Effect of blue-green light on growth rate and chemical composition of three diatoms

The diatomsChaetoceros sp.,Skeletonema costatum andThalassiosira pseudonana were grown with different irradiances of white and of blue-green light, and with a mixture of blue-green plus 6.5 mol m^–2 s^–1 of white light. Exponential growth rates were higher in mixed blue for the first two, whileT. pseudonana grew faster in white light but, in all cases, mean cell division rates did not differ with increasing irradiances. Harvesting in stationary, rather than in late exponential growth phase, resulted in higher protein contents forChaetoceros sp. andS. costatum, but forT. pseudonana the highest value was in the exponential phase. The highest protein content was in blue-green light for the three species and it increased with irradiance. As to other fractions, the three strains showed different responses, related to quality and quantity, as well as to culture ages.     

Photon requirement for O2-Revolution in red (λ= 680 nm) light for some C3 and C4 plants and a C3–C4 intermediate species*

Photon requirements for O₂-evolution in red (λ=680nm) light (Ф_r) were measured for six C₃ species, one C₃-like, C₃–C₄ intermediate species, and three C₄ species, including examples of NADP-malic enzyme and PEP-carboxykinase C₄ sub-groups. Variation in Ф_r within the C₃ species was small with a mean value of 7.96 ±0.12 mol photon mol⁻¹ O₂, whereas the mean value for the C₄ species was 12.27± 1.53 mol photon mol⁻¹ O₂, with the lowest value, 9.24 ±0.13 mol photon mol⁻¹ O₂, for the PEP-carboxykinase C₄ species Spartina townsendii. The C₃–C₄ intermediate species Panicum milioides had a value of 9.05 ±0.29 mol photon mol⁻¹ O₂, approximately 1 mol photon mol⁻¹ O₂ greater than the C₃ species. The possibility that this extra cost is due to PEP-carboxylase-dependent recycling of CO₂ is discussed. No correlation was found between Ф_r and chlorophyll content or leaf absorptance. Based on white (Ф_W) and red light measurements of the photon requirement, values in red light were approximately 20% higher than white-light estimates. These results are discussed with reference to accepted mechanisms of energy transduction in thylakoid membranes (Z-scheme), expected inefficiencies and losses during light-harvesting and electron transport reactions, and the influence of respiratory processes.     

Growth rates and the salinity response of an Antarctic ice microflora community

Summary An ice microflora community collected from the bottom of seasonal pack-ice off the Amery Ice Shelf, Antarctica, was grown at salinities which varied from 11.5 to 34. The response exhibited by the community and by individual species was characterized by an initial lag phase-adaptation period followed by a short period of exponential growth. Doubling rates based on changes in chlorophyll a had a range from 0.05 to 0.23 day^-1 during the time required to reach maximum chlorophyll a concentration and a range of 0.04 to 0.42 day^-1 during a period of exponential growth. Exponential growth rates of individual species ranged from 0.2 to 1.0 doublings day^-1. Growth occurred at all salinities above 11.5. Community growth rates increased with increasing salinity, and the growth-salinity response of most species was shifted toward higher salinities suggesting that this Antarctic ice microalgal community was adapted to the ambient salinity regime: 34.     

PIGMENT TURNOVER IN THE MARINE DIATOM THALASSIOSIRA WEISSFLOGII. I. THE 14CO2-LABELING KINETICS OF CHLOROPHYLL a1

The turnover of chlorophyll a (chl a) was investigated in the diatom Thalassiosira weissflogii (Grunow) Fryxell and Hasle using a new method based on the incorporation of ¹⁴C into chl a. The alga was maintained in its exponential growth phase under continuous light; ¹⁴C was supplied as bicarbonate. The time course of label accumulation into the tetrapyrrole ring and the phytol side chain was determined for time periods equivalent to 1–2 cell doublings. The labeling kinetics of the tetrapyrrole ring and the phytol side chain were described satisfactorily by a simple precursor-pigment model with two free parameters, the precursor turnover rate and the pigment turnover rate, both having dimensions of time^?1. The model was fit to the experimental data to determine the values of these two free parameters. The turnover rates of the tetrapyrrole ring and the phytol side chain were not significantly different, ranging from 0.01 to 0.1 per day. These rates are equivalent to turnover times ranging from days to weeks. Growth rate-normalized turnover rates did not vary with irradiance (7.5–825 μE · m^?2· s^?1). The precursor turnover rates of the tetrapyrrole ring and the phytol side chain differed by an order of magnitude. These results indicate that chl a is not degraded significantly in cultures of T. weissflogii grown under continuous light. Neither irradiance nor growth rate affected growth rate-normalized chlorophyll turnover rates. Our results are inconsistent with the hypothesis that steady-state cellular concentrations of chl a are maintained by a dynamic equilibrium between rates of synthesis and degradation.     

