μM Phosphate Research Articles

Alkaline phosphatase activity and its relationship to inorganic phosphorus in the transition zone of the North-western African upwelling system

The enzymatic activity of alkaline phosphatase (APA) was studied in the transition zone between the African upwelling system and the open ocean waters of the Canary Islands region. This region is recurrently dominated by the presence of upwelling filaments that may transport nutrient-enriched waters out into the open ocean before nutrients become exhausted by plankton. Turnover rates by APA were generally low in the whole region, but detectable in all the measurements carried out. On average, turnover rates were higher in the upwelling stations, and APA in those waters seemed to be mainly generated by heterotrophic bacteria to supply easily assimilable organic C. APA outside the upwelling area showed an inverse hyperbolic relationship with increasing phosphate, suggesting the presence of both constitutive and Pi-inducible APA. In these offshore waters, a threshold of 0.1 μM of phosphate could be defined for the regulatory function of Pi on APA. Thus, APA in nutrient-poor waters seemed to be induced to compensate for Pi-deficiency. Turnover rates in the filaments showed basal (probably constitutive) levels, whereas they increased in the surrounding waters, where phosphate concentration presumably did not satisfy plankton P-demands. The fertilising effect of the filaments and associated cyclonic eddies extended to at least 175 km offshore, where basal alkaline phosphatase activities were still found. The magnitude of this effect depends probably on the intensity of upwelling events and the degree of recirculation of filament water back to the coastal jet.

Growth and uptake kinetics for nitrate, ammonium and phosphate by the toxic dinoflagellate Gymnodinium catenatum isolated from Hiroshima Bay, Japan

: Growth and uptake kinetics for nitrate, ammonium and phosphate by Gymnodinium catenatum isolated from Hiroshima Bay were experimentally investigated. Maximum uptake rate (ρmax) and half saturation constant (Ks), which were obtained by short-term uptake experiments, were 6.48 pmol/cell per h and 7.60 µM for nitrate, 3.37 pmol/cell per h and 33.6 µM for ammonium, and 1.42 pmol/cell per h and 3.40 µM for phosphate, respectively. Specific maximum growth rate (µ′m) and minimum cell quota (Q0), which were obtained by semicontinuous growth experiments, were 0.36/day and 31.3 pmol/cell for the N-limited conditions, respectively. The µ′m and QP0 for P-limited conditions were 0.37/day and 1.83 pmol/cell, respectively. These results indicate that G. catenatum is a poor competitor in terms of utilization of inorganic nutrients and is unlikely to form blooms in Hiroshima Bay where phosphate is chronically depleted unless the growth is supported by organic species (i.e. dissolved organic phosphorus) of the nutrients.

In vitro Study of Remineralization of Dentin: Effects of Ions on Mineral Induction by Decalcified Dentin Matrix

We examined the effects of various ions on the mineralization of dentin matrix in vitro. Demineralized dentin matrix was incubated in a metastable calcium phosphate solution with or without silicate, fluoride, calcium, phosphate, magnesium or silver. Insoluble dentin matrix induced mineral formation after incubation for 10.2 h in the metastable solution without added ions. Silicate at 5 µM and fluoride at 40 µM significantly reduced the mineral induction time. At least 200 µM calcium or 100 µM phosphate was required to promote mineral induction. Conversely, magnesium and silver concentrations as low as 10 and 2 µM inhibited mineral induction. The mineral induced by each sample after incubation for 24 h was identified by its X-ray diffraction pattern as apatite. We concluded that silicate is a stronger inducer of remineralization of dentin matrix than fluoride, calcium or phosphate, and that magnesium and silver inhibit the induction of remineralization of dentin matrix.

