bluuebunny/crossref_metadata_2025 huggingface dataset:
Methodological problems in the simultaneous assessment of photosynthesis and nutrient uptake in phytoplankton as functions of light intensity and cell size
Authors: Nalewajko C. , Garside C.
Published: April 2010

The processes of nitrate, ammonia, and phosphate uptake in marine phytoplankton differed in the extent of dependence on light. Phosphate uptake in the 3–8‐µm size class, but not in the whole population, showed a saturation‐type relationship to light. Biomass‐specific photosynthesis and nutrient uptake rates were highest in the smallest, 0.2–3‐µm, size class, and decreased in the 3–8‐µm, and in the >8‐µm classes.

C:N:P uptake ratios at ambient light were different in the 0.2–3‐µm, 3–8‐µm, and >8‐µm size classes. In the whole population, uptake ratios at ambient light differed from ratios based on light‐optimized data. However, the measurements are subject to many problems which preclude an assessment of the accuracy of the ratios.
The trophic role of colonial Radiolaria in oligotrophic oceanic environments1,2
Authors: Swanberg Neil R.
Published: April 2010

Five species of colonial Radiolaria collected by divers on 27 cruises were used for experimental metabolic measurements. Carbon content as an indicator of colony size correlated well with cell number in three species, with approximately 50, 100, and 200 ng C per cell. Chlorophyll a per radiolarian cell (from symbiotic dinoflagellates) varied widely between colonies and could not be predicted from colony size by better than a factor of 2. Photosynthetic carbon incorporation at high levels of natural light ranged from 10 to 76 pmol C · cell−1 · h−1. Mean respiration in two species was 5.3–5.5 µl O2 · mg C−1 · h−1. Respiration is probably balanced by photosynthesis under normal light conditions.

Colonial Radiolaria were present at 92% of 268 oceanic stations and very abundant at 34%. Measured abundances ranged from 0.04 to 14 colonies · m−3 in the water column and reached 540 colonies · m−3 in patches at the surface. Because the primary productivity of their symbionts is probably consumed in maintenance metabolism, colonial Radiolaria may be most important to the epipelagic oligotrophic ecosystem as gelatinous predators.
Feeding and assimilation rates of Daphnia pulex fed Aphanizomenon flos‐aquae1
Authors: Holm Nancy Peterson , Ganf George G. , Shapiro Joseph
Published: April 2010

Feeding and filtering rates of Daphnia pulex on the blue‐green alga Aphanizomenonflosaquae were measured in laboratory experiments. Single filaments (broken from colonies) and small colonies of A. flos‐aquae <1.5 mm long could be grazed by D. pulex at maximum rates of 15,000–50,000 cells·Daphnia−1·h−1. The filtering rate increased as a function of the cube of the body length of D. pulex. Colonies >1.5 mm long were not grazed appreciably by D. pulex. Daphnia pulex continued to feed on A. flos‐aquae in the presence of another alga, Ankistrodlesmus falcatus. Colonies ofA. flos‐aquae > 1.5 mm long tended to lower the feeding and filtering rates on A. falcatus. The net assimilation efficiency (uncorrected for respiration) of D. pulex was about 11% for A. flos‐aquae and about 35% for A. falcatus. The presence in lakes of Aphanizomenon as the large colony type (A. flos‐aquae) or as single filament types may be determined by the grazing ability of D. pulex.
Vertical distribution patterns of copepods, chlorophyll, and production in northeastern Baffin Bay
Authors: Herman Alex W.
Published: April 2010

High resolution vertical distributions of chlorophyll and zooplankton were collected with an instrumented Batfish vehicle in northeastern Baffin Bay. The dominant copepod species were Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus V and VI. Copepod layers consisting of C. finmarchicus and C. glacialis were commonly situated ≈3–4 m above the chlorophyll maximum in a depth region corresponding to the peak in the derived vertical profile of primary production. Calanus hyperboreus V and VI coincided with the chlorophyll maximum. Estimates of daily copepod grazing rations based on daily primary production and the density of copepods, with the assumption of steady state, were ≈20% body C· d−1.
Diel vertical migration by zooplankton: Constant and fluctuating temperature effects on life history parameters of Daphnia1
Authors: Orcutt John D. , Porter Karen G.
Published: April 2010

The thermal demographic advantage of vertical migration was tested using life‐table studies of Daphnia parvula cohorts fed on Chlamydomonas reinhardi. At a high food level, lifespan and body size at death were relatively insensitive to temperature differences. Fecundity parameters (brood size, brood number, total number of young per reproductive female, and net reproduction rate) were highest at an optimal midrange temperature (15°C). However, age at onset of reproduction, instar at first reproduction and brood duration decreased with increasing temperature, resulting in an overall increase in the realized rate of increase (r) with increasing temperature. Realized rates of increase were higher in fluctuating temperatures than at comparable average constant temperatures but were always lower than those at the highest constant temperature in each range. A low food level reduced the effect of temperature on some growth and fitness parameters from those at a high food level, but r was still greater at the higher temperatures. Therefore, there is no apparent thermal demographic advantage to vertical migration at either a high or low food level within the natural range experienced by D. parvula. Maximum fitness is achieved by remaining in the warmest surface waters at all times.
A simple, steady state description of phytoplankton growth based on absorption cross section and quantum efficiency1
Authors: Kiefer Dale A. , Mitchell B. Greg
Published: April 2010

