Cultures Of Marine Phytoplankton Research Articles

Improving quantification of particulate phosphorus

AbstractTotal particulate phosphorus (TPP) is often determined using the high‐temperature dry combustion (HTDC) method followed by hydrolysis of the ash and then molybdenum colorimetry. Here, we show that a higher than traditionally used combustion temperature, 800°C vs. 450–550°C, improves phosphorus recovery from several phosphorus standard compounds, marine phytoplankton cultures, and particulate samples from the field. The ashing auxiliary MgSO4 further improves P recovery by improving decomposition, reducing volatilization during combustion, and increasing the efficiency of hydrolysis. A 0.2 M HCl hydrolysis, under 90°C for 30 min yields a higher P recovery compared with hydrolysis at room temperature or 60°C. In aggregate, these improvements to the method double the P recovery from phospholipids to 97%. TPP recovery from laboratory phytoplankton cultures and field samples increased an average of 11%, primarily due to the improvements in P recovery from phospholipids, polyphosphate, and nucleic acids. We refer to this new method as the eXtra high temperature dry combustion (X‐HTDC) Ash/Hydrol method and recommend its application for measuring particulate phosphorus from organic compounds in aquatic systems.

Proteomic responses of the coccolithophore Emiliania huxleyi to zinc limitation and trace metal substitution.

Zinc concentrations in pelagic surface waters are within the range that limits growth in marine phytoplankton cultures. However, the influence of zinc on marine primary production and phytoplankton communities is not straightforward due to largely uncharacterized abilities for some phytoplankton to access zinc species that may not be universally bioavailable and substitute zinc with cobalt or cadmium. We used a quantitative proteomic approach to investigate these strategies and other responses to zinc limitation in the coccolithophore Emiliania huxleyi, a dominant species in low zinc waters. Zinc limitation resulted in the upregulation of metal transport proteins (ZIP, TroA-like) and COG0523 metallochaperones. Some proteins were uniquely sensitive to growth under replete zinc, substitution of zinc with cobalt, or enhancement of growth with cadmium, and may be useful as biomarkers of zinc stress or substitution in situ. Several proteins specifically upregulated under cobalt-supported or cadmium-enhanced growth appear to reflect stress responses, despite titration of these metals to optimal nutritive levels. Relief from zinc limitation by zinc or cadmium resulted in increased expression of a δ-carbonic anhydrase. Our inability to detect metal binding enzymes that are specifically induced under cobalt- or cadmium-supported growth suggests cambialism is important for zinc substitution in E. huxleyi.

Patterns of dark respiration in aquatic systems

We used continuous measurements of dissolved oxygen (DO) in dark bottles to characterise patterns of the dark respiration rate (Rdark) for three marine phytoplankton monocultures and in natural-water samples from two marine coastal systems. Furthermore, patterns of ecosystem community respiration rate were determined from open-water changes in DO in a fjord and in a lake. We considered two models of Rdark to describe temporal changes in DO: constant Rdark and decreasing Rdark; increasing Rdark. In addition, the effect of incubation time on Rdark was investigated in bottle incubations. Constant Rdark was observed in short-term (12-h) bottle incubations in natural-water samples from two marine coastal systems. Declining Rdark was observed in marine phytoplankton cultures and open-water measurements in a lake. Increasing Rdark was observed in open-water measurements in a fjord, particularly during summer. Long-term (120-h) bottle incubations in natural-water samples showed an increase in Rdark after 48 and 72h. We show that the conventional expectation of constant rates of respiration in darkness is far from typical, because non-linear changes are common under both controlled experimental conditions, as well as for open-water measurements of ecosystem respiration.

