bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterotrophic feeding by gorgonian corals with symbiotic zooxanthella
Authors: Ribes Marta , Coma Rafel , Gili Josep‐Maria
Published: May 2010

Gorgonians are one of the most characteristic groups in Caribbean coral reef communities. In this study, we measured in situ rates of grazing on pico‐, nano‐, and microplankton, zooxanthellae release, and respiration for the ubiquitous symbiotic gorgonian coral Plexaura flexuosa. Zooplankton capture by P. flexuosa and Pseudoplexaura porosa was quantified by examination of stomach contents. In nature, both species captured zooplankton prey ranging from 100 to 700 µm, at a grazing rate of 0.09 and 0.23 prey polyp−1 d−1, respectively. Because of the greater mean size of the prey and the higher mean prey capture per polyp, P. porosa obtained 3.4 × l0−5 mg C polyp−1 d−1 from zooplankton, about four times the grazing rate of P. flexuosa. On average, P. flexuosa captured 7.2 ± 1.9 microorganisms polyp−1 d−1 including ciliates, dinoflagellates, and diatoms, but they did not appear to graze significantly on organisms <5 µm (heterotrophic bacteria, Prochlorococcus sp., Synechococcus sp., or picoeukaryotes). Zooplankton and microbial prey accounted for only 0.4% of respiratory requirements in P. flexuosa, but they contributed 17% of nitrogen required annually for new production (growth and reproduction). Although the contribution of microbial prey to gorgonian energetics was low, dense gorgonian populations found on many Caribbean reefs may be important grazers of plankton communities.
Laboratory measurements of angular distributions of light scattered by phytoplankton and silt
Authors: Volten H. , de Haan J. F. , Hovenier J. W. , Schreurs R. , Vassen W. , Dekker A. G. , Hoogenboom H. J. , Charlton F. , Wouts R.
Published: May 2010

We present laboratory measurements of scattering properties of 15 different types of coastal and inland water phytoplankton species and two types of estuarine sediments. These properties are the scattering function as well as the angular distribution of a ratio of scattering matrix elements, which in practice equals the degree of linear polarization of the scattered light if the incident light is unpolarized. Laser light with a wavelength of 633 nm was used, and a scattering angle range from 20° to 60° was covered. The results can be used in the context of water quality studies and to test results of theoretical models. The measured scattering functions are all strongly peaked in forward directions, but not equally so. For the covered angles, they vary significantly as a function of scattering angle. The measured angular distributions of the degree of linear polarization are mostly bell shaped, showing a maximum near 90°, whose magnitude is clearly different for the phytoplankton compared to the silt particles. We find that the morphology and structural features of the particles studied play an important and complex role in their light‐scattering behavior. In particular, internal cell structures such as gas vacuoles alter the scattering patterns of the phytoplankton species considerably. The external shape of the cells appears to have a much smaller influence. The experimental results are compared with results of Mie calculations and with the “standard scattering function” of San Diego Harbor water. In most cases, Mie calculations cannot provide an adequate approximation of the measured scattering behavior, which indicates that more sophisticated models are required. Only 3 of the 17 measured scattering functions resemble the San Diego Harbor standard scattering function. One of these pertains to small silt particles, showing that this function is representative for water dominated by these particles.
Microbiological mediation of spectral reflectance from intertidal cohesive sediments
Authors: Paterson D. M. , Wiltshire K. H. , Miles A. , Blackburn J. , Davidson I. , Yates M. G. , McGrorty S. , Eastwood J. A.
Published: May 2010

Analysis of upwelling radiation (spectral reflectance) by remote sensing may provide valuable information on the nature and distribution of the primary producers, the microphytobenthos, on intertidal mudflat systems. Spatial and temporal variation in the spectral reflectance signal (400–900 nm) from the surface of an exposed intertidal mudflat was investigated in relation to the density and vertical position of microphytobenthos assemblages within the sediment. Spatial measurements were obtained from areas of sediment colonized by different assemblages of microphytobenthos (mainly mixtures of diatoms and euglenids). In addition, a station was selected to examine temporal changes in spectral reflectance (corrected for variations in ambient light) over an exposure period. It was shown that the spectral reflectance signal varied, depending on the pigment compliment and biomass of the surface assemblages of microphytobenthos. The qualitative variation in composition of the assemblages visualized by low‐temperature scanning electron microscopy was confirmed by analysis of species composition (light microscopy) and by pigment fingerprinting (diode array high‐performance liquid chromatography [HPLC]). Time‐series analysis showed that the migration of cells to the surface of the sediment during a daytime emersion period rapidly changed the optical properties of the sediment surface. Analysis of sediment pigment content was conducted using standard surface scrapes (0.5‐cm depth) and a high resolution sectioning technique (200‐µm layers). The migration influence was only detected by fine‐scale analysis of pigments. This was demonstrated by a step‐wise elimination analysis, which showed that correlations between the absorbance characteristics of the sediment and pigment content improved as premigration data were excluded. Maximum light penetration into the natural sediment was of the order of 2 mm under light conditions comparable with ambient levels. Two main conclusions were drawn from this study: (1) interpretation of spectral reflectance data must be consistent with knowledge of the ecology and behavior (cyclic migration patterns) of intertidal microphytobenthos, and (2) ground truthing of pigment‐related signals from intertidal flats should be conducted on a scale relevant to the process of spectral reflectance from sediments. The implications of these findings are discussed.
Groundwater flow influences the biomass and nutrient ratios of epibenthic algae in a north temperate seepage lake
Authors: Hagerthey Scot E. , Kerfoot W. Charles
Published: May 2010

