bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐resolution remote sensing of intertidal ecosystems: A low‐cost technique to link scale‐dependent patterns and processes
Authors: Guichard Frédéric , Bourget Edwin , Agnard Jean‐Paul
Published: June 2010

Linking experimentally tested local processes to natural patterns in intertidal ecosystems requires data‐acquisition techniques that provide spatiotemporal data from the scale of local processes to the scale of patterns. We developed a low‐cost, high‐resolution remote‐sensing technique based on the use of a 6‐m helium‐inflated blimp, a standard 35‐mm camera, and photogrammetric numerical tools in order to acquire high‐resolution data of environmental (i.e.,\ topographic) and biological (i.e., algal biomass) variables over intertidal landscapes. The camera was calibrated for photogrammetric analysis, and overlapping color aerial photographs were taken at an altitude of 80 and 50 m. We performed stereo analysis of digitized images and numeric topographic restitution over an 18 3 18 m area with an error of 0.02 m along the Z axis. A normalized vegetation index (NDVI) from color‐infrared images at 0.02‐m resolution over the same area was computed. Algal biomass sampled within the photographed area allowed us to calibrate NDVI with algal biomass (R2 = 0.73, p < 0.01). Aggregation analysis performed on a height above zero level, local topographic heterogeneity, and algal biomass confirmed, at the landscape level, previous local experi‐mental evidence of a relationship between topographic heterogeneity and algal biomass increasing from scales of 0.5 to 2 m. Our method permits multiscale testing of local scale‐dependent processes over a natural landscape.
Seasonal dynamics of the Lake Kinneret food web:The importance of the microbial loop
Authors: Hart Deborah R. , Stone Lewi , Berman Tom
Published: June 2010

The role of bacteria and protozoa in the food web of Lake Kinneret was examined for 14 seasons over a 4‐yr period (1989–1992) using a mass‐balanced carbon flux model and network analysis. These microorganisms supplied nearly half of the carbon requirements of metazoan zooplankton grazers during the late winter‐spring Peridinium bloom, when the lake was in its most eutrophic phase. The level of primary productivity was not seen to have a significant effect on the relative amounts of carbon passing from bacteria and protozoa to higher trophic levels. Rather, this depended on the proportion of photosynthetically fixed carbon that originated from “inedible” net‐phytoplankton and the efficiency with which bacterial carbon was transferred to metazoans. The importance of the microbial loop as a carbon source to higher trophic levels in Lake Kinneret was a result of the often high levels of inedible net‐phytoplankton (mostly Peridinium gatunense). The higher levels also occurred because bacterial production was transferred to metazoans in a relatively efficient one‐ or two‐step process. These results indicate that even in eutrophic environments, bacteria and protozoa can supply significant amounts of carbon to metazoans.
Bacterial production and growth efficiencies: Direct measurements on riverine aggregates
Authors: Grossart Hans-Peter , Ploug Helle
Published: June 2010

Heterotrophic bacteria transform organic matter by respiration and production of new biomass. Because there are only a limited number of studies on the respiration of bacteria attached to particulate organic matter, their role in the carbon cycle of aquatic systems is not well known. In this study, we combine radiotracer with microsensor techniques to measure bacterial production and respiration rates on the same aggregate and to directly determine the growth efficiency of the microbial community attached to aggregates. Aggregates of defined age were formed after incubation of water samples of the river Weser, Northern Germany, in roller tanks and their bacterial community was analyzed by in situ hybridization. The growth efficiency was 0.45± 0.04 (SE) on 1–3‐d‐old aggregates, and it was independent of the growth rate (µ). There was no correlation between respiration and the particulate organic carbon (POC) or particulate organic nitrogen (PON) content of the same aggregate. Bacterial growth efficiencies on aggregates decreased after 5 d of incubation, as bacterial production decreased and respiration increased. On 7‐ and 14‐d‐old aggregates, the growth efficiency was 0.23 ± 0.06 and 0.04 ± 0.01, respectively, and proportional to µ. The bacterial production was thus apparently substrate limited. Respiration was then correlated with both POC and PON content of the same aggregates. The changes in bacterial production and respiration occurred with con‐current changes in the bacterial community. The percentage of members of the a‐ and b‐subclass of Proteobacteria decreased from 13% and 33.7% to 2.6% and 9.0%, respectively, whereas those of the g‐subclass of filamentous Proteobacteria and Cytophaga increased from 31.9% to 50.4% and from 8.5% to 24.9%, respectively, during the 14 d of incubation. These results demonstrate that bacterial production and respiration on aggregates are dependent on the bacterial community and the substrate composition of aggregate. High growth efficiencies of aggregate‐associated bacteria, especially during the first days of colonization, suggest that aggregates are spots of high bacterial growth where a rapid and efficient transfer of organic matter into bacterial biomass takes place.
Temporal variations in plutonium and americium inventories and their relation to vertical transport in the northwestern Mediterranean Sea
Authors: Fowler Scott W. , Noshkin Victor E. , Jacques La Rosa , Gastaud Janine
Published: June 2010

