bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of iron deficiency on diatom cell size and silicic acid uptake kinetics
Authors: A. Leynaert , Bucciarelli E. , Claquin P. , Dugdale R. C. , Martin‐Jézéquel V. , Pondaven P. , Ragueneau O.
Published: July 2010

We studied the silicic acid uptake kinetics of the pennate diatom Cylindrotheca fusiformis grown under a wide range of iron concentrations (from Fe‐limiting to Fe‐sufficient conditions) to assess the effect of iron availability on diatom cell size, silicon content, and silicic acid uptake kinetic parameters. As the iron stress increased, the growth rate slowed, cell size decreased, and silicification increased. A series of Si kinetic uptake experiments (from Si‐limiting to Si‐sufficient conditions) performed at different iron concentrations demonstrated the extent of the colimitation domain, where the specific Si uptake rate (VSi) varied as a function of both silicic acid and Fe availability. A decrease in maximal specific uptake rate of silicic acid (VSi‐max) under iron limitation was observed along with a decrease in half‐saturation constant for silicic acid uptake (KSi). Because VSi‐max and KSi vary in the same direction, the specific affinity for silicic acid does not change under iron stress. The variation in cell size is an acclimation to low nutrient concentrations. Our study shows that Si uptake kinetics parameters, especially VSi‐max, are strongly related to cell size, which is itself constrained by the degree of iron limitation. Thus, the surface to volume ratio should be related to silicic acid flows in size‐based biogeochemical models of planktonic ecosystems. Another way to describe the observed variations of Si uptake over the full range of Si and Fe concentrations tested in the present study would be to implicitly take into account the variations in cell size through a scaling of the maximal specific uptake rate (Vmax) by the iron‐limitation term in a multiplicative manner.
Tissue carbon, nitrogen, and sulfur stable isotope turnover in transplanted Bathymodiolus childressi mussels: Relation to growth and physiological condition
Authors: Dattagupta S. , Bergquist D. C. , Szalai E. B. , Macko S. A. , Fisher C. R.
Published: July 2010

The growth and physiological condition of the methanotrophic hydrocarbon seep mussel Bathymodiolus childressi reflects the habitat quality of the sites it occupies on the seafloor of the upper Louisiana slope of the Gulf of Mexico. Here, tissue stable isotope compositions, growth, and physiological health of B. childressi mussels transplanted between different seep sites changed within a year to reflect conditions at the new environment. Tissue stable carbon and nitrogen isotope turnovers, although substantial, were not complete at the end of the 1‐yr transplant period; they were strongly correlated with each other, and the extent of turnover of both varied by site and was related to the growth of the mussels. Carbon and nitrogen isotopic turnovers caused by metabolic tissue turnover were about 35% per year. This slow isotopic turnover in B. childressi is presumably due to its relatively slow growth and low metabolic rate. On the other hand, tissue stable sulfur isotope turnover was not correlated with either stable carbon or nitrogen isotope turnover or growth and was higher in the site with higher levels of sulfide in the environment. This indicated that tissue stable sulfur isotope turnover in these mussels is influenced by sulfide detoxification activities.
Changes to zooplankton community structure following colonization of a small lake by Leptodora kindti
Authors: McNaught A. Scott , Kiesling Richard L. , Ghadouani Anas
Published: July 2010

The predaceous cladoceran Leptodora kindti (Focke) became established in Third Sister Lake, Michigan, after individuals escaped from experimental enclosures in 1987. By 1988, the Leptodora population exhibited seasonal dynamics characteristic of natural populations. The maximum seasonal abundance of Leptodora increased to 85 individuals m−3 3 yr following the introduction. After the appearance of Leptodora, small‐bodied cladocerans (Ceriodaphnia and Bosmina) virtually disappeared from the lake. There were strong seasonal shifts in the dominance patterns of both cladocerans and copepods, and Daphnia species diversity increased. Results from this unplanned introduction suggest that invertebrate predators can have a rapid and lasting effect on prey populations, even in the presence of planktivorous fish. Small‐scale (<20 km) geographic barriers might be as important as large‐scale barriers to dispersal of planktonic animals.
Physical, chemical, and biotic effects on arctic zooplankton communities and diversity
Authors: O'Brien W. John , Barfield Michael , Bettez Neil D. , Gettel Gretchen M. , Hershey Anne E. , McDonald Michael E. , Miller Michael C. , Mooers Howard , Pastor John , Richards Carl , Schuldt Jeff
Published: July 2010

We examined how physical and chemical factors and fish populations affected the presence and density of zooplankton species in 104 Alaskan arctic lakes. Five fish species and nine zooplankters were sampled from the lakes. Lake depth was related to the distribution of zooplankton in that smaller zooplankton species were found in deep lakes and large species in shallow lakes. Neither ionic strength nor chlorophyll was a major factor in zooplankton presence or absence. When fish were present, few, if any, very large zooplankton occurred together. However, the relationship between the presence and density of smaller‐sized zooplankton species and the presence of specific species of fish was complex and did not fit anticipated patterns. The diversity of zooplankton in these arctic lakes was not related to chemistry or fish distribution, but species richness increased with increasing lake area and depth. For a few zooplankters (notably Holopedium gibberum), the fraction of lakes containing the zooplankter varied by region.
Mechanisms for emergence from diapause of Calanoides carinatus in the Somali current
Authors: Idrisi Nasseer , Olascoaga M. Josefina , Garraffo Zulema , Olson Donald B. , Smith Sharon L.
Published: July 2010