Enhanced Dissolved Organic Matter Recovery from Saltwater Samples with Electrodialysis

Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. DOM isolation efficiency by electrodialysis (ED) from salt-containing waters was optimized and evaluated on samples including coastal ocean seawater, open ocean seawater, artificial seawater from axenic cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2–10 L sample volumes. Additionally, the combination of ED and solid-phase extraction, using Bond Elut PPL exchange resin, was evaluated. Using only ED, the following DOC recoveries were achieved: coastal seawater, 71.3 ± 6.5 %; open ocean, 50.5 ± 3.1 %; phytoplankton cultures, 70.3 ± 12.5 %; glucose, 90.2 ± 2.1 %; EDTA, 67.5 ± 9.9 %; and vitamin B12, 98.3 ± 1.6 %. With the combination of PPL and ED techniques, an average DOC recovery of 76.7 ± 2.6 % was obtained for coastal seawater, but this recovery was not statistically different from seawater recoveries using only ED. Comparison of C/N ratios and fluorescence excitation emission matrices taken at the beginning and end of the recovery process for coastal samples processed using only ED indicated that the final recovered material was representative of the DOM present in the original samples. Typical recoveries using combined PPL and ED exceed those of previous isolation methods.

Methanol Production by a Broad Phylogenetic Array of Marine Phytoplankton.

Methanol is a major volatile organic compound on Earth and serves as an important carbon and energy substrate for abundant methylotrophic microbes. Previous geochemical surveys coupled with predictive models suggest that the marine contributions are exceedingly large, rivaling terrestrial sources. Although well studied in terrestrial ecosystems, methanol sources are poorly understood in the marine environment and warrant further investigation. To this end, we adapted a Purge and Trap Gas Chromatography/Mass Spectrometry (P&T-GC/MS) method which allowed reliable measurements of methanol in seawater and marine phytoplankton cultures with a method detection limit of 120 nanomolar. All phytoplankton tested (cyanobacteria: Synechococcus spp. 8102 and 8103, Trichodesmium erythraeum, and Prochlorococcus marinus), and Eukarya (heterokont diatom: Phaeodactylum tricornutum, coccolithophore: Emiliania huxleyi, cryptophyte: Rhodomonas salina, and non-diatom heterokont: Nannochloropsis oculata) produced methanol, ranging from 0.8–13.7 micromolar in culture and methanol per total cellular carbon were measured in the ranges of 0.09–0.3%. Phytoplankton culture time-course measurements displayed a punctuated production pattern with maxima near early stationary phase. Stabile isotope labeled bicarbonate incorporation experiments confirmed that methanol was produced from phytoplankton biomass. Overall, our findings suggest that phytoplankton are a major source of methanol in the upper water column of the world’s oceans.

Response of polyamine pools in marine phytoplankton to nutrient limitation and variation in temperature and salinity

Previous field observations suggest that the composition of intracellular polyamine pools in phytoplankton determines the profile of polyamines released to the surrounding environ- ment; thus, knowing how these pools vary among species and in response to factors affecting phytoplankton growth provides a basis for understanding fluctuations in dissolved polyamines. Our analyses of the polyamine content of axenic marine phytoplankton cultures show that intra- cellular polyamine pools are large (100s to 1000s µmol l �1 of biovolume) and that putrescine and spermidine are the major compounds present; however, composition varied with species. Norsper- midine and norspermine were the dominant compounds found in the diatom Thalassiosira pseudonana and the dinoflagellate Amphidinium carterae, respectively. We explored the effects of temperature, salinity and nutrient limitation on polyamine pools in T. pseudonana, and found that either increasing temperature or decreasing salinity increased polyamine concentrations in cells and in the growth medium. Nutrient (N, P or Si) limitation caused reductions of intracellular polyamine concentrations, but release was enhanced under N or Si limitation. Polyamine ratios in the media were not the same as in intracellular pools, suggesting selective release or uptake of polyamines by phytoplankton. Thus, the composition of the dissolved polyamine pool in seawater can vary significantly and on short time scales, depending on phytoplankton community composi- tion and environmental factors affecting phytoplankton physiology. Our work provides experi- mental verification that biological mechanisms support inferences derived from environmental correlations about the factors controlling polyamine distributions in the sea.

