bluuebunny/crossref_metadata_2025 huggingface dataset:
Photophysiology in two major Southern Ocean phytoplankton taxa: Photoprotection in Phaeocystis antarctica and Fragilariopsis cylindrus
Authors: Kropuenske Lindsey R. , Mills Matthew M. , van Dijken Gert L. , Bailey Shaun , Robinson Dale H. , Welschmeyer Nicholas A. , Arrigoa Kevin R.
Published: January 2011

Phytoplankton communities in the Ross Sea, Antarctica, are characterized by the haptophyte Phaeocystis antarctica Karsten, which dominates deep mixed layers, and diatoms, including Fragilariopsis cylindrus Grunow, that thrive in shallower mixed layers. To investigate whether differences in photoprotective strategies explain these distributions, photosynthetic parameters, pigments, and fluorescence properties were measured in cultures grown under several irradiance regimes and during acclimation to increased irradiance. In P. antarctica, cellular concentrations of all pigments declined with increasing growth irradiance under continuous light, but xanthophyll cycle pigment concentrations increased with increasing irradiance under dynamic conditions without changes in chlorophyll. In contrast, F. cylindrus exhibited declines in chlorophyll cell−1 with increasing irradiance under both continuous and dynamic conditions, but xanthophyll cycle cell21 pigments increased under continuous irradiance and declined under dynamic irradiance. P. antarctica did not exhibit non‐photochemical quenching (NPQ) unless exposed to irradiance in excess of the mean growth irradiance. F. cylindrus exhibited NPQ in response to lower irradiances but displayed less photoinhibitory quenching than P. antarctica after exposure to very high irradiance. Inhibitor experiments suggest that both taxa rely upon xanthophyll cycle photoprotection to maintain photosynthetic performance but only P. antarctica relies heavily upon protein synthesis, presumably for D1 protein repair. F. cylindrus can thrive in shallow mixed layers because its high capacity for heat dissipation minimizes photoinhibition. P. antarctica utilizes xanthophyll cycle photoprotection to a lesser degree, but is able to dominate deeper mixed layers by effectively repairing the photodamage incurred when it is mixed to the surface.
Mass deposition event of Pyrosoma atlanticum carcasses off Ivory Coast (West Africa)
Authors: Lebrato M. , Jones D. O. B.
Published: January 2011

Thousands of moribund thaliacean carcasses (Pyrosoma atlanticum) were deposited between February and March 2006 at the seafloor in the Ivory Coast area (West Africa). Remotely operated vehicle surveys were conducted in a continuous depth gradient between 20 and 1275 m along an oil pipeline. Video and still photography were used to estimate the carcass distribution, density, and size on the seabed, as well as recording the local megafauna interactions with the gelatinous material. Large patches of dead pyrosomids covered extensive areas on the continental slope, whereas minor aggregations were found on the shelf. The carcasses were in many instances trapped along the pipelines, accumulating extensively in troughs and furrows in the slope, and especially in soft sediment channels. Pyrosoma atlanticum dried samples were used to calculate the carbon content, enabling the extrapolation to the densities and sizes recorded in the video surveys. The average standing stock of organic carbon associated with the carcasses was >5 g C m−2 in the whole slope and canyon, with values as high as 22 g C m−2 in certain areas. Eight megafaunal species from three different phyla were observed 63 times directly feeding on the decomposing carcasses. The gelatinous carbon may have contributed substantially to the detrital food web including microbes at the seabed, and certainly to the diet of larger benthic organisms. The organism‐level carbon measurements and documented fate of pyrosomid organic carbon is new evidence of the importance of gelatinous material in large‐scale processes and elemental cycling.
Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean
Authors: Buesseler Ken O. , Boyd Philip W.
Published: January 2011

Pelagic food webs drive a flux of >10 x 1012 kg C yr−1 that exits surface waters, mostly via sinking particles through the ocean's "biological pump." Much of this particle flux is remineralized in the poorly studied waters of the twilight zone, i.e., the layer underlying the euphotic zone and extending to 1000 m. We present a reanalysis of selected upper‐ocean studies of particulate organic carbon (POC) flux and relate these observations to a simple one‐dimensional biological model to shed light on twilight zone processes. The ecosystem model first predicts particle flux from the base of the euphotic zone, and then its attenuation below based on transformations by heterotrophic bacteria and zooplankton, and active downward transport of surface‐derived particles by zooplankton. Observations and simulations both suggest that future sampling strategies for the twilight zone should take regional variability of the euphotic zone depth (Ez) into account. In addition, conventional curvefitting of particle flux data (i.e., power law or exponential) skews our interpretation of twilight zone processes. To overcome these artifacts, we introduce two new terms: the Ez‐ratio (POC flux at Ez relative to net primary production [NPP]) and T100 (the ratio of POC flux 100 m below Ez to POC flux at Ez). A comparison of NPP, Ez‐ratios, and T100 provides a new set of metrics to classify the ocean into different regimes, representing high and low surface export and subsurface flux attenuation.
Bioavailability and export of dissolved organic matter from a tropical river during base‐ and stormflow conditions
Authors: Wiegner Tracy N. , Tubal Randee L. , MacKenzie Richard A.
Published: January 2011

