bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of viruses and bacteria in relation to diagenetic activity in an estuarine sediment
Authors: Middelboe Mathias , Glud Ronnie N. , Finster Kai
Published: July 2010

The distribution of viruses and bacteria was investigated in relation to bacterial sulfate reduction and total respiration (production of dissolved inorganic carbon, [DIC]) in a coastal sediment. Viral and bacterial abundance ranged from about 0.5 × 108 to 8 × 108 viruses cm−3 and 0.1 × 108 to 4 × 108 bacteria cm−3 in the upper 16 cm of the sediment and showed large and systematic changes within scales of a few centimeters. In general, viral abundance was highest in the sediment surface (0DK–1 cm); however subsurface peaks at 3DK–5 cm depth associated with increased diagenetic activity were also observed. The virusDK‐bacterium ratio ranged from 1.4 to 7.8 and increased significantly with depth in the upper 6 cm (P < 0.001). Viral abundance showed significant positive correlation with both bacterial abundance and activity (P ≪ 0.001), suggesting that the distribution and abundance of viruses were closely coupled to the activity of the bacterial community and that viruses are produced by bacteria within the sediment. The significant coupling between viral abundance and sulfate reduction rate and DIC production is the first indication of viral production associated with diagenetic active bacteria in marine sediments. This coupling between viral abundance and bacterial activity and the distinct pattern of vertical distribution show that viruses are a dynamic component of the benthic community. The morphological analysis indicated that interstitial viral communities were dominated by long (>1 µm) filamentous forms with a helical symmetry. Several types of these filamentous forms were observed, as well as a variety of tailed forms with icosahedral symmetry. Filamentous forms are rarely found in the water column, which suggests that they are adapted to the benthic environment and specific to the interstitial hosts.
Subsurface maxima of phytoplankton and chlorophyll: Steady‐state solutions from a simple model
Authors: Fennel Katja , Boss Emmanuel
Published: July 2010

In oligotrophic lakes and oceans, the deep chlorophyll maximum may form independently of a maximum of phytoplankton biomass, because the ratio of chlorophyll to phytoplankton biomass (in units of carbon) increases with acclimation to reduced light and increased nutrient supply at depth. Optical data (beam attenuation as proxy for phytoplankton biomass and chlorophyll fluorescence and absorption as proxies for chlorophyll concentration) and conventional measurements of biovolume, particulate organic carbon, and chlorophyll from two oligotrophic systems (Crater Lake, Oregon, and Sta. ALOHA in the subtropical North Pacific Ocean) are presented and show a vertical separation of the maxima of biomass and chlorophyll by 50–80 m during stratified conditions. We use a simple mathematical framework to describe the vertical structure of phytoplankton biomass, nutrients, and chlorophyll and to explore what processes contribute to the generation of vertical maxima. Consistent with the observations, the model suggests that biomass and chlorophyll maxima in stable environments are generated by fundamentally different mechanisms. Maxima in phytoplankton biomass occur where the growth rate is balanced by losses (respiration and grazing) and the divergence in sinking velocity, whereas the vertical distribution of chlorophyll is strongly determined by photoacclimation. A deep chlorophyll maximum is predicted well below the particle maximum by the model. As an interpretation of these results, we suggest a quantitative criterion for the observed coexistence of vertically distinct phytoplankton assemblages in oligotrophic systems: the vertical position at which a species occurs in highest abundance in the water column is determined by the “general compensation depth”— that is, the depth at which specific growth and all loss rates, including the divergence of sinking/swimming and vertical mixing, balance. This prediction can be tested in the environment when the divergence of sinking and swimming is negligible.
Seasonal shift in net ecosystem production in a tropical estuary
Authors: Ram A. S. Pradeep , Nair Shanta , Chandramohan D.
Published: July 2010

Net ecosystem production was examined in the Mandovi and Zuari estuaries (southwestern India) and the adjoining coastal waters for a period of 1 yr (January to December 1998). The study period encompassed premonsoon, monsoon, and postmonsoon seasons. At the estuarine stations, net ecosystem production showed monthly variation and a transition from net autotrophy of 49 mmol C m−2 d−1 during the nonmonsoon seasons (premonsoon and postmonsoon) to net heterotrophy of —46 mmol C m−2 d−1 in the monsoon season. Seasonal monsoon‐driven changes such as increased allochthonous inputs resulted in enhanced heterotrophic respiration and reduced primary production in the estuaries. In the coastal station, the monthly variation in net ecosystem production was not significant, and net heterotrophy was prevalent whenever measurements were made, thereby potentially serving as the net source of carbon dioxide to the atmosphere. Results suggest that the excess organic matter from these tropical estuaries supports heterotrophy in the adjacent coastal ecosystem.
Ultraviolet radiation blocks the organic carbon exchange between the dissolved phase and the gel phase in the ocean
Authors: Orellana MÓnica V. , Verdugo Pedro
Published: July 2010

