bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatiotemporal dynamics of bacterial populations in the anoxic Cariaco Basin
Authors: Lin Xueju , Scranton Mary I. , Chistoserdov Andrei Y. , Varela Ramon , Taylor Gordon T.
Published: November 2010

Distributions of bacterial populations in the anoxic Cariaco Basin were studied over 2 yr (five cruises) at three stations using fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T‐RFLP) of 16S ribosomal ribonucleic acid (rRNA) genes. FISH results demonstrate that the contribution of ɛ‐proteobacterial abundances to total prokaryotic inventories was relatively constant among cruises, and this group was dominant in the redoxcline, accounting for 18% of DAPI (4'6‐diamidino‐2‐phenylindole)‐stained counts on average. In contrast, β‐proteobacteria were more variable. Sulfate reducers, α‐, and γ‐proteobacteria accounted for minor components of the anaerobic microbial communities. T‐RFLP fingerprinting also showed significant temporal shifts in bacterial community composition. The greatest variations in bacterial community structure were evident among oxic, transitional, and anoxic zones, but significant horizontal variations were also evident within redoxclines of three different stations. A statistical analysis of T‐RFLP patterns revealed clear spatiotemporal patterns in bacterial community structure along the redox gradient among sites and over time. Total prokaryotic abundances corresponded well with seasonal variations in organic carbon fluxes above the redoxcline. However, no single measured environmental variable (O2, H2S, S2O32‐, H4SiO4, NO3−, PO43‐, microbial biomass, chemoautotrophic production) explained the temporal oscillations of the dominant bacterial groups. Analyses suggest that redox gradients, terrestrial inputs, and disturbance due to lateral intrusions of adjacent waters could significantly affect bacterial community composition in the Cariaco Basin.
Ammonium regeneration and nitrification rates in the oligotrophic Atlantic Ocean: Implications for new production estimates
Authors: Clark Darren R. , Rees Andrew P. , Joint Ian
Published: November 2010

N regeneration was measured on a transect of the North and South Atlantic, from the United Kingdom to the Falkland Islands, that included extreme oligotrophic conditions. NH4+ and NO{2 oxidation rates were measured from the surface and base of the photic zone at 16 stations, using an isotope dilution technique in conjunction with gas chromatography/mass spectrometry analysis. NH4+ regeneration rates were 10‐160 nmol L−1 d−1, NH4+ oxidation was ~1‐10 nmol L−1 d−1, and NO2− oxidation was 1‐30 nmol L−1 d−1. Outside the oligotrophic central gyres, high rates of NH4+ regeneration were found in the northwest African upwelling region. In the central gyres, nitrification and NH4+ regeneration rates were sufficient to completely replace the dissolved inorganic nitrogen (DIN) pool within 1 d. These high turnover rates of the DIN pool indicate that both NH4+ regeneration and nitrification must be considered when estimating N assimilation rates by the 15N technique. Even in incubations of short duration, N assimilation rates are likely to be underestimated and may introduce error in the estimation of the F‐ratio. In the majority of experiments with near‐surface samples, nitrification could replace the NO3− pool in less than 8 h, suggesting that a substantial majority of the NO3− pool in the surface oligotrophic Atlantic is derived from the regeneration of N. These findings increase the uncertainty of current new production estimates. The combined effect of the errors in estimating N‐assimilation rates without determining N regeneration and the reclassification of NO3− as a regenerated N source in oligotrophic regions may question the accuracy of C export estimations based on F‐ratios.
Regional distributions of nitrogen‐fixing bacteria in the Pacific Ocean
Authors: Church Matthew J. , Björkman Karin M. , Karl David M. , Saito Mak A. , Zehr Jonathan P.
Published: November 2010

We evaluated the regional distributions of six nitrogen (N2)‐fixing bacteria in the North Pacific Ocean using quantitative polymerase chain reaction amplification of planktonic nifH genes. Samples were collected on four oceanographic research cruises between March 2002 and May 2005 that spanned a latitudinal range from 12°S and 54°N between 152°W and 170°W. Samples were collected throughout the upper ocean (<200 m) in the northern regions of the South Pacific Subtropical Gyre (SPSG), equatorial waters, the North Pacific Subtropical Gyre (NPSG), the North Pacific Transitional Zone (NPTZ), and within the Pacific Sub Arctic Gyre (PSAG). There were distinct spatial gradients in concentrations of nutrients, chlorophyll, and the abundances of N2‐fixing bacteria within the various oceanic biomes. In general, nifH‐containing bacteria were most abundant in the midregions of the NPSG (latitudes between ~14°N and 29°N), where unicellular cyanobacterial phylotypes dominated nifH gene abundances. The abundances of all nifH‐containing groups declined within the northern and southern regions of NPSG. Although nifH‐containing groups were detectable in the northern regions of the SPSG, throughout the equatorial waters, and within the NPTZ, gene copy abundances of most groups were lower in these regions than those found the in the NPSG. In the NPSG, surface water abundances of the various nifH phylotypes examined ranged from <50 copies L−1 to ~105 nifH copies LS−1. Overall, the abundances of an uncultivated, presumed unicellular nifH sequence‐type (termed Group A) were the most abundant and widely distributed of the phylotypes examined. Our results indicate that the distributions of N2‐fixing plankton were largely restricted to the subtropical regions of the North and South Pacific Oceans.
Assessing nutrient limitation of Prochlorococcus in the North Pacific subtropical gyre by using an RNA capture method
Authors: Van Mooy Benjamin A. S. , Devol Allan H.
Published: November 2010