EFFECTS OF LONG TERM EXPOSURE TO LOW TEMPERATURE ON THE PHOTOSYNTHETIC APPARATUS OF DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of long term exposure to suboptimal growth temperature on the photosynthetic apparatus of Dunaliella tertiolecta Butcher were investigated using carbon fixation rate versus irradiance curves and the variable fluorescence induction method. Carbon fixation rates per unite chlorophyll a at saturating (p^B_m) and subsaturating (α^B) irradiances were 55% and 39% lower, respectively, at 12° C than at 20° C. Chlorophyll a quotas and the spectrally averaged in vivo absorption cross section normalized to chlorophyll a (a^*) were not significantly different at these two temperatures. Analysis of the fluorescence kinetics revealed 1) no significant variations of the amount of PSII photoactive reaction centers per unit chlorophyll a, 2) a 14% decrease of the PSII quantum yield(+) and 3) a 29% decrease of the energy transfer efficiency between the light harvesting chlorophyll a pigment bed and the PSII reaction centers. The decrease in energy transfer efficiency between the antennae and the PSII reaction centers at 12° C was interpreted as a mechanism to avoid photoinhibition.     

Can suspension feeding by bivalves regulate phytoplankton biomass in Lake Waccamaw, North Carolina?

Suspension feeding by bivalves has been hypothesized to control phytoplankton biomass in shallow aquatic ecosystems. Lake Waccamaw, North Carolina, USA is a shallow lake with a diverse bivalve assemblage and low to moderate phytoplankton biomass levels. Filtration and ingestion rates of two relatively abundant species in the lake, the endemic unionid, Elliptio waccamawensis, and an introduced species, Corbicula fluminea, were measured in experiments using natural phytoplankton for durations of 1 to 6 days. Measured filtration and ingestion rates averaged 1.78 and 1.121 ind.^–1 d^–1, much too low to control phytoplankton at the observed phytoplankton biomass levels and growth rates. Measured ingestion rates averaged 4.80 and 1.50 µg chlorophyll a ind.^–1 d^–1, too low to support individuals of either species. The abundance of benthic microalgae in Lake Waccamaw reaches 200 mg chlorophyll a m^–2 in the littoral zone and averages almost an order of magnitude higher than depth-integrated phytoplankton chlorophyll a. Total microalgal biomass in the lake is therefore not controlled by suspension feeding by bivalves.     

The use of dialysis culture in a study of chlorophyll budget in a brackish lagoon,Japan

Growth rates of the entire phytoplankton community of a brackish lagoon in northeastern Japan were estimated by measuring increasing chlorophyll a content in dialysis bags during the summer and early autumn of 1986. The chlorophyll a contents of lagoon water fluctuated between 20 and 200 mg m^–3. At lower densities of phytoplankton (20–50 mg chl. a m^–3), growth rates (the rate of increase of chlorophyll a) exceeded 1 turnover per day, while at higher densities (more than 50 mg chl. a m^–3), the growth rate decreased rapidly. Tidal exchanges of chlorophyll a showed net exports of chlorophyll a from the lagoon to adjacent waters. The exchange rate of chlorophyll a was estimated to be 0.65 d^–1. At about 140 mg m^–3 of chlorophyll a concentration, the increase of chlorophyll in the lagoon water compensated for tidal export. Only a small proportion of primary production was consumed by zooplankton in the lagoon. There were also net exports of ammonium and phosphate from the lagoon. Nutrient flux from sediment exceeded the phytoplankton requirement and was the major source of the ammonium and phosphate exports from the lagoon. The low inorganic N/P atom supply ratio in the lagoon suggests that nitrogen is a major nutrient limiting phytoplankton growth.     