Dissolved organic carbon (DOC) is one of the major reservoirs of active organic carbon on Earth. Although the bulk of the marine DOC pool is largely composed of small refractory polymeric material, new evidence suggests that ;10% of the DOC pool (1016 g C) can enter the microbial loop by forming microscopic gels that can eventually be colonized and degraded by bacteria. Marine microgels result from a spontaneous and reversible assembly/ dispersion equilibrium of DOC polymers forming hydrated Ca‐bonded tangled polymer networks. Here we test the hypothesis that ultraviolet (UV) photocleavage should strongly inhibit the formation of microgels, because the stability of tangled networks decreases exponentially with polymer length. Because of the loss of ozone shielding, the UV‐B spectral component of solar radiation (λ = 280–320 nm) has undergone a dramatic increase in the past few decades, particularly in the polar regions. We used dynamic laser‐scattering spectroscopy and flow cytometry to investigate UV‐induced DOC polymer cracking and the effect of UV on DOC assembly/dispersion equilibrium in 0.2 µm filtered seawater. Results indicate that exposure of seawater to UV‐B fluxes equivalent to those found in Antarctica during summer solstice can cleave DOC polymers, inhibit their spontaneous assembly, and/or disperse assembled microgels. Our results agree with previous observations that indicated that fragmentation produced by UV photolysis increases exponentially with exposure time and suggested that UV could limit the supply of microbial substrate by hindering microgel formation. UV cleavage yields short‐chain polymers that do not assemble and could eventually account for the old refractory DOC pool found in seawater.
Biotic, chemical, and morphometric factors contributing to winter anoxia in prairie lakes
Authors: Meding Marianne E. , Jackson Leland J.
Published: July 2010

To assess how features of lakes and their watersheds influence winter oxygen decay rates and the frequency of anoxia in shallow prairie lakes, we measured lake and watershed characteristics for 21 south‐central Alberta lakes and related these to measured oxygen decay rates during 1998–2000. Oxygen decay rates were functions of macrophyte biomass, percentage littoral area, and total phosphorus and ranged from 0.006 to 0.216 mg O2 m−3 d−1. Oxygen decay rates were ~4 times higher in shallow polymictic lakes compared to deep, stratified lakes. Within shallow lakes, those classified as turbid had decay rates ~1.5 times higher than those classified as clear. Chlorophyll a was not a predictor of the oxygen decay rate in shallow lakes; however, macrophyte‐derived carbon averaged ~150 times more than phytoplankton‐derived carbon in the shallow lakes we examined. Reasons that lakes frequently or never become anoxic are related to productivity and morphometry; however, processes explaining occasional anoxia appear not to be related to factors we measured.
Elemental composition of marine Prochlorococcus and Synechococcus: Implications for the ecological stoichiometry of the sea
Authors: Bertilsson S. , Berglund O. , Karl D. M. , Chisholm S. W.
Published: July 2010

The elemental composition of marine cyanobacteria is an important determinant of the ecological stoichiometry in low‐latitude marine biomes. We analyzed the cellular carbon (C), nitrogen (N), and phosphorus (P) contents of Prochlorococcus (MED4) and Synechococcus (WH8103 and WH8012) under nutrient‐replete and P‐starved conditions. Under nutrient‐replete conditions, C, N, and P quotas (femtogram cell21) of the three strains were 46 ± 4, 9.4 ± 0.9, and 1.0 ± 0.2 for MED4; 92 ± 13, 20 6 3, and 1.8 ± 0.1 for WH8012; and 213 ± 7, 50 ± 2, 3.3 ± 0.5 for WH8103. In P‐limited cultures, they were 61 ± 2, 9.6 ± 0.1, and 0.3 ± 0.1 for MED4; 132 ± 6, 21 ± 2, and 0.5 ± 0.2 for WH8012; and 244 ± 21, 40 ± 4, and 0.8 ± 0.01 for WH8103. P limitation had no effect on the N cell quota of MED4 and WH8012 but reduced the N content of WH8103. The cellular C quota was consistently higher in P‐limited than in nutrient‐replete cultures. All three strains had higher C: P and N: P ratios than the Redfield ratio under both nutrient‐replete and P‐limited conditions. The C:N molar ratios ranged 5–5.7 in replete cultures and 7.1–7.5 in P‐limited cultures; C: P ranged 121–165 in the replete cultures and 464–779 under P limitation; N: P ranged 21–33 in the replete cultures and 59–109 under P limitation. Our results suggest that Prochlorococcus and Synechococcus may have relatively low P requirements in the field, and thus the particulate organic matter they produce would differ from the Redfield ratio (106C : 16N : 1P) often assumed for the production of new particulate organic matter in the sea.
The balance between silica production and silica dissolution in the sea: Insights from Monterey Bay, California, applied to the global data set
Authors: Brzezinski Mark A. , Jones Janice L. , Bidle Kay D. , Azam Farooq
Published: July 2010