Groundwater flow influenced epibenthic algal biomass and N:P ratios at a seepage lake (Sparkling Lake, Wisconsin). During seasonal studies, biomass and seepage flux were positively associated (r = 0.453; P < 0.001). Pore‐water soluble reactive phosphorus (SRP) concentrations (29.2–110.7 µg PO, liter−1), SRP fluxes, and algal biomass were significantly higher at high groundwater discharge sites than at low flow sites (< 10.0 to 27.7 µg PO4 liter−1). Pore‐water ammonia (NH4+) concentrations were significantly lower at high groundwater discharge sites (<10.0 to 566.0 µg NH4+ liter−1) than at low groundwater discharge and recharge sites (61.4–1464.9 µg NH3 liter−1). The coupling between pore‐water nutrient concentrations and local groundwater flow dynamics suggests a mechanism for the observed spatial patterns in biomass. In situ experimental chambers evaluated coupling between epibenthic algal biomass, N:P ratios, and groundwater flow patterns. Biomass responded rapidly in chambers, reaching ambient levels within 1.5 months of initiation. Free‐flow chambers in discharge regions had consistently higher soluble reactive phosphorus (SRP), NO3‐NO2, and O2 concentrations, higher phosphate and nitrate‐nitrite fluxes, higher algal biomass, and lower N:P ratios in the developing mat. Free‐flow chambers in recharge regions had high ammonia (NH3) concentrations, lower algal biomass, and higher N:P ratios. These results confirm that groundwater‐related nutrient fluxes influence the local physicochemical environment and affect epibenthic algal biomass.
Photosynthetic production and photoadaptation of phototrophic sulfur bacteria in Lake Cadagno (Switzerland)
Authors: Schanz F. , Fischer‐Romero C. , Bachofen R.
Published: May 2010

Lake Cadagno is a meromictic lake of 21‐m depth in the central Swiss Alps at 1,923 m asl. Its mixolimnion reaches from the surface down to 10‐m depth. A dense population of phototrophic bacteria dominated by Chromatium okenii is located in the subsequent 2‐m layer containing up to 200 mg bacteriochlorophyll (Bchl) m−3. Maximum cell concentration was found at 10.‐m depth during the summer season. The light intensity at the upper edge of the bacterial layer averages 4.7% of the subsurface radiation (at 0.05 m depth) and at the density peak of the layer it averages 0.4%. Variations over the summer season in the photosynthetic properties of the bacterial population at the depth of highest cell density have been observed in in situ 14C‐CO2 incorporation experiments. These changes are random, and no photoadaptation effect was found. Thus, the population of phototrophic bacteria was physiologically uniform during the investigation period and it had the following photosynthetic properties (medians for the 25th and 75th percentiles are in parentheses): Pmax, 0.154 mg C (mg Bchl)−1 h−1 (0.048, 0.174); Ik, 0.016 mol quanta m−2 h−1 (0.012, 0.019); (α, 7.7 mg C (mg Bchl)−1 h−1 (mol quanta m−2 h‐−1)−1 (4.8, 11.6). The specific dark production rate was 0.016 mg C (mg Bchl)−1 h−1 (0.014, 0.023). The average quantum yield for CO2 assimilation at the depth of maximum cell density, φ, was low at 0.012 (0.007, 0.020). The cells were sensitive to light intensities higher than the optimum found at ~0.036 mol quanta m−2 h−1. Maximum inhibition by excessive light was determined to be 80% at light intensities >0.108 mol quanta m−2 h−1 (=30 µmol quanta m−2 s−1) when cells were exposed for periods of 2.5 h or longer. The bacterial biomass increment assuming no losses, µ*, was calculated to be 0.05 d−1 (0.03, 0.08) and the loss rate, λ, to be 0.03 d−1 (−0.10, 0.06).
The effects of the moss Fissidens rigidulus (Fissidentaceae: Musci) on near‐bed flowstructure in an experimental cobble bed flume
Authors: Nikora Vladimir I. , Suren Alastair M. , Brown Stephanie L. R. , Biggs Barry J. F.
Published: May 2010

The effects of the aquatic moss Fissidens rigidulus on near‐bed flow structure in a cobble‐lined flume were investigated. Moss‐covered cobbles were placed in the flume, and velocities were measured at six vertical profiles upstream, above, and downstream of the cobbles. All measurements were replicated at three different discharges. An acoustic doppler velocimeter (ADV) was used to measure velocity fluctuations in three dimensions at each point, at a 0.04‐s sampling interval for 2 min. Following this, the moss was removed without disturbing the cobbles' spatial arrangement, and measurements were repeated to characterize background hydraulic conditions. We investigated mean local velocities, Reynolds stresses, total turbulence energy, relative turbulence intensities, and velocity spectra with and without the moss. Two flow layers were observed in all our experiments: an upper logarithmic layer and a lower roughness sublayer. Velocities in the upper layer followed the standard logarithmic law, whereas velocities in the roughness sublayer did not, because of interaction between flow and the roughness elements. The presence of Fissidens caused a reduction in average longitudinal velocity, Reynolds stress, and total turbulence energy. Relative turbulence intensity was much higher in the presence of the moss. An internal boundary layer (IBL) around the moss was also observed; this IBL was destroyed behind the moss by turbulent mixing in the roughness sublayer. The IBL thickness increased with increasing flow.
Size‐dependent C:N uptake by phytoplankton as a function of irradiance: Ecological implications
Authors: Frenette Jean‐Jacques , Vincent Warwick F. , Legendre Louis
Published: May 2010