We studied mechanisms that might control the emergence of the last juvenile stage of Calanoides carinatus from diapause in the Arabian Sea. Diapaused copepods are modeled as Lagrangian particles that include a simplified means for lipid catabolism during diapause. The advective field for the particles, which are released at intermediate and deep layers off the Somali shelf, is determined by a regional version of the Miami isopycnic coordinate model (MICOM). Dormant copepods emerge from diapause in response to either onshore advection (physical upwelling) or depletion of lipid reserves to an assumed critical level (internal biological clock). The majority of the diapaused copepods that successfully complete their life cycle are those retained within the coastal upwelling zone and emerge as a consequence of depletion of the lipid reserves.
Zooplankton life cycles: Direct documentation of pelagic births and deaths relative to diapausing egg production
Authors: Jarnagin S. Taylor , Kerfoot W. Charles , Swan Brandon K.
Published: July 2010

Zooplankton demographics operate over multiple time scales corresponding to pelagic parthenogenetic generations, an overwintering stage, and an “egg bank.” Comparisons of pelagic birth and death rates with seasonal diapausing egg production provide insights into local species persistence. The spiny cladoceran (Bythotrephes) possesses morphological adaptations (spines and thick‐walled diapausing eggs) that lessen, but do not eliminate, predation effects by fish. Because caudal spines are retained throughout life and are indigestible in fish guts, spine accumulation in sediment traps directly documents patterns of seasonal mortality. Here, we contrast deposition of spines and diapausing eggs in a recently colonized inland lake (Lake Michigamme) with deposition in a larger source lake (Lake Michigan). Direct mortality estimates at the inland lake correspond well with traditional indirect estimates from egg ratio techniques. Although spines are effective against abundant small fish in the inland lake, individuals are susceptible to ingestion by late‐season young of year and larger fish. Laboratory experiments confirm that fish are responsible for spine breakage in the water column, accounting for an estimated 62–71% of seasonal mortality. Effects of late‐season predation are lessened because diapausing eggs survive gut passage, yet yearly production of diapausing eggs is low in Lake Michigamme. A more balanced pelagic birth(death) to diapausing egg relationship exists in Lake Michigan, probably because egg‐carrying adults find better refuge in central, deeper waters. Since spines catch on seines and diapausing eggs survive gut passage, use of bait fish and live wells promotes Bythotrephes dispersal.
Winter storms: Sequential sediment traps record Daphnia ephippial production,resuspension, and sediment interactions
Authors: Kerfoot W. Charles , Budd Judy Wells , Eadie Brian J. , Vanderploeg Henry A. , Agy Megan
Published: July 2010

For species that do not over‐winter, an essential part of the life cycle is the production of diapausing eggs. We use sequential sediment traps in southern Lake Michigan (1997‐2000) to capture settling Daphnia ephippia and sediments, characterizing ephippial production and sediment interactions during hazardous conditions. Each year, there was an enormous pulse of D. mendotae ephippia (ca. 7.2 × 1013 ephippia, 1.2 × 1014 diapausing eggs) that coincided with autumn population decline. Most ephippia settled through the water column, although a few were captured at the water surface and blown shoreward. The duration and amplitude of the autumn ephippial fluxes were similar among years. Ephippial production was positively correlated with water column depth, a consequence of Daphnia spatial abundance. In contrast, resuspension of ephippia was inversely related to water column depth and spatially complex, influenced by waves, coastal currents, and offshore gyre circulation. Large winter storms created nearshore sediment plumes, could resuspend vast numbers of ephippia (e.g., 10 March 1998 storm; 1.9 × 1012 ephippia and 3.1 × 1012 diapausing eggs), and were important in the formation of ÂÂegg banks.ÂÂ Almost all newly produced and resuspended diapausing eggs came from D. mendotae, with very few from two other species (D. retrocurva, D. dentifera) that dominated waters 12 yr ago. These observations suggest a relatively short relaxation time for species cycling out of egg banks in Lake Michigan (<10 yr), due in part to (1) differential resuspension of unconsolidated versus consolidated sediments and (2) the spatially restricted nature of ÂÂhigh‐sedimentationÂÂ zones. Our study is the first use of sequential sediment traps to document diapause egg production.
Phytoplankton growth and stoichiometry under multiple nutrient limitation
Authors: Klausmeier Christopher A. , Litchman Elena , Levin Simon A.
Published: July 2010

Phytoplankton growth and stoichiometry depend on the availability of multiple nutrients. We use a mathematical model of phytoplankton with flexible stoichiometry to explain patterns of phytoplankton composition in chemostat experiments and nutrient drawdown dynamics that are found in the field. Exponential growth and equilibrium represent two distinct phases, each amenable to mathematical analysis. In a chemostat at a fixed dilution (growth) rate, phytoplankton stoichiometry matches the nutrient supply stoichiometry over a wide range at low growth rates and over a narrow range at high growth rates. In a chemostat with a fixed nutrient supply stoichiometry, phytoplankton stoichiometry varies with dilution rate nonlinearly, between the supply stoichiometry at low dilution rates and a species‐specific optimal ratio at high dilution rates. The flexible‐stoichiometry model we study predicts low equilibrium concentrations of two nutrients over a wide range of supply ratios, contrary to the predictions of a traditional fixed‐stoichiometry model. The model is in quantitative agreement with experimental data, except at extreme nutrient supply ratios, which require a negative feedback from quota to uptake to fit the data. Our analysis points to the importance of better understanding the regulation of uptake rates in determining phytoplankton stoichiometry and incorporating this knowledge into phytoplankton models.
Chironomids (Diptera) and oxy‐regulatory capacity: An experimental approach to paleolimnological interpretation
Authors: Klaus PeterBrodersen Klaus Peter , Pedersen Ole , Lindegaard Claus , Hamburger Kirsten
Published: July 2010