We present a simple, quantitative formulation of steady state growth and metabolic regulation by phytoplankton, which describes well the nutrient‐limited and light‐limited growth of Thalassiosira weissflogii. The specific growth rate is a function of the quantum efficiency of carbon assimilation, the absorption cross section of cellular carbon, the incident light level, and the specific rate of respiration. The quantum efficiency is solely a function of light level, the absorption cross section is a function of light level and nutrient supply, and the respiration rate is a function of specific growth rate. The formulation, which resembles those proposed by Bannister and Shuter, is consistent with the thermodynamic model of Kiefer and the principle of optimization of energy conversion.
Sediment community oxygen consumption and nutrient exchange in the central and eastern North Pacific1
Authors: Smith K. L. , Laver M. B. , Brown N. O.
Published: April 2010

Sediment community oxygen consumption (SCOC) and nutrient exchange rates (NH4+, NO3‒, NO2‒) were measured along a transect of five stations from the oligotrophic central North Pacific to the eutrophic upwelling off the coast of southern California. These rates were measured using a free vehicle grab respirometer at three spatial scales: intergrab (cm), intersubstation (km), and interstation (102 km). Sediment community oxygen consumption increased along a gradient of increasing surface primary productivity from west to east. Macrofaunal abundance and biomass, and surface organic carbon and total nitrogen also increased from west to east, with a trend toward larger animals at the eastern stations. Most of the variability in SCOC at both the interstation and intersubstation level is correlated with depth and macrofaunal abundance. Predictive equations for SCOC were generated using these parameters. Nitrogenous nutrient exchange rates were highly variable and showed no east— west trends.
The effect of food quality on feeding and respiration by Daphnia and Diaptomus1
Authors: Richman Sumner , Dodson Stanley I.
Published: April 2010

Filtering, ingestion, and respiration rates for Daphnia pulex and Diaptomus siciloides were measured in southern Green Bay water mixed with algal cultures to produce varying proportions of blue‐green algae. These measurements along with observations of Daphnia mouthpart responses to these foods were used to assess the relative competitive potential of Daphnia and calanoid copepods in lakes of varying trophy. Ratios of filtering and ingestion rate to respiration rate were used as a measure of energy input per unit of energy expended. Passive filtering and subsequent rejection of inedible algae by Daphnia result in higher ratios than those shown by Diaptomus in high quality foods, suggesting a competitive advantage in oligotrophic or mesotrophic lakes. Diaptomus selective feeding, on the other hand, results in higher ratios in the low quality food characteristic of eutrophic conditions. These results and data from the literature are used to propose a two‐dimensional niche model to demonstrate the interaction between food quality and abundance on the competitive interaction between calanoid copepods and Daphnia‐like cladocerans.
Freeze‐out of salts in hard‐water lakes1
Authors: Canfield Daniel E. , Bachmann Roger W. , Hoyer Mark V.
Published: April 2010

A 15‐year series of daily measurements of pH and total alkalinity recorded at the water intake of a municipal water‐treatment plant on Clear Lake, Iowa, demonstrated that rapid chemical changes occur annually as the ice cover melts. Additional measurements of total and calcium hardness on this and three other eutrophic, hard‐water lakes showed that total and calcium hardness concentrations declined rapidly as the main ice mass was destroyed. This decline was not caused by chemical or biological precipitation of carbonates, but by a dilution effect of melting ice. The magnitude of the declines could be predicted from measurements of hardness under the ice, lake volume, and volume of ice.
Sulfate reduction in Georgia salt marsh soils: An evaluation of pyrite formation by use of 35S and 55Fe tracers1
Authors: King Gary M.
Published: April 2010

A time‐course analysis of sulfate reduction in Sapelo Island marsh soils using 35SO42‒ indicated that acid‐volatile H235S formation was a linear function of time for the 0–12‐cm depth interval of both tall and short Spartina alterniflora soils. Aqua regia‐soluble 35S was present in significant amounts at all depths in both sites in killed controls and did not increase significantly during a 72‐h incubation. The activity of 35S in aqua regia digests of marsh soils was dependent on the type of acid used to distill H235S before aqua regia digestion; the greatest activity was with 6 N HCl and the least was with 1 N H3PO4. No consistent formation of [55Fe]pyrite was observed during a 72‐h incubation of 55Fe in short S. alterniflora soils. These data indicate that the incorporation of 35S into aqua regia‐soluble compounds was at least in part an artifact of the distillation procedure and that the use of aqua regia‐soluble 35S to calculate sulfate reduction rates could result in a significant overestimation of this process.
The 14C method: Patterns of dark CO2 fixation and DCMU correction to replace the dark bottle1,2
Authors: Legendre Louis , Demers Serge , Yentsch Clarice M. , Yentsch Charles S.
Published: April 2010