Dual‐labeling assays were performed on the phytoplankton community of Lake Biwa (Japan) to estimate the ratio of inorganic carbon to nitrate‐N uptake as a function of cell size and irradiance. The assays were conducted during a period of change in underwater light and phytoplankton species composition associated with typhoon‐induced mixing events. There were consistent qualitative differences in the C:N uptake characteristics of large (>2 µm) versus small (<2 µm) phytoplankton. For both fractions, the ratio of C:N uptake versus irradiance was well described by a log‐log model; however, in the majority of assays, the slope of the relationship was positive for the >2‐µm fraction and negative for the small cells. This striking difference between the two fractions also corresponded to patterns in the C:N stoichiometry of the plankton. Surface samples of the >2‐µm fraction had a higher C:N ratio than deep populations; this pattern was not seen in the <2‐µm seston. Similarly, a decrease in water‐column transparency associated with the typhoon events was accompanied by a significant correlative trend of increasing C:N ratios in the <2‐µm fraction and decreasing C:N ratios in the >2‐µm fraction. These observations imply that in aquatic ecosystems where nitrate plays an important role in the nitrogen economy of the phytoplankton, high‐irradiance conditions favor maximum biomass production per unit of nitrogen uptake by large phytoplankton, and low‐irradiance conditions favor a high biomass increment per unit of nitrogen uptake by small cells. These observations are consistent with the ecological distribution of large‐ versus small‐cell phytoplankton in several types of freshwater and marine environments.
Photochemical transformations of surface and deep marine dissolved organic matter: Effects on bacterial growth
Authors: Benner Ronald , Biddanda Bopaiah
Published: May 2010

The effects of photochemical transformations on the bioavailability of marine dissolved organic matter (DOM) were investigated in surface and deep water from the Gulf of Mexico. Seawater samples were collected from eight depths (15–1,000 m), passed through 0.2‐µm pore‐size filters, and exposed to sunlight in quartz bottles in a flowing seawater deck incubator for 5‐9 h. Following sunlight exposure, samples were inoculated (1:10) with unfiltered seawater from 15‐m depth, and bacterial growth rates were estimated from rates of 3H‐leucine incorporation in dark incubations. Exposure of surface‐water DOM to sunlight resulted in a 75% reduction in bacterial production, whereas exposure of deep‐water DOM resulted in a 40% enhancement in bacterial production. Photomineralization of bioreactive DOM likely contributed to the reduction of bacterial growth in surface water, but the photoproduction of biorefractory DOM also appeared to contribute to reduced bacterial growth. Enhanced bacterial growth in irradiated deep water was consistent with previous studies demonstrating the photoproduction of bioavailable substrates from deep‐water DOM. Phototransformations of DOM appeared to be multifaceted and to play a critical role in the cycling of DOM in the ocean.
Coral reef sponges: Do predatory fishes affect their distribution?
Authors: Pawlik Joseph R.
Published: May 2010

The predatory activities of fishes are thought to have little impact on the distribution and abundance of sponges on Caribbean coral reefs. To test this premise, 15 species of sponges were transplanted from mangrove and grassbed habitats, where spongivorous fishes are rare, to shallow patch reefs, where spongivorous fishes are common. Twelve of these 15 sponge species could also be found in cryptic locations, but not in conspicuous locations, on nearby reefs. After 3 d, there was significant loss of wet mass of uncaged sponges versus caged sponges for nine sponge species because of consumption by spongivores, primarily angelfishes. A mean of >50% of the sponge tissue was consumed for seven species: Chondrilla nucula, Chondrosia collectrix, Geodia gibberosa, Halichondria sp., Halichondria melanodocia, Myriastra kalitetilla, and Tedania ignis. These results, in addition to other recent data on the chemical defenses of Caribbean reef sponges against generalist predatory fishes, suggest that predation plays an important role in structuring the reef sponge community and that predation limits the distribution of some Caribbean sponges.
Chemical cues: Why basic peptides are signal molecules in marine environments
Authors: Decho Alan W. , Browne Kenneth A. , Zimmer‐Faust Richard K.
Published: May 2010

Waterborne chemical cues are critical in mediating interactions among marine organisms, yet mechanisms controlling the extinction of these signals have not been described. Exogenous factors, such as uptake by bacteria or adsorption to suspended clays or biofilms, could influence the concentrations of environmental signal molecules. In this study, we chose glycyl‐glycyl‐L‐arginine (GGR) to examine the rates and mechanisms of peptide uptake by a natural assemblage of marine bacteria. GGR is a potent synthetic analog of the natural cue‐inducing settlement by oyster larvae. Kinetic parameters for the microbial uptake and colloidal adsorption of glycine, L‐arginine, and GGR were determined from the decay of 14C‐radiolabeled substrates and from high‐performance liquid chromatography (HPLC) analyses. The bacterial uptake rate constant (ksubstrate) was 3.5‐fold smaller for GGR (0.019 h−1 for 40‐1,000 nM substrate concentration) than for its component amino acids. Nonspecific adsorption of GGR onto colloids had a similar rate constant (0.021 h−1). HPLC analyses of peptide solutions did not indicate any build‐up of glycine, Larginine, glycyl‐L‐arginine, or glycyl‐glycine, the potential proteolytic products of GGR, during experiments. Thus, it is unlikely that the nonradiolabeled portion of GGR was cleaved extracellularly before internalization. Our results show that the tripeptide GGR is taken up by marine bacteria at significantly slower rates than are its component amino acids. The slow utilization of GGR by bacteria and low adsorption to colloids could provide at least one rationale‐signal persistence‐for the selection of basic peptides as chemical cues in marine environments.
Modelling cadmium accumulation by benthic invertebrates in situ: The relative contributions of sediment and overlying water reservoirs to organism cadmium concentrations
Authors: Warren Lesley A. , Tessier André , Hare Landis
Published: May 2010