Vertical fluxes of 239+240Pu and 241Am and temporal changes in their inventories in the northwestern Mediterranean Sea have been examined through high‐resolution water column sampling coupled with direct measurements of the vertical flux of particle‐bound transuranics using time‐series sediment traps. Water column profiles of both radionuclides showed well‐defined sub‐surface maxima (239+240Pu between 100–400 m; 241Am at 100–200 m and 800 m), the depths of which are a result of the different biogeochemical scavenging behavior of the two radionuclides. Comparison of deep water column (0–2,000 m) transuranic inventories with those derived from earlier measurements demonstrate that the total 239+240Pu inventory had not substantially changed between 1976–1990 whereas 241Am had decreased by approximately 24%. Enhanced scavenging of 241Am and a resultant, more rapid removal from the water column relative to 239+240Pu was also supported by the observation of elevated Am/Pu activity ratios in sinking particles collected in sediment traps at depth. Direct measurements of the downward flux of particulate 239+240Pu and 241Am compared with transuranic removal rates derived from observed total water column inventory differences over time, show that particles sinking out of deep waters (1,000–2,000 m) could account for 26‐72% of the computed total annual 239+240Pu loss and virtually all of the 241Am removal from the water column. Upper water column (0–200 m) residence times based on direct flux measurements ranged from 20‐30 yr for 239+240Pu and 5‐10 yr for 241Am. The observation that 241Am/239+240Pu activity ratios in unfiltered Mediterranean seawater are six times lower than those in the north Pacific suggests the existence of a specific mechanism for enhanced scavenging and removal of 241Am from the generally oligotrophic waters of the open Mediterranean. It is proposed that atmospheric inputs of aluminosilicate particles transported by Saharan dust events which frequently occur in the Mediterranean region could enhance the geochemical scavenging and resultant removal of 241Am to the sediments.
Declining carrying capacity in the Bering Sea: Isotopic evidence from whale baleen
Authors: Schell Donald M.
Published: June 2010

The Bering Sea is a rich marine ecosystem with 1995 U.S. landings of finfish and shellfish in excess of 2 × 106 tons. Recently, major declines of marine mammal and bird populations have occurred, with the question arising as to whether the causes were top down, i.e., from fishing pressure, or bottom‐up, i.e., driven by climate‐change effects. We assessed the latter scenario by using the inverse relationship between phytoplankton cell‐growth rates and carbon isotope fractionation to compare seasonal rates of primary productivity. The isotope ratios in the long baleen plates from bowhead whales (Balaena mysticetus) laid down while the whales fed in the Bering and Chukchi seas were used as a proxy for the average annual isotope ratios in their zooplankton prey and, by extension, phytoplankton. Plates from 37 whales produced a continuous isotopic record from 1947‐1997 and indicate that seasonal productivity was higher in 1947‐1976, peaking in 1966. Since that time, average d13C values have declined by over 2.7‰ until 1997, inferring a drop in seasonal carbon fixation of ∼‐40%. Alternatively, lowered isotope ratios could arise if phytoplankton stocks significantly increased over time while cell‐growth rates declined. However, long‐term literature estimates for phytoplankton in the Western and Eastern Pacific Ocean and Eastern Bering Sea show either no trend or a decrease over time. Archaeological samples of baleen from ca. 100 and 2,200 yr. B.P. showed average d13C values higher than any in the last five decades, implying still higher productivity in the past. The lowered carrying capacity is a likely contributor to the decline of top consumers in the region.
Optical discrimination of a phytoplankton species in natural mixed populations
Authors: Kirkpatrick Gary J. , Millie David F. , Moline Mark A. , Schofield Oscar
Published: June 2010

Developing optical detection techniques for discriminating particular phytoplankon species in mixed assemblages has long been a goal of aquatic scientists. Previously, a processing algorithm for phytoplankton absorption spectra was reported that suggested detection of the red tide dinoflagellate Gymnodinium breve was possible. The algorithm evaluated the fourth derivative of the particulate absorption spectrum of an unknown sample and compared it to a standard fourth derivative spectrum for G. breve using a similarity index. We report here the first‐time application of this technique to the detection of G. breve in natural, mixed phytoplankton communities. Pigment and spectral absorption data were collected from natural blooms of G. breve in the eastern Gulf of Mexico. This dinoflagellate is the only species of phytoplankton in the Eastern Gulf of Mexico observed to contain the pigment gyroxanthin‐diester, and it appears in constant proportion to cellular chlorophyll a (Chl a) in G. breve. The in vitro absorption spectrum of gyroxanthin‐diester is nearly identical to other xanthophylls (including diadinoxanthin, lutein, and 199‐hexanoyloxyfucoxanthin) and is not singularly responsible for imparting a unique absorption signature. Quantifying gyroxanthin‐diester and Chl a allowed us to estimate the fraction of the biomass in mixed populations associated with G. breve. Subsequent regression of the G. breve similarity indexes to the G. breve biomass fractions yielded a significant linear correlation. Finally, the liquid waveguide capillary cell appears to be a promising technology for automating this technique.
Production of biogenic silica by spring diatoms
Authors: Kristiansen Svein , Farbrot Tove , Naustvoll Lars‐Johan
Published: June 2010

The radioactive isotope 32Si was used to measure Si uptake during a spring bloom dominated by the diatom Thalassiosira nordenskioeldii. The diatoms converted virtually all dissolved silicic acid in the surface layer into biogenic silica. The rate of Si uptake was unsaturated in all the experiments conducted during the bloom. The half‐saturation constant for Si uptake declined from 6–12 mmol m‐3 early in the bloom to 2 mmol m‐3 when dissolved silicic acid concentration was low. The highest specific Si‐uptake rates measured (ca. 0.3 d‐1) were comparable to average net growth rates calculated from cell abundance measurements.
Effect of nutrient kinetics and cytoarchitecture on bacterioplankter size
Authors: Button D. K. , Robertson Betsy
Published: June 2010