We measured the ability to regulate oxygen uptake of 16 chironomid taxa from lakes in low‐arctic West Greenland by means of oxygen microelectrodes in custom‐made respiration chambers. The respiration patterns were modeled using piecewise linear regression with break‐point and simple hyperbolic functions. The mathematical constants obtained from the controlled laboratory experiments were good ecophysiological indicators of species‐specific "oxyregulatory capacity." The oxy‐regulatory capacity of different chironomid communities was calculated for subfossil assemblages collected from 52 lakes in West Greenland. The overall assemblage structure was expressed using detrended correspondence analysis (DCA). The oxy‐regulatory capacity was as strongly correlated to DCA axis 1 (r = 0.72–0.86, p < 0.001), as were surface water temperature (r = 0.82, p < 0.001) and nutrients (r = 0.47– 0.86, p < 0.001). Warm‐water chironomid assemblages characterized by taxa such as Chironomus, Dicrotendipes, Ablabesmyia, and Procladius had a high oxy‐regulatory capacity. Cold‐water assemblages were dominated by oxyconformers such as Heterotrissocladius, Micropsectra, Hydrobaenus, and Diamesa. An expression of the oxyregulatory capacity of a given chironomid assemblage can be directly inferred from a simple model using weighted averaging of the ecophysiological mathematical constants. The autecological information from controlled experiments provides important additional information for interpretations in chironomid paleolimnology. The results can also be used to identify secondary changes or mismatches in multiproxy down‐core paleoclimate studies.
Paleoproductivity of eastern Lake Ontario over the past 10,000 years
Authors: McFadden Melany A. , Mullins Henry T. , Patterson William P. , Anderson William T.
Published: July 2010

We evaluated relative levels of paleo‐primary productivity in eastern Lake Ontario during the past ~10,000 yr via analysis of inorganic and organic sediment from the Rochester Basin. There was significant natural variability in primary production correlative with Holocene climate change. The cold post‐Younger Dryas interval (~10–9.4 ka) was a time of minimal levels of primary production. The warm Holocene Hypsithermal interval (~9.4–5.3 ka) had much higher levels of primary production but was more variable, including five well‐defined cycles that have an average period of ~750 yr. The largest negative anomaly in primary productivity occurred during the 8.2‐ka climate event (~8.4–8.0 ka), a time of cold, dry conditions. Another negative anomaly occurred in association with the Nipissing flood (~6.3–5.3 ka), which triggered a regional cooling event. The cool Holocene Neoglacial interval (~5.3 ka to ~1850 A.D.) was characterized by lower, but more stable, levels of primary production, as well as by a cessation of calcite precipitation and the onset of diatom productivity. During the historic interval (~1850–1940 A.D.), there was a dramatic increase in primary production to unprecedented levels over the past 10,000 yr, as well as a 30–fold increase in sediment accumulation rates. These large, abrupt changes occurred in response to regional deforestation, anthropogenic nutrient loading, and increased chemical weathering due to acid rain. We project that, during 21st century global warming, eastern Lake Ontario will evolve into an ecosystem similar to that during the Holocene Hypsithermal.
Nutrient budget for the Eastern Mediterranean: Implications for phosphorus limitation
Authors: Krom M. D. , Herut B. , Mantoura R. F. C.
Published: July 2010

The eastern Mediterranean has a high nitrate to phosphate (N : P) ratio (~28 : 1) in the deep water and a highly unusual P limitation of the primary productivity. We present a detailed nutrient budget of inputs to the basin, which shows that there is a high N: P ratio (>16 : 1) in all the input sources, particularly from the atmospheric source, where the N: P ratio was 117 : 1. The high N: P ratio is retained within the system because there is no significant denitrification in either the sediments or intermediate water. This is because of the extreme oligotrophic nature of the system, which is caused by the unusual anti‐estuarine flow at the Straits of Sicily. Support for this conclusion is provided by the observation that the only area of the eastern Mediterranean where the N: P ratio in deeper water is ~16 : 1 is the northern Adriatic, which is also the only area with significant denitrification. The N budget (total input to basin vs. net output at the straits of Sicily) balances closely. This N balance suggests that N fixation is an insignificant process in this P‐limited system. The unusually light 15N values in the deep water nitrate and particulate organic nitrogen can be explained by processes other than nitrogen fixation. These processes include a lack of significant denitrification in the basin and by particulate organic matter exported from surface waters during the Plimited winter plankton bloom.
Phosphonates and particulate organic phosphorus cycling in an anoxic marine basin
Authors: Benitez-Nelson C. R. , O'Neill Lauren , Kolowith Lauren C. , Pellechia Perry , Thunell Robert
Published: July 2010