Silicon isotope tracers were used to examine the relative magnitude of silica dissolution and silica production in the Monterey Bay, California, upwelling system. A diatom bloom dominated by Skeletonema costatum and Chaetoceros spp. was encountered under conditions of moderate upwelling. Profiles of silica production and dissolution rates were obtained at seven stations that sampled both inside and outside the bloom. Integrated silica production rates ranged from 5.4 to 108 mmol Si m−2 d−1, averaging 42.8 mmol Si m−2 d−1. Integrated silica dissolution rates were considerably lower than production rates with values between 0.63 and 6.5 mmol Si m−2 d−1 (mean = 2.90 mmol Si m−2 d−1). The mean ratio of integrated silica dissolution to integrated silica production (∫ D:∫ P) between the surface and the 0.1% light depth was 0.075, omitting one station with an unusually high ∫ D:∫ P of 0.61, indicating that, on average, 93% of silica production was supported by new silicic acid. The f‐ratio for diatom nitrogen use estimated from silicic acid and nitrate depletion curves and the mean ∫ D:∫ P ratio was found to be 0.83, indicating that silica was being regenerated at a rate that was only slightly slower than that for particulate organic nitrogen. These data provide direct evidence confirming earlier hypotheses that the silica pump is weak in Monterey Bay. Analysis of the global data set on ∫ D:∫ P in the surface ocean leads to the hypothesis that low ∫ D: ∫ P (~0.10 or less) are typical of diatom bloom events, with ∫ D:∫ P rising to values in excess of 0.50 during nonbloom periods. This pattern is shown to be consistent with previous estimates that the annual mean ∫ D:∫ P ratio in the upper 200 m of the global ocean is 0.5–0.6. A regional analysis reveals that the fraction of silica production supported by new silicic acid varies as a hyperbolic function of the level of gross silica production similar to the variation in the f‐ratio for N use with primary productivity. These trends suggest that diatom blooms, especially those occurring in more productive waters, are the main vectors of silica export in the sea, with the majority of the silica produced during nonbloom periods being recycled in the euphotic zone.
Iron requirements for dinitrogen‐ and ammonium‐supported growth in cultures of Trichodesmium (IMS 101): Comparison with nitrogen fixation rates and iron: carbon ratios of field populations
Authors: Kustka Adam B. , Sañudo‐Wilhelmy Sergio A. , Carpenter Edward J. , Capone Douglas , Burns James , Sunda William G.
Published: July 2010

We quantified the relationships among the specific growth rate, intracellular iron content, and steady state iron uptake rate for cultures of the marine diazotrophic cyanobacterium Trichodesmium (IMS 101) grown under differing conditions of Fe and N availability. The Fe quotas necessary to support a moderately Fe‐limited growth rate (70% mmax) of 0.1 d−1 under diazotrophy and ammonium were 38 and 8 µmol mol−1, indicating a fivefold increased Fe cost for diazotrophy. This increased demand reflects the influences of both the ninefold lower marginal use efficiency and the greater maintenance Fe :C requirement at zero growth rate under diazotrophy (13.5 versus 5.2 µmol mol−1). For diazotrophic growth at µ = 0.1 d−1, we estimate that 19%–53% of the cellular Fe is bound in nitrogenase. Trichodesmium is capable of luxury uptake of at least 13‐fold greater amounts of Fe than needed for moderately Fe‐limited growth. At least half of the populations sampled from the continental shelf of northern Australia had Fe :C ratios within the range of iron limitation of laboratory cultures. Bottle incubations showed that, after 3–4 d with added iron, a low Fe :C population (21 µmol mol−1) had higher N2 fixation rates than controls, whereas a high Fe :C population (78 µmol mol−1) showed no response. The cellular N: P quotas and N2 fixation rates were compared to those previously reported for the Atlantic Ocean. Empirically, these data suggest a critical N: P ratio ~40–50 for the onset of P limitation of growth. Only 10% of the Trichodesmium populations from coastal Australia had N: P ratios within the putative P‐limitation range (>40), whereas 40% the Atlantic populations fell within this range. These comparisons, along with those for N fixation versus colony Fe :C ratio, suggest that Fe limitation is more prevalent in the Australia Trichodesmium populations, while P limitation predominates in the Atlantic populations.
Evidence for nutrient enrichment of high‐elevation lakes in the Sierra Nevada, California
Authors: Sickman James O. , Melack John M. , Clow David W.
Published: July 2010

Long‐term measurements (1983–2001) of nutrients and seston in Emerald Lake (Sierra Nevada, California) have revealed ecologically significant patterns. Nitrate, both during spring runoff and during growing seasons, declined from 1983 through 1995. Declining snowmelt nitrate was caused primarily by changes in snow regime induced by the 1987–1992 drought: years with shallow, early melting snowpacks had lower snowmelt nitrate concentrations owing to less labile N production in catchment soils and longer plant growing seasons. However, nitrate declines during growing seasons carried through the wetter years of 1993–2000 and are likely the result of increased P loading to the lake and the release of phytoplankton from P limitation. Contemporaneous with these changes was an increase in algal biomass and a shift from P limitation toward more frequent N limitation of phytoplankton abundance. Particulate carbon concentrations in the late 1990s were two‐ to threefold greater than in the early 1980s. These trends were reflected in a larger set of Sierra Nevada lakes sampled as part of synoptic surveys (n = 28). Between 1985 and 1999, nitrate decreased and total P increased in .>0% of the lakes sampled. Our data suggest that lakes throughout the Sierra Nevada are experiencing measurable eutrophication in response to the atmospheric deposition of nutrients.
Abundance and distribution of planktonic Archaea and Bacteria in the waters west of the Antarctic Peninsula
Authors: Church Matthew J. , DeLong Edward F. , Ducklow Hugh W. , Karner Markus B. , Preston Christina M. , Karl David M.
Published: July 2010