Expanded specific affinity theory specifies the advantages of small dry mass and dilute cytoarchitecture in impoverished systems. For marine samples, bacterioplankton mean dry mass, according to flow cytometry, was near 24.5 fg cell−1. Conversion to volume with buoyant density gave a cell volume of 0.124 mm3 . Total DNA was 2.9 fg cell−1. This compared with the size of a single genome of a small extinction‐ culture isolate, Sphingomonas sp. RB2256, of 3.96 fg or 3.6 Mb. The genome size of such isolates and other cultures decreased with metabolic simplicity. It was found that bacterioplankton could be exposed to radiolabeled amino acids and then sorted for size and that the specific affinities of the fraction of small organisms were as great as the fraction of large cells. Size, DNA, and metabolic‐complexity distributions were concordant with the concepts that cell volume approaches a minimum set by sufficient space for the smallest genome that can provide sufficient information for competitive dissolved‐nutrient acquisition, and that space requirements are further alleviated by the expression of few cytoplasmic‐enzyme molecules in each of the various pathways and a dilute cytoplasm. Bacterioplankton approached a minimum genome size of 1.7 Mb with a minimum cell volume of about 0.06 mm3 and a DNA content of 16% dry weight. The property of small dry mass with a low DNA content was common in in situ bacteria but absent from cultivated representatives, which led to speculation that failure to grow in the laboratory is related to missing regulatory information.
Comparing two vertical plankton distributions
Authors: Solow Andrew R. , Bollens Stephen M. , Beet Andrew
Published: June 2010

Traditional statistical methods for testing for differences in vertical plankton distributions are invalid when the distributions are patchy. This note describes a modification of the Kolmogorov‐Smirnov test that is insensitive to patchiness. The modified test is applied to some data on day‐night differences in the vertical distribution of two zooplankton taxa.
Sequential extraction and analysis of phosphorus in marine sediments: Streamlining of the SEDEX procedure
Authors: Anderson L. D. , Delaney M. L.
Published: June 2010

We streamlined the five‐step SEDEX (sedimentary extraction) procedure for characterizing sedimentary phosphorus to a four‐step procedure. We combined extraction of adsorbed and oxide‐associated pools into a single step, retaining steps for authigenic, detrital, and organic P. In addition, we used automated spectrophotometric flow injection analysis (FIA) to determine P concentrations, rather than traditional spectrophotometric techniques. We decreased our total extraction and analytical time from 12 d for 24 replicate samples to 5 d without sacrificing our geo‐chemical\objectives, detection limits, or analytical reproducibility.
Advective particle transport into permeable sediments—evidence from experiments in an intertidal sandflat
Authors: Huettel Markus , Rusch Antje
Published: June 2010

Advective transport of artificial and natural particles into permeable sediments was demonstrated in situ by field experiments in an intertidal Wadden Sea sandflat. Using dyed sediment, advective interfacial solute exchange was shown to reach down at least 1.5 cm below surface. Particle depth distributions depended on sediment permeability and particle size. Sandy sediments were found to efficiently trap particulate material. At the beginning of the local phytoplankton spring bloom, an average m2 of coarse‐grained sediment received 850‐mg organic carbon per day by filtration of 14 liters of overlying water per hour. We discuss the relative importance of different transport mechanisms, and data from parallel studies on natural sediments at the same site are interpreted in close correlation to the results of the in situ experiment.
Benthic organism biomass size‐spectra in the Baltic Sea in relation to the sediment environment
Authors: Duplisea Daniel E.
Published: June 2010

Biomass size‐spectra of benthic organisms (BBSS) were constructed for 44 stations in three basins of the Baltic Sea: Bothnian Bay, Bothnian Sea, and the Baltic Proper, which represents a salinity gradient from about 3‰ to 18‰, respectively. In addition, BBSS were regrouped and analyzed according to an encompassing sediment environmental variable: Loss of weight on ignition (LOI). LOI correlates with many other sediment environmental variables and can characterize the sedimentary environment in a location. BBSS from the Bothnian Bay were different than those of the Bothnian Sea and Baltic Proper, though BBSS from the latter two basins did not differ from each other. This difference of Bothnian Bay BBSS was indirectly attributed to salinity as it is a region impoverished in both marine and freshwater species; hence individual species size‐distributions contribute considerably to the whole resulting in a different BBSS. BBSS grouped according to sediment LOI did not differ from each other. As there were no differences between LOI‐grouped size‐spectra yet geographical and hence species diversity groupings did differ, it is apparent that the sediment environment is less important than species diversity in determining BBSS patterns in the Baltic Sea. This is in contrast to common environmental explanations for BBSS patterns in other regions.
Carbon to volume relationships for dinoflagellates, diatoms, and other protist plankton
Authors: Menden-Deuer Susanne , Lessard Evelyn J.
Published: June 2010

Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume (C:vol) and nitrogen to volume (N:vol) relationships. Cellular C and N content ranged from 48 to 3.0 × 104 pgC cell−1 and 11 to 2,656 pgN cell−1 for cells ranging in volume from 180 to 2.8 × 105 µm3. C and N density in dinoflagellates decreased significantly with increasing cell volume. C:N ratios ranged from 3.44 to 6.45. C:vol and N:vol in dinoflagellates are significantly related as expressed by the equations pgC cell−1 = 0.760 × volume0.819 and pgN cell−1 = 0.118 × volume0.849. Previously published data were combined to compare C:vol relationships in different phylogenetic protist groups, including chlorophytes, chrysophytes, prasinophytes, and prymnesiophytes. Our analysis indicated differences between the C:vol relationships available for ciliates. A new C:vol relationship for diatoms was established (pgC cell−1 = 0.288 × volume0.811). Dinoflagellates are significantly more C dense than diatoms. Except for diatoms, we found few significant differences between C:vol relationships of different phylogenetic groups. Consequently, one C:vol relationship for taxonomically diverse protist plankton excluding diatoms was determined (pgC cell−1 = 0.216 × volume0.939). In the combined data set, carbon density was not constant but decreased significantly with increasing cell volume. Using constant C:vol conversion factors for plankton over large size ranges will cause systematic errors in biomass estimates.
The influence of climate on phytoplankton community biomass in San Francisco Bay Estuary
Authors: Lehman P. W.
Published: June 2010

The distribution of biomass within the phytoplankton community in northern San Francisco Bay Estuary was influenced by environmental conditions resulting from an interdecadal climate regime shift between 1975 and 1993. A decrease in percentage of diatom biovolume characterized the period 1975–1989 and was caused by both a decrease in diatom and an increase in green and bluegreen algae and flagellate species biovolume. Among the diatoms, there was a greater loss of pennate than centric diatoms. The direct role of climate variation on phytoplankton community biovolume was determined using climatically‐related environmental variation that was isolated from the total environmental variation using the covariance between a California climate index and a suite of physical and chemical variables and summarized by principal component analysis. Significant correlation between climatically‐related environmental variation and phytoplankton species and species group biovolume suggested a link between climate and the distribution of biovolume in the phytoplankton community. Further analysis of the possible mechanisms controlling the association between climatically‐related environmental variation and phytoplankton community biovolume confirmed the importance of water temperature, specific conductance, and water transparency to pennate diatom biovolume. Comparison of natural and anthropogenic processes indicated that diatom biovolume at each station was influenced by environmental conditions even though total diatom biovolume in the estuary was strongly influenced by water diversion.
Nutrient and temperature control of the contribution of picoplankton to phytoplankton biomass and production
Authors: Agawin Nona S. R. , Duarte Carlos M. , Agustí Susana
Published: June 2010

The observation that the relative importance of picophytoplankton is greatest in warm and nutrient‐poor waters was tested here based on a comprehensive review of the data available in the literature from oceanic and coastal estuarine areas. Results show that picophytoplankton dominate (≥50%) the biomass and production in oligotrophic (chlorophyll a [Chl a] < 0.3 mg m−3), nutrient poor (NO3 + NO2 < 1 µM), and warm (>26°C) waters, but represent <10% of autotrophic biomass and production in rich (Chl a > 5 mg m−3) and cold <3°C) waters. There is, however, a strong covariation between temperature and nutrient concentration (r = −0.95, P < 0.001), but the number of observations where both temperature and nutrient concentrations are available is too small to allow attempts to statistically separate their effects. The results of mesocosm nutrient addition experiments during summer in the Mediterranean Sea allowed the dissociation of the effects of temperature from those of nutrients on pico phytoplankton production and biomass and validated the magnitude at which picoplankton dominates (≥50%) autotrophic biomass and production obtained in the comparative analysis. The fraction contributed by picoplankton significantly declined (r2 = 0.76 and 0.90, respectively, P < 0.001) as total autotrophic production and biomass increased. These results support the increasing importance of picophytoplankton in warm, oligotrophic waters. The reduced contribution of picophytoplankton in warm productive waters is hypothesized here to be due to increased loss rates, whereas the dominance of picophytoplankton in warm, oligotrophic waters is attributable to the differential capacity to use nutrients as a function of differences in size and capacity of intrinsic growth of picophytoplankton and larger phytoplankton cells.
Spectrum of the quantum yield for photochemical mineralization of dissolved organic carbon in a humic lake
Authors: V äh ätalo Anssi V. , Salkinoja ‐Salonen Mirja , Taalas Petteri , Salonen Kalevi
Published: June 2010

We measured photochemical mineralization of dissolved organic carbon in a humic lake in situ. At a depth of 1 cm, solar radiation mineralized 19 mmol C m−3 d−1. The rate of mineralization decreased with increasing depth with an attenuation coefficient of 23 m−1. Consequently, most photochemical mineralization in the water column (0.99 mmol C m−2 d−1) took place in the top 10 cm. The rate of photochemical mineralization was also modeled as a product of three spectra: (1) scalar photon flux density, (2) the apparent quantum yield, and (3) the absorption of chromophoric dissolved organic matter. We described the spectrum for apparent quantum yield as ϕλ = c × 10−dl, where c (dimensionless) and d (nm−1) are positive constants. Mathematical optimization for the best fit between the measured and the modeled photochemical mineralization resulted in ϕλ of 7.52 × 10 −0.0122 λ. The ϕλ based on the measurements in situ agreed with ϕλ determined in a laboratory at 320, 355, and 390 nm. Using the determined ϕλ, we calculated that UV ‐B contributed 9%, UV ‐A 68%, and visible light 23% to the photochemical mineralization. Half of total photochemical mineralization was due to wavelengths <360 nm. Our method for the determination of ϕλ is applicable in situ, improves the prediction of photochemical reaction rates in surface waters, and offers an alternative to the determination of quantum yields at discrete wavelengths.
Leucine incorporation by Microcystis aeruginosa
Authors: Kamjunke Norbert , Jähnichen Sabine
Published: June 2010