How phosphorus deficiency affects physiology and morphometry of Baltic Picocyanobacteria

Inorganic phosphorus (P inorg ) starvation and limitation experiments were performed in two unicellular picoplanktic cyanobacteria strains, isolated from the Central Baltic Sea, using P inorg -free medium and a range of phosphate concentrations (1, 0.02, 0.002 μM K 2 HPO 4 ). The effects of P inorg -deprivation and P inorg -reduced availability on growth, pigment content, photosynthesis, alkaline phosphatase activity and cell morphometry were investigated. Weak differences in growth and pigment content were detected among the cultures grown at 1 and 0.002 μM phosphate in both strains. An increase of photosynthetic efficiency and alkaline phosphatase activity was observed in a phycoerythrin-rich strain at low concentration and in P ιnorg -free medium. Growth, chlorophyll a and phycobiliproteins content of the two strains decreased in response to P inorg -starvation. Morphometrical analysis of both strains showed a reduction of cell volume at the lowest concentration tested.

Determination of phosphate in nanomolar range by an enzyme-coupling fluorescent method

We have successfully configured a new ultrasensitive fluorescent phosphate assay that detects free phosphate in solution through the formation of the fluorescent product resorufin. The phosphate assay relies on coupling phosphate generation to purine nucleoside phosphorylase, xanthine oxidase, and horseradish peroxidase. The response is excellent in the nanomolar range, being linear between 50 nM and 5 μM phosphate. This method is more sensitive (more than 10-fold) than other reported methods and is amenable to miniaturization. In particular, we have demonstrated the utility of this new method in a format suitable for ultra-high-throughput screening.

171 Light‐Induced Growth of Winter Phytoplankton Collected from the Benthic Boundary Layer in Coastal Oregon Waters

It has been speculated that overwintering phytoplankton in the benthic boundary layer (BBL) are seed stocks for spring blooms in coastal upwelling systems. Experiments were conducted in Jan/Feb 2003 to test the hypothesis that phytoplankton in the BBL are light limited. Water collected from the BBL at four sites across the northern Oregon shelf was incubated at in situ temperature and nutrient concentrations (∼1 μM phosphate, 10 μM nitrate, 15 μM silicate) and exposed to two different daylengths and four light levels. The daylengths were 9 h (winter) and 12 h (early spring), and the light levels (in μmol photons·m−1 ·s−1) were 0 (Control), 20 (L), 70 (M), and 160 (H). Light‐induced growth was observed in all four incubations. Exponential growth was reached in the 12 H, 12 M, and 9 H treatments after 4 to 6 days, and stationary growth was reached after 5 to 10 days. Maximum in vivo fluoresence was obtained in the 12 H, 12 M, and 9 H treatments, while maximum particulate organic carbon (POC) was obtained in the 12 H treatment. In vivo fluorescence increased in the L light treatments relative to the control, but POC did not. Blooms were terminated by nitrate or silicate depletion. These results demonstrate that growth of winter phytoplankton off Oregon is primarily light‐limited, and that input of light of sufficient intensity and constancy (i.e. water column stabilization) can lead to blooms on time scales typical of upwelling blooms (<1 week).

Regulation of root elongation under phosphorus stress involves changes in ethylene responsiveness.

We characterized the growth of the primary root of Arabidopsis under phosphorus sufficiency (1 mM phosphate) and deficiency (1 microM phosphate), focusing on the role of ethylene. We quantified the spatial profile of relative elongation with a novel method based on image processing, as well as the production rates of cortical cells, trichoblasts, and atrichoblasts. Phosphorus deficiency moderately decreased the maximal rate of relative elongation, shortened the growth zone, and decreased the production rate of both epidermal cell types but not of cortical cells. Inhibiting ethylene production (with aminoethoxyvinyl-glycine) or action (with 1-methylcyclopropene) increased elongation in high phosphorus and decreased it in low phosphorus. That these effects were specific to ethylene was confirmed by negating the effect of inhibited ethylene production with simultaneous treatment with an ethylene precursor (1-aminocyclopropane-1-carboxylic acid). Under both phosphorus regimes, ethylene regulated the maximal rate of relative elongation rather than the size of the growth zone. In addition, inhibiting ethylene action in high versus low phosphorus elicited opposite responses for the position of root hair initiation and for the production rates of cortex cells and atrichoblasts. We conclude that the root system acclimates to phosphorus deficiency by changing the signal transduction pathway connecting ethylene levels to growth and division.

