bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)
Authors: Schlüter Michael , Sauter Eberhard J. , Andersen Claus E. , Dahlgaard Henning , Dando Paul R.
Published: July 2010

Submarine groundwater discharge (SGD) from subseafloor aquifers, through muddy sediments, was studied in Eckernförde Bay (western Baltic Sea). The fluid discharge was clearly traced by 222Rn enrichment in the water column and by the chloride profiles in pore water. At several sites, a considerable decrease in chloride, to levels less than 10% of bottom‐water concentrations, was observed within the upper few centimeters of sediment. Studies at 196 sites revealed that >22% of the seafloor of the bay area was affected by freshwater admixture and active fluid venting. A maximal discharge rate of .9 L m−2 d−1 was computed by modeling pore water profiles. Based on pore water data, the freshwater flow from subseafloor aquifers to Eckernförde Bay was estimated to range from 4 x 106 to 57 × 106 m3 yr−1. Therefore, 0.3–4.1% of the water volume of the bay is replaced each year. Owing to negligible surface runoff by rivers, SGD is a significant pathway within the hydrological cycle of this coastal zone. High‐resolution bathymetric data and side‐scan sonar surveys of pockmarks, depressions up to 300 m long, were obtained by using an autonomous underwater vehicle. Steep edges, with depths increasing by more than 2 m within 8–10 m in lateral directions, equivalent to slopes with an angle of as much as 11°, were observed. The formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents. Fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread, but easily overlooked, pathway affecting the cycle of methane and dissolved constituents to coastal waters of the Baltic Sea.
Models for ultraviolet radiation—dependent photoinhibition of Lake Erie phytoplankton
Authors: Hiriart‐Baer Véronique P. , Smith Ralph E. H.
Published: July 2010

We calibrated a model for ultraviolet radiation (UVR) and photosynthetically active radiation‐dependent photoinhibition, with explicit damage and recovery processes (the R model), against observations of photosynthesis by Lake Erie phytoplankton exposed to natural sunlight in the summer of 1998. The model explained 74%–96% of the variation in photosynthetic rates and indicated active recovery processes at 4 of the 5 experimental stations. UVR‐dependent photoinhibition kinetics were not as well explained by two simpler models that assumed either a lack of recovery processes or an instantaneous equilibrium between damage and recovery. The 1998‐calibrated R model also provided consistently significant predictions of photoinhibition in 10 experiments done the previous year, albeit with a reduced goodness‐of‐fit, whereas simpler models did not. Biological weighting functions (BWFs) derived for UVR effects in 1998 were similar in shape throughout the UVR part of the spectrum, with an especially steep decrease from 300 to 320 nm, compared with BWFs published for other phytoplankton communities and/or species. The R model predicted photoinhibitory losses of primary production, integrated through the photic zone, that were intermediate between the two simpler models and showed that Lake Erie phytoplankton varied in both their spectral sensitivity (as expressed by the BWF) and recovery rates.
Optical control of fish and zooplankton populations
Authors: Aksnes Dag L. , Nejstgaard Jens , Sædberg Eivind , Sørnes Tom
Published: July 2010

Aquatic food webs are affected from the bottom up by light through its effect on photosynthesis and productivity. But light also has a top‐down effect, because it is crucial for the visual foraging efficiency in many fish. Here we present data suggesting that marine pelagic food webs are primarily structured top‐down by light through its effect on vision in fish. For light‐limited fjord ecosystems, we show that the abundance of zooplanktivorous fish is proportional to the vertical extension of a visual feeding habitat, represented by the inverse of the light absorbance coefficient of the water column. We also show that both zooplankton abundance and body size are proportional to the size of a vision‐protected habitat that can be defined as the dimensionless product of the light absorbance coefficient and the depth of the water column. Natural and human‐driven environmental change may involve alterations in the amount of surface radiation as well as in the optical properties of the water column. Our results imply that such changes are likely to affect aquatic food webs top‐down through vision as well as bottom‐up through photosynthesis.
High intraspecific variability in carbon and nitrogen stable isotope ratios of lake chironomid larvae
Authors: Grey Jonathan , Kelly Andrew , Jones Roger I.
Published: July 2010

Stable isotope analyses of chironomid trophic interactions have recently indicated the potential importance of isotopically light biogenic methane as a carbon source. Mass balance of isotope ratios suggests that small proportional differences in ingestion of such an isotopically distinct basal resource by individual consumers can result in considerable intraspecific variability. To test this, we collected individual larvae of two closely related chironomid species (Chironomus anthracinus and Chironomus plumosus) from six lakes and analyzed their δ13C and δ15N. Intraspecific variability in larval δ13C and δ15N values was greater in lakes where chironomids were more 13C depleted. C. plumosus exhibited higher intraspecific variability relative to C. anthracinus. In two lakes, individual C. plumosus exhibited a range of 35‰ for δ13C and 16‰ for δ15N (equivalent to five trophic levels). There was a strong positive relationship between larval δ13C and δ15N, both between individuals from the same lake and also between lakes, suggesting that the underlying causative mechanisms are similar. Furthermore, larvae from deeper sites, which are more susceptible to prolonged anoxia, exhibited greater intraspecific variability, and larger larvae were significantly 13C depleted. Such high intraspecific variability can confound the interpretation of benthic food web stable isotope values. We advocate the reporting of more intraspecific isotopic variability as a means to further examine niche breadth and feeding behavior.
Recovery of Thalassiosira weissflogii from nitrogen and silicon starvation
Authors: De La Rocha Christina L. , Passow Uta
Published: July 2010

