bluuebunny/crossref_metadata_2025 huggingface dataset:
Defensive spine formation in Daphnia pulex Leydig and induction by Chaoborus crystallinus De Geer
Authors: Vuorinen Ilppo , Ketola Matti , Walls Mari
Published: April 2010

We found a clone in which Daphnia pulex is born with defensive spines even when not exposed to Chaoborus. Using this clone in individual culture experiments, we found that a European phantom midge, Chaoborus crystallinus, also releases a morphogen. Spine induction was not restricted to the embryo stage, since in transfer experiments organisms were induced to develop spines although they had spent the embryo stage in water uncontaminated by Chaoborus. The study suggests that the use of individual culture methods instead of stock cultures is crucial to revealing the details of spine induction.
A detailed organic carbon budget as an ecosystem‐level calibration of bacterial respiration in an oligotrophic lake during midsummer
Authors: Cole Jonathan J. , Caraco Nina F. , Strayer David L. , Ochs Clifford , Nolan Scott
Published: April 2010

During a 1‐month period at the peak of summer stratification, we made intensive measurements of the major inputs and outputs of organic carbon to and from the epilimnetic water column of oligotrophic Mirror Lake, New Hampshire. These measurements included allochthonous and autochthonous components, as well as changes in storage, and were designed to construct a complete carbon budget. Bacterial respiration was compared directly to our budget in an effort to use ecosystem‐level constraints to test the major assumptions used to estimate bacterial production and respiration. On the basis of the difference between all other inputs and outputs, bacterial respiration must lie between 0.4 and 6 nmol C m−2 d−1. With measured rates of thymidine incorporation and measured bacterial cell sizes, this organic‐C budget constrains the thymidine conversion factor (cell nM−1 thymidine) to be between 1 and 6 × 109 cells nM−1 thymidine for growth yields between 10 and 80%. If the thymidine conversion factor were > 10 × 109 cells nmol−1, bacterial respiration alone would exceed the total input of C to the system, even at assumed growth yields of 80%. The same analysis indicates that the carbon conversion factor cannot exceed 3 × 10−7 µg µm−3 for any reasonable values of growth yield and thymidine conversion factor.

On the basis of our best estimates for all parameters, bacterial production was equal to 16% of primary production and bacterial respiration was about 40% as large as the respiration of macrozooplankton. The respiration of nanoflagellate microzooplankton was <10% as large as the respiration of macrozooplankton and could account for the remineralization of only 25% of bacterial production.
Interannual fluctuations in primary production: Meteorological forcing at two subalpine lakes
Authors: Goldman Charles R. , Jassby Alan , Powell Thomas
Published: April 2010

Meteorological factors are associated with most of the interannual variability in primary production at both Castle Lake, California (41°N, 122°W) and Lake Tahoe, California‐Nevada (39°N, 120°W). At Castle Lake, extreme values of annual primary production, either much higher or lower than the long‐term average, are likely to occur during the phenomenon of El Niño/Southern Oscillation. Two plausible pathways for the impacts of these large‐scale climate events at Castle Lake were identified: winter snowfall, acting through its effect on the snow‐ice pack and timing of the spring thaw; and total precipitation, acting through its effect on outwash rates. In contrast, no influence of large‐scale climate events is apparent at Lake Tahoe, but a plausible pathway involving the impact of synoptic‐scale phenomena on interannual variation was identified: local weather events occurring in the late winter‐early spring period near the time of minimal stratification, acting through their effect on the depth of spring mixing. The difference between the two lakes can be attributed to absence of an ice cover and long hydraulic retention time at Lake Tahoe. Time‐series models that incorporate meteorological information adequately forecast primary production at both lakes.
Energy budgets of latitudinally separated Scottolana canadensis (Copepoda: Harpacticoida)
Authors: Lonsdale D. J. , Levinton J. S.
Published: April 2010

We tested the hypothesis that evolution in a local population shifts individual metabolic properties to maximize energy budgets under the prevailing temperature regime. We measured scope for growth [ng C(µg dry mass)−1 h−1] in latitudinally separated adult females of Scottolanacanadensis (Willey) and used common‐rearing techniques to assess the degree of genetic differentiation. Florida (low latitude) females were at an energetic disadvantage at 15°C, but Maine (high latitude) females were not always disadvantaged at 25° or 28°C. At high test temperatures, Maine females had higher oxygen consumption rates [n1 O2 (µg dry mass)−1 h−1] than those from Maryland (middle latitude) or Florida. The higher cost of respiration of the Maine individuals was offset bygrazing rates [cells (µg dry mass)−1 h−1] on the algae Isochrysis galbana (ISO) comparable or higher than Maryland or Florida.
Possible role of carbonate dissolution in estuarine phosphate dynamics
Authors: de Jonge V. N. , Villerius L. A.
Published: April 2010