Time series of seasonal variation of primary productivity at station KNOT (44°N, 155°E) in the sub-arctic western North Pacific

Abstract Phytoplankton biomass and primary productivity were measured as a part of the station KNOT (44°N, 155°E) time-series observation program in the western North Pacific, which began in June 1998 and continued on a nearly monthly basis until February 2000. Primary productivity was measured by the 13C uptake method using a clean sampling technique. The surface temperature changed from 2°C to 15°C, and the minimum and maximum temperatures were in February and August, respectively. The minimum and maximum concentrations of surface-layer nutrients were 2.2 and 19.6 μM for nitrate+nitrite, 0.32 and 1.64 μM for phosphate, and 3.3 and 33.3 μM for silicate. The averaged depth of euphotic zone was about 50 m, which did not show clear seasonality. Integrated chlorophyll a in the euphotic zone ranged between 20 and 40 mg Chl a m−2, except for the high values (51–64 mg Chl a m−2) in early June and middle October 1998 and May 1999, and the low value (17 mg Chl a m−2) in late June 1998. The integrated primary productivities in the upper part of the euphotic zone for spring (May), summer (June–August), autumn (October–November), and winter (December–February) were 517–535 (av. 526), 153–304 (av. 227), 101–307 (av. 173), and 25–121 (av. 48) mg C m−2 d−1, respectively. The annual productivity was estimated to be 90 g C m−2 yr−1. The results showed that primary productivity had a distinct seasonal variation, with a 10-fold range during winter–spring, which is far larger than that at Ocean Station Papa (OSP) in the eastern North Pacific. However, the annual productivity at station KNOT was lower than the at OSP. It was found that the light utilization index was constant during all seasons, and the annual average (±1 SD) was 0.30±0.10 g C (g Chl a)−1 m2 (mol quanta)−1.

Elevated levels of nitrogen and phosphorus reduce fertilisation success of gametes from scleractinian reef corals

Spawned gametes were collected from colonies of Acropora longicyathus at One Tree Island and Goniastrea aspera at Magnetic Island, Great Barrier Reef, Australia, for use in fertilisation trials. Mean fertilisation rates were significantly reduced compared with controls (P<0.003), when gametes from the branching coral A. longicyathus were exposed to elevated ammonium concentrations at 1 µM and above in one cross (60–64% reduction), and at 100 µM in another cross (16% reduction). Mean fertilisation success of A. longicyathus gametes was also significantly reduced compared with controls in both crosses (P=0.000) at concentrations of 1 µM phosphate and above (35–75% reduction), and at 1 µM ammonium plus 1 µM phosphate and all higher concentrations (68–74% reduction). Similarly, the mean percentage of regular embryos that were developing normally was significantly reduced in most nutrient treatments compared with controls (P=0.000). Fertilisation trials using gametes from the brain coral G. aspera resulted in a significantly lower percentage of regular embryos (P=0.001) and a significantly higher percentage of deformed embryos (P=0.001) developing after exposure to elevated nutrient treatments compared with controls. Mean fertilisation rates for this species were only significantly reduced (P=0.034) in the 50 µM ammonium plus phosphate treatment in one cross (8% reduction), compared with the control. Therefore, ammonium and phosphate enrichment significantly impairs fertilisation success and embryo development in scleractinian reef corals.

The effects of feeding or addition of dissolved inorganic nutrients in maintaining the symbiosis between dinoflagellates and a tropical marine cnidarian