Concentrations, bioavailability, and export of dissolved organic matter (DOM), particulate organic matter (POM), and nutrients from the Wailuku River, Hawai'i, U.S.A., were examined under base‐ and stormflow conditions. During storms, DOM and POM concentrations increased approximately by factors of 2 and 11, respectively, whereas NO3− concentrations decreased by a third. The organic carbon (OC) pool was dominated by dissolved OC (DOC) during baseflow conditions, whereas DOC and particulate OC contributed equally during storms. The nitrogen (N) pool was dominated by NO3− during baseflow conditions and by particulate organic N (PON) during storms. Dissolved organic N (DON) comprised a similar percentage of the N pool under base‐ and stormflow conditions. DOC and DON bioavailability both decreased by half during storms in the Wailuku River. Differences in DOM concentrations and bioavailability between base‐ and stormflow conditions suggest that DOM flowpaths to the river changed from deep to shallow, and that DOM sources switched from autochthonous to allochthonous. Although DOM bioavailability decreased during storms, calculations suggest that storms contributed >90% to the annual OC and N yields and >80% to the bioavailable DOM yield from the Wailuku River to coastal waters. Overall, our results suggest that storms are important for delivering bioavailable DOM to coastal waters, where they may stimulate primary and secondary production.
Effect of fully characterized unsteady flow on population growth of the dinoflagellate Lingulodinium polyedrum
Authors: Latz Michael I. , Allen Jeffrey , Sarkar Sutanu , Rohra Jim
Published: January 2011

Dinoflagellate population growth is inhibited by fluid motion, which is typically characterized by some average flow property, regardless if the flow is steady or unsteady. This study compares the effect of fully characterized steady and unsteady flow on net population growth of the red tide dinoflagellate Lingulodinium polyedrum. The unsteady flow fields were generated using oscillatory laminar Couette flow and characterized analytically to provide complete knowledge of the fluid shear exposure over space and time throughout the chamber. Experimental conditions were selected so all cells experienced a similar shear exposure regardless of their position within the chamber. Unsteady flow with maximum shears of 6.4 s−1 and 6.7 s−1 and an average absolute shear of 4 s−1, comparable with levels found at the ocean surface on a windy day, resulted in higher levels of growth inhibition than for steady Couette flow with shears of 4 and 8 s−1. Over the parameter space studied, growth inhibition increased with increasing treatment duration (5–120 min) but was insensitive to oscillation period (60–600 s) or whether the unsteady flow changed in direction. These results indicate that over the parameter space studied, unsteady flow is more inhibitory to net growth than steady flow, for the same average flow conditions, and demonstrate that flow characterization on the basis only of average flow properties is inadequate for comparing population growth in unsteady and steady flows.
Spectral variations of light scattering by marine particles in coastal waters, from the visible to the near infrared
Authors: Doxaran David , Ruddick Kevin , McKee David , Gentili Bernard , Tailliez Dominique , Chami Malik , Babin Marcel
Published: January 2011

Field measurements and Mie calculations of the particulate light‐scattering coefficient (bp, in m−1) in the nearinfrared and visible spectral domains are combined to quantify and model the effect of particulate absorption on the bp spectral variations. The case of particles of coastal origin and assumed to follow a Junge‐type size distribution is considered. A simple power‐law function closely reproduces the near‐infrared bp spectral variations, with a spectral slope varying in the range 0.1–1.4. In the visible (e.g., 440 nm), particulate absorption effects systematically lead to bp values 5–30% lower than values predicted using a power‐law function fitted in the near infrared and extrapolated to 440 nm. The respective influences of the particle size distribution and composition are investigated for both mineral and organic particle populations. Finally, an empirical model derived from theoretical calculations closely reproduces the actual bp spectral variations from near‐infrared to short visible wavelengths, taking into account particulate absorption effects.
Multi‐decadal shoaling of the euphotic zone in the southern sector of the California Current System
Authors: Aksnesa Dag L. , Ohman Mark D.
Published: January 2011

We document a long‐term reduction in Secchi depth of 0.06–0.13 m yr−1 in the southern California Current System (CCS) over the period 1969–2007, reflecting a long‐term shoaling of the euphotic zone. Calibrated water clarity observations from 1949 to 1954 reinforce the results indicating a progressive shoaling. For the inshore area, 150 km off the coast, Secchi disk has shoaled 8.4 ± 1.2 m since 1949. This change has been accompanied by a nitracline shoaling of 18.2 ± 6.4 m since 1969 and an increase in chlorophyll a since 1978. These changes have occurred despite an increase in density stratification in the CCS. Increased stratification has been linked by others to decreased nutrient fluxes, reduced primary production, increased water transparency, and a deepening of the euphotic zone, contrary to our findings. We explore this apparent paradox with a simple steady‐state model of the thickness of the euphotic zone. A sensitivity analysis suggests that the observed shoaling of the euphotic zone is consistent with a doubling in nutrient upwelling, but in this analysis we also consider alternative causes for such shoaling: water‐column darkening caused by freshening, increased residence time of the phototrophic biomass in the euphotic zone, and supply of nutrients of anthropogenic origin.
Metabolism and resources of spherical colonies of Nostoc zetterstedtii
Authors: Sand-Jensen Kaj , Raun Ane Løvendahl , Borum Jens
Published: January 2011

