Planktonic Microalgae Research Articles

Diatom artificial medium (DAM): a new artificial medium for the diatom Haslea ostrearia and other marine microalgae

Artificial media are used in physiological studies of microalgae to maintain consistent conditions from one experiment to another and these media must be adapted to the needs of the organism studied. The artificial medium, in this case named diatom artificial medium (DAM), was designed to maintain long-term cultures of Haslea ostrearia and 19 other planktonic microalgae, and to allow physiological studies related to metal metabolism. The biomass and biochemical composition of H. ostrearia grown in the DAM and in a modified Provasoli medium were compared to assess the suitability of this new artificial medium for the culture of this diatom. The DAM provided sufficient nutrients to allow H. ostrearia to grow as efficiently as in the enriched seawater medium, without negative impact on metabolism. The DAM was tested with 19 other microalgae in order to widen its potential use, and 18 of the 19 showed a good adaptation to this medium. The chemical speciation of metals (Cd, Cu, Pb, Zn) was assessed using a speciation mathematical model. The presence of EDTA resulted in the total complexation of the trace metals implying that they were present in a sole chemical species in the DAM.

Exploitation of natural food sources by two sympatric, invasive suspension-feeders: Crassostrea gigas and Crepidula fornicata

The natural diets of the introduced suspension-feeders Crassostrea gigas (Thunberg) and Crepidula fornicata (L.) were determined at a mid-latitudinal oyster-farming site within their European range (Bourgneuf Bay, France). Carbon and nitrogen stable isotope deviations of Pacific oysters and slipper limpets were compared with potential food sources on 3 sampling dates (March, July and November 2003). Four end-members were assimilated by the 2 species: C3 angiosperm detritus, macroalgae-C4 plant detritus, marine phytoplankton and benthic diatoms. Given the lack of source digestibility data for suspension-feeders, and these 2 species in particular, extreme feasible combinations of relative end-member contributions were calculated according to 2 assimilation sce- narios, using either IsoSource software or a concentration-dependent model. For both Crassostrea gigas and Crepidula fornicata, benthic and planktonic microalgae dominated diets on the 3 sampling dates. Planktonic microalgae were ingested in greater proportions than benthic species in July and November; however, benthic diatoms also formed a constant and significant part of diets in these months, and were consumed in greater proportions than planktonic species in March. Plant (espe- cially macroalgal) detritus played a major role in the diets of the 2 suspension-feeders, notably in March 2003 when it became the principal ingested source. The substantial contribution of plant detri- tus to the natural diets of these species has not previously been reported. Although Crassostrea gigas and Crepidula fornicata showed significantly different isotopic deviations in March and July 2003, trophic niches of Crassostrea gigas and Crepidula fornicata overlapped on all 3 sampling dates, with a greater ingestion of identical sources in November. These 2 invasive species could therefore be trophic competitors in the context of end-member supply limitation. Contrary to previous analyses conducted on these 2 species in Europe, this study reports significant dietary overlap. Ecosystem- specific diet studies of invasive species are thus necessary in order to understand trophic overlap/ competition as a function of the diversity and availability of local food sources.

Chemistry of oxylipin pathways in marine diatoms

Abstract Oxylipins are important signal transduction molecules widely distributed in animals and plants where they regulate a variety of events associated with physiological and pathological processes. The family embraces several different metabolites that share a common origin from the oxygenase-catalyzed oxidation of polyunsaturated fatty acids. The biological role of these compounds has been especially studied in mammalians and higher plants, although a varied and very high concentration of these products has also been reported from marine macroalgae. This article gives a summary of our results concerning the oxylipin chemistry of marine diatoms, a major class of planktonic microalgae that discourage predation from their natural grazers, zooplanktonic copepods, using chemical warfare. These apparently harmless microscopic cells produce a plethora of oxylipins, including short-chain unsaturated aldehydes, hydroxyl-, keto-, and epoxyhydroxy fatty acid derivatives, that induce reproductive failure in copepods through abortions, congenital malformations, and reduced larval growth. The biochemical process involved in the production of these compounds shows a simple regulation based on decompartmentation and mixing of preexisting enzymes and requires hydrolysis of chloroplast-derived glycolipids to feed the downstream activities of C16 and C20 lipoxygenases.

