PHOTOSYNTHESIS-IRRADIANCE PATTERNS IN BENTHIC MICROALGAE: VARIATIONS AS A FUNCTION OF ASSEMBLAGE THICKNESS AND COMMUNITY STRUCTURE

Photosynthesis-irradiance (P-I) characteristics of periphyton (microphytobenthos) have been considered primarily for entire assemblages. How P-I responses vary with mat thickness and with community composition has not been considered in detail. We used a combined approach of modeling, microscale determinations of photosynthetic rate and light attenuation, and whole-assemblage O₂ flux measurements to explore P-I relationships. The modeling approach suggested that the onset of photosynthetic saturation and photoinhibition will occur at higher irradiance and that whole-mat photoinhibition (decreased photosynthesis at very high irradiance), biomass-specific maximum photosynthetic rate, and initial slope of the P-I function (α) should decrease as assemblage thickness increases or light attenuation increases. Spherical light microsensor profiles for a variety of stream algae indicated a strongly compressed photic zone with attenuation coefficients of 70–1791 m^?1 for scalar photosynthetic photon fluence density. The O₂ microelectrode measurements showed little if any photoinhibition at 2 and 4 mm depths in one filamentous green algal (Ulothrix) assemblage, with a relatively low attenuation coefficient, and no photoinhibition in a second Ulothrix community. An assemblage dominated by a unicellular cyanobacterium exhibited little photoinhibition at 2 and 4 mm, and a dense cyanobacterial (Phormidium)/xanthophyte (Vaucheria) community exhibited no photoinhibition at all. The microelectrode data revealed increases in α over several millimeters of depth (photoacclimation). These data supported the model predictions with regard to the effects of mat optical thickness on whole-assemblage values for α and photoinhibition. Whole-community O₂ flux data from 15 intact assemblages revealed positive relationships between chlorophyll a density and maximum photosynthetic rate or α expressed per unit area; the relationships with chlorophyll a were negative when photosynthetic rates were expressed per unit chlorophyll a. None of the whole assemblages exhibited photoinhibition. Thus, the data from the whole communities were consistent with model predictions.     

MODELING THE ANNUAL PRODUCTION OF INTERTIDAL BENTHIC MICROALGAE IN ESTUARINE ECOSYSTEMS1

The purpose of this study was to develop and validate a habitat-specific production simulation model to quantify annual benthic microalgal production in North Inlet estuary, South Carolina. Using hourly measurements of incident irradiance during 1990–1991 as the forcing function, the simulation model was used to obtain hourly estimates of areal benthic microalgal gross primary production in five habitat types. The model, which was validated using actual measurements of production, showed good (r²= 0.63, P < 0.001) agreement between observed and predicted production in the short Spartina alterniflora Loisel zone habitats showed the highest mean hourly production (61.1 mg C m^?2 h^?1) while intertidal mudflats had the maximum hourly rate (166.9 mg C m^?2 h^?1). Daily production was highly variable, primarily due to daily fluctuations in irradiance. Annual estimates of habitat-specific production were multiplied by the mates of habitat-specific production were multiplied by the known area of each habitat type to determine total microalgal production for the estuary (3.423 × 10⁹ g C yr^?1). Short Spartina zone habitats provided 45% of total microalgal annual production, followed by intertidal mudflats (22%), tall Spartina zones (18%), shallow subtidal (13%) and microalgal production exceeds phytoplankton and microalgal production but is less than Spartina production.     

Marine species in the algal flora of the Anzali Swamp (Iran)

The composition of marine species in the algal flora of the Anzali Swamp, which is situated parallel to the Caspian Sea coast, is examined. Sampling was carried out at seven stations. A total of 74 species with 89 infraspecific taxa were identified: Cyanophyta, 20 species; Cryptophyta, 2 species; Bacillariophyta, 51 species (66 infraspecific taxa); and Chlorophyta, 1 species.     