Total particulate phosphorus (TPP), particulate inorganic P (PIP), and particulate organic P (POP) concentrations were measured in a year‐long series of sediment trap samples collected throughout the oxic‐anoxic water column (275 m, 455 m, 930 m, and 1,255 m) of the Cariaco Basin. TPP, PIP, and POP fluxes varied seasonally and decreased significantly with depth, from 65 to 19 µmol TPP m−2 d−1, 43 to 8 µmol PIP m−2 d−1, and 22 to 11 µmol POP m−2 d−1. Significant flux relationships (p < 0.001) were found between POP and particulate organic carbon (POC) and particulate organic nitrogen (PON). The lack of a relationship between POC and PIP fluxes and the large fraction of TPP associated with the PIP pool in both oxic and anoxic traps suggests that future analyses must separate PIP and POP when evaluating biological relationships between C, N, and P. The strong relationships between POC, PON, and POP also suggest that POP is not preferentially remineralized relative to PON and POC with increasing depth in this anoxic environment. P composition was also determined using solid state 31P nuclear magnetic resonance (NMR), and it was found that phosphonates, chemically and thermally inert compounds, are a significant fraction of the TPP pool. Furthermore, these compounds were preferentially removed relative to more bioavailable P esters during a low flux event. Their selective removal suggests that these compounds may be an unrecognized source of bioavailable P under anoxic conditions.
Enrichment of amino acids in the sea surface microlayer at coastal and open ocean sites in the North Atlantic Ocean
Authors: Kuznetsova Marina , Lee Cindy , Aller Josephine , Frew Nelson
Published: July 2010

We investigated how regional differences in environmental parameters influenced enrichment of amino acids in the sea surface microlayer relative to underlying bulk seawater. Concentrations and compositions of dissolved free (DFAA), dissolved combined (DCAA), and particulate (PAA) amino acids were measured in the sea surface microlayer and corresponding subsurface waters along a transect from coastal Massachusetts to open ocean waters of the Sargasso Sea. We also measured total bacteria concentrations, the percent bacteria with damaged membranes, and concentrations of virus‐like particles. Microlayer samples taken by two different techniques—screen sampler (thickness 200–400 µm) and rotating drum (thickness 30–60 µm)—were compared. On average, concentrations of bacteria and amino acids in both subsurface and microlayer water were higher in water masses with higher fluorescence, lower temperature and salinity, and historically higher chlorophyll. The microlayer was enriched with amino acids and bacteria and, in most instances, virus‐like particles. Consistent microlayer features such as nonuniform preferential enrichment with DFAA and PAA and a uniform difference in dissolved amino acid compositio between microlayer and subsurface water, were unrelated to environmental parameters measured. Wind, humidity, and light also had no apparent effects on amino acid concentration, composition, or enrichment in the microlayer in this study.
The influence of substratum type and nutrient supply on biofilm organic matter utilization in streams
Authors: Romaní Anna M. , Giorgi Adonis , Acuña Vicenç , Sabater Sergi
Published: July 2010

We investigated the effect of benthic substratum type (sand and rocks) and nutrient supply (N and P) on biofilm structure and heterotrophic metabolism in a field experiment in a forested Mediterranean stream (Fuirosos). Rock and sand colonization and biofilm formation was intensively studied for 44 d at two stream reaches: control and experimental (continuous addition of phosphate, ammonia, and nitrate). Structural (C, N, and polysaccharide content and bacterial and chlorophyll density) and metabolic biofilm parameters ( β‐glucosidase, peptidase, and phosphatase enzyme activities) were analyzed throughout the colonization process. The epilithic biofilm (grown on rocks) had a higher peptidase activity at the impacted reach, together with a higher algal and bacterial biomass. The positive relationship between the peptidase activity per cell and the N content of the epilithic biofilm suggested that heterotrophic utilization of proteinaceous compounds from within the biofilm was occurring. In contrast, nutrient addition caused the epipsammic biofilm (grown on sand) to exhibit lower β‐glucosidase and phosphatase activities, without a significant increase in bacterial and algal biomass. The differential response to nutrient addition was related to different structural characteristics within each biofilm. The epipsammic biofilm had a constant and high C:N ratio (22.7) throughout the colonization. The epilithic biofilm had a higher C:N ratio at the beginning of the colonization (43.2) and evolved toward a more complex structure (high polysaccharide content and low C:N ratio) during later stages. The epipsammic biofilm was a site for the accumulation and degradation of organic matter: polysaccharides and organic phosphorus compounds had higher degradation activities.
Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton
Authors: Granger Julie , Sigman Daniel M. , Needoba Joseph A. , Harrison Paul J.
Published: July 2010

We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations of nitrate (NO ) during its assimilation by laboratory cultures of marine phytoplankton and derive the N and O kinetic isotope effects for nitrate assimilation by three species of diatoms (Thalassiosira weissflogii, Thalassiosira oceanica, and Thalassiosira pseudonana) and a coccolithophorid (Emiliana huxleyi). Large interspecies and intraspecies variations in the N isotope effects were observed. The O isotope effect associated with nitrate consumption was consistently close to the N isotope effect, such that the 18O/16O and 15N/14N of nitrate varied in a ratio of ~1 : 1, regardless of species or of the magnitude of the isotope effect. In addition, the 18O/16O and 15N/14N of internal nitrate of T. weissflogii grown under various environmental conditions were elevated relative to the medium nitrate by a proportion of ~1 : 1. These findings are consistent with a nitrate isotopic fractionation mechanism that involves nitrate reduction as the chief fractionating step. The observed N:O isotopic coupling during nitrate assimilation suggests that combined N and O isotopic measurements of water column nitrate can provide new constraints on the ocean N cycle.
A role for manganese in superoxide dismutases and growth of iron‐deficient diatoms
Authors: Peers Graham , Price Neil M
Published: July 2010