Constraints imposed by the spherical form and gelatinous matrix of centimeter‐thick colonies of the cyanobacterium Nostoc zetterstedtii on its functional properties were tested by examining the scaling of its composition, light absorption, photosynthesis, and respiration to individual size. In three summer experiments with colonies collected from the bottom of oligotrophic lakes of low inorganic carbon concentrations (dissolved inorganic C, DIC), metabolism and pigment density of colonies were scaled to their surface area as most algal filaments were confined to a 2‐mm‐thick outer shell. Nostoc absorbed 96% of incident light from the surface to the center because of high areal pigment density, but absorbed photons were used with low quantum efficiency (11–38 mmol O2 mol−1 photon) and photosynthesis was low relative to dark respiration (2.0–5.4). Therefore, N. zetterstedtii is threatened by reduced light availability and only extended to lake depths receiving about 12% of surface irradiance, whereas mosses, characeans, and angiosperms with thin photosynthetic tissues grew deeper (3.1–7.5% of surface irradiance). Nostoc ameliorated the restrictions of low lake DIC and long diffusion paths by active transport that could extract most external DIC, accumulate DIC in the colony 150–fold above external concentrations, and retain respiratory CO2. The energy cost of solute transport and gel formation in Nostoc colonies and extensive self shading restrict their potential growth, whereas colony formation should prevent grazing and increase longevity and nutrient recirculation. Nostoc zetterstedtii has become one of rarest freshwater macroalgae because of widespread lake eutrophication reducing water transparency and increasing competition from taller and faster‐growing stands of filamentous algae and higher plants.
Contrasting the influences of stream inputs and landscape position on bacterioplankton community structure and dissolved organic matter composition in high‐elevation lake chains
Authors: Nelson Craig E. , Sadro Steven , Melack John M.
Published: January 2011

We examined bacterioplankton community composition (BCC; using polymerase chain reaction‐based phylogenetic fingerprinting) and the composition of dissolved organic matter (DOM; using scanning fluorometry) within lake chains in high‐elevation catchments of the Sierra Nevada, California. We compared temporal BCC dynamics in two connected cirque lakes and their inlets and found that lake : inlet community similarity of both lakes declined with increasing residence time because of seasonal snowpack melting. However, for over 3 yr the headwater lake remained distinct from its inlet even during peak snowmelt (residence time <5 d), whereas the downstream lake was consistently similar to both its inlet and the upstream lake. We subsequently sampled 17 lake chains (4–8 lakes each) throughout the Sierra Nevada longitudinally to examine how landscape position and catchment characteristics influenced the similarity in BCC and DOM among lakes and their connecting streams. Headwater lakes were significantly less similar to their inlet streams than were downstream lakes. BCC was heterogeneous throughout each catchment, but headwater inlet BCC was consistently distinct from all downstream samples. In contrast, DOM exhibited a trend of increasing homogeneity as water moved downstream: upstream and downstream waters were distinct but without clear headwater outliers. The similarity in BCC and DOM between any two lakes within a chain declined with geographic distance. Our results illustrate the contrasting roles of environmental selection and dispersal in structuring bacterioplankton communities, supporting both strong within‐lake environmental selection for communities distinct from terrigenous inputs and a weaker effect of geographic dispersal differentiating communities among lakes linked by advective flow.
Lake‐wide distributions of temperature, phytoplankton, zooplankton, and fish in the pelagic zone of a large lake
Authors: Rinke Karsten , Huber Andrea M. R. , Kempke Sebastian , Eder Magdalena , Wolf Thomas , Probst Wolfgang N. , Rothhaupta Karl-Otto
Published: January 2011

We studied three‐dimensional distribution patterns of temperature, phyto‐ and zooplankton, and fish in the large, prealpine Lake Constance during spring 2007. A strong westerly wind induced an intense eastward displacement of epilimnetic water and upwelling of hypolimnetic water in the western part of the lake. This led to the formation of an internal front separating cold, hypolimnetic water depleted of chlorophyll in the western part from epilimnetic, warm water with high chlorophyll concentrations in the eastern part. Hydroacoustic detection of zooplankton (by Acoustic Doppler Current Profiler) and juvenile fish (by echosounding) revealed both to be passively transported by the wind. Consequently, zooplankton and fish showed comparable horizontal distributions as temperature and chlorophyll. During periods of low wind velocities (<6 m s−1), water temperature was more evenly distributed, whereas phytoplankton distribution was still heterogeneous, probably because of local differences in resource supply. The relative influence of biotic factors for the distribution of organisms increased when external forcing was low. At periods with weak wind forcing, phytoplankton typically showed highest concentrations in the metalimnion, where zooplankton also aggregated in thin layers. In conclusion, we found spatial distributions of temperature and organisms to be strongly controlled by wind forcing when wind velocities were sufficiently high, whereas the importance of internal biotic factors for distribution of organisms increased when wind velocities were less strong. Abiotic factors appeared to act over relatively large spatial scales and affected distributions within the entire ecosystem, whereas biotic factors affected distributions of algae, zooplankton, and fish on a more local scale.
Combined effects of food quality and temperature on somatic growth and reproduction of two freshwater cladocerans
Authors: Masclaux HÉlène , Bec Alexandre , Kainz Martin J. , Desvilettes Christian , Jouve Lionel , Bourdier Gilles
Published: January 2011