NITROGEN ASSIMILATION OF AN OCEANIC DIATOM IN NITROGEN-LIMITED CONTINUOUS CULTURE1

The oceanic diatom Thalassiosira pseudonana Hasle and Heimdal (formerly Cyclotella nana) was grown with 12L:12D illumination cycles in nitrogen-limited continuous culture with a mixture of ammonium and nitrate as the N source. Measurements included, at 3 different growth rates (degrees of N limitation), cell concentration, cell carbon, nitrogen, and chlorophyll a contents, cell volume, photosynthetic carbon assimilation vs. irradiance, short-term uptake of ammonium and nitrate vs. their ambient concentrations, and in vitro activities of the assimilatory enzymes nitrate reductase and glutamic dehydrogenase. The various parameters showed either an increase (pattern a) or a decrease (pattern b) with increasing N limitation. Those following pattern a were nitrate reductase activity and the capacity to assimilate nitrate and ammonium. Those following pattern b were glutamic dehydrogenase activity, photosynthetic rate, nitrogen:carbon and chlorophyll a:carbon composition ratios. Results are discussed in terms of the interpretation such measurement for natural phytoplankton and effects of circadian periodicity.     

Effects of UVB radiation on the carragenophyte <Emphasis Type="Italic">Kappaphycus alvarezii</Emphasis> (Rhodophyta,Gigartinales): changes in ultrastructure,growth, and photosynthetic pigments

Damage to the ozone layer has led to increased levels of ultraviolet radiation at the earth’s surface. Increased ultraviolet radiation can affect macroalgae in many important ways, including reduced growth rate, changes in cell biology and ultrastructure. Kappaphycus alvarezii is a red macroalga of economic interest due to its production of kappa carrageenan. In this study, we examined two strains of K. alvarezii (green and red) exposed to ultraviolet B radiation (UVBR) for 3 h per day during 28 days of cultivation in vitro. UVBR caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. While the green strain exposed to photosynthetically active radiation (PAR) showed growth rates of 6.75% day⁻¹, the red strain grew only 6.35% day⁻¹. Upon exposure to PAR + UV-B, a decreasing trend in growth rates was observed for both strains, with the green strain growing 3.0% day⁻¹ and the red strain growing 2.77% day⁻¹. Significant differences in growth rates between control and UV-B-exposed algae were also found in both strains. Furthermore, compared with control algae, phycobiliprotein contents (phycoerythrin, phycocyanin, and allophycocyanin) were observed to decrease in both strains after PAR + UV-B exposure. However, while the chlorophyll a levels increased in both strains, the green strain showed no significant differences in chlorophyll a levels. Taken together, these findings strongly suggested that UVBR negatively affects the ultrastructure, growth rates, and photosynthetic pigments of intertidal macroalgae and, in the long term, their economic viability.     

Riboflavin content of six species of microalgae used in mariculture

Concentrations of riboflavin — a vitamin essential for maricultured animals—were measured in six species of microalgae commonly used in mariculture. These were two diatoms (Chaetoceros gracilis, Thalassiosira pseudonana); two prymnesiophytes (Isochrysis sp. (clone T.ISO),Pavlova lutheri); one chlorophyte (Nannochloris atomus) and one eustigmatophyte (Nannochloropsis oculata). Cultures were analysed during both logarithmic and stationary growth phase.The proportions of riboflavin (µg g^-1 dry weight) during logarithmic growth-phase ranged from 20 (T. pseudonana) to 40 µg g^-1 (Isochrysis sp. T.ISO). With the onset of stationary phase, the proportion of riboflavin increased in all species; the increase was most dramatic in cultures ofC. gracilis, T. pseudonana andN. atomus (2- to 3-fold).Chaetoceros gracilis contained more riboflavin (106 µg g^-1) than all other species (48 to 61 µ g^-1).Despite the differences in the composition of the different microalgae, across both logarithmic and stationary growth-phases, all species should provide a rich source of riboflavin for maricultured animals.Author for correspondence     

