Cell Biovolume Research Articles

Growth, nutrient uptake and chemical composition of Chlorella sp. and Nannochloropsis oculata under nitrogen starvation

The production of microalgae biomass shows wide valuable uses, in the aquaculture, biotechnology, and food science, among others. However, microalgae show fluctuations in their chemical profile generated mainly by the culture conditions. This study was designated to assess the effects of nitrogen starvation on growth, nutrient uptake, and gross chemical composition of Chlorella sp. and Nannochloropsis oculata. The control experiments were performed with Conway culture medium in 13-day batch cultures, 12 h photoperiod, and aeration. A second experimental condition was the addition of the nutrients except nitrogen, one week after the start of growth (experiments designed as N-). Cell yield were similar in the control and in the N- experiments for both species. Cell biovolumes did not vary over growth in the control, but both microalgae exhibited larger cell biovolumes in N- experiments, probably as a consequence of the higher accumulation of storage substances. Dissolved nitrogen was exhausted before the end of the experiments, but phosphorus was not totally consumed. Protein and total carotenoid did not vary from the exponential to the stationary growth phase of the control in both species. For Chlorella sp., concentrations of lipid did not vary in the control either, but there was a significant increase of carbohydrate over growth. In the N- experiment, concentrations of all substances varied throughout growth of Chlorella sp., except lipid. For N. oculata , all substances exhibited significant variations over growth, except protein and total carotenoid in the control. Protein and chlorophyll-a concentrations decreased over growth in N- experiments for both species. In contrast, concentrations of carbohydrate increased throughout growth in N- experiments, especially in Chlorella sp. Nitrogen starvation caused accumulation of carbohydrate, but increments of lipid were restricted to N. oculata . Both species showed a fast growth, but the small content of lipid in Chlorella sp. is unfavorable for its use as a food-species in a monospecific diet in mariculture, and as a feedstock for biodiesel production. N. oculata is a lipid-rich species, and its lipid content can be successfully incremented through nitrogen starvation. This species is promising in uses that demand high concentrations of lipid, such as the production of biodiesel.

Formation of Escherichia coli biofilm on LLDPE sheets by incorporation of 2-hydroxypropyl-3-piperazinyl-quinoline carboxylic acid methacrylate or silver-substituted zeolite

This work mainly aimed to examine biofilm formation and prevention on linear low-density polyethylene (LLDPE) thermoplastic. LLDPE sheets with various levels of surface roughness, in a range of 0.50–8.50 (±0.05) μm, were incorporated with either 2-hydroxypropyl-3-piperazinyl-quinoline carboxylic acid methacrylate (HPQM) or silver-substituted zeolite (Zeomic). The results suggested that the surface roughness of LLDPE and the addition of HPQM or Zeomic agents had no significant effect on the mechanical properties and hydrophilicity of the LLDPE. The mechanism of Escherichia coli biofilm formation on LLDPE sheets involved an attachment and colonization of E. coli cells on LLDPE surface in the first day of incubation before the E. coli biofilm was fully developed on the 6th day, and finally detached from the LLDPE surface at the 9th day of incubation. HPQM and Zeomic could be used as E. coli inhibitors, but HPQM was more effective against E. coli than Zeomic. The recommended loading of HPQM for complete growth inhibition of E. coli on the LLDPE surface was 1500–2000 ppm. LLDPE with low surface roughness was found to be preferable if HPQM treatment was used. Physical schematics for migrations of HPQM and Zeomic molecules to prevent the biofilm formation on LLDPE surfaces were also proposed and discussed. The results of biofilm thickness were not necessarily correlated with the number of adhered viable cells. The results from maximum intensity projection (MIP) images and three-dimensional (3D) confocal images indicated that cell density in the biofilm matrix on LLDPE doped with HPQM increased with increasing incubation time, while cell density on neat LLDPE and LLDPE doped with Zeomic decreased with time. The biovolume of bacterial cells in the biofilm matrix also showed a correlation with the qualitative analysis of cell density observed by MIP and 3D confocal images.

Efficacy of antimicrobial solutions against polymicrobial root canal biofilm.

