bluuebunny/crossref_metadata_2025 huggingface dataset:
Protozoan control of bacterial abundances in freshwater
Authors: Berninger Ulrike‐G. , Finlay Bland J. , Kuuppo‐Leinikki Pirjo
Published: April 2010

We have quantified the bacteria, heterotrophic nanoplankton (HNAN), and other microorganisms in 108 lakes, ponds, rivers, and bogs worldwide. These water bodies span the range of biological productivities in freshwater. Numbers of HNAN and bacteria are correlated over four orders of magnitude in each (3 × 102 to 4 × 106 ml−1 and 3 × 105 to 1 × 109 ml−1, respectively) and both increase with the productivity of the water body. Most HNAN are small (2– 5 µm), colorless, flagellated protists. They grow at about the same rate as bacteria (µ = 0.01–0.02 h−1) and are capable of consuming the entire bacterial production. We suggest that bacterial abundances are regulated by substrate supply and HNAN grazing pressure. Ciliates and other grazing microzooplankton probably limit HNAN abundance, especially in the more productive water bodies. The structure and function of microbial food webs in freshwater environments may thus be similar to those suggested for marine systems.
Chlorophyll a degradation by Calanus pacificus: Dependence on ingestion rate and digestive acclimation to food resources
Authors: Penry Deborah L. , Frost Bruce W.
Published: April 2010

Relative extents of Chl a degradation by Calanus pacificus were determined with ratios of a conservative tracer, 68Ge, to Chl a‐derived pigment. The extent to which Chl a is degraded to colorless products can vary with food acclimation and ingestion rate. The fraction of ingested Chl a degraded by copepods acclimated to a high food concentration (4,000 cells ml−1 Thalassiosira weissflogii) for 3 d was 2–4 times greater than the fraction degraded by those acclimated to a low food concentration (1,000 cells ml−1). A fourfold decrease in ingestion rate corresponded to a twofold increase in relative extent of Chl a degradation by copepods acclimated to high food, but a similar decrease in ingestion rate had little effect on degradation by those acclimated to low food. Extent of degradation cannot be described with one overall mean value. Chl a and Chl a‐derived pigments thus cannot be used as quantitative tracers of zooplankton feeding. Extension of our laboratory results to the field suggests that relative extents of degradation of pigments by copepods may increase over the course of a phytoplankton bloom. Fecal pellets produced during the early stages of a bloom may have relatively more undegraded pigment and other labile organic materials than pellets produced as the bloom declines.
Effects of a Chaoborus‐released chemical on Daphnia ambigua: Reduction in the tolerance of the Daphnia to summer water temperature
Authors: Hanazato Takayuki
Published: April 2010

Daphnia ambigua was reared at eight different temperatures (5°, 10°, 15° 20° 23°, 25°, 28°, and 30°C) in water conditioned by a predator, Chaoborus flavicans. D. ambigua developed spikelike helmets in juvenile stages probably in response to a chemical released from the Chaoborus larvae. Helmet size was affected by water temperature (max size at 23°C) and decreased with decreasing temperature from 23° to 10°C. At high temperatures (28° and 30°C), survival rate of juveniles exposed to the Chaoborus‐released chemical decreased greatly. Molting to the high‐helmeted morph might increase the risk of mortality at those temperatures. Results suggest that the predator releases a chemical that reduces the tolerance of cyclomorphic Daphnia to high tem
Shifts in fish vertical distribution in response to an internal seiche in a stratified lake
Authors: Levy David A. , Johnson Robert L. , Hume Jeremy M.
Published: April 2010

Juvenile sockeye salmon in Quesnel Lake were nocturnally thermoselective and distributed in a narrow vertical band within the thermocline. Differences in vertical position across and between lake transects occurred when an internal seiche was active, as evidenced by a short‐term alteration in the thermal structure of the lake. The results provide qualitative evidence for a direct relationship between Quesnel Lake physics and the vertical distribution of juvenile sockeye.
Probing the fine structure of ocean sound‐scattering layers with ROVERSE technology
Authors: Greene Charles H. , Wiebe Peter H. , Miyamoto Robert T. , Burczynski Janusz
Published: April 2010

A 420‐kHz, dual‐beam SONAR system, deployed on a remotely operated vehicle (ROV), was used to examine the fine structure of sound‐scattering layers (SSLs) in Puget Sound and the Arctic Ocean. The Puget Sound SSL, initially detected with a shipboard, 200‐kHz SONAR system, was correlated with a high biomass of sound scatterers in the size range of macrozooplankton and micronekton. Its vertical position appeared unrelated to profiles of temperature, salinity, or chlorophyll fluorescence. The Arctic Ocean SSL was composed of similar‐sized sound scatterers, although its volume backscattering intensity was 10–100 times lower than that observed for the Puget Sound SSL. The vertical position of the Arctic SSL was closely associated with the thermocline separating Arctic Water from North Atlantic Water.