The ecological success of marine diatoms comes despite their unusual additional requirement for silicon, a nutrient that often limits their growth in the ocean. There may be, however, some physiological and ecological advantages to silicon limitation. A model of nitrogen and silicon metabolism in diatoms (Flynn et al. 1997; Flynn and Martin‐Jézéquel 2000) suggests that silicon‐starved diatoms will recover more quickly than nitrogen‐starved (but otherwise identical) diatoms on the resupply of nutrients. In culture, following 24 h of stationary phase induced by nutrient exhaustion, silicon‐starved Thalassiosira weissflogii displayed maximum growth rates within a few hours of the readdition of silicon. But 37 h elapsed before nitrate‐starved cultures began dividing again and nitrate‐starved cultures did not reattain maximum growth rates over the period investigated. The model suggests that, in terms of number, cells descended from the nitrate starved will never catch up to cells descended from the silicon starved if both populations are simultaneously supplied with a pulse of nutrients. The longer the lag between nutrient supply and the resumption of growth in the nitrate‐starved cells, the greater the proportion of the supplied nutrients that ends up in the descendants of the silicon starved. In the model run, the silicon‐starved cells acquired 75% of the added nutrients and the nitrate starved acquired only 25%. Silicon limitation may thus be a mechanism by which diatoms ensure they respond more quickly than other phytoplankton to the upwelling of nutrients into the euphotic zone.
Dynamics of silicon metabolism and silicon isotopic discrimination in a marine diatomas a function of pCO2
Authors: Milligan Allen J. , Varela Diana E. , Brzezinski Mark A. , Morel François M. M.
Published: July 2010

Opal accumulation rates in sediments have been used as a proxy for carbon flux, but there is poor understanding of the factors that regulate the Si quota of diatoms. Natural variation in silicon isotopes (δ30Si) in diatom frustules recovered from sediment cores are an alternative to opal mass for reconstructing diatom Si use and potential C export over geological timescales. Understanding the physiological factors that may influence the Si quota and the δ30Si isotopic signal is vital for interpreting biogenic silica as a paleoproxy. We investigated the influence of pCO2 on the Si quota, fluxes across the cell membrane, and frustule dissolution in the marine diatom Thalassiosira weissflogii and determined the effect that pCO2 has on the isotopic fractionation of Si. We found that our Si flux estimates mass balance and, for the first time, describe the Si budget of a diatom. The Si quota rose in cells grown with low pCO2 (100 ppm) compared with controls (370 ppm), and the increased quota was the result of greater retention of Si (i.e., lower losses of Si through efflux and dissolution). The ratio of efflux : influx decreased twofold as pCO2 decreased from 750 to 100 ppm. The efflux of silicon is shown to significantly bias measurements of silica dissolution rates determined by isotope dilution, but no effect on the Si isotopic enrichment factor (ε) was observed. The latter effect suggests that silicon isotopic discrimination in diatoms is set by the Si transport step rather than by the polymerization step. This observation supports the use of the v signal of biogenic silica as an indicator of the percentage utilization of silicic acid.
Interspecific and intraspecific variation of δC and δN in deposit‐ and suspension‐feeding bivalves (Macoma balthica and Cerastoderma edule): Evidence of ontogenetic changes in feeding mode of Macoma balthica
Authors: Rossi F. , Herman P. M. J. , Middelburg J. J.
Published: July 2010

Deposit and suspension feeders can switch feeding behavior and show variations in feeding mode as individuals pass through life‐cycle stages. Stable carbon and nitrogen isotopes were used to trace changes in diet of the tellinid bivalves M. balthica (facultative deposit feeder) and C. edule (obligatory suspension feeder), according to their size class. Analyses of variance showed differences in the d13C between the species. C. edule showed a diet composed of microphytoplankton, whereas M. balthica could feed on a mixed diet of microalgae from benthos and plankton. Values of Δ13C depended significantly on body size in M. balthica, providing evidence of ontogenetic variation in diet with small juveniles feeding entirely on microphytobenthos, while there was a gradual tendency for larger sizes to feed more on microphytoplankton. Therefore, although these species rely on different sources of food, large animals of M. balthica can overlap the trophic niche of C. edule. Population dynamics of the animals should be considered in food‐web studies.
Dominance of the noxious cyanobacterium Microcystis aeruginosa in low‐nutrient lakes is associated with exotic zebra mussels
Authors: Raikow David F. , Sarnelle Orlando , Wilson Alan E. , Hamilton Stephen K.
Published: July 2010