To evaluate the antibiofilm activity of 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), 2% alexidine (ALX) and 0.2% cetrimide (CTR) alone and in combination on mature polymicrobial root canal biofilms on human dentine using confocal laser scanning microscopy (CLSM). Twenty-eight human dentine specimens were infected for 21days with microbial samples collected from infected root canals of three volunteers. Antibiofilm activity of the irrigating solutions was evaluated after 3min of contact time under CLSM. For quantification purposes, bioimage_L software was used. The variables evaluated were the log10 of total biovolume (μm3 ) and percentage of live cells (green) population. Statistical analysis of both variables was performed using an anova test and a post hoc Duncan test to determine significant clusters amongst groups. The variable green population percentage was previously subjected to the normalized Anscombe transformation. The NaOCl group had a total biovolume and percentage of live cells significantly lower than the other groups (P˂0.001). The addition of 0.2% CTR significantly increased the antimicrobial effect of 2% CHX (P˂0.001). There were no significant differences between 0.2% CTR, 2% ALX and the combination of both (P˂0.05). Overall, 2.5% NaOCl dissolved and killed bacteria significantly more efficiently when used against polymicrobial mature biofilm on human dentine. Cetrimide improved the antimicrobial activity of chlorhexidine and alexidine.

Short-term arsenic exposure reduces diatom cell size in biofilm communities.

Arsenic (As) pollution in water has important impacts for human and ecosystem health. In freshwaters, arsenate (As(V)) can be taken up by microalgae due to its similarity with phosphate molecules, its toxicity being aggravated under phosphate depletion. An experiment combining ecological and ecotoxicological descriptors was conducted to investigate the effects of As(V) (130μgL(-1) over 13days) on the structure and function of fluvial biofilm under phosphate-limiting conditions. We further incorporated fish (Gambusia holbrooki) into our experimental system, expecting fish to provide more available phosphate for algae and, consequently, protecting algae against As toxicity. However, this protection role was not fully achieved. Arsenic inhibited algal growth and productivity but not bacteria. The diatom community was clearly affected showing a strong reduction in cell biovolume; selection for tolerant species, in particular Achnanthidium minutissimum; and a reduction in species richness. Our results have important implications for risk assessment, as the experimental As concentration used was lower than acute toxicity criteria established by the USEPA.

New data-driven method from 3D confocal microscopy for calculating phytoplankton cell biovolume.

Confocal laser scanner microscopy coupled with an image analysis system was used to directly determine the shape and calculate the biovolume of phytoplankton organisms by constructing 3D models of cells. The study was performed on Biceratium furca (Ehrenberg) Vanhoeffen, which is one of the most complex-shaped phytoplankton. Traditionally, biovolume is obtained from a standardized set of geometric models based on linear dimensions measured by light microscopy. However, especially in the case of complex-shaped cells, biovolume is affected by very large errors associated with the numerous manual measurements that this entails. We evaluate the accuracy of these traditional methods by comparing the results obtained using geometric models with direct biovolume measurement by image analysis. Our results show cell biovolume measurement based on decomposition into simple geometrical shapes can be highly inaccurate. Although we assume that the most accurate cell shape is obtained by 3D direct biovolume measurement, which is based on voxel counting, the intrinsic uncertainty of this method is explored and assessed. Finally, we implement a data-driven formula-based approach to the calculation of biovolume of this complex-shaped organism. On one hand, the model is obtained from 3D direct calculation. On the other hand, it is based on just two linear dimensions which can easily be measured by hand. This approach has already been used for investigating the complexities of morphology and for determining the 3D structure of cells. It could also represent a novel way to generalize scaling laws for biovolume calculation.