Rapid and highly sensitive analysis of chlorophylls and carotenoids from marine phytoplankton using ultra-high performance liquid chromatography (UHPLC) with the first derivative spectrum chromatogram (FDSC) technique

We developed a rapid and highly sensitive analytical method for chlorophylls and carotenoids derived from marine phytoplankton using ultra-high performance liquid chromatography (UHPLC). High-performance liquid chromatography (HPLC) has been widely used in phytoplankton pigment analysis since the 1980s for estimating the abundance, composition, and photosynthetic physiology of natural algal assemblages or laboratory cultures. However, the run-time of the HPLC analyses is generally ca. 30min or more, which is time-consuming for analysts. Our UHPLC technique enabled us to complete the separations of chlorophylls and carotenoids from marine phytoplankton within 7min with similar resolution as conventional HPLC methods. The analytical method was tested on authentic pigment standards, marine phytoplankton cultures, and field samples that were collected from the central tropical and subarctic Pacific plus the neritic Bering Sea. Critical pigment pairs that generally co-eluted as a single peak were successively resolved by obtaining the first derivative spectrum chromatograms (FDSCs) with a photodiode array (PDA) detector based on differences in pigment absorption spectra, e.g., chlorophyll (Chl) c2 and Mg 2,4 divinyl (DV) pheoporphyrin a5 monomethyl ester (MgDVP), as well as DVChl b and Chl b. Because the maximum injection volume of UHPLC is generally lower than that of HPLC to minimize the unwanted broadening of chromatographic peaks, the detection sensitivity needed to be increased, especially for oligotrophic seawater samples with low pigment concentration. To overcome this sensitivity issue, a PDA detector equipped with an 85mm path length capillary cell was used with a fluorescence detector. As a result, the limit of quantitation (LOQ) as determined by absorbance was of the order of 0.1ng for chlorophylls and carotenoids. Furthermore, a bead-beating technique using N,N-dimethylformamide (DMF) and zirconia beads was utilized to minimize the volume of the organic solvent used for pigment extraction. Our UHPLC method can replace the conventional HPLC techniques, and allows us to yield high-throughput data of the chlorophylls and carotenoids derived from marine phytoplankton.

Exudation of organic carbon by marine phytoplankton: dependence on taxon and cell size

We determined the relationship between photosynthetic production of dissolved organic carbon (OC) and phytoplankton cell size and taxonomic composition in cultures of marine phytoplankton at 3 different growth stages. We measured OC exudation in 22 species belonging to 5 phyla and spanning >7 orders of magnitude in cell volume. The extracellular release of OC in our cultures represented on average ~2% of total carbon fixation, was not statistically different between growth stages, and was not correlated to cell size. The cell- specific OC exudation rate held an isometric relationship with cell size during the different growth phases (average slope: 0.95), which implies that general allometric models cannot be used to predict exudation in marine phytoplankton.

Porticoccus hydrocarbonoclasticus sp. nov., an aromatic hydrocarbon-degrading bacterium identified in laboratory cultures of marine phytoplankton.

A marine bacterium, designated strain MCTG13d, was isolated from a laboratory culture of the dinoflagellate Lingulodinium polyedrum CCAP1121/2 by enrichment with polycyclic aromatic hydrocarbons (PAHs) as the sole carbon source. Based on 16S rRNA gene sequence comparisons, the strain was most closely related to Porticoccus litoralis IMCC2115(T) (96.5%) and to members of the genera Microbulbifer (91.4 to 93.7%) and Marinimicrobium (90.4 to 92.0%). Phylogenetic trees showed that the strain clustered in a distinct phyletic line in the class Gammaproteobacteria for which P. litoralis is presently the sole cultured representative. The strain was strictly aerobic, rod shaped, Gram negative, and halophilic. Notably, it was able to utilize hydrocarbons as sole sources of carbon and energy, whereas sugars did not serve as growth substrates. The predominant isoprenoid quinone of strain MCTG13d was Q-8, and the dominant fatty acids were C(16:1ω7c), C(18:1ω7c), and C(16:0). DNA G+C content for the isolate was 54.9 ± 0.42 mol%. Quantitative PCR primers targeting the 16S rRNA gene of this strain showed that this organism was common in other laboratory cultures of marine phytoplankton. On the basis of phenotypic and genotypic characteristics, strain MCTG13d represents a novel species of Porticoccus, for which the name Porticoccus hydrocarbonoclasticus sp. nov. is proposed. The discovery of this highly specialized hydrocarbon-degrading bacterium living in association with marine phytoplankton suggests that phytoplankton represent a previously unrecognized biotope of novel bacterial taxa that degrade hydrocarbons in the ocean.