Field observations on the phosphate distribution in the Ems estuary show a nonconservative concentration gradient, with high summer values in the middle reaches. Experiments indicate the existence of two antagonistic mechanisms that can regulate the phosphorus cycle. Calcite is formed at sea and in the estuary and transported onshore and to the upper reaches of the estuary like other suspended matter. During this transport, part of the phosphate adsorbs onto calcite. Because pH is lower in the upper reaches of the estuary, some of the calcite dissolves and consequently some of the phosphate desorbs. Other suspended matter components, such as clay minerals and iron oxyhydroxide can also adsorb phosphate. The conditions in the upper reaches of the estuary (lower salinities and pH) are particularly favorable for these minerals to adsorb the phosphate that is available there as a result of calcite dissolution. Thus, during transport upstream, part of the calcite‐bound phosphate fraction of the suspended matter switches to adsorption sites of suspended noncalcite minerals, producing the nonconservative concentration gradient in phosphate along the estuary. This process of phosphate release may be stimulated by high carbon dioxide production resulting from the biological mineralization of organic matter in the middle and upper reaches of the estuary. The processes of sediment transport and phosphate adsorption and desorption favor the accumulation of marine phosphates as well as retention of fluvial phosphates in the estuary.
Phosphorus‐dependent growth kinetics of 11 species of freshwater algae
Authors: Grover James P.
Published: April 2010

Mixed‐species batch cultures were used to measure kinetics of phosphorus‐dependent growth for 11 species of freshwater algae. Results were fitted to the Monod model, and significant interspecific differences were found. Indices of competitive ability calculated from the Monod parameters suggest that Synedra radians, Synedra rumpens, Nitzschia acicularis, and Chlamydomonas sp. are good competitors for P, and that Nitzschia palea and several nonsiliceous algae are poor competitors for P. These indices of competitive ability are largely consistent with competitive outcomes in a companion experiment with these species and with other studies. No relation was found between maximal growth rate and the effect that fluctuations in P supply had on a species’ performance in the competition experiment. Growth parameters and competitive indices were not significantly correlated with cell volume, surface area, or surface: volume ratio.
Chemical and structural defenses of Caribbean gorgonians (Pseudopterogorgia spp.): Intercolony localization of defense
Authors: Harvell C. Drew , Fenical William
Published: April 2010

We have adopted an integrated approach to assessing the function of gorgonian defenses by analyzing within‐colony patterns in the distribution of both structural elements and chemical compounds in two morphologically similar species of Pseudopterogorgia. In both species, crude extract concentrations are higher in polyp‐bearing regions of colonies than in more proximal, nonpolyp‐bearing regions of colonies. The concentration of the ichthyodeterrent terpene from Pseudopterogorgia acerosa (pseudopterolide) is also higher in polyps than in axial tissue. In Pseudopterogorgia rigida, an ichthyodeterrent terpene (curcuhydroquinone) occurs almost exclusively in the polyps and is undetectable in most samples from the axial coenenchyme. The distribution of the calcium carbonate structural elements (sclerites) within colonies is negatively correlated with the concentration of extract. Sclerites comprise the largest percent composition in the axial tissue and a very small proportion of branch tissue. Geographic variation in the negative within‐colony correlation between chemical and structural components indicates the range of variation possible in these defensive traits.
Effects of predator‐induced spines on individual fitness in Daphnia pulex
Authors: Walls Mari , Ketola Matti
Published: April 2010

We studied both the cues for spine induction and costs of spine production in Daphnia pulex (Cladocera). A significant number of D. pulex cultured individually in water treated with Chaoborus crystallinus larvae that were fed carried spines to the end of the fourth instar. Water treated with Chaoborus that were starved induced only minor morphological changes in D. pulex. Treatments with crushed D. pulex did not affect neck spine induction.

Spine production carries a cost evident in the timing of first reproduction of D. pulex. Over half (58%) of D. pulex grown in culture conditions with a high density of Chaoborus postponed first reproduction from the fifth to the sixth instar. A decrease in growth of the spined morphs was attributable to an increase in duration of instars. Fitness effects persisted through the third reproductive instar. The intrinsic rate of increase was lowest in D. pulex populations cultured in Chaoborus‐treated water. Treatments with crushed D. pulex did not affect growth but did significantly increase clutch size of D. pulex.
Zooplankton abundance in the lower Orinoco River, Venezuela
Authors: Saunders James F. , Lewis William M.
Published: April 2010

Zooplankton were sampled quantitatively in the lower Orinoco River and three major tributaries (Apure, Caura, Caroni). Dominant taxa were euplanktonic, which suggests origin from standing waters. In the Orinoco, densities for rotifers (mean, 7.6 ind. liter−1) were greater than those for cladocerans (0.9 ind. liter−1) or copepods (1.2 ind. liter−1), but cladocerans accounted for more than halfof total biomass (0.5 µg C liter −1). Average tributary contributions to zooplankton transport in the lower Orinoco (873 kg C d−1) were proportional to their average discharges. Extensive fringing floodplain along the lower Orinoco contributed very little to total transport. At low water in the Orinoco, when there was no contact with the floodplain, the transport of copepods (mainly nauplii) and Bosmina increased downstream by more than could be ascribed to additions from the tributaries or to reproduction in transit. These zooplankton appear to originate along the river margin, within the channel, and are probably significant as an energy input for food webs in the channel and as an inoculum to floodplain habitats at the time of inundation.
Adenine incorporation into DNA as a measure of microbial production in freshwaters
Authors: Bell Russell T. , Riemann Bo
Published: April 2010