Digital holographic microscopy for microalgae biovolume assessment

The relative amount of biomass in a body of water is one of the various indicators widely used in water quality evaluation. This implies complex tasks such as identification and characterization of microorganisms and measurement of their biovolume. Particularly, the latter is estimated by assuming simple geometrical shapes for the microorganism and by calculating its dimensions from images taken with a conventional microscope. In order to have a more precise and automatic method for biovolume evaluation, a hybrid methodology based on digital holographic microscopy and image processing is proposed. The whole volume of a specimen under study is obtained combining the phase contrast image of an off-axis hologram with the thickness-profile data of the specimen extracted from the cell silhouette. This technique has been used for determining the biovolume of Ceratium Hirundinella cells in water samples. The methodology proposed also shows that it is possible to estimate accurately an effective refractive index of the microorganism. Experimental results have shown that this technique is not only an efficient and fast alternative, but also suitable for automatizing the entire process.

Cell biovolume and biomass in carbon of microphytoplankton species of oceanic regions, Equatorial Atlantic

As interações entre os recursos físicoquímicos no oceano refletem diretamente no comportamento da comunidade fitoplactô-nica, assim, estudá-las torna-se fundamental para o conhecimento das ilhas em regiões oceânicas. O presente trabalho teve como objetivo, obter os valores de biomassa em carbono orgânico através do biovolume celular das espécies do microfitoplâncton do Arquipélago São Pedro e São Paulo no intuito de contribuir e atualizar os modelos citados na literatura. Foram realizadas coletas em março/2008, em quatro transectos perpendiculares ao Arquipélago. Dentre as 110 espécies identificadas na composição microfitoplanctônica, 33 espécies foram selecionadas para a medida do biovolume celular. Foram elaboradas três formas geométricas combinadas inéditas para o gênero Ceratium cuja complexidade morfo-lógica não foi observada em protocolos anteriores e verificada a carência, na literatura, de medidas mais precisas das dimensões celulares de determinados organismos. Os maiores valores de biovolume celular e biomassa em carbono foram de Pyrocystis noctiluca Murray ex Haeckel. Espera-se que a aplicação das recomendações propostas, no presente trabalho, sobre os modelos venha encorajar estudos nesta área e aumentar a precisão na determinação das medidas morfológicas. Palavras chave: fitoplâncton marinho, medições morfológicas, ilha oceânica.

A finely tuned symphony of factors modulates the microbial food web of a freshwater reservoir in spring

We employed high frequency sampling to determine the major factors modulating microbial food‐web composition and dynamics through the spring phytoplankton bloom and clear‐water phases in a freshwater reservoir. We examined effects of a changing trophic structure of the planktonic community cascading from the level of zooplankton, through phytoplankton composition and exudation rates to the level of growth responses and losses to grazers of phylogenetically narrow bacterial lineages. Specific probes for fluorescence in situ hybridization (FISH) revealed important short‐lived peaks of genus‐like (Fluviiciola sp. and Limnohabitans spp.) or even taxonomically narrower populations of Betaproteobacteria and Flavobacteria (such as FlavB and Flav2 lineages). Protozoan grazing on bacterioplankton was studied by using fluorescently labeled bacteria and by direct analyses of FISH‐probe—targeted bacterial phylotypes in flagellate food vacuoles. Evaluations of selective bacterivory, growth responses, and cell biovolumes of various bacterial groups during the spring bloom indicated that certain bacterial groups such as Limnohabitans can contribute to carbon flow to the grazer food chain up to 10‐fold more than similarly abundant small cells from the Ac1 lineage of Actinobacteria. During the clear‐water phase, filter‐feeding cladocera had dominant effects on bacterioplankton abundance and community dynamics, likely through direct grazing on larger bacteria along with altering major substrate pools (via e.g., the herbivores' sloppy feeding on algae). Fine‐temporal resolution data revealed several environmental scenarios, in which the interplay of distinct top‐down and bottom‐up factors resulted in a competitive advantage of particular bacterial lineages.

Is the toxicity of pesticide mixtures on river biofilm accounted for solely by the major compounds identified?

