Natural Phytoplankton Populations Research Articles

Bioassay for phosphate demand in phytoplankton from acidified lakes: Lake Njupfatet, an example of phosphate deficiency induced by liming

A bioassay was developed, involving steady-state ATP level determinations, for estimation of phosphate demand and deficiency in natural phytoplankton communities. The studies were performed on phytoplankton from the moderately acidified Lake Njupfatet in central Sweden before and after liming. Phytoplankton samples from in situ enclosure experiments with low-dose enrichments of nitrate and phosphate and removal of large (> 100 µm) zooplankton and from the lake water were collected. The phytoplankton were concentrated by through-flow centrifugation and post-cultured in the laboratory with or without the addition of phosphate. A relative increase in the ATP:chlorophyll a ratio after the phosphate treatment as compared to samples without phosphate enrichment was found to be a highly reproducible indicator of phosphate deficiency in the natural phytoplankton population. In contrast, the absolute ATP:chlorophyll a ratio varied substantially between different sampling occasions. No phosphate deficiency was detected in phytoplankton from the acidic lake or from fertilized in situ enclosures. However, phytoplankton from in situ enclosures without added nutrients showed evidence of phosphate limitation after 21 days incubation. Also, the phytoplankton community developed a significant phosphate deficiency the summer after lake liming. The results from the ATP analyses are compared with chemical data of the lake water, phytoplankton community structure and phosphatase activities in the lake before and after liming. The average total biomass of phytoplankton and the average Tot-P measured during May to September decreased with appr. 30% after liming while Tot-N was essentially unaffected and the phosphatase activities increased by 1000–2000%.

Diel photosynthetic production of cellular organic matter in natural phytoplankton populations, measured with13C and gas chromatography/mass spectrometry

Diel photosynthetic production of water-extractable and residual carbohydrates in natural phytoplankton populations was investigated by analyzing monosaccharide components with combined gas chromatography/mass spectrometry (GC/MS) and13C tracer methods. The applicability of this technique for measuring the photosynthetic production of natural phytoplankton populations was examined. Phytoplankton was collected in August 1984 from Kinu-ura Bay, Japan, and incubated under natural light and dark conditions for 24 h. Cell density and concentration of chlorophylla increased about four- and three-fold, respectively, during the experimental period. Production of glucose, galactose, mannose, rhamnose, ribose, fucose, xylose and arabinose was measured in the water-extractable and residual carbohydrate fractions of the phytoplankton. Most of the monosaccharides in both fractions were produced the monosaccharides in both fractions were produced mainly during the daytime. Glucose was a major component in the water-extractable carbohydrate fraction produced by the phytoplankton, and decreased markedly at night. Thus, most of the glucose in the water-extractable carbohydrates seemed to be a constituent of the storage glucan of algal cells. Most monosaccharide components of the water-extractable carbohydrate fraction except glucose did not decrease significantly at night. Ribose of the water-extractable carbohydrate fraction was synthesized at a maximum rate in the morning, prior to the other monosaccharide constituents of this fraction. The major monosaccharide constituent in the residual carbohydrate fraction produced by the phytoplankton was glucose, which decreased significantly at night. Diel change in the production of monosaccharide constituents in residual carbohydrates indicated wide variability in the monosaccharide composition of cell-wall material in algae. The ratios of production of water-extractable and residual carbohydrates to POC production ranged from 8.8 to 28% and from 3.7 to 5.9%, respectively, throughout the daytime and nighttime.

Diel photosynthetic production of cellular organic matter in natural phytoplankton populations, measured with13C and gas chromatography/mass spectrometry

Diel photosynthetic production of cellular organic matter in natural phytoplankton populations, measured with13C and gas chromatography/mass spectrometry

Zooplankton feeding ecology: grazing during enclosure studies of phytoplankton blooms from the west coast of Sweden