The use of [3H]adenine incorporation into DNA as a means of estimating total microbial production in freshwaters was assessed with both algal cultures and natural assemblages of microorganisms. By adding [3H]adenine over a wide range of concentrations (10–200 nM), we determined that in mesotrophic and eutrophic environments >50 nM and probably >100 nM of [3H]adenine is required to maximally label the internal precursor pools of both algae and bacteria. With bacterioplankton assemblages the incorporation of [3H]thymidine and [3H]adenine gave equivalent estimates of DNA synthesis. Growth rates of Scenedesmus in turbidostats determined from 14C assimilation and [3H]adenine incorporation (DNA synthesis) also agreed well. Our results suggest that the use of [3H]adenine to measure total microbial (bacteria + algae) production combined with the use of [3H]thymidine to measure “bacterial” production could provide an interesting complement to current procedures.
Effects of conspecifics and phytoplankton on predation rates of the omnivorous copepods Epischura lacustris and Epischura nordenskioldi.
Authors: Schulze Peter C. , Folt Carol L.
Published: April 2010

We measured the effects of conspecifics and phytoplankton on the rate at which Epischura lacustris and Epischura nordenskioldi prey upon calanoid nauplii. Per capita predation rates of Epischura in the presence of conspecifics and phytoplankton were 73% lower than those of lone individuals in the absence of phytoplankton. Because these effects occurred at common field densities of Epischura, animal prey, and phytoplankton, it is likely that they occur in situ. Therefore, estimates of the effect of spatial and temporal patchiness on predation rates of omnivorous copepods should consider phytoplankton and conspecifics, not simply the abundance and composition of the animal prey assemblage.
Field observations on the ontogeny of schooling of Euphausia superba furciliae and its relationship to ice in Antarctic waters.
Authors: Hamner W. M. , Hamner P. P. , Obst B. S. , Carleton J. H.
Published: April 2010

We investigated the ontogeny of behavior during the transition in Euphausia superba from dispersed solitary larvae to clumped swarms and schools of furciliae. We directly observed behavior of krill larvae in the Gerlache Strait, Antarctica, with open‐ocean SCUBA techniques. In the absence of ice, isolated furciliae occurred at the surface at a density of 0.003 m−3. In the presence of ice, density of isolates was 102 times higher and density of furciliae in schools was 109 times higher than in open water. Larvae first exhibited schooling behavior at furcilia IV–V(body length 1 cm). Furcilia V larvae segregated by size in immediately adjacent schools, with highly significant differences in body lengths of as little as 0.5 mm. Late stage furciliae moved the thoracic basket in the same way that adults filter phytoplankton, and furciliae fed like adults on epontic ice algae. For larval krill in the Gerlache Strait, ice provided concentrated algal food and protection from predators and facilitated aggregation and formation of swarms of nonpolarized individuals and of small, ice‐oriented schools that contained 102−104 individuals per school.
Preliminary results from an inexpensive motion analyzer for free‐swimming zooplankton
Authors: Ramcharan Charles W. , Sprules W. Gary
Published: April 2010

Mirrors are used to reflect two orthogonal views of a small aquarium into the lens of a single video camera, thus creating distortion‐free, three‐dimensional images. Zooplankton motion is quantified with computer software that categorizes different zooplankton behaviors and measures parameters such as distance, duration, angle of movement, and overall swimming speed. Using this system, we have found a strong behavioral response of Diaptomus minutus to the presence of conspecifics; Diaptomus greatly increases swimming speed and frequency of jumps under moderately crowded conditions.
Nitrogen exchange between a portion of vegetated salt marsh and the adjoining creek
Authors: Whiting Gary J. , McKellar Henry N. , Spurrier John D. , Wolaver Thomas G.
Published: April 2010

We measured net exchange of nitrogen between a portion of vegetated salt marsh (dominated by Spartina alterniflora) and the adjacent tidal creek. During tidal inundation, the marsh imported ammonium, nitrate + nitrite, and particulate nitrogen and exported dissolved organic nitrogen over an annual cycle. The low marsh (characterized by the tall form of S. alterniflora) had higher uptake and release rates compared to high marsh areas dominated by shorter forms of S. alterniflora. When creek‐water levels were below the marsh surface during the late ebb and early flood, residual water on the marsh surface drained into the tidal creek and exported substantial amounts of particulate and dissolved organic nitrogen but relatively small amounts of dissolved inorganic nitrogen. Rainfall during exposure of the marsh surface increased particulate nitrogen export to the tidal creek 40‐fold. With respect to tidal exchange via inundation and drainage, the vegetated marsh exported ~4.5 g N m−2 yr−1, largely as dissolved organic nitrogen.
Organic nitrogen mineralization and substrate limitation of bacteria in Lake Michigan
Authors: Gardner Wayne S. , Chandler Joann F. , Laird Gwenyth A.
Published: April 2010

Labile organic nitrogen mineralization and the apparent degree of bacterial substrate limitation were examined to consider seasonal relationships between substrate availability and bacterial activity in Lake Michigan. Accumulation rates of ammonium nitrogen in amino acid fortified and unfortified samples of epilimnetic Lake Michigan water, incubated in the dark, provided reasonable estimates of potential and actual rates of organic nitrogen mineralization. The labile organic nitrogen demand (LOND), defined as the difference between these respective rates, provided an index of heterotrophic potential. LOND ranged from ∼1–3 ng‐atoms N liter h−1 (during May–June and November) to 3–9 ng‐atoms N liter h−1(during July–October) as compared to actual organic nitrogen mineralization rates of < 1 ng‐atom N liter h−1 in some unfortified samples. The high LOND, relative to actual turnover, observed in late summer is consistent with the hypothesis that growth rates of epilimnetic Lake Michigan bacteria are strongly limited by organic substrate during late stratification.
Biological nitrogen cycling in the nitracline
Authors: Ward B. B. , Kilpatrick K. A. , Renger E. H. , Eppley R. W.
Published: April 2010