Removal of Technetium from Solution by Algal Flagellate Euglena gracilis

Based on limited data for the removal of radioactive (99)Tc by freshwater phytoplankton, it has been thought that phytoplankton are unsuitable for remediation of (99)Tc-contaminated waters. This work sought to verify the validity of this assumption by studying the removal of (99)TcO(4)(-) by freshwater and brackish water phytoplankton. The phytoplankton used were Euglena gracilis, Chlamydomonas pulsatilla, Chlorella vulgaris, and Spirulina platensis. Each of them was incubated for 63 d, and the removal of (99)Tc from solution was periodically determined. Significant removal of (99)Tc was observed only for E. gracilis, and the maximum removal was 70% of the total (99)Tc added. The killed cells of E. gracilis, however, removed hardly any (99)Tc. When E. gracilis cells were washed with fresh culture medium, only 13% of the total (99)Tc was desorbed. These results suggested that intracellular uptake of (99)Tc by E. gracilis occurred. These results are the first documented example of significant removal of (99)Tc by planktonic microalgae.

Formation of Halogenated Medium Chain Hydrocarbons by a Lipoxygenase/Hydroperoxide Halolyase-Mediated Transformation in Planktonic Microalgae

A rapid transformation of eicosapentaenoic acid is initiated upon disintegration of cells of the marine diatom Stephanopyxis turris. In contrast to any other fatty acid cleaving activity known, this diatom releases a blend of chlorinated C8 hydrocarbons in addition to an unsaturated 12-oxo acid. Using labeled precursors, trapping experiments, and selective inhibition of enzyme activities, we were able to show that a lipoxygenase activates the C20 fatty acid to a hydroperoxide, which is subsequently cleaved by a new hydroperoxide halolyase to the C8 and C12 products. This adds a fundamentally new pathway to the limited set of halogenating enzymatic activities known from nature.

EXPLORING THE NATURAL ROLE OF MICROCYSTINS—A REVIEW OF EFFECTS ON PHOTOAUTOTROPHIC ORGANISMS1

Cyanobacterial blooms and the production of cyanotoxins represent a serious global problem. Although the effects of a group of important cyanotoxins, microcystins (MCs), have been studied intensively in various organisms, little is known about the natural functions of these cyclic heptapeptides. MCs may have allelopathic effects. This paper summarizes the information from the studies that have investigated the effects of MCs on photoautotrophs in vitro and in vivo. Interactions with terrestrial plants, macrophytes, macroalgae, and planktonic microalgae are reported in detail with respect to the ecological relevancy of experimental conditions related to allelopathy. Our review shows that only a limited number of studies described harmful effects of MCs at concentrations that are typical for the environment. Consequently, the ability of MCs to act as general allelopathic compounds against photoautotrophs seems unlikely. However, further research is needed for definitive confirmation or rejection of the allelopathic hypothesis as well as, an explanation of the crucial question of MC function in the context of new information from evolutionary and molecular biology.

Spatial and temporal variation in algal-assemblage structure in isolated dryland river waterholes, Cooper Creek and Warrego River, Australia

The scale at which algal biodiversity is partitioned across the landscape, and the biophysical processes and biotic interactions which shape these communities in dryland river refugia was studied on two occasions from 30 sites in two Australian dryland rivers. Despite the waterholes studied having characteristically high levels of abiogenic turbidity, a total of 186 planktonic microalgae, 253 benthic diatom and 62 macroalgal species were recorded. The phytoplankton communities were dominated by flagellated cryptophytes, euglenophytes and chlorophytes, the diatom communities by cosmopolitan taxa known to tolerate wide environmental conditions, and the macroalgal communities by filamentous cyanobacteria. All algal communities showed significant differences between catchments and sampling times, with a suite of between 5 and 12 taxa responsible for ~50% of the observed change. In general, algal assemblage patterns were poorly correlated with the measured environmental variables. Phytoplankton and diatom assemblage patterns were weakly correlated with several waterhole geomorphic measures, whereas macroalgal assemblage patterns showed some association with variability in ionic concentration.