The fine‐scale, horizontal variability of water‐column volume backscattering was examined at both study sites. The highest variability observed was associated with the Puget Sound SSL where the mean intensity of volume backscattering was also the highest. These findings are consistent with the common observation that, whatever methods are used to measure zooplankton and micronekton abundance, sampling variance nearly always increases with the mean.
Improving zooplankton samplers with simple electronics
Authors: Filion Jean‐Marc
Published: April 2010

The addition of simple, inexpensive electronic circuitry to plankton nets and traps can significantly improve their performance. It is often difficult, particularly at great depth on windy days, to determine the exact depth at which the doors of a plankton trap close. The addition of a magnet to the trap door, and a magnetic switch to the trap housing allows delivery of a telemetered signal to the operator indicating that the trap doors have closed. Commercially available tow nets cannot detect changes in filtration efficiency during the course of a haul. A telemetered net is introduced that can detect such changes, allowing the operator to determine if efficiency changes due to clogging have occurred during the tow.
Nutrients and chlorophyll at the interface of a watershed and an estuary
Authors: Jordan Thomas E. , Correll David L. , Miklas Joseph , Weller Donald E.
Published: April 2010

We investigated the fates of nutrients entering the Rhode River estuary from its watershed and from atmospheric deposition. Production or consumption of materials in the upper estuary was calculated from a mixing model with chloride as a conservative tracer. The upper estuary produced chlorophyll and dissolved PO43− (DPO43−) but consumed particulate PO43− (PPO43−), total inorganic N, dissolved organic N, and particulate organic C. These net fluxes were influenced more by shallow, open‐water areas than by the tidal marshes which cover two‐thirds of the area of the upper estuary. Ratios of chlorophyll to organic C, N, and P suggest that most of the suspended particulate organic matter in the upper estuary was produced by phytoplankton rather than derived from watershed inputs. The consumption of nitrate due to phytoplankton production and the production of DPO43− due to release from particulate P after deposition in sediments resulted in low inorganic N : P ratios, contrasting sharply with the lower estuary and adjacent Chesapeake Bay. Dissolved inorganic N and P entered the upper estuary from the watershed at an atomic ratio of 26 but left the upper estuary at a ratio of 2.7. The release of DPO43− from watershed‐derived sediments may be a common feature among estuaries and could promote N limitation of primary production in estuarine and coastal waters.
Optical‐digital measurements of energy reserves in Calanoid copepods: Intersegmental distribution and seasonal patterns
Authors: Arts Michael T. , Evans Marlene S.
Published: April 2010

We present a simple optical‐digital method to measure visible energy reserves in calanoid copepods. Seasonal patterns (spring‐fall) of triacylglycerol energy reserves in Diaptomus sicilis were determined in a hypereutrophic and in a saline prairie lake. In addition to optical measurement of energy reserves, two well‐established chemical techniques (microgravimetric and Iatroscan TLC‐FID analyses) were used over the same period. Seasonal patterns of visible energy reserves measured by the optical method were positively correlated with both the Iatroscan measurements of triacylglycerol (Pearson’s r was between 0.72 and 0.87, P < 0.005) and the microgravimetric measurements of total lipid (r was between 0.73 and 0.88, P < 0.005). Thus, the optical method can be used to investigate seasonal changes in energy reserves in calanoid copepods but at a substantially lower cost (equipment, handling time) than chemical‐based methods. Moreover, the optical method offers increased resolution because energy reserves can be measured for each animal so that individual feeding success can be assessed, provides data on the partitioning of lipids in various body regions, and is nondestructive because anesthetized animals can be measured and returned to culture. Patterns of storage lipid reabsorption within discrete body regions may predict starvation risk in culture and in natural populations of copepods.
Estimating bacterial DNA synthesis from [3H]thymidine incorporation: Discrepancies among macromolecular extraction procedures
Authors: Torréton J. P. , Bouvy M.
Published: April 2010

The estimation of bacterial DNA synthesis in trophic studies with [3H]thymidine requires quantitative extraction of labeled DNA. To determine the DNA contribution to total macromolecular labeling in a eutrophic ecosystem, we tested three extraction procedures currently used to estimate DNA labeling from thymidine incorporation: enzymatic fractionation, acid‐base hydrolysis, and phenol‐chloroform extraction. Because labeled macromolecular fractions are generally defined as DNA, RNA, and proteins, we used incorporation of tritiated thymidine, uridine, and leucine to preferentially label DNA, RNA, and proteins. Our data showed that each fractionation method yielded different apparent macromolecular distributions of the same radiolabeled substrates. Enzymatic digestions of the fractions obtained by acid‐base hydrolysis and phenol‐chloroform extraction showed that these two procedures are inadequate for estimating bacterial DNA labeling in our ecosystem. Finally, using the enzymatic procedure at different sites, DNA labeling appeared to represent a nearly constant proportion of the labeled macromolecules (20.1%, r = 0.952, n = 101) over a wide range of incorporation rates.
Predictions of surficial sediment composition in the littoral zone of lakes
Authors: Petticrew Ellen L. , Kalff Jacob
Published: April 2010

Lacustrine sediment focusing presumes the removal of fine‐grained littoral particles (silt and clay) to storage sites in the deeper, less productive zone of a lake. In the littoral zone, shorter term sediment storage, on the time scale of biological transfers, demands attention as these clays and silts represent potential vectors in aquatic contaminant transfers. Two empirical models that predict surficial fine‐grained sediment composition of the littoral were developed in Lake Memphremagog, Quebec. A 5‐variable model explained 67% of the variance in the proportion of clay at 62 nearshore sites. A 3‐variable model including measures of fetch, depth, and slope explained 58% of the variance while the additional variables of plant presence or absence and sediment organic matter contributed the remaining 9% of explained variation. The two models performed exceedingly well when tested at 41 sites not used in the original derivation of the model. Of these 41 test sites, 13 represent samples from littoral zones of five eastern Canadian lakes (maritime provinces) representing different geologies and morphologies.
A semiautomatic, wet‐oxidation method for the determination of particulate organic nitrogen collected on filters
Authors: Raimbault Patrick , Slawyk Gerd
Published: April 2010