Subtracting dark 14C fixation from light 14C fixation can lead to serious underestimates of phytoplankton production in aquatic environments. Light, temperature, and nutrient time‐course experiments show that there is an active and an inactive incorporation component of 14C in the dark. The active incorporation can be prevented by adding DCMU (dissolved in water) to either a light or a dark bottle, thus estimating the inactive component. It is therefore recommended that a DCMU treatment be subtracted from the standard light carbon dioxide fixation for accurate estimation of phytoplankton production.
Porewater in coral heads: Evidence for nutrient regeneration1
Authors: Risk Michael J. , Muller Hans R.
Published: April 2010

Porewater from live coral heads was extracted by centrifugation and analyzed for pH, O2, and nutrients. Decreased pH and O2 concentrations and elevated nutrient concentrations are evidence for possible microbial regeneration. The stoichiometry fits a respiration model.
Carboxylating enzyme activity and photosynthetic end products of phytoplankton in the shallow and deep chlorophyll layers of Castle Lake1
Authors: Priscu John C. , Goldman Charles R.
Published: April 2010

The patterns of carbon assimilation of the Castle Lake phytoplankton were measured under various environmental conditions. The flow of carbon into polysaccharides and lipids plus low molecular weight metabolites was generally highest at low temperatures and low light (i.e, under‐ice and deep‐water populations). Enrichment with nitrogen to nitrogen‐deficient algae did not significantly alter the patterns of carbon assimilation during time‐series experiments. However, the relative rates of polysaccharide and protein synthesis were increased when the entire epilimnion of the lake was fertilized with nitrogen.

On the average about 15% more carbon could potentially be fixed by the anaplerotic enzyme phosphoenolpyruvate carboxylase (PEPCase) than the Calvin Cycle enzyme ribulose‐1,5‐biphosphate carboxylase (RuBPCase). The parameter, RuBPCase : PEPCase/photon saturated in vivo photosynthesis (Pmax), was consistently >1.0 liter ·h‒1·µg‒1 C and showed significant differences between the 3‐m and 20‐m algal populations, indicating that they may be physiologically distinct with respect to carbon metabolism.

The proportion of 14C incorporated into protein increased as the ratio of RuBPCase to PEPCase increased. The converse was true for the relative synthesis of lipid + low molecular weight (LMW) compounds while the proportion of 14C incorporated into polysaccharide varied little with RuBPCase : PEPCase. These findings and others from the literature do not corroborate existing simple biochemical models for this relationship, implying that other carboxylating enzymes may be important in the carbon metabolism of certain algae.
Spectral differences and temporal stability of phycoerythrin fluorescence in estuarine and coastal waters due to the domination of labile cryptophytes and stabile cyanobacteria
Authors: Exton R. J. , Houghton W. M. , Esaias W. , Haas L. W. , Hayward D.
Published: April 2010

Laser fluorosensing and epifluorescence microscopy were used jointly to identify the origin of different spectral peaks of phycoerythrin in estuarine and coastal samples. The fluorescence of the samples was also examined as a function of the time elapsed after a water circulation system was turned on. Coastal samples were dominated by cyanobacteria and exhibited a constant phycoerythrin fluorescence with time. The phycoerythrin fluorescence of the Chesapeake Bay estuarine samples first increased strongly, reached a maximum, and then decreased to below the original level; these samples were dominated by cryptophytes which epifluorescence techniques revealed were being destroyed by the circulation system. A simple mathematical model was developed to describe the effects of cell disruption, the uncoupling of energy transfer between pigments, and the subsequent breakdown of the solubilized phycoerythrin.
A method of isolating clean and viable zooxanthellae by density gradient centrifugation
Authors: Tytler E. M. , Davies P. Spencer
Published: April 2010

Attempts to prepare viable suspensions of zooxanthellae isolated from coelenterate hosts have been hampered by the large amounts of mucus secreted by the host tissues. A method is described which overcomes this by density gradient ultracentrifugation of the isolate, using the silica sol Percoll which forms its own density gradient during ultracentrifugation. Between 106 and 107 zooxanthellae can be isolated per gradient. Contamination is reduced to the occasional nematocyst or piece of animal cell debris. The zooxanthellae thus isolated are viable and appear to show normal respiration and photosynthesis.
Sources and distributions of sedimentary organic matter in the Columbia River drainage basin, Washington and Oregon1
Authors: Hedges John I. , Turin H. J. , Ertel John R.
Published: April 2010

Nonwoody angiosperm tissues and gymnosperm woods are the major types of vascular plant debris in bottom sediments from 16 sites within the Columbia River and its tributaries. In tributary sediments relative abundances of these types of tissue vary regionally and are consistent with drainage basin vegetation. Within the extensively dammed main river, vascular plant debris mixtures are more uniform, indicating downstream mixing of sedimentary material from reservoir to reservoir. Vascular plant tissues account for an average of a third of the total sedimentary organic matter at the 16 river sites. The remaining organic material has an atomic C:N of 10–15 and a stable carbon isotope composition similar to “average” land plants. Organic matter in sediments of the Columbia River system is generally enriched in nonwoody angiosperm tissues and lignin‐poor organic matter in comparison to Columbia River‐derived organic matter in modern marine sediments from the southern Washington continental shelf.
Porewater evidence for a dynamic sedimentary iron cycle in salt marshes1
Authors: Giblin Anne E. , Howarth Robert W.
Published: April 2010

Dynamic transformations of iron occur seasonally at Great Sippewissett Marsh, Massachusetts. Small changes in the dissolved iron concentration in porewater represent only a small fraction of the iron involved in transformation reactions during the year. During the growing season, salt marsh grasses oxidize the sediment, and a large percentage of sedimentary pyrite is converted to an oxidized iron mineral. Over the fall and winter there is a net increase in pyrite as the grass is anaerobically decomposed.

