Chaetoceros Simplex Research Articles

Effect of Temperature on the Growth of Marine Diatom, Chaetoceros simplex (Ostenfeld, 1901) with Different Nitrate: Silicate Concentrations

ObjectiveTo study the combined effect of temperature, nitrate and silicate on the growth, of the marine diatom, Chaetoceros simplex (Ostenfeld, 1901). MethodsSamples were analysed for the effect of temperature, nitrate and silicate on the growth, chlorophyll ‘a’, protein and carbohydrate contents. Totally fifteen experiments were conducted for 12 days under three different temperature (20, 25 and 29 °C), 68 μmol photon m−2 s−1 light intensity and at five concentrations of nitrate: silicate propositions (882 μM [NO3−] −106 μM [SiO32−], 1323 μM [NO3] −159 μM [SiO32−], 1764 μM [NO3−]-212 μM [SiO32−], 2205 μM [NO3−]-265 μM [SiO32−] and 2646 μM [NO3−]-318 μM [SiO32−] respectively). ResultThe maximum cell density reached 23.5 × 105 cells ml−1 with 1764 μM [NO3−] and 212 μM [SiO32−] concentrations at 29 °C, in 10th day of culture. The high chlorophyll ‘a’ content of 1.57 ± 0.05 pg/cell at 20°C and 2205 μM [NO3−]-265 μM [SiO32−]. The high protein content of 4.48 ± 0.17 pg/cell was found in 2205 μM [NO3−]-265 μM [SiO32−] at 25°C. The high carbohydrate contents of 0.78 ± 0.03 pg/cell were found in 1764 μM [NO3−]-212 μM [SiO32−] at the temperature of 25°C. ConclusionsThe growth rate was directly proportional to nutrient concentration and temperature whereas chlorophyll ‘a’ and biochemical concentration was directly proportional to nutrient concentration. Based on the present results, furture work on growth optimization with the other physical and nutritional factors will yield noteworthy information on the mass cultivation of C. simplex for aquaculture purposes.

Effect of Industrial Effluent on the Growth of Marine Diatom, <i>Chaetoceros simplex</i> (Ostenfeld, 1901)

The marine centric diatom,Chaetoceros simplex (Ostenfeld, 1901) was exposed to five different concentrations of industrial effluent for 96 hrs to investigate the effect on growth. The physico-chemical parameters viz. colour, odour, temperature, salinity, dissolved oxygen, turbidity, pH, alkalinity, hardness, ammonia, nitrite, nitrate, inorganic phosphate, total phosphorous, reactive silicate, calcium and magnesium were estimated in the effluent. The Ammonia (326 μg. L-1), Nitrite (19.53 μg. L-1) and Nitrate (471.4 μg. L-1) were observed at higher levels. About 50% of the cell density of C. simplex reached a lesser dilutions of effluent viz. 1:625 and 1:1250 than the control. The highest cell density (14.3 × 104 cell ml-1) was recorded in 1:10000 diluted effluent followed by control and the lowest cell density was observed in 1:625 diluted effluents. From the results, it is evidenced that the lower volume of effluent discharge into higher volume of water could not affect the growth rate of phytoplankton. It is more important that to reduce the effect of pollution and environmental sustainability. @JASEMJ. Appl. Sci. Environ. Manage. December, 2010, Vol. 14 (4) 35 - 37

Microalgal composition and primary production in Arctic sea ice: a seasonal study from Kobbefjord (Kangerluarsunnguaq), West Greenland