We investigated the effect of food quality on somatic growth and reproduction of zooplankton at different temperatures (12°C, 15°C, 20°C, and 25°C). Standardized growth experiments of two cladocerans, Daphnia magna and Simocephalus vetulus, were performed on (1) high‐quality food (Cryptomonas sp.), (2) relatively low‐quality food (Scenedesmus obliquus), and (3) intermediate‐quality food (Cryptomonas : Scenedesmus mixture). Food quality constraints on somatic growth and reproduction of the two cladocerans decreased with increasing temperature. For D. magna and for S. vetulus, differences between clutch size and growth rate of individuals fed on the three food sources were highly pronounced when they were reared at 12°C and 15°C; however, such differences decreased at 20°C and were negligible at 25°C. Variations in food quality constraints with temperature can be explained by the variability of dietary polyunsaturated fatty acids, such as eicosapentaenoic acid and stearidonic acid requirements of these cladocerans. We conclude that dietary constraints exerted by food quality for zooplankton development vary as a function of different temperature conditions.
Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
Authors: Berggren Martin , Laudon Hjalmar , Jansson Mats
Published: January 2011

We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7–d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.
Toxicity of violacein‐producing bacteria fed to bacterivorous freshwater plankton
Authors: Deines Peter , Matz Carsten , JÜrgens Klaus
Published: January 2011

Chemical defenses have been hypothesized to be widespread among aquatic bacteria, but few studies have assessed the susceptibility of pelagic consumers to bacterial secondary metabolites. In this study, we determined the effect of bacteria containing the indole alkaloid violacein on a range of freshwater plankton organisms that ingest bacteria. Growth and survival of two nanoflagellates (Bodo saltans, Ochromonas sp.), two ciliates (Colpidium campylum, Tetrahymena pyriformis), two rotifers (Keratella cochlearis, Brachionus calcyfloris), and adults and juveniles of the cladoceran Daphnia magna were examined in laboratory experiments in which these organisms were fed bacterial diets supplemented with violacein‐producing bacteria such as Janthinobacterium lividum and Chromobacterium violaceum. Unselective uptake of violacein‐producing bacteria resulted in significantly lower survivorships, indicating acute toxicity to all zooplankton taxa tested. The presence of 10% C. violaceum in an otherwise nontoxic bacterial diet, equivalent to 9 ng violacein mL−1, reduced growth rates and peak abundances of flagellates, ciliates, and rotifers by 18–100%. For D. magna, wild‐type C. violaceum was poisonous starting at concentrations <1 x 106 cells mL−1, whereas a violacein‐deficient mutant did not have any lethal effect on the animals. Species‐specific variability in predator susceptibility was explained by the negative correlation between toxin sensitivity and biomass‐specific clearance rates. The susceptibility of a broad spectrum of planktonic bacterial consumers to violacein‐producing bacteria illustrates the potential effect of bacterial bioactives on the structure of aquatic food webs, biodiversity, and ecosystem functioning.
Observations of turbulent mixing in a phytoplankton thin layer: Implications for formation, maintenance, and breakdown
Authors: Steinbuck Jonah V. , Stacey Mark T. , McManus Margaret A. , Cheriton Olivia M. , Ryan John P.
Published: January 2011

Coincident measurements of chlorophyll a (Chl a) and temperature microstructure from Monterey Bay, California, U.S.A., are used to investigate the dynamics of a phytoplankton thin layer in the context of vertical turbulent mixing. The thin layer was situated in the thermocline of a 20.5‐m water column, between a strongly turbulent surface mixed layer and a weakly turbulent stratified interior. The differential mixing established an asymmetric layer with a stronger Chl a gradient at the base of the layer than at the top. Sinking by Akashiwo sanguinea could have balanced turbulent mixing above the layer, but cannot explain the mid‐column convergence needed to maintain the thin layer. Swimming by A. sanguinea directed towards a mid‐column nitracline could have balanced turbulent mixing on both sides of the layer and supported the observed Chl a gradients. Results from a Eulerian advection‐diffusion model suggest that cell swimming may have varied over the lifetime of the layer, with stronger or more directed swimming required for layer formation and weaker or less directed swimming needed to maintain the layer. In‐layer growth is unlikely to have played a primary role in supporting the observed Chl a gradients. From the one‐dimensional (vertical) observations, the role of shear‐induced straining cannot be evaluated, but shear instabilities appear important to forcing elevated rates of turbulent diffusion within the layer. Finally, a Lagrangian particle‐tracking model is used to explore the implications of a balance of vertical velocity and turbulent diffusion on the vertical motions of individual cells that constitute the thin layer.
Characterizations of minerogenic particles in support of modeling light scattering in Lake Superior through a two‐component approach
Authors: Peng Feng , Effler Steve W. , Donnell David O' , Weidemann Alan D. , Auer Martin T.
Published: January 2011