Comparative effects of long-term exposure to Polar Organic Chemical Integrative Sampler (POCIS) extracts (PE) and to a reconstituted mixture based on the major compounds quantified in the PE were evaluated on river biofilm communities. The study aimed to characterize the effects of long-term and low-dose exposure to pesticides on natural biofilm communities and to evaluate if the effects due to PE exposure could be explained solely by the major compounds identified in the extracts. Biofilms from an uncontaminated site were exposed in artificial channels to realistic environmental concentrations using diluted PE, with the 12 major compounds quantified in the extracts (Mix) or with water not containing pesticides (Ctr). Significant differences between biofilms exposed to pesticides or not were observed with regard to diatom density, biomass (dry weight and ash-free dry mass), photosynthetic efficiency (ΦpsII) and antioxidant enzyme activities. After 14days of exposure to the different treatments, the observed trend towards a decrease of mean diatom cell biovolumes in samples exposed to pesticides was related to the control biofilms' higher relative abundance of large species like Cocconeis placentula or Amphora copulata and lower relative abundance of small species like Eolimna minima compared to the contaminated ones. Principal component analyses clearly separated contaminated (PE and Mix) from non-contaminated (Ctr) biofilms; on the contrary, the analyses did not reveal separation between biofilms exposed to PE or to the 12 major compounds identified in the extract.

Experimental Assessment of Temperature Thresholds for Arctic Phytoplankton Communities

We examined the responses of two different natural arctic plankton communities to warming in an attempt to find temperature thresholds for abrupt changes in growth or biomass. We conducted two experiments in situ using two different plankton communities; incubation temperatures represented the annual variation in these Arctic waters plus 3–4 °C to account for the potential warming expected for the Arctic Ocean during the twenty-first century. We evaluated changes in nutrient and chlorophyll a concentrations, primary production, cell abundances, and growth rates as well as cell biovolume and percentage of living cells for the main groups found during our study. Phytoplankton communities were composed of diatoms, Phaeocystis sp., Micromonas, as well as other flagellates. Results indicate a decrease in chlorophyll a concentration and growth rate at the highest temperatures tested. We also found a differing effect on cell abundance and growth rates depending on the taxonomic group or cell size: diatom abundance decreased with warming while small-sized phytoplankton showed an increasing trend at the intermediate temperature treatments. Biovolume estimates also tended to decrease with increasing temperature. We find a perceptible change in trends at intermediate temperature treatments for most of the parameters which suggests a possible thermal threshold around 5–6 °C for the arctic plankton communities examined here.

An assessment of the usefulness of the cyanobacterium Synechococcus subsalsus as a source of biomass for biofuel production

Nowadays algal biofuels are considered one of the most promising solutions of global energy crisis and climate change for the years to come. By manipulation of the culture conditions, many algal species can be induced to accumulate high concentrations of particular biomolecules and can be directed to the desired output for each fuel. In this context, the present study involved the assessment of the effects of CO 2 availability and nitrogen starvation on growth and chemical composition of the cyanobacterium Synechococcus subsalsus , testing a fast-growing native strain. The control experiments were performed with Conway culture medium in 12-day batch cultures, in 6-liter flasks and 12 h photoperiod, with addition of 2 L min -1 filtered air to each flask. Other two experimental conditions were also tested: (i) the placement into the cultures of additional dissolved nutrients except nitrogen, one week after the start of growth (N-), and (ii) the input of pure CO 2 into the flasks from the 5th day of growth (C+). In all cultures, daily cell counts were done throughout the cultivation, as well as measurements of pH and cell biovolumes. Maximum cell yield were found in N-experiments, while cell yields of C+ and control were similar. Dissolved nitrogen was exhausted before the end of the experiments, but dissolved phosphorus was not totally consumed. Protein and chlorophyll-a concentrations decreased from the exponential to the stationary growth phase of all experiments, except for protein in the control. In all experiments, carbohydrate, lipid and total carotenoid increased from the exponential to the stationary growth phase, as an effect of nitrogen limitation. Increments in carbohydrate concentrations were remarkable, achieving more than 42% of the dry weight (dw), but concentrations of lipid were always lower than 13% dw. The addition of pure CO 2 did not cause a significant increase in biomass of S. subsalsus nor generated more lipid and carbohydrate than the other treatments. Nitrogen starvation caused an intense accumulation of carbohydrate, but the increments of lipid were small. Despite the fast growth, the cyanobacterium S. subsalsus has a virtually null potential for biodiesel production, given its low lipid concentrations. The high concentrations of carbohydrate combined with fast growth point to the potential use of this species as raw material for other possible biotechnological processes, after a demonstration of technical and economic viability.