A wet‐oxidation method with peroxydisulfate digestion at 120°C is presented for routine analysis of particulate organic N (PON) collected on glass‐fiber filters. The technique was adapted from a previous procedure for oxidizing total N in seawater to NO3− . Comparisons with PON determinations by dry combustion at 800°C indicated high efficiency of the procedure, giving 100% recovery of N with cell cultures and natural seawater samples. Neutralizing buffer and pH adjustment proved to be necessary but were simplified by using a Technicon AutoAnalyzer system. The method was applied to follow NO3−assimilation by phytoplankton cultures and revealed excretion of N compounds by the cells at the end of the exponential phase of growth. The sensitivity of the method makes it possible to filter smaller quantities of seawater than needed for the combustion method (by 1–2 orders of magnitude) and can easily be adapted to shipboard use.
A potentiometric back‐titration method for determining sulfate in seawater and marine pore waters
Authors: Mucci Alfonso
Published: April 2010

Sulfate concentrations can be determined accurately by potentiometric back‐titration of excess Ba2+ with a mercury electrode following precipitation of BaSO4. The filtered seawater solution is eluted through a cation exchange column and the eluate reacted with excess BaCl2. The BaSO4 precipitate is removed by filtration and the solution titrated potentiometrically with EGTA. The method applies over a wide range of salinities and in the presence of 0.001 M HgCl2 which is used to inhibit bacterial activity during preservation. The oxidation of sulfides may interfere, but several remedial procedures can be adopted. The potentiometric titration and endpoint determination can be automated easily. The method determines the SO42− concentration in 1 ml or less of seawater with a SD of <0.6% (28.26±0.16 mmol kg−1 seawater, n = 28).
Phosphorus limitation of primary productivity in the eastern Mediterranean Sea
Authors: Krom M. D. , Kress N. , Brenner S. , Gordon L. I.
Published: April 2010

Although NO3 is generally considered to limit primary productivity in most of the world’s oceans, previous studies have suggested the Mediterranean Sea may be an exception. In this study of the southeastern Mediterranean, we found that all the PO43− was removed from the upper water column during the winter phytoplankton bloom in the core and boundary of a warm‐core eddy, while measurable (0.3–0.6 µM) NO3− remained. The N : P (NO3−:PO43−) ratio in the core and boundary of the Cyprus eddy was 27.4 and the slope of the linear portion of the N vs. P scattergram was 25.5 with a positive intercept of 0.5 µM on the NO3− axis. A similar N : P ratio (28–29), slope (21–23), and intercept (0.9–1.1) was found for the water column across much of the southern Levantine basin. These data, taken together with the results of incubation experiments, lead us to conclude that the southeastern Mediterranean is strongly P limited. The degree of P limitation increases from west to east across the entire basin. We suggest that removal of PO43− by adsorbtion on Fe− rich dust particles may be an important process controlling the concentration of P in the water column.
Release of dissolved free and combined amino acids by bacterivorous marine flagellates
Authors: Nagata Toshi , Kirchman David L.
Published: April 2010

We measured the release of dissolved free (DFAA) and combined (DCAA) amino acids and ammonium by a microflagellate (Paraphysomonas imperforata) grazing on bacteria. The release rate of DFAA was determined from changes in DFAA concentrations and uptake rates of DFAA. Exponentially growing flagellates released 4–22% of ingested nitrogen as DFAA. The release of DFAA by flagellates was comparable to or higher than ammonium release when ingestion was high, but lower than ammonium release when ingestion was low. DCAA accumulated during the exponential growth phase of flagellates, suggesting that flagellates released DCAA. We also measured the release rate of 3H‐labeled compounds by flagellates grazing on bacteria labeled with [3H]amino acids. The results suggested that flagellates release significant amounts of dissolved organic matter during the exponential growth phase, consistent with the measurements of amino acid release. Bacterivorous flagellates could be an important source of DFAA and DCAA in aquatic environments.
Computations of oxygen fluxes through the sea surface and the net production of organic matter with application to the Baltic and adjacent seas
Authors: Stigebrandt Anders
Published: April 2010

The transfer Fot of oxygen between the ocean and the atmosphere is computed from the formula Fot = V[O2 − (1 + x)O2s] where V is the transfer velocity, O2 the actual oxygen concentration of the surface water, O2s the saturation concentration, and x a factor that takes into account the effect of gas transfer due to bubbles. Monthly mean oxygen fluxes were calculated from the formula with historical hydrographical data. By adjusting the value of x, the formula was tuned to obtain a vanishing net annual oxygen flux through the sea surface in the Baltic proper. This occurs when x equals 0.025. Bubble‐driven gas transfer thus tends to supersaturate surface water.