It has been hypothesized that the planktonic community of the North Pacific subtropical gyre (NPSG) underwent a "domain shift" in the early 1980s in which phytoplankton of the domain Eukarya were supplanted by phytoplankton of the domain Bacteria, primarily Prochlorococcus. P limitation of eukaryotic phytoplankton was implicated as the causative chemical factor in the domain shift, and we sought to investigate the current nutrient limitation status of Prochlorococcus, now 2 decades since this event. We measured ribonucleic acid (RNA) synthesis rates by NPSG plankton at Station ALOHA in 33PO43‐ tracer incubations and found that RNA synthesis was the single largest biochemical sink for dissolved P, accounting for about half of the total PO43‐ uptake. We also found that NH4+ stimulated RNA synthesis but that PO43‐ did not, which suggested N limitation of plankton growth. We developed a new RNA capture procedure, termed radioisotope‐based tracking of RNA synthesis by hybridization and capture (RIBOTRACE), to measure RNA synthesis rates by Prochlorococcus exclusively. Data from this procedure showed that NH4+ stimulated RNA synthesis by Prochlorococcus and confirmed that Prochlorococcus was N limited and not P limited. Our RIBOTRACE data do not necessarily refute the domain shift hypothesis, but suggest that any critical period of P limitation required for the domain shift must have subsided and given way to the N‐limiting conditions that existed previously.
Major bacterial contribution to the ocean reservoir of detrital organic carbon and nitrogen
Authors: Kaiser Karl , Benner Ronald
Published: November 2010

Bacterial biomarkers (D‐amino acids and muramic acid) were measured in various organic matter size fractions collected in the North Pacific and North Atlantic, and they were used to quantitatively estimate bacterial contributions to particulate and dissolved organic carbon and nitrogen reservoirs. The origins and yields of biomarkers were determined in cultured marine bacteria, and the results indicated that D‐amino acids are derived from numerous macromolecules in addition to peptidoglycan and are not solely from peptidoglycan. Bacterial detritus was a major component of particulate organic matter (POM) and is an important source of submicronsize particles and colloids in the ocean. Peptidoglycan was a substantial component of POM but not of dissolved organic matter (DOM). Compositional differences between POM and DOM primarily reflected the selective incorporation of specific bacterial components into these reservoirs. Autotrophic and heterotrophic bacterial sources were not quantified separately, but the presence of D‐aspartic acid (D‐Asx) and D‐serine (D‐Ser) suggested that heterotrophic sources were substantial. The average reactivity of bacterial organic matter was comparable to that of the bulk organic carbon pool. Bacteria were important sources of labile, semilabile, and refractory dissolved organic carbon. Bacterial organic matter accounted for ~25% of particulate and dissolved organic carbon and ~50% of particulate and dissolved organic nitrogen. These results demonstrate the importance of bacteria in regulating the ocean carbon and nitrogen cycles.
Changes in phosphorus biogeochemistry along an estuarine salinity gradient: The iron conveyer belt
Authors: Jordan Thomas E. , Cornwell Jeffrey C. , Boynton Walter R. , Anderson Jon T.
Published: November 2010

We used sequential extractions to quantify different forms of particulate phosphorus (PP) in sediments along the salinity gradient of the Patuxent River estuary. About 50‐90% of the PP was phosphate bound to iron oxides (Fe‐P), and 8‐30% was organic P (org‐P). Loosely sorbed phosphate (sorb‐P), detrital apatite, and authigenic plus biogenic apatite each made up <10% of the PP. Suspended sediments from the watershed and deposited sediments in tidal freshwater had the highest concentrations of Fe‐P, ranging about 30‐55 µmol g−1 sediment. As pore‐water salinity increased to 7 along the estuarine gradient, Fe‐P declined to 15‐25 µmol g−1, org‐P increased from 4 to 10 µmol g−1, sorb‐P increased from 0.5 to 2.5 µmol g−1, and total sediment PP declined from 60 to 40 µmol g−1. Concentrations of pore‐water solutes also changed with salinity. As salinity increased, dissolved Fe and ammonium decreased, while dissolved phosphate increased. Near the freshwater end of the gradient, the molar ratio of pore‐water ammonium : phosphate was generally >16 (the Redfield ratio) and ranged up to >700, while at the saline end of the gradient the ratio was generally <16 and ranged down to <1.5. Our observations are consistent with the hypothesis that phosphate is released from terrigenous sediments when they are deposited in saline portions of the estuary where sulfide may enhance dissolution of Fe‐P and form Fe sulfide precipitates. Such phosphate release may contribute to the generally observed switch from phosphorus limitation in freshwater to nitrogen limitation in coastal marine water.
Relative independence of organic carbon transport and processing in a large temperate river: The Hudson River as both pipe and reactor
Authors: del Giorgio Paul A. , Pace Michael L.
Published: November 2010