Physical transport of nitrate across the nitracline is the main nitrogen source for new production by phytoplankton in the surface ocean. The intersection of the nitracline with the bottom of the photic zone makes this depth interval a region of rapid nitrogen cycling, involving assimilatory and regenerative transformations, as well as physical transport. We investigated the pathways of nitrogen transformations in surface, nitracline, and subnitracline samples by following changes in concentration and 15N : 14N ratio in dissolved and particulate pools in the same bottles for 24 h. Fluxes of nitrite and nitrate among pools were detected from tracer distributions but were not always reflected in changes in nutrient concentrations. For example, the production of nitrate by nitrification could be detected by tracer methods even when nitrate concentration decreased. Nitrification was detected within and below the nitracline by both oxidation of 15NO2− and dilution of initially labeled nitrite (ammonium oxidation) or nitrate (nitrite oxidation) pools. Significant nitrate production by nitrification, relative to nitrate assimilation, implies that some of the nitrate assimilated by phytoplankton is functionally regenerated rather than new nitrogen. Our observations also suggest an important role for a labile organic nitrogen pool of unknown identity, possibly involving bacterial mediation, in the nitrogen cycling of surface waters.
Bacterial uptake of dissolved free and combined amino acids in estuarine waters
Authors: Coffin Richard B.
Published: April 2010

The Delaware estuary was sampled at 10–14 stations along the main salinity axis from February to August 1985. Dissolved free and combined amino acid concentrations ranged from 50 nM to 1.4 µM and 0.1 to 8.0 µM, respectively. Combined amino acid concentrations were generally higher than dissolved free amino acids. Highest amino acid concentrations were measured in the lower estuary in early spring. Molecular weight analysis of the dissolved combined amino acids revealed that a high percentage of the pool contained peptides of <1,000 daltons.

Uptake of 14C‐labeled amino acids and an algal protein were used to estimate the relative importance of these potential bacterial substrates. Laboratory experiments verified that peptide and protein uptake was nonspecific and that labeled algal protein was a good model substrate. Combined and free amino acid uptake rates ranged spatially and temporally from 15 to 600 nM h−1. Combined amino acid uptake averaged 51% of the bacterial amino nitrogen demand.
The seasonality of nutrient regeneration in an organic‐rich coastal sediment: Kinetic modeling of changing pore‐water nutrient and sulfate distributions
Authors: Klump J. Val , Martens Christopher S.
Published: April 2010

Measured pore‐water concentration profiles for dissolved ammonium, phosphate, total inorganic carbon, and sulfate show a distinct seasonal cycle in response to the temperature dependence of rates of microbially mediated organic matter oxidation in sediments at Cape Lookout Bight, N.C. The depth and temperature dependence of measured production and consumption rates, adsorption coefficients, apparent diffusion coefficients, and sediment porosities were combined to construct a diagenetic model of ammonium production, ΣCO2 production, and sulfate reduction that was time‐temperature‐ and depth‐dependent. Numerical predictions of pore‐water concentrations from a set of initial spring conditions agree well with measured pore‐water profiles through summer and fall—the period of greatest change in reaction rates in response to seasonal fluctuations in temperature. Modeling also indicates that inclusion of complex, porosity‐dependent terms, even in the time‐ and temperature‐dependent case, is probably unnecessary in these sediments; simpler, constant‐porosity models give results that generally deviate <4% from the predictions of complex models.
Sulfate reduction and other sedimentary biogeochemistry in a northern New England salt marsh
Authors: Hines Mark E. , Knollmeyer Stephen L. , Tugel Joyce B.
Published: April 2010

Sulfate reduction rates, dissolved iron and sulfide concentrations, and titration alkalinity were measured in salt marsh soils along a transect that included areas inhabited by both the tall and short forms of Spartina alterniflora and by Spartina patens. Pore waters were collected with in situ “sippers” to acquire temporal data from the same location without disturbing plant roots. During 1984, data collected at weekly intervals showed rapid temporal changes in belowground biogeochemical processes that coincided with changes in S. alterniflora physiology. Rates of SO42 reduction increased fivefold (to >2.5 µmol ml−1 d−1) when plants began elongating aboveground yet decreased fourfold upon plant flowering. This rapid increase in rates of SO42 reduction must have been fueled by dissolved organic matter released from roots only during active growth. Once plants flowered, the supply of oxidants to the soil decreased and sulfide and alkalinity concentrations increased despite decreases in SO42− reduction and increases in SO42−: Cl− ratios. Sulfide concentrations were highest in soils inhabited by tallest plants.

During 1985, S. alterniflora became infested with fly larvae (Chaetopsis apicalis John) and aboveground growth ceased in late June. This cessation was accompanied by decreased rates of SO42− reduction similar to those noted during the previous year when flowering occurred. After the fly infestation, the pore‐water chemical profiles of these soils resembled profiles of soils inhabited by the short form of S. alterniflora.