The gas transfer formula is tested by a comparison between published estimates of the net production of organic matter in the photic layer and estimates obtained with computed oxygen fluxes through the sea surface. The test indicates that the formula is reliable. The test further shows that it is possible to compute the net production of organic matter in the photic zone, using the formula for oxygen exchange presented here, and salinity, temperature, and oxygen data from the surface layer.
Geographically specific recruitment and postsettlement mortality as influences on coral communities: The cross‐continental shelf transplant experiment
Authors: Sammarco Paul W.
Published: April 2010

The importance of geographic isolation in larval availability vs. postsettlement mortality as factors influencing coral community structure was examined. Coral recruitment and mortality patterns were assessed on the Great Barrier Reef (Australia) via settling plates implanted on three reefs located 16, 58, and 117 km from shore (across the continental shelf) at depths of 3 and 15 m. In a controlled experiment, plates were transplanted after 6 months of exposure to other reefs, covering all possible between‐reef combinations. Recruitment was higher on the outer half of the shelf and in deeper water. Acropora and Seriatopora were the major recruits on the mid‐ and outershelf reefs, where adult Acropora dominates. Porites and Alveopora dominated the inner‐shelf reef where Porites is a dominant adult. Mortality was lowest on the midshelf reef. Inshore recruits suffered greater losses in competition for space. Coral larvae settled cryptically, except in deeper inshore waters (low light). Taxonomic gradients occurred across the shelf, suggesting some geographic isolation, and implying that local larval pools differ. Spat transplanted from the midshelf reef to inshore or offshore reefs suffered higher mortality rates. Transplants from offshore survived better on the midshelf reef. Transplants from inshore to mid‐ or offshore reefs appeared to survive well. Larval availability, regional seeding of reefs, and postsettlement mortality may together play important roles in influencing coral community structure.
Nutrient cycling and the biogeochemistry of manganese, iron. and zinc in Jellyfish Lake, Palau
Authors: Landing William M. , Burnett William C. , Lyons W. Berry , Orem William H.
Published: April 2010

The oxic waters in Jellyfish Lake, a stagnant marine lake in Palau, are depleted in NO3−, PO43−, dissolved Si, Mn, Fe, and Zn, while the underlying anoxic waters are significantly enriched in these species and NH3. NH3 and PO43 regeneration and dissolved sulfide production in the anoxic zone yield a stoichiometry of C138N13P for organic matter undergoing recycling in the anoxic waters. In the anoxic zone, dissolved Mn, Fe, and Zn reach maximum concentrations of 30, 22, and 2.5 nM. The Fe concentrations are consistent with mackinawite or greigite solubility control. Mn approaches saturation with respect to haurite. Zn may be controlled by the solubility of ZnS coprecipitate. The sediments are enriched in Fe and depleted in Zn relative to Asian dust at Enewetak. A two‐box model is used to calculate an eddy diffusion coefficient of 0.0015 cm2 s−1 across the chemocline. The upward diffusive loss of NH3 added to the sedimentation rate of N and multiplied by the stoichiometric C : N ratio yields an organic carbon flux into the anoxic waters of 1,200 µmol C cm−2 yr−1, which is ∼ 13% of the total primary productivity.
Seasonal signals in Lake Malawi sediments
Authors: Pilskaln Cynthia H. , Johnson Thomas C.
Published: April 2010

The sedimentary record of Lake Malawi, one of the large rift valley lakes of east Africa, contains thick sequences of biologically undisturbed, finely laminated muds and silts. Laminated sequences were recovered in cores from the extensive diatom ooze and silty diatom clay facies of the lake basin that is permanently anoxic below 250 m. The sequences consist of light‐dark laminae couplets with average thickness of 1 mm. The light laminae are completely dominated by the diatom genus Melosira with a relatively minor contribution from the genus Stephanodiscus. The dark laminae consist of 50% diatoms (equal proportions of Melosira and Stephanodiscus, few Nitzschia, and occasional littoral diatom genera) and 50% terrestrial plant debris, mineral grains, and fine clay and organic material. Based on a 210Pb and 14C calculated sedimentation rate of 1 mm yr−1 for Lake Malawi basin sediments and the well‐defined seasonal variations in fluvial input and diatom productivity levels, our data suggest that the lamination couplets are annual varves, representing biannual sedimentation sequences. The light laminae result from diatom blooms occurring during the dry, windy season (April–October) when the upper 250 m of the lake is well‐mixed, localized upwelling occurs, and the epilimnion becomes enriched with nutrients. The dark laminae represent sedimentation in the rainy, low‐wind velocity season (November–March) when runoff and allochthonous terrestrial input are at a maximum and primary productivity is at a minimum.
Preliminary prey digestion in a predacious estuarine ciliate and the use of digestion data to estimate ingestion
Authors: Dolan John R. , Coats D. Wayne
Published: April 2010

Digestion of ciliate prey (Pleuronema sp. and Metanophrys sp.) in Euplotes woodruffi was examined in laboratory experiments. Similar exponential declines in recognizable food vacuole contents were found in feeding and nonfeeding cells. Ingestion rates, based on digestion rates and food vacuole contents, yielded estimates of 0.4–1.6 Pleuronema and 3.7–4.2 Metanophrys consumed per E. woodruffi h−1 at 20°C, in agreement with rates obtained by other methods. Cells starved for 24 h showed faster digestion rates; temperature variation over a range of 15°– 25°C gave a Q10 of ∼ 1.5.
Deoxygenation of a Florida lake during winter mixing
Authors: Whitmore Thomas J. , Brenner Mark , Rood Brian E. , Japy Kate E.
Published: April 2010