An in situ experiment was designed (1) to determine the relative importance of Cd in the sediment versus Cd in the overlying water for its accumulation in benthic animals and (2) to test in situ the acid volatile sulfide (AVS) model. Sediments of a low‐Cd shield lake were artificially contaminated with various amounts of Cd and placed at a littoral site in open plastic containers in the lake bottom for 11 months to allow colonization by indigenous lake bcnthos. Gradients in sedimentary and interstitial water Cd concentrations were, thus, created in situ, although Cd concentrations in the overlying water remained low. Accumulation of Cd by benthic invertebrates was significantly and linearly correlated with sediment Cd concentrations across treatment levels for most taxa. The magnitude of the response to the sediment Cd gradient was taxon specific and consistent with differences in animal ecology. Despite the high Cd contamination levels attained in the experiment, the population densities of most taxa appear to have been unaffected by the presence of Cd. We used the results from the experimental containers to predict the sources of Cd for benthic animals in the environs. For almost all of the taxa studied, individuals living in the low‐Cd sediments outside the experimental containers accumulated their Cd almost exclusively from the overlying water; only the burrowing, sediment‐feeding taxa Chironomus stuegeri and members of the Tubificidae obtained substantial Cd from the sediment. Cadmium activities in the pore waters of the containers were in agreement with the AVS model, but the Cd concentrations found in the benlhic organisms did not. Our results from this shield lake suggest that predictions of Cd concentrations in most benthic animals would be more accurate if they were based on water column rather than on sedimentary Cd concentrations.
Hypolimnetic methylmercury and its uptake by plankton during fall destratification:A key entry point of mercury into lake food chains?
Authors: Herrin Russell T. , Lathrop Richard C. , Gorski Patrick R. , Andren Anders W.
Published: May 2010

Seasonal concentration changes in monomethylmercury (MMHg) and total Hg (T‐Hg) were determined in Devil's Lake, Wisconsin, a lake with a mercury consumption advisory for walleye. Mercury dynamics were studied in water and several lower food chain fractions during the ice‐free seasons in 1994 and 1995, and limited data for Hg in water were collected in 1993. MMHg concentrations increased in hypolimnetic waters before turnover each year, although maximum concentrations declined from 1993 to 1995. As the hypolimnion eroded, MMHg concentrations increased in both particulate matter and Daphnia. Maximum concentrations were obtained near the time of complete mixis. The magnitude of this increase correlated with the mass of hypolimnetic MMHg that had built up prior to turnover in 1994 and 1995. Hg concentrations in yearling planktivorous fish exhibited a decline corresponding to the decline in hypolimnetic MMHg from 1993 to 1995. Our results suggest that fall destratification represents an important time period for entry of MMHg to the food chain of lakes exhibiting a hypolimnetic MMHg buildup.
Interpretation of measured concentration profiles in sediment pore water
Authors: Berg Peter , Risgaard‐Petersen Nils , Rysgaard Søren
Published: May 2010

A robust numerical procedure for biogeochemical interpretation and analysis of measured concentration profiles of solutes in sediment pore water has been developed. Assuming that the concentration‐depth profile represents a steady state, the rate of net production or consumption as a function of depth can be calculated, together with the flux across the sediment‐water interface. Three kinds of vertical transport can be included in the analysis: molecular diffusion, bioturbation, and irrigation. The procedure involves finding a series of least square fits to the measured concentration profile, followed by comparisons of these fits through statistical F‐testing. This approach leads to an objective selection of the simplest production‐consumption profile that reproduces the concentration profile. Because the numerical procedure is optimized with respect to speed, one prediction can typically be done in a few minutes or less on a personal computer. The technique has been tested successfully against analytical solutions describing the transport and consumption of O2 in sediment pore water. In other tests, measured concentration profiles of O2, NO3−, NH4+, and ΣCO2 have been interpreted using the new procedure.
Spatial and temporal dynamics of major solute chemistry among Mackenzie Delta lakes
Authors: Lesack Lance F. W. , Marsh Philip , Hecky Robert E.
Published: May 2010