Microcystin production by cyanobacteria in the Mwanza Gulf (Lake Victoria,Tanzania)

In order to investigate the potential for microcystin (MC) production by cyanobacteria in the Mwanza Gulf (Lake Victoria, Tanzania), nutrients, phytoplankton and microcystins were sampled inshore (3 m depth) and offshore (18 m depth) from May to August 2002. Significant differences in soluble reactive phosphorus (SRP) and nitrate concentrations between offshore and inshore indicated eutrophication via terrestrial run-off. Though the concentrations of SRP and nitrate ranged between 36–127 and 35–726 μg l ⁻¹ each, the phytoplankton biovolume was generally low. The phytoplankton community was dominated by diatoms (Nitzschia acicularis), a number of cyanobacterial species (Aphanocapsa sp., Anabaena sp., Planktolyngbya spp., Microcystis sp.) and cryptomonads. The water column was completely mixed and Nitzschiapeaked in abundance during July. All cyanobacteria were low in abundance during the entire study period (0.1–1.6 mm ³ l ⁻¹). Microcystins were analysed using high performance liquid chromatography coupled with diode array detection High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) and in most samples no microcystins were detected. The highest concentration of [Asp ³]-MC-RR was found in open water at the surface on July 2nd, 2002 (1 μg l ⁻¹). MC concentrations did not pose a potential health risk in the Mwanza Gulf during the study period, however, it is possible that the period of higher cyanobacterial biovolumes has been missed during the sampling period of this study.     

FURTHER EVIDENCE FOR ANOMALOUS SIZE SCALING OF RESPIRATION IN PHYTOPLANKTON1

Respiration per unit mass decreases as organism size increases among metazoans and heterotrophic unicells. The rate of decrease is described by a power function of organism mass; the exponent of the power function is 0.75 (Three-fourths Rule). Previously unanalyzed respiration rates for 11 species of phytoplankton ranging in size over four orders of magnitude show a size-scaling exponent of 1.13 (SE, ±0.15), which is statistically different from 0.75. This result confirms the result of an earlier study of eight phytoplankton species indicating that size scaling of respiration is absent or minimal in phytoplankton, in contrast to the pattern of heterotrophic unicells. The size-related range of respiration rates per unit mass across the full size spectrum of phytoplankton would be approximately 18–fold if respiration were scaled according to the Three-fourths Rule. If respiration does not scale with size or scales minimally with size, as suggested by present evidence, the size-related range of rates will be much smaller or negligible. The apparent anomaly of size scaling for phytoplankton respiration is potentially of great ecological and adaptive significance in unicellular algae.     

DNA:ATP RATIOS IN MARINE MICROALGAE AND BACTERIA: IMPLICATIONS FOR GROWTH RATE ESTIMATES BASED ON RATES OF DNA SYNTHESIS1

DNA: ATP and carbon: DNA (C:DNA) ratios were measured in a total of 14 species of marine microalgae and bacteria. Comparison of several DNA assay methods with results obtained with cultures uniformly labeled with ³³P indicated that by far the most accurate results were obtained using diaminobenzoic acid (DABA) or diphen-ylamine, with DABA having the highest precision. Both the Hoechst and DAPI methods seriously underestimated DNA concentrations in algal cultures. Average DNA: ATP ratios in the algal and bacterial cultures were I7 and 34 by weight, respectively, with almost all values lying in the range of 10–40. DNA: ATP ratios in the microalgae showed no correlation with growth conditions but varied by about a factor of 3 among species. C:DNA ratios for individual species of microalgae and bacteria ranged from 21 to 155 by weight and averaged 50 for the microalgae and bacteria taken together. Growth rates of microalgal species grown in cyclostats were estimated to within 8% of dilution rates when calculated from the uptake of ³H-adenine and the DNA: ATP ratio of the species. Use of the ³H-adenine method for estimating microalgal growth rates in the field may thus be a useful tool for investigating the physiology of microalgae in nature.     

MICROPHOTOMETRIC ASSESSMENT OF SPECTRAL ABSORPTION AND ITS POTENTIAL APPLICATION FOR CHARACTERIZATION OF HARMFUL ALGAL SPECIES

A comparison was made of microphotometric measurements and spectrophotometric measurements of particulate spectral absorption of four algal species, including the chlorophyte Dunaliella tertiolecta Butcher; a nontoxic dinoflagellate, Amphidinium carterae Hulburt; a diatom, Chaetoceros gracilis Schütt; and a toxic dinoflagellate, Gymnodinium breve Steidinger. Particulate spectral absorption of monospecies cultures was estimated as the product of the average absorption efficiency factor, Q _a, determined by microphotometry, the cellular cross-sectional area, and the cell number density. Estimates of particulate spectral absorption from microphotometric measurements were, in most cases, within one standard deviation of values determined from spectrophotometric measurements of algal suspensions. Estimates of Q_a(675) were shown to be consistent with values reported in previous studies for cells of similar size and pigmentation and were consistent with theoretical predictions. Absorption spectra of mixtures of C. gracilis and G. breve were numerically decomposed into contributions by absorption signatures of monospecies cultures using either spectrophotometric or microphotometric measurements as the basis for end members. Modeled contributions assigned to either species displayed trends consistent with the actual proportions contributed to the spectrum by each algal culture. However, the technique was sensitive to measurement variability, which reduced the level of agreement between modeled and actual contributions. The utility of this approach for identification of algal taxa will depend on the degree to which algal spectral absorption signatures differ and the capabilities for acquiring high-resolution data with low signal-to-noise ratios.     