Johnson Pond occupies a small, deep, solution basin (A = 2.2 ha, zmax = 17.5 m) in north Florida. This warm, monomictic lake gains and loses 5,945 cal cm−2 annually. Dissolved color and algal turbidity limit light and heat penetration, causing steep gradients in temperature, oxygen, dissolved inorganic C, and remobilized sedimentary P during stratification from March through November. Water below 5 m is cool (<14°C) and anoxic throughout the year. Weak chemical gradients can persist in the water column during homothermy. The lake is ineffectively mixed because of morphometry, wind sheltering by trees, and the brevity of homothermy. An unusual consequence of winter mixing is very low oxygen concentrations in surface waters (< 1 mg liter−1). Surface‐water oxygen is diluted by upward mixing of deeper anoxic waters, and O2 is consumed by BOD and reduced Fe and S. Deoxygenation at mixis occurs in several African lakes, but is unreported in warm, monomictic lakes of North America.
Estimates of high absolute densities and emergence rates of demersal zooplankton from the Agatti Atoll, Laccadives
Authors: Madhupratap M. , Achuthankutty C. T. , Sreekumaran Nair S. R.
Published: April 2010

Direct sampling of the sandy sub stratum of the Agatti Lagoon with a corer showed the presence of very high densities of epibenthic forms. On average, densities were about 25 times higher than previously estimated with emergence traps. About 80% of the organisms migrated into the water column within an hour after sunset, and maximal resettlement occurred soon after dawn.
Separation and concentration of living dinoflagellate resting cysts from marine sediments via density‐gradient centrifugation
Authors: Schwinghamer P. , Anderson D. M. , Kulis D. M.
Published: April 2010

A method for separating and concentrating resting cysts of dinoflagellates from marine sediments via centrifugation in a nontoxic, isosmotic density gradient has been developed and tested. The density‐gradient medium is an aqueous suspension of colloidal silica (Nalco 1060) made isosmotic with seawater of salinity 32‰ using sucrose. The density of the medium, which is isosmotic throughout a density range of 1.086–1.405 g cm−3, may be adjusted by varying the proportion of sucrose solution mixed with the colloidal silica. Unlike other methods, there is no problem with jelling of the silica in seawater with this method, and Nalco 1060 is not highly toxic to aquatic organisms as are some other commonly used formulations. Cysts of Scrippsiella trochoidea and Alexandrium fundyense were extracted quantitatively from a muddy silt marine sediment and showed no sign of differential mortality related to the centrifugation procedure. Cultures of S. trochoidea were successfully initiated with centrifuged cysts.
Calcification in Chara corallina: CO2 hydroxylation generates protons for bicarbonate assimilation
Authors: McConnaughey Ted
Published: April 2010

The alga Chara corallina (Charophyta, Charophyceae) apparently generates protons through the hydroxylation and precipitation of CO2, which leaks from the cell into highly alkaline pericellular regions. Under mildly alkaline conditions, the loss of CO2 to calcification is compensated by the production of twice as much CO2 from HCO3−, using the protons generated during calcification.

Experiments capitalize on Chara’s large cells with their alternating alkaline (calcareous) and acidic (noncalcareous) pericellular zones. 14C uptake into carbonate and organic phases is fastest when the isotope is applied to the acidic zones. The ratio of calcification to photosynthesis is ∼ 1 at pH 8 and increases with pH approximately as simulated by a model in which both calcification and photosynthesis use carbon assimilated in the acidic zones. PIPES buffer (pKa = 6.8) inhibits calcification and photosynthesis equally, suggesting competition with bicarbonate as a proton acceptor in the acidic zones. CAPS buffer (pKa = 10.4) has little effect, suggesting that exogenous bicarbonate is not very important for calcification. Divalent Sr and Mn added to the medium precipitate primarily between the cell and calcareous encrustations, but phosphate does not. This result is consistent with the use of cellular Ca and CO2 in extracellular calcification.
Density‐dependent effects of protozoans on specific growth rates in pico‐ and nanoplanktonic assemblages
Authors: Ferrier Christine , Rassoulzadegan Fereidoun
Published: April 2010

We experimentally assess nutrient feedback of oligotrichous ciliates and phagotrophic flagellates on growth in naturally occurring Mediterranean autotrophic microbial populations as well as on the microphytoplankton. Dialysis bags were used to separate cultured protozoa from the <7‐µm plankton filtrates yet allow nutrient exchange. Growth rates in microbial autotrophic populations increased with protozoan densities added to bags. Microbial growth half‐saturation constants, expressed in terms of protozoan densities added, varied from 11 to 17 ciliates ml−1 and 2–5 × 103 flagellates ml−1. The “transdialysis contact” of protozoa with microbial planktonic populations led to growth rates 2 to > 10 times higher than those observed without added protozoa. These findings suggest that in situ, autotrophic pico‐ and nanoplanktonic growth is limited by protozoan standing stocks. Lower generation times and half‐saturation constants were obtained for autotrophic nanoplankton (∼3 h, Kµ = 10 ciliates ml−1 and 1.7 × 103 phagotrophic flagellates ml−1, respectively). Microphytoplankton (e.g. diatoms and dinoflagellates) showed no significant functional responses to the addition of microprotozoa, suggesting a possible dependence of the latter on new rather than on recycled nutrients.
Export of fine organic particles from headwater streams: Effects of season, extreme discharges, and invertebrate manipulation
Authors: Wallace J. Bruce , Cuffney T. F. , Webster J. R. , Lugthart G. J. , Chung K. , Goldowitz B. S.
Published: April 2010