The roles of Pseudomonas aeruginosa extracellular polysaccharides in biofouling of reverse osmosis membranes and nitric oxide induced dispersal

The roles of Pseudomonas aeruginosa polysaccharides (Pel, Psl, alginate) in reverse osmosis (RO) membrane biofouling and nitric oxide (NO) induced dispersal were investigated. While mutants deficient in Psl formed significantly lower biofilm (total cell and polysaccharide) biovolumes than the PAO1 wild-type on glass surfaces, total cell biovolumes were similar during fouling of RO membranes. However, biofilms of the Psl deficient mutants exhibited a striated pattern, leaving large areas of membrane unfouled and contained up to 70% less polysaccharide and 24% less protein than the wild-type. Membranes fouled by the psl mutants exhibited a 69% reduction in the rate of biofouling (pressure rise over a given period), while the pel and alginate mutants were similar to the wild-type, suggesting functional differences in the polysaccharides. Overproduction of alginate by a PDO300 mutant increased the biofouling rate (59%) relative to wild-type, highlighting the ability of this polysaccharide to promote biofilm adherence and increase hydraulic resistance to permeate flow in an RO system. These results emphasize the importance of attachment specific polysaccharides for bacteria when fouling industrial RO membranes. When exposed to NO, dispersal of the PDO300 mutant biofilm was 25% lower than the wild-type, whilst dispersal of the alginate deficient mutant was 11% greater. Alginate thus appears to play an important role in NO induced dispersal of PAO1 biofilms.

Accuracy of biovolume formulas for CMEIAS computer-assisted microscopy and body size analysis of morphologically diverse microbial populations and communities.

Cell biovolume is a commonly used metric of microbial abundance analyzed by computer-assisted microscopy, but the accuracies of most biovolume formulas have not been validated by ground truth data. We examined the accuracy of 17 biovolume formulas by comparing the computed volumes of 3D models representing 11 microbial morphotypes (cocci, spirals, curved rods, U-shaped rods, regular straight rods, unbranched filaments, ellipsoids, clubs, prosthecates, rudimentary branched rods, and branched filaments) to the volume displacement of the same objects as ground truth. As anticipated, formula accuracy was significantly influenced by the morphotype examined. A few formulas performed very accurately (> 95 %), especially those that adapted to the cell's shape, whereas others were consistently inaccurate or only accurate for one or two morphotypes. As an example of application, indices of morphological diversity in a freshwater biofilm assemblage were shown to be significantly different when microbial abundance among morphotype classes was measured as biovolume body mass rather than cell counts. Spatial analysis of biovolume body mass can also provide insights on the in situ ecophysiological attributes among individuals in microbial populations and communities, including their spatially autocorrelated allometric scaling interrelationships between body size, metabolic activity, resource apportionment and use, food web dynamics, and various cell-cell interactions affecting their growth and colonization behavior within spatially structured biofilm landscapes. This improved computing technology of biovolume algorithms with proven accuracy identifies which formula(s) should be used to compute microbial biovolumes in 2D images of morphologically diverse communities acquired by conventional phase-contrast light microscopy at single-cell resolution.

Phytoplankton dynamic and bioindication in the Kondopoga Bay, Lake Onego (Northern Russia)