Spectral backscattering properties of marine phytoplankton cultures

The backscattering properties of marine phytoplankton, which are assumed to vary widely with differences in size, shape, morphology and internal structure, have been directly measured in the laboratory on a very limited basis. This work presents results from laboratory analysis of the backscattering properties of thirteen phytoplankton species from five major taxa. Optical measurements include portions of the volume scattering function (VSF) and the absorption and attenuation coefficients at nine wavelengths. The VSF was used to obtain the backscattering coefficient for each species, and we focus on intra- and interspecific variability in spectral backscattering in this work. Ancillary measurements included chlorophyll-a concentration, cell concentration, and cell size, shape and morphology via microscopy for each culture. We found that the spectral backscattering properties of phytoplankton deviate from theory at wavelengths where pigment absorption is significant. We were unable to detect an effect of cell size on the spectral shape of backscattering, but we did find a relationship between cell size and both the backscattering ratio and backscattering cross-section. While particulate backscattering at 555 nm was well correlated to chlorophyll-a concentration for any given species, the relationship was highly variable between species. Results from this work indicate that phytoplankton cells may backscatter light at significantly higher efficiencies than what is predicted by Mie theory, which has important implications for closing the underwater and remotely sensed light budget.

Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton

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

Detection of iron(III)-binding ligands originating from marine phytoplankton using cathodic stripping voltammetry.

The sample preparation and analytical methodology are described for detecting biologically produced iron(III)-binding ligands in laboratory cultures of coastal marine phytoplankton. The iron(III)-binding ligands from the culture media were purified by passage through a column packing with a hydrophobic absorbent. The concentrations and stability constants of the ligands were determined by adsorptive cathodic stripping voltammetry with competitive ligand equilibration. The analytical results of the cultivated cultures suggest that eukaryotic phytoplankton would produce iron(III)-binding ligands in analogy with other microorganisms.

The transformation of iodate to iodide in marine phytoplankton cultures

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 237:27-39 (2002) - doi:10.3354/meps237027 The transformation of iodate to iodide in marine phytoplankton cultures George T. F. Wong*, Ajcharaporn U. Piumsomboon**, William M. Dunstan Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, Virginia 23529-0276, USA *E-mail: gwong@odu.edu **Present address: Department of Marine Science, Chulalongkorn University, 254 Phyathai Road Patumwan, Bangkok 10330, Thailand ABSTRACT: Six species of phytoplankton, representing 6 major phylogenetic groups (2 oceanic species: a cyanobacteria, Synechococcus sp., and a coccolithophorid, Emiliania huxleyi; and 4 coastal species: a prasinophyte, Tetraselmis sp., the green algae Dunaliella tertiolecta, the diatom Skeletonema costatum and a dinoflagellate Amphidinium carterae) were tested for their ability to reduce iodate to iodide in batch cultures. They all did so to varying degrees. Thus, the reduction of iodate to iodide by phytoplankton may be a general phenomenon in the marine environment. At ambient concentrations of iodate, the rates of depletion of iodate and appearance of iodide varied between 0.8 and 0.02, and between 0.3 and 0.02 nmol µg chlorophyll a-1 d-1, respectively. E. huxleyi was the least efficient while A. carterae was the most efficient in the depletion of iodate. However, in the formation of iodide, while E. huxleyi was also the least efficient, Synechococcus sp. were the most efficient. The rates of appearance of iodide were noticeably slower than the corresponding rates of depletion of iodate, suggesting that part of the iodate might have been converted to forms of iodine other than iodide in these cases. The slight mismatch in the rank order of the rates of depletion of iodate and appearance of iodide between the phytoplankton species was traced to this variable and incomplete conversion of iodate to iodide. These rates were increased by up to over an order of magnitude upon enriching the culture medium with 5 and 10 µM of iodate. The depletion of iodate and appearance of iodide occurred in all growth phases. However, the rates might vary with growth phase and the patterns of these variations might be species-specific. Phytoplankton growth was not impeded even under unnaturally high concentrations of iodate implying that there is little interaction between iodine processing and the metabolic activity of cell growth. KEY WORDS: Iodine · Elemental speciation · Nitrate reductase · Marine phytoplankton · Oxidation-reduction Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 237. Online publication date: July 18, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

