg Charles N.
Published: June 2010

Convergence of shelf water flows from the Middle and South Atlantic Bights (MAB and SAB) upon Cape Hatteras, North Carolina, presents a potential barrier to the exchange of fish larvae between bights. Impinging water often turns northeastward with the Gulf Stream, and larvae of both cool temperate and warm temperate/subtropical shelf fishes suffer expatriation. Transient oceanographic features exist, however, facilitating shelf retention, cross‐bight exchange, and return of expatriated larvae. The impact of these features is mitigated by specific distribution with relation to hydrography, resulting in a selective permeability of this barrier. Dynamic oceanography may result in dynamic recruitment success. We measured the springtime (1996) flux of seven larval fish species assemblages across the confluence by coupling measured water mass/depth specific larval fish concentration with water mass transport values obtained from an extensive moored instrument survey. Strong flows of shallow shelf water from the MAB to the SAB dominated transport of MAB spawned larvae even for groups with highest concentrations in waters without strong net flows. Most of these larvae passed from the MAB or the open sea into the study region shelf and from there into the SAB. Net flow of SAB water into the convergence retained SAB‐affiliated larvae arriving from the south, but nearshore MAB flows transported low numbers from the MAB to the SAB. The importance of this is tied to the unknown point of introduction of these SAB larvae to MAB waters (e.g., well north of the confluence), but northward exchange of SAB‐spawned fish was always prevented along the southern MAB shelf.
Relating nutrient uptake with transient storage in forested mountain streams
Authors: Hall Robert Jr. O. , Bernhardt Emily S. , Likens Gene E.
Published: June 2010

Streams control the timing and delivery of fluvial nutrient export from watersheds, and hydraulic processes such as transient storage may affect nutrient uptake and transformation. Although we expect that hydraulic processes that retain water will increase nutrient uptake, the relationship between transient storage and nutrient uptake is not clear. To examine this relationship, we injected a conservative tracer and nutrients (ammonium and phosphate) into 13 streams for a total of 37 injections at Hubbard Brook Experimental Forest (HBEF), New Hampshire. Transient storage was estimated by fitting conservative solute data to a one‐dimensional advection, dispersion, transient storage model. To correct for variation in depth and velocity among streams, we considered nutrient uptake as a masstransfer coefficient (Vf), which estimates benthic demand for nutrients relative to supply. Transient storage decreased with increasing specific discharge (discharge per unit stream width). Transient storage explained only 14% of variation in ammonium Vf during the entire year and 35% of variation during summer months. Phosphate uptake was not related to transient storage, presumably because P uptake is predominantly by chemical sorption at HBEF. At HBEF, surface water pools can store water but were not modeled as such by use of the transient storage model. These pools were probably not important areas of nutrient uptake; further variation in the relationship between nutrient uptake and transient storage may be explained by biological demand.
UV‐induced pigmentation in subarctic Daphnia
Authors: Rautio Milla , Korhola Atte
Published: June 2010

The distribution of the planktonic crustacean Daphnia and the occurrence of ultraviolet (UV)‐protective melanin pigmentation in its body wall were studied in relation to the UV transparency in subarctic ponds and lakes in Finnish Lapland. In shallow ponds, Daphnia only occurred in those with sufficient amounts of UV‐screening dissolved organic matter. The highest pigment concentration was found in these Daphnia and in populations that occurred in lakes with low organic carbon content (<2 mg L−1). Pigment synthesis was extremely low during the long winter and peaked immediately after the ice break‐up at the time of the maximum underwater UV intensity. We propose that the predicted increase in UV irradiance from ozone depletion in the Northern Hemisphere spring, along with the earlier ice break‐up associated with Arctic warming may favor the survival of those organisms with the ability to produce UV photoprotective pigments.
Interpreting stable isotopes in food webs: Recognizing the role of time averaging at different trophic levels
Authors: O'Reilly C. M. , Hecky R. E. , Cohen A. S. , Plisnier P.-D.
Published: June 2010

Lake Tanganyika, East Africa, has a simple pelagic food chain, and trophic relationships have been established previously from gut‐content analysis. Instead of expected isotopic enrichment from phytoplankton to upper level consumers, there was a depletion of 15N in August 1999. The isotope signatures of the lower trophic levels were an indicator of a recent upwelling event, identified by wind speed and nitrate concentration data, that occurred over a 4‐d period several days prior to sampling. The isotope structure of the food web suggests that upwelled nitrate is a nutrient source rapidly consumed by phytoplankton, but the distinctive signature of this nitrate is diluted by time averaging in the upper trophic levels. This time averaging is a consequence of the fact that the isotopic signature of an organism is related to variable nitrogen sources used throughout the life of the organism. This study illustrates the importance of recognizing differences in time averaging among trophic levels.