Selective assimilation by deposit feeders: Experimental evidence using stable isotope ratios

Summary Deposit-feeding animals form important links between sediment organic matter (SOM) and carnivorous fish in aquatic ecosystem food webs. They inevitably assimilate food from different origins in a selective manner from SOM, including benthic and planktonic microalgae. Lake Katanuma has a very simple community structure due to its strong acidity. It includes chironomid larvae ( Chironomus acerbiphilus ) as the consumer, and two primary producers: a benthic diatom ( Pinnularia acidojaponica ) and a planktonic green alga ( Chlamydomonas acidophila ). We collected the deposit feeder C. acerbiphilus , its potential food (phytoplankton, benthic diatoms, and terrestrial plant litter), and the sediments forming its diet from Lake Katanuma, and conducted feeding experiments to determine the required parameters for the mixing model. The results of the isotope-mixing model clearly showed that C. acerbiphilus larvae selectively assimilated phytoplankton and benthic diatoms as fresh deposits from bulk sediments, and assimilated phytoplankton more readily than benthic diatoms. Moreover, the assimilation rate of benthic diatoms from sediments by C. acerbiphilus larvae tended to decrease with increasing water depth due to the decrease in benthic primary production, while the rate of phytoplankton tended to increase with depth.

Diet and Food Web Support of the White Perch, Morone americana, in the Hackensack Meadowlands of New Jersey

I analyzed stomach contents of white perch, Morone americana, caught throughout the year in the Hackensack River in northern New Jersey. The dominant prey items were amphipods, with shrimp and fish being less important. Stable isotope analysis indicated that the primary producers of importance in the food web leading to white perch were benthic or planktonic microalgae and secondarily Phragmites australis, the dominant macrophyte in the Hackensack Meadowlands. Despite their large size, white perch do not generally appear to feed any higher in the food web than killifish, Fundulus heteroclitus.

The algae-lytic ability of bacterium DC10 and the influence of environmental factors on the ability

A lysing-bacterium DC10, isolated from Dianchi Lake of Yunnan Province, was characterized to be Pseudomonas sp. It was able to lyse some algae well, such as Microcystis viridis, Selenastrum capricornutum, and so on. In this study, it was shown that the bacterium lysed the algae by releasing a substance; the best lytic effects were achieved at low temperatures and in the dark. Different concentrations of CaCl2 and NaNO3 influenced the lytic effects; the ability to lyse algae decreased in the following order: pH 4 > pH 9 > pH 7 > pH 5.5. It was significant to develop a special technology with this kind of bacterium for controlling the bloom-forming planktonic microalgae.

In situ measurements of benthic primary production during emersion: seasonal variations and annual production in the Bay of Somme (eastern English Channel, France)

A survey of benthic primary production during periods of emersion was performed in a muddy-sand station of the Bay of Somme. Primary production and respiration were estimated by in situ measurements of carbon dioxide fluxes using infra-red analysis. Photosynthetic response of the community to incident light and temperature was analysed at different periods of the year. Seasonal variations of the photosynthetic parameters were estimated using the photosynthesis versus irradiance (P–I) curves constructed in February, April, July, August and October. The rate of maximum gross community primary production (Pm), highly correlated to sediment chlorophyll a (Chl a) content, was low in February (6.7mg Cm−2h−1) and high in July (97.7mg Cm−2h−1). Photosynthetic efficiency at low light intensity (α) was positively correlated to Pm. The very high production (Pm=126.8mg Cm−2h−1) and productivity (ratio of Pm and sediment Chl a content) measured in March may be related to the set down of active planktonic microalgae. At five dates, the effects of temperature on primary production seemed to overshadow the role of light. The Q10 for primary production varied from 1.2 in August to 3.0 in December. Daily potential primary production was calculated as a function of theoretical and measured irradiance for the period of superimposition of day and emersion. At the annual scale, the potential gross community primary production was 147g Cm−2 with theoretical irradiance and 110g Cm−2 with measured irradiances. The annual community respiration was 188g Cm−2, leading to a heterotrophic annual budget. The annual pattern of daily production can be largely explained by changes in day length. It is also characterized by a fortnightly variability due to the variation of the total daily irradiance available for photosynthesis caused by the superimposition of the tidal and day/night cycles. Finally, sharp variations occurring with nebulosity can overshadow this fortnightly variability.

Interactions between planktonic microalgae and protozoan grazers.