Polyribonucleotide probes targeting planktonic archaeal (Group I and II) and bacterial rRNA revealed that Archaea comprised a significant fraction of total prokaryote cell abundance in the marine waters west of the Antarctic Peninsula. Determinations of Archaea and Bacteria cell abundances were made during two research cruises to the Palmer Long‐Term Ecological Research region during the austral winter and summer of 1999. During the austral summer, surface water abundances of Group I (GI) Archaea were generally low, averaging 4.7 x 103 cells ml−1 and accounting for 1% of the total picoplankton assemblage. The abundance of GI Archaea increased significantly with depth, averaging 2.1 X 104 cells ml−1 and comprising 9–39% of the total picoplankton abundance in the meso‐ (150–1,000 m) and bathypelagic (1,000–3,500 m) circumpolar deep water (CDW). Relative to summertime distributions, GI cells were more evenly distributed throughout the water column during the winter, averaging 10% of the picoplankton in the surface waters and 13% in the CDW. Surface water GI abundance increased 44% between the summer and winter, coincident with a fivefold decrease in GI abundance in the deeper waters. The abundance of Group II (GII) Archaea was persistently <2% of the total picoplankton throughout the water column in both summer and winter. Bacterial abundance was greatest in the upper water column (0–100 m) during the summer, averaging 3.9 x 105 cells ml−1 and comprised 89% of the total picoplankton assemblage. Generally, GI Archaea varied seasonally in the deeper waters, whereas bacterial abundance varied more in the upper waters. The observed variability in bacterial and archaeal abundance suggests that these two groups of marine picoplankton are dynamic components of Southern Ocean microbial food webs.
Growth of marine planktonic copepods: Global rates and patterns in relation to chlorophyll a, temperature, and body weight
Authors: Hirst A. G. , Bunker A. J.
Published: July 2010

We compiled a global data set of copepod in situ weight‐specific fecundity and growth rates, together with measurements of their body weights, and the chlorophyll a and temperature of the natural water in which these animals were growing. Juveniles can achieve half‐saturation of their growth (Km) at chlorophyll a concentrations almost an order of magnitude lower than adult females can their weight‐specific fecundity. Adult weight‐specific fecundity rates in situ are correlated with temperature, but the Q10s of 1.59 and 1.43 in broadcast and sac spawners, respectively, are much lower than under food saturated laboratory conditions (Q10s of 2.75 and 3.98). By comparing the in situ and laboratory food saturated results we are able to assess food limitation in the environment. The degree of food limitation increases with increasing temperature for adults; in situ rates approximate food saturated rates at low temperatures (0–10°C), at 25°C they are on average only about one‐fifth of those at food saturation. By contrast, in situ juvenile rates are more strongly temperature‐dependent than their adults and close to food saturation even at high temperatures. Juveniles grow much more rapidly and closer to food saturation than do adults of a similar size. There are several possible reasons for this. Compounds needed for egg production may simply be more dilute than those used in somatic growth. However, it is also possible that food limitation acts very differently in adults than juveniles. Molting rates in juveniles are strongly temperature dictated, and if sufficient weight is not added between molts, these slower growing juveniles do not survive. Adults, by contrast, can survive for long periods without having sufficient food to produce eggs.
Bioaccumulation of polonium‐210 in marine copepods
Authors: Stewart Gillian M. , Fisher Nicholas S.
Published: July 2010

210Po, a naturally occurring radioisotope that is ubiquitous in seawater, is especially enriched in proteinaceous tissues of marine organisms and may therefore be useful as a tracer of organic carbon flux in marine systems. Due in part to its biomagnification in marine food chains, 210Po provides the largest radiation dose to any organism under natural conditions. To better understand the extent to which zooplankton can influence the fluxes of 210Po and serve as a conduit between phytoplankton, which concentrate it greatly from ambient water and higher trophic levels, we conducted a series of laboratory experiments with the calanoid copepod Acartia tonsa. A. tonsa was presented with either dissolved 210Po or with one of eight different phytoplankton species and sterile glass beads, all labeled with 210Po. Assimilation efficiencies (AEs) of ingested 210Po in copepods ranged from 19% to 55% among the phytoplankton diets, and correlated directly with 210Po's cytoplasmic distributions in the algal cells. The AE of 210Po from ingested glass beads was 0%. The high AE and low efflux rates (mean of 3% d−1) of 210Po in copepods can explain its biomagnification in marine food chains. Uptake and loss parameters of 210Po in copepods measured in these experiments were used in a model to quantify the relative sources of 210Po for copepods. Under all realistic scenarios, >90% of 210Po in copepods appears to be taken up through diet. Model‐predicted 210Po concentrations in copepods in different ocean regions closely matched independent measurements, suggesting that we understand the processes governing this element's enrichment in zooplankton and thus can make quantitative predictions of its bioconcentration on a site‐specific basis.
Synchronization in the molting and spawning activity of northern krill (Meganyctiphanes norvegica) and its effect on recruitment
Authors: Tarling Geraint A. , Cuzin‐Roudy Janine
Published: July 2010