The SO42− reduction rates in S. patens soils are the first reported. Rates were similar to those in S. alterniflora except that they did not increase greatly when S. patens was elongating. Tidal and rainfall events produced desiccation‐saturation cycles that altered redox conditions in the S. patens soils, resulting in rapid changes in the dissolution and precipitation of iron and in the magnitude and spatial distribution of SO42 reduction.
Biosynthesis and photosynthate allocation patterns of arctic ice algae
Authors: Smith Ralph E. H. , Clement Pierre , Head Erica
Published: April 2010

Biochemical composition of the sea ice microbial community was measured in populations of different light histories in the Canadian Arctic (Resolute, N.W.T.). The average composition of the particulate organic matter [soluble and insoluble polysaccharide, particulate protein, intracellular free amino acids (IFAA), lipid, and chlorophyll a] was within the published range for microalgae, but lipid was a relatively large (31–59%) and protein a small (20–24%) part of the total. Protein and IFAA pools apparently comprised about 50% of the particulate organic nitrogen, of which 6–10% was in the IFAA pool. Over the entire spring growth season, the net synthesis of protein, IFAA, and Chl a (relative to total cell carbon) decreased with increasing light while relative synthesis of lipid and soluble polysaccharide increased, consistent with patterns of short‐term photosynthate allocation. In the early growth season patterns of synthesis were relatively insensitive to light, and rates of lipid synthesis were large for all light histories. Photosynthate allocation in 24‐h incubations greatly underestimated actual rates of net lipid synthesis and probably overestimated protein synthesis. Microalgae of cold, low‐light environments can display rates of lipid synthesis much larger than rates normally encountered in microalgae without displaying a corresponding pattern of shorter term photosynthate allocation.
A new isotopic method for measurmg diel grazing rates of marine zooplankton in situ
Authors: Napp Jeffrey M. , Long Dennis L.
Published: April 2010

Snap‐Traps are transparent chambers designed to concentrate mesozooplankton and then close for in situ grazing measurements. Six traps are obliquely mounted on an aluminum frame, lowered rapidly to flush, then towed horizontally at slow speeds. Messenger‐activated closure also causes the injection of dissolved 33PO43 which will label the particulate matter by day or night. The labeling protocol was dependent on the nutrient history of the seston; when dissolved phosphate concentrations were low (≤0.05 µM), unlabeled phosphate was added with the labeled carrier to produce linear or near‐linear uptake. The mean zooplankton catch per bottle is larger for this design than for other designs, thus facilitating the precise analytical determination of the isotopic burden. Trap‐to‐trap variability of measured weight‐specific grazing rate was large. When these rates are combined with the distribution of grazer biomass, the result— an estimate of total community grazing rate—is likely to be very imprecise.
Fluorometric detection of tracer particles used to study animal‐particle dynamics
Authors: Carey Drew A.
Published: April 2010

I describe a fluorometric procedure to measure concentrations of fluorescent resin used as a tracer of particle dynamics. The technique has sufficient spectral resolution to estimate weights of very small volumes of marked sediment (equivalent to 15 µg mass) and to distinguish concentrations of individual tracer colors from background fluorescence. Concentrations of tracer particles in available and egested sediment were used to estimate sediment weight of small fecal pellets (15–35 µg) of deposit feeders and compared with volumetric measurements of the same pellets. Experiments with scintillation fluor indicated that the quantitative measurement of sediment weight can be performed in concert with radiolabeling techniques.
An upper slope “cold” seep community: Northern California.
Authors: Kennicutt Mahlon C. , Brooks James M. , Bidigare Robert R. , McDonald Susanne J. , Adkison Daniel L. , Macko Stephen A.
Published: April 2010

Piston coring and trawling on the northern California continental slope (450–600 m) recovered shells and live organisms typical of a “cold” seep community. The presence of gas‐charged sediments, hydrates, and nearby oil seepage suggests that this habitat is like the hydrocarbon seeps of the Louisiana slope. Carbon, sulfur, and nitrogen isotopic compositions of organism tissues confirm the presence of bacterial chemosynthesis at these locations. This dicovery and previous reports suggest that the general occurrence of animals dependent on chemosynthesis is widespread.
Decomposition and the annual flux of detritus from fallen timber in tropical mangrove forests
Authors: Robertson Alistar I. , Daniel Paul A.
Published: April 2010

Single exponential decay models fitted to dry mass and carbon decomposition data for tree trunks in mixed Rhizophora mangrove forests in tropical Australia had decay constants of 0.083 and 0.108 yr−1 respectively. Decay of twigs and small branches was more rapid with decay constants of 0.276 (dry mass) and 0.310 yr−1(carbon). Aboveground standing stocks of dead wood components in young and mature forests were (g C m−2): trunks, 15.3 and 221.9; prop roots, 5.7 and 86.8; branches, 3.5 and 32.2; twigs, 3.2 and 3.1. Combining decomposition and standing stock data gave flux estimates for wood detritus of 4 and 44 g C m−1 yr−1 in young and mature forests. By comparison, leaf burial by crabs, a major pathway by which mangrove detritus is retained in these forests, has previously been estimated at 62 g C m−2 yr−1.
Characterization and significance of β‐glucosidase activity in lake water
Authors: Chróst Ryszard J.
Published: April 2010