Bacterial respiration (BR) of organic matter is an important flux in the carbon budgets of large rivers, yet the regulation of BR and the relationship of this respiration to various organic matter sources is poorly understood. Using detailed spatial transects, we evaluated transport and consumption of dissolved organic matter in the Hudson River estuary, and compared both with BR. Dissolved organic carbon (DOC) concentration, long‐term DOC lability, and in situ BR were measured at 24 stations on each of five transects. DOC lability, measured in long‐term bioassays, averaged 15 µg L−1 d−1 and was similar to the average net rate of decline of DOC from the upper to lower estuary. BR averaged 156 µg L−1 d−1 C, far exceeding the net downriver DOC decline and measured DOC lability. BR was well predicted by a model that included seston, chlorophyll, and DOC consumption. Rate coefficients derived from this model indicate that BR is primarily supported by carbon derived from seston and chlorophyll. Changes in DOC concentration along the Hudson flow path were well predicted from a combination of freshwater input, DOC concentration in the headwaters, and long‐term DOC lability. Although most of the total respiration is due to free‐living bacteria and thus mediated by DOC, <20% of this respiration is actually supported by DOC loaded in the headwaters, and transported downstream. The Hudson River, therefore, acts as a pipe transporting dissolved terrestrial organic matter seaward while also functioning as a reactor where intense bacterial activity degrades organic matter associated primarily with particles or generated locally.
Copepod reproduction is unaffected by diatom aldehydes or lipid composition
Authors: Dutz Jörg , Koski Marja , Jínasdí ttir Sigrún H.
Published: November 2010

We investigated whether reduced reproductive success of copepods fed with diatoms was related to nutritional imbalances with regard to essential lipids or to the production of inhibitory aldehydes. In 10‐d laboratory experiments, feeding, egg production, egg hatching success, and fecal pellet production of Temora longicornis were measured for six different diatom species as well as for a nondiatom control diet (Rhodomonas sp.). The experiments were accompanied by determinations of fatty acids, sterols, and polyunsaturated aldehydes (PUA) in the food. Although diatoms were generally ingested at high rates, they yielded a variable egg production response in copepods, ranging from high egg production in four species (two strains of Thalassiosira rotula, Chaetoceros affinis, and Thalassiosira weissflogii) to low egg production in two species (Leptocylindricus danicus and Skeletonema costatum). Egg hatching rates decreased after 4 d in all diatom treatments, irrespective of the egg production rate and without any relationship to diatom aldehyde production. Similarly, no evidence was found that diatoms are per se nutritionally inferior to nondiatom food. The lack of a distinct mechanism for the observed inhibitory activity of diatoms suggests that the cause(s) might be more complex. We suggest, as one possible explanation, that hatching‐specific nutritional deficiencies might be induced by incomplete digestion following from the low gut passage time of diatoms, as indicated by a strong correlation between egg viability and fecal pellet production.
The cryptic origins of environment‐indicating phantom midges (Chaoborus)
Authors: Dupuis Derrick D , Svensson Jan-Erik , Taylor Derek J.
Published: November 2010

Fragile freshwater ecosystems have acted as important sentinels for global environmental change. A detailed understanding of the implications of global change in aquatic ecosystems relies on indicator species whose body parts are preserved in aquatic sediments for millennia. The phantom midge, Chaoborus flavicans (Meigen, 1830), for example, has well‐preserved mandibles in aquatic sediments and may act as an indicator of boreal zone temperatures, lake depth, and the presence of fish. Nevertheless, we report that Chaoborus with C. flavicans‐type mandibles are common in fishless tundra ponds above the tree line in western Alaska. We carried out genetic comparisons of nuclear and mitochondrial deoxyribonucleic acid (mtDNA) sequences in Chaoborus at a Holarctic scale to determine the origins of the Alaskan “C. flavicans”. Nuclear DNA, mtDNA, and morphological results indicated that the Alaskan C. flavicans represents a unique lineage of Chaoborus. The average mtDNA divergence (Kimura’s two‐parameter) between the Palearctic C. flavicans and the Alaskan C. flavicans was >17%. mtDNA strongly supported Chaoborus crystallinus (De Geer, 1776) as the sister species to the Alaskan C. flavicans. Our present understanding of larval mandible morphology disagrees with the major ecological properties and evolutionary lineages of Chaoborus. We identify a new mandible character and highlight the value of validating the diagnostic morphologies of environmental indicator species with genetic studies.
Stoichiometric regulation of carbon and phosphorus in P‐deficient Daphnia magna
Authors: He Xuejia , Wang Wen-Xiong
Published: November 2010

Daphnia magna were fed phosphorus‐sufficient (+P) and P‐deficient (2P) green algae Chlamydomonas reinhardtii (carbon : phosphorus ratio of C: P = 90 and 930 in molar, respectively) for 5 d to produce different body C: P ratios. The dietary absorption as well as the elimination of body C and P were then quantified under contrasting dietary qualities (+P and 2P). The 2P animals fed with 2P algae had a higher absorption efficiency (AE) of both C (46%) and P (52%) than the control (+P animals fed +P algae) and the recovery group (2P animals fed +P food). During the physiological efflux, the 2P animals fed with 2P diet eliminated their body C at the highest rate (0.41 d−1) and their body P at the lowest rate (0.10 d21) among the three groups of animals. Mass‐specific C loss rates through dissolved release, respiration, and molting increased significantly, and the mass‐specific P loss through dissolved release, molting, and reproduction decreased in the 2P animals compared with the +P animals, in agreement with the stoichiometric models. Consequently, the C: P ratio of dissolved release, molting, and reproduction all increased with the increase in P deficiency. The recovered Daphnia had medium values of AE, efflux rate constant, and mass‐specific loss rates, indicating the reversibility of P limitation. Our study demonstrated that all the pathways (excretion, reproduction, molting, and respiration) may be involved in the stoichiometric regulation in Daphnia.
Some thoughts on the concept of colimitation: Three definitions and the importance of bioavailability
Authors: Saito Mak A. , Goepfert Tyler J. , Ritt Jason T.
Published: November 2010