For an algal bloom to develop, the growth rate of the bloom-forming species must exceed the sum of all loss processes. Among these loss processes, grazing is generally believed to be one of the more important factors. Based on numerous field studies, it is now recognized that microzooplankton are dominant consumers of phytoplankton in both open ocean and coastal waters. Heterotrophic protists, a major component of microzooplankton communities, constitute a vast complex of diverse feeding strategies and behavior which allow them access to even the larger phytoplankton species. A number of laboratory studies have shown the capability of different protistan species to feed and grow on bloom-forming algal species. Because of short generation times, their ability for fast reaction to short-term variation in food conditions enables phagotrophic protists to fulfill the function of a heterotrophic buffer, which might balance the flow of matter in case of phytoplankton blooms. The importance of grazing as a control of microalgae becomes most apparent by its failure; if community grazing controls initial stages of bloom development, there simply is no bloom. However, if a certain algal species is difficult to graze, e.g. due to specific defense mechanisms, reduced grazing pressure will certainly favor bloom development. The present contribution will provide a general overview on the interactions between planktonic microalgae and protozoan grazers with special emphasis on species-specific interactions and algal defense strategies against protozoan grazers.

가마미 해수욕장(전남 영광) 갯벌의 미세조류의 분포에 관한 연구

Distributional patterns of microalgae were studied in the tidal flats of Gamami Beach(Young-Gwang, Korea) from November 1999 to 2000 July. The tidal flats of Gamami Beach was composed mainly of sandy sediment. The concentrations of nutrients were low compared with other tidal flats. In the present study, 68 species of microalgal flora were identified. These were comprised of 25 species of benthic microalgae and 59 species of planktonic microalgae. Diatoms predominated the benthic microalgae with 96.0% of total species occurred. Dominant species were Amphora sp., Cocconeis sp., Coscinodiscus asteromphalus, Coscinodiscus sp., Nitzschia sigma var. intermedia, Nitzschia distans, Navicula spp., Paralia sulcata, Pleurosigma sp. Skeletonema coastatum, and Surirella sp. Among them, Amphora sp., Paralia sulcata, and species of Pleurosigma and Nitzschia were observed throughout the studied period. Planktonic microalgae of Gamami Beach was also predominated by diatoms. They occupied 88.1% of total planktonic microalgae. The density of microalgal population was higher in silty sediment than in sandy sediment. The population density of microalgae was higher in high tide zone than that in low tide zone. The density of the benthic microalgae in the surface layer of tidal flats showed increasing tendency for 2 hours after the beginning of ebb tide. On the contrary, benthic microalgal density of subsurface layer was decreased during the period. Concentrations of chlorophyll <TEX>${\alpha}$</TEX> from sediment and water were not synchronized during the study period. Therefore, the distributional patterns of the benthic microalgae and planktonic algae seemed not to be related. Chlorophyll <TEX>${\alpha}$</TEX> of water was highly related with the concentration of NH<TEX>$_4$</TEX>-N, whereas, chlorophyll <TEX>${\alpha}$</TEX> of sediment uas related with NO<TEX>$_3$</TEX>-N concentration.

162 Interactions Between Planktonic Microalgae and Protozoan Grazers

For an algal bloom to develop, the growth rate of the bloom‐forming species must exceed the sum of all loss processes. Among these loss processes, grazing is generally believed to be one of the more important factors. Based on numerous field studies it is now recognised that microzooplankton are dominant consumers of phytoplankton in both open ocean and coastal waters. Heterotrophic protists, a major component of microzooplankton communities, constitute a vast complex of diverse feeding strategies and behaviour which allow them access to even the larger phytoplankton species. A number of laboratory studies have shown the capability of different protistan species to feed and grow on bloom forming algal species. Because of short generation times, their ability for fast reaction to short‐term variation in food conditions enables phagotrophic protists to fulfil the function of a heterotrophic buffer, which might balances the flow of matter in case of phytoplankton blooms. The importance of grazing as control of microalgae becomes most apparent by its failure; if community grazing controls initial stages of bloom development, there simply is no bloom. However, if a certain algal species is difficult to graze, e.g. due to specific defence mechanisms, a reduced grazing pressure will certainly favour bloom development. The present contribution will provide a general overview on the interactions between planktonic microalgae and protozoan grazers with special emphasis on species‐specific interactions and algal defence strategies against protozoan grazers.