Kinetics of β‐glucosidase activity (βGlcA) and bacterial activity (glucose uptake, thymidine incorporation) and cell numbers were measured in the euphotic zone and in the water column of Pluβsee during spring phytoplankton bloom development and after its breakdown. Heterotrophic bacteria were the major producers of the enzyme. Activity of free β‐glucosidase, unassociated with microbial cells, was negligible. βGlcA displayed a distinct temporal and spatial distribution pattern in lake water. βGlcA was low when algal populations grew actively, but during the algal bloom breakdown βGlcA increased rapidly. The increase in βGlcA was proportional to the abundance of bacteria and to their heterotrophic uptake of glucose, as well as to bacterial production, measured by the thymidine incorporation method. In contrast with its response to pH, β‐glucosidase exhibited no obvious adaptation to ambient temperature of lake water. βGlcA produced by aquatic bacteria was under control of a repression‐induction mechanism, and synthesis was derepressed when the level of directly assimilable hexoses (glucose or galactose) fell below a critical level. The tight relationship between the rates of βGlcA and glucose uptake indicated the existence of a specific, coupled hydrolysis‐uptake system in lacustrine bacteria.
Seasonal patterns of bacterivory by flagellates, ciliates, rotifers, and cladocerans in a freshwater planktonic community
Authors: Sanders Robert W. , Porter Karen G. , Bennett Susan J. , DeBiase Adrienne E.
Published: April 2010

Bacterivory in eutrophic Lake Oglethorpe, Georgia, was determined by direct observation of tracer particle uptake by all members of the planktonic community. Heterotrophic flagellates dominated grazing at all times, accounting for 49–81% of grazing on an areal basis and up to 98% of grazing at some depths. Pigmented (mixotrophic) flagellates were major grazers during winter and spring blooms, when they contributed up to 45% of community grazing on an areal basis and 79% at depths of maximum abundance. In late spring to early summer, rotifers and ciliates were responsible for as much as 25 and 30% of bacterivory at some depths, but averaged 3 and 11% over the year, respectively. Grazing impact of cladoceran crustaceans was generally <1% of the total. Bacterivory by copepods was not detected. Total bacterial mortality due to grazing ranged from 11 to 162% of bacterial cell production estimated from the incorporation of [3H]thymidine.

Use of 0.57‐µm microspheres as tracers gave similar estimates of ingestion to fluorescently labeled bacteria in this system. The use of 4% ice‐cold glutaraldehyde mixed 1 : 1 with the water sample was found to be equally effective to an acrolein‐tannic acid mixture for reducing egestion of particles by protists. We therefore consider our findings to be representative of bacterivory by the planktonic community in this eutrophic system.
Modeling the distribution of acetate in anoxic estuarine sediments
Authors: Michelson A. R. , Jacobson M. E. , Scranton M. I. , Mackin J. E.
Published: April 2010

Concentrations and rates of production and oxidation of acetate were studied in anoxic, estuarine sediments of Flax Pond, New York. Molecular weight separations by Sephadex gel indicated that in some, but not all, cases pore‐water acetate consisted of multiple “pools.” We developed a one‐dimensional kinetic model that uses measured oxidation rates (14C‐labeled acetate conversion to 14CO2) and production rates (MoO42‐ inhibition experiments) as model parameters. Appropriate diffusion coefficients were calculated with a free‐solution value (1.3 ±0.3 × 10−5 cm2 s−1) measured in this study. In general, oxidation rate constants estimated from modeled profiles agree well with those from [14C]acetate incubation experiments. Results imply that differences in acetate oxidation rates inferred from the two methods (MoO42− inhibition, [14C]acetate oxidation) can be caused by diffusion of acetate along sharp concentration gradients in sediments. [14C]acetate uptake experiments account for such diffusion by using measured steady state acetate concentrations to infer oxidation rates, whereas MoO42− inhibition experiments do not account for in situ acetate diffusion.
during upwelling off the Biochemical indicators of N utilization by phytoplankton Washington coast
Authors: Dortch Quay , Postel James R.
Published: April 2010

The manner in which N utilization by phytoplankton responds to persistent upwelling was examined along the Washington coast. Biochemical indicators of N deficiency, source of N supporting growth, and relative phototrophic and heterotrophic biomass, as well as time‐courses of 15N and 14C uptake, nutrient and chlorophyll concentrations, and routine hydrography were measured from 11 to 24 June 1982 from a ship which completed a transect perpendicular to the coast every 1–3 d and a second ship which followed drogues deployed at the upwelling source. From 11 to 12 June a spatial separation was observed between increased nutrients and high chlorophyll. The lag was probably due to the need of phytoplankton to adapt both N and C utilization to higher light. Despite a very N‐depleted euphotic zone, N deficiency was only apparent quite far offshore. Later (15–23 June), extraordinarily high phytoplankton biomass developed nearshore. It was N sufficient, highly productive, and fueled by both nitrate and ammonium. Most was located in a pronounced, metabolically active, subsurface chlorophyll maximum. Although benthic and water‐column regeneration of ammonium and diffusion of nitrate across the steep nutracline are probably important, there was also evidence of sporadic nitrate supply which correlated with slight changes in the wind. Nitrate pumping into an already N‐sufficient, fully shifted‐up phytoplankton population during weak upwelling may result in maximal phytoplankton response to upwelling.
Water filtration by dissipative beaches
Authors: McLachlan Anton
Published: April 2010

Dissipative or low‐gradient beaches arc expected to filter low volumes of seawater. This idea was tested on the Oregon coast on two high‐energy dissipative beaches with medium and fine sand and found to be correct, filtered volumes being 0.1–7 m3 m−1 d−1. Input was mainly due to tidal effects as most wave energy was dissipated in the surf zone. During a very high‐energy event on a high tide, however, filtered volume increased by an order of magnitude as a consequence of increased wave input.
Potential microbial utilization rates of sublittoral gastropod mucus trails
Authors: Herndl Gerhard J. , Peduzzi Peter
Published: April 2010