WATER COLUMN PRODUCTIVITY ATTRIBUTABLE TO DISPLACED BENTHIC DIATOMS IN WELL-MIXED SHALLOW ESTUARIES1

We attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow-water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A perliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary, Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K-systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity. Benthic pennate diatoms, represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well-mixed shallow estuarine waters is often greatly aumented by displaced benthic algae.     

DISTRIBUTION OF INTRACELLULAR NITROGEN IN MARINE MICROALGAE: BASIS FOR THE CALCULATION OF SPECIFIC NITROGEN-TO-PROTEIN CONVERSION FACTORS

The utilization of nitrogen-to-protein conversion factors (N-Prot factors) is a widely accepted and practical way to determine total protein content. The accuracy of protein determination depends on the establishment of specific N-Prot factors, since the conventional factor of 6.25 may be unsuitable for all species. This study was designed to determine the concentrations of the main nitrogenous compounds and to establish N-Prot factors specific for the following marine microalgae: Chlorella minutissima, Dunaliella tertiolecta, Hillea sp., Isochrysis galbana, Nannochloropsis oculata, Phaeodactylum tricornutum, Prorocentrum minimum, Skeletonema costatum, Synechococcus subsalsus, and Tetraselmis gracilis. Cultures were maintained under a 12-h photoperiod (300 μmol photons·m^?2·s^?1) at temperatures of 20.0°± 1.0° C (dark) to 23.0°± 2.0° C (light) in Walne’s culture medium without additional external carbon sources. The distribution of intracellular nitrogen was studied by determining total nitrogen (TN, by CHN [carbon, hydrogen, and nitrogen] analysis), protein N (PN, by analysis of total amino acids), and nonprotein N (NPN, determined by analysis of DNA, RNA, chlorophylls (chl) a,b, and c, and intracellular inorganic nitrogen—NO₃^?, NO₂^?, and NH₃+ NH₄⁺) in logarithmic and stationary growth phases of cultures. Variations occurred in both accumulation and distribution of PN and NPN among the species, as well as in each species during the different growth phases. Inorganic nitrogen compounds were observed to be the most important NPN source (from 6.4 ± 0.1% to 41.8 ± 4.2% of total N) in all species (except D. tertiolecta), followed by nucleic acids (from 0.8 ± 0.1% to 26.1 ± 2.4% of TN) and chlorophylls (from 0.2 ± 0.0% to 3.1 ± 0.3% of TN). Total amino acid residues ranged from 63.1 ± 4.6% up to 88.1 ± 11.2% of TN, which is in agreement with the presence of high NPN concentrations. N-Prot factors are proposed for each growth phase in the studied species, based on the ratio of amino acid residues to TN, establishing specific N-prot factors ranging from 3.60 ± 0.27 to 4.99 ± 0.64. The mean N-Prot factor for all species/growth phases was 4.58 ± 0.11. The present study shows that the use of the traditional factor 6.25 is not suitable for these marine microalgae, and possibly for other species, because it overestimates their actual protein content.     

SHORT-TERM EFFECTS OF UVB RADIATION ON CHLOROPHYLL FLUORESCENCE, BIOMASS, PIGMENTS, AND CARBOHYDRATE FRACTIONS IN A BENTHIC DIATOM MAT

The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated. Chlorophyll fluorescence parameters ( F _v/ F _m, φ_PSII), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and +15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels. Increases in φ_PSII values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield ( F _s) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G. balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the +15% UVBR treatment also had significantly higher concentrations of β-carotene after 5 days of treatment. Although G. balticum responded to enhanced UVBR by migration and increased β-carotene concentrations, significant reduction in maximum quantum yield of PSII ( F _v/ F _m) and in minimal fluorescence ( F _o) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass.     