Export of fine particulate organic matter (FPOM) was measured from streams draining Catchments 53, 54, and 55 (C53, C54, and C55) at the Coweeta Hydrologic Laboratory for 5 yr, encompassing the driest and wettest years of the past 55‐yr record. Macroinvertebrate populations in C54 were reduced for 3 yr by seasonal treatments with insecticide. During pesticide treatment, FPOM concentrations decreased abruptly in C54, remained well below those of reference streams for the 3‐yr treatment period, and then increased during the 1st yr of recovery. Macroinvertebrate reduction resulted in an estimated 170–200 kg loss in FPOM export during the 3 yr of treatment and 1 st yr of recovery. Annual export of FPOM was strongly related to annual discharge, but the impact of biotic manipulation on FPOM export in C54 was at least as great as that produced by extreme high and low discharges. FPOM export during sampling intervals was directly related to maximum discharge during the intervals. Treatment of C54 significantly reduced FPOM export per unit maximum discharge. Seasonal relationships between FPOM export and maximum discharge indicated more export per unit maximum discharge in summer in reference streams and C54 in untreated years. In contrast, during treatment years of C54, export per unit maximum discharge was lowest in summer. FPOM concentrations measured during storms showed increasing concentrations with increasing discharge in all streams, however, much more FPOM was suspended in the reference streams than in C54. Thus, macroinvertebrate reduction altered the magnitude of FPOM export during storms, the seasonal pattern of export, and the annual export of FPOM.
The relative importance of bacteria and algae as food sources for crustacean zooplankton
Authors: Wylie John L. , Currie David J.
Published: April 2010

There is increasing evidence that the main role of the microbial loop in aquatic food webs is rapid remineralization of organic nutrients with little C being transferred to higher trophic levels. There is also evidence, however, that the transfer of C from algae to crustaceans is equally inefficient. This finding suggests that simultaneous determination of C flow from both bacteria and algae to crustaceans is necessary to determine if bacteria might represent an important source of C for higher trophic levels. Our data suggest that when copepods dominate a crustacean community bacteria and picoplankton contribute insignificant amounts of C to crustaceans. When cladocerans predominate, the significance of these trophic links increases. At our study site, up to 16–21% of the C input to crustaceans may have originated from bacteria and picoplankton when cladocerans were present in large numbers. For some of our analyses, percentage of algal or heterotrophic bacterial C transferred per hour to crustaceans was of a similar magnitude, which suggests that if bacterial and algal biomass is similar much of the C flow to crustaceans could originate from bacteria.
Pathways of carbon incorporation in marine copepods: Effects of developmental stage and food quantity
Authors: Roman Michael R.
Published: April 2010

Incorporation of carbon (14C) into various biochemical fractions (protein, polysaccharide, lipid) was measured in developmental stages (N3–N4, C3–C4, adult females) of the copepod Acartia tonsa fed labeled algae. Nauplii had the highest weight‐specific incorporation of C into protein whereas adult females had the highest weight‐specific incorporation of C into lipid. Incorporation rates of C into protein, lipid, and polysaccharide increased with food concentration. At the highest food concentration (1,055 µg C liter−1) C3–C4 stages of A. tonsa had a daily, weight‐specific incorporation rate of 18% of their body protein, 15% of their lipid, and 2% of their polysaccharides. Incorporation of C into the various biochemical compounds responded rapidly to increases in food concentration. Within 1.5 h after food was increased (5 ×), A. tonsa incorporated more algal C into its low molecular weight, protein, lipid, and polysaccharide fractions. Pulse‐chase experiments showed that once incorporated, C in protein had a much lower turnover rate and was thus conserved more than C in polysaccharides and lipids.
Carbon, nitrogen, and phosphorus content of freshwater zooplankton
Authors: Andersen Tom , Hessen Dag O.
Published: April 2010

The amounts of C, N, and P in relation to dry weight were measured in natural populations of crustacean zooplankton from a humic lake. The elemental composition within a given species showed little seasonal variation, and experimental starvation or feeding did not cause any significant changes in the P content. C constituted 48±1% of dry weight with only minor variation among species. The mean C : N : P atomic ratios reflected large interspecific differences in P and N content and ranged from 212 : 39 : 1 in Acanthodiaptomus denticornis to 85 : 14 : 1 in Daphnia longispina. Comparisons with published measurements indicate that this pattern is quite general and probably constitutional. These findings suggest that the species composition of the zooplankton community can have strong influence on the N : P ratio of recycled nutrients and thereby affect resource competition between phytoplankton species.
An improved fluorescence method for the determination of nanomolar concentrations of ammonium in natural waters
Authors: Jones Ronald D.
Published: April 2010