We discuss the concept of colimitation of primary productivity in aquatic environments, with an emphasis on reconciling this concept with recent advances in marine bioinorganic chemistry. Colimitations are divided into three categories on the basis of their mathematical formulations and visualizations: type I, independent nutrient colimitation (e.g., N and P); type II, biochemical substitution colimitation (e.g., Co and Zn); and type III, biochemically dependent colimitation (e.g., Zn and C), where the ability to acquire one nutrient is dependent upon sufficient supply of another. The potential for colimitation occurring in the marine environment and the critical importance of understanding nutrient bioavailability are discussed.
Physiological steady state of phytoplankton in the field? An example based on pigment profile of Emiliania huxleyi (Haptophyta) during a light shift
Authors: Leonardos Nikos
Published: November 2010

A calcifying strain of Emiliania huxleyi was used to study the photoacclimation process during a shift from low (LL) to high (HL) photon flux density (PFD) under nutrient‐replete and pH‐ and [CO2]‐controlled continuous cultures. Physiological steady states were obtained after culturing the alga in each PFD for more than a month, and pigment profiles and cell volume changes were monitored for 25 d after the light shift. Fucoxanthin was the major carotenoid in LL, while under HL this role was assumed by 19'hexanoyloxyfucoxanthin (19Hex). The photoprotective pigments diadinoxanthin and diatoxanthin (Dd+Dt), normalized to chlorophyll a (Chl a), increased with increasing PFD, while Chl a content per cell and Chl c's and fucoxanthin, normalized to Chl a, decreased with increasing PFD. The sum of all carotenoids normalized to Chl a and the 19Hex+Fuco : Chl c ratio were remarkably constant from LL to HL conditions. The results confirm that the total amount of carotenoids was synthesized/catabolized in tandem with Chl a to a genetically predefined level independent of PFD. When normalized to a per cell basis, Chl a content reached the long‐term HL steady state after 17‐20 d, while Chl c, Fuco, and Dd+Dt, normalized to Chl a, reached the long‐term HL steady state after 5‐7 d. Growth rate adjustment was completed within 3 d after the transition to HL. When Chl a was normalized to cellular volume, the transition to a fully acclimated HL state was complete within 3 d. The results highlight the need for the critical evaluation of the normalization "currency" (i.e., cell number, volume, Chl a) to which mass is expressed during the photoacclimation process and suggest that natural phytoplankton populations are unlikely to ever be in true physiological steady state.
The biogeochemistry of tropical lakes: A case study from Lake Matano, Indonesia
Authors: Crowe Sean A. , O’Neill Andrew H. , Katsev Sergei , Hehanussa Peter , Haffner G. Douglas , Sundby Bjørn , Mucci Alfonso , Fowle David A.
Published: November 2010

We examined the chemical composition of the water column of Lake Matano, Sulawesi Island, Indonesia, to document how the high abundances of Fe (hydr)oxides in tropical soils and minimal seasonal temperature variability affect biogeochemical cycling in lakes. Lake Matano exhibits weak thermal stratification, yet a persistent pycnocline separates an oxic epilimnion from anoxic meta‐ and hypolimnions. The concentration of soluble P in the epilimnetic waters is very low and can be attributed to scavenging by Fe (hydr)oxides. Chromium concentrations in the epilimnion are high (up to 180 nmol L−1), but below U.S. Environmental Protection Agency guidelines for aquatic ecosystems. The concentration of chromium decreases sharply across the oxic‐anoxic boundary, revealing that the hypolimnion is a sink for Cr. Flux calculations using a one‐dimensional transportreaction model for the water column fail to satisfy mass balance requirements and indicate that sediment transport and diagenesis play an important role in the exchange of Fe, Mn, P, and Cr between the epilimnion and hypolimnion. Exchange of water between the epilimnion and hypolimnion is slow and on a time scale similar to temperate meromictic lakes. This limits recycling of P and N to the epilimnion and removal of Cr to the hypolimnion, both of which likely restrict primary production in the epilimnion. Owing to the slow exchange, steep concentration gradients in Fe and Mn species develop in the metalimnion. These concentration gradients are conducive to the proliferation of chemoautotrophic and anoxygenic phototrophic microbial communities, which may contribute a significant fraction to the total primary production in the lake.
Internal wave effects on photosynthesis: Experiments, theory, and modeling
Authors: Evans Mary Anne , MacIntyre Sally , Kling George W.
Published: November 2010

Using field experiments and mathematical models, we tested whether internal waves enhance photosynthesis as they move phytoplankton through a nonlinear light field in situations where photosynthesis is light limited. Phytoplankton circulated at depths mimicking isotherm displacement for moderate wind speeds had elevated photosynthetic rates compared to static incubations. Experiments and modeling revealed that surface light variation due to cloud cover interacts strongly with the effects of internal waves and may have positive or negative effects on photosynthesis depending on the relative phase of internal wave displacement and light variation. The combined effects of internal waves and fluctuations in surface irradiance ranged from a 15% reduction up to a 200% enhancement. The distribution (sine wave vs. Gaussian) of the vertical displacement of internal waves is also important in determining the internal wave effect on photosynthesis. Internal waves in a wide variety of aquatic systems and with hourly to weekly periods show a strong potential for internal wave‐induced enhancement of photosynthesis. The realization of this enhancement is dependent on characteristics of the internal waves, of algal photosynthetic response, and of variable surface light.
Wind‐shear‐generated high‐frequency internal waves as precursors to mixing in a stratified lake
Authors: Gómez-Giraldo Andrés , Imberger Jörg , Antenucci Jason P. , Yeates Peter S.
Published: November 2010