In experiments with axenic cultures of Microcystis aeruginosa, we tested whether this cyanobacterium incorporates leucine, a compound that is often used for the measurement of heterotrophic bacterioplankton production. Microcystis showed significant leucine incorporation, and the uptake of exponentially growing cells was higher than the uptake of cells in stationary growth phase. Therefore, the leucine method may not be suitable for measuring bacterial production in highly eutrophic waters with a dominance of cyanobacteria.
Evolutionary and ecological perspectives on carbon acquisition in phytoplankton
Authors: Tortell Philippe D.
Published: June 2010

Statistically significant differences exist among the major algal and cyanobacterial taxa in the catalytic efficiency of Ribulose‐1,5 bisphosphate carboxylase/oxygenase (RubisCO)—the rate limiting carboxylase in C‐fixation. With the notable exception of the red algae, a comparison of the kinetic properties of RubisCO among phytoplankton of different geological ages suggests that the enzyme has evolved towards higher CO2 affinity in response to decreasing atmospheric CO2/O2 ratios over geological time. Taxonomic differences in the kinetic properties of RubisCO influence the mechanisms of C acquisition among phytoplankton groups. A significant negative correlation exists between the CO2 specificity factor of RubisCO and the capacity of cells to concentrate inorganic C through active uptake mechanisms. Differential resource requirements associated with C acquisition could affect the relative fitness of phytoplankton groups and thus their ecological interactions. I argue that inorganic C may play a more important role in phytoplankton productivity and community ecology than has been previously recognized and highlight some outstanding questions for future research.
Laboratory and field studies of colloidal iron oxide dissolution as mediated by phagotrophy and photolysis
Authors: Barbeau K. , Moffett J. W.
Published: June 2010

In a previous work, we have employed colloidal ferrihydrite impregnated with an inert radiotracer to probe the mechanistics of iron redox cycling in seawater via phagotrophic and photochemical processes. This paper reports further studies using the inert tracer technique, directed towards obtaining a more quantitative sense of the importance of phagotrophy relative to photolysis as a pathway for the production of bioavailable iron in oxygenated seawater. Our results indicate a maximal (i.e., near‐surface at noon) rate of 12% per day for the photochemically‐mediated dissolution of colloidal ferrihydrite. Protozoan‐mediated dissolution of the same iron oxide phase proceeds at a rate ranging from 1–6% per day, depending on grazing turnover rates. Thus, while photolysis should dominate the redox cycling of refractory iron solids in near‐surface waters under bright daytime conditions, phagotrophy is likely to be a more important process overall when the entire euphotic zone is considered on a time‐averaged basis.
Development and application of elemental fingerprinting to track the dispersal of marine invertebrate larvae
Authors: DiBacco Claudio , Levin Lisa A.
Published: June 2010

The early life history of many marine benthic invertebrate and fish species involves a planktonic larval stage that allows exchange of individuals among separated adult populations. Here, we demonstrate how natural and anthropogenic trace elements can be used to determine larval origins and assess bay‐ocean exchange of invertebrate larvae. Trace elements can be effective site markers for estuaries because run‐off and pollutant loading often impart distinct elemental signatures to bay habitats relative to nearshore coastal environments. Crab larvae originating from San Diego Bay (SDB) were distinguished from those originating in neighboring embayments and exposed coastal habitats by comparing multiple trace‐element concentrations (“fingerprint”) in individuals. Discriminant function analysis (DFA) was used to characterize stage I zoeae of the striped shore crab, Pachygrapsus crassipes, of known origin (reference larvae) via trace‐elemental composition (i.e., Cu, Zn, Mn, Sr, Ca). Linear discriminant functions were used to identify the origin and characterize the exchange of stage I P. crassipes zoeae between SDB and the nearshore coastal environment during one spring tidal cycle. Elemental fingerprinting revealed that most (87%) of the stage I larvae collected at the bay entrance during the flood tide were larvae of SDB origin that were reentering the bay. Nearly one third of zoeae sampled (32%) at the entrance during ebb tide were coastal larvae leaving the bay and returning to open water. The observed bidirectional exchange contrasts with the unidirectional transport of zoeae out of the bay predicted from stage I vertical migratory behavior. Because P. crassipes zoeal survivorship is lower in SDB than in coastal waters, bay‐ocean exchange has significant implications for the dynamics of P. crassipes populations. Trace‐elemental fingerprinting of invertebrate larvae promises to facilitate investigations of many previously intractable questions about larval transport and dynamics.
East—west gradient in ectoenzyme activities in the subarctic Pacific: Possible regulation by zinc
Authors: Fukuda Rumi , Sohrin Yoshiki , Saotome Nobue , Fukuda Hideki , Nagata Toshi , Koike Isao
Published: June 2010