The availability of solid food (Artemia nauplii) and dissolved inorganic nutrients (ammonium, nitrate, phosphate) to the shallow-water marine hydroid Myrionema amboinense was manipulated for 1–8 days in order to investigate their role in the growth of intracellular symbiotic dinoflagellates (zooxanthellae) of the genus Symbiodinium. Symbionts from hydroids collected from the field or maintained under laboratory conditions (25°C, 12 h:12 h light:dark cycle, 80 µE m–2 s–1 fluorescent lighting) always exhibited a single peak in mitotic index (MI) at dawn. Symbionts in freshly collected field animals had an MI peak of about 15%. Symbiotic dinoflagellates in hydroids fed Artemia nauplii twice daily in the laboratory maintained this dawn peak of MI between 10% and 15%, but in the absence of feeding or added inorganic nutrients, this peak declined to less than 1% within 2–4 days. In contrast, when hydroids were placed in solutions containing ammonium (20 µM NH4Cl), nitrate (10 µM NaNO3), and a combination of ammonium and phosphate (2 µM Na2HPO4) immediately after collection, the algal MI remained between 5% and 15% for 4–7 days; the addition of 2 µM phosphate did not increase MI relative to unfed rates. When unfed animals were placed in dissolved nitrogen or fed Artemia, the symbiont MI increased from <1% to 10–17% within 2–3 days; P alone had no effect. However, the increase resulting from added inorganic nutrients was temporary, lasting only 5–7 days. These observations suggest that algal division in the host is maintained indefinitely in the field or by feeding particulate foods twice daily in the laboratory, but the addition of inorganic nutrients alone (ammonium, nitrate and ammonium/phosphate) appeared to support the completion of a maximum of one additional round of cell division. Nutrients required for continued growth and division of symbiotic dinoflagellates are linked to host feeding and host growth; without external food, neither host nor symbiont continue to grow. The same phenomenon is seen in zooxanthellate anemones, clams and corals, where total numbers of symbionts appear to be linked to changes in host-tissue biomass (protein), achieving relatively stable densities in M. amboinense, corals and other cnidarian symbioses, depending on their local environmental conditions. The results of the present study help explain the cellular responses of algal symbionts in reef-dwelling invertebrates to additions of dissolved inorganic nutrients to coral-reef ecosystems.

Root hairs confer a competitive advantage under low phosphorus availability

Root hairs are presumably important in the acquisition of immobile soil resources such as phosphorus. The density and length of root hairs vary substantially within and between species, and are highly regulated by soil phosphorus availability, which suggests that at high nutrient availability, root hairs may have a neutral or negative impact on fitness. We used a root-hairless mutant of the small herbaceous dicot Arabidopsis thaliana to assess the effect of root hairs on plant competition under contrasting phosphorus regimes. Wildtype plants were grown with hairless plants in a replacement series design at high (60 μm phosphate in soil solution) and low (1 μm phosphate in soil solution) phosphorus availability. At high phosphorus availability, wildtype and mutant plants were equal in growth, phosphorus acquisition, fecundity and relative crowding coefficient (RCC). At low phosphorus availability, hairless plants accumulated less biomass and phosphorus, and produced less seed when planted with wildtype plants. Wildtype plants were unaffected by the presence of hairless plants in mixed genotype plantings. Wildtype plants had RCC values greater than one while hairless plants had RCC values less than one. We conclude that root hairs increase the competitiveness of plants under low phosphorus availability but do not reduce growth or competitiveness under high phosphorus availability.

Primary productivity off the coast of East Antarctica (80–150°E): January to March 1996

During February and March 1996, an interdisciplinary research project was undertaken off the coast of East Antarctica, south and southwest of Australia, from approximately 63 to 66.25°S and 80 to 150°E. Coastal, continental shelf and open ocean waters were sampled, encompassing the Antarctic Slope Front (ASF) and the Antarctic Divergence (AD). Sea ice coverage during the previous winter exhibited a gradual decline in northwards extent from 80°E, where its edge was located at 57°S, to 150°E, where it reached 62–63°S. Productivity versus irradiance ( P– I) experiments were conducted to calculate primary productivity, and measurements of the photochemical quantum efficiency of photosynthesis ( F v/ F m) were made using a fast repetition rate (FRR) fluorometer. Phytoplankton pigment (HPLC) and nutrient (nitrate, phosphate and silicate) concentrations also were obtained. Mean chlorophyll a concentrations in the mixed layer were highest (>1 μg l −1) on the continental shelf along 93.5°E and in the shelf and shelf-break waters of a meridional transect along 120°E. Integrated production over the mixed layer ranged from greater than 700 mg C m −2 d −1 slightly north of the AD along 80°E, to less than 50 mg C m −2 d −1 in open ocean water at the northeastern corner of the survey area. The elevated biomass and productivity west of approximately 120°E was attributed to macro- and micro-nutrient release and upper water column stratification following the spring/summer ice melt that preceded and coincided with the sampling period. Macronutrient concentrations were not found to be limiting, and in the upper 75 m of the water column ranged between 20.8 and 32.7 μM for nitrate, from 0.75 to 2.3 μM for phosphate, and from 22.6 to 74.9 μM for silicate. Nutrient uptake rates, inferred from depletion in the mixed layer, indicated that silicate uptake was uncoupled from that of nitrate and phosphate in the northeastern region of the survey area. The mixed layer deepened slightly and critical depths shoaled by a factor of three as the survey moved eastwards from 80 to 150°E, a pattern most likely due to the onset of winter. Daily irradiance also decreased between January and March, and manipulations of the light field used in the production modelling of the eastern transects resulted in productivity estimates similar to the western transects. These observations, together with the analysis of the FRR data, suggest that the phytoplankton community east of approximately 120°E may have been co-limited by iron concentrations and incident irradiance. The lower biomass and productivity in the east also coincided with greater southwards extension of warmer oceanic waters, and a shift from a krill/diatom to salp/picoplankton biological community.