Mucus trails produced by the herbivorous gastropod Monodonta turbinata, a common species of the rocky intertidal and sublittoral zone in the Mediterranean Sea, were found in the laboratory to be rapidly colonized by heterotrophic microbes (bacteria and protists). Bacterial turnover times of 2.2 h were obtained for the mucus‐associated microbes during the exponential growth on mucus trails while free‐living bacteria in overlying water exhibited a turnover time of 5 h. Heterotrophic nanoflagellates associated with the mucus grazed the bacterial population at rates of 18 bacteria flagellate−1 h−1; for the free‐living bacteria grazing rates of about 15 bacteria flagellate−1 h−1 were obtained. Only about 25% of the mucus‐derived carbohydrates remained on the substrate after 26 h.
Wax esters in two species of freshwater zooplankton
Authors: Cavaletto Joann F. , Vanderploeg Henry A. , Gardner Wayne S.
Published: April 2010

Livid classes were determined in three Lake Michigan hypolimnetic calanoid copepods, Limnocalanus macrurus, Diaptomus sicilis, and Senecella calanoides. Limnocalanus macrurus and S. calanoides contained large stores of wax esters (57–80% of total lipid). Wax esters in this amount have not previously been reported for freshwater zooplankton. Diaptomus sicilis exhibits a typical freshwater lipid profile and contains triacylglycerols as its lipid reserves. Lipid storage sites are morphologically different in the copepods. Limnocalanus macrurus and S. calanoides store their wax esters in a large sac that surrounds the intestine, whereas D. sicilis maintains lipid droplet morphology typical of freshwater “triacylglycerol‐storing” zooplankton. Limnocalanus macrurus and S. calanoides are “glacial relicts,” which may explain the origin of their typically marine wax ester lipid class.
The eastern tropical Pacific as a source of 15N‐enriched nitrate in seawater off southern California
Authors: Liu Kon‐Kee , Kaplan Isaac R.
Published: April 2010

Dissolved nitrate in the subsurface water (200–650 m) off southern California is unusually high in δ15N compared with waters from the same depth in the central and western Pacific, which have δ15N values similar to the deep oceans. More than 150 seawater samples from the sea off southern California and the North Atlantic were analyzed for the δ15N of nitrate. The mean δ15N (± 1 SD) of deep waters (>1,500 m) is 5.7±0.7‰. The mean δ15N in the 15N‐anomaly zone off southern California is 9.0±0.7‰. Maxima of δ15N were found to coincide with salinity maxima, which occurred in the same isopycnal levels as the 15N‐enriched denitrifying zone in the eastern tropical North Pacific (ETNP). Using the correlation between δ15N and salinity, we can show the southern California waters to be of mixed origin with the denitrifying water from the ETNP as one end member. Our observations support the notion that the oxygen‐deficient waters in the eastern tropical Pacific are important sources of 15N‐enriched nitrate.
The effect of light and temperature on DOC excretion by phytoplankton
Authors: Zlotnik I. , Dubinsky Z.
Published: April 2010

The separate effects of light intensity (0–3,000 µmol quanta m−2 s−1) and temperature (5°–45°C) on excretion of dissolved organic carbon (DOC) by three phytoplankton species were examined under controlled laboratory conditions in axenic cultures. Ours is the first comparative study of the effects of a wide temperature and irradiance range on DOC excretion by different species of phytoplankton under identical conditions. Tight coupling was found between the rates of carbon fixation and of absolute DOC excretion over a wide range of irradiances (0–1,500 µmol quanta m−2 s−1) in all three species with excretion ranging from 1 to 55% of production. Chlorella vulgaris and Synechococcus sp. showed parallel temperature‐dependent changes in photosynthesis and of absolute DOC excretion (5°–45°C); in Isochrysis galbana absolute excretion was temperature‐independent, but photosynthesis was temperature‐dependent. In all cases, increased excretion percentages were found under extreme irradiances and temperatures that depressed photosynthesis. In general, we suggest that high fluxes of DOC toward bacterial food chains may be expected only under conditions favorable for photosynthesis, although the percentage of DOC excretion is then low.
Cycling of organic carbon in the photic zone of a eutrophic lake with special reference to the heterotrophic bacteria
Authors: Vadstein Olav , Harkjerr Bjørn Ola , Jensen Arne , Olsen Yngvar , Reinertsen Helge
Published: April 2010

Cycling of organic carbon in the photic zone was investigated in a eutrophic Norwegian lake during the ice‐free period. Special attention was paid to heterotrophic bacteria and the factors influencing their production and biomass development.

The average proportions of the biomass of phytoplankton, zooplankton, and bacteria were 17 : : 1 on a carbon basis. Phytoplankton primary production averaged 580 mg C m−2 d−1, and 22% of the fixed carbon was exuded. Bacterial production, estimated by frequency of dividing cells, averaged 160 mg C m−2 d−1 and equaled 25% of the gross primary production on a seasonal basis. Increased bacterial activity was either correlated with increased exudation or followed a collapse in the phytoplankton community. Grazing was estimated to amount to 35–180% and 41–84% of the total losses of phytoplankton and bacteria. Cladocerans were the main grazers on phytoplankton, and heterotrophic flagellates were the main grazers on bacteria.