The molting, spawning, and recruitment of northern krill (Meganyctiphanes norvegica) were analyzed over an annual cycle (1999–2000) in the Clyde Sea (west coast of Scotland). Results supported the hypothesis of a functional relationship between egg production and molt development for the duration of the reproductive season (March to August), with one reproductive cycle being made up of two molt cycles. Females remained in reproductive condition throughout the reproductive season, and the timing of their spawning and molting was synchronized at the population level throughout this period. A semiempirical model predicted that the krill population produced an egg pulse every 20 to 26 d (depending on temperature), and three cohorts were evident in net samples taken later in the year. The likely date on which the first cohort was spawned was around 26 d after the main phytoplankton bloom, suggesting that the bloom triggered egg development in all adult females. Such a synchronized spawning period was observed directly in adult females 26 d after a bloom in March 2000. A total of three cohorts over the 6‐month reproductive season is less than the maximum of seven that would be possible if spawning occurred at a periodicity of between 20 and 26 d, suggesting that larval recruitment was not always successful. Analysis showed that successful recruitment was only achieved when chlorophyll a levels were adequate during both the period of egg maturation in the ovary and the subsequent development of larvae, especially the furcilia stages.
Breathing sediments: The control of diffusive transport across the sediment—water interface by periodic boundary‐layer turbulence
Authors: Lorke Andreas , Müller Beat , Maerki Martin , Wüest Alfred
Published: July 2010

We performed combined in situ measurements of bottom boundary‐layer turbulence and of diffusive oxygen fluxes at the sediment‐water interface in a medium‐sized mesotrophic lake. The turbulence was driven by internal seiching with a period of 18 h. This periodic forcing, a prominent feature of enclosed water bodies, led to distinct deviations of the structure and the dynamics of the bottom boundary layer from the classical law‐of‐the‐wall theory. A major feature was a phase lag between the current velocity and the turbulent energy dissipation of approximately 10% of the seiching period (1.5–2 h). The oxygen flux into the sediment was controlled by the diffusive boundary layer, the thickness of which varied between 0.16 and 0.84 mm during the course of a seiching period, and was strongly affected by the periodic bottom boundary‐layer turbulence. The rate of dissipation of turbulent energy in the bottom boundary layer allowed us to define the Batchelor length for dissolved oxygen, which quantifies the smallest scales of oxygen fluctuations and provides an appropriate scaling for the diffusive boundary‐layer thickness and the corresponding oxygen fluxes. An analysis of the governing time scales revealed the importance of turbulence in controlling the small‐scale spatial heterogeneity of the diffusive fluxes. Higher turbulence causes the diffusive boundary layer (DBL) to follow the sediment topography more smoothly, resulting in an increased area‐averaged flux due to the greater effective surface area.
Clams as CO2 generators: The Potamocorbula amurensis example in San Francisco Bay
Authors: Chauvaud Laurent , Thompson Janet K. , Cloern James E. , Thouzeau Gérard
Published: July 2010

Respiration and calcium carbonate production by the invasive Asian clam, Potamocorbula amurensis, were calculated to assess their importance as CO2 sources in northern San Francisco Bay. Production, calculated using monthly population density and size structure measured at three sites over 7 yr and a shell length/CaCO3 conversion factor, averaged 221 (±184) g CaCO3 m−2 yr−1. Net calcium carbonate production by this exotic bivalve releases CO2 at a mean rate of 18 (±17) g C m−2 yr−1. Respiration by P. amurensis, estimated from secondary production, releases additional CO2 at a mean rate of 37 (±34) g C m−2 yr−1. Therefore, total net CO2 production by P. amurensis averages 55 (±51) g C m−2 yr−1 in an estuarine domain where net primary production consumes only 20 g inorganic C m−2 yr−1. CO2 production by P. amurensis in northern San Francisco Bay is an underestimate of the total CO2 supply from the calcified zoobenthic communities of San Francisco Bay, and results from other studies have suggested that this rate is not unusual for temperate estuaries. Global extrapolation yields a gross CO2 production rate in the world's estuaries of 1 x 1014 g C yr−1, which suggests that calcified benthic organisms in estuaries generate CO2 equal in magnitude to the CO2 emissions from the world's lakes or from planetary volcanism (the net source is determined by the highly variable rate of CO2 consumption by carbonate dissolution). This biogenic CO2 source is increasing because of the continuing global translocation of mollusks and their successful colonization of new habitats.
Propagule transport as a key method of dispersal in benthic foraminifera (Protista)
Authors: Alve Elisabeth , Goldstein Susan T.
Published: July 2010

The distributional patterns of benthic foraminifera provide key information for paleoclimatic, paleoecologic, and paleoceanographic studies. Yet the dispersal mechanisms that provide a crucial link between local populations and large‐scale biogeographic patterns are not well documented. We experimentally demonstrate the dispersal of propagules, which include both sexually and asexually produced young (perhaps only the proloculus), though the sexually produced young appear to have a greater potential for dispersal. The propagules can rest in a cryptic state for months, constitute a substantial bank of individuals in sediments from water depths beyond the natural distribution of conspecific adults, and grow in these sediments when exposed to favorable conditions. Propagule dispersal probably provides an effective mechanism for colonization of widely separated habitats in a fashion broadly similar to other eukaryotic microbial groups and many groups of marine invertebrates.
Nitrate uptake in the scleractinian coral Stylophora pistillata
Authors: Grover Renaud , Maguer Jean-François , Allemand Denis , Ferrier-Pagés Christine
Published: July 2010