The effects of grazing on natural phytoplankton populations was examined during enclosure studies on the effects of nutrients, zooplankton, and ctenophores on phytoplankton bloom dynamics on the west coast of Sweden in May, 1990. Grazers included the copepods Acartia clausi Giesbrecht, Centropages hamatus Lilljeborg, and Oithona similis Claus, and the marine cladoceran Podon polyphemoides Leuckart. These species ingested various diatoms, dinoflagellates and athecate microflagellates, but grazing was minimal. Clearance rates of the copepods were < 1 ml · animal −1 · h −1, while those of cladocerans reached 2.5 ml · animal −1 · h −1, at microflagellate concentrations of 1442–3519 cells · ml −1. Despite the low levels of copepod and cladoceran grazing, there was considerable removal of Chl a by grazers < 90 μm in longest dimension. These micrograzers were present in experimental and control containers. Athecate ciliates < 20 μm in longest dimension were abundant (up to 1730 cells · ml −1) in some samples, and these ciliates were the most probable micrograzers. Rates of clearance of these ciliates by A. clausi (0.13–0.81 ml · animal −1 · h −1) and C. hamatus (0.46–0.81 ml · animal −1 · h −1) were high, even though ciliates were less abundant than most co-occurring phytoplankton taxa. Copepod and cladoceran grazing appeared to have little impact on phytoplankton dynamics. Rather, copepods were selective consumers of the ciliates that were probably the dominant grazers.

Fatty acid composition in photosynthetic products of natural phytoplankton population in Lake Biwa, Japan

Fatty acid composition in photosynthetic products of natural phytoplankton population in Lake Biwa, Japan

A daily study of the diatom spring bloom at Roscoff (France) in 1985. III. Free amino acids composition studied by HPLC analysis

The growth of a natural phytoplankton population was studied during a monospecific spring bloom of the diatom Rhizosolenia delicatula at Roscoff (western English Channel). Direct examination of the intracellular pool of 19 free amino acids (FAA) was used as an index of the physiological status of the cells. Total FAA in the particulate matter shows a general decrease during the bloom, and FAA cell content varies from 200 mM 1 cell volume−1 to 10 mM at the time of maximum biomass. FAA-N/particulate N is <3% during the study, slightly decreasing at the time of maximum biomass. Individual free amino acids appear reliable for the development of the diatom biomass and good indicators of the growing population. At maximum biomass, major compounds are glutamic acid (30.8 mol%), glutamine (11.7%), alanine (9.9%), isoleucine (6.6%) and lysine (6.4%). Serine, glycine, arginine and aspartic acid appear also as major components during other periods of the study. We suggest that the observed changes are an indication of the physiological state of the cells during the bloom. In particular glutamine (GLN), glutamic acid (GLU) and the GLN/GLU ratio allow the metabolic evolution of the natural population to be characterized. GLN is strictly linked to the living biomass (Chla) while GLU is present at high percentage throughout the study. The ecological significance of β-alanine (BALA) is also revealed during this study, being strongly correlated to degraded matter represented by phaeopigments. These results demonstrate the validity of using individual free amino acids as an aid in understanding the physiological status of algae in natural bloom conditions.

Photosynthesis-irradiance relationships in natural phytoplankton populations of the Barents Sea

An analysis is made of the photosynthesis-irradiance relationships in natural phytoplankton populations in the Barents Sea. The data set comprises 232 experiments carried out during a 10-year period, both in open and ice-covered waters. The variability on the P-I parameters is discussed and examined in relation to the variation in a variety of environmental conditions. The results suggest that in the Barents Sea, as in other Arctic areas, phytoplankton photosynthesis is mainly controlled by physical variables. However, control of the phytoplankton stock, i.e. by zooplankton grazing, seems also to have a considerable indirect influence on P-I parameters, especially after the spring bloom and the depletion of winter nutrients.

Inhibition of bacterial and phytoplanktonic metabolic activity in the lower River Rhine by ditallowdimethylammonium chloride

The effects of a quaternary ammonium compound, ditallowdimethylammonium chloride (DTDMAC), on natural populations of bacteria and phytoplankton from the lower River Rhine were examined to estimate their sensitivity to the discharges of cationic surfactants in the river basin. In short-term experiments, significant decreases in the growth rate of bacterioplankton and in the photosynthetic rate of phytoplankton were observed at a nominal concentration of 0.03 to 0.1 mg of DTDMAC liter-1. Nitrification was measured with an ion-selective electrode and by the rate of acid production in ammonium-spiked river water and was found to be only sensitive to the addition of concentrations higher than 1 mg of DTDMAC liter-1. This does not support an earlier suggestion that ammonium-oxidizing bacteria are specifically sensitive to quaternary ammonium compounds. The effect of DTDMAC on thymidine incorporation was shown to depend strongly on the concentration of suspended material, which varied with the sampling date. This effect was also quantified in experimental manipulations with Rhine water. Calculations on the partitioning of DTDMAC between water and suspended matter confirmed the role of suspended solids and showed that an increase of the dissolved DTDMAC concentration in Rhine water by circa 0.01 mg liter-1 leads to a slight inhibition of the growth of heterotrophic bacteria. It is concluded that a total concentration of circa 0.01 mg of DTDMAC liter-1 measured in the River Rhine is likely to have biological consequences.