Field data were used to estimate the wavelength, phase speed, direction of propagation, frequency, and the vertical structure of high‐frequency internal waves observed on the crests of basin‐scale waves of Lake Kinneret during periods of strong wind. Shear stability analysis indicates that these waves were generated by shear in the surface mixing layer. The characteristics of the high‐frequency internal waves changed within a wind event as the result of the evolution of the background flow conditions following the deepening of the surface layer and the propagation of the basin‐scale internal waves. When the background conditions were appropriate, the vertical structure of the unstable mode was such that the perturbations generated visible sinuous internal waves that in turn modified the density profile in the metalimnion in such a way that secondary shear instabilities were triggered. The high‐frequency internal waves were observed over larger distances, but poor coherence in temperature records from stations 200 m apart indicated that individual high‐frequency internal waves were dissipated locally; these waves are thus a local mechanism allowing energy to be drawn from the energized surface layer and transported to the metalimnion, where it sustains turbulence. Part of the energy extracted from the surface layer was also returned to the mean flow in the metalimnion; high‐frequency internal waves are therefore also a source of momentum for the metalimnetic currents. The vertical excursions of the waves also indicate that they could potentially play a role in phytoplankton growth by significantly altering the light regime at relatively high frequencies.
Optical scattering properties of phytoplankton: Measurements and comparison of various species at scattering angles between 1° and 170°
Authors: Zugger Michael E. , Messmer Alicia , Kane Timothy J. , Prentice Jennifer , Concannon Brian , Laux Alan , Mullen Linda
Published: November 2010

We describe the results of a laboratory scattering experiment performed to investigate differences in the optical scattering properties between five common phytoplankton species (Dunaliella tertiolecta, Isochrysis galbana, Nanochloropsis, Skeletonema costatum, and Thalassiosira weissflogii). Data sets were taken at scattering angles 1° to 170° at incident polarizations parallel and perpendicular to the scattering plane. Differences between the species were especially apparent in the slopes at near‐forward (1°‐10°) angles and the enhanced scattering at nearbackward (150°‐165°) angles. There were also notable differences observed between the depolarization ratios, especially at scattering angles between 70° and 110°. The data are shown to be not only helpful in differentiating several species from each other, but also in separating the phytoplankton from bubble/hydrosol contributions to the ocean's inherent optical properties. The results presented here motivate the development of in situ large‐angle polarimetric scatterometers and associated retrieval algorithms.
Emulsions versus micelles in the digestion of lipids by benthic invertebrates
Authors: Voparil Ian M. , Mayer Lawrence M. , Jumars Peter A.
Published: November 2010

Lipids can be valuable sources of energy and nutrition for organisms, but their assimilation into organisms is hampered by the difficulty of transporting these hydrophobic compounds through water. In the digestive tract of metazoans, extracellular digestion of lipids requires transport of insoluble materials from the zone of digestion to the site of absorption, which is facilitated by formation of lipid aggregates in the form of micelles or emulsions. We examined the use of these two transport modes in benthic invertebrate animals via experiments and cross‐phyletic characteristics of gut fluids. We examined seven benthic species for emulsions versus micelles. An obligate carnivore used emulsions (most droplet diameters were 1‐20 µm), whereas deposit feeders used much smaller micelles, and a suspension feeder used neither. We tested two possible forcing factors for this trend. First, we found emulsions but not micelles to be subject to straining by sediment—a filtration process that reduces permeability to colloidal materials. Second, we varied the ratio of gut fluid to food concentration. High ratios, found with dilute food conditions characteristic of deposit feeding, favored micelles, and low ratios favored emulsions. Both of these findings are consistent with the cross‐phyletic results.
Cooling lakes while the world warms: Effects of forest regrowth and increased dissolved organic matter on the thermal regime of a temperate, urban lake
Authors: Andrew J. Tanentzap , Norman D. Yan , Keller Bill , Girard Robert , Heneberry Jocelyne , Gunn John M. , Hamilton David P. , Taylor Peter A.
Published: November 2010

Depending on the magnitudes and directions of changes in air temperatures, winds, and underwater light attenuation, lakes may either warm or cool. Here we report a 28‐yr decrease in the whole‐lake average temperature of Clearwater Lake, Canada, despite regional signatures of climate warming. Using a one‐dimensional lake mixing model, we demonstrate that this pattern was attributable to a 35% reduction in surface wind speeds, itself explained by forest regrowth following local SO2 emission reductions and tree planting, and a 10‐fold increase in dissolved organic carbon concentrations causing a substantial increase in vertical light attenuation following deacidification of the lake. Long‐term trends in lake temperatures do not necessarily follow those of air temperatures. The Clearwater Lake data demonstrate that any factors that influence local wind speeds and underwater light attenuation should be considered as modifiers of the effects of climate warming on lake thermal regimes.
The interactive effects of calcium concentration and temperature on the survival and reproduction of Daphnia pulex at high and low food concentrations
Authors: Ashforth Dawn , Yan Norman D.
Published: November 2010