We determined depth profiles of potential activities of leucine aminopeptidase (LAPase) and β—glucosidase (BGase) in the subarctic Pacific between July and September 1997. The data revealed a systematic shift in vertical patterns of the LAPase:BGase ratios along the east‐west axis of the investigated area. The ratio increased by over 10‐fold with depth in the eastern region (139°W‐159°W), while it varied little (<3‐fold) in the central region (169°W‐179°E, including the Bering Sea). It decreased with depth by about six‐fold in the western region (169°E–161°E). The decrease of LAPase:BGase ratio with depth is consistent with a general pattern in the decomposition of sinking particles, i.e., protein is degraded faster than polysaccharides, but the increase of the ratio with depth suggests that export of proteinaceous materials to the mesopelagic zone is high. Cell specific LAPase activity in the upper layer (0–100 m) was positively correlated (r = 0.92, P < 0.05) with the concentration of dissolved zinc, a catalytic element of proteases. We hypothesize that the low level of dissolved zinc stresses LAPase activity in the euphotic zone, leading to high export of protein to the mesopelagic zone in the eastern subarctic Pacific. These results have important implications for modeling the carbon and nitrogen pump in open oceans where surface concentrations of trace metals are extremely low.
A 200,000‐year, high‐resolution record of diatom productivity and community makeup from Lake Baikal shows high correspondence to the marine oxygen‐isotope record of climate change
Authors: Edlund Mark B. , Stoermer Eugene F.
Published: June 2010

Siliceous microfossil succession was analyzed in a 200,000‐yr sediment sequence recovered from the Buguldeika Saddle in Lake Baikal, Russia. Siliceous microfossil abundance varied among core depths from no preserved microfossils during inferred colder climate conditions to recent interglacial sediments containing over 300 × 106 microfossils per g dry sediment. Depth‐age microfossil assemblage zones (CA‐I to CA‐IV) identified using correspondence analysis had high correspondence to stages in the marine d18O isotope record and could be partially aligned with Late Pleistocene glacial‐interglacial cycling models from the mid‐Siberian Highland. These observations suggest that Lake Baikal phytoplankton communities have responded to climatic changes driven by insolation parameters and global ice volumes on temporal scales similar to tropical and polar oceans. Microfossil zone CA‐I (0–11.4 kyr B.P.) corresponded to the Holocene interglacial or d18O stage 1 (0–11.4 kyr B.P.), a period of higher production in Lake Baikal during a climatic optimum. Microfossil zone CA‐II (12.3–18.7 kyr B.P.) corresponded to the Sartan glaciation and d18O stage 2 (12–24 kyr B.P.). Zone CA‐III (21.3–73.2 kyr B.P.) comprised d18O stages 3 and 4. However, within zone CA‐III, subzones CA‐IIIa and IIIb (21.3–56.8 kyr B.P.) grouped were well aligned with d18O stage 3 and contained sediments deposited during the inferred Karginskiy interstade. Microfossil zone CA‐IVa (77.4–129.2 kyr B.P.) and CA‐IVb (130.3–172.5 kyr B.P.) included d18O stages 5 and 6, respectively, with sediments that were most likely deposited during the Taz glaciation and the Kazantsevo interstade. Climate‐induced changes are reflected in production differences and in community composition specificity within microfossil zones or climate stages. This suggests that climate change drives major historical successional patterns in Lake Baikal's primary producer community; changes in primary producers must have further impacted the system's entire biota.
Trimethylamine does not trigger antipredatory life history shifts in Daphnia
Authors: Sakwińska Olga
Published: June 2010

I studied the responses of Daphnia galeata and Daphnia hyalina × galeata life history traits to trimethylamine (TMA) and fish kairomone. TMA and fish exudate had opposite effects on age at maturity and fecundity in two different experiments. The effects on size at maturity and offspring size were similar. Specific antipredatory life history shifts occurred only in response to fish exudate, whereas TMA caused changes that could be expected from any mildly harmful substance.
Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific
Authors: Mann Elizabeth L. , Chisholm Sallie W.
Published: June 2010

Prochlorococcus, a small unicellular cyanobacterium, is an important member of the phytoplankton community in the eastern equatorial Pacific. When these waters were enriched with iron during IronEx II, the chlorophyll per cell and cell size of Prochlorococcus increased, implying that they were iron limited. The extent of this limitation was unclear, however, and the number of Prochlorococcus remained constant. To examine whether cell division rates were stimulated significantly by iron, we used a cell cycle analysis approach to measure them in and out of the Fe‐enriched patch and in Fe‐enriched bottles. The cell division rate increased from 0.6 to 1.1 d−1 over 6 d of exposure to the elevated iron concentrations in the patch. Cells incubated in bottles with additional iron had rates of 1.4 d−1 or two doublings per day. Prochlorococcus mortality rates, measured independently, nearly doubled after the addition of iron. This matched the increase in the cell division rate and maintained a relatively constant population size. Thus the cell division rates of even the smallest phytoplankton in the equatorial Pacific are significantly iron limited, but biomass is constrained by both iron limitation and microzooplankton grazing. The differential response of individual phytoplankton groups to the addition of iron during IronEx II was at least partially a result of differential mortality rates over the time course of the experiment. How the community would respond to sustained fertilization, however, is not obvious.
No ecological relevance of trimethylamine in fish—Daphnia interactions
Authors: Pohnert Georg , von Elert Eric
Published: June 2010