BIO-OPTICAL CHARACTERISTICS AND PHOTOADAPTIVE RESPONSES IN THE TOXIC AND BLOOM-FORMING DINOFLAGELLATES GYRODINIUM AUREOLUM,GYMNODINIUM GALATHEANUM,AND TWO STRAINS OF PROROCENTRUM MINIMUM1

Photoadaptive responses in the toxic and bloom-forming dinoflagellates Gyrodinium aureolum Hulbert, Gymnodinium galatheanum Braarud, and two strains of Prorocentrum minimum (Pavillard)Schiller were evaluated with respect to pigment composition, light-harvesting characteristics, carbon and nitrogen contents, and growth rates in shade- and light-adapted cells. The two former species were grown at scalar irradiances of 30 and 170 μmol · m ^?2 at a 12-h daylength at 20° C. The two strains of P. minimum were grown at 35 and 500 μmol. m^?2· s^?1 at a 2-h daylength at 20° C. For the first time, chlorophyll (chl) c₃, characteristic of several bloom-forming prymnesiophytes, was detected in G. aureolum and G. galatheanum. Photoadaptional status affected the pigment composition strongly, and the interpretation of the variation depended on whether the pigment composition was normalized per cell, carbon, or chl a. Species-specific and photoadaptional differences in chl a-specific absorption (°a_c, 400–700 nm) and chl a-normalized fluorescence excitation spectra of photosystem II fluorescence with or without addition of DCMU (°F and °F_DCMU 400–700 nm) were evident. Gyrodinium aureolum and G. galatheanum exhibited in vivo spectral characteristics similar to chl c₃-containing prymnesiophytes in accordance with their similar pigmentation. Prorocentrum minimum had in vivo absorption and fluorescence characteristics typical for peridinin-containing dinoflagellates. Species-specific differences in in vivo absorption were also observed as a function of package effect vs. growth irradiance. This effect could be explained by differences in intracellular pigment content, cell size/shape, and chloroplast morphology/numbers. Light- and shade-adapted cells of P. minimum contained 43 and 17% of photoprotective carotenoids (diadino + diatoxanthin) relative to chl a, respectively. The photoprotective function of these carotenoids was clearly observed as a reduction in °F and °F ^DCMU at 400–540 nm compared to °ac in light-adapted cells of P. minimum. Spectrally weighted light absorption (normalized to chl a and carbon, 400–700 nm) varied with species and growth conditions. The use of quantum-corrected and normalized fluorescence excitation spectra with or without DCMU-treated cells to estimate photosynthetically usable light is discussed. The usefulness of in vitro absorption and fluorescence excitation spectra for estimation of the degradation status of chl a and the ratio of chl a to total pigments is also discussed.     

The distribution and nutrient status of phytoplankton in the Southern Ocean between 20° and 70° W

Summary The distribution of phytoplankton along transects amounting to about 10,000 nautical miles in the sector of the Southern Ocean between 20° and 70°W was determined during the austral summer of 1978/79. Chlorophyll a concentration was monitored by the continuous measurement of in vivo fluorescence (IVF). Surface samples were collected for the determination of temperature, salinity, chlorophyll a concentration, carbon fixation rate and species of the phytoplankton. Phytoplankton distribution was found to be extremely patchy both locally and regionally. High phytoplankton concentrations were often associated with either hydrographic features, such as upwelling or the presence of sea-ice, or with bathymetric features, such as shelf breaks, submarine mountain ranges or islands. Enrichment experiments, in which the effects of various nutrient additions on the rate of ¹⁴C fixation by the natural phytoplankton were compared, and bioassay experiments, in which the growth of Thalassiosira pseudonana (Hustedt) Hasle and Heimdal in enriched water samples was measured, were carried out using water samples collected at various stations throughout the study area. Although these techniques were effective in demonstrating nutrient limitation elsewhere, the results suggest that availability of nitrate, phosphate, silicate, trace metals or vitamins exerts no primary control over phytoplankton abundance south of the Polar Front.     