Because of high death rates of zooplankton and cycling of carbon within the microbial loop, the available substrate for bacteria equaled the primary production on a seasonal basis. Exudates, egestion products from grazers, and dead zooplankton constituted two‐thirds of the available substrate, and these sources were of equal magnitude.
General patterns in the seasonal development of chlorophyll a for temperate lakes
Authors: Marshall C. Tara , Peters Robert H.
Published: April 2010

The seasonal cycle of phytoplankton biomass in temperate lakes is often represented as spring and fall blooms with intervening biomass minima, but the generality of this pattern has never been critically evaluated. Chlorophyll a time series from 56 north‐temperate lakes and reservoirs were collected and general patterns in the seasonal distribution of Chl a determined for oligotrophic and eutrophic lakes separately. The magnitude of temporal variation is greater in eutrophic lakes (mean [Chl a] > 12 mg m−3) and is partitioned into discrete spring and fall blooms. Chlorophyll a concentrations in oligotrophic lakes (mean [Chl a] < 7 mg m−3) are low for the first 4 months of the year, then increase through April and May. Synchronous summer depressions and fall blooms are not evident for oligotrophic lakes overall. Mean [Chl a] and mean annual air temperature were negatively correlated with the date of spring bloom. The date of spring bloom was not correlated with mean depth.
Natural fluorescence of chlorophyll a: Relationship to photosynthesis and chlorophyll concentration in the western South Pacific gyre
Authors: Kiefer D. A. , Chamberlin W. S. , Booth C. R.
Published: April 2010

A new optical instrument, designed specifically to measure the natural or solar‐induced fluorescence of chlorophyll a, was deployed in the tropical and temperate waters of the western South Pacific gyre. During the 12 days of transit from Papeete, Tahiti, to Auckland, New Zealand, measurements were made of the vertical distribution of temperature, salinity, upwelling radiance and downwelling irradiance at selected wavelengths, the beam attenuation coefficient at 683 nm, the scalar irradiance of photosynthetically available radiation (PAR), and the nadir radiance at 683 nm, which is the wavelength of peak emission by Chl a. In addition, water samples were collected at regular depth intervals and analyzed for the concentration of Chl a and for the spectral absorption coefficient of cells and associated detrital particles.

To examine the relationship between natural fluorescence and the size and photosynthetic rate of the phytoplankton crop, we derived several simple equations and applied them to the analysis of the data. One relates the nadir radiance at 683 nm to the total fluorescence emitted by the phytoplankton crop within the field ofview, another relates natural fluorescence to the concentration of Chl a, and a third relates natural fluorescence to the gross rate of photosynthesis of the crop. We found that even in the extremely oligotrophic waters of the central South Pacific gyre, natural fluorescence was easily measured throughout the euphotic zone at depths >6 m. As found in previous studies, the value of natural fluorescence varied spatially and temporally with ambient scalar irradiance of PAR and the concentration of Chl a. The quantum yield of fluorescence, which varied fivefold, averaged about 0.035 photons emitted to photons absorbed and generally decreased with increasing levels of exciting irradiance. Most importantly, we found natural fluorescence covaried closely with calculated rates of photosynthesis. A linear regression of calculated photosynthetic rate on fluorescence yielded a correlation coefficient of 0.84 and a slope of 2.0 atoms of carbon fixed per photon emitted as fluorescence.
Benthopelagic biomass distribution and oxygen consumption in a deep‐sea benthic boundary layer dominated by gelatinous organisms
Authors: Childress James J. , Gluck David L. , Carney Robert S. , Gowing Marcia M.
Published: April 2010

A quantitative plankton net sampler with a multicompartment cod‐end for use with deep submersible vehicles was developed. This cod‐end protects samples from surface temperatures so that deep‐sea animals can be recovered alive. The DSV Alvin used it to sample the benthopelagic faunas of two southern California basins, East Cortes and San Clemente, in August 1979 and February 1982. Samples filtering an average of 336 m3 were taken at altitudes of 1, 5, 10, 20, 50, and 100 m as well as 1,000‐m depth over bottom depths of 1,800–1,900 m. These samples were divided into three categories for weighing and compositional analysis. The pelagic holothuroid Scotoanassa sp. dominated the 20 m immediately above the bottom, averaging 533 mg wet wt m−3 at 1‐m altitude in 1982. “Other gelatinous” organisms became dominant at 50 and 100 m, averaging 267 mg wet wt m−3 at 50 m. “Nongelatinous” forms, a group dominated by copepods and larger crustaceans, were more uniformly distributed and ranged from 2.1 to 7.9 mg wet wt m−3. Abundances of Scotoanassa sp., but not the other categories, varied greatly between years and between basins. Scotoanassa sp. had a low oxygen consumption rate of 0.0009 µl O2 (mg wet wt)−1 h−1; the near‐bottom crustaceans had rates similar to those of bathypelagic crustaceans. Total metabolism of the sampled groups was dominated by Scotoanassa sp. and nongelatinous plankton near the bottom with other gelatinous plankton becoming dominant higher. Scotoanassa sp. may be a rapid growing, opportunistic species that can respond reproductively to short‐term environmental changes.
Mixing across a lutocline
Authors: Wolanski Eric , Asaeda Takashi , Imberger Jorg
Published: April 2010

The results of a laboratory experiment showed that mixing across a lutocline (the interface between clear water on top and a fluid‐mud mixture underneath) is controlled not only by mud‐induced buoyancy effects through a Richardson‐number dependence, but also by the sediment‐induced collapse of turbulence in the fluid‐mud layer. The dependence of particle settling velocity on the concentration of suspended sediment can limit the height of resuspension of sediments and stop lutocline erosion after an initial period of active mixing.