We reared Daphnia pulex in a fully defined medium at seven calcium (Ca) concentrations (0.1, 0.5, 1, 1.5, 2, 5, and 10 mg Ca L−1), two mixed algal densities (high food: 30 mg chlorophyll a L−1 and low food: 3 mg Chl a L−1), and four temperatures (20ºC, 24ºC, 28ºC, and 32ºC) in a fully factorial design. The minimum Ca concentration required for the survival and reproduction of D. pulex was between 0.1 and 0.5 mg Ca L−1. Daphniids reared at 0.1 mg Ca L−1 lived no longer than 10 d and did not reproduce. Although offspring were produced at 0.5 mg Ca L−1 and above, reproduction was reduced below 1.5 mg Ca L−1 due to delays in maturity and reductions in both the brood size and number of broods produced within the 15 d of the experiment. As a result, the intrinsic rate of natural increase, r, decreased dramatically between 1.5 and 1 mg Ca L−1, and was undefined at 0.1 mg Ca L−1. Higher temperatures and reduced algal biomass enhanced the susceptibility of D. pulex to low Ca concentrations by raising the reproductive threshold to 1.5 mg Ca L−1. Thermal stress at 32ºC was so great that daphniids lived no longer than 5 d and did not reproduce. Hence, r was undefined at 32ºC. In order to sustain D. pulex populations and potentially other Ca‐sensitive daphniids, fresh waters must maintain a Ca concentration of at least 0.5 mg Ca L−1, although concentrations as high as 1.5 mg Ca L−1 may be required for daphniids to withstand the concurrent reductions in algal biomass and rising water temperatures that are now commonplace on the south‐central Canadian Shield.
Heterospecific mating and partial prezygotic reproductive isolation in the planktonic marine copepods Centropages typicus and Centropages hamatus
Authors: Goetze Erica
Published: November 2010

Using three‐dimensional (3D) video observations in laboratory experiments, I describe interspecific and intergeneric mating behaviors and motility patterns of the common planktonic marine copepods Centropages typicus, Centropages hamatus, and Temora longicornis. These observations are then used to estimate heterospecific and conspecific male mate‐search volume rates and mate encounter rates in North Sea Centropages populations. Behavioral prezygotic reproductive isolation between Centropages species is incomplete, since males of each species pursued, contacted, captured, and, in rare cases, placed a spermatophore on the urosome of heterospecific females. T. longicornis males also detected the diffusible pheromone trail and pursued C. typicus females to the point of mate contact. Male mate‐search tracking behavior was equally effective on diffusible pheromone trails of heterospecific and conspecific females, indicating that pheromone and hydromechanical precontact mating cues lack species specificity. Males attempted mating with both heterospecific and conspecific females at high frequencies in the laboratory, and species recognition is inferred to occur through contact chemosensory cues or morphological incompatibility between species. Heterospecific mate encounter rates in the North Sea were maximal in late summer (August), up to~2,000 encounters m−3 d−1, and were comparable in magnitude to conspecific encounter rates during the same period. C. typicus females experience the highest incidence of heterospecific mating interactions, since they encounter heterospecific males at rates up to 100+ encounters female−1 d−1, ca. one order of magnitude higher than encounter rates with conspecifics. Heterospecific mating attempts may be a common feature of the reproductive ecology of planktonic copepods and may incur substantial fitness costs to the individuals involved.
Nutritional constraints at the cyanobacteria—Daphnia magna interface: The role of sterols
Authors: Martin-Creuzburg Dominik , von Elert Eric , Hoffmann Klaus H.
Published: November 2010

In past decades, a considerable amount of research has been conducted to elucidate the factors that affect the carbon transfer across the cyanobacteria‐Daphnia interface. It is well accepted that cyanobacteria are a nutritionally inadequate food source for cladocerans, but the underlying mechanisms are still controversial. Morphological properties, toxicity, and the absence of essential lipids, i.e., polyunsaturated fatty acids (PUFAs) and sterols, are discussed as the most important factors that account for this nutritional inadequacy. Here, we conducted standardized growth experiments with the herbivore Daphnia magna feeding on coccal, filamentous, and putatively toxic cyanobacterial strains comprising the genera Synechococcus, Anabaena, Aphanizomenon, and Microcystis and on a cyanobacterial mixture containing strains of these genera. The relative importance of PUFAs and sterols in determining the food quality of cyanobacteria for Daphnia was assessed by supplementation of eicosapentaenoic acid‐ and/or cholesterol‐containing liposomes to the cyanobacterial carbon. We provide evidence that somatic growth of daphnids on coccal as well as on filamentous cyanobacteria is primarily constrained by the absence of sterols, provided that the cyanobacterial carbon is readily ingested and nontoxic. The absence of PUFAs in cyanobacteria appears to be of minor importance for somatic growth but potentially affects egg production in Daphnia. Thus, the absence of sterols has to be considered a major food‐quality constraint that potentially affects the efficiency of carbon transfer across the cyanobacteria‐Daphnia interface.
Differential grazer‐mediated effects of high summer temperatures on pico‐ and nanoplankton communities
Authors: Weitere Markus , Dahlmann Johanna , Viergutz Carsten , Arndt Hartmut
Published: November 2010