We assessed the uptake rates of nitrate by the scleractinian coral Stylophora pistillata by following 15N from seawater into the coral tissue. Two sets of corals were first prepared, with “nitrate‐enriched” corals grown in 5 µmol L−1 NO3− and control corals grown in ≤µmol L−1 NO3−. Uptake rates at 0.3 and 3 µmol L−1 [15N]NO3− were then measured. Most of the %15N enrichment occurred in the zooxanthellae fraction. Uptake rates were not significantly different between nitrate‐enriched and control corals, suggesting that they were not dependent on a nitrate acclimation. These rates increased with the in situ nitrate concentration and varied from 1.2 ± 0.2 ng h−1 cm−2 N to 6.1 ± 1.1 ng h−1 cm−2 N in the algal fraction at 0.3 and 3 µmol L−1 [15N]NO3−, respectively. In a second experiment, two sets of corals were prepared, with “ammonium‐enriched” corals grown in 5 µmol L−1 NH4+ and control corals grown in <1 µmol L−1 NH4+. Uptake rates at 3 µmol L−1 [15N]NO3− were measured. These rates were significantly lower with high NH4+ concentrations in seawater. In the algal fraction, they ranged from 0.1 to 0.6 ng 14 h−1 cm−2 N in NH4+‐enriched corals and from 2.2 to 4.5 ng h−1 cm−2 N in control corals. Nitrate can therefore be considered as an important source of nitrogen for corals, at least when ammonium concentrations are low in seawater.
Cycling of colloidal organic carbon and nitrogen during an estuarine phytoplankton bloom
Authors: Gobler Christopher J. , Sañudo-Wilhelmy Sergio A.
Published: July 2010

To establish the influence of phytoplankton blooms on the cycling of dissolved and particulate species of organic carbon and nitrogen, we conducted a field study during a series of blooms in a coastal embayment on Shelter Island, NY. Using cross‐flow filtration, we collected high‐ and low‐molecular‐weight (HMW and LMW) dissolved organic matter (DOM), along with particulate organic matter (POM). There was a significant and near equivalent enhancement in levels of particulate organic carbon (POC) and dissolved organic carbon (DOC) during phytoplankton blooms. HMW organic carbon was responsible for most (80%) of the DOC increase. In contrast, substantial amounts of organic nitrogen were produced in all size fractions (particulate organic nitrogen [PON], HMW, and LMW) during blooms. POC:PON and HMW C:N ratios exceeded Redfield stoichiometry and were well correlated with chlorophyll concentrations, which suggests that phytoplankton were the primary source of C‐enriched particles and colloids in this system. DOM C:N ratios were higher during periods of elevated nitrate than during low nitrate conditions, which were dominated by phytoplankton with heterotrophic capabilities. This suggests that, in some coastal systems, the accumulation of C‐enriched organic matter may be more dependent on algal species composition than ambient inorganic nitrogen levels. After the collapse of algal blooms, bacterial densities rose markedly, and all organic pools rapidly decreased to near prebloom levels. Despite substantial production and turnover rates of HMW organic carbon during blooms, longer residence times of other, more refractory, organic carbon pools such as the LMW fraction indicated that considerable portions of organic matter produced during estuarine phytoplankton blooms may be exported to continental shelves.
Increasing temperature decreases aluminum concentrations in Central European lakes recovering from acidification
Authors: Veselý Josef , Majer Vladimír , Kopáček Jiří , Norton Stephen A.
Published: July 2010

As acidic water percolates through mineral soils, Al is mobilized and transported into streams and lakes. We evaluate the effect of increasing temperature (climate warming) on Al concentrations in four strongly acidified lakes in the Bohemian Forest, southwestern Czech Republic, over a 17‐yr period (1984–2001). Pronounced decreases in atmospheric S and N deposition resulted mainly in a sharp monotonic decrease in lake water concentration of total Al (—0.49 to —1.38 µmol L−1 yr−1). Residuals from the linear relationship between total Al concentrations and the sum of strong acid anions were inversely correlated with air temperature and the North Atlantic Oscillation index. An increase in the average annual air temperature of +1.27 ± 0.49°C between 1984 and 2001 was correlated with decreases in toxic Al3+ and explained, on average, 13% of the total Al decrease in three lakes and 11% of the Al3+ decrease in Černé Lake. The inverse relationship between Al solubility and temperature caused lower Al mobilization in soil horizons and/or enhanced precipitation of Al in the lakes at higher temperature but otherwise similar conditions. As a consequence, the recent period of warmer years and mild winters significantly contributed to the trend of decreasing Al in lakes recovering from acidification.
Effect of pH on measurement of strong copper binding ligands in lakes
Authors: Averyt Kristen B. , Kim Jonathan P. , Hunter Keith A.
Published: July 2010

We investigated the effect of pH on Cu2+ binding by natural organic ligands in two New Zealand lakes on the South Island, New Zealand, using competitive ligand equilibration with salicylaldoxime and detection by cathodic stripping voltammetry. When the pH of a lakeߚwater sample was adjusted to different values in the range 6.3ߚ8.0, the conditional Cu2+ binding constant K" was found to increase, with a slope log K" versus pH of nearly 12, as would be expected for functional groups having a proton dissociation constant pKa > 9. In support of this, a comparison of log K" values measured on samples taken from surface and subsurface waters of two New Zealand alpine lakes over a 2ߚyr period showed a very similar log K"ߚpH dependence. These results imply that the functional group chemistry of strong Cu2+ߚbinding ligands in such lakes is relatively uniform and may involve phenolic OH groups. In Lake Hayes, the Cuߚbinding ligand concentration [L]T exceeded that of total dissolved Cu, [Cu]T at almost all times of the year and all depths. However, in Lake Manapouri, little evidence of Cuߚbinding ligand was observed during late summer in the mixed layer, which suggests a seasonal cycle in Cuߚbinding ligands that is perhaps driven by enhanced ultraviolet irradiation in summer or by seasonal changes in phytoplankton community structure. This may have important consequences for the toxicity of Cu2+ to organisms in these lakes during summer.
Trophic transfer of trace metals from protozoa to mesozooplankton
Authors: Twining Benjamin S. , Fisher Nicholas S.
Published: July 2010