The possible metabolic role of C 37 alkenones in Emiliania huxleyi

Ratios of C 37 alkenones ( U 37 K′ ratios) produced by the haptophyte microalgae Emiliania huxleyi and Gephyrocapsa oceanica are often used as proxies for past sea surface temperatures. Previous studies suggested that these lipids might be either membrane molecules or metabolic storage molecules. In order to assess their cellular role, we cultured two strains of E. huxleyi at 12:12 and 0:24 light/dark cycles (North Pacific clone 55a and Sargasso Sea clone BT6). For both strains, alkenone concentrations (ng/ml) generally increased through both logarithmic and stationary phase in cultures with 12:12 light/dark cycles. This pattern of increasing concentration closely resembles the pattern of increasing triacylglycerol concentration observed in cultures of other marine phytoplankton. Triacylglycerols are used as metabolic storage molecules by many marine algae, but are under-represented or absent in E. huxleyi. When the E. huxleyi cultures were placed in continuous darkness, their alkenone concentrations fell. These findings, that alkenones increase in abundance from logarithmic to stationary phase and decrease in concentration when E. huxleyi is energy-deprived, suggest that Emiliania huxleyi uses alkenones for metabolic storage. Alkenone unsaturation ( U 37 K′ ) ratios changed only slightly during net alkenone degradation in our dark experiments (by −0.035 and +0.046 U 37 K′ units in the dark incubations of BT6 and 55a, respectively), suggesting that metabolic utilization of C 37 alkenones by E. huxleyi is unlikely to be a major source of uncertainty for paleotemperature estimation. If C 37 alkenones are primarily used for metabolic storage, the temperature dependence of their unsaturation may result from differences in melting point, density, or enzymatic optima of biochemical pathways of the differently saturated alkenones.

A method for the measurement of particulate C and P on the same filtered sample

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 217:59-65 (2001) - doi:10.3354/meps217059 A method for the measurement of particulate C and P on the same filtered sample G. G. Lampman, N. F. Caraco*, J. J. Cole Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545, USA *Corresponding author. E-mail: caracon@ecostudies.org ABSTRACT: There is substantial interest in measuring C:P ratios in aquatic systems because these particulate ratios may influence food quality of phytoplankton to zooplankton grazers. In most analyses C is measured by dry combustion using a CN analyzer requiring that P be measured on a separate sample. We show for marine and freshwater phytoplankton cultures and naturally occurring seston that C can be measured by a variation of the same wet-persulfate digestion method frequently used for P analysis, allowing C and P to be measured on the same filter. Over a large range of C values (1 to 40 µmol C filter-1), the persulfate method for measuring C gave the same C value for lake seston, estuarine seston, and marine and freshwater phytoplankton cultures as high temperature dry combustion on a Carlo-Erba CN analyzer. For C, the wet digestion method is much less expensive than the dry combustion method in terms of both equipment and per-sample materials costs. Further, the persulfate method is more precise (CV = 3%) than the dry combustion method (CV = 12%) for the measurement of C. This greater precision of C measurement, and the fact that C and P are measured on the same sample, means that small differences in C:P ratios can more readily be detected. KEY WORDS: Particulate · Phosphorus · Carbon · Method · C:P ratio Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 217. Online publication date: July 31, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

New fluorimetric method of liquid chromatography for the determination of the neurotoxin domoic acid in seafood and marine phytoplankton