南黄海近岸底栖有孔虫分布与环境因子转换函数的建立

本文对南黄海西北陆架边缘的300个表层沉积物样品中的底栖有孔虫数据,与相应站位的水深、底层水温、盐度、沉积物粒度、有机碳含量等环境参数作了分析研究。除趋势对应分析(DCA)、典型对应分析(CCA)表明有孔虫种群分布与水深、夏季底层水温(Ts)和冬季底层水盐度(Sw)之间存在着显著的数值对应关系。利用加权平均偏最小二乘回归方法(WA-PLS)建立了底栖有孔虫数据与上述环境因子之间的数值转换函数。水深、Ts与Sw转换函数的预测均方根误差(RMSEP)分别是10.8%、11.5%和12.5%,与利用其他指标建立的此类转换函数水平(8%—20%)相当。利用此类统计建模方法建立近岸底栖有孔虫分布与浅海环境因子之间的数值关系是一项新的尝试,结果表明在我国近海底层水体古环境研究中底栖有孔虫转换函数是一种具有一定潜力的研究方法。     

A MODEL APPROACH FOR SIZE-SELECTIVE COMPETITION OF MARINE PHYTOPLANKTON FOR FLUCTUATING NITRATE AND AMMONIUM1

Phytoplankton size-selective competition for fluctuating nutrients was studied with the use of a numerical model, which describes nitrate and ammonium uptake, nitrate reduction to ammonium, and growth as a function of cell she under fluctuating nitrogen limitation. The only size-dependent parameter in the model was the cell nutrient quota. Related to this, the cell surface area per biomass was negatively correlated to cell volume, and the vacuole volume per biomass ratio was positively correlated to cell volume. Simulations showed an inverse correlation between the maximum specific growth rate and cell size under steady-state conditions. With nitrate as the limiting nitrogen source, nitrogen quotas were always higher than with ammonium at the same specific growth rate. Net passive transport of ammonium due to unspecific diffusion of ammonia across the plasma membrane decreased the affinity for ammonium, whereas the affinity for nitrate was not influenced. Transient state-specific ammonium uptake was not dependent on cell size. However, small algae always have the highest specific growth rate in ammonium-controlled systems according to our model. Transient state nitrate uptake rate was positively correlated to cell size because larger algae have a higher vacuole volume per biomass, in which nitrate can be stored. Despite their lower maximum growth rate, larger algae became dominant during simulations under fluctuating nitrate supply when amplitude of and the period between nitrate pulses were high enough. Results from model simulations were qualitatively validated by earlier observations that large diatoms become dominant under fluctuating conditions when nitrate is the main nitrogen source.     

FLOW CYTOMETRIC ANALYSES OF VIRAL INFECTION IN TWO MARINE PHYTOPLANKTON SPECIES, MICROMONAS PUSILLA (PRASINOPHYCEAE) AND PHAEOCYSTIS POUCHETII (PRYMNESIOPHYCEAE)

Cell characteristics of two axenic marine phytoplankton species, Micromonas pusilla (Butscher) Manton et Parke and Phaeocystis pouchetii (Hariot) Lagerheim, were followed during viral infection using flow cytometry. Distinct differences between noninfected and infected cultures were detected in the forward scatter intensities for both algal species. Changes in side scatter signals on viral infection were found only for P. pouchetii. Chlorophyll red fluorescence intensity per cell decreased gradually over time in the infected cultures. DNA analyses were performed using the nucleic acid–specific fluorescent dye SYBR Green I. Shortly after infection the fraction of algal cells with more than one genome equivalent increased for both species because of the replication of viral DNA in the infected cells. Over time, a population of algal cells with low red autofluorescence and low DNA fluorescence developed, likely representing algal cells just prior to viral lysis. The present study provides insight into basic virus–algal host cell interactions. It shows that flow cytometry can be a useful tool to discriminate between virus infected and noninfected phytoplankton cells.     