Radiotracer techniques were used to quantify the assimilation and subsequent efflux of silver, cadmium, iron, mercury, thallium, and zinc by mesozooplankton fed ciliates, heterotrophic dinoflagellates, or heterotrophic flagellates, and the results were compared with published values measured for phytoplankton prey. The subcellular distribution of the metals within the prey cells was also determined and related to their bioavailability. Marine copepods assimilated 59ߚ82% of Ag, 83ߚ92% of Cd, 32ߚ66– of Fe, 14ߚ49% of Hg, and 71ߚ78% of Zn ingested with protozoan prey. Higher Ag, Cd, Fe, and Hg assimilation efficiencies were observed for at least one of the species of protozoa than reported in the literature for phytoplankton. Significant differences in assimilation were not observed for Zn or for Tl fed to freshwater Ceriodaphnia in either protozoa or phytoplankton. The higher assimilation efficiencies of protozoan metals, when observed, were matched by higher fractions of metals in the cytoplasm of protozoa. A biokinetic model used to calculate steadyߚstate metal concentrations in copepods indicates that copepods may contain 119% more Ag and 44% more Zn when feeding on ciliates instead of diatoms, possibly resulting in sublethal toxic effects at Ag and Zn concentrations reported for the Hudson River estuary. Further, higher assimilation and efflux rates of protozoan Fe may enhance remineralization of this limiting nutrient by mesozooplankton in high nutrient, low chlorophyll regions.
Predation as a factor mediating resource competition among rotifer sibling species
Authors: CirosߚPérez Jorge , Carmona María José , Lapesa Sara , Serra Manuel
Published: July 2010

The relevance of predation as a factor mediating the competitive interaction among ecologically very similar species is investigated by experimentally analyzing the effect of the copepod predator Diacyclops bicuspidatus odessanus on three sibling rotifer species belonging to the Brachionus plicatilis species complex. These rotifer species are similar in shape but show notable differences in body size. Predator and prey species coߚoccur in brackish waterbodies close to the Mediterranean coast of Spain. First, we characterized differential vulnerability of rotifers to predation. A consistent tendency of higher predation rates on smaller prey (i.e., smaller species and younger individuals) was observed. Analysis of predation showed that predator contact rate did not differ significantly among prey species, but that attack, capture probabilities, and handling time did. Second, we performed population dynamics experiments with two prey species competing for a single resource at different levels of predation. Predation extended coexistence of the competing rotifers, whereas the inferior competitor was excluded in the absence of the predator. In some pairwise experiments, we found that the greater the predation level, the larger the relative increase in density of the inferior competitor. Our results suggest that predation can affect the dynamics of very similar competing species in natural aquatic communities, promoting coexistence.
Evidence for constant and highly specific active food selection by benthic ciliates in mixed diatoms assemblages
Authors: Hamels Ilse , Mussche Heidi , Sabbe Koen , Muylaert Koenraad , Vyverman Wim
Published: July 2010

Observational and experimental studies have shown that phagotrophic ciliates are highly selective predators. However, little is as yet known about the actual mechanisms involved in prey selection. We used direct behavioral observations to study the mechanism of prey selection in benthic algivorous ciliates feeding on mixed assemblages of diatom species. Four ciliate species, viz. three Strombidium species and a Pseudochilodonopsis species, and three diatom species from intertidal sediments in the Schelde estuary were used for the experiments. In each experiment, a single ciliate species was offered a mixture of two diatom species. The feeding preferences of the ciliates were estimated as well as relative encounter rates, attack probabilities, and capture successes for the prey species. The feeding preferences of the ciliates were distinctly predatorߚspecific and highly discerning with respect to the nature of the prey species. They appeared to result mainly from active selection at the time of the encounters and between the encounter and attack of the diatoms. Our observations suggest that selective encounters with the diatoms were caused by noncontact detection of individual prey items, at least for the Strombidium species. Additional experiments confirmed that these ciliates were able to distinguish between diatom species on the basis of soluble chemical cues. Grazing was also constant, i.e., prey switching was not observed. Moreover, neither total prey density nor feeding history influenced the preferences. We hypothesize that these highly specialized trophic interactions may be an important driving force in shaping structure and diversity of benthic diatom communities in intertidal sediments.
Observations of particle capture on a cylindrical collector: Implications for particle accumulation and removal in aquatic systems
Authors: Palmer Molly R. , Nepf Heidi M. , Pettersson Thomas J. R. , Ackerman Josef D.
Published: July 2010