CELL DIVISION PERIODICITY IN 13 SPECIES OF MARINE PHYTOPLANKTON ON A LIGHT: DARK CYCLE1

The division rates of 26 clonal cultures representing 13 species of planktonic marine algae (6 diatoms, 2 flagellated chrysophytes, 2 coccolithophores, 1 cryptomonad flagellate, I dinoflagellate, 1 green alga) were determined every 2 h for 48 h during exponential growth on a 14:10 LD cycle in nutrient-replete batch culture. Cyclic oscillations in the division rate were detectable in 22 of these clones. Of 14 diatom clones examined, four displayed nearly constant division rates throughout the LD cycle and ten showed strong periodicity favoring division during the light periods. In contrast, all other algae (12 clones) exhibited division rate maxima during periods of darkness, and clearly detectable decreases in cell number for time intervals of 4–8 h during periods of illumination. Intraspecific differences in division periodicity were found among eight clones of the diatom Thalassiosira pseudonana (Hustedt) Hasle & Heimdal and six clones of the coccolithophore Emiliania huxleyi (Lohm.) Hay & Mohler.     

COMPARATIVE PHYSIOLOGICAL STUDY OF MARINE DIATOMS AND DINOFLAGELLATES IN RELATION TO IRRADIANCE AND CELL SIZE. II. RELATIONSHIP BETWEEN PHOTOSYNTHESIS,GROWTH, AND CARBON/CHLOROPHYLL a RATIO1,2

Photosynthetic rates, growth rates, cell carbon, cell protein, and chlorophyll a content of two diatom and two dinoflagellate species were measured. The microalgae were chosen to have one small and one large species from each phylogenetic group; the two size categories differed from each other by 1.5 orders of magnitude in terms of cell carbon or cell protein. The cultures for the experiments were grown under continuous light at an irradiance high enough for the light-saturation of growth for all four species. The four species were found to have similar maximum photosynthetic rates per unit chlorophyll a. The diatom species showed lower carbon/chlorophyll a ratios and higher photosynthetic rates per unit carbon than the dinoflagellates. The higher growth rates of the diatoms were shown to be related to their higher photosynthetic rates per unit carbon. The ecological significance of the physiological difference between these two groups of microalgae is discussed.     

Intraspecific egg size variation and sperm limitation in the broadcast spawning bivalve Macoma balthica

Bottom-ice algae within Antarctic sea ice were examined using chlorophyll fluorescence imaging. The detailed structure of the bottom-ice algal community growing in the platelet and congelation layers of solid pieces of sea ice was evident for the first time in chlorophyll imaging mode. Strands of fluorescence representing algal cells were clearly visible growing upward into brine channels in a fine network. Images of effective quantum yield (Ф_PSII) revealed that the Ф_PSII of algae embedded in the sea ice was approximately 0.5. Furthermore, Ф_PSII decreased slightly with distance from the ice-water interface.The response of Antarctic sea ice algae to changes in irradiance and salinity, and the effects of slowly warming and melting the ice block sample were examined using this system. The Ф_PSII of bottom-ice algae decreased as irradiance increased and salinities decreased. Bottom-ice algae appear to be most vulnerable to changes in their environment during the melting process of the ice, and this suggests that algae from this region of the ice may not be able to cope with the stress of melting during summer.Chlorophyll fluorescence imaging provides unprecedented imagery of chlorophyll distribution in sea ice and allows measurement of the responses of sea ice algae to environmental stresses with minimal disruption to their physical habitat. The results obtained with this method are comparable to those obtained with algae that have been melted into liquid culture and this indicates that previous melting protocols reveal meaningful data. In this chlorophyll imaging study, rapid light curves did not saturate and this may prevent further use of this configuration.     