We investigated the role of a macrograzer (the filter feeding mussel Dreissena polymorpha) in mediating effects of high summer temperatures on the dominant components of natural river plankton (i.e., bacteria, algae, and heterotrophic flagellates) in flow channel experiments. Effects of adaptation (by comparing mussels from a southern and a northern population) and thermal acclimation of the mussels were considered. Both heterotrophic flagellates and algae are released from grazing pressure and increase in abundance at temperatures above 20°C. Bacterial abundance, however, decreased with increasing temperature, suggesting a trophic cascade (mussel‐flagellates‐bacteria) that is altered by the temperature response of the mussel ingestion rate. Warm acclimation of the mussels did not change the outcome of the experiments. The dreissenids from the southern population showed a significantly higher ingestion rate than those from the northern population only in July. The general pattern (i.e., decreasing ingestion rates at high temperatures) was found in both populations. Microbial communities controlled by macrofauna can experience substantial changes in warm summers because of differential development of direct and indirect grazing effects with increasing temperature.
Acclimation to elevated carbon dioxide and ultraviolet radiation in the diatom Thalassiosira pseudonana: Effects on growth, photosynthesis, and spectral sensitivity of photoinhibition
Authors: Sobrino Cristina , Ward Mary Love , Neale Patrick J.
Published: November 2010

We studied the effects of elevated CO2 concentrations (0.03% vs. 0.1%) on light absorption, membrane permeability, growth, and carbon fixation under photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) exposures in the diatom Thalassiosira pseudonana. Susceptibility of photosynthesis to UVR was estimated using biological weighting functions (BWFs) for the inhibition of photosynthesis and a model that predicts primary productivity under PAR and UVR exposures. Elevated CO2 concentrations reduced chlorophyll content and increased chlorophyll specific cross section, carbon fixation per chlorophyll, and growth rates. In addition, cells acclimated to high CO2 were more sensitive to photoinhibitory UVR than those under atmospheric levels. Sensitivity to UVR was also related to the growth light regime; despite the fact that no UVR effects were observed on growth, light absorption, or carbon fixation, cells pre‐exposed to UVR showed reduced photoinhibition compared to those grown under PAR for both normal and elevated CO2 cultures. Thus, acclimation to UVR partially counteracted the increased susceptibility observed under elevated CO2 conditions.
Dissolved organic nitrogen uptake by seagrasses
Authors: Vonk Jan Arie , Middelburg Jack J. , Stapel Johan , Bouma Tjeerd J.
Published: November 2010

We examined the ability of seagrasses to take up dissolved organic nitrogen (DON) with leaves (in situ) and roots (laboratory) in an oligotrophic tropical offshore meadow in Indonesia using 15N‐labeled nitrogen (N) substrates. We compared the uptake of urea and amino acids with that of ammonium (NH4+) and nitrate (NO3−) and determined uptake kinetics of amino acids for the seagrasses Thalassia hemprichii, Halodule uninervis, and Cymodocea rotundata in comparison with the macroalgae Sargassum sp. and Padina sp. Uptake rates of small DON substrates for macroalgae were higher than those for seagrass leaves for all N substrates, but the seagrass roots also had a considerable uptake capacity. Seagrass leaves preferred urea, NH4+, and NO3− over amino acids, and there were differences between species. Seagrass roots, however, took up amino acids at rates comparable to NH4+, whereas uptake rates of urea and NO3− were much lower. The ability to take up DON enables seagrasses and macroalgae to shortcut N cycling and gives them access to additional N resources. In oligotrophic environments, uptake of amino acids by roots may provide seagrasses with a competitive advantage over macroalgae.
Identifying four phytoplankton functional types from space: An ecological approach
Authors: Raitsos Dionysios E. , Lavender Samantha J. , Maravelias Christos D. , Haralabous John , Richardson Anthony J. , Reid Philip C.
Published: November 2010

Deriving maps of phytoplankton taxa based on remote sensing data using bio‐optical properties of phytoplankton alone is challenging. A more holistic approach was developed using artificial neural networks, incorporating ecological and geographical knowledge together with ocean color, bio‐optical characteristics, and remotely sensed physical parameters. Results show that the combined remote sensing approach could discriminate four major phytoplankton functional types (diatoms, dinoflagellates, coccolithophores, and silicoflagellates) with an accuracy of more than 70%. Models indicate that the most important information for phytoplankton functional type discrimination is spatio‐temporal information and sea surface temperature. This approach can supply data for large‐scale maps of predicted phytoplankton functional types, and an example is shown.
Tracking carbon flow in a 2‐week‐old and 6‐week‐old stream biofilm food web
Authors: Augspurger Clemens , Gleixner Gerd , Kramer Christiane , KÜsel Kirsten
Published: November 2010

We studied the carbon flow of an allochthonous carbon source (sucrose) in a biofilm food web using stable isotope analysis and lipid biomarkers. Initial biofilms were grown for 2 weeks in a third order stream in Thuringia, Germany, and then incubated in replicate flow channels in climate‐controlled chambers. Either of two sucrose types, differing in their δ13C values, was added either immediately (2‐week‐old biofilm) or after a preincubation of 4 weeks (6‐week‐old biofilm). Although sucrose decrease rates were similar with both biofilms, 2‐week‐old biofilms showed a higher carbon uptake capacity cell−1. The 2‐week‐old biofilm was characterized by low abundances of all trophic levels, which increased one to two orders of magnitude during sucrose consumption. The 6‐week‐old biofilm had higher abundances. Biofilm bacteria incorporated added sucrose carbon, but algae showed no significant carbon incorporation, although a part of this carbon should be mineralized to carbon dioxide by bacteria. Sucrose carbon was also incorporated into ciliates and possibly other protozoans. Grazing rates indicated that up to 23.3% of the sucrose carbon reached higher trophic levels in 2‐week‐old biofilms. Less sucrose carbon was transferred to higher trophic levels in 6‐week‐old biofilms, where similar carbon amounts might have been channelled via filter feeding from the water column to ciliates. Ciliate community composition seemed to be affected by highly abundant rotifers. Whereas total carbon flow in 2‐week‐old biofilms was controlled by bacteria capable of high carbon uptake rates, higher trophic levels were more important in 6‐week‐old biofilms.
Episodic high intensity mixing events in a subterranean estuary: Effects of tropical cyclones
Authors: Smith Christopher G. , Cable Jaye E. , .Martin Jonathan B
Published: November 2010