Growth rates, grazing, sinking, and iron limitation of equatorial Pacific phytoplankton

Concentrations of phytoplankton and NO3 are consistently low (0.2–0.4 µg Chl a liter‒1) and high (4–12 µM) in surface waters of the oceanic eastern and central equatorial Pacific, and phytoplankton populations are dominated by small solitary phytoplankton (<10 µm). Growth rates of natural phytoplankton populations, needed to assess the relative importance of many of the processes considered important in maintaining the high-nutrient, low-phytoplankton biomass condition observed in the equatorial Pacific, were estimated by several methods. The growth rates of natural phytoplankton populations were found to be ∼0.7 d‒1 or 1 biomass doubling d‒1 and were similar for all methods. To keep this system in its observed balance requires that loss rates approximate observed growth rates. Grazing rates, measured with a dilution grazing experiment, were high (∼0.5 d‒1), accounting for a large fraction of the daily production. Additions of various forms of Fe to 5–7-d incubations utilizing ultraclean techniques resulted in significant shifts in autotrophic (from picoplankton to diatom dominated) and heterotrophic assemblages between initial samples, controls, and Fe enrichments, which were presumably due to Fe, grazing by both protistan and metazoan components, and incubation artifacts. Estimated growth rates of small pennate diatoms (2 × 10 µm) showed increases in Fe enrichments (mean ± SD = 1.60±0.04 d‒1) with respect to controls (mean ± SD = 1.21±0.33 d‒1). The growth rates of the pennate diatoms were similar to those estimated for the larger (>5 µm) size fraction of the natural populations (mean = 1.42 d‒1). We hypothesize that biomass regulation of the larger size fraction of phytoplankton is by a combination of grazing, Fe limitation, and sinking and that understanding the controls over the larger phytoplankton is fundamental to unraveling the high-nutrient, low-biomass paradigm.

Nutrient-induced competition between two species of marine diatoms

Competition experiments betweenPhaeodactylum tricornutum andSkeletonema costatum showed that even at temperatures higher than 10°C (i.c. 14°C), the development ofSkeletonema can be favoured by adjusting nutrient levels and nutrient ratios. Low N∶Si ratios were found to favourSkeletonema. Additionally, high N∶P ratios further enhanced the ability ofSkeletonema to dominate the cuftures. Contrary to some statements in literature, it seems that high concentrations of silicates are more important for the dominance ofSkeletonema costatum in large-scale cultures than just low temperatures. This finding is important with regard to stimulating the blooming ofSkeletonema costatum in natural phytoplankton populations as food for bivalve molluscs.

Response of bacteria and phytoplankton to contaminated sediments from Trenton Channel, Detroit River

Several types of bioassays were used in 1986 and 1987 to investigate the effect of contaminated sediments on natural populations of bacteria and phytoplankton from the Trenton Channel, Detroit River. The approach included the measurement of uptake of 3H-glucose or 3H-adenine by bacteria and 14C-bicarbonate by phytoplankton in the presence of different amounts of Trenton Channel and Lake Michigan (control) sediments. Trenton Channel sediments are contaminated by high levels of toxic organic compounds and metals, especially zinc, lead, and copper. Because levels of biomass of bacteria and phytoplankton varied widely among the different bioassays, it was necessary to adjust uptake rates for biomass. Biomass adjustments were made using acridine orange counts for bacteria and chlorophyll measurements for phytoplankton. The results show a statistically significant suppression of uptake of substrates for both bacteria and phytoplankton with increasing amounts of sediment. Uptake was suppressed as much as 90 percent for bacteria and 93 percent for phytoplankton at 1200 mg l-1 of Trenton Channel sediments compared to bioassays without sediment. Uncontaminated Lake Michigan sediment suppressed uptake much less than Detroit River sediment; the difference in suppression of uptake between the two types of sediment was statistically significant for both bacteria and phytoplankton.