We investigated the microalgal community in sea ice and in the water column of Kobbe- fjord, West Greenland, through an entire sea ice season. Temporal variation in physical (photosynthet- ically active radiation (PAR), temperature, brine volume) and chemical (salinity, nutrient concentra- tion) properties confirmed that sea ice is a very dynamic habitat. Nevertheless, a viable sea ice algal community was present throughout the year, with a species succession from flagellate dominance (di- noflagellates and cryptophytes) in December to February, followed by Chaetoceros simplex (a centric diatom) in March and pennate diatoms in May. Sea ice algal composition, biomass and productivity were influenced by PAR and brine volume, with colonization (enhanced by large brine volume) appar- ent during sea ice melt. Sea ice chlorophyll levels were generally low (<0.5 µg chl l -1 ), with 2 distinct blooms (maxima of 1.8 and 2.6 µg chl l -1 in March and May, respectively). Primary production mirrored biomass dynamic, which had 2 seasonal peaks of ca. 21 and 15 mg C m -2 d -1 . Integrated primary pro- duction over 7 mo was 0.8 g C m -2 in sea ice and 94.4 g C m -2 in the water column, with the vast major- ity of the pelagic production occurring just after sea ice melt (when primary production peaked at 4.2 g C m -2 d -1 ). There was no conclusive evidence of algal seeding. Sea ice algae contributed 30% of total (sympagic plus pelagic) primary production during the sea ice season, but less than 1% annually.

The decomposition of hydrogen peroxide by marine phytoplankton

All nine species of marine phytoplankton tested (a cyanobacterium: Synechococcus sp., three diatoms: Chaetoceros simplex, Thalassiosira oceanica and Skeletonema costatum, two prymnesiophytes: Pleurochrysis carterae and Isochrysis galbana, a prasinophyte: Tetraselmis sp., a green alga: Dunaliella tertiolecta, and a dinoflagellate: Amphidinium carterae) were able to decompose hydrogen peroxide in the dark. Since these phytoplankton species can be found widely in a variety of marine sub-environments, this indicates that the dark decomposition of hydrogen peroxide by phytoplankton is a general phenomenon in the oceans. The decomposition rates were first order with respect to the concentration of hydrogen peroxide and biomass. The second-order rate constants for these nine species of phytoplankton ranged between 2 × 10 –4 and 2.7 × 10 –2 μg Chl- a –1 1 h –1. Synechococcus sp. and S. costatum were the most efficient, while P. carterae and D. tertiolecta were the least efficient decomposers. While the magnitudes and patterns in the changes were species-dependent, in general, increasing salinity, temperature, the presence of light and the depletion of nutrients enhanced the decomposition of hydrogen peroxide. The effect of growth phase was small.

Nitrogen isotope fractionation in 12 species of marine phytoplankton during growth on nitrate

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 255:81-91 (2003) - doi:10.3354/meps255081 Nitrogen isotope fractionation in 12 species of marine phytoplankton during growth on nitrate Joseph A. Needoba1,*, N. A. Waser2, P. J. Harrison1,3, S. E. Calvert2 1Department of Botany, and 2Department of Earth and Ocean Sciences, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada 3Atmospheric and Marine Coastal Environmental Program, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR *Email: needoba@interchange.ubc.ca ABSTRACT: The nitrogen isotopic composition of 12 species of marine phytoplankton were determined by isotope ratio mass spectrometry in order to investigate isotope fractionation associated with growth on nitrate. The species, representing diatoms, coccolithophores, dinoflagellates, green algae, and cyanobacteria, were grown in batch cultures in artificial seawater under the same laboratory conditions of constant light and temperature. The species (with isotope fractionation values in parenthesis) were: Thalassiosira weissflogii (6.2 ± 0.4‰); Chaetoceros simplex (2.7 ± 0.3‰); Ditylum brightwellii (3.3 ± 0.4‰); Skeletonema costatum (2.7 ± 0.3‰); Phaeodactylum tricornutum (4.8 ± 0.3‰); Emiliania huxleyi (4.5 ± 0.2‰), Isochrysis galbana (3.2 ± 0.4‰); Pavlova lutheri, (3.6 ± 0.5‰); Amphidinium carterae (2.2 ± 0.3‰); Prorocentrum minimum (2.5 ± 0.3‰); Dunaliella tertiolecta (2.2 ± 0.2‰); and Synechococcus sp. (5.4 ± 0.6‰). There was no relationship between isotope fractionation and organism group, nor was there a direct effect of cell size or growth rate on the degree of isotope fractionation among all the groups. Overall, the results show that isotope fractionation during growth on nitrate is lower than values obtained from field samples (i.e. 4 to 9‰). These results indicate that there is no simple mechanism for describing differences in isotope fractionation between groups of phytoplankton, and that a physiological understanding of isotope fractionation during uptake and assimilation of nitrate is needed to properly understand the δ15N signal generated by phytoplankton in the ocean. KEY WORDS: Marine phytoplankton · Nitrogen isotope fractionation · Nitrate · 15N:14N · Stable isotopes · Batch culture Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 255. Online publication date: June 24, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Bacterial control of silicon regeneration from diatom detritus: Significance of bacterial ectohydrolases and species identity

