Natural Populations Of Marine Phytoplankton Research Articles

A simple combined method for determination of β-1,3-glucan and cell wall polysaccharides in diatoms

A new method is described for the combined determination of β-1,3-glucan and cell wall polysaccharides in diatoms, representing total cellular carbohydrate. The glucan is extracted by 0.05 mol l−1 H2SO4 at 60 °C for 10 min, and the cell wall polysaccharides are subsequently hydrolyzed by 80% H2SO4 at 0–4 °C for 20 h. Each carbohydrate fraction is determined by the phenol-sulphuric acid method. The method has been demonstrated for axenic cultures of the marine diatom Skeletonema costatum and natural marine phytoplankton populations dominated by diatoms. Cellular glucan and cell wall polysaccharides were determined with standard deviations of 1–3% and 2–5%, respectively.

Production and neutral aldose composition of dissolved carbohydrates excreted by natural marine phytoplankton populations

Natural populations of diatoms were incubated for 4–12 h with H13CO3−1. The production of particulate and dissolved fractions of organic carbon and neutral aldoses (NAld) was followed by gas chromatography/mass spectrometry. The extracellular production rate of dissolved organic carbon (DOC) ranged from 4.1% to 6.4% of total (particulate and dissolved) production rate. Glucose was a major component of the excreted dissolved neutral aldoses (DNAld), and galactose, rhamnose, fucose, xylose, and mannose were found as secondary components of the excreted DNAld. The comparison of NAld composition with cellular products suggests that glucose in the excreted DNAld is composed mainly of storage glucan. On the other hand, the high ratios of dissolved production to total (dissolved and particulate) production of galactose, rhamnose, fucose, xylose, and mannose probably reflect the active excretion of heteropolysaccharides by diatoms. By assuming steady‐state concentrations, turnover rates of DOC and DNAld can be estimated from the phytoplankton production of 13C‐labeled material. The estimated turnover rates of DNAld through phytoplankton photosynthesis is 4.2–5.1 times higher than that of total DOC, which indicates the bioreactive nature of DNAld. This high turnover rate of DNAld mainly resulted from the high turnover rate of glucose, and it is likely that dissolved glucan is important as a carbon and energy carrier in the marine food web. The fact that the turnover rates of DNAld, which is considered to constitute heteropolysaccharides, are lower than that of glucose, would suggest that heteropolysaccharides are more resistant to biological degradation than glucan.

Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer

Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer

Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer

The maximum uptake rate (ρmax) and affinity constant (Ks) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average ρmax/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average ρmax/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the ρmax/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of “new” production to total production was estimated by ρmax[ρmax−No3/(ρmax−NO3+ρmax−NH4)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04).

Some Observations on Morphological Variation in the Red-Water Ciliate Mesodinium Rubrum

Living cells of the ciliate Mesodinium rubrum were observed and photographed during summer red-water events in the Southampton Water estuary, southern England. These blooms were characterized by increases in maximum cell diameter and range of cell size, a pronounced morphological variation of the ‘oral’ hemisphere, and the presence of free-swimming ‘fragments’ of larger cells.Red-water occurrences caused by the planktonic, phototrophic ciliate Mesodinium rubrum (Lohmann) Hamburger & Buddenbrock, have been characterized by some of the highest recorded levels of chlorophyll and primary productivity for natural populations of marine phytoplankton (Lindholm, 1985; Taylor, 1982). However, as these events are rather unpredictable and all attempts to culture M. rubrum have failed, descriptions of the morphology of living cells have been rather limited. A study into the impact of red-tides caused by M. rubrum in the Southampton Water estuary presented a useful opportunity to observe morphological variation in living cells. Water samples were taken with a ‘Van-Dorn’ sampler, and transported in polyethylene bottles in a cool box. Living cells were observed and photographed at 400x magnification using the phase-contrast optics of an Olympus BH2 photomicroscope. Autofluorescence of living cells was examined using a Zeiss fluoresence microscope.