Detection of Gene Expression in Genetically Engineered Microorganisms and Natural Phytoplankton Populations in the Marine Environment by mRNA Analysis

A simple method that combines guanidinium isothiocyanate RNA extraction and probing with antisense and sense RNA probes is described for analysis of microbial gene expression in planktonic populations. Probing of RNA sample extracts with sense-strand RNA probes was used as a control for nonspecific hybridization or contamination of mRNA with target DNA. This method enabled detection of expression of a plasmid-encoded neomycin phosphotransferase gene (nptII) in as few as 10Vibrio cells per ml in 100 ml of seawater. We have used this method to detect expression of the ribulose-1,5-bisphosphate carboxylase large-subunit gene (rbcL) in Synechococcus cultures and natural phytoplankton populations in the Dry Tortugas, Florida. During a 36-h diel study, rbcL expression of the indigenous phytoplankton was greatest in the day, least at night (1100, 0300, and 0100 h), and variable at dawn or dusk (0700 and 1900 h). These results are the first report of gene expression in natural populations by mRNA isolation and probing. This methodology should be useful for the study of gene expression in microorganisms released into the environment for agricultural or bioremediation purposes and indigenous populations containing highly conserved target gene sequences.

Daily zooplankton filtration rates off baja California

During summer 1986 we generated a 14-day time series (27 June to 10 July) of daily filtration rates at a fixed station off Punta Banda, B.C. Mexico, in the California Current System. Filtration rates were measured for natural zooplankton populations, fed with 14C-labelled natural phytoplankton populations. Two upwelling events were characterized, at the beginning and at the end of the sampling period. There were mixed responses in the filtration rates: during the first event, zooplankton presented high filtration rates (up to 50 ml copepod −1 day −1), while during the last event, minima (5 ml copepod −1 day −1) filtration rates were measured. Significant ( P ⩽ 0·05) day to day fluctuations of the zooplankton filtration rates were measured during our study. Due to the great variability of the daily filtration rates, we suggest that to understand fully the coupling between the grazing processes and the environment in upwelling areas, the generation of time and space data series is vital.

Photosynthesis-irradiance relationships in natural phytoplankton populations of the Barents Sea

Photosynthesis-irradiance relationships in natural phytoplankton populations of the Barents Sea

Variação nictemeral da clorofila α, produção primária do fitoplâncton e fatores ambientais da região de Ubatuba (Lat. 23º30'S Long. 45º06'W)

A series of experiments with natural phytoplankton populations was carried out to study the diel variation of chlrophyll a, primary production and some environmental factors. Samples were collected from surface over a period of 24 hours and always from one fixed station located in Flamengo Inlet, Ubatuba region, southern Brazil The experiments were performed in situ and simulated conditions to verify the patterns of diel cycles of both biotic and abiotic factors. The results obtained showed that diel variations were markedly pronounced mainly in relation to primary production and chlorophyll a. Diel variations of biological factors seems to be due to exogenous and endogenous phenomena.

The effects of pH and aluminum on the growth of the acidophilic diatom Asterionella ralfsii var. americana

The effects of pH and Al on the acidophilic diatom Asterionella ralfsii var. americana Körn. were examined in axenic batch cultures. Experiments were performed under conditions of both high (pH 5) and low (pH 6) Al solubility over a range of concentrations from 0 to 30 µmol liter−1 total Al. Growth rates were analyzed with respect to analytically determined Al concentrations and to predicted changes in dissolved metal ion speciation in response to Al additions.Growth rates of A. ralfsii were significantly reduced above 15 µmol liter−1 total Al at both pH 5 and 6. Al additions increased estimated free ion activities of Al3+, Fe3+, and Cu2+ through indirect chelator interactions at pH 5 and 6; therefore, all three were significantly correlated with growth rate reductions. Independent manipulations of total Fe and Cu, however, suggested that Al was not indirectly increasing either Fe3+ or Cu2+ free ion activities to toxic levels. Relationships of growth rates to both inorganic monomeric Al (Alr) and to estimates of pAl were strongly pH‐dependent with toxicity being greater per unit of dissolved Al concentration at pH 6 than at pH 5. These results are consistent qualitatively with predictions that H ions can ameliorate dissolved metal toxicity by competitively excluding Al3+ ions from binding to cell‐surface ligands. The impact of Al on natural phytoplankton populations therefore is likely to depend on a combination of pH‐dependent Al solubility, the protonation of cell‐surface ligands, and chelator‐mediated metal speciation.