Capture of suspended particles by cylindrical collectors is an important mechanism in many aquatic processes, such as larval settlement, suspension feeding, and vegetative filtration. In these processes, the collector Reynolds number (Rec), based on the collector diameter, ranges from well below 1 to 1,000. No analytical solutions exist to describe capture over most of this range. Capture is typically described by the efficiency, η, defined as the ratio of the upstream span of particles that are captured on the collector to the collector diameter. Here, laboratory experiments are used to measure capture efficiency of a single cylinder as a function of Rec and particle ratio, R, which is the ratio of particle diameter to collector diameter. Rec is varied from 50 to 500 and three values of R are used: 0.03, 0.015, and 0.008. The selected particles have a specific gravity of 1.03. For smooth cylinders, capture increases with both Rec and R but is more strongly dependent on R. This result indicates that, in aquatic systems, where flow velocity and suspended particle type and size are fixed, higher capture efficiency will occur on the smallest collectors (those with largest R). Furthermore, we examine a similar experiment in which particles are collected by branched structures. We show that capture to individual cylindrical branches within a compound structure can be predicted by single‐cylinder efficiencies. Finally, capture was increased when roughness elements were added to the collectors.
Competition between biological and photochemical processes in the mineralization of dissolved organic carbon
Authors: Obernosterer Ingrid , Benner Ronald
Published: July 2010

The photo‐ and bioreactive components of dissolved organic matter (DOM) from three different environments were determined during long‐term decomposition experiments. Terrigenous DOM was collected from a black‐water system, plankton DOM was harvested from phytoplankton cultures, and lake water served as a DOM source with both terrigenous and plankton components. Photomineralization accounted for the removal of 46 and 7% of terrigenous and lake‐dissolved organic carbon (DOC), respectively, while no loss in DOC was observed when plankton DOM was exposed to irradiation. Biomineralization accounted for the removal of 27% each of terrigenous and lake DOC and 74% of plankton DOC. Phototransformations of terrigenous and lake DOM resulted in 7% and 2% increases in biodegradable DOC, respectively, while no increase in biodegradable DOC was observed for irradiated plankton DOM. In two different experimental approaches, terrigenous DOM was exposed to sequential and alternating bio‐ and photodegradation, respectively, to determine the fractions of DOC that were bioreactive and photoreactive. About 15% of terrigenous DOC was susceptible to both biomineralization and photomineralization. These results demonstrate that biological and photochemical processes compete in the mineralization of DOC. Photomineralization of bioreactive DOC is likely an important factor determining the net effect of irradiation on the bioreactivity of DOM.
Influence of inlet bacteria on bacterioplankton assemblage composition in lakes of different hydraulic retention time
Authors: Lindström Eva S. , Bergström Ann-Kristin
Published: July 2010

The influence of inlet bacteria on the assemblage composition of bacterioplankton was investigated in two Swedish forest lakes of different hydraulic retention time. Assemblage composition of the bacteria in lakes and running waters was determined by denaturing gradient gel electrophoresis (DGGE) and sequencing of polymerase chain reaction (PCR)‐amplified 16S rDNA. The amount of bacterial cells imported via the inlets in relation to bacterioplankton cells produced in the epilimnion of the lakes was also determined. In the lake with short retention time (theoretical hydraulic retention time of 0.3 yr) the lake bacterioplankton assemblage largely resembled the riverine assemblages, although the extent of similarity varied among inlets, depending on water flow. In the lake with long retention time (theoretical hydraulic retention time of 10 yr) the bacterioplankton assemblage in the lake had low similarity to the inlet assemblages. The degree of similarity between inlets and lakes was well correlated to the amount of imported cells. Thus, our data suggest that import of inlet bacteria could have a large effect on the composition of lake bacterioplankton assemblages and that hydrological factors determined the magnitude of this effect. Since short hydraulic retention times are very common in lakes in the boreal zone, input of allochthonous bacteria can be one major factor influencing bacterioplankton assemblage composition in boreal lakes.
Evidence for terrigenous dissolved organic nitrogen in the Arctic deep sea
Authors: Dittmar Thorsten
Published: July 2010

To trace the fate of terrigenous dissolved organic nitrogen (DON) in the Arctic Ocean, principal‐components analyses (PCA) was used on a data set of 13 amino acids released via hydrolyses from a total of 110 water samples from Russian rivers, adjacent near‐shore locations, and the Laptev Sea. The first component of the PCA distinguished significantly between terrigenous DON from the rivers (1.2 ± 0.1) and marine‐derived DON in the deep central Arctic Ocean (−1.1 ± 0.2). The significance of this distinction was validated with amino acid data from seawater and river samples from other regions. The second PCA component correlated significantly with the proportion of D‐alanine, a tracer for microbial degradation. The percentage of terrigenous DON in the Arctic Ocean was assessed from the first PCA component. The model was calibrated using data from the rivers (100% terrigenous) and the deep central Arctic Ocean (~0% terrigenous) as end members. Terrigenous DON accounted for 28 ± 13% of the total DON on the Laptev Sea shelf, which is in good agreement with independent, lignin‐based estimates. High proportions of terrigenous DON (up to 100%) were calculated for the continental slope down to 2,000 m depth and are probably due to downward convection of brine‐enriched shelf waters. The model presented here provides the first direct evidence of terrigenous DON in the deep sea. The model may be directly applied to trace the fate of terrigenous DON in other terrestrially dominated marine environments.