Arsenic Adsorption and Oxidation at Manganite Surfaces. 1. Method for Simultaneous Determination of Adsorbed and Dissolved Arsenic Species

Arsenic occurs in the +III oxidation state as a metastable species in oxic waters. Under oxic conditions, As(III) is both more mobile in natural waters and less efficiently removed by water treatment processes than As(V). Other oxidants, however, can react with As(III) more rapidly than oxygen. The oxidation of As(III) by manganite occurs on the time scale of hours. Here, a method is introduced for the rapid determination of the total and dissolved concentrations of arsenic species in this heterogeneous system; adsorbed arsenic concentrations are calculated by difference. The oxidation reaction is quenched by the addition of ascorbic acid to effect the reductive dissolution of manganite and concomitant release of adsorbed As(III) and As(V) into solution. Once in solution, As(III) and As(V) are separated using anion-exchange chromatography. Comparison of dissolved and total concentrations of As(III) and As(V) clearly illustrates that the overall conversion rate of As(III) to As(V) in this system would be overpredicted based solely on dissolved As(III) concentrations and underpredicted based solely on dissolved As(V) concentrations. The overall conversion of As(III) to As(V) was more rapid at pH 4 than at pH 6.3 and was unaffected by the presence of boric acid at 95 μM or 3 mM. However, the presence of 200 μM phosphate (at pH 4) decreased the overall rate of conversion of As(III) to As(V). Comparison of total and dissolved As(III) concentrations during the reaction time course demonstrates that the effects of pH and phosphate on adsorbed As(III) concentrations are generally consistent with these kinetic observations.

Daily Variations in Nutrient Concentrations of Seawater at 321 m Depth in Toyama Bay, Japan Sea

Nutrient concentrations (nitrate + nitrite, phosphate and silicate) in deep seawater (321 m depth) of Toyama Bay, Japan, were measured from August 1996 to July 1997 to determine the magnitude of daily variations. Significant daily variations were observed; concentrations ranged from 4.42 to 22.4 µM for nitrate + nitrite, from 0.86 to 1.98 µM for phosphate, and from 9.91 to 47.7 µM for silicate, respectively. However, there were not significant relationships between nutrient concentrations and water temperature, or between nutrients and salinity. Since temperature and salinity in the >300 m depth layer were constant through the year, the results suggest that there may be water masses with different nutrient concentrations in the deep layers (at about 320 m depth) of the bay, and a horizontal advection of these water masses may be responsible for the observed daily variations.