When oxidation rates in summer are high enough to neutralize the alkalinity produced by sulfate reduction and substantially lower the pH, oxidized iron minerals become increasingly soluble and iron levels in the porewater increase. If large amounts of soluble iron are lost by tidal flushing, iron availability may limit pyrite formation in later years. Sulfide concentrations in the porewater would then increase, leading to depressed growth of Spartina alterniflora.

For most of the year the porewaters of Great Sippewissett were undersaturated with respect to all iron monosulfide minerals and supersaturated with respect to pyrite (FeS2). Thus pyrite formation at Great Sippewissett probably occurs directly by reaction of polysulfides with iron and not by reactions of FeS with elemental sulfur. Porewaters were always undersaturated with respect to manganese minerals. Porewaters taken from marshes at Sapelo Island, Georgia, in fall were supersaturated with respect to pyrite at all depths and appear to be saturated for iron monosulfides below 12 cm at all sites.
Does Paracalanus feed with a leaky sieve?1
Authors: Paffenhöfer Gustav-Adolf
Published: April 2010

It has been assumed that calanoid copepods gather and ingest food particles by filtration using their mouthparts which means solely mechanical retention of food particles. Experiments in which juveniles and adult females of Paracalanus were offered a mixture of phytoplankton cells of different sizes show that cells are not eaten in the same proportions as the copepods increase in size. Changes in the proportion of various particles in the diet are attributed to behaviorally mediated changes in copepod feeding patterns.
Determination of substrates oxidized by sulfate reduction in intact cores of marine sediments1
Authors: Christensen Dorte
Published: April 2010

A method is presented for quantifying the in situ rates of substrate oxidation by sulfate‐reducing bacteria in sediment. Molybdate (100 µl of 2 M Na2MoO4) injected into intact sediment cores inhibited sulfate reduction efficiently. The subsequent accumulation of acetate was linear. The accumulation rate in molybdate‐inhibited cores was determined from linear regressions of the acetate concentrations as a function of incubation time. The acetate contributed about 65% of the electron donor for sulfate reduction. In the surface layers the acetate accumulation rate leveled off with time, indicating that acetate was transported by diffusion to the surface where it could be oxidized by O2 and NO3‒ respiration. On the basis of linear regressions of the accumulation of propionate, butyrate, and isobutyrate, it was calculated that these substrates contributed 14, 5, and 8% of the electron donors for sulfate reduction.
Spatial heterogeneity of Daphnia genotypes: Vertical migration and habitat partitioning1
Authors: Weider Lawrence J.
Published: April 2010

Diel vertical migration surveys of a Daphnia pulex population consistently demonstrated significant differences in vertical distribution and migratory activity among electrophoretically distinct genotypes, strongly suggesting a genetic component to vertical migration. These results imply that a population’s pattern of vertical migration can be highly dependent on its genetic composition and that temporal shifts in the overall vertical migration pattern may result from clonal succession as well as from individual clonal variation. Vertical separation of genotypes can also influence the horizontal structure of the population; genotypes residing in deep water become rarer toward the shallow littoral zone.
Ammonium adsorption in marine sediments1
Authors: Mackin James E. , Aller Robert C.
Published: April 2010

One important reaction which affects dissolved NH4+ distributions in marine sediments is reversible adsorption on sediment solids. We investigate both the temperature dependency and spatial variability of the NH4+ linear adsorption coefficient, K, in marine sediments. For a wide range of environments, because of approximately offsetting variations in sediment porosity and properties such as clay mineral and organic matter content, K is nearly constant (1.3 ± 0.1) in terrigenous, surface, marine sediments. The value of K also does not vary significantly as a function of temperature. In biogenic and very high porosity (≳0.95) sediments K may be somewhat lower than for other sedimentary environments. Sediments containing seagrass detritus such as Thalassia may be expected to exhibit relatively high K values.
Utilization of amino acids by planktonic marine bacteria: Importance of clean technique and low substrate additions1,2
Authors: Ferguson Randolph L. , Sunda William G.
Published: April 2010

Rapid turnover of dissolved free amino acids (DFAA) by bacterioplankton in the Gulf of Mexico was observed with techniques designed to eliminate contamination of samples with trace metals and organic compounds. The mean turnover rate of DFAA, based on incorporation of 0.5 nM additions of a mixture of amino acids, was 4.9·d‒1 for high productivity neritic environments and 1.3·d‒1 for low productivity oceanic environments. These rates are faster than those in parallel samples measured by traditional techniques and are consistently faster than previously reported values. Data for multiple level (0.01–7 nM) additions of the mixed substrate were in accord with the Michaelis‐Menten enzyme kinetics model. Kinetic parameters derived from this model (Vmax,Ki + Sn, and R), bacterial cell numbers, and Vmax/cell were highest at photic depths of the neritic zone, intermediate at photic depths of the oceanic zone, and lowest at aphotic depths of the oceanic zone. Estimates of secondary productivity by bacterioplankton (based on Vmax) on an equal water volume basis were 6.6 ± 1.5% (±SE, n = 5) of the light‐saturated primary productivity at the maximum productivity depth. Estimated turnover time of the bacterioplankton community ranged from 2.4 d at 5 m at the highest productivity station to 130 days at 250 m at the lowest productivity station.
Effect of food acclimation on assimilation efficiency of Calanus pacificus1
Authors: Landry M. R. , Hassett R. P. , Fagerness V. , Downs J. , Lorenzen C. J.
Published: April 2010