Bacteria (and possibly archaea) accelerate silica dissolution in the sea by colonizing and enzymatically degrading the organic matrix of diatom frustules. We tested whether colonizer species composition and ectohydrolase profiles critically control silicon regeneration by allowing diatom (Thalassiosira weissflogii and Chaetoceros simplex) detritus to be colonized by natural bacterial assemblages and 12 phylogenetically characterized marine isolates. We characterized the colonizers' ectohydrolase profiles and rates of silicon regeneration. The colonizers' cell‐specific protease activity was consistently the dominant ectohydrolase, and it strongly correlated with silica dissolution rates. Cell‐specific glucosidase, lipase, and chitinase activities showed no correlation with silicon regeneration. Denaturing gradient gel electrophoresis (DGGE) of PCR‐amplified 16S rRNA genes was used to monitor colonization of detritus by natural microbial assemblages and to identify colonizing phylotypes. Representatives from gammaproteobacteria and sphingobacteria‐flavobacteria classes dominated colonizer populations by comprising 65% and 25% of detected phylotypes, respectively. Archaea were not detected among colonizer populations. All bacterial isolates accelerated silica dissolution, but individual rates varied by &gt;300%. Significant variability was observed within the Alteromonadaceae, which indicates different abilities to process diatom organic matter. Isolates that displayed enhanced colonization and protease activities were the most effective at regenerating silicon. The most effective isolate belonged to the sphingobacteria‐flavobacteria, a group specialized in colonizing marine particles. Other effective isolates grouped with Pseudoalteromonas, Alteromonas, and Vibrio genera. One isolate caused intense aggregation of diatom detritus, significantly reducing silicon regeneration. Our results indicate that bacterial species identity strongly controlled silicon regeneration by influencing the colonization potential and ectohydrolytic profiles of bacteria as well as aggregate formation. Mechanistic models of oceanic silica cycling should incorporate species composition and ectohydrolase profiles of bacteria involved in silicon regeneration.

Effect of uv-b on lipid content of three antarctic marine phytoplankton

The effects of UV-B radiation on the fatty acid, total lipid and sterol composition and content of three Antarctic marine phytoplankton were examined in a preliminary culture experiment. Exponential growth phase cultures of the diatoms, Odontella weissflogii and Chaetoceros simplex, and the Haptophyte, Phaeocystis antarctica, were grown at 2 (±1)° and exposed to 16.3 (±0.7) Wm −2 photosynthetically active radiation (PAR). UV-irradiated treatments were exposed to constant UV-A (4.39 (±0.20) Wm −2) and low (0.37 Wm −2) or high UV-B (1.59 Wm −2). UV-B treatments induced species-specific changes in lipid content and composition. The sterol, fatty acid and total lipid content and profiles for O. weissfloggi changed little under low UV-B when compared with control conditions (PAR alone), but showed a decrease in the lipid content per cell under high UV-B treatment. In contrast, when P. antarctica was exposed to low UV-B irradiance, storage lipids were reduced and structural lipids increased, indicating that low UV-B enhanced cell growth and metabolism. Phaeocystis antarctica also contained a higher proportion of polyunsaturated fatty acids under low UV-B in comparison with PAR-irradiated control cultures. The flagellate life stage of P. antarctica dies under high UV-B irradiation. However, exposure of P. antarctica to high UV-B irradiance increased total lipid, triacylglycerol and free fatty acid concentrations, indicating that increases in lipid content were associated with the colonial life stage. Lipid concentrations per cell also increased when C. simplex was exposed to high UV-B irradiance. This resulted from increases in free fatty acid concentration, principally saturated fatty acids, and may indicate degradation of complex lipid during high UV-B treatment. Under low UV-B, there was no statistically significant difference when compared with the control. In comparison with the PAR-exposed controls, low UV-B benefited or did not affect cellular metabolism and growth of the three microalgae examined. Our results indicate that the effect of UV-B irradiances on the lipid content of Antarctic marine phytoplankton is species-specific. Changes in ambient UV-B may alter the nutritional quality of food available to higher trophic levels.