An automatic flow-injection analysis system for determining phosphate ion in river water using pyruvate oxidase G (from Aerococcus viridans)

An automated flow-injection system combining a pyruvate oxidase reaction and chemiluminescence for the detection of phosphate ion in river water has been developed. In this research, we used pyruvate oxidase G (PyrOxG), from Aerococcus viridans, immobilizing it on N-hydroxysuccinicacidimido beads without a cross-linker. In this sensor system, which was constructed as a trial system of desktop type, the temperature was precisely controlled. After the sensor system was optimized, a calibration curve was obtained with a detection limit of 96 nM phosphate ion, a range between 96 nM and 32 μM phosphate ion, and a relative standard deviation of 2.3% ( n=5) at 25°C. The sensitivity of this sensor was sufficient to determine the maximal permissible phosphate-ion concentration in the environmental waters of Japan (0.32 μM). In addition, the sensor could determine the calibration curves between 0.16 and 32 μM phosphate ion (five points, n=3; averaged correlation, r=1.00) for at least 2 weeks, demonstrating enough stability for practical use. Furthermore, we investigated the influence on the sensor response of dissolved substances in river water such as metal ions, heavy metal ions, inorganic ions, and organic compounds. Treatment with activated carbon could improve the response of the sensor when inhibited by dissolved substances in river water, except for manganese ion and uric acid. The sensor system could determine the concentrations of phosphate ion in various samples of river water from the Tone River. The results obtained by this sensor system and the modified molybdenum blue method were compared, and good correlation ( r=0.94) was obtained.

Development of a highly sensitive chemiluminescence flow-injection analysis sensor for phosphate-ion detection using maltose phosphorylase

A chemiluminescence flow-injection analysis biosensor has been constructed for phosphate-ion detection. This system is coenzymeless and employs a maltose phosphorylase, mutarotase, and glucose-oxidase (MP–MUT–GOD) reaction system combined with an Arthromyces ramosus peroxidase–luminol reaction system. The system consists of a column packed with MP–MUT–GOD immobilized on N-hydroxysuccinimide beads, a mixing joint for the chemiluminescence reaction, and a photomultiplier. The response provided by this system was linear, with a wide range between 10 nM and 30 μM phosphate ion, and a measuring time of 3 min per sample. Under the optimal condition, the sensor was able to detect 1.0 μM phosphate ion for at least 2 weeks. For a practical application, the determination of phosphate ion in river water was examined using ethylenediaminetetraacetic acid, and the results were estimated by comparing with the molybdenum-blue method.

Environmental factors influencing the nitrogen fixation activity of free-living terrestrial cyanobacteria from a high arctic area, Spitsbergen

The influence of environmental factors on the nitrogen fixation activity of free-living, terrestrial cyanobacteria from a high arctic area were investigated using experimental manipulations with two different types of field samples, including macroscopic sheets of Nostoc commune and soil samples with a cyanobacterial crust from a Puccinellia salt marsh. In addition, a cultured Anabaena sp. previously isolated from the salt marsh was examined. Nitrogen fixation activity was measured using the acetylene reduction method. The nitrogen fixation mainly took place in the light, but even after 12 h incubation in darkness, low activities were maintained. Phosphorus fertilization stimulated the nitrogen fixation activity, and the highest activities were obtained with about 300 μM phosphate, both in the field samples and the cultured Anabaena sp. Ammonium (28 mM) immediately inhibited the nitrogen fixation activity of the cultured Anabaena sp, whereas 14 mM urea and 540 μM glutamate led to a weaker and slower inhibition of the nitrogen fixation activity, showing that the cultured Anabaena sp. was able to assimilate these combined nitrogen sources. Nitrate did not have any inhibitory effect on nitrogen fixation activity, either in the field samples or in the cultured Anabaena sp. Both the field samples and the cultured Anabaena sp. showed tolerance against sodium chloride concentrations corresponding to the concentration in seawater. The temperature optimum of the nitrogen fixation activity of the cultured Anabaena sp. was about 20°C. Key words: nitrogen fixation, cyanobacteria, Nostoc commune, Anabaena sp., high arctic.