Diel periodicity in dark uptake of ammonium by natural populations of marine phytoplankton

We discovered the phenomenon that dark uptake of ammonium increases at night and maximizes around midnight. The maximum values at midnight are 2 or 3 times higher than the values in the daytime.

Impact of UV-B radiation on uptake of 15N-ammonia and 15N-nitrate by phytoplankton of the Wadden Sea

Natural marine phytoplankton populations from the German Wadden Sea and unialgal cultures of the haptophycean Phaeocystis pouchetii were tested in 1989 under controlled UV-B stress conditions. Assimilation of 15N-nitrate in phytoplankton consisting mainly of P. pouchetii, or in pure cultures of this alga, was found to be very sensitive to enhanced UV-B dosage in comparison 15N-ammonia uptake. In contrast, in phytoplankton samples containing Ceratium spp., Coscinodiscus sp., Noctiluca sp. or others, rate of 15NO3- uptake was higher and only slightly affected by UV-B irradiance compared to the P. pouchetii sample. UV-B inhibitory effect on uptake of inorganic nitrogen by P. pouchetii was more pronounced under strong white-light conditions and after a UV-B pre-illumination period of several hours than under low white light. Pools of glutamine and alanine decreased after UV-B exposure. Results are discussed with reference to the damaging effects of white light and UV-B on nitrogen metabolism.

Impact of Solar UV Radiation on Uptake of 15N-Ammonia and 15N-Nitrate by Marine Diatoms and Natural Phytoplankton

Summary Natural marine phytoplankton populations and a community of cultured marine microalgae were tested in UV-transparent and non-transparent Plexiglas vessels after addition of 15 N labelled inorganic nitrogen under natural light. Uptake rates of 15 N-ammonia and 15 N-nitrate were reduced after solar radiation at UV exceeding 590 J m -2 d -1 and in near surface waters of the North Sea. Assimilation of 15 N-ammonia was found to be more sensitive to enhanced UV levels than uptake of 15N-nitrate. Patterns of 15N label of several amino acids varied in dependence of UV influence and phytoplankton species. Results were discussed with reference to photoinhibitory effects and UV damages on nitrogen metabolism.

Nutrient Limitation of Phytoplankton Growth in Georgia Nearshore Waters

Nutrient enrichment experiments were conducted to investigate the utilization of dissolved organic and inorganic nitrogen by marine phytoplankton in Georgia coastal waters. Natural populations of marine phytoplankton, enriched with different concentrations of ammonium chloride and other plant nutrients, were grown under controlled temperature and irradiance conditions until the populations reached “stationary phase.” Results showed that (1) phytoplankton are limited by DIN up to ca. 20μM, when another nutrient (phosphate or silicate) becomes limiting, (2) very little naturally-occurring DON is directly utilized for growth, (3) very little DON is indirectly made available for growth over time periods of days to ca. 1 week, and (4) trace metals and vitamins do not significantly limit phytoplankton growth.

Effect of ammonium on the regulation of nitrate assimilation in natural phytoplankton populations

The effect of ammonium additions (0.5 to 10 μg-at. N · 1 −1) on the nitrate reductase activity and on the nitrate uptake of natural marine phytoplankton populations was investigated. Specific nitrate reductase activity was significantly reduced at all ammonium concentrations after 24 h of the addition, but not after 6 h. Total nitrate reductase activity did not decrease even at the highest ammonium concentrations. From this it is concluded that the ammonium concentrations used during this study affected mostly the synthesis of new active enzyme. Nitrate uptake rates were also reduced by the addition of ammonium. In contrast to the nitrate reductase results, maximum inhibition was, however, observed after 6 h rather than after 24 h. The lag in the time of response between the inhibition after the ammonium addition suggests 1. (1) that NH 4 + affects nitrate assimilation in two steps, first nitrate uptake and second nitrate reduction; and 2. (2) that the mechanisms controlling these processes are to a certain extent independent of each other.

Is atmospheric particulate matter inhibiting marine primary productivity?