A technique, based on quantitative conversion of chlorophyll a to pheophorbide during digestion, is described for determination of assimilation efficiencies of particle‐feeding zooplankton. Calanus pacificus had assimilation efficiencies ranging from 68.5 to 85.4% for carbon and 73.9 to 92.5% for nitrogen. Assimilation efficiencies for copepods first acclimated to different food concentrations of Thalassiosira weissflogii and then fed at the same food level varied systematically, with animals acclimated to low food having higher efficiencies than animals acclimated to high food.
Geothermal and cold springs faunas: Inorganic carbon sources affect isotope values
Authors: Rounick J. S. , James M. R.
Published: April 2010

Stable carbon isotope ratios of algae and grazing invertebrates at four hot springs and an alpine cold spring in New Zealand were at the extreme end of the range reported for freshwater organisms. This apparently resulted from the influences of diverse inorganic carbon sources, geothermal carbon and biogenic (respiration) CO2, being incorporated into biomass carbon at the study sites. Despite similar feeding behavior at all sites (algal ingestion), the isotope ratios of the invertebrates varied because of site‐specific biogeochemistry. This further underscores the need to understand inorganic carbon sources and their influences on resulting isotope ratios for future stable carbon isotope work in freshwater environments.
Effects of flow rate on fluorescence in vivo during continuous measurements on Gulf of Mexico surface water1
Authors: Sweet Stephen T. , Guinasso Norman L.
Published: April 2010

The intensity of in vivo fluorescence changed with the rate of sample flow during continuous measurements made in the Gulf of Mexico. Most previous measurements have indicated no relationship between fluorescence intensity and sample flow rate.

The effect was not observed at flow rates between 0 and 250 cm3·min‒1; however, above 500 cm3·min‒1 fluorescence increased promptly when flow rate increased. Residence time of sample in the illuminated zone of the fluorometer ranged from 0.29 s (at 1,500 cm3·min‒1) to 1.7 s (at 250 cm3·min‒1). This flow rate effect implies that phytoplankton fluoresce with an intensity which varies as a function of illumination time. The Kautsky induction effect may provide an explanation for the observed variation.
Combined autoradiography and immunofluorescence for estimation of single cell activity by ammonium‐oxidizing bacteria1,2
Authors: Ward B. B.
Published: April 2010

Immunofluorescence and 14CO2 autoradiography were used for simultaneously enumerating and assaying the autotrophic activity of ammonium‐oxidizing bacteria in seawater. Relative activity (14CO2 assimilation as measured by autoradiography) and abundance were measured in simulated in situ incubations at seven stations in the primary NO2‒ maximum region of the Northeast Pacific Ocean. More than 104 cells· liter were present; relative activity often showed a peak near the surface and an increase in the NO2‒ max region below the photic zone. The method permits assessment of individual cell activity; most cells at all depths were active in CO2 assimilation, usually at low and quite variable levels. There were no differences in relative activity between samples incubated under simulated in situ conditions and in the dark.

Relative activity was positively correlated with the abundance of ammonium‐oxidizing bacteria, temperature, total dark CO2 assimilation (as measured by liquid scintillation counting of replicate samples), and pheopigment concentration, and negatively correlated with oxygen concentration.
An evaluation of freeze fixation as a phytoplankton preservation method for microautoradiography1
Authors: Paerl Hans W.
Published: April 2010

Quantitative microautoradiography of marine and freshwater phytoplankton has been hampered by the fact that chemical techniques used to maintain structural integrity cause leakage of isotopically labeled cell constituents. Furthermore, some chemical preservatives have led to chemography or chemical exposure of autoradiographic emulsions. Chemography, poor preservation of structural integrity, and leakage of cell constituents can all be avoided by quick‐freezing filtered samples in liquid N2 and then freeze‐drying them before autoradiographic preparation. Freeze fixation is superior to commonly used preservatives including ethyl alcohol, formaldehyde, glutaraldehyde, and Lugol’s iodide. Leakage of fixed 14C and 33P and preservation of cell shapes and sizes by these preservation techniques are evaluated in diverse marine and freshwater phytoplankton communities.
A technique for subsampling an abundant taxon while completely sorting other taxa1
Authors: Sherman K. M. , Meeter D. A. , Reidenauer J. A.
Published: April 2010