13 Viral control of phytoplankton

Viral control of phytoplankton Virus ecology is a young rapidly developing field that is changing our understanding of the functioning of marine ecosystems. Viruses are known to be ubiquitous, numerically dominant members of the aquatic microbial communities, infecting a wide spectrum of hosts, including planktonic microalgae. They are typically host‐specific agents of mortality and thus likely influence the dynamics and succession of phytoplankton. As well, viral infection can have major biogeochemical implications through cell lysis and the resulting transformation of released POM into DOM. Bloom forming algal species with their high cell abundance may allow a rapid propagation of lytic viruses, resulting in a direct and significant controlling impact of viruses on bloom dynamics. Besides the concentration of host and virus, other potential factors influencing the quantitative importance of viral control of phytoplankton are resistance of host strains to virus infection (host range), variations in morphotypes of the phytoplankton species, the type of limiting nutrient, and variables affecting the fate of viruses (UV, grazing, adsorption to aggregates). The current presentation will provide examples of viral infected phytoplankton and will address some of the processes involved in viral mediated mortality of microalgae.

The Otelfingen Aquaculture Project

ABSTRACT A wastewater-fed, partly indoor aquaculture plant (36 basins, 360 m2 and 420 m3 in total) was designed in Otelfingen/Zurich, Switzerland. It was charged with the effluent from a methanization plant processing organic household waste and started operation in spring 1998. The aim of the successive arrangement of the different modules and steps was to efficiently recycle water-borne nutrients in the form of aquatic biomass products, such as floating (ornamental) macrophytes, fish, zoo- and phytoplankton, suitable for selling on the Swiss market. Besides treating the effluent (total organic carbon [TOC], total nitrogen, nitrate [NO3-N], ammonium [NH4-N], and total phosphorus concentrations being 670 g/m3, 255 g/m3, 150 g/m3, 95 g/m3, and 52 g/m3, respectively) according to Swiss law requirements, the research focused on the search for suitable aquatic organisms and their testing at different environmental conditions. During the 16-week experimental period, a total of 2,150kg fresh weight (FW) ofbiomass (97% as floatingmacrophytes) was harvested. This way, 176 g/week nitrogen and 47 g/week phosphorus wereeliminated by assimilation, corresponding to 25-35% of the system's inflow. Due to relatively high evapotranspiration rates (on average 35.4 mm/week) and for water reconditioning purpose in the fish stocking basins, fresh water was added. Nevertheless, the system's final effluent was very low (21% of total inflow plus rainfall) and was carrying only about 2% and 0.5% of the input loads of nitrogen and phosphorus, respectively. Hence, the elimination rate was significantly above the average performance of a conventional system normally applied in Middle Europe, althoughthe concentration values of most parameters in the outflow were comparable. Macrophyte production (and thus nutrient assimilation) was close to theoretical maxima in basins with high nutrient levels. Both plankton and fish growth were, at their best, only moderately satisfying. The semi-continual planktonic microalgae culture, and therefore also zooplankton culture, could be improved if the light absorbing humic substances were removed in a pre-treatment. Under given conditions (i.e., temperate climate) fish would rather play an accompanying role in the ecological production process. A wastewater-fed aquaculture facility resembles an integrated production plant rather than a wastewater disposal site. In addition to that, it has potential to prove advantageous over the highly developed conventional wastewater treatment plants established in Middle Europe. Further research in this field is essential and also recommended, considering political programs like Agenda 21, which contemplate the need for sustainable strategies for handling resources.