We have discovered that coastal and oceanic diatoms require more manganese (Mn) to grow in iron (Fe) ‐deficient than in Fe‐sufficient seawater. At low inorganic concentrations, like those of the open sea, Fe and Mn can thus colimit Thalassiosira pseudonana and T. oceanica so that maximum rates of cell division are achieved only when both resources are added simultaneously to cultures. Colimited diatoms amended with either Fe or Mn alone show unique physiological responses, which implies that the observed interaction between Fe and Mn is not caused by a substitution of one metal for the other. Iron deficiency increases the Mn quota of T. pseudonana by three times compared with controls and enhances the production of reactive oxygen species by 1.7 times in T. weissflogii. Both diatoms respond to this oxidative stress by increasing the activities of the antioxidant enzyme superoxide dismutase (SOD). The Mn content of the SODs increases by 1.8 to 2.8 times when Fe is limiting, which suggests that the SODs contain Mn and may account for part of the observed increase in the Mn quota. Such an increased biochemical requirement may elevate the Mn content of low Fe diatoms, and possibly other phytoplankton, resulting in high Mn: Fe ratios in surficial particulate matter in Fe‐limited regions of the sea.
Essential fatty acids in the planktonic food web and their ecological role for higher trophic levels
Authors: Kainz Martin , Arts Michael T. , Mazumder Asit
Published: July 2010

We measured concentrations of essential fatty acids (EFAs) in four size categories of planktonic organisms— seston (10–64 µm), microzooplankton (100–200 µm), mesozooplankton (200–500 µm), and macrozooplankton (≫500 230m)—and in rainbow trout (Oncorhynchus mykiss) in coastal lakes. Size‐dependent patterns in concentrations of specific fatty acids (FAs) are important for ecosystem function, because planktivorous fish and some invertebrates are size‐selective predators. We demonstrate that the retention of individual FAs differs among the four size categories of planktonic organisms in our study systems. Changes in individual EFA concentrations within the planktonic food web were similar in all coastal lakes sampled, which indicates the generality of our findings. Although concentrations of arachidonic acid, eicosapentaenoic acid (EPA), and linoleic acid increased steadily with plankton size, the concentration of a‐linolenic acid decreased slightly in larger size fractions of zooplankton. Concentrations of another EFA, docosahexaenoic acid (DHA), declined sharply from mesozooplankton to the cladoceran‐dominated macrozooplankton size class. Our results indicate that the retention of EFAs, as a function of plankton size, is related, in part, to the taxonomic composition of planktonic food webs. We suggest that, in general, zooplankton exhibit an EPA‐retentive metabolism with increasing body size, whereas different taxonomic groups within the planktonic food web retain DHA differently. Finally, we conclude that EPA is highly retained in zooplankton, whereas in rainbow trout DHA is highly retained.
Odor compounds from cyanobacterial biofilms acting as attractants and repellents for free‐living nematodes
Authors: Höckelmann Claudia , Moens Tom , Jüttner Friedrich
Published: July 2010

Nematodes can both taste and smell an array of compounds, but whether and how these senses effect their capacity to locate microhabitats in aquatic environments is not known. Cyanobacterial biofilms may offer structure, shelter, and food for nematodes and are known to produce a variety of odor compounds. We studied the chemotaxis response of the freshwater nematode Bursilla monhystera (Rhabditidae) and the terrestrial model organism Caenorhabditis elegans (Rhabditidae) to odors of cyanobacterial biofilms. We used gas chromatography‐mass spectometry ultra‐trace analysis to identify odor compounds produced by two epilithic cyanobacterial biofilms of Lake Zurich. We also studied artificial, axenic biofilms of Plectonema sp., Calothrix sp., and Calothrix parietina, to assign these compounds to the metabolism of the cyanobacteria. The axenic cyanobacteria and epilithic biofilms had many odor compounds in common. B. monhystera was significantly attracted to Plectonema sp. and C. parietina but not to Calothrix sp. C. elegans, in contrast, was not attracted to any of these cyanobacterial biofilms. Furthermore, we applied a multicomponent mixture of odor compounds and found significant attraction for both nematodes. Although C. elegans was also attracted by a variety of single odor compounds, B. monhystera was not attracted to any of the volatiles tested. β‐ionone even repelled this species. Our experiments demonstrate that aquatic nematodes are attracted to cyanobacterial biofilms using odor compounds as chemical cues. In contrast to the model organism, C. elegans, the chemotaxis of the aquatic nematode is elicited by a multicomponent odor rather than by single compounds.
Mass‐transfer limitation of nutrient uptake by a wave‐dominated reef flat community
Authors: Falter James L. , Atkinson Marlin J. , Merrifield Mark A.
Published: July 2010