VARIABILITY IN RATIOS OF PHYTOPLANKTON CARBON AND RNA TO ATP AND CHLOROPHYLL A IN BATCH AND CONTINUOUS CULTURES1,2

The feasibility of estimating phytoplankton carbon and RNA concentrations from measurements of ATP and chlorophyll a (chl a) concentrations was studied using chemostat populations of the marine diatom Thalassiosira weissflogii (Grunow) Fryxell & Hasle (= T. fluviatilis Hustedt). C:ATP and RNA:ATP ratios were studied for six additional marine species in batch culture representing five classes of phytoplankton. Statistical analyses revealed that both the growth rate and the factor limiting growth (NO₃^-, NH₄⁺, PO₄^3- or light) could alter C:ATP, RNA: ATP, C:chl a and RNA:chl a ratios by amounts which were large compared to measurement error. An analysis of variance of the batch culture results indicated that both species and the source of inorganic nitrogen (NO₃^-, or NH₄⁺) had a significant effect on C:ATP and RNA:ATP ratios. Light had less of an influence on C:ATP and RNA:ATP ratios than on C:chl a and RNA:chl a ratios, and for this reason we feel that phytoplankton C and RNA concentrations can be estimated with greater reliability from ATP than from chl a measurements. The range of C:ATP and RNA:ATP values found for T. weissflogii under a variety of growth conditions was similar to that for the six additional species grown in batch culture, suggesting that this range of values is indicative of the extremes likely to occur in living cells. Our results and additional data in the literature indicate that phytoplankton C and RNA concentrations can be estimated to within a factor of two by multiplying ATP concentrations by 311 and 35, respectively, in N limited systems, and by 341 and 36, respectively in PO₄^3- limited systems.     

LIGHT DEPENDENCE OF GROWTH AND PHOTOSYNTHESIS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Phaeodactylum tricornutum Bohlin was maintained in exponential growth over a range of photon flux densities (PFD) from 7 to 230 μmol·m^?2s^?1. The chlorophyll a-specific light absorption coefficient, maximum quantum yield of photosynthesis, and C:N atom ratio were all independent of the PFD to which cells were acclimated. Carbon- and cell-specific, light-satuated, gross photosynthesis rates and dark respiration rates were largely independent of acclimation PFD. Decreases in the chlorophyll a-specific, gross photosynthesis rate and the carbon: chlorophyll ratio and increases of cell- or carbon-specific absorption coefficients were associated with an increase in cell chlorophyll a in cultures acclimated to low PFDs. The compensation PFD for growth was calculated to be 0.5 μmol·m^?2s^?1. The maintenance metabolic rate (2 × 10^?7s^?1), calculated on the basis of the compensation PFD, is an order of magnitude lower than the measured dark respiration rate(2.7 × 10^?6mol O₂·mol C^?1s^?1). Maintenance of high carbon-specific, light-saturated photosynthesis rates in cells acclimated to low PFDs may allow effective use of short exposures to high PFDs in a temporally variable light environment.     

PHYSIOLOGICAL ACCLIMATION OF MARINE PHYTOPLANKTON TO DIFFERENT NITROGEN SOURCES1

We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH₄⁺, NO₃^?, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO₃^? and NH₄⁺ grown cells had similar growth rates and C and X quotas. Therefore, NO₃^? grown cells used up to 48% more energy than NH₄⁺ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a^?1, we suggest that NO₃^?, grown cells do not compensate for the greater energy requirements of NO₃^? reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO₃^?, compared to NH₄⁺ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh₄⁺ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO₃^?, or urea.     

RESPONSE OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) TO LIGHT OF DIFFERENT SPECTRAL QUALITIES AND IRRADIANCES: GROWTH AND PIGMENTATION1

Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m^?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m^?2· s^?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m^?2· s^?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m^?2· s^?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.     

Light absorption by marine macrophytes

Tissues of 338 marine macrophytes comprising 103 species, collected from the Atlantic, Mediterranean, South China, and Caribbean Seas, and encompassing a broad range in thallus form and pigmentation, were examined to quantify the importance of phylogenetic differences, spectral variability, and plant form and pigment content to account for differences in the absorption of light by marine macrophytes. Phylogenetic differences accounted for 2.5% of the variance in absorption observed, non-phylogenetic spectral differences being much larger (26%). Differences among individual specimens were much larger (72%), absorption at 675 nm increasing non-linearly as chlorophyll a density^1/2, indicating that light absorption increases with increasing chlorophyll a density following a law of diminishing returns, as predicted by theory. The energy return per unit tissue produced (i.e. light absorption per unit plant weight) increased linearly with increasing chlorophyll a concentration. However, the light absorbed per unit weight decreased, for a given chlorophyll a concentration, as plant thickness increased. This indicates that while increasing thickness may increase chlorphyll a density and, hence, the light absorbed by marine macrophyte thalli, this strategy represents a burden limiting potential carbon turnover and plant growth. These results indicate that the diverse repertoire of light absorption by marine macrophytes can be adequately modeled as a continuum, dependent on plant thickness and pigment content, independent of phylogenetic differences.