To examine the hypothesis that invasion by zebra mussels (Dreissena polymorpha) promotes phytoplankton dominance by the noxious cyanobacterium Microcystis aeruginosa, 61 Michigan lakes of varying nutrient levels that contain or lack zebra mussels were surveyed during late summer. After accounting for variation in total phosphorus (TP) concentrations, lakes with Dreissena had lower total phytoplankton biomass, as measured by chlorophyll a and algal cell biovolume. Phytoplankton biomass increased with TP in both sets of lakes, although the elevations of the relationship differed. The percentage of the total phytoplankton comprised by cyanobacteria increased with TP in lakes without Dreissena (R2 = 0.21, P = 0.025) but not in lakes with Dreissena (P = 0.79). Surprisingly, there was a positive influence of Dreissena invasion on Microcystis dominance in lakes with TP ≪ 25 µg L−1 (P 5 0.0018) but not in lakes with TP ≫ 25 µg L−1 (P = 0.86). The finding that Microcystis, a relatively grazing‐resistant component of the phytoplankton, was favored by Dreissena in low‐ but not in high‐nutrient lakes is somewhat counterintuitive, but predator‐prey models make this prediction in certain cases when the cost for the prey of being consumption resistant is a low maximum population growth rate. This Dreissena‐cyanobacteria interaction contradicts well‐established patterns of increasing cyanobacteria with nutrient enrichment in north‐temperate lakes and suggests that the monitoring and abatement of nutrient inputs to lakes may not be sufficient to predict and control cyanobacterial dominance of Dreissena‐invaded lakes.
Supplementation of a diatom diet with cholesterol can enhance copepod egg‐production rates
Authors: Hassett R. Patrick
Published: July 2010

Cholesterol is required for animal growth, yet it cannot be biosynthesized de novo by crustaceans. Dietary sterols are thus necessary for the growth and reproduction of copepods. Sterols vary widely in both composition and concentration in phytoplankton. To explore the potential for sterol limitation of copepod growth, I did experiments with adult copepods feeding on diatoms with and without cholesterol supplementation. Cholesterol was added to the diet by (1) homogenizing the insoluble cholesterol with an ultrasonic disintegrator or (2) preparing gelatin/acacia microcapsules with and without cholesterol using triolein as a carrier. egg‐production rates were measured after 2–4 d on the experimental diets, except in one experiment, in which an 18‐d feeding period was used. Eggproduction rates increased 1.5–2‐fold for Acartia hudsonica, Acartia tonsa, and Calanus finamrchicus when the diatom Thalassiosira weissflogii was supplemented with 5–20 µg L−1 cholesterol; supplementation at 1 µg L−1 had no effect. Nearly three‐fold higher rates of egg production were observed with C. finmarchicus after feeding for 18 d on the supplemented diet. Cholesterol had a positive effect on egg‐production rates when added by either method. Egg hatch rates for A. hudsonica were also higher when they were fed T. weissflogii supplemented with cholesterol (91% hatched) than when they were fed an unsupplemented diet (40% hatched). Egg production of Centropages hamatus feeding on T. weissflogii was unaffected by supplementation. egg‐production rates of A. hudsonica were unaffected when Chaetoceros affinis, Phaeodactylum tricornutum, or Thalassiosira rotula were supplemented. Higher egg‐production rates in supplemented treatments were caused by a decrease in the frequency of small clutches during spawning events rather than an increase in maximum clutch size. These experiments demonstrate the potential for limitation of egg production by dietary sterols when copepods feed exclusively on diatoms.
Phosphorus and trace metal limitation of algae and bacteria in Lake Superior
Authors: Sterner Robert W. , Smutka Tanya M. , McKay R. Michael L. , Xiaoming Qin , Brown Erik T. , Sherrell Robert M.
Published: July 2010

We performed a set of nutrient‐enrichment bioassay experiments using metal‐clean protocols, testing for macronutrient and micronutrient limitation of algae and bacteria in western Lake Superior. Our analysis involved a novel approach to estimating the strength of nutrient limitation in factorial enrichment designs. We found that phytoplankton and bacterioplankton growth both increased with added phosphorus alone but not with iron, manganese, or zinc alone. However, even very small increases in growth rates following P supplementation (on the order of an additional 0.1 d−1) induced iron limitation in the phytoplankton, indicating that the algae in this large lake may be on the cusp of micronutrient and macronutrient limitation. In contrast, and contrary to expectations, bacteria responded only to P and not to metals. Spatial and temporal variability in degree and quality of nutrient limitation was considerable.
Light driven seasonal patterns of chlorophyll and nitrate in the lower euphotic zone of the North Pacific Subtropical Gyre
Authors: Letelier Ricardo M. , Karl David M. , Abbott Mark R. , Bidigare Robert R.
Published: July 2010

The euphotic zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long‐term oligotrophic habitat assessment; 22°45′N, 158°00′W) transects the nearly permanently stratified upper thermocline. Hence, seasonal changes in solar radiation control the balance between photosynthesis and respiration in this lightlimited region. Combining profiles of radiance reflectance, algal pigments, and inorganic nutrients collected between January 1998 and December 2000, we explore the relationships between photosynthetically available radiation (PAR), phytoplankton biomass (chlorophyll a), and the position of the upper nitracline in the lower euphotic zone. Seasonal variations in the water‐column PAR attenuation coefficient displace the 1% sea‐surface PAR depth from approximately 105 m in winter to 121 m in summer. However, the seasonal depth displacement of isolumes (constant daily integrated photon flux strata) increases to 31 m due to the added effect of changes in sea‐surface PAR. This variation induces a significant deepening of the DCML during summertime with a concomitant increase in chlorophyll a and the removal of 36 mmol m−2 inorganic nitrogen [NO3− + NO2−] in the 90–200‐m depth range, equivalent to approximately 34% of the annual flux of particulate nitrogen collected in sediment traps placed at 150 m. We conclude that in this oceanic region the annual light cycle at the base of the euphotic zone induces an increase in the phototrophic biomass analogous to a spring bloom event.
Genetic diversity in the Gammarus pecos species complex: Implications for conservation and regional biogeography in the Chihuahuan Desert
Authors: Gervasio1 Vivianaluxa , Berg2 David J. , Lang Brian K. , Allan Nathan L. , Guttman Sheldon I.
Published: July 2010