MORPHOLOGY AND ECOLOGY OF THE MARINE BENTHIC DINOFLAGELLATE SCRIPPSIELLA SUBSALSA (DINOPHYCEAE)1

The thecal surface morphology of Scrippsiella subsalsa (Ostenfeld) Steidinger et Balech was examined using the scanning electron microscope. This species is distinguished by a number of morphological characteristics. Apical plate 1′ is wide, asymmetric, and pentagonal, and it ends at the anterior margin of the cingulum. Intercalary plates 2a and 3a are separated by apical plate 3′. The apical pore complex includes a large P_o plate with a raised dome at the center and a deep canal plate with thickened margins at plates 2′, 3′, and 4′. The intercalary bands are wide and deeply striated. The cingulum is deep, formed by six cingular plates; its surface is transversely striated and aligned with a row of minute pores. The cingular list continues around postcingular plate 1′” to form a sulcal list. The sulcal list is a flexible ribbon with a rounded tip that protrudes posteriorly, partially covering the sulcal plates. The hypotheca is lobed, and the antapical plates are irregularly shaped and wide in antapical view. The thecal surface is vermiculate to reticulate. A comparison in morphology and ecology is presented between S. subsalsa and other known Scrippsiella species.     

A RAPID, HIGHLY EFFICIENT METHOD FOR COLLECTING, FIXING, AND EMBEDDING PLANKTONIC AND OTHER SMALL CELLS FOR ELECTRON MICROSCOPY

A rapid, highly efficient method is described for fixation, dehydration, and embedding of small (e.g. planktonic) cells dispersed in large volumes of culture medium. The entire protocol, based on continuous filtration, can be completed within about an hour, and the yield of cells is very high. Fixation quality has been excellent with several different types of samples.     

SCANNING ELECTRON MICROSCOPY OF CORALLINA AND HALIPTILON (CORALLINACEAE,RHODOPHYTA): SURFACE FEATURES AND THEIR TAXONOMIC IMPLICATIONS1

Scanning electron microscopy of intergenicula in members of the subfamily Corallinoideae reveals two distinctive surface morphologies: a Corallina-type (C-type) with round to irregular cell outlines and round trichocyte bases, and a Jania-type (J-type) with elongate, polygonal cell outlines and elongate trichocyte bases with excentric pores. The surface results from the calcified lateral walls of the epithallial cells projecting up from around collapsed protoplasts. Since J-type surfaces and trichocytes only occur in unequivocal members of the tribe Janieae—especially the genera Jania and Haliptilon, the presence of J-type surfaces in questionable members of Corallina reveals that they in fact belong to Haliptilon. Thus the two surface types clarify previously difficult taxonomic distinctions between Haliptilon and Corallina and allow identification to genus from purely vegetative material. Seventeen new combinations in Haliptilon are proposed. These results have considerable biogeographic implications with tropical species found to belong to Haliptilon, and Corallina sensu stricto being recognized primarily as a temperate and cold water genus.     

A SIMPLE METHOD FOR THE ISOLATION AND ENUMERATION OF SPARSE POPULATIONS OF CYANOBACTERIA IN ESTUARINE WATERS1

A simple, sensitive assay method for the isolation and enumeration of sparse populations of cyanobacteria in an estuarine system is described. The method, based on the standard membrane-filter plate count technique, differentiates between viable and nonviable cells. It was found that an estuarine water-based agar medium was the most suitable medium for isolation of cyanobacteria. Because of the restricted nature of colony development, isolation of individual species is easily accomplished.     

INFLUENCE OF IRRADIANCE ON CELL VOLUME AND CARBON QUOTA FOR TEN SPECIES OF MARINE PHYTOPLANKTON1

Ten species of marine phytoplankton were grown under a range of photosynthetic photon flux densities (PFDs) and examined for variation in cell volume and carbon quota. Results suggest that in response to low PFDs phytoplankton generally reduce their cell volume and frequently reduce their carbon quota. A significant linear relationship between the log of PFD (I) and cell volume (in nine of ten species) and log I and carbon quota (four of ten species) was demonstrated. When exposed, to a transient in light intensity, Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal underwent a rapid adaptation in cell volume and carbon quota. Cells going from low light to high light reached maximum mean cell volume within 5 h, and cells going from high light to low light reached a minimum mean cell volume within 12 h. The resulting kinetic constant (k; a measure of the rate of adaptation) was considerably larger than previously reported k values. Ditylum brightwellii (West) Grunow increased in length but did not increase in width during a transient to increased irradiance. Nutrient limitation was shown to override PFD in determining cell volume and carbon quota for Heterosigma akashiwo Hada. Cells grown at equivalent irradiances but N-limited, were smaller than light-limited and nutrient-saturated cells. Therefore, cell volume and carbon quota do not have the same relationship with PFD when factors other than PFD control growth rate. The ecological implications of reduced cell volumes and carbon quotas with decreasing PFD include possible impacts on CO₂ budgets, an influence on sinking rates, potential changes in predation rates, and surface area/cell volume benefits.