Assessment of the nutritional value of three species of tropical microalgae, dried Tetraselmis and a yeast-based diet for larvae of the blacklip pearl oyster, Pinctada margaritifera (L.)

This paper reports on two experiments in which three species of tropical microalgae, Isochrysis (T-ISO), Pavlova salina and Chaetoceros simplex, dried Tetraselmis suecica and a commercial yeast-based diet (`L-10', Microfeast®) were assessed for their nutritional value for larvae of the blacklip pearl oyster, Pinctada margaritifera. In the first experiment, T-ISO supported significantly greater growth of D-stage larvae than either Pav. salina, C. simplex or a ternary algal diet (TAD) composed of an equal mixture of the three species. Fifty percent of the mixed algal diet could be replaced with dried Tetraselmis without significantly affecting larval growth rate or survival. Indeed, growth of larvae fed a 1:1 mixture of TAD and dried Tetraselmis was significantly greater than that of larvae fed the three species of microalgae alone or the TAD. In the second experiment, umbo larvae were fed either the TAD, dried Tetraselmis, `L-10' or 1:1 combinations of these diets. Survival of unfed larvae was significantly lower than that of fed larvae and larvae receiving food had significantly greater antero-posterior shell length than unfed controls. Larvae fed dried Tetraselmis were significantly larger than those fed `L-10' but did not differ significantly in size from those fed the TAD. Larvae fed the 1:1 mixture of dried Tetraselmis and `L-10' were significantly larger than those fed `L-10' alone but significantly smaller than those fed dried Tetraselmis alone. The largest larvae at the end of Experiment 2 were those fed a 1:1 mixture of TAD and `L-10' which were significantly larger than larvae fed the TAD.

Influence of irradiance on the nutritional value of two phytoplankton species fed to larval Japanese scallops (Patinopecten yessoensis)

Japanese scallop (Patinopectin yessoensis Jay) larvae grew faster and were larger after 18 d when fed a diet of high-light(HL)-grown Chaetoceros simplex or HL Pavlova lutheri relative to diets of the same phytoplankton species grown at low light (LL). When provided as saturating rations to larval scallop, these diets could be ranked: HL C. simplex>LL C. simplex>HL P. lutheri>LL P. lutheri. In both phytoplankton species, HL-grown cells contained more of the short-chain saturated fatty acid (FA), 16:0 than LL-grown cells. Scallop growth rates were a significant function of the amounts (mg g-1 dry wt) and the proportions (as percentage of total FAs) of the FAs 14:0 and 14:0+16:0 (total saturated FAs) in their diet. The proximate biochemical composition of HL- versus LL-grown phytoplankton showed no significant differences in protein, total lipid, carbon, carbohydrate or nitrogen per cell which were consistently associated with the greater nutritional value of HL cells. In spite of this high variability in proximate composition, the larval growth rate was a significant function of the average carbon content, nitrogen content and cell volume of the phytoplankton cells. Increased amounts of the “essential” polyunsaturated FAs 20:5 ω3 and 22:6 ω3 in the phytoplankton were negatively correlated with larval scallop growth rates. Thus HL-grown phytoplankton cells were nutritionally superior to LL-grown cells. This nutritional superiority seems to be determined by the fatty acid composition of the cells which, in turn, is controlled by variation in irradiance. The general tendency of predator FA profiles to resemble that of their prey was not observed in larvae fed P. lutheri. The much greater amounts of 18:4 ω3, 20:5 ω3, and 22:6 ω3 FA in P. lutheri relative to C. simplex were not evident in the scallop larvae fed these cells.