Domoic acid (DA) is a neurotoxic amino acid that is responsible for the human toxic syndrome, amnesic shellfish poisoning (ASP). A new rapid, sensitive liquid chromatographic (LC) method has been developed for the determination of DA in various marine samples. DA in marine biological materials was derivatised with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) and analysed using isocratic reversed-phase LC with fluorimetric detection. The calibration, based on standard DA solutions, was linear in the range 0.04–2 μg/ml ( r 2=0.998) and the detection limit (3:1, signal/noise) was better than 1 ng/ml. Using the certified reference material (MUS-1B), recoveries of DA from shellfish tissue were >95% ( n=5). When a strong anion exchange SPE cartridge was used for sample clean-up the detection limit was 6 ng DA/g mussel tissue. Good reproducibility was achieved with RSD values ranging from 3% for 8 μg DA/g ( n=5), to 5% for 0.04 μg DA/g ( n=5). This new method was successfully applied to the determination of DA in naturally contaminated shellfish and in marine phytoplankton cultures of Pseudonitzschia sp.

Carbon disulphide production in laboratory cultures of marine phytoplankton

Carbon disulphide (CS 2) data were collected from axenic monocultures of six species of marine phytoplankton. The tested species included Chaetoceros calcitrans, Phaeodactylum tricornutum, Phaeocystis sp., Porphyridium purpureum, Synechococcus sp. and Isochrysis sp. For a period of between two weeks and forty days, substantial accumulation of CS 2 was found in the cultures of C. calcitrans, P. tricornutum and Phaeocystis sp., whereas the change of CS 2 concentration in the remaining cultures was insignificant. C. calcitrans had a potential for CS 2 production about 10 times higher than P. tricornutum or Phaeocystis sp. The formation of the compound was strongly dependent on the physiological state of the cultured species. More investigation is needed to elucidate the mechanisms responsible for the formation of this sulphur compound in these cultures.

An optical method for the rapid measurement of micromolar concentrations of nitrate in marine phytoplankton cultures

This method of nitrate determination by ultraviolet absorption spectrometry is based on the measurement of sample absorbance at a single wavelength (220 nm), which was chosen on the basis of the absorption spectra of the main components of artificial seawater in the ultraviolet domain. No reagents are used and no sophisticated instruments are necessary. For standards prepared in artificial seawater, the relationship between absorbance and nitrate concentration is linear up to 500 μmol N L−1 and the detection limit is 1 μmol N L−1. Precision is 1.5%. Urea and amino acids did not interfere at concentrations typical of seawater. The method also measures nitrite, but this interference only becomes important for species which excrete large amounts of nitrite. The method is extremely rapid, simple to implement and does not require the use of toxic chemicals such as cadmium. It should prove useful for monitoring quickly the nitrate concentrations in laboratory cultures of marine phytoplankton.

Ultraviolet fluorescence excitation and emission spectroscopy of marine algae and bacteria

Ultraviolet (UV) excitation and emission spectra of cultures of marine bacteria and phytoplankton were investigated. The intensity of the emission band at 340 nm wavelength (λex=230 nm) is compared with cell number and protein content, and specific efficiencies are derived. Another weak emission band at 305 nm is found with most phytoplankton species. The same fluorescence signatures are observed with protein fragments and proteins of known composition and are caused by their tryptophan and tyrosine content. The UV fluorescence of marine particles is related to these aromatic amino acids bound to proteins.

Biological production of methyl bromide by cultures of marine phytoplankton

Methyl bromide production was followed in cultures of a selection of marine phytoplankton species throughout their growth cycle. The cultures were species common to coastal and(or) open ocean areas, as well as originating from various latitudinal bands. Methyl bromide was produced by 13 out of 19 species tested, with production rates ranging from 1.7 to 30.1 pg CH3Br µg−1 Chl a d−1. Species that are strictly coastal or more abundant in coastal areas appeared to be stronger producers of CH,Br than species that are more abundant in open ocean areas. The prymnesiophyte Phaeocystis sp., a bloom‐forming, ubiquitous species, showed the highest daily production rate normalized to Chl a of 30.1 pg CH3Br µg−1 Chl a d−1. The range of methyl bromide production by the phytoplankton cultures tested suggests that the input of methyl bromide by marine phytoplankton can be significant in coastal oceans.