Diel vertical migration (DVM) is a widespread predator‐avoidance behavior in Daphnia and can be induced by kairomones released by fish. It has recently been shown in laboratory experiments that DVM in Daphnia hyalina can be induced by micromolar concentrations of trimethylamine (TMA). The authors concluded, after spectrophotometrical determination of the amine content in fish incubation water, that TMA is an active component of the kairomone. Using a selective solid phase microextraction (SPME)/GCMS method, we show that the TMA content in fish incubation water was overestimated by several orders of magnitude. The amounts of TMA released by any of the three cyprinids Leuciscus idus, Leucaspius delineatus, and Carassius carassius have no relevance for DVM induction and TMA concentrations detected in fish incubation water did not induce DVM. Further, we show that efficient removal of existing TMA traces from fish incubation water did not decrease the kairomone activity. This excludes TMA as part of a kairomone cocktail. Hence TMA must not be called a kairomone in the fish‐Daphnia context.
Mass transfer versus kinetic control of uptake across solid‐water boundaries
Authors: Sanford Lawrence P. , Crawford Sean M.
Published: June 2010

We present general nondimensional solutions for uptake across a solid‐water boundary, considering the combined influences of mass transfer flux limitation and uptake reaction kinetics. Mass transfer processes are represented by a general mass transfer velocity. Reaction kinetics are represented by first‐order and Monod models. Mathematical solutions are well approximated by standard mass transfer models for low values of the derived nondimensional mass transfer velocity and by standard kinetic models for high values. Approximate limiting values of the nondimensional mass transfer velocity are defined for mass transfer control and kinetic control. The intermediate region, where both mass transfer and kinetics influence the solution, is relatively broad for first‐order kinetics and Monod kinetics in oligotrophic environments. Both limits decrease as concentration increases in the Monod solution, such that under increasingly eutrophic conditions mass transfer control becomes less important, the intermediate range shrinks, and kinetic control becomes an increasingly good approximation. Example calculations using data from experimental ecosystems indicate that boundary nutrient uptake was mass transfer controlled or intermediate under oligotrophic conditions. Nutrient pulses applied to the systems caused temporary eutrophication, which resulted in temporary kinetic control.
The fate of intertidal microphytobenthos carbon: An in situ 13C‐labeling study
Authors: Middelburg Jack J. , Barranguet Christiane , Boschker Henricus T. S. , Herman Peter M. J. , Moens Tom , Heip Carlo H. R.
Published: June 2010

At two intertidal sites (one sandy and one silty, in the Scheldt estuary, The Netherlands), the fate of microphytobenthos was studied through an in situ 13C puls‐chase experiment. Label was added at the beginning of low tide, and uptake of 13C by algae was linear during the whole period of tidal exposure (about 27 mg m−2 h−1 in the top millimeter at both sites). The 13C fixed by microphytobenthos was rapidly displaced toward deeper sediment layers (down to 6 cm), in particular at the dynamic, sandy site. The residence times of microphytobenthos with respect to external losses (resuspension and respiration) were about 2.4 and 5.6 d at the sandy and silty stations, respectively. The transfer of carbon from microphytobenthos to benthic consumers was estimated from the appearance of 13C in bacterial biomarkers, handpicked nematodes, and macrofauna. The incorporation of 13C into bacterial biomass was quantified by carbon isotope analysis of polar lipid derived fatty acids specific for bacteria. The bacterial polar lipid‐derived fatty acids (i14:0, i15:0, a15:0, i16:0, and 18:1ω7c) showed rapid, significant transfer from benthic algae to bacteria with maximum labeling after 1 d. Nematodes became enriched after 1 h, and 13C assimilation increased until day 3. Microphytobenthos carbon entered all heterotrophic components in proportion to heterotrophic biomass distribution (bacteria > macrofauna > meiofauna). Our results indicate a central role for microphytobenthos in moderating carbon flow in coastal sediments.
Effect of hydroxamate ferrisiderophore complex (ferrichrome) on iron uptake and growth of a coastal marine diatom, Chaetoceros sociale
Authors: Kuma Kenshi , Tanaka Junya , Matsunaga Kensuke , Matsunaga Katsuhiko
Published: June 2010

Recent studies point out that dissolved iron in seawater is bound to strong organic complexes that have stability constants consistent with microbially produced siderophores. In the present study, the growth and iron uptake of the coastal marine diatom Chaetoceros sociale were experimentally measured in culture experiments at 10°C in media containing a terrestrial fungal hydroxamate ferrisiderophore, desferriferrichrome (DFC)‐Fe(III) (2 DFC:1 Fe and 10 DFC:1 Fe) complex with an Fe concentration of 100 nM. The DFC‐Fe(III) (2:1) medium as well as EDTA‐Fe(III) (2:1) medium in the previous study induced high cell yields and fast growth of C. sociale. The short‐term iron uptake rate in the DFC‐Fe(III) (2:1) medium aged for 9 d at 10°C was much faster than the uptake rates in the DFC‐Fe(III) (2:1 and 10:1) media aged for 1 d and in the DFC‐Fe(III) (10:1) medium aged for 9 d at 10°C. Furthermore, the DFC‐Fe(III) (2:1) medium induced the fastest iron uptake rate in the organic‐Fe(III) complexes [DFC‐Fe(III), EDTA‐Fe(III), citric‐Fe(III) and fulvic‐Fe(III)] and solid amorphous Fe(III) hydroxide [am‐Fe(III)] media in the present and previous studies. The addition of excess DFC stopped iron uptake by C. sociale. The dissociation of DFC‐Fe(III) complex in seawater was determined by simple filtration (0.025 °m). Fast Fe(III) release was observed over 6–12 d in the DFC‐Fe(III) (2:1) complex at 10°C, resulting from the thermal and microbial decomposition of the DFC complexed with Fe(III). This result is consistent with the faster iron uptake rate and growth rate of C. sociale observed in the DFC‐Fe(III) (2:1) medium at 10°C. These results show that the dissolved DFC‐Fe(III) complex in seawater supplies biologically available inorganic Fe(III) species, which may determine the iron uptake rate in culture media by providing bioavailable Fe as the DFC decomposes. The thermal, photochemical, and microbial decomposition of organic chelators complexed with Fe(III) in aquatic environments is probably one of the most important mechanisms for providing bioavailable inorganic Fe(III) species into these environments.
Interstitial dissolved organic carbon (DOC) concentrations within sinking marine aggregates and their potential contribution to carbon flux
Authors: Alldredge Alice L.
Published: June 2010