We used allozyme electrophoresis to quantify genetic variation in nine populations of the Gammarus pecos species complex endemic to spring systems of the northern Chihuahuan Desert. There was significant within‐population and high among‐population genetic variation. Two populations exhibited heterozygote deficiencies and high proportions of polymorphic loci, which suggests the presence of cryptic species. Genetic distances among populations were negatively correlated with previously published morphological similarities, which suggests congruence between allozyme and morphological phenotypes. Cluster analysis of genetic distances showed four major groups of populations within the G. pecos complex. Genetic identities and fixed allelic differences support the presence of at least four distinct species: Gammarus desperatus, G. pecos, Gammarus hyalleloides, and one or more undescribed species. Relatively large genetic distances between populations suggest long periods of isolation and allopatric speciation. Patterns of among‐population genetic variation were similar between amphipods and several groups of endemic fishes and snails, which suggests a coherence to biogeographic patterns within this region. Thus, the understanding of the genetic structure and taxonomic status of the G. pecos species complex provides insight into the biogeography of other aquatic organisms in the northern Chihuahuan Desert. Given the alarming rate at which desert spring systems are being altered and the unique biotic assemblages present, protection of these habitats is imperative.
Sources and cycling of carbonyl sulfide in the Sargasso Sea
Authors: Cutter Gregory A. , Cutter Lynda S. , Filippino Katherine C.
Published: July 2010

The cycling of the radiatively important gas carbonyl sulfide (OCS) was studied in surface waters of the Sargasso Sea. In August 1999, surface OCS concentrations averaged 8.6 pmol L−1, showed minor diel variations, and varied little with depth. An OCS precursor, total dissolved organic sulfur (DOS), was lowest at the surface (40 nmol L−1) and increased with depth. The photoproduction rate of OCS from in situ incubations averaged 9.6 pmol L−1 h−1, whereas dark production was 7.0 pmol L−1 h−1. Apparent quantum yields were 10−5−10−7 from 313–436 nm and varied with the water depth irradiated. In March 2000, there were strong diel variations in surface OCS (highest in late afternoon; overall average, 16.9 pmol L−1). Depth profiles in the afternoon showed surface water maxima and decreases with depth, whereas DOS had a surface maximum of 419 nmol L−1 and decreased with depth. Dark production was 4.0 pmol L−1 h−1. Modeling of the diel cycle suggested a photoproduction rate of 16.4 pmol L−1 h−1. Overall, the photochemical production of OCS strongly depended on DOS and chromophoric dissolved organic matter, whereas dark production was influenced by the presence of particles and perhaps microbial respiration, showing a direct biotic influence on OCS cycling.
Light dependence of selenium uptake by phytoplankton and implications for predicting selenium incorporation into food webs
Authors: Baines Stephen B. , Fisher Nicholas S. , Doblin, Martina A. , Cutter, Gregory A. , Cutter Lynda S. , Cole Brian
Published: July 2010

The potentially toxic element selenium is first concentrated from solution to a large but highly variable degree by algae and bacteria before being passed on to consumers. The large loads of abiotic and detrital suspended particles often present in rivers and estuaries may obscure spatial and temporal patterns in Se concentrations at the base of the food web. We used radiotracers to estimate uptake of both selenite (Se(IV)) and C by intact plankton communities at two sites in the Sacramento/San Joaquin River Delta. Our goals were to determine (1) whether C and Se(IV) uptake were coupled, (2) the role of bacteria in Se(IV) uptake, and (3) the Se :C uptake ratio of newly produced organic material. Se(IV) uptake, like C uptake, was strongly related to irradiance. The shapes of both relationships were very similar except that at least 42–56% of Se(IV) uptake occurred in the dark, whereas C uptake in the dark was negligible. Of this dark Se(IV) uptake, 34–67% occurred in the 0.2–1.0‐ µm size fraction, indicating significant uptake by bacteria. In addition to dark uptake, total Se(IV) uptake consisted of a light‐driven component that was in fixed proportion to C uptake. Our estimates of daily areal Se(IV) :C uptake ratios agreed very well with particulate Se :C measured at a site dominated by phytoplankton biomass. Estimates of bacterial Se :C were 2.4–13 times higher than for the phytoplankton, suggesting that bacteriovores may be exposed to higher dietary Se concentrations than herbivores.
Biological stoichiometry of Daphnia growth: An ecophysiological test of the growth rate hypothesis
Authors: Acharya Kumud , Kyle Marcia , Elser James J.
Published: July 2010