A method is described which allows an abundant taxon (Nematoda) to be subsampled while rarer taxa are completely sampled. A triply balanced F‐square design is used to choose a quarter of the sorting field for counting the nematodes. The technique showed no evidence of bias in estimating total numbers of nematodes, and a quarter subsample was accurate to within ±0.8% when there were > 200 nematodes in a sample. Estimates of the total number of nematodes in a sample were accurate to within ± 3.2% of their actual values. The technique gave subsamples of abundant nematode species which did not differ significantly from expectation.
Prevention of growth of potentially dense phytoplankton populations by zooplankton grazing, in the presence of zooplanktivorous fish, in a shallow wetland ecosystem
Authors: Timms R. M. , Moss Brian
Published: April 2010

In two linked, shallow, freshwater basins, phytoplankton densities in summer were very different. Hudsons Bay supported a large stand of water lilies, and the adjacent open water was clear with chlorophyll a concentrations generally <10 µg·liter‒1. In contrast, Hoveton Great Broad, which received inflow water from the same very fertile source, the River Bure, had chlorophyll a concentrations > 100 µg·liter‒1. Hudsons Bay water, in bioassays, could support great phytoplankton growth in summer and did so in spring and fall. The period of clear water coincided with the presence of the lily stand. Zooplankton populations were of rotifers and small‐bodied Cladocera in Hoveton Great Broad, but mostly of Cladocera, including large‐bodied individuals of plant‐associated species, in Hudsons Bay. Zooplanktivorous fish were present and there was evidence of feeding by them in both basins. Coexistence with fish of the large, apparently efficiently grazing Cladocera in Hudsons Bay depended on provision of daytime refuges for the Cladocera among the lilies, and grazing was greatest in the adjacent open water at night. Grazing control was helped by a hydrological regime which favored small and rapidly growing phytoplankters, rather than inedible colonial forms with slow growth. Weed‐associated grazers may be important in maintaining the dominance of aquatic plants in shallow lakes which would otherwise more rapidly become dominated by phytoplankton as nutrient loading increased.
Relationships between habitat stability, ionic composition, and the distribution of aquatic invertebrates in the desert regions of Israel
Authors: Herbst G. N. , Bromley H. J.
Published: April 2010

Biological and chemical samples were collected from aquatic habitats in the southern deserts of Israel. A wide range of chemical characteristics was found among sites. Na+ and Cl‒ were the dominant ions in springs and wells, while Ca2+, Mg2+, and HCO3‒ were dominant in rockpools. Greatest species richness was found at intermediate salinities (chlorinity = 1,000 mg·liter‒1; conductivity = 5.00 mS·cm‒1). The relative ionic composition also influences community structure. It is suggested that habitat instability structures the invertebrate community and is a strong selective force for salinity tolerance and euryhalinity.
Temporal and spatial variability of phytoplankton in a subtropical ecosystem1,2
Authors: Bienfang P. K. , Szyper J. P. , Okamoto M. Y. , Noda E. K.
Published: April 2010

Phytoplankton conditions were examined at two stations off the leeward coast of Oahu, Hawaii. Significant temporal variability was observed in the chlorophyll and pheopigment data. Significant temporal and spatial variability was observed in the ATP and productivity data. Most (60–80%) of the microbial biomass occurred in the <3‐µm fraction. Pigment profiles showed distinct subsurface maxima at 90 m. Annual primary production was estimated at 60.4 g C·m‒2·yr‒1, and low nutrient levels and P:B ratios indicated persistent nutrient limitation.

Dissimilar inflection depths for nitrate, phosphate, and silicate indicated nitrate availability and phosphate limitation in the lower photic zone. Production between January and May was 11 × that between May and November; productivity below 44 m accounted for most of this variation. Biological and physical analyses indicate that variations in vertical nutrient supply, related to differences in current shear, caused this temporal variation.
Radium in the Dead Sea: A possible tracer for the duration of meromixis1
Authors: Stiller M. , Chung Y. C.
Published: April 2010

Three profiles of 226Ra in the meromictic Dead Sea measured during 1963–1978 indicate that the radium activities in the upper water mass were higher than in the lower water mass. All three profiles indicate a similar radium inventory. The Jordan inflow is not the primary source of radium to the Dead Sea. Mineral springs and submerged seepages are probably more important contributors.

The age of the meromictic structure is estimated by a model which requires that the radium inventory of the lake be at a steady state, that sometime in the past the radium profile of the lake had been uniform (when either the lake was monomictic or an overturn had ended an earlier meromictic phase) and that the contemporaneous profiles of radium have been built up by inflows of radium solely into the upper water mass, while the monimolimnion is relict, isolated, and loses radium only by radioactive decay. Supporting evidence is presented suggesting that the above conditions may be fulfilled. Thus, it is possible to estimate that the Dead Sea was meromictic for about 300 years before the turnover in 1979.