Accurate estimates of the quantity of organic carbon sedimenting to the sea floor are important in evaluating the rate at which carbon is sequestered in the deep sea and the impact of the ocean on the global carbon cycle. However, extensive studies quantifying marine sedimentation over the past decades have considered only the particulate fraction of sinking material. Dissolved organic carbon (DOC) carried along in the interstices of sinking marine snow, the particles that comprise the bulk of particle flux throughout most of the ocean, has not been included previously. Empirical measurements of the interstitial DOC concentrations of individual aggregates of marine snow from coastal California and Washington revealed high values ranging from 8.9 to 140 mg L−1 that were significantly correlated with aggregate size, decreasing as aggregate size increased. Solubilization of particulate matter within aggregates by associated bacteria and reduced diffusion rates due to the fractal geometry of aggregates help maintain these high interstitial concentrations against diffusive processes. Although interstitial DOC concentrations were one to two orders of magnitude higher than ambient DOC concentrations in the surrounding seawater, the cumulative interstitial DOC in aggregates contributed <2.5% to total DOC in the water column. However, DOC comprised up to 31% of the total organic carbon in aggregates, averaging about 20%, indicating that previous measurements of sedimenting carbon in the ocean that have included only the particulate fraction have significantly and systematically underestimated the vertical flux of organic carbon.
Ultraviolet attenuation by dissolved and particulate constituents of first‐year ice during late spring in an Arctic polynya
Authors: Belzile Claude , Johannessen Sophia C. , Gosselin Michel , Demers Serge , Miller William L.
Published: June 2010

Vertical profiles of ultraviolet radiation (UVR) and photosynthetically available radiation (PAR) were measured under five large ice floes located in the North Water Polynya, northern Baffin Bay, in June 1998. Together with incident irradiance measurements, these profiles were used to assess the irradiance attenuation by the ice and its constituents. We also measured vertical distribution of absorption by colored dissolved organic matter (CDOM) and particulate organic matter (POM) in three melted ice cores. The ice thickness and snow depth varied from 0.5 to 1.3 m and from 1 to 9 cm, respectively. The ice–snow interface was infiltrated by meltwater. About 2–13% of incident UV‐B irradiance was transmitted through the snow, ice, and ice algae biomass; transmittance increased to 5–19% for UV‐A and to 5–12% for PAR. CDOM and POM contributed significantly to the attenuation of irradiance within the ice. The relatively high UVR transparency found in this study coincided with the seasonal maximum of incident UV irradiance. Hence, the resulting very high UVR:PAR ratio could affect the communities in the sea ice, at the ice–water interface, and in the surface waters underneath the ice cover. In addition, the strong absorption by CDOM found in this high‐UVR environment indicates that significant photochemical reactions could occur.
Attenuation of ultraviolet radiation in mountain lakes: Factors controlling the among‐ and within‐lake variability
Authors: Laurion Isabelle , Ventura Marc , Catalan Jordi , Psenner Roland , Sommaruga Ruben
Published: June 2010

High‐altitude lakes are exposed to high fluence rates of solar ultraviolet radiation (UVR; 29–400 nm) and contain low concentrations of dissolved organic carbon (DOC). While in most lowland lakes, DOC can be used to predict UV transparency with sufficient accuracy, current models fail to estimate UVR in clear alpine lakes. In these lakes, phytoplankton may contribute significantly to the UV attenuation either as particles or as a source of chromophoric dissolved organic matter (CDOM) with distinctive properties. We investigated a series of 26 lakes in the Alps and Pyrenees, situated at elevations ranging from 422 to 2,799 m above sea level and having DOC concentrations ranging from 0.2 to 3.5 mg L−1. CDOM, as measured by the absorptivity of filtered lake water, explained most of the variability in the attenuation of underwater UVR among lakes (r2 = 0.94, P < 0.001). However, within‐lake variation in the UV attenuation revealed a significant contribution from phytoplankton in deeper waters (UV attenuation increasing with chlorophyll a concentration; r2 = 0.97, P = 0.002), only apparent when DOC concentrations were low (∼0.3 mg L−1). The DOC‐specific absorptivity (ag*) was also important for characterizing the optical conditions in this series of lakes. Epilimnetic values of ag* were significantly lower in lakes located at high elevations (with low allochthonous CDOM inputs from the catchment), compared to lakes surrounded by trees and meadows. Moreover, ag* was generally lower in surface waters than in deeper water layers, suggesting the influence of photobleaching on UV transparency. The slope S of the exponential regression between CDOM absorptivity and wavelength did not show clear patterns, such as found in marine systems, and often presented lower values in the epilimnetic waters (in association with lower ag*). Collectively, our results suggest that in transparent alpine lakes, the dynamics of the CDOM pool and phytoplankton production will have a strong effect on temporal changes in UV underwater attenuation.