The growth rate hypothesis (GRH) proposes that variation in organism C: P and N: P ratios reflects variation in P content associated with altered allocation to P‐rich ribosomal RNA under different growth rates. We tested the GRH by examining the effects of food quantity and stoichiometric quality (differing carbon : nitrogen : phosphorus [C :N: P] ratios) on juvenile growth and chemical composition (C :N: P, RNA, and DNA contents) of two species of Daphnia (D. galeata, D. pulicaria). Daphnia in P‐limited experiments were fed saturating and limiting concentrations of food (Scenedesmus acutus) of high P (C: P = 110 ± 7.3), medium P (456 ± 20.7), and low P (934 ± 23.6), and in an N‐limited experiment D. pulicaria was fed saturating concentrations of high N (C:N = 6.31 ± 0.35), medium 1 and medium 2 (9.0 ± 0.42; 15.0 ± 0.49, respectively), and low N (18.22 ± 0.56) food. In P‐limited experiments, both Daphnia species grew fastest under P‐rich, high food conditions and grew slowest under P‐deficient, low food conditions, showing effects of both food quality and quantity. Daphnia body percentage P, C: P, N: P, and percentage RNA were tightly correlated with growth rates, and RNA contributed a significant fraction of total body P (48.8% [62.0%]). This strong three‐way (growth‐RNA‐P) set of correlations supports the GRH. In the N‐limited experiment, food C:N had a moderate effect on Daphnia growth. While there was a good linear correlation between P and RNA, growth rate was uncorrelated with RNA content and P content, suggesting that the three‐way coupling of growth, RNA, and P content is broken under N limitation of growth, but more data for these conditions are needed. These data help in delineating the physiological conditions under which the GRH holds and may be useful in interpreting variation in body stoichiometry of zooplankton from field and lab studies.
Daphnia can protect diatoms from fungal parasitism
Authors: Kagami Maiko , Van Donk Ellen , de Bruin Arnout , Rijkeboer Machteld , Ibelings Bas W.
Published: July 2010

Many phytoplankton species are susceptible to chytrid fungal parasitism. Much attention has been paid to abiotic factors that determine whether fungal infections become epidemic. It is still unknown, however, how biotic factors, such as interactions with zooplankton, affect the fungal infection process. Because the size of fungal zoospores is well within the preferred range of food particle size for Daphnia, we hypothesize that Daphnia will affect the fungal infection process by reducing the abundance of fungal zoospores. To examine the effects of zooplankton on the fungal parasitism of phytoplankton, we performed grazing experiments. These experiments revealed that Daphnia significantly decreased fungal parasitism by grazing on the fungal zoospores. Daphnia also had a small positive effect on fungal infection, probably by increasing the encounter rate between fungi and host phytoplankton cells. These results suggest that Daphnia can affect the seasonal succession of chytrids and their host phytoplankton species. In addition, these results imply that zoospore‐producing fungi may play an ecological role as food sources for Daphnia in aquatic food webs.
Oxygen dynamics in permeable sediments with wave‐driven pore water exchange
Authors: Precht Elimar , Franke Ulrich , Polerecky Lubos , Huettel Markus
Published: July 2010

The effects of advective pore water exchange driven by shallow water waves on the oxygen distribution in a permeable (k = 3.3 x 10−12 to 4.9 x 10−11 m2) natural sediment were studied with a planar oxygen optode in a wave tank. Our experiments demonstrate that pore water flow driven by the interaction of sediment topography and oscillating boundary flow changes the spatial and temporal oxygen distribution in the upper sediment layer. Oxygenated water intruding in the ripple troughs and deep anoxic pore water drawn to the surface under the ripple crests create an undulating oxic‐anoxic boundary within the upper sediment layer, mirroring the topographical features of the sediment bed. Anoxic upwelling zones under ripple crests can separate the oxic sediment areas of neighboring ripple troughs with steep horizontal oxygen concentration gradients. The optode showed that migrating wave ripples are trailed by their pore water flow field, alternately exposing sediment volumes to oxic and anoxic pore water, which can be a mechanism for remobilizing particulate oxidized metal precipitates and for promoting coupled nitrification‐denitrification. More rapid ripple migration (experimental threshold ~20 cm h−1) produces a continuous oxic surface layer that inhibits the release of reduced substances from the bed, which under slowly moving ripples is possible through the anoxic vertical upwelling zones. Swift, dramatic changes in oxygen concentration in the upper layers of permeable seabeds because of surface gravity waves require that sediment‐dwelling organisms are tolerant to anoxia or highly mobile and enhance organic matter mineralization.
Environment drives physiological variability in the cold seep mussel Bathymodiolus childressi
Authors: Bergquist Derk C. , Fleckenstein Clint , Szalai Emily B. , Knisel Julie , Fisher Charles R.
Published: July 2010