From tentative balances of the Dead Sea dissolved salts it is shown that a previous overturn might have occurred at a lower lake level than in 1979.
Radon‐222 tracing of sediment‐water chemical transport in an estuarine sediment1
Authors: Gruebel Karen A. , Martens Christopher S.
Published: April 2010

In situ benthic chamber flux measurements and 222Rn deficiency core measurements were made in fine‐grained sediments of the White Oak River estuary during August through October 1980. Benthic chamber flux values ranged from 27 to 60 atoms·ms‒2·s‒1; on a given date triplicate emplacements yielded a range of <30%. Apparent whole sediment diffusivities calculated from the fluxes measured yielded coefficients ranging from 0.35 to 1.6 × 10‒5 cms2·s‒1, within the range expected for control of sediment‐water transport by molecular diffusion. Sampling and analytical problems with accurate radon‐radium disequilibrium measurements in small‐diameter cores appear to compromise their usefulness for studying sediment‐water transport at our site. 222Rn values determined in 17‐cm‐long sectioned cores never reached secular equilibrium activities of 226Ra.
Winter mixing and the vertical stratification of phytoplankton—Another look
Authors: Venrick E. L.
Published: April 2010

A series of samples was collected in order to examine the null hypothesis that phytoplankton species cannot stratify within the oceanic isothermal layer. Analysis of phytoplankton abundance within a 140‐m isothermal layer gave no evidence of vertical stratification. Abundances of many species were strongly nonrandom, but there was no consistency of vertical pattern from one station to the next. The situation is better described in terms of vertical patches than of strata.
The foraging strategy of a subtidal and deep‐sea deposit feeder1
Authors: Nowell Arthur R. M. , Jumars Peter A. , Fauchald Kristian
Published: April 2010

The ampharetid polychaete Amphicteis scaphobranchiata is a marine, surface‐deposit feeder inhabiting cohesive sediments from continental shelf depths off British Columbia to abyssal habitats off southern California. It uses a previously undescribed method of removing fecal pellets from its feeding area via an elastic (Young’s modulus = 7 MN·m‒2), mucous sling fashioned about the modified anterior median branchiae for which the species was named. This sling imparts a force of 4 × 10‒1 Pa, sufficient to yield a maximal pellet velocity of 27 cm·s‒1 and thereby to remove the pellet from the normal radius swept out by the animal’s feeding tentacles. These observations indicate that this sedentary animal’s food supply depends predominantly on the rate of sedimentation into the pit that is produced via its feeding and defecating activities, rather than on the rate of microbial regeneration or production that goes on within its feeding radius.
Evaluation of an ATP photometer for measuring 14C activity
Authors: Cole Brian E.
Published: April 2010

An evaluation was made of the suitability of an ATP photometer for field measurements of phytoplankton 14C activity. Over a wide range of 14C activity the light output recorded by the photometer was linear. The activity of a natural phytoplankton sample can be accurately determined with such an instrument; samples must be allowed to dark‐adapt before analysis.
Seasonal patterns of seston characteristics in Bedford Basin, Nova Scotia, relative to zooplankton feeding: A multivariate approach1
Authors: Mayzaud P. , Taguchi S. , Laval Ph.
Published: April 2010

Seasonal changes of the characteristics of the particulate organic matter from Bedford Basin were studied at four different depths during 15 months. The data (particle counts in Coulter Counter channels, counts of taxonomic categories, and chemical measurements) are best analyzed as multivariate parameters. Principal component analyses show for each depth the groups of channels responsible for the maximum variability; taxonomic categories and chemical measurements projected onto the graphs as “supplementary” items reveal their potential associations with some channels. Correspondence analysis allows a dual analysis of the size spectra and the sampling dates. In the surface waters, size spectra are influenced by biological productivity, whereas at depth the analyses mostly specify the type of sedimenting material. Regardless of depth, the size spectral diversity is associated with particles ranging from 8 to 25.4 µm. They are responsible for most spring production and some summer and fall. production. Several multivariate associations are found (e.g. between flagellates and particles in the 8.0–12.7‐µm size range, diatoms and particles in the 16.0–25.4‐µm size range, dinoflagellates and particles in the 40.3–50.8‐µm size range). Size heterogeneity at depth is related to pulses of sedimenting small and medium size particles, although the particulate standing stock at 30 m consists of large detrital material. The association between microzooplankton and nanoplankton observed at 2.5 and 5 m illustrates a trophic relationship. The grazing pressure by the large population of ciliates limits the growth of small cells, and their distribution, to the surface layer. A summer maximum of ATP without associated chlorophyll is probably related to such feeding activity and to the high growth rate and short division time of protozoans.
Empirical analysis of zooplankton filtering and feeding rates1
Authors: Peters Robert Henry , Downing John A.
Published: April 2010

Multiple regression analysis of published zooplankton filtering and feeding rates yielded separate regression equations for cladocerans, marine calanoid copepods, and all zooplankton. Ingestion rate was found to increase significantly with animal size, food concentration, and temperature. Filtering rate also increased with animal size and temperature, but declined as food concentration increased. The analysis suggests a difference in particle size preference between cladocerans and copepods. Experimental conditions such as crowding and duration also significantly affected filtering and feeding rates. The regression models allow examination of differences and similarities among zooplankton taxa, functional response, particle size selection, energy allocation, and threshold food concentration. The statistical models describe suspension feeding more precisely than either average literature values or verbal descriptions of trend. The results also suggest possible mechanisms of feeding limitation and provide a heuristic framework for the design of experimental analyses of zooplankton feeding in marine and freshwater systems.
The long and short term feeding condition in field‐caught Calanus pacificus, as determined from the lipid content
Authors: Hakanson John L.
Published: April 2010

The wax ester and triglyceride contents of Calanus pacificus were measured as indices of feeding condition. The copepod was reared to copepodite V on 100, 300, and 900 µg C·liter‒1 of the diatom Thalassiosira weissflogii and also subjected to changing food concentrations at the fifth copepodite stage. The resulting lipid content was measured. The naupliar stages did not appear to benefit from a food concentration higher than 100 µg C·liter‒1 although there was an increasing difference in wax ester content after C III among the three food concentrations. The triglyceride content seemed a good indicator of recent feeding, being completely lost after 3 days of starvation. The wax ester content was a good indicator of feeding over a period of a week.