A Comparison of the Droop and the Monod Models of Nutrient Limited Growth Applied to Natural Populations of Phytoplankton

The extent of nutrient limitation of phytoplankton in eutrophic Pluβsee was studied by enrichment bioassays and by analysing the cellular stoichiometry of monospecific fractions obtained by size fractionation and density-gradient separation. In this lake silicate and nitrogen, but not phosphorus, at times limit the reproductive rates of phytoplankton. The dependence of nutrient-limited reproductive rates on the cellular content of the limiting nutrient (cell quota) could well be described by the Droop model. Biomass specific minimal cell quotas of nitrogen ranged from 0.014 to 0.061 mol N mol-1 C, minimal cell quotas of silicon ranged from 0.055 to 0.127 mol Si mol-1 C. The cell quotas of the non-limiting nutrients usually increased with the cell quotas of the limiting nutrient. In contrast to the Droop model, the Monod model which relies on ambient concentrations of limiting nutrients was a much poorer predictor of growth rates.

Bivariate and trivariate analysis in flow cytometry: Phytoplankton size and fluorescence

A curve‐fitting method was used to characterize bivariate and trivariate flow cytometric data (cell volume, chlorophyll a fluorescence, phycoerythrin fluorescence) from a mixture of cultured algae and from natural populations of phytoplankton. The frequency distribution of cells in two or three dimensions was approximated by a sum of n bivariate or trivariate log‐normal distributions, where n was the number of subpopulations in the assemblage. Each subpopulation was parameterized by the number of cells, the mean and standard deviation for each of the two or three variables, and a correlation coefficient for each pair of variables.

Phytoplankton primary production and nutrients in the Oosterschelde (The Netherlands) during the pre-barrier period 1980–1984

Phytoplankton primary production, nutrient concentrations and turbidity were monitored at three stations in the Oosterschelde during 1980–1984 as part of an ecosystem study. From comparisons of dissolved nutrient ratios with the nutrient requirements of phytoplankton, and of ambient nutrient concentrations with half-saturation constants for nutrient uptake by natural phytoplankton populations it was concluded that silicate was a limiting nutrient for diatoms after the spring bloom until the end of the summer. Dissolved inorganic nitrogen and phosphate were not considered to be limiting to phytoplankton growth. In general, the phytoplankton growing season started during the first fortnight of April and ended at the end of September. Column production in the whole Oosterschelde varied between 201 and 540 g C m−2 yr−1 and was, on average, 25% higher in the western part than in the eastern part. ‘Basin’ production in the Oosterschelde varied between 120 and 466 g C m−2 yr−1 and was, on average, 55% higher in the western part than in the eastern part; this difference could be explained by differences in the ratio of euphotic depth to mean depth of the compartments. Estimated carbon-specific growth rates in the eastern part varied between < 0.1 and 3 d−1 and in the western part between < 0.1 and 1 d−1. This difference could be explained by the great differences in depth of the compartments. Carbon-specific growth rates are discussed in relation to phytoplankton loss rates. It is suggested that in the eastern part sedimentation must be an important sink for phytoplankton.

Optical assessment of phytoplankton nutrient depletion

The ratio of light absorption at 480 and 665 nm by 90% acetone extracts of marine phytoplankton pigments has been examined as a potential indicator of phytoplankton nutritional status in both laboratory and field studies. The laboratory studies demonstrated a clear relationship between nutritional status (carbon/nitrogen ratio) and the absorption ratio that was independent of light and temperature climate. The absorption ratio for nutrient-replete cells was shown to vary between taxonomic groups. However, the inter-specific variation was less than the differences observed between nutrient-replete and nutrient-depleted cells. The field data suggest that the absorption ratio may be a useful indicator of nutritional status of natural phytoplankton populations, and can be used to augment the interpretation of other data.