Short-term nutrient pulses as tools to assess responses of coral reef macroalgae to enhanced nutrient availability

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 182:305-310 (1999) - doi:10.3354/meps182305 Short-term nutrient pulses as tools to assess responses of coral reef macroalgae to enhanced nutrient availability Britta Schaffelke* Australian Institute of Marine Science, PMB 3, Townsville, MC 4810, Australia Cooperative Research Centre: Reef Research, James Cook University, Townsville 4811, Australia *E-mail: b.schaffelke@aims.gov.au ABSTRACT: Inshore coral reefs of the Great Barrier Reef, Australia, are subjected to episodic nutrient inputs, mainly by rain and riverine run-off during the summer wet season. Increased nutrient availability, potentially caused by human activity, is assumed to enhance the production of primary producers. To simulate increased nutrient inputs, 6 species of coral reef macroalgae were treated with short-term (24 h) nutrient pulses of 10 µM ammonium and/or 1 µM phosphate. Sargassum baccularia, an inshore perennial algae, had a ~50% higher net photosynthetic rate and ~40% higher tissue nutrients after nutrient addition. The net photosynthetic rates of the inshore, ephemeral species Chnoospora implexa, Hydroclathrus clathratus, and Padina tenuis increased by ~30 to 50% and the tissue nutrient levels by 10 to 20% after a single nutrient pulse. Two perennial species, Chlorodesmis fastigiata and Turbinaria ornata, which occur inshore as well as on reefs further offshore, did not respond to nutrient addition with higher production, however, accumulated 15 to 20% more tissue nutrients than untreated thalli. The different responses to nutrient pulses of macroalgal species with different life cycles and distributional ranges provide important information for the prediction of the response of whole inshore reef communities. KEY WORDS: Nutrient pulse · Coral reef macroalgae · Photosynthesis · Tissue nutrients Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 182. Publication date: June 11, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

The effect of cold- and warm-core eddies on the distribution and stoichiometry of dissolved nutrients in the northeastern Mediterranean

The nutrient distribution and phytoplankton production in the Levantine Sea of the eastern Mediterranean are principally determined by the duration and the intensity of deep winter mixing in the quasi-permanent anticyclonic and cyclonic eddies. In the seasons of stratification, a nutrient-poor aphotic layer is formed between the euphotic zone and the nutricline; interestingly, it consistently extends down to depths of about 29.0–29.05 isopycnal surfaces, but nearly vanishes in the core of the cyclonic Rhodes Gyre (RG) due to the upwelling of the Levantine deep water (LDW) up to the base of the euphotic zone. Accordingly, the nutricline is much sharper and shallower in the cyclonic RG; nevertheless, it is consistently established between the density surfaces of 29.00–29.05 and 29.15 throughout the basin. In the severe winters of 1992 and 1993, the upper 1000 m of the cyclonic Rhodes Gyre was occupied by the LDW with its associated chemical properties and abnormally high nutrient concentrations (NO 3=3.8–4.7μM; PO 4=0.14–0.16μM and Si=7.3–7.8μM) were observed in the euphotic zone. However, the surface nutrient concentrations of the anticyclonic regions were raised merely from the summer–autumn values of <0.02 and nearly 0.2μM to about 0.03 and 0.8μM for phosphate and nitrate, respectively. The molar ratios of nitrate to phosphate in the water column range between 5 and 20 in the euphotic zone but exhibit well-defined peak values (as large as 40–120) at the top of the nutricline (corresponding to nearly the depths of the 29.05 isopycnal surfaces) for most of the year. Such prominent maxima are the result of the apparent shift between the onsets of the nitracline and phosphacline due to as yet undefined factors. Below the nutricline the N/P ratios decrease regularly and reach an almost constant deep value (=28) over the basin. The mean ratio, derived from linear regression of the pooled phosphate and nitrate data from March 1991 to March 1994 is about 23.6, substantially higher than deep ocean values.

Observation of regeneration of nitrate, phosphate and silicate during upwelling off Ubatuba, Brazil, 23°S

Off the Brazilian coast near Ubatuba, an upwelling event of South Atlantic Central Water (SACW) has been observed that transfer nutrient-rich water from 300 to 400 m depth onto the continental shelf to depths less than 35 m. Earlier work showed that SACW is present on the shelf quite frequently; however, nutrient data as natural tracers of water masses, are largely undocumented so far. During the upwelling process the water advanced over the shelf increasing its nutrients concentrations and depleting its content of dissolved oxygen due to the regeneration process. The ratios of regeneration relative to their open ocean origin amount to 4.6 μM for nitrate, 0.43 μM for phosphate and 5.7 μM for silicate on average, while the dissolved oxygen depletes by 114.9 μM.