Maximum rates of phosphate, nitrate, and ammonium uptake by a reef flat community were estimated from rates of frictional dissipation that were calculated from the attenuation of waves propagating over the Kaneohe Bay Barrier Reef flat. Time‐averaged flow speeds across the entire study area ranged from 0.08 to 0.22 m s−1. Observed decreases in wave energy fluxes and near‐bottom orbital velocities gave a mean estimate for the bottom friction coefficient (cf) of 0.22 ± 0.03. Friction coefficients were used to estimate nutrient mass‐transfer coefficients of 5–9 m d−1 for phosphate and 9–16 m d−1 for ammonium and nitrate. Wave heights offshore of Kaneohe Bay were also used to estimate an annual phosphate mass‐transfer coefficient of 8 ± 2 m d21. This value is similar to a published value of 9 ± 2 m d−1 that was determined from measured changes in phosphate concentrations across the reef flat. We conclude that rates of phosphate uptake by the Kaneohe Bay Barrier Reef flat community are occurring near the limits of mass transfer.
Long‐term changes in the abundance of Jesogammarus annandalei (Tattersall) in Lake Biwa
Authors: Ishikawa Toshiyuki , Narita Tetsuya , Urabe Jotaro
Published: July 2010

Changes in the abundance of an endemic amphipod, Jesogammarus annandalei, that inhabits the profundal zone of Lake Biwa were examined from 1966 to 1999. The abundance of J. annandalei increased suddenly during the mid‐1980s and thereafter stayed at a level that was seven‐fold higher than that before 1980. Compared with the amphipod in the 1960s, both the clutch and body size of the matured individuals decreased during the 1990s, which suggests that per capita food supply decreased. Thus, the increase in the abundance of J. annandalei appeared to be due largely to an increase in their survival rate and not their growth or reproduction rates. In accord with the increase in amphipod abundance, the fishery catch of an endemic gobiid fish species that is dominant in the profundal zone and preys on this amphipod as a major food, decreased dramatically during the mid1980s. These results suggest that long‐term changes in abundance of J. annandalei in Lake Biwa are mainly regulated by fish predation rather than by food supply.
A species invasion mediated through habitat structure, intraguild predation, and parasitism
Authors: MacNeil Calum , Dick Jaimie T. A. , Johnson Mark P. , Hatcher Melanie J. , Dunn Alison M.
Published: July 2010

With field, laboratory, and modeling approaches, we examined the interplay among habitat structure, intraguild predation (IGP), and parasitism in an ongoing species invasion. Native Gammarus duebeni celticus (Crustacea: Amphipoda) are often, but not always, replaced by the invader Gammarus pulex through differential IGP. The muscle‐wasting microsporidian parasite Pleistophora mulleri infects the native but not the invader. We found a highly variable prevalence of P. mulleri in uninvaded rivers, with 0–91% of hosts parasitized per sample. In addition, unparasitized natives dominated fast‐flowing riffle patches of river, whereas parasitized individuals dominated slower‐flowing, pooled patches. We examined the survivorship of invader and native in single and mixed‐species microcosms with high, intermediate, and zero parasite prevalence. G. pulex survivorship was high in all treatments, whereas G. duebeni subsp. celticus survivorship was significantly lower in the presence of the invader. Further, parasitized G. duebeni subsp. celticus experienced near‐total elimination. Models of the species replacement process implied that parasite‐enhanced IGP would make invasion by G. pulex more likely, regardless of habitat and parasite spatial structure. However, where heterogeneity in parasite prevalence creates a landscape of patches with different susceptibilities to invasion, G. pulex may succeed in cases where invasion would not be possible if patches were equivalent. The different responses of parasitized and unparasitized G. duebeni subsp. celticus to environmental heterogeneity potentially link landscape patterns to the success or failure of the invasion process.
Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land‐ sea fluxes
Authors: Humborg Christoph , Smedberg, Erik , Blomqvist Sven , Mörth Carl‐Magnus , Brink Jenni , Rahm Lars , Danielsson Åsa , Sahlberg Jörgen
Published: July 2010

We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Luleälven and Kalix%lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.
Denitrification and hydrologic transient storage in a glacial meltwater stream, McMurdo Dry Valleys, Antarctica
Authors: Gooseff Michael N. , McKnight Diane M. , Runkel Robert L. , Duff John H.
Published: July 2010

In extreme environments, retention of nutrients within stream ecosystems contributes to the persistence of aquatic biota and continuity of ecosystem function. In the McMurdo Dry Valleys, Antarctica, many glacial meltwater streams flow for only 5–12 weeks a year and yet support extensive benthic microbial communities. We investigated NO3− uptake and denitrification in Green Creek by analyzing small‐scale microbial mat dynamics in mesocosms and reach‐scale nutrient cycling in two whole‐stream NO3− enrichment experiments. Nitrate uptake results indicated that microbial mats were nitrogen (N)‐limited, with NO3− uptake rates as high as 16 nmol N cm−2 h−1. Denitrification potentials associated with microbial mats were also as high as 16 nmol N cm−2 h−1. During two whole‐stream NO3−−enrichment experiments, a simultaneous pulse of NO2− was observed in the stream water. The one‐dimensional solute transport model with inflow and storage was modified to simulate two storage zones: one to account for short time scale hydrologic exchange of stream water into and out of the benthic microbial mat, the other to account for longer time scale hydrologic exchange with the hyporheic zone. Simulations indicate that injected NO3− was removed both in the microbial mat and in the hyporheic zone and that as much as 20% of the NO3− that entered the microbial mat and hyporheic zone was transformed to NO2− by dissimilatory reduction. Because of the rapid hydrologic exchange in microbial mats, it is likely that denitrification is limited either by biotic assimilation, reductase limitation, or transport limitation (reduced NO2− is transported away from reducing microbes).
Floods can cause large interannual differences in littoral net ecosystem productivity
Authors: Larmola TuulanNames , Alm JukkanNames , Juutinen SarinNames , Saarnio SannanNames , Martikainen Pertti J.nNames , Silvola JoukonNames
Published: July 2010