The Mackenzie Delta of the Canadian arctic is a complex environment, containing ~25,000 lakes, where annual river flooding may exert a considerable degree of control over the ecological characteristics of lakes in the system. The solute composition of 92 lakes representing differing frequencies and durations of flooding was determined from among three clusters of lakes distributed over a north‐south (N‐S) gradient along the eastern margin of the delta. The solute compositions yield an end‐member system of dominant solutes (shifting among Ca2+ plus HCO3−, Mg2+ plus HCO3−, Ca2+ plus SO42−) in correspondence with a gradient from frequently flooded lakes to infrequently flooded lakes. This end‐member system is consistent between years and along the N‐S elevational gradient of the delta. The solute composition of the frequently flooded lakes appears to be stable among years, while the composition among infrequently flooded lakes is not stable. The end‐member system is consistent with the seasonal dynamics in solute composition observed for three lakes, representing differing flooding regimes, plus the dynamics of the nearest main distributary channel. The dominance of local hydrological and biogeochemical processes in about one‐third of the lakes in the delta, where flooding occurs less frequently than every year, is not consistent with a common paradigm where flooding from river channels is thought to dominate the annual flushing, nutrient replenishment, and reinitialization of lacustrine ecosystems on the floodplains of major world rivers.
Characterization of dissolved organic phosphorus in coastal seawater using ultrafiltration and phosphohydrolytic enzymes
Authors: Suzumura Masahiro , Ishikawa Kimitoshi , Ogawa Hiroshi
Published: May 2010

Dissolved reactive and organic phosphorus (DRP and DOP, respectively) in samples from river and coastal areas of Tokyo Bay, Japan, was size fractionated into high‐molecular‐weight (HMW; <0.1 µm but >10 kDa) and lowmolecular‐weight (LMW, <10 kDa) size classes using a stirred‐cell ultrafiltration system. The LMW fraction accounted for 54–76% of the bulk DOP. LMW‐DOP exhibited conservative behavior during mixing with saline waters, with high concentrations at the river mouth decreasing seaward. HMW‐DOP was a rather minor component, accounting for 14–36% of the bulk DOP. Concentrations of HMW‐DRP, a trace component of all samples, decreased with increasing salinity. Characterization using two phosphohydrolytic enzymes, alkaline phosphatase and phosphodiesterase, demonstrated the presence of three forms of HMW‐DOP: easily hydrolyzable mono‐ and diesters and unhydrolyzable nonreactive DOP. The nonreactive DOP was a significant fraction (up to 67%) of HMW‐DOP. Further size fractionation and characterization revealed the importance of hydrophobic compounds (presumably phospholipids) and phosphate esters as the nonreactive DOP. The esters in the nonreactive fraction are potentially labile but may be protected against decomposition by forming submicron particles and/or macromolecular complexes.
Application of a novel method for phosphorus determinations in the oligotrophic North Pacific Ocean
Authors: Thomson‐Bulldis Angie , Karl David
Published: May 2010

Phosphorus (P) is an essential macronutrient and is present in seawater as both dissolved inorganic (primarily orthophosphate, Pi) and organic compounds. Current analytical techniques measure soluble reactive phosphorus (SRP) as a surrogate for Pi and soluble nonreactive phosphorus as a surrogate for dissolved organic phosphorus (DOP). A new method provides a measure of Pi concentrations directly and eliminates interference from other reactive P compounds. The same method can also be used to make direct measurements of non‐Pi phosphorus (NPiP) concentrations (i.e., [total dissolved P] — [Pi]) with greater precision and accuracy limits than current methods provide. With this new method, Pi concentrations in North Pacific surface waters were found to be lower, by up to 50% or more, than SRP concentrations measured with standard autoanalyzer techniques. Mean (±SD) N‐PiP concentrations in the deep (>1,000 m) North Pacific were determined to be 16.2 ± 12.5 nM. These results have significant implications for turnover and residence times of dissolved P pools and for utilization of DOP in the deep sea. This new method for Pi and N‐PiP measurements has numerous potential applications in marine and freshwater research.
Genetic diversity in Prochlorococcus populations flow cytometrically sorted from the Sargasso Sea and Gulf Stream
Authors: Urbach Ena , Chisholm Sallie W.
Published: May 2010

An investigation into the genetic structure of Prochlorococcus picophytoplankton in depth profiles from the Sargasso Sea and the Gulf Stream revealed a high degree of genetic heterogeneity within local populations. Partial sequencing of cloned polymerase chain reaction products amplified from flow cytometrically sorted cells was used to identify 6–21 different Prochlorococcus perB/D alleles recovered from each of eight sorted samples, with 68 alleles identified among 187 clones in the combined data set. Rarefaction analyses indicated that many additional unsampled alleles were present at each level of sample aggregation. Overlapping sets of alleles were recovered from Prochlorococcus populations in the two water columns, from different depths within each water column, and from flow cytometrically distinguishable subpopulations sorted from the same water sample, suggesting that each of these populations drew their membership from a single gene pool. Consistent with results of autecological studies, members of a high‐light‐adapted Prochlorococcus clade predominated in clone libraries from surface waters. It thus appears that wild Prochlorococcus populations consist of individuals drawn from a variety of evolutionary lineages and that populations at different depths and in two distinct hydrographic rcgimcs recruit their members from the same gene pool. Natural selection favors the predominance of high‐light‐adapted genotypes in near‐surface populations drawn from this gene pool.
Microheterotrophy in the zooxanthellate coral Stylophora pistillata: Effects of light and ciliate density
Authors: Ferrier‐Pagès C. , Allemand D. , Gattuso J.‐P. , Jaubert J. , Rassoulzadegan F.
Published: May 2010