An improved fluorescence method is described for measuring nanomolar concentrations of NH4+ in natural waters. This method is based on the conversion of NH4+ to NH3 and subsequent diffusion of NH3 across a microporous hydrophobic Teflon membrane into a flowing stream of o‐phthaldialdehyde reagent to produce a fluorescent adduct. The product is detected fluorometrically with a lower detection limit of better than 1.5 nM. Up to 30 determinations h−1 can be made. The method works well in freshwater or salt water. Field tests of the method in the Dry Tortugas and Gulf Stream gave NH4+ concentrations that ranged from 18.0 nM in Gulf Stream waters to 2,254.7 nM in interstitial waters from coralline reef sands. The method can be used to measure near real‐time NH4+ concentrations in situations where it was previously difficult or impossible.
Differential survival of bacteria ingested by zooplankton from a stratified eutrophic lake
Authors: King C. Harold , Sanders Robert W. , Shot Emmett B. , Porter Karen G.
Published: April 2010

Field studies were performed in stratified Lake Oglethorpe to isolate and identify culturable, free‐living bacterioplankton from lake water and those associated within zooplankton. Heterotrophic colony counts of whole water were lower than acridine orange epifluorescent direct counts by 3–4 orders of magnitude, whereas colony counts were increased by an order of magnitude when the lake water was fractionated for zooplankton, then treated and sonicated to release bacteria from within zooplankton. Cultured bacterial species were segregated by sampling depth among the epilimnion, metalimnion, and hypolimnion and the zooplankton fractions. Laboratory feeding experiments with Daphnia ambigua and mixed suspensions of these lake bacteria demonstrated that zooplankton‐associated bacteria survived induced gut retention in D. ambigua for 23 h longer than free‐living bacteria. Feeding rate experiments showed no difference between ingestion or clearance rates of the mixed cultured bacteria, but bacterial inhibition studies showed that survivors inhibited nonsurvivors. These studies suggest that some bacterioplankton can survive digestion and interact in guts of zooplankton.
Characterization of a dense, purple sulfur bacterial layer in a meromictic salt lake
Authors: Overmann Jörg , Beatty J. Thomas , Hall Ken J. , Pfennig Norbert , Northcote Tom G.
Published: April 2010

In meromictic Mahoney Lake (British Columbia), purple sulfur bacteria formed a dense, 10‐cm‐thick layer at the primary chemocline. The dominant species (Amoebobacter purpureus) reached a maximal cell concentration of 4 × 108 cells ml‒1, 27% of which were viable. A maximal concentration of 20,900 µg bacteriochlorophyll a liter‒1 was determined—the highest concentration ever found in a natural body of water. Steep vertical gradients of conductivity, light, and sulfide concentration were detected across the bacterial layer, while the concentration of oxygen increased above it. Integrated primary production of the layer was 15 mg C m‒2 h‒1. Bacteriochlorophyll‐specific assimilation rates reached maxima at the top of the layer. Anoxygenic photosynthesis was limited by reduced sulfur compounds at the top of the layer, whereas strong attenuation of irradiance resulted in light limitation for most of the cell population below. The sulfide flux from below the layer accounted for <37% of the sulfide oxidized in the layer. Thus >63% of the sulfide oxidized during anoxygenic photosynthesis must have been produced within the layer. This calculation agrees well with sulfide production rates measured in situ (12.4 µmol liter‒1 h‒1). In contrast to other lakes, considerable uptake of [14C]acetate by purple sulfur bacteria and comparatively high numbers of purple nonsulfur bacteria indicate an important role of dissolved organic matter and a short cycle of carbon and redox compounds in the dense purple microbial layer.
Seasonal variations in size structure and procaryotic dominance in sulfurous Lake Cisó
Authors: Gasol Josep M. , Guerrero Ricardo , Alió Carlos Pedró
Published: April 2010

To be useful in understanding natural communities, the analysis of size spectra should reveal seasonal and interlake variability. We calculated size spectra for the planktonic community of Lake Cisó. Data from 3 yr were used to analyze seasonal patterns of size distribution. The average spectrum showed peaks of biomass at 0.5–0.7, 4, 15, 32, 64, 85, and 200 µm of equivalent spherical diameter. These peaks corresponded to the dominant organisms in the lake: heterotrophic bacteria, purple phototrophic bacteria, Cryptomonas phaseolus, small ciliates including Coleps hirtus, large ciliates, rotifers including Anuraeopsis fissa, and copepods. The peak at 4 µm was the largest (3 or more times the biomass of the others). We used these data to test the utility of the size spectral approach to describe seasonal changes in the lake. Both linear and polynomial equations were fitted to the normalized spectra. Although the slope of the linear fit did not show any seasonal trend, the second‐order coefficient of the polynomial fit presented a clear pattern that made it a useful index of the degree of procaryotic dominance. The lake alternated between anaerobic conditions during mixing, when procaryotes dominated and polynomial fits were best, and stratification, when polynomial and linear curves fit equally well.
Bacterivory by sestonic protists in a southeastern blackwater river
Authors: Carlough Leslie A. , Meyer Judy L.
Published: April 2010

As part of a study examining the trophic base of secondary production in the Ogeechee River, Georgia, bacterial grazing by sestonic protists was measured directly with fluorescently labeled bacteria. For the period April 1988 through September 1989, flagellates and ciliates ingested an average of 18.6 (range, 1.7–43) and 314 (range, 25–1,140) bacteria individual‒1 h‒1. These grazing rates are comparable to those of protists in marine and lentic habitats. When combined with bacterial and protist densities in the river, an average of 15.6% (range, 0.2–59%) of the water column was cleared by protists per day. On the basis of literature values of microbial C content and assimilation efficiencies, this percentage translates to a production rate of 11.7 µg C liter‒1 d‒1. Protist bacterivory can facilitate carbon flow to higher trophic levels by turning bacteria into larger parcels of carbon and nutrients that are then available to a greater portion of the filter‐feeding community. The microbial loop in this lotic system differs from pelagic systems; bacteria are derived from external sources, and bacteria and protists are directly consumed by macroinvertebrates.
Filter mesh size of cladocerans predicts retention efficiency for bacteria
Authors: Brendelberger Heinz
Published: April 2010