The role of suspended minerogenic particles in light scattering in eastern Lake Superior and Keweenaw Bay (11 sites) during July of 2006 was evaluated with an individual particle analysis technique (scanning electron microscopy interfaced with automated image and X‐ray analyses, SAX), along with bulk measurements of particulate scattering and backscattering coefficients (bp and bbp) and chlorophyll a concentration ([Chl]). SAX measurements provided information on light‐scattering attributes of minerogenic particles, including chemical composition and particle size distribution (PSD). The data were used in Mie theory calculations for estimations of minerogenic scattering and backscattering coefficients (bm and bb,m). The bay had higher concentrations of minerogenic particles and higher values of bm, bb,m, bbp, and the backscattering ratio (bbp : bp) than the pelagic sites. Minerogenic scattering was primarily attributable to clay mineral particles in the size range of 1‐10 mm. The PSDs deviated from the (Junge) pattern of monotonic increase of particle numbers with decreasing particle size. The estimates of bm and bb,m combined with those of organic particulate components, as represented by empirical Case 1 bio‐optical models, showed reasonably good closure with bp and bbp, supporting the credibility of the SAX‐Mie approach. Variations in the bbp : bp ratio are strongly related to spatial differences in the relative contributions of phytoplankton vs. minerogenic particles to scattering, with higher values observed where the minerogenic component is more important. SAX can advance the understanding of optical variability by establishing the contributions of well‐defined minerogenic constituents that strongly influence optical properties.
Edge gradients provide evidence of ecological interactions in planktonic thin layers
Authors: Benoit-Bird Kelly J. , Cowles Timothy J. , Wingard Christopher E.
Published: January 2011

Physical, optical, and acoustical data from Monterey Bay, California, USA, describing the distributions of phytoplankton, zooplankton, and small fish as well as gradients in the physical habitat were used to examine the interactions between vertically compressed plankton structures (thin layers), their consumers, and the local physical forces they experience. The relationship between upper and lower edge gradients of a layer were used to define layer ‘shape'. The steepness of the vertical gradient on the top vs. the bottom of the plankton layer was correlated to the difference in the relative abundance of consumers above and below the layer. Phytoplankton layer gradients were steeper when more zooplankton were present on one side of the layer vs. the other while zooplankton layers were more diffuse when a greater number of fish were adjacent to one side of the layer than the other. Both layer types showed nearly symmetrical gradients when predators were in low abundance or absent. Predator‐associated differences in phytoplankton and zooplankton layer shape were not correlated with vertical gradients in shear or mixing potential surrounding layers. In the absence of strong physical gradients, grazers can play an important role in structuring plankton thin layers. These observations likely represent one end of a continuum of biological and physical forcing responsible for formation and maintenance of thin plankton layers.
Abundance and variation of colloidal organic phosphorus in riverine, estuarine, and coastal waters in the northern Gulf of Mexico
Authors: Cai Yihua , Guo Laodong
Published: January 2011

The abundance of colloidal organic phosphorus (COP) and colloidal inorganic phosphorus (CIP) was quantitatively determined using an ultrafiltration permeation model for riverine, estuarine, and coastal waters in the northern Gulf of Mexico. Dissolved inorganic phosphorus (DIP) was the dominant species in Mississippi and Pearl River waters, while dissolved organic phosphorus was dominant in marine environments. The abundance of COP was highest in the Pearl River (up to 88%), followed by the Mississippi Bight (~67%), and the Bay of St. Louis (~59%), but was lowest in the Mississippi River (41–50%). These variations highlight the roles of terrestrial inputs, autochthonous production, and anthropogenic activities in controlling the COP abundance in different aquatic environments. In the Gulf of Mexico, COP abundance generally decreased with increasing depth and coincided with chlorophyll a, reflecting the production of COP by phytoplankton and remineralization during downward transportation in the water column. The colloidal organic C: P molar ratios were substantially higher than the Redfield ratio but consistently lower than those of the bulk dissolved organic matter except for the Mississippi River, indicating a diagenetically fresher or younger COP pool. The percentage of CIP in the DIP pool was generally negligible or very low (≤3%) except in the Pearl River, where CIP abundance was as high as 27–47%, likely contributed from colloidal soils, minerals, and iron oxyhydroxides. We hypothesize that high COP abundance and seasonal P‐limitation play an important role in regulating the biogeochemical cycling of P and the development of hypoxia in the northern Gulf of Mexico.
Nitrogen isotopic fractionation associated with growth on dinitrogen gas and nitrate by cyanobacteria
Authors: Bauersachs Thorsten , Schouten Stefan , Compaoré Justine , Wollenzien Ute , Stal Lucas J. , Sinninghe Damsteé Jaap S.
Published: January 2011

This study investigated the bulk nitrogen isotopic composition and fractionation of marine and freshwater cyanobacteria growing at the expense of atmospheric dinitrogen gas (N2) or nitrate (NO3−). In agreement with previous studies, cyanobacteria using N2 had Δ15N values ranging from ‐2‰ to ‐1‰ and fractionated by 2‐3‰ against atmospheric N2. When grown on NO3−, the analyzed cyanobacteria had a remarkably large range in Δ15N, from ‐14‰ to 1‰, and fractionated by 4‐19‰ relative to the supplied NO3−. Interestingly, several of the NO3−‐utilizing cyanobacteria expressed a nitrogen isotopic signal similar to the one expected for diazotrophic species. Extrapolation to the natural environment indicates that Δ15N signals considered to be associated with dinitrogen fixation could also be generated by NO3− utilization, depending on the isotopic composition of the nitrogen source, the degree of fractionation, and the type of cyanobacterium involved.
Spatial distribution of detrital resources determines the outcome of competition between bacteria and a facultative detritivorous worm
Authors: Nugteren Paul van , Herman Peter M. J. , Moodley Leon , Middelburg Jack J. , Vos Matthijs , Heip Carlo H. R.
Published: January 2011