We examined the ability of the zooxanthellate coral Stylophora pistillata (Esper, 1797) to feed on microhcterotrophs (bacteria and oligotrichous ciliates). The effect of light on the feeding rates was also investigated. Grazing experiments were first conducted by exposing coral colonies to known amounts of 3H‐thymidine‐labeled bacteria and ciliates and measuring the appearance of radioactivity in coral tissues. A method was developed to obtain clean cultures of 3H‐labeled ciliates. Results showed that 7% of the labeled bacteria and 90% of the labeled ciliates were ingested after 4–6 h incubation. Corals were then incubated in medium containing different concentrations of unlabeled ciliates (200, 500, 800 cells ml−1), Replicates of each concentration were exposed to one of three light levels (0, 80, 250 µmol m−2 s−1). Coral feeding rate increased with prey density, from 1.40 to 4.10 × 104 ciliates (0.22–0.65 µg C mg protein−1 h−1) for 200–800 ciliates ml−1, respectively. However, a plateau was observed after a total ingestion of 4 × 104 ciliates (1.7 µgC mg protein−1). The total number of ciliates ingested, as well as the ingestion rates decreased when the light intensity increased. During dark experiments, the maximal amount of carbon ingested was twice as much as that ingested in light experiments. However, heterotrophic nutrition occurred even if the colonies could satisfy their carbon metabolism via photosynthesis. Zooplankton feeding seems therefore to complement autotrophic nutrition. Under high light, the small amount of microplankton ingested may provide nitrogen, phosphorus, or vitamins to corals, and this food supply may be especially important in tropical waters where inorganic nutrient concentrations are low. Conversely, when light is limiting, predation may also provide most of the energy necessary for coral maintenance.
Theoretical and experimental approaches to improve the accuracy of particulate absorption coefficients derived from the quantitative filter technique
Authors: Roesler Collin S.
Published: May 2010

The quantitative filter technique (QFT), whereby particles are concentrated onto glass‐fiber filters and analyzed in a spectrophotometer, is used extensively to estimate the absorption coefficients of aquatic particles. A number of empirically derived correction factors (β) have been developed to account for the amplified optical path length associated with the highly scattering glass‐fiber filters. Published results are inconsistent, and β remains the largest source of uncertainty in estimated absorption coefficients. In this study, path‐length amplification was estimated from the average cosine of diffusely traveling photons in the filter pad using a theoretical approach. This amplification factor, combined with variability in blank filter pad optical density, explains many of the confounding observations in the literature. Absorption coefficients for phytoplankton cultures and field samples were estimated from a modified QFT using the new model for path‐length amplification and tested against absorption coefficients measured with a nine‐wavelength absorption and attenuation meter (ac9, WETLabs). A linear regression between the modeled and measured particulate absorption coefficients was highly significant (r2 > 0.99, n = 99), with estimated slope and intercept not significantly different from 1 and 0, respectively (P < 0.001). The model outperforms published, empirically derived correction factors over a broad range of absorption coefficients and particulate compositions. Results indicate that the modified QFT combined with the new model for path‐length amplification yields accurate estimates of spectral particulate absorption coefficients regardless of the concentration or composition of the particulate material.
Tidally oriented vertical migration and position maintenance of zooplankton in a temperate estuary
Authors: Kimmerer W. J. , Burau J. R. , Bennett W. A.
Published: May 2010

In many estuaries, maxima in turbidity and abundance of several common species of zooplankton occur in the low salinity zone (LSZ) in the range of 0.5–6 practical salinity units (psu). Analysis of zooplankton abundance from monitoring in 1972–1987 revealed that historical maxima in abundance of the copepod Eurytemora affinis and the mysid Neomysis mercedis, and in turbidity as determined from Secchi disk data, were close to the estimated position of 2 psu bottom salinity. The copepod Sinocalanus doerrii had a maximum slightly landward of that of E. affinis. After 1987 these maxima decreased and shifted to a lower salinity, presumably because of the effects of grazing by the introduced clam Potamocorbula amurensis. At the same time, the copepod Pseudodiaptomus forbesi, the mysid Acanthomysis sp., and amphipods became abundant with peaks at salinity around 0.2–0.5 psu.
Meroplanktonic distribution and circulation in a coastal retention zone of the northern California upwelling system
Authors: Wing Stephen R. , Botsford Louis W. , Ralston Stephen V. , Largier John L.
Published: May 2010

123°00′W) occurs primarily during relaxation from upwelling, when warm water flows poleward from the Gulf of the Farallones. During 1994 and 1995 we sampled planktonic larval distributions and hydrography both south and north of Point Reyes during upwelling to test whether high concentrations of crab and rockfish larvae were concentrated in the source of the relaxation flow to the south of Point Reyes. An upwelling plume off Point Reyes and an “upwelling shadow,” indicated by warmer, less saline water in the northern Gulf, were evident in both years, as were frontal regions that marked the boundaries between water types of three different types: (1) newly upwelled, (2) oceanic, and (3) San Francisco Bay outflow. In addition, there was a fourth type, termed Gulf water, that was a mixture of these three types. Concentrations of larvae of cancrid, pinnotherid, and “coastal” crabs and rockfishes were high south of Point Reyes but were low or absent in the newly upwelled water north of the point. Within the upwelling shadow, these meroplankton taxa were associated with different water masses. Several intertidal crab species and early‐stage cancrid crabs were concentrated in San Francisco Bay outflow water, and coastal Gulf water late‐stage cancrid crabs, early‐ and late‐stage pinnotherid crabs, and rockfishes were concentrated at the frontal region between newly upwelled and Gulf water. Of the taxa examined, only rockfishes were found offshore in oceanic water. The high concentrations of meroplankton observed suggest that the Gulf of the Farallones is an important retention area for larvae that settle into coastal populations in the Gulf and to the north via poleward transport during upwelling relaxation.
Motion of diatom chains in steady shear flow
Authors: Karp‐Boss Lee , Jumars Peter A.
Published: May 2010