This study tested the hypothesis that filter mesh size can predict retention efficiency of very small particles by cladocerans. Morphology of the filtering apparatus and size distribution of the food particles were measured by scanning electron microscopy. From these morphological data the retention of food particles could be predicted for individual animals. Short‐term, dual‐label experiments were used to measure the uptake of small food particles by four species of Cladocera (Daphnia magna, Daphnia pulex, Simocephalus vetulus, and Diaphanosoma brachyurum). The green alga Scenedesmus acutus was paired with each of six classes of small particles; three size fractions of free‐living planktonic bacteria, two cyanobacterial species of different sizes, and the green alga Stichococcus minutissima were fed. The clearance rates for these very small particles were divided by the clearance rate for Scenedesmus to calculate retention efficiencies.

Retention efficiencies were between 33 and 154%. Cladoceran species with coarser filtering meshes showed lower retention efficiencies for bacteria and cyanobacteria. Within species, both predicted and observed retention efficiencies were greater for juveniles than for adults. Although collection mechanisms other than sieving probably operate, the size distribution of particles collected by cladocerans is closely predicted by the size‐frequency distribution of meshes of the thoracic feeding limbs.
Dependent coupling of inorganic and organic nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary and its regulation by large heterotrophs
Authors: Glibert Patricia M. , Garside Chris , Fuhrman Jed A. , Roman Michael R.
Published: April 2010

Nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary was studied during a series of four cruises (1985–1986). During each season we followed the short‐term patterns in inorganic (NH4+, NO3‒, NO2‒), and organic (urea and dissolved free amino acids—DFAA) nitrogen uptake and regeneration as plume water aged and became incorporated into ambient coastal water over 1–3 d. There was little influence of seasonally changing temperature on inorganic nitrogen uptake rates: the highest specific and absolute hourly rates of uptake occurred in April, when the availability of total N was at a seasonal high; rates were somewhat lower in early and late summer and were lowest in February. NH4+ regeneration rates, on the other hand, were highly correlated with temperature, with the highest rates occurring in late summer. Rates of DFAA uptake were highest in June. Urea contributed up to 70–80% of the total N utilized during winter and summer; in spring most nitrogen uptake was in the forms of NO3 and NH4+. The seasonal differences in the patterns of release of dissolved organic N, and the role of zooplankton in mediating this flux, paralleled the patterns previously reported for the release of dissolved organic C in the Chesapeake Bay plume. That is, in winter most organic N release was not grazer mediated, but instead was more likely due to nutrient‐deficient phytoplankton. In contrast, in late summer, there seemed to be more dissolved organic N release by grazers, either directly or from “sloppy feeding.” At all seasons, in the transition from the bay environment to coastal waters, autotrophic populations appeared to become nutrient deficient, and a system dominated by heterotrophic processes rapidly became established.
Absorption, fluorescence, and quantum yield for growth in nitrogen‐limited Dunaliella tertiolecta
Authors: Sosik Heidi M. , Mitchell B. Greg
Published: April 2010

The effects of steady state nitrogen limitation on the optical properties of Dunaliella tertiolecta were investigated. Growth rate was varied in a continuous culture under constant irradiance and temperature with absorption, fluorescence, and cellular characteristics including pigment contents determined at each steady state. The cellular concentration of Chl a increased with growth rate while Chl‐a‐specific absorption and fluorescence both decreased. In addition, the quantum yield for growth varied by more than a factor of 3.5 over the growth conditions examined, with the highest yield in the most rapidly growing cells. The decrease in magnitude of Chl‐a‐specific optical properties is caused by pigment package effects and changes in the abundance of accessory pigments relative to Chl a. Changes in absorption and fluorescence properties are consistent with theoretical predictions for discrete packages. In addition, pigment‐based reconstruction techniques overestimate the magnitude of both in vivo and unpackaged absorption by D. tertiolecta under these growth conditions. The observed variability in Chl‐a‐specific absorption and quantum yield is a fundamental aspect of phytoplankton physiology that should be incorporated into models of oceanic primary production.
In situ measurements of flow effects on primary production and dark respiration in reef corals
Authors: Patterson Mark R. , Sebens Kenneth P. , Olson R. Randolph
Published: April 2010

The effects of flow on the physiological ecology of Montastrea annularis, an important frame‐building species of Caribbean coral reefs, were investigated in situ with a recirculating flow respirometry system deployed from an underwater habitat. For this species, primary production and respiration rates increase with increasing water motion. The slope of a nondimensional Sherwood ‐Reynolds(Re) number plot indicates that forced convection increases dark respiration in a manner consistent with oxygen transfer through a turbulent boundary layer . A similar analysis for maximal photosynthetic rate yields a lower but significant slope A simple conceptual model of diffusional depletion in the boundary layer over the coral fits the data and accounts for the distribution of zooxanthellae. Calculations of phototrophic capacity for this species indicate that water motion can enhance the local productivity of the reef.