Present deposition rates of atmospheric particulate matter do not appear great enough to inhibit marine primary productivity except, perhaps, at the sea-surface microlayer. Milligram/liter quantities of air particulate matter added to seawater result in an exponential reduction in photosynthetic /sup 14/C assimilation of natural marine phytoplankton populations. Urban particles are 6 times more toxic than rural particles. The ratios of soluble trace elements from equal amounts of urban (Seattle) to rural (Quillayute) atmospheric particles are as follows: As, 112; Br, 6.4; Cr, 3.4; Cu, 3.7; Ni, 3.0; Pb, 36; V, 2.7; and Zn, 2.2.

Extracellular release of carbon by marine phytoplankton; a physiological approach1

The production of soluble, 14C‐labeled organic material from H14CO3− by cultures and natural populations of marine phytoplankton has been examined with particular attention to experimental technique. Extracellular release is a normal function of healthy cells, is closely related to photosynthetic rate, and is a minor component (up to 5 µg C · liter−1 h−1) of total primary productivity in coastal waters. Time‐course studies and chemical cell‐fractionations indicate that newly synthesized organic 14C is distributed among various cell polymers and the extracellular medium from a rapidly labeled, soluble intracellular pool of small molecules. The rate of supply of carbon to this pool may determine the relative rate of release. Extracellular 14C appearing during transient light shock may preferentially arise from rapidly mobilized polysaccharide and is not simply the result of cell lysis.

Steady-State Growth and Chemical Composition of the Marine Chlorophyte Dunaliella tertiolecta in Nitrogen-Limited Continuous Cultures

The marine chlorophyte Dunaliella tertiolecta was grown in continuous cultures under NH(4)-N, NO(2)-N, NO(3)-N, and urea-N limitations. The effect of the nitrogen cell quota (Q(n)) on the steady-state growth rate (mu) was the same regardless of the N source. The relationship between mu and Q(n) was well described by the Droop equation, but only up to the true maximum growth rate ;mu (= cell washout rate). The ratio between the minimum cell quota (k(Q)) and the maximum cell quota (Q(m)) was 0.19. Hence, there is no substitute for determining ;mu experimentally. That there was no difference in growth response to different N sources suggests that no internal pooling of inorganic nitrogen occurred. Both the carbon (Q(c)) and phosphorus (Q(p)) cell quotas under N limitation increased with increasing mu in a threshold fashion: virtually no change in either cell quota up to approximately 0.8 ;mu, followed by a rapid and large increase up to ;mu. In addition, in the region of low mu, there was an increase in Q(p) with a decreasing medium N/P ratio of between 15 and 5 (by atoms). The results generally indicate the physiological limits in cellular constituency under N limitation. The usefulness of this information, however, in describing the response of natural populations of marine phytoplankton to transient nutrient exposures on the temporal and spatial microscales that most likely exist is of limited value.

Buoyancy of natural populations of marine phytoplankton

Buoyancy of natural populations of marine phytoplankton was studied in a fjord in western Norway during the diatom bloom and in autumn. The study was carried out under approximate in situ conditions by means of an apparatus described in the paper. During the spring bloom, positive buoyancy was observed only once. Sinking rates of individual fractions ranged from 0 to more than 9 m day-1, and the mean sinking rates of the total chlorophyll content from 0 to at least 2. 2 m day-1. The highest rates occurred in the post-bloom period, while sinking appeared negligible from the onset of the bloom up to its culmination. In autumn, the population was dominated by small, flagellated cells. Positive buoyancy, or upward migration, was then observed in two out of three experiments.

Diel variation in nitrogen fixation by a marine blue-green alga, Trichodesmium thiebautii

Abstract A diel variation was demonstrated with respect to nitrogen fixing capacity of a marine blue-green alga, Trichodesmium thiebautii, collected from subtropical waters of the western North Pacific. A 200-fold difference was observed between day and night activities when measured at a light intensity of 12,000 lx. The pattern and extent of variation were different from diel variations reported for photosynthesis, nutrient uptake, and nitrogen fixation of natural populations of marine phytoplankton.