Flow Cytometry studies of marine phytoplankton populations

Abstract Flow cytometry has been applied to the study of phytoplankton populations and cell components. In this work, cells cycle studies on three marine diatoms cultures were carried out by a flow cytometer. Phaeodactylum tricomutum, Chaetoceros simplex and Thalassiosira allenii, showed different DNA patterns in G1, G2, S, phases. This situation may be related to the specific algal physiology. Cultures of P. tricomutum were maintained in 4 media with different silicates concentrations. The lack of silicates did not seem produced a significative cells arresting in the cell cycle phases. During the experiment, the cell fraction in S phase, decreased in all media tested. These preliminary results could be further developed to apply flow cytometry to environmental problems in order to identify general algal groups and study algal physiology in different growth conditions.

EFFECTS OF VARIATION IN TEMPERATURE. II. ON THE FATTY ACID COMPOSITION OF EIGHT SPECIES OF MARINE PHYTOPLANKTON1

ABSTRACTEight species of marine phytoplankton showed significant variation in the relative amount of some fatty acids (FAs) in response to variation in temperature. Large changes in relative amounts of certain FAs occurred as a result of a 15° C change in growth temperature. For example, 14:0 increased from ≃4% of total FAs at 10° C to &gt; 20% at 25° C for Chaetoceros simplex and Isochrysis aff. galbana but decreased for Phaeodactylum tricornutum. The percentage of the polyunsaturated fatty acid (PUFA) 16:ω1 was consistently greater at 10° C than at 25° C, and the converse was usually true for 16: 4ω3. Calculated over all eight species, there was a modest but significant inverse relationship between the percentage of PUFAs and temperature. Only for Thalassiosira pseudonana was the percentage of either of the PUFAs and nutritionally essential fatty acids (EFAs) also an inverse function of temperature. For T. pseudonana, the percentage of the EFA 22:6ω3 decreased linearly with increasing temperature over the range from 10 to 25° C.For three species, the ratio of unsaturated/saturated FAs was correlated with growth rate when growth rate was controlled by variation in irradiance and temperature. Only for Thalassiosira pseudonana was the ratio of unsaturated/saturated FAs also an inverse function of temperature alone.

INFLUENCE OF IRRADIANCE ON THE FATTY ACID COMPOSITION OF PHYTOPLANKTON1

ABSTRACTEight species of marine phytoplankton commonly used in aquaculture were grown under a range of photon flux densities (PEDs) and analyzed for their fatty acid (FA) composition. Fatty and composition changed considerably at different PFDs although no consistent correlation between the relative proportion of a single FA and μ or chl a · cell−1 was apparent. Within an individual species the percentage of certain fatty acids covaried with PFDs, growth rate and/or chl a · cell−1. The light conditions which produced the greatest proportion of the essential fatty acids was species specific. Eicosapentaenoic acid. 20:5ω3 increased from 6.1% to 15.5% of the total fatty acids of Chaetoceros simplex Ostenfield grown at PFDs which decreased from 225 μE · m−2· s−1 to 6 μE · m−2· s−1, respectively. Most species had their greatest proportion of 20: 5ω3 at low levels of irradiance. Conversely, docosahexaenoic acid, 22:6ω3, decreased from 9.7% to 3.6% of the total fatty acids in Pavlova lutheri Droop as PFD decreased. The percentage of 22:6ω3 generally decreased with decreasing irradiances. In all diatoms the percentage of 16:0 was significantly correlated with PFD, and in three of five diatoms, with growth rate (μ). Results suggest that fatty acid composition is a highly dynamic component of cellular physiology, which responds significantly to variation in PFD.

THE INLAND CHAETOCEROS (BACILLARIOPHYCEAE) SPECIES OF NORTH AMERICA1

ABSTRACT Five taxa of Chaetoceros occur in inland waters of North America. These most commonly occur in waters with elevated total dissolved solids in arid regions of the western United States and Canada. Chaetoceros amanita Cleve‐Euler is characterized by consistently forming relatively long chains of cells and having very spinose primary resting spore valves. Chaetoceros elmorei Boyer also forms long chains of cells which are connected by evident valvar processes; spores are nearly always smooth. Chaetoceros muelleri Lemm. may form short chains with processes between sibling valves, but also produces solitary cells lacking processes. Chaetoceros muelleri var. subsalsum (Lemm.)Johansen et Rushforth is similar to the nominate but never produces cells with Processes. Both of the C. muelleri varieties produce spores with smooth primary valves. Chaetoceros simplex Ostenfeld is characterized by a noncolonial habit, cells lacking processes and the production of resting spores with warty to some what spinose primary valves.