Macrobenthic deposit feeders and bacteria compete for the same detrital food resources. We hypothesize that the spatial scale at which food is distributed in the sediment is an important factor determining the outcome of this competition. Macrobenthic deposit feeders are better adapted for fast consumption of food in concentrated patches, whereas diluted food can only be exploited by bacteria. This hypothesis was tested in an experiment in which a fixed quantity of isotopically labeled algal detritus was offered to a natural bacterial community and the polychaete worm Nereis (=Hediste) diversicolor, either as a concentrated patch or mixed through the sediment matrix. Worms dominated food uptake in the concentrated treatment, while bacterial uptake was much greater in the diluted treatment. The experiment demonstrated scale‐based niche differentiation between these taxonomically distant groups. It also showed that worms spatially redistributed food and made it available to bacteria in that way. Together, these mechanisms may stimulate stable co‐existence through a scale‐based partitioning of resources.
Shallow water dissolution of settling calcite at station ALOHA
Authors: Greenwood J.
Published: January 2011

The dissolution of settling calcite at the Hawaii Ocean Time‐Series Sta. ALOHA in the North Pacific is examined using a calculation of the calcite saturation state based on 5 yr of alkalinity measurements and contemporary understanding of calcite dissolution kinetics. The results are consistent with previously reported field observations of calcite dissolution in the upper 1000 m at Sta. ALOHA. At low settling velocities, uncertainties in the parameterization of the dissolution equation can result in between 20% and 100% dissolution of sinking calcite in the upper 1000 m. The results introduce some doubt with regard to previous claims that field results at ALOHA provide evidence of biologically mediated calcite dissolution.
Coastal oceanographic processes influence the growth and size of a key estuarine species, the Olympia oyster
Authors: Kimbro David L. , Largier John , Grosholza Edwin D.
Published: January 2011

Here we empirically demonstrate that a tidal exchange gradient in a central California estuary leads to inversely related spatial gradients in upwelled nutrients and water residence times. As a result, seasonal phytoplankton blooms (summer‐fall) occur in the middle of the bay, where nutrient levels and water residence times are intermediate, while seasonal temperature maximums occur in the inner bay, where water residence times are highest and nutrient levels are lowest. By experimentally out‐planting juvenile Olympia oysters (Ostrea lurida) throughout the estuary, we found that the growth and size of juvenile oysters are better explained by the spatial pattern of phytoplankton concentrations than by that of water temperature. Furthermore, this benthic‐pelagic link helps explain the distribution of adult oyster sizes throughout the estuary. Because a phytoplankton maximum can be maintained by a physical interaction between intensive upwelling and a seasonal low‐inflow estuary, benthic invertebrates within protected embayments of upwelling regions may not conform to the regional generalization that their growth and size are negatively correlated with upwelling intensity.
Cross‐basin comparison of phosphorus stress and nitrogen fixation in Trichodesmium
Authors: Hynes Annette M. , Chappell P. Dreux , Dyhrman Sonya T. , Doney Scott C. , Webbd Eric A.
Published: January 2011

We investigated the phosphorus (P) status and N2 fixation rates of Trichodesmium populations from the North Pacific, western South Pacific, and western North Atlantic. Colonies of Trichodesmium were collected and analyzed for endogenous alkaline phosphatase (AP) activity using enzyme‐labeled fluorescence (ELF) and for nitrogenase activity using acetylene reduction. AP hydrolyzes dissolved inorganic phosphate (DIP) from dissolved organic phosphorus and is active in Trichodesmium colonies experiencing P stress. Across multiple stations in the subtropical North and South Pacific, there was low to moderate ELF labeling in Trichodesmium, although labeling was present in other taxa. In contrast, Trichodesmium ELF labeling in the North Atlantic ranged from low to high. Low ELF labeling corresponded with high DIP concentrations while high ELF labeling occurred only at North Atlantic stations with DIP concentrations #40 nmol L21, indicating that Trichodesmium was not experiencing dramatic P stress in the Pacific Ocean while P stress was evident in the western North Atlantic. However, nitrogenase activity was significantly higher in the P‐stressed western North Atlantic than in the Pacific Ocean (0.40‐1.30 compared to 0.01‐0.46 nmol C2H4 h−1 colony−1). These data underscore the differential basinlevel importance of P availability to Trichodesmium and suggest that factors other than P are constraining their N2 fixation rates in the Pacific.
Spatiotemporal distribution of dissolved acid polysaccharides (dAPS) in a tidal estuary
Authors: Thornton Daniel C. O.
Published: January 2011