The ability of an organism to respond to changes in its environment depends upon its short‐term physiological plasticity and the constraints of its genetic makeup. At hydrothermal vents and cold seeps, the spatially variable physiological characteristics of symbiont‐bearing animals are often assumed to reflect short‐term physiological adjustments to a patchy and dynamic chemical environment. However, the extent to which these spatially variable responses represent fixed characteristics unique to animals inhabiting the different environments (such as might arise from genetic differentiation) has not been tested. The seep mussel Bathymodiolus childressi depends upon methanotrophic bacteria for the bulk of its nutrition and inhabits a range of environments where it displays varying growth and body condition. In this study, we first investigated the multiscale environmental and physiological variability of B. childressi by measuring dissolved gas concentrations and mussel body condition in 12 mussel beds at four geographically distinct sites. Brine‐dominated seeps tended to have higher methane and sulfide concentrations and host mussels of better body condition than petroleum‐dominated sites. Then, using two transplant experiments, we evaluated whether local environmental conditions or stock effects determined the observed differences in growth and body condition of B. childressi. In all cases, mussels transplanted to new sites acquired or nearly acquired the characteristics of their host population, illustrating the primary role of the environment in determining the physiological characteristics of resident mussels. However, mussels from different sites sometimes responded differently to the same environment, suggesting stock‐related effects also play a role in the spatial variation observed in the physiology of chemosynthetic fauna.
Optical properties of Asian mineral dust suspended in seawater
Authors: Stramski Dariusz , Woźniak Slawomir B. , Flatau Piotr J.
Published: July 2010

The spectral optical properties of Asian mineral dust suspended in seawater exhibit significant variability associated with the origin (and, hence, the chemistry and mineralogy) and particle size distribution of the samples. The measurements of dust samples from different locations show that the mass‐specific absorption coefficient of particles, a*p, at a wavelength of light λ = 440 nm, varies from about 0.028 m2 g−1 for the soil dust from Chinese desert near Dunhuang to 0.15 m2 g−1 for the soil dust of volcanic origin in Cheju Island (South Korea). At l5 400 nm, this range is 0.05–0.23 m2 g−1. The aerosol sample collected in the Sea of Japan during a massive dust storm in East Asia shows a*p(λ) > 0.1 m2 g−1 for λ < 425 nm. The mass‐specific scattering coefficient, b*p(λ, ranges from about 0.8 to 1.5 m2 g−1 at blue and green wavelengths for the samples examined. The single scattering albedo, ωo, increases with wavelength. For λ > 400 nm, ωo was >0.78 for the sample from Cheju Island and >0.9 for other samples. In the near‐infrared region (750–850 nm), where absorption by dust particles is small or undetectable, ωo was close to 1.
Composition and temporal variability of picoeukaryote communities at a coastal site of the English Channel from 18S rDNA sequences
Authors: Romari Khadidja , Vaulot Daniel
Published: July 2010

We analyzed picoeukaryote assemblages at a French coastal site of the English Channel by sequencing cloned eukaryotic 18S rRNA genes in eight genetic libraries constructed from environmental samples (seven coastal, one estuarine) collected at different periods of the year. Eight hundred clones were examined by amplified restriction fragment length polymorphism (RFLP) using the restriction enzyme HaeIII. The coverage value calculated from the relative distribution of RFLP types was low, indicating that the library diversity was not entirely recovered. A variable region of the rRNA gene was partially sequenced (550 bases) and analyzed for 397 clones. Thirty‐two clones were affiliated with metazoans. Of the remaining clones, 132 were affiliated to algal classes (especially Prasinophyceae, Cryptophyceae, Dinophyceae, and Prymnesiophyceae) and 107 to known heterotrophic groups (Cercozoa, choanoflagellates, stramenopiles, and ciliates). One hundred three sequences fell into uncultivated groups of stramenopiles (43 clones) and alveolates (60 clones). We also found two potentially novel eukaryotic lineages, represented by 9 and 14 clones, respectively, not belonging to any known eukaryotic group. The overall composition of the picoeukaryote community remained fairly stable at the class/division level except during the early summer diatom bloom, when groups such as the Cryptophyceae and the ciliates completely disappeared. However, at a finer taxonomic level (corresponding to 98% sequence identity), the majority of the operational taxonomic units (OTU) were only observed once.
Role of wetlands and developed land use on dissolved organic nitrogen concentrations and DON/TDN in northeastern U.S. rivers and streams
Authors: Pellerin Brian A. , Wollheim Wilfred M. , Hopkinson Charles S. , McDowell William H. , Williams Michael R. , Vörösmarty Charles J. , Daley Michelle L.
Published: July 2010

Previous studies have shown that watersheds with significant human development (i.e., urban and agricultural land use) generally have higher concentrations and fluxes of dissolved inorganic nitrogen (DIN) in comparison to less‐developed or forested watersheds. However, the impact of watershed development on dissolved organic nitrogen (DON) concentrations in drainage waters has received little attention. We present data from 39 watersheds in Massachusetts (Ipswich River watershed) encompassing a gradient of developed land use (0%–92% urban plus agriculture) and wetland abundance (0%–32%) to assess controls on mean annual DON concentrations and DON/total dissolved nitrogen (TDN) in drainage waters. In addition, we compiled published data from 119 northeastern U.S. watersheds to evaluate broader‐scale relationships between DON, developed land use, and wetlands. The percentage of developed land is a poor predictor of DON concentrations in the Ipswich watersheds (r2 = 0.09) and the compiled dataset (r2 = 0.27). In contrast, wetland percentage explains 56% of the variability in DON concentrations in the Ipswich watersheds, and 60% when all literature data are included. Excluding watersheds with direct wastewater inputs to surface waters improves the regional relationship significantly (r2 = 0.79). The DON:TDN ratio is best explained by a multiple regression of wetland percentage and developed land use percentage for both the Ipswich watersheds (r2 = 0.73) and the compiled dataset (r2 = 0.50). Watersheds with abundant wetlands may therefore have high DON concentrations and DON:TDN ratios despite elevated anthropogenic nitrogen inputs associated with human development.
Basin‐scale motion in stratified Upper Lake Constance
Authors: Appt Jochen , Imberger Jörg , Kobus Helmut
Published: July 2010