On the basis of our collected material and historical information we assess phytoplankton dynamics in Kondopoga Bay, the Lake Onego in 1993-2011. The summer communities from continuously studied sampling stations contain 100 species belonging to eight divisions: Bacillariophyta, 40; Chlorophyta, 25; Cyanobacteria, 13; Chrysophyta, 12; Euglenophyta, 2; Dinophyta, 4; Cryptophyta, 3; and Xanthophyta, 1. Sample richness varied between 16 and 54 species, with a negative overall trend during the study period, but increases in Cyanobacteria and Dinophyta. Bioindication analysis shows that water acidification slowly rising from 1993 to 2011 with organic pollution (Index saprobity S) and the number of species with heterotrophic ability. In 1990s, the total abundance and biomass were on average 1.5 times higher than in 2000-2011, having similar fluctuation ranges (Pearson 0.74), with peaks in 1996 and 2006. At the same time, species richness decreased, showing a depletion of algal communities. Two critically impacted periods are revealed with the Shannon index in 1996 and 2007 and on the basis of the Aquatic Ecosystem State Index (WESI) calculation in 1995 and 2007, related to Kondopoga industrial wastewater influx enriched in nutrients and other contaminants. As a whole, the WESI was extremely high, reflecting a high self-purification capacity in respect to phosphate concentration in the bay. The canonical corresponded analysis (CCA) shows two different sets of taxa, those stimulated by temperature and nitric nitrogen (Anabaena scheremetievii Elenkin, Dolichospermum lemmermannii (Ricter) P.Wacklin, L.Hoffmann & J.Komárek, and Aulacoseira alpigena (Grunow) Krammer), and sensitive autotroph species inhabiting cool to temperate clear waters (Aulacoseira distans (Ehrenberg) Simonsen, Ankistrodesmus fusiformis Corda ex Korshikov, Mucidosphaerium pulchellum (H.C.Wood) C.Bock, Proschold & Krienitz). The comparative statistics with GRAPS program revealed two cores of species richness in years 1996 and 2011 that included most of species. The long-term dynamics of relative cell volume shows that phytoplankton communities were enriched with small-celled species, such as Cyanobacteria (Microcystis aeruginosa (Kützing) Kützing) and Cryptophyta (Cryptomonas sp. and Katablepharis ovalis Skuja) in the period between 1998 and 2006. Pearson correlation for Shannon index and relative cell biovolume is negative (-0.79), showing high stability of species rich communities under environmental impacts. Two periods of dinoflagellate blooms (1998, 2007) followed the peaks of total abundance and biomass (1996, 2006). Such correlation makes the Kondopoga Bay ecosystem comparable to those of large lakes in spite of a heavier anthropogenic impact from Kondopoga pulp and paper mill wastewater.

A slide preparation technique for light microscopy analysis of ciliates preserved in acid Lugol's fixative

A slide preparation method for seawater samples preserved in acid Lugol's is presented here as an alternative to the traditional Utermöhl settling chamber method for microplankton analysis. This preparation maintains the integrity of fragile cells, such as ciliates, resolves issues associated with the transience of samples prepared in settling chambers, and allows the use of automated image acquisition methods. Samples are filtered onto polycarbonate membranes and analyzed with transmitted light microscopy. The visibility of pore outlines is minimized by using mounting oil (Cargille Series A immersion oil, Certified Refractive Index, nD25°C 1.5840 ± 0.0002) with a refractive index matching that of the membrane material. We assessed the efficacy of this new method by comparing abundance and biomass estimates for ciliates in settled and filtered samples. Acceptable results were found for the most delicate of samples stored long‐term in acid Lugol's. Some cell shrinkage occurred during the filtration and brief drying steps. Therefore, corrections for ciliate length and width measurements in filtered samples were determined to counteract this effect on total cell biovolume. Overall, the method provides a simple and stable alternative to settling chamber analysis for ciliates preserved in acid Lugol's.

Induction of triacylglycerol production in Chlamydomonas reinhardtii: Comparative analysis of different element regimes

In this study, impacts of different element absence (nitrogen, sulfur, phosphorus and magnesium) and supplementation (nitrogen and zinc) on element uptake and triacylglycerol production was followed in wild type Chlamydomonas reinhardtii CC-124 strain. Macro- and microelement composition of C. reinhardtii greatly differed under element regimes studied. In particular, heavy metal quotas of the microalgae increased strikingly under zinc supplementation. Growth was suppressed, cell biovolume, carbohydrate, total neutral lipid and triacylglycerol levels increased when microalgae were incubated under these element regimes. Most of the intracellular space was occupied by lipid bodies under all nutrient starvations, as observed by confocal microscopy and transmission electron micrographs. Results suggest that sulfur, magnesium and phosphorus deprivations are superior to nitrogen deprivation for the induction triacylglycerol production in C. reinhardtii. On the other hand, FAME profiles of the nitrogen, sulfur and phosphorus deprived cells were found to meet the requirements of international standards for biodiesel.