Concentrations of dissolved acidic polysaccharides (dAPS) were measured in an estuarine tidal creek in North Inlet (South Carolina) during June and August 2007. There was a predictable pattern of dAPS concentrations in Crab Haul Creek, with the highest concentrations of dAPS occurring at low tide (2490 ± 300 µg L−1 [mean ± SD] as gum xanthan equivalents). Suspended sediment load positively correlated with dAPS concentrations during a 12‐h survey over a complete tidal cycle at a single location. There was a significant correlation between chlorophyll a and dAPS in the upper 5 mm of intertidal salt marsh sediments. High dAPS concentrations (3170‐7820 mg m2) in emersed intertidal sediment at low tide compared with depth‐integrated water‐column dAPS (100‐370 mg m2) indicate that the sediment was potentially the major source of dAPS to the water column. Total dAPS in the water column overlying the 1.1‐km2 area of Crab Haul Creek basin varied between 109±7 to 406±225 kg (mean±SD) as gum xanthan equivalents over a tidal cycle. Conservative estimate of dAPS export from North Inlet to the Atlantic Ocean as organic carbon was 5.00 × 108 g C during the summer, or 1.32 × 109 g C annually. The spatiotemporal distributions of dAPS indicate that they are a significant pool of organic carbon in estuaries.
An ecological study of a massive bloom of toxigenic Pseudo‐nitzschia cuspidata off the Washington State coast
Authors: Trainer Vera L. , Wells Mark L. , Cochlan William P. , Trick Charles G. , Bill Brian D. , Baugh Keri A. , Beall Benjamin F. , Herndon Julian , Lundholmf Nina
Published: January 2011

In September 2004 a large, nearly monospecific diatom bloom of Pseudo‐nitzschia cuspidata off the coast of the state of Washington reached cell concentrations of 6.1 × 106 cells L−1 and produced maximum particulate domoic acid (pDA), dissolved domoic acid (dDA), and cellular domoic acid concentrations of 43 nmol L−11, 4 nmol L−1, and 63 pg cell−1, respectively. This bloom co‐dominated the phytoplankton assemblage with the euglenoid Eutreptiella sp. in the Juan de Fuca eddy region, a known initiation site for toxigenic Pseudo‐nitzschia blooms. Two isolates of P. cuspidata collected during separate cruises produced domoic acid (DA) in culture. During the September 2004 survey, 84% of the stations (n = 98) had detectable Pseudo‐nitzschia and 78% had detectable pDA. There were no significant correlations between either pDA or cellular DA and ambient concentrations of macronutrients; however, when considering only those stations where Pseudo‐nitzschia was present, pDA was positively correlated with chlorophyll a and negatively correlated with temperature (p ≪ 0.01) at both 1‐ and 5‐m depths. Correlations between cellular DA concentrations and total bacteria or cyanobacteria abundances were not significant. Variable ratios of pDA:dDA in the eddy region suggest that DA release was under cellular regulation by Pseudo‐nitzschia. Stations where dissolved Fe concentrations were limiting (,0.5 nmol L−1) had the highest Pseudo‐nitzschia abundances and pDA and cellular DA values. These results provide enticing field evidence of the role of Fe limitation in controlling cellular DA levels.
Assessing the applicability of Emiliania huxleyi coccolith morphology as a sea‐surface salinity proxy
Authors: Fielding Samuel R. , Herrle Jens O. , Bollmann Jórg , Worden Richard H. , Montagnesd David J. S.
Published: January 2011

Culture experiments were used to assess the applicability of Emiliania huxleyi coccolith morphology as a palaeo‐sea‐surface salinity (SSS) proxy. Coccolith morphology was dependent on salinity over a range reflecting present day marine conditions; both coccolith size and the number of coccolith elements increased linearly with increasing salinity. Using regression analysis, the effect of salinity on coccolith morphology was compared to those previously observed in sediment core‐top and plankton data. No significant differences were found between the slopes of these data, suggesting that salinity is the primary control on E. huxleyi coccolith size and element number in the ocean. However, the intercepts of the culture data were significantly higher. A combination of experimental and literature analysis indicated that temperature and nutrients were unlikely to be the causes of this discrepancy. Literature analysis also highlighted that coccolith size data from marginal environments displayed different intercepts to those from the open‐ocean data. This suggests that discrete morphotypes exist in these marginal locations. We, therefore, recommend that the original E. huxleyi coccolith morphology palaeo‐SSS transfer function requires further evaluation before being routinely applied.
Annual recruitment of three species of tide‐pool fishes is driven by variation in springtime coastal hydrodynamics
Authors: Shanksa Alan L. , Pfisterb Catherine A.
Published: January 2011