Evaluation of phytoplankton as diets for juvenile Ostrea edulis L.

Of 16 phytoplankton species tested as juvenile oyster diets, those superior to the reference diet Isochrysis galbana clone T-iso emerged with the following descending ranking: Chaetoceros gracilis Schütt, C. calcitrans Takano, Skeletonema costatum (Grev.) Cleve, Chaetoceros simplex Ostenfeld, Rhodomonas sp., and Thalassiosira pseudonana Hasle & Heimdal. The daily oyster growth rate with Chaetoceros gracilis was 1.5 to 1.8 times that with Isochrysis galbana clone T-iso. Biochemical analysis on some of the good and poor algal diets provided insight into the nutritional requirements of Ostrea edulis (L.) juveniles. Level of the essential fatty acids 20: 5ω3 and 22: 6ω3 and carbohydrate level are important factors in a good algal diet for O. edulis juveniles. Variation in the amino-acid composition among the seven algal diets analysed was small and did not explain the observed differences in oyster growth response with the diets. There was no clear trend between the protein level of the diet and the growth response of the oysters.

Dark CO2 uptake by the diatom Chaetoceros simplex in response to nitrogen pulsing

In a continuing investigation of dark CO2 uptake by nitrogen-limited cultures of the marine diatom Chaetoceros simplex (Bbsm), we expanded on several of our earlier conclusions regarding the potential application of this physiological response for measuring the degree and type of nitrogen limitation in phytoplankton populations. First, the duration over which the maximal enhancement of dark 14CO2 uptake was sustained after NH4+enrichment was a function both of the concentration of added NH4+and the standing crop of phytoplankton nitrogen — in effect, the total N demand. Second, pulsing with NH4+for a given degree of N-limitation always produced the same level of enhanced dark CO2 uptake regardless of whether the cultures were preconditioned with oxidized or reduced nitrogen. In contrast, urea pulsing led to reduced dark CO2 uptake, but the effect was most pronounced in cells grown on NO3−. And third, the assay could be used to distinguish readily between no, moderate, and severe N limitation. The degree of severe N limitation was quantitatively correlated with the degree of enhanced dark CO2 uptake, but this relationship was not so clear in the region of moderate N limitation. The main advantage of the assay is that it is a relatively simple and effective alternative to more complicated techniques for gauging the degree and form of N limitation in phytoplankton. Further evaluation will be required, both in the laboratory and field, before the assay can be calibrated for quantitative use.

Effect of nitrogen source on short-term light and dark CO2 uptake by a marine diatom

Based on a series of short-term incubations involving the marine diatom Chaetoceros simplex (Bbsm), precultured in NH 4 + -, NO 3 - -and urea-limited continuous cultures at several dilution rates, we found that both the short-term specific rate of 14CO2 uptake and the amount of CO2 fixed after 8- and 16-min incubations were unaffected by enrichment with NH 4 + , urea, or NO 3 - when NH 4 + or urea were the preconditioning forms of N, but were slightly suppressed when the cells were first grown on NO 3 - . Similar enrichments in the dark, however, led to significant CO2 uptake under all conditions of NH 4 + enrichment and to similarly enhanced CO2 uptake, but only at high growth rates, when urea was the source of enrichment nitrogen. Our light results are contrary to some contemporary findings, but there does seem to be agreement that photosynthetic rates of rapidly growing phytoplankton will not be affected by exposure to pulses of nitrogen. Enhanced dark uptake, in contrast, appears to be characteristic of phytoplankton under all degrees of N limitation, and, as such, may be useful as an “all or nothing” index of the nitrogen status of natural waters. There is some indication that the index may be useful in determining both the form of and the degree of N limitation as well.