Temporal Succession of Phytoplankton Assemblages in a Tidal Creek System of the Sundarbans Mangroves: An Integrated Approach

Sundarbans, the world's largest mangrove ecosystem, is unique and biologically diverse. A study was undertaken to track temporal succession of phytoplankton assemblages at the generic level (≥10 µm) encompassing 31 weeks of sampling (June 2010–May 2011) in Sundarbans based on microscopy and hydrological measurements. As part of this study, amplification and sequencing of type ID rbcL subunit of RuBisCO enzyme were also applied to infer chromophytic algal groups (≤10 µm size) from one of the study points. We report the presence of 43 genera of Bacillariophyta, in addition to other phytoplankton groups, based on microscopy. Phytoplankton cell abundance, which was highest in winter and spring, ranged between 300 and 27,500 cells/L during this study. Cell biovolume varied between winter of 2010 (90–35281.04 µm3) and spring-summer of 2011 (52–33962.24 µm3). Winter supported large chain forming diatoms, while spring supported small sized diatoms, followed by other algal groups in summer. The clone library approach showed dominance of Bacillariophyta-like sequences, in addition to Cryptophyta-, Haptophyta-, Pelagophyta-, and Eustigmatophyta-like sequences which were detected for the first time highlighting their importance in mangrove ecosystem. This study clearly shows that a combination of microscopy and molecular tools can improve understanding of phytoplankton assemblages in mangrove environments.

The contribution of rare species to coastal phytoplankton assemblages

AbstractAnalysis of quantitative and qualitative composition of rare phytoplankton species was performed using a data set collected over a large geographic area (four eutrophic gulfs of the Aegean Sea, E. Mediterranean Sea) during 2002–2003. We examined the effects of excluding rare species on comparisons of species richness, diversity, similarity and niche breadth as well as the regional and seasonal contribution of rare species to cell abundance and carbon biomass. Overall, the total of 401 species included 182 rare species contributing 45.1% of the total species number. However, there was a considerable variation in this relationship among the other parameters, as rare species contributed only 6.4% of total cell abundance, 13.1% of total species diversity, 21.2% of total cell biovolume and 16.6% of total carbon biomass. The results showed that rarity may be a significant issue in studies detecting and quantifying phytoplankton community structure.

Diel variation in high-frequency acoustic backscatter from Cochlodinium polykrikoides

The integrated backscatter power (IBP) from Cochlodinium polykrikoides was measured every 15 min by a 5-MHz acoustic system during a 5-day cultivation with an irradiation cycle. IBP increased by 0.6 dB in 5 days, but varied by 0.83 dB during the irradiation cycle. The daily increase and diel variation in IBP were postulated to be affected by an increase in cell numbers and a diel variation in cell biovolume or density via photosynthesis, respectively. Cell division/separation might also affect a total variation in IBP. This study suggests that high-frequency acoustics may be a potential tool for investigating phytoplankton cell functions.

Cell biovolume and surface area in phytoplankton of Mediterranean transitional water ecosystems: methodological aspects

1 - A series of experimental researches highlighted the role of morphometric parameters of phytoplankton guilds as descriptors of the ecological status of transitional water ecosystems (TWs). 2 - However, at present, standardized or common methodologies for their use do not exist. In this work, we develop a procedure for the determination of biovolume and surface area in phytoplankton guilds of Mediterranean TWs. 3 - Phytoplankton biovolume and surface area are included among the most studied morphometric descriptors. They can be estimated by associating the algae with similar geometric forms and determining the volume of these by measuring the linear dimensions required for its calculation under the light microscope. 4 - Here, a set of geometric models is suggested for calculating the cell biovolumes and surface area of 235 phytoplankton genera, deriving from the analysis of 869 phytoplankton species, found in transitional water ecosystems of the Mediterranean Ecoregion. The equations were designed to minimize the effort of microscopic measurements. 5 - The similarities and differences between the geometric models here proposed and previously published are discussed.