Littoral wetlands comprise a terrestrial to aquatic continuum along which carbon dioxide is exchanged with the atmosphere and organic carbon is transferred to lakes. Net ecosystem productivity—the difference between atmospheric CO2 uptake and total ecosystem respiration—in these shore areas depends partly on the extent and duration of spring flooding. Ecosystem‐atmosphere CO2 fluxes were studied at a boreal lake in Finland to analyze how flooding affects the dynamics of littoral net ecosystem productivity. Two shore transects with different hydrological conditions and vegetation distributions were studied during consecutive ice‐free periods with contrasting flooding patterns. Net ecosystem productivity in different vegetation zones did not respond consistently to extended flooding; the response depended on the phenology of plant emergence during the flood and on the decrease in the water level after flooding. The decrease in the water level was steeper in silt‐mud sediment than in fen peat. With an exceptionally high water level relative to the height of the vegetation, net ecosystem productivity decreased by 50–100% (net loss, 0.4–7.4 mol m−2 of CO2 during the wetter open‐water period). However, the wetter season could also have a 60–140% higher net ecosystem productivity (net CO2 gain of 0.7 mol m−2 to net loss of 6.8 mol m−2) because of the decreased decomposition rate. An extended flooding period greatly reduces the amount of litter produced in a specific year. In both flooding patterns, the littoral zone was an overall net CO2 emitter, but the large variation in the decomposition rate suggests that there are differences in the load of organic matter from the littoral to the pelagic zone.
Circadian cycles in growth and feeding rates of heterotrophic protist plankton
Authors: Jakobsen Hans H. , Strom Suzanne L.
Published: July 2010

Growth and feeding rates of four species of planktonic marine heterotrophic protists showed pronounced diel cycles. In most cases, rates were higher during the day and lower at night. However, for the ciliate Strobilidium sp., growth was highest at night. In another ciliate species, Balanion comatum, no day‐night difference in growth and feeding rates was found. Maintenance of day‐night rate differences during 24‐h exposures to continuous darkness demonstrated that most of these protists had circadian cycles. The heterotrophic dinoflagellate Oxyrrhis marina exhibited a clear irradiance threshold for maintenance of the circadian cycle: day‐night differences in growth and feeding rates were observed at irradiances as low as 2.6 × 10−3 µmol photons m−2 s−1 but not at 3.1 × 10−4 µmol photons m−2 s−1. We also studied growth and feeding in transition from complete darkness to culturing in a day : night light cycle in O. marina and found that resetting the circadian cycle in this dinoflagellate temporarily arrested growth and feeding. We suggest that protists use a time‐integrated light threshold rather than an instantaneous irradiance to maintain the circadian cell cycle. This allows them to avoid temporary arrests in growth and feeding when they are mixed over depth across the 3.1 × 10−4 µmol photons m−2 s−1 irradiance threshold. Overall, higher rates of feeding and growth during the light period, when phytoplankton are photosynthetically active, may strongly influence predator‐prey cycles in the euphotic zone.
Mass‐transfer‐limited nitrogen and phosphorus uptake by stream periphyton:A conceptual model and experimental evidence
Authors: Larned Scott T. , Nikora Vladimir I. , Biggs Barry J. F.
Published: July 2010

We conducted flow‐tank experiments to examine nitrate (NO3) and dissolved reactive phosphorus (DRP) uptake by stream periphyton over a wide range of near‐bed velocities and turbulence levels. Our aims were to characterize the hydraulic conditions under which nutrient uptake is controlled by mass transfer through diffusive boundary layers (DBLs) or by membrane kinetics and to identify factors that affect mass‐transfer rates. Nutrient uptake was mass‐transfer limited under all hydraulic conditions used; there was no indication of kinetic control. We developed a conceptual model describing mass‐transfer‐limited uptake in terms of periphyton canopy height relative to DBL thickness. Three uptake regimes comprise the model: (1) when the canopy is submerged within the DBL covering the substratum, uptake is controlled by the thickness of this DBL; (2) when canopy height is greater than but comparable with the substratum DBL thickness, uptake is controlled jointly by the substratum DBL and by individual DBLs surrounding the periphyton elements that protrude above the substratum DBL; and (3) when the substratum DBL is very thin and most of the canopy protrudes above it, uptake is controlled by the DBLs surrounding periphyton elements. Patterns of NO3 and DRP uptake in the experiments were consistent with the third regime. Periphyton extended well above the substratum DBL even at the slowest near‐bed velocities (~1 cm s−1). We suggest that, in oligotrophic streams, the second and third uptake regimes prevail, DBLs around periphyton elements pose greater diffusive resistance to nutrient transport than the substratum DBL, and nutrient uptake is generally mass‐transfer controlled and rarely kinetically controlled.
Relationship between sediment organic matter, bacteria composition, and the ecosystem metabolism of alpine streams
Authors: Logue Jürg Brendan , Robinson Christopher T. , Meier Christoph , der Meer Jan Roelof Van
Published: July 2010