Information on the motion of phytoplankton in shear flows is essential for predicting or understanding effects of turbulence on processes such as nutrient uptake, aggregate formation, and phytoplankter‐herbivore interactions. Of particular interest is the motion of diatom chains because they are expected to benefit most from enhancement of nutrient flux due to turbulence and are often the most abundant components in aggregates. We studied the motion of two chain‐forming diatoms, Skeletonema costatum and Thalassiosira nordenskiiildii, in steady shear flow and in the light of available theory for rigid, elongated spheroids. Both species underwent periodic rotation upon exposure to a simple shear flow, as predicted by theory. Whereas the rotational orbits of S. costutum resembled those predicted by theory for rigid spheroids, the rotational motion of T. nordenskiiildii was more like the motion of flexible fibers observed in engineering applications. Periods of rotation of S. costutum increased linearly with increasing axis ratio, whereas no clear relationship was observed between periods of rotation and axis ratios for T. nordenskiiildii. Measured periods of rotation of both species were smaller than predicted by theory for rigid spheroids of similar axis ratios. The diverse behaviors observed imply that fluxes of nutrients and collision frequencies experienced vary greatly with detailed shapes and mechanical properties of chains and their unit cells.
Enhanced chlorophyll at the shelfbreak of the Mid‐Atlantic Bight and Georges Bank during the spring transition
Authors: Ryan John P. , Yoder James A. , Cornillon Peter C.
Published: May 2010

In 8 yr (1979–1986) of Coastal Zone Color Scanner (CZCS) imagery, we find annual enhancement of chlorophyll at the shelfbreak of the Mid‐Atlantic Bight (MAB) and Georges Bank during the spring transition from well‐mixed to stratified conditions. Spatial and temporal extents of enhancement vary interannually, and expression is intermittent intraannually. This feature can span the entire MAB and southern flank of Georges Bank (∼1,100 km) and can be expressed for as long as 10 weeks (mid‐April to late June). Pigment concentrations within the feature average more than two times that of adjacent shelf and slope waters. Enhanced shelfbreak chlorophyll consistently coincided with the shelf‐slope front and often extended inshore of the surface outcrop of the front a few to ∼10 km. In all years except 1986, it coincided with seaward entrainment of shelf water by Gulf Stream warm‐core rings (WCRs) or meanders. Shelfbreak chlorophyll enhancement was most pronounced during 1980. Using satellite and in situ observations, we found that during 1980, it coincided with the shelf‐slope front for 10 weeks, and, unlike the spring bloom, it was dominated by the nanophytoplankton (<20 um) size fraction. During the peak of the 1980 occurrence, four WCRs simultaneously interacted with shelf water, and chlorophyll enhancement inshore of one WCR coincided with a slope‐water intrusion onto the shelf. Empirical orthogonal function (EOF) decomposition of CZCS images for late March–June 1980 showed that shelfbreak enhancement was strongly pronounced in an EOF that accounted for >10% of the variance about the mean. This annual biological feature, brought to light in satellite ocean color imagery, is an important aspect of the shelf‐slope ecology of the MAB and Georges Bank.
Growth and grazing on Prochlorococcus and Synechococcus by two marine ciliates
Authors: Christaki Urania , Jacquet Stéphan , Dolan John R. , Vaulot Daniel , Rassoulzadegan Fereidoun
Published: May 2010

The two most abundant marine autotrophic prokaryotes, Prochlorococcus and Synechococcus, often have different distributions in the ocean. For example, Synechococcus is restricted to the first 100 m, whereas Prochlorococcus extends much deeper in oligotrophic waters. This is in part explained by differences in adaptation to nutrient and light regimes. However, they could also be subjected to different predation rates. To explore this hypothesis, we compared the consumption of these two picoplankters by an algivorous ciliate, Strombidium sulcatum, and a bactivorous ciliate, Uronema sp. For both ciliate species, removal rates were higher, by a factor of 3 to 10, for Synechococcus compared to Prochlorococcus when prey items were presented alone or together. The growth of the two ciliates fed Synechococcus and/or Prochlorococcus also differed. S. sulcatum grew well on both prey items, whether alone or together, whereas Uronema sp. grew slowly when fed Synechococcus and very poorly when fed Prochlorococcus either alone or with Synechococcus. Our results suggest that Prochlorococcus may be less subject to ciliate predation than Synechococcus.
Modeling the relative contributions of autotrophs and heterotrophs to carbon flow at a Lagrangian JGOFS station in the Northeast Atlantic: The importance of DOC
Authors: Fasham Michael J. R. , Boyd Philip W. , Savidge Graham
Published: May 2010