Comparative rapid ammonium uptake by four species of marine phytoplankton1

A series of 15NH4+ uptake studies with four species of marine phytoplankton, Dunaliella tertiolecta (Dun), Phaeodactylum tricornutum (TFX‐1), Chaetoceros simplex (BBsm), and Thalassiosira weissflogii (Actin), maintained in NH4+‐limited continuous cultures at varying specific growth rates (µ) and temperatures, was done to examine the time‐dependency of NH4+ uptake and the relationship between physiological state and NH4+ uptake. The effect of growth rate on short term NH4+ uptake varied tremendously with species, but the trend of increasing V′M: µ̂ with decreasing relative growth rate (µ:µ̂) was demonstrated by all species down to µ ≃ 0.25% of µ̂. The diatoms, especially, were capable of sustaining a high V′M:µ̂ even at very high relative growth rates. Growth rate also influenced the time‐course of NH4+ uptake: for cells grown at ≈ 0.20–0.35 µ̂ an enhancement in NH4+ uptake was observed in the first 5 min of incubation, but not for cells at &gt;0.90 µ̂. These data are consistent with the hypothesis that phytoplankton may be able to exploit short‐lived nutrient micropatches and may be growing at relatively rapid rates in oceanic waters.

Variação sazonal do fitoplâncton da região do Saco da Ribeira (lat. 23º30'S; long, 45º07'W), Ubatuba, Brasil

Seasonal changes in phytoplankton populations in the chlorophyll-a concentration and on some environmental factors were studied monthly from June 1974 to September 1975 at Ubatuba, northern coast of Sao Paulo. Water temperatures ranged from 20oC in August to 29.5oC in March and salinities from 33.06 o/.. in March to 35.80 o/.. in January. The maximum salinity value observed in January near the bottom, associated with the thermal stratification found only during this month, seems to indicate an oceanic contribution to the enrichment of the local water mass. Pluviometric values ranged from 37.2 mm in August to 468.5 mm in January. Phytoplankton cell counts fluctuated from 64,000 to 1,028,000 cells/l and chlorophyll-a values varied from 0.52 to 6.86 µg/l. Maximum standing-stock was observed during summer, particularly in March, and it is probably associated with land drainage due to precipitation. A second bloom was observed in September 1975, and it is associated probably with the discontinuous impact of the wind. The phytoplankton populations were dominated by unidentified phytoflagellates, followed by diatoms and dinoflagellates. Nitzchia closterium and Thalassionema nitzschioides, along with Navicula sp., were the most representative species of diatoms. Among the dinoflagellates, Gymnodinium sp. was the most important. Blue-green algae and silicoflagellates were poorly represented. The diatoms Chaetoceros simplex, Chaetoceros spp, Nitzchia longissima, Nitzchia spp, Rhizosolenia delicatula and Rhizosolenia stolterfothi were found with high densities, only during bloom periods. The chlorophyll-a fractionation experiments demonstrated that organisms in size classe smaller than 20 µm represented, for all depths, between 54.93 and 98.15 o/.. of the total phytoplankton population.

La diatomée marine Chaetoceros simplex calcitrans paulsen et son environnement. VII. Aspects dynamiques des échanges en lipides entre la diatomée et son milieu

The results of three experiments dealing with the total lipids exchanged between the diatom Chaetoceros simplex calcitrans Paulsen and its surroundings are reported. Each study which involved four different culture samples and lasted 24 h has shown that the exchanges follow a definite rhythm with a period of 1 to 3 h, light being present or not. The increase of the total lipids in the medium through the agency of the diatom may be considerable after 24 h (4.66–4.75 mg/40 ml) but this amount is almost entirely regained by the algae, and sometimes more after nine days of culture. Using labelled dotriacontane-16,17- 14C shows that labelled lipids are preferentially rejected by the diatom in the absence of light.

Sur une méthode de récolte de diatomées vivantes après culture

The best conditions for collecting living diatoms (Chaetoceros simplex calcitrans) after culture and their introduction into a replacement medium have been determined. Traumatisms (such as ionic, thermic, gravimetric) have been minimized.