We tested whether sediment bacteria abundance (4’,6‐diamidino‐2‐phenylindole‐stained cell counts) were related to sediment organic content (ash‐free dry mass [AFDM]) in 11 nonforested streams of three different Alpine catchments during summer 2003. We used terminal restriction fragment‐length polymorphism (T‐RLFP, a molecular genetic technique) to test for seasonal and spatial differences in bacterial composition in these same streams. We then related the above parameters, in conjunction with periphyton biomass and hyporheic respiration, to whole stream estimates of gross primary production (GPP) and ecosystem respiration (ER) in a glacial and nonglacial stream, representing environmental extremes, in one of the catchments. The percentage of organic matter of sediments was 4–14% (0.01–0.04 g AFDM ml sediment−1), and counts of bacteria cells per millimeter of sediment averaged 2 × 106−4 × 106. Bacteria counts correlated with sediment AFDM only for streams in the catchment with highest sediment AFDM levels. Bacteria composition (based on the presence and absence of terminal restriction fragments from T‐RFLP analysis) changed seasonally in the different streams and differed between glacial—and groundwater‐fed streams. In the one catchment, hyporheic respiration averaged 0.0004 and 0.0003 g O2 h−1 kg sediment−1 and was positively correlated with AFDM (r2 = 0.23). Ecosystem metabolism displayed a strong seasonality, with GPP averaging 4.5 and 8.4 and ER averaging 5.4 and 9.9 g O2 m−2 d−1 for the two sites, respectively, thus indicating a predominance of heterotrophy (P :R < 1) in these high‐elevation, open‐canopied systems. Bacteria play a strong role in the trophic dynamics of alpine streams.
Availability of iron and major nutrients for phytoplankton in the northeast Atlantic Ocean
Authors: Blain Stèphane , Guieu Cècile , Claustre Hervè , Leblanc Karine , Moutin Thierry , Quèguiner Bernard , Ras Josèphine , Sarthou Gèraldine
Published: July 2010

Because of recent findings that Fe is a limiting factor for phytoplankton activity even at relatively high dissolved iron (DFe) concentrations, the potential importance of Fe limitation was revisited in the northeast Atlantic Ocean (39−45°N, 17−21°W). We report data gathered during deck incubation experiments performed at three stations in February‐March 2001 with surface seawater containing DFe concentrations of ~0.40 nmol L−1. At all stations, Fe addition enhanced phytoplankton growth. Fe limitation was moderate and occurred simultaneously with limitation by major nutrients. This was clearly demonstrated for diatoms that were colimited by orthosilicic acid. Micro‐, nano‐, and picoplankton benefited from Fe enrichment. Experiments performed with the trihydroxamate siderophore desferrioxamine mesylate B (DFOB) indicated that Fe reserves exist within the cells, especially within the larger cells. This reserve could result from luxurious storage of Fe by colimited cells during episodic atmospheric deposition of Saharan dust. Simulating concentrations of dust resulting from aerosol deposition in well‐stratified surface waters, we determined that the solubility of Saharan dust was very low (<0.1% w/w) but the amount of DFe released in seawater was sufficient to relieve the Fe limitation of the ambient phytoplankton community.
Responses of elemental and biochemical composition of Chaetoceros muelleri to growth under varying light and nitrate : phosphate supply ratios and their influence on critical N: P
Authors: Leonardos Nikos , Geider Richard J.
Published: July 2010

The critical nitrogen‐to‐phosphorous ratio (N:P) defines the transition between N and P limitation of growth rate and is not a biological constant. To test the effect of environmental conditions on the critical N:P, we cultured the diatom Chaetoceros muelleri in chemostats with inflow nitrate : phosphate ratios ranging from 5 to 90 mol N (mol P)−1 at two photon flux densities (PFDs; 50 and 700 µmol photons m−2 s−1). The nitrate : phosphate ratio marking the transition between N and P limitation increased from between 15‐30 mol N:mol P at the high PFD to 45 mol N: mol P at the low PFD. The particulate ratio marking this transition increased from 16‐23 mol N:mol P at low PFD to 35 mol N:mol P at high PFD. Cell phosphorus and RNA contents decreased with increasing N:P ratio up to the critical N:P ratio for each PFD, above which they remained stable. In contrast, cell dry weight, chlorophyll a, C, N, and protein were not influenced by nitrate : phosphate in the inflow medium, although they were influenced by PFD. Total protein per RNA increased with increasing N:P ratio at the low light conditions, suggesting increased ratio of protein synthesis per RNA. Our results showed the effect of PFD, growth rate, or both on the critical N:P ratio. Agreement was found in the assessment of the transition between N and P limitation on the basis of nutrient enrichment bioassays, cellular elemental (N and P) quotas, and cell RNA content. Our results are consistent with theoretical predictions of higher N requirements under low light conditions due to the coupling of the photosynthetic mechanism with N uptake. In contrast, P‐rich cellular components, such as RNA, were dependent on P availability rather than light.