This paper describes experimental and modeled wind‐induced oscillations in Upper Lake Constance with an emphasis on a coherent understanding of the basin‐scale internal dynamics in this example of a large and stratified lake. Data were collected with eight Lake Diagnostic Systems (LDSs) consisting of thermistor chains and wind anemometers. The isotherm displacements as measured by the LDSs were interpreted using the three‐dimensional hydrodynamic Estuary and Lake Computer Model (ELCOM). Three types of basin‐scale waves were found to dominate the wave motion: the vertical mode‐one Kelvin wave that had an observed period around 90 h, two vertical mode‐one Poincaré waves that had periods near 8 h and 12 h, and a vertical mode‐two Poincaré wave that had a period near 14 h. After strong westerly winds, upwelling of cold bottom water was observed east of the Sill of Mainau, where the lake's two subbasins connect. The width and length ratios of the subbasins, spatial variations of the wind field, and rotational effects over the lake are shown to play critical roles in the details of the upwelling structure. A sudden fall of the isotherms in Lake Überlingen formed a surge. The reflection of the surge from the northwestern boundary induced a vertical mode‐two response leading to an intrusion in the metalimnion that caused a three‐layer velocity structure in the smaller subbasin.
Characterization of particulate proteins in Pacific surface waters
Authors: Saijo Sachiko , Tanoue Eiichiro
Published: July 2010

We investigated molecular characteristics of particulate proteins in Pacific surface waters using two‐dimensional electrophoresis (2DE). Most proteinaceous materials estimated by dye‐binding methods were characterized by the 2DE unresolved acidic materials with a broad range of molecular mass and the 2DE unresolved low molecular mass materials with a broad range of isoelectric point. The 2DE unresolved acidic and low molecular mass materials were considered to comprise peptides conjugated with acidic saccharides and degradation products (peptides) of proteins, respectively, which indicates that almost all proteins in living organisms failed to survive in detrital particulate organic matter (POM). Nevertheless, 23 discrete proteins were distinguished by the 2DE. Electrophoretic patterns of the discrete proteins indicated that they were a component of detrital POM. Three discrete proteins were subjected to N terminal amino acid sequence analysis. Two proteins out of three could not be determined because their N termini were blocked, and one protein was determined from the N terminus to the ninth amino acid residue. A homology search revealed that the N terminal amino acid sequence of the protein agreed completely with that of 70 kDa heat shock protein (HSP70) derived from photosynthetic organisms. HSP70 is a major member of the molecular chaperones that protect or repair proteins from damage under conditions of environmental stress. The occurrence of HSP70 in this study demonstrated that phytoplankton were able to induce the molecular chaperone(s). Clarification of factor(s) controlling induction of chaperones will enable us to assess the actual environmental stress on phytoplankton at the biomolecular level.
Fast repetition rate fluorometry is not applicable to studies of filamentous cyanobacteria from the Baltic Sea
Authors: Raateoja Mika , Seppälä Jukka , Ylöstalo Pasi
Published: July 2010

Fast repetition rate (FRR) fluorometry has been used successfully to investigate the variable fluorescence characteristics of cyanobacteria in oceanic Case 1 waters. In these waters, the effective absorption bands of the light harvesting pigments for photosystem II (PSII) of the dominant cyanobacterial taxa overlap with the peak of the FRR excitation at 470 nm. The effective PSII absorption of the ecologically‐significant filamentous cyanophytes in the Baltic Sea—Nodularia spumigena (Mertens ex Bornet and Flahault 1886) and Aphanizomenon sp. ((L.) Ralfs ex Bornet and Flahault 1886)—is, however, restricted to beyond 550 nm. We tested the applicability of a currently commercially available FRR fluorometer to studies of these two cyanobacterial taxa. We propose that the FRR technique should not be used in studies on these taxa, or on any cyanophyte containing phycoerythrocyanin instead of phycoerythrin, the former having inefficient PSII light harvesting in the wave band of the FRR excitation. This issue should be taken into account whenever field studies utilizing the FRR system are planned in those Case 2 water bodies, in which cyanobacteria lacking phycoerythin are among the dominant phytoplankton groups.
Distribution of eukaryotic picoplankton assemblages across hydrographic fronts in the Southern Ocean, studied by denaturing gradient gel electrophoresis
Authors: Diíez Beatriz , Massana Ramon , Estrada Marta , Pedrós‐Alió Carlos
Published: July 2010