Hydrostatic balances between fresh and saline groundwater and saline surface water control the physical and chemical framework of subterranean estuaries, but they are responsive to high frequency (waves and tides), low frequency (seasonal recharge patterns), and episodic (storm) events. In this study, we document a salinity and pressure perturbation to the subterranean estuary in east‐central Florida during and after the passage of Tropical Storm Tammy on 04 Oct 2005–05 Oct 2005 and Hurricane Wilma on 24 Oct 2005. These storms reversed hydraulic gradients, forced lagoon water into the aquifer, and shifted the outflow face landward. Salinity at 1.5 m and 2.5 m below a common datum converged on similar values intermediate between fresh and lagoon water salinities. The outflow face reestablished pre‐storm conditions after 80 days at 15 m offshore, but more than 160 days at 30 m offshore, confirming that both the flow field and fluid sources control the position of the subterranean estuary. Episodic, high intensity events could influence the biogeochemical setting of the subterranean estuary and the overlying water body by altering redox conditions in the subterranean estuary during the landward migration of the dispersive mixing zone, increasing short‐term discharge of potentially contaminated groundwater, and/or changing pore fluid residence time within the seepage face and along the mixing zone‐seepage face front.
Disturbance gradients on inshore and offshore coral reefs caused by a severe tropical cyclone
Authors: Fabricius Katharina E. , De'ath Glenn , Puotinen Marji Lee , Done Terry , Cooper Timothy F. , Burgess Scott C.
Published: November 2010

Tropical storms (cyclones, hurricanes, or typhoons) are the most severe form of mechanical disturbance of coral reefs. In 2005, severe tropical cyclone Ingrid crossed the far northern Great Barrier Reef, a region that had not been affected by a major disturbance for several decades, and where benthic data had been collected before the cyclone crossed. This storm provided a unique opportunity to improve understanding of the extent and type of damage inflicted on inshore and offshore coral reefs along a gradient of wind speeds. Modeled maximum wind speeds ranged from 46 m s−1 (equivalent to category 4) near the path to 22 m s−1 (category 1) ~70 km to either side of the path. Surveys of 82 sites on 32 reefs along the wind gradient showed that the types and intensity of disturbance were well explained by local maximum wind speed, and by spatial and biotic factors. While offshore reefs had the deepest depth of damage, inshore reefs had the greatest rates of coral breakage and dislodgement. On a severely affected inshore reef, hard coral cover decreased about 800%, taxonomic richness decreased 250%, the density of coral recruits decreased by 30%, while massive coral cover remained unaltered. Maximum winds <28 m s−1 for <12 h inflicted only minor damage on any reef, but winds >33 m s−1 and >40 m s−1 caused catastrophic damage on inshore and offshore reefs, respectively. Observations from this cyclone were used to predict potential changes in storm‐related coral loss under altered cyclone‐intensity scenarios.
Electron budgets for the hypolimnion of a recovering urban lake, 1989‐2004: Response to changes in organic carbon deposition and availability of electron acceptors
Authors: Matthews David A. , Effler Steven W. , Driscoll Charles T. , O'Donnell Susan M. , Matthews Carol M.
Published: November 2010

Hypolimnetic electron budgets were developed for sulfate‐rich, eutrophic Onondaga Lake, New York, for the summer stratification periods of 16 years (1989–2004) to describe seasonal, long‐term, and interannual changes in hypolimnetic metabolism. A mass balance approach was applied to the hypolimnion to estimate the consumption of electron acceptors (e.g., O2, NO3− and production of reduced by‐products (e.g., H2S, CH4) associated with the decomposition of organic matter. The stoichiometry of the associated redox reactions supported calculation of electron transfer in the hypolimnion and partitioning of the contributions of various metabolic pathways. In 12 of the 16 study years SO42‐ reduction was the most important decomposition pathway, accounting for an average of 44% of the electron transfer in the hypolimnion. Aerobic decomposition (28%), methanogenesis (19%), and denitrification (9%) were also quantitatively important mineralization processes. The relative importance of the various decomposition pathways to overall hypolimnetic metabolism varied widely in response to an abrupt decrease in organic carbon deposition in 1987, incomplete spring turnover in 1993, and improved nitrification treatment at a contributing wastewater treatment facility in 2004. Changes in the importance of the different decomposition pathways were generally consistent with the thermodynamic constraints that regulate the spatial and temporal patterns of redox processes in aquatic sediments. On average, the discrepancy between observed dissolved inorganic carbon accumulation and that calculated from the four redox pathways was 14%; potential causes for this discrepancy include storage of reduced forms of particulate organic carbon and metabolic byproducts in the sediment.