Using an 18‐yr time series of annual recruitment of three tide‐pool fishes, Clinocottus globiceps, Clinocottus embryum, and Oligocottus maculosus, we investigated the relationship between recruitment and upwelling and downwelling, date of the spring transition, and spring wave climate. There were no significant regressions between springtime upwelling and recruitment in any species. The timing of the spring transition, however, was related to the recruitment of C. globiceps and C. embryum: the later the spring transition the larger their annual recruitment. We found a negative exponential relationship between timing of the spring transition and O. maculosus recruitment, though only after removing one outlying data point (the strong 1997 El Nino year). Significant negative exponential regressions were also found between O. maculosus recruitment and hours in April and May when waves were ≪2 and ≪3 m in amplitude. In these regressions, 1997 was no longer an outlier. O. maculosus recruitment also varied positively with seawater temperature on the shore. The different hydrodynamic correlates of recruitment in this assemblage of species, as well as published observations, suggest that the larvae of these species are occupying different nearshore areas. Clinocottus species likely develop in coastal waters, while O. maculosus develops very close to shore, essentially in the surf zone, where its larvae may be swept offshore by currents generated during large wave events. Abiotic factors driving larval success can explain persistent differences in recruitment among these species over 18 yr.
Across margin export of organic matter by cascading events traced by stable isotopes, northwestern Mediterranean Sea
Authors: Vidal A. Sanchez‐ , Pasqual C. , Kerhervé P. , Heussner S. , Calafat A. , Palanques A. , Durrieu de Madron X. , Canals M. , Puig P.
Published: January 2011

We present a 1‐yr (2005‐2006) record of organic carbon (OC) and total nitrogen (TN) contents and their isotopic ratios (Δ13COC and Δ15N) in sinking particles from the western Gulf of Lions. Maximum OC and TN fluxes recorded in January 2006 and March‐April 2006 were associated with negative near‐bottom temperature anomalies. This reveals large inputs of resuspended organic matter from the shelf basinwards to depths ≫1500 m by dense shelf‐water cascading. The first pulse of organic matter had low Δ13COC (‐25.5‰) and N:C (0.08) and high Δ15N (6.6‰) values, indicative of the arrival of organic matter of terrestrial origin. In contrast, the second pulse had high Δ13COC (‐21.9‰) and N:C (0.15) and extremely low Δ15N (0.0‰) values, indicative of the transfer of organic matter with higher marine contribution. Though downslope export of organic matter from the adjacent shelf predominated, particles escaping from surface waters remained an important source of organic matter during low‐energy and low‐flux periods and especially during summer conditions, with significant contribution of N2 fixation to organic matter export. Overall, our results suggest the export of organic matter from different sources to the deep Mediterranean basin, which in turn might alter within a couple of months the quality of the sedimentary organic matter deposited on the sea floor and thus the dynamics of the deep ecosystems.
Microbial oceanography of the dark ocean's pelagic realm
Authors: Arístegui Javier , Gasol Josep M. , Duarte Carlos M. , Herndld Gerhard J.
Published: January 2011

The pelagic realm of the dark ocean represents a key site for remineralization of organic matter and long‐term carbon storage and burial in the biosphere. It contains the largest pool of microbes in aquatic systems, harboring nearly 75% and 50% of the prokaryotic biomass and production, respectively, of the global ocean. Genomic approaches continue to uncover the enormous and dynamic genetic variability at phylogenetic and functional levels. Deep‐sea prokaryotes have comparable or even higher cell‐specific extracellular enzymatic activity than do microbes in surface waters, with a high fraction of freely released exoenzymes, probably indicative of a life mode reliant on surface attachment to particles or colloids. Additionally, evidence increases that chemoautotrophy might represent a significant CO2 sink and source of primary production in the dark ocean. Recent advances challenge the paradigm of stable microbial food web structure and function and slow organic‐matter cycling. However, knowledge of deep‐ocean food webs is still rudimentary. Dynamics of particle transformation and fate of the exported material in deep waters are still largely unknown. Discrepancies exist between estimates of carbon fluxes and remineralization rates. Recent assessments, however, suggest that integrated respiration in the dark ocean's water column is comparable to that in the epipelagic zone, and that the dark ocean is a site of paramount importance for material cycling in the biosphere. The advent of new molecular tools and in situ sampling methodologies will improve knowledge of the dark ocean's microbial ecosystem and resolve current discrepancies between carbon sources and metabolic requirements of deep‐sea microbes.
Towards understanding the relationship between wind conditions and plankton patchiness
Authors: Blukacz E. A. , Shuter B. J. , Sprulesc W. G.
Published: January 2011

We used (1) water temperature (a proxy for water movement), (2) chlorophyll (a proxy for phytoplankton), and (3) zooplankton (bulk, small, and large size classes) to investigate the relationship between changing wind conditions and spatial patterns along linear transects (n 5 150) in two basins, South Arm and Annie Bay, of Lake Opeongo (Ontario, Canada). The basins have similar biological characteristics, but South Arm is larger and is oriented along the prevailing westerly wind direction. Large‐scale patterns (.1 km) were described with an accumulation index, and wavelet analysis was used to describe small‐scale patterns (≪1 km). Spatial descriptors were correlated with five descriptors of wind conditions: (1) wind force, (2) scalar wind speed, (3) vector wind speed, (4) wind persistence, and (5) wind direction. Persistent westerly winds in South Arm resulted in more downwind accumulation of warm water and total and large‐bodied zooplankton than in Annie Bay, while chlorophyll and small zooplankton did not show consistent downwind accumulation. The predominance of small‐scale variability, particularly in large zooplankton, increased in the South Arm as the persistence and strength of westerly winds blowing parallel to the sampling transects increased. Only temperature showed such a pattern in the smaller Annie Bay. These patterns were not related to winds blowing at the time of sampling but rather to those blowing up to 12 h before sampling. Our observations provide a basis for future consideration of how simple surface winds may actually shape the nature of trophic interactions in lake ecosystems.