Products of photosynthesis in natural populations of marine phytoplankton from the Gulf of Maine

We have measured the photosynthetic assimilation of 14C-carbon dioxide into (1) ethanol-soluble, (2) hot-trichloroacetic acid (TCA)-soluble (polysaccharide), and (3) protein fractions of natural populations of marine phytoplankton. Diurnal studies showed a continuing incorporation of carbon-14 into the protein fraction during hours of darkness. This was accompanied by a concomitant decrease in the proportion assimilated into polysaccharide. When incorporation was measured under constant experimental conditions, the pattern of photosynthesis did not vary from one time of day to another. At one station approximately 12 km south of Boothbay Harbor, the proportion of carbon entering protein showed marked seasonal changes. During the winter, approximately 10 to 20% of the fixed carbon was incorporated into protein. During the summer the value increased to 22 to 35%. Between these times, a transient high value of 37 to 47% of the fixed carbon entering protein coincided with the spring bloom. The increases in proportion incorporated into protein were largely paralleled by equivalent decreases in the polysaccharide fraction. The proportion of carbon incorporated into protein during photosynthesis also increased markedly at reduced light intensities. This increase occurred both when populations were incubated in neutral-density filters and when incubated at increasing depths in the photic zone. There was little consistent and significant difference between the neutral-density filters and depth in the water column, suggesting a minimal role for light quality. The extent of the increased relative rate of protein synthesis at the lower light intensities depended on the nutritional state of the phytoplankton. For example, summer populations from water containing low concentrations of inorganic nutrients responded less dramatically to reduced light intensities than did populations from nutrient-rich waters.

Biomass production in mass cultures of marine phytoplankton at varying temperatures

Natural populations of marine phytoplankton obtained from a large outdoor pond were grown on waste water-sea water mixtures in laboratory continuous cultures in the temperature range 5–33 °C. Virtually all of the influent inorganic nitrogen (14.0 mg l −1) was assimilated at every temperature tested. There was, however, a distinct change in dominant species with temperature: below 19.8 °C Phaeodactylum tricornutum was dominant, at 27 °C Nilzschia sp. was the main species, and as the temperature increased above 27 °C a blue-green alga, Oscillatoria sp., became increasingly dominant. There is some indication that the excellent growth of P. tricornutum below 10 °C was related to a dramatic increase in the nutrient content per cell as the temperature decreased. Thus at low temperatures reduced division rates are compensated for by increased nutrient uptake rates. It follows that there is a transfer of phytoplankton protein from numerous small cells at intermediate temperatures to large cells that are reduced in numbers at lower temperatures but which represent the same total organic matter. The effect of this phenomenon on annual food chain efficiencies in both controlled and natural marine ecosystems is unknown.

A stable isotope tracer method to measure silicic acid uptake by marine phytoplankton

A tracer method is described that uses the stable isotope 30Si to measure rates of silicic acid uptake by diatom cultures and natural populations of marine phytoplankton. The method involves (i) incubation of organisms requiring silicic acid for growth in the presence of 30Si-labeled silicic acid, (ii) collection of the resulting particulate silicon, (iii) conversion of the particulate silicon to BaSiF6, (iv) determination of the 30Si content of BaSiF6 by solid sample mass spectrometry, and (v) calculation of the uptake rate from the 30Si enrichment of the particulate matter during the incubation. The maximum overall error in the uptake rate measurement is ±10%.

Short-term variability of photosynthesis in natural marine phytoplankton populations : TAGUCHI S., 1976. Mar. Biol., 37 (3): 197–207

Short-term variability of photosynthesis in natural marine phytoplankton populations : TAGUCHI S., 1976. Mar. Biol., 37 (3): 197–207

Mathematical formulation of the relationship between photosynthesis and light for phytoplankton

Eight different mathematical formulations of the photosynthesis—light curve for phytoplankton (up to and including light saturation) were recast in terms of the same two parameters: the initial slope α, and the assimilation number PmB. Each equation was tested for its ability to describe empirical data from natural populations of marine phytoplankton: the results of 188 light‐saturation experiments at three coastal locations in Nova Scotia over a 2‐year period. The most consistently useful mathematical representation of the data was found to be the hyperbolic tangent function.