A size‐structured ecosystem model was developed and fitted to an extensive set of observations of size‐fractionated biomass, primary and heterotrophic bacterial production, respiration, particle flux, and zooplankton herbivory obtained on a cruise in the NE Atlantic during 20 days of the spring bloom. Rates of water‐column‐integrated primary production and heterotrophic bacterial production were used to force the model, and the model parameters were determined by optimizing the model to the remaining observations. A unique model solution was not possible in the absence of dissolved organic carbon (DOC) measurements. By setting a weak constraint on the DOC concentrations (that they should remain broadly constant), a solution was obtained that predicted a small DOC increase during the bloom period; this increase was similar in magnitude to observations in other areas and produced a good fit with the other data. Major conclusions: (1) gross primary production (GPP) was over twice the measured 14C production estimates; (2) phytoplankton exudation was a major source of DOC, and 35% of the GPP flowed through the DOC and was utilized by the bacteria, with a low gross growth efficiency (17%); (3) 62% of the community respiration came from organisms <5 µm in size; (4) the major source of food for microzooplankton was phytoplankton 1–5 µm in size, but the mesozooplankton ingested more microzooplankton than phytoplankton; and (5) only 8% of the total net primary production was grazed by mesozooplankton. These results provide quantitative support to the emerging consensus on the relative roles of large and small organisms in the euphotic zone and demonstrate the necessity of measuring DOC to constrain the carbon budget within the euphotic zone.
Carbon utilization in the Eurasian sector of the Arctic Ocean
Authors: Olsson Kristina , Anderson Leif G. , Frank Markus , Luchetta Anna , Smethie William
Published: May 2010

Production and remineralization of carbon in the Eurasian sector have been estimated based on a combined data set of the Oden—91 and Polarstern—93 (ARK IX—4) expeditions. This sector includes the deep Nansen and Amundsen Basins and their linked shelf seas, i.e., the Barents, Kara, and Laptev Seas. The water masses in this region are composed of Atlantic water, river runoff, and sea ice‐melt water. The fractionation between these source waters is elucidated from the δ18O—salinity relation and conservation of mass. By combining preformed nitrate concentrations of the source waters with the fractionation model and the measured nitrate concentrations, nitrate deficits and excesses are calculated. These concentrations are then converted to carbon equivalents by applying a C/N ratio, whereby a measure of apparent carbon utilization (ACU) is obtained. From the relative inventory of ACU along the slope and deep basin sections, we conclude that the shelf areas are the dominant productivity sites and that the productivity signal is transported to all water masses in the Eurasian Basin. The flux of utilized carbon from the Barents‐Kara and Laptev Seas is about 0.022 Gton C yr−1.
Dissolved organic nitrogen and phosphorus pools and fluxes in the central Atlantic Ocean
Authors: Vidal Montserrat , Duarte Carlos M. , Agusti Susana
Published: May 2010

The variation in the concentration and the turbulent fluxes of dissolved organic nitrogen and phosphorus (DON and DOP) across the thermocline in the central Atlantic were studied along a quasi‐meridional transect from the Canary Islands to Argentina (22°N to 31°S). In general, DON concentrations were high in surface waters and declined toward the thermocline, whereas DOP concentrations were less variable with depth. Vertical, gradient‐driven fluxes of DON and DOP generally involved a downward flux, with a median DON:DOP ratio of 28:1. The downward flux of DON was closely correlated with the nitrate supply to the mixed layer and sufficed to remove an amount of nitrogen equivalent to that associated with the upward nitrate influx into the mixed layer (median = 104%). The downward flux of DON exceeded the supply of nitrate off the NW African coast, where Trichodesmium sp. was abundant. The downward flux of DOP was also very closely correlated with the phosphate supply to the mixed layer (r = 0.87; P = 0.0007), but the downward export of phosphorus as DOP accounted for only 9% of the upward phosphate supply to the mixed layer. There was also evidence of a deep upward flux of DON and DOP from below the thermocline, which, combined with the general downward flux in the upper waters, indicates the presence of a strong sink for DON and DOP within the thermocline, tentatively identified to be microplankton respiration. Our results point to a dominant role of downward DOM fluxes as a path for the removal of nutrients, and probably carbon, from the biogenic layer of the ultraoligotrophic central Atlantic.
Restoration of the food web of an alpine lake following fish stocking
Authors: McNaught A. S. , Schindler D. W. , Parker B. R. , Paul A. J. , Anderson R. S. , Donald D. B. , Agbeti M.
Published: May 2010

Trout stocking in the mid‐1960s eliminated the calanoid copepod Hesperodiaptomus arcticus and other large‐bodied crustaceans such as Gammarus lacustris, Daphnia middendorffiana, and Daphnia pulex from many alpine lakes in the Rocky Mountain Parks of Canada. H. arcticus frequently dominates the plankton communities of fishless lakes, preying on rotifers and nauplius larvae. Following the extirpation of H. arcticus, rotifers and small‐bodied cyclopoid copepods dominate the zooplankton assemblages of alpine lakes.

We studied the zooplankton community of Snowflake Lake, Banff National Park, from 1966 to 1995. H. arcticus was eliminated following stocking of the lake with trout in the 1960s. It failed to become reestablished after the disappearance of the fish population in the mid‐1980s. Several species of rotifers and small‐bodied crustaceans, species originally rare or absent from the plankton, became abundant following fish stocking and remained so after the fish population declined.

In 1992, we reintroduced H. arcticus to Snowflake Lake. The H. arcticus population grew exponentially for 4 yr, but had not reached stable densities typical of unmanipulated alpine lakes by 1995. By 1994, however, even the small population of Hesperodiaptomus was beginning to suppress populations of rotifers, copepod nauplii, and large diatoms. Because H. arcticus is omnivorous, a simple model of cascading trophic interactions did not predict the outcome of trophic manipulations in this alpine lake.