Morphology of Prorocentrum minimum (Dinophyceae) in the Baltic Sea and in Chesapeake Bay: Comparison of Cell Shapes and Thecal Ornamentation

Prorocentrum minimum (Dinophyceae) is a red tide-forming toxin-producing planktonic microalga from coastal waters worldwide. In this study, the morphology of natural and cultured populations of P. minimum was examined to investigate whether the species can be split morphologically into more species. The diacritical features of cell shape and size, ornamentation of thecal plates, and architecture of the apical pore area and intercalary band were studied from scanning and light micrographs. Cell size of P. minimum is similar in Baltic Sea samples and a culture from the Chesapeake Bay, USA. Cell shape varies from triangular to oval-round including intermediate forms in valve view. The thecal surface is covered by evenly distributed short spines, while the circular thecal pores are mainly situated near the valve margin. The intercalary band is rim-like, striated and covered with short evenly distributed spines. The architecture of the apical pore area is ornate and more complex than previously pointed out. It is V-shaped, located on the right valve in a shallow depression and accommodates a large elongated flagellar pore, and a small round auxiliary pore. Four distinct apical features are present: next to the auxiliary pore there is a curved collar, and adjacent to the flagellar pore arise a forked double tooth, a short single tooth, and a ridged edge near the left valve margin. Our study suggests that the ornamentation of the apical pore area of P minimum is independent of cell shape or growth place, and it is considered a stable morphological character of this cosmopolitan morphospecies.

The Role of Phytoplankton from the Ob River in Biological Productivity of the Ob–Yenisei Shoal

The program of investigations on the taxonomic composition and spatial distribution of planktonic microalgae in the Gulf of Ob and the southern Kara Sea in different seasons was carried out. Throughout the observation period, from July to October, high values of phytoplankton biomass were recorded in the Gulf of Ob and adjacent areas of the Ob–Yenisei shoal. This is evidence for a higher productivity of waters off the Ob estuary, compared to other coastal areas of the Kara Sea. The main factor responsible for this phenomenon is permanent (during the warm season) transport of living and dead organic matter by river runoff to the shelf.

Determination of limiting polyunsaturated fatty acids in Daphnia galeata using a new method to enrich food algae with single fatty acids

A new method that allows the highly reproducible supplementation of free fatty acids to planktonic microalgae was used to investigate the role of particular highly unsaturated fatty acids (PUFAs) in somatic growth limitation of Daphnia galeata feeding on Scenedesmus obliquus or Stephanodiscus hantzschii. No evidence for biotransformation of the supplemented fatty acids into other fatty acids by the algae was found. Using the algal cell itself as a transfer vehicle, the supplemented fatty acids were incorporated by D. galeata. In standardized growth experiments with juvenile D. galeata, growth on S. obliquus was improved by supplementation with the PUFAs α‐linolenic acid (α‐LA, 18:3n–3), eicosapentaenoic acid (EPA, 20:5n–3), and docosahexaenoic acid (DHA, 22:6n–3), but not by arachidonic acid (ARA, 20:4n–6), which illustrates that PUFAs should not be regarded as a single resource. Corresponding changes in the fatty acid pattern of D. galeata indicated that EPA is the limiting PUFA during growth on S. obliquus and that D. galeata converts DHA and C18‐PUFAs into EPA. Growth on S. hantzschii was not improved by supplementation with EPA and ARA but was with α‐LA, which indicates that α‐LA is the limiting PUFA and that EPA cannot be converted into α‐LA. These results suggest that the availability of EPA determines which PUFA is limiting for growth. Because of the ability of the daphnids to convert α‐LA into EPA, both PUFAs are substitutable resources under EPA limitation, but because EPA cannot be converted into α–LA, both PUFAs are nonsubstitutable resources under α–LA limitation.

Pyrolytic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis

Two kinds of autotrophic microalgae, Spirulina platensis (SP) and Chlorella protothecoides (CP) were pyrolyzed at the heating rates of 15, 40, 60 and 80°C/min up to 800°C in a thermogravimetric analyzer to investigate their pyrolytic characteristics. Three stages (dehydration, devolatilization and solid decomposition) appeared in the pyrolysis process. SP and CP mainly devolatilized at 190–560°C and 150–540°C, respectively. A total volatile yield of about 71% was achieved from each microalga. As the heating rate increased, a lateral shift to higher temperatures was observed in their thermograms, and the instantaneous maximum and average reaction rates in the devolatilization stage were increased while the activation energy was decreased. The value of activation energy for CP pyrolysis was 4.22–5.25×10 4, lower than that of SP (7.62–9.70×10 4), and the char in final residue of CP was 14.00–15.14%, less than that of SP by 2–3%. This indicated that CP is preferable for pyrolysis over SP. The experimental results may provide useful data for the design of pyrolytic processing systems using planktonic microalgae as feedstock.