We used a molecular fingerprinting technique to analyze the distribution and composition of eukaryotic picoplankton along latitudinal transects in the Southern Ocean. First, primers specific for eukaryotic 18S rDNA were used in a polymerase chain reaction (PCR) with environmental DNA. The amplification products were subjected to denaturing gradient gel electrophoresis (DGGE). Transect DOVETAIL (44°W) went from the ice edge (at 60°S) across the Weddell‐Scotia confluence and north to 58°S; it was sampled in January 1998 (summer). Transect DHARMA (between 53°W and 58°W) went from the ice edge in the Weddell Sea (63°S) across the Drake Passage to the South American continental platform (55°S); it was sampled in December 1998 (late spring). DGGE band patterns were used to build dendrograms combining samples from each cruise. Samples were grouped in several distinct clusters that were generally consistent with the hydrography of the area. In DOVETAIL, the upper water column was stratified and the DGGE band patterns varied with depth. In DHARMA the upper mixed layer showed the same composition of the eukaryotic picoplankton at all depths. The most dominant DGGE bands were excised and sequenced. Some were closely related to well‐known components of the plankton such as prasinophytes, prymnesiophytes, dinoflagellates, and diatoms. A significant number of sequences were related to previously unknown phylogenetic groups, including novel stramenopiles and alveolates or to poorly known groups such as cercomonads. This fingerprinting technique is useful for a rapid evaluation of the spatial distribution of picoeukaryotic assemblages in the oceans.
Interactions among dissolved organic carbon, microbial processes, and community structure in the mesopelagic zone of the northwestern Sargasso Sea
Authors: Carlson Craig A. , Giovannoni Stephen J. , Hansell Dennis A. , Goldberg Stuart J. , Parsons Rachel , Vergin Kevin
Published: July 2010

At the Bermuda Atlantic Time‐Series Study (BATS) site, the field observations of dissolved organic carbon (DOC) dynamics indicate that seasonally produced “semilabile” DOC is resistant to rapid microbial degradation in the surface waters but available for microbial remineralization once it is delivered into the mesopelagic zone after convective overturn. In this study, we employed an experimental simulation of convective overturn events to determine whether the remineralization of semilabile DOC would occur in a controlled laboratory setting. Seawater culture experiments were conducted in which surface (≤10 m) and mesopelagic (250 m) 0.2‐mm filtrates were inoculated with unfiltered water from ≤10 and 250 m in an assortment of combinations to simulate various mixtures of nutrients, DOC quantity and quality, and microbial assemblages. Results indicate that (1) microbial inocula from the upper euphotic zone were incapable of remineralizing the seasonally accumulated semilabile DOC (µmol C L−1 resolution) on the timescales of the incubations; (2) the utilization of semilabile DOC was greatest when the inoculum source was from 250 m and the filtrate source was from the upper 10 m; and (3) the decrease in bacterioplankton diversity, estimated with the Shannon‐Wiener diversity index, was greater in treatments in which inoculum from 250 m was mixed with filtrate from 10 m than in treatments in which the surface inoculum was mixed with the surface filtrate. Our findings are that a portion of the surface semilabile DOC can be metabolized by microorganisms in a laboratory setting and that mesopelagic nutrients alone are insufficient to stimulate DOC drawdown >1.3 µmol L−1. Transformations of microbial community structure were associated with the drawdown of surface DOC in simulated mixing events and suggest that microbial community structure is a factor in surface‐layer DOC dynamics.
Nitrogen and phosphorus requirements of an Alexandrium minutum bloom in the Penzé Estuary, France
Authors: Maguer Jean‐François , Wafar Mohideen , Madec Christian , Morin Pascal , Denn Evelyne Erard‐Le
Published: July 2010

During an intense (up to 33 X 106 cells L−1) Alexandrium minutum bloom in the Penzé estuary (France), total NO3, NH4, and PO4 requirements of the bloom were, respectively, 184, 25, and 20 µmol L−1, with peak uptake rates of 43, 6, and 4.8 µmol L−1 d−1. The measured ambient concentrations of NH4 and PO4 were far short of this peak demand, whereas those of NO3 were far in excess, indicating that PO4 supply is important for sustaining the bloom. Comparison of the measured NO3 uptake rates with advective fluxes indicates that a reduction of NO3 concentrations in river waters to <200 µmol L−1 would be necessary to contain the bloom in the Penzé estuary. The role of NO3 was restricted to sustenance of the bloom, whereas warm conditions resulting in a water column stability seem to have triggered the bloom, and a self‐shading, probably coupled with a phosphorus limitation, caused its decline.
Recruitment of coastal planktonic diatoms from benthic versus pelagic cells: Variations in bloom development and species composition
Authors: McQuoid Melissa R. , Godhe Anna
Published: July 2010

Although phytoplankton blooms are major events in aquatic systems, the importance of benthic resting stages in seeding planktonic blooms is still unclear. Using microcosms, we tested the influence of benthic versus planktonic inocula on the development and taxonomic composition of diatom communities in a temperate fjord. Experiments in early spring 2002, fall 2002, and late spring 2003 showed that the type and quantity of inoculum influenced bloom development and composition. Species composition was vastly different when seeded by cells from the benthos. Species such as Detonula confervacea and Thalassiosira minima showed strong dependence on benthic propagules. Populations of Chaetoceros debilis and Thalassiosira nordenskioeldii were initiated by both benthic and planktonic cells, and benthic seeding was most successful when experiments were preceded by a planktonic bloom. Skeletonema costatum was abundant in all treatments but showed variations in size, depending on the type of inoculum. Species that do not have a resting stage, such as Pseudo‐nitzschia spp., were present only in plankton treated microcosms. Seasonal factors were especially important in determining the successful growth of newly seeded populations. Our results indicate that benthic resting stages provide an important source for some species. Because the introduction of benthic resting stages to surface waters can greatly influence species composition of the plankton, it is important that studies of plankton blooms include life‐history stages from both the sediments and the water column.