Field samples were collected on six occasions off San Diego, in summer 1982 and spring 1983. At five of the six stations the field‐caught animals were very well fed, having a much higher wax ester content than at 300 µg C·liter‒1 of T. weissflogii in the laboratory. On one occasion the wax ester and triglyceride contents indicated that the field population was more poorly fed. The variability in lipid content was measured at each station.

Data are shown to suggest that quality of food is very important and that Chl a or particulate carbon are poor indicators of food for late stage C. pacificus.
Transport of carbon, nitrogen, phosphorus, and major solutes in the Gambia River, West Africa1
Authors: Lesack Lance F. W. , Hecky Robert E. , Melack John M.
Published: April 2010

Transport of solutes and particulate materials and their variation with discharge were studied for 1 year (July 1980–June 1981) in the Gambia River in the tropical savanna of West Africa. The water is a dilute (flow‐weighted mean total solutes, 40.6 mg·liter‒1) solution of SiO2 and HCO3‒ (75% of total solutes by weight). Na+, K+, Cl‒, and total dissolved nitrogen showed no significant relation with discharge. Ca2+, Mg2+, HCO3+, conductivity, and SO42‒ decreased as discharge increased, while total dissolved phosphorus increased with discharge. After an initial increase SiO2 was independent of discharge. Dissolved organic carbon displayed counterclockwise hysteresis with rising and falling discharge. Particulate phosphorus and total particulate materials displayed clockwise hysteresis. Total transport amounted to 9.66 t·km‒2·yr‒1. The transport rates of both dissolved and particulate organic C are among the lowest ever reported. The low transport of total particulates and solutes is attributed to lack of relief and the lithology of the catchment.
Mixing and the dynamics of the deep chlorophyll maximum in Lake Tahoe1
Authors: Abbott Mark R. , Denman Kenneth L. , Powell Thomas M. , Richerson Peter J. , Richards Robert C. , Goldman Charles R.
Published: April 2010

Chlorophyll‐temperature profiles were measured across Lake Tahoe about every 10 days from April through July 1980. Analysis of the 123 profiles and associated productivity and nutrient data identified three important processes in the formation and dynamics of the deep chlorophyll maximum (DCM): turbulent diffusion, nutrient supply rate, and light availability. Seasonal variation in these three processes resulted in three regimes: a diffusion‐dominated regime with a weak DCM, a variable‐mixing regime with a pronounced, nutrient supply‐dominated DCM, and a stable regime with a deep, moderate light availability‐dominated DCM. The transition between the first two regimes occurred in about 10 days, the transition between the last two more gradually over about 3 weeks. The degree of spatial variability of the DCM was highest in the second regime and lowest in the third. These data indicate that the DCM in Lake Tahoe is constant in neither time nor space.
Direct evidence for the role of light‐mediated gas vesicle collapse in the buoyancy regulation of Anabaena flos‐aquae (cyanobacteria)1
Authors: Oliver R. L. , Walsby A. E.
Published: April 2010

Quantitative measurements were made of the changes in gas vacuole volume and the major components of cell mass (protein and carbohydrate) on cultures of anabaena flos‐aquae which lost buoyancy as they were shifted from low to high light intensity. Assuming densities of 1,300 kg· m‒3 for protein and 1,600 for carbohydrate, we calculated the change in ballast brought about by changes in these components and compared them with ballast changes resulting from gas vacuole collapse. We also compared the calculated excess density of filaments with direct measurements of filament density in gradients of percoll. the results clearly demonstrated that increased density resulted from the loss of gas vacuoles. Small variations in density could be attributed to changes in protein and carbohydrate but these would not have caused a loss of buoyancy in the absence of a decrease in gas vacuole content. Analyses of the type described can be used to determine the cause of buoyancy change in other microorganisms and can be performed on phytoplankton collected from lakes.
Nutrient status of metalimnetic phytoplankton peaks
Authors: Pick F. R. , Lean D. R. S. , Nalewajko C.
Published: April 2010

The nutrient state of the chrysophyte, Chrysosphaerella longispina, forming a large metalimnetic chlorophyll a peak in Jacks Lake, Ontario, was examined over several summers. Turnover times of phosphate were fast in the epilimnion (minutes) but slow (hours) at the depth of the peak. Long turnover times, high concentrations of polyphosphate, low P debt, low Vmax, and high Kt values for phosphorus all indicated that initially the peak was not more P‐deficient than epilimnetic phytoplankton. However, with time it became P‐deficient and this factor coincided with its demise in August. At no time was the peak population N‐deficient. The peak population was not supplied by nutrients from the hypolimnion nor from the mineralization of sedimenting epilimnetic material but instead seemed to have brought cellular reserves of phosphorus when it migrated down from the epilimnion.