Extracellular Release of Organic Matter from Two Freshwater Diatoms

The ¹⁴C-labelled extracellular materials released from culturesof Synedra acus and Stephanodiscus hantzschii were separatedby paper chromatography. The major components were identifiedand their rates of release measured. Stephanodiscus in axenicculture released the same extracellular materials under optimumlight conditions as did the natural population from which thediatom was isolated. The major extracellular product of Stephanodiscuswas glycollate; polysaccharide and amino acids were also released.The major extracellular product of Synedra was polysaccharide;amino acids were also released, but no glycollate. Under lightintensities so high as to inhibit photosynthesis the arraysof extracellular substances were unchanged, but some rates ofrelease were reduced. The array of products and the rates ofrelease from Stephanodiscus in darkness are quite differentfrom extracellular release during photosynthesis. Glycollaterelease from Stephanodiscus is greatest when the cultures areyoung and growing rapidly, older cultures release less.     

A Light Microscope Study of Carposporophyte Development in Gracilaria verrucosa (Hudson) Papenfuss

Gracilaria verrucosa is a very common marine red alga of Greekcoasts. The diploid carposporophyte which develops attachedto the female gametophyte of Gracilaria is described. The immaturecystocarps are very small while the mature ones are globose,ostiolate and are borne profusely all over the surface of thethallus. The earliest observed fusion cell is small and fusesprogressively with adjacent vegetative cells to form a largemultinucleate cell. From this fusion cell gonimoblast initialsoriginate, dividing further and giving rise to a large numberof gonimoblast cells. The resultant carposporophyte consistsof a basal-central, multinucleate cell surrounded by a conicalor hemispherical mass of gonimoblast cells. Chains or clustersof successively maturing carpospores are borne from the terminalgonimoblast cells. The liberation of mature carpospores takesplace through the ostiole of the cystocarp. The liberated carposporeslack cell walls and are naked in a mucilage mass. Gracilaria verrucosa (Hudson) Papenfuss, Gigartinales, Gracilariaceae, Rhodophyta, carposporophyte, development     

The effect of irradiance and irradiation time on the size of initial cells in vegetative cell enlargement of Coscinodiscus wailesii (Centrales, Bacillariophyceae) in culture

The effect of irradiance and irradiation time were examined on rates of pseudo-auxospore formation and the size of initial cells in vegetative cell enlargement of the giant diatom Coscinodiscus wailesii Gran in culture. The mean rate of pseudo-auxospore formation ranged from 25.9% to 47.8% between experimental incubation conditions. No significant difference was detected in rates among different irradiances and irradiation times, and parent cell sizes. However, the mean valve diameter of the initial cells of the diatom was affected by an interaction between the light conditions and the diameter of the parent cells. Initial cells size tended to be larger with combined conditions of higher irradiance levels and longer irradiation time. There appears to be a relationship (a steady increase, although not a straight line) between the total daily irradiance and the valve diameter of the initial cells. The mean valve diameter of initial cells from larger parent cells was significantly larger than those from smaller parent cells under the same light conditions.     

Physico-chemical control of the growth of a diatom, Asterionella formosa Hass., in a shallow eutrophic lake

Physico-chemical environmental control of the growth rate ofan algal population, the pennate diatom Asterionella formasaHass., was investigated for a year in natural water. This speciesoccurred in vegetative form in the water column all the time,although its population density varied by five orders of magnitudefrom a maximum of 1.4?10⁶ cells l^–1 in February to a minimumof 0.8?10¹ cells l^–1 in August. A mathematical model ofa combination of multiplicative and Liebig types suggested thatvegetative cells were severely limited in their growth rate,reaching almost 80% depression of the maximum rate between Decemberand February by low temperatures and nearly 50% depression inwarm seasons by light intensity. Nutrient limitations were onlyobserved in May, August and September, although they were notas great as by temperature and light intensity in the studylake. Population changing rates of A.formosa determined in thelake were low and agreed well with the estimated growth ratesduring winter, but those in summer were low and disagreed withthe estimated high growth rates. This suggests that populationchange of the species was highly dependent upon the specificgrowth rate in winter, but other factors became predominantin summer.     

The Changing Shape of Plant Cells: Transformations During Cell Proliferation

Shapes of ideal cells can be inspected for the dynamic, or gnomonic,feature of producing daughter cells of the same shape. Suchfeatures can be found for (a) elongating epidermal cells, (b)isdiametrically enlarging epidermal cells, (c) elongating parenchymatouscells and (d) parenchymatous cells enlarging in three dimensions.Since each cell passes through a series of changes to finallyassume the form of the parental cell, a gnomonic cell must passthrough a gnomonic sequence of shapes during the cell cycle.A model tissue composed of gnomonic cells has complete stabilityof form through subsequent generations. Each of six parameters of ideal cells can be inspected in realcells in order to evaluate the effects of deviations from theideal on the stability of tissue pattern. (1) Cell plates ofreal and ideal cells do not expand for one generation. (2) Theangles in vertices of real cells shift over three cell cyclesfrom 170.1° to 137.3° to 124.0°, values close tothe expected set of 163°, 133° and 120° (3) Cellplates of real cells are not perpendicular to the longitudinalaxis of the cell. (4) Real cells do not divide synchronouslyas do ideal cells. (5) Real cells do not divide equally in halfas do ideal cells. (6) Finally, ideal cells have the same durationof the cell cycle whereas real cells have cycle times inverselyrelated to the initial size of the cell. It appears that a population of meristematic cells do not adhereto the restrictions of ideal cells, and consequently a significantamount of variance of form is added at each generation. Thereare two compensating mechanisms, one to hold size variationin check and one to keep shape deviations under control. Becauseof the probabilistic nature of cell division, cells increasein volume at various rates while the cell edges of all cellsexpand at a constant rate, indicating that the latter is theprimary element of growth while facet area and cell volume increasein dimension only for accommodation. Cell shape, gnomonic cells, Aponogeton elongatus, Lupinus alba     

THE NATURAL LIFE CYCLE IN WILD POPULATIONS OF DIATOMA MONILIFORMIS (BACILLARIOPHYCEAE) AND ITS DISRUPTION IN AN ABERRANT ENVIRONMENT1

We studied how size variation in populations of Diatoma moniliformis Kütz. was influenced by environmental effects on the diatom life cycle. One of the two populations sampled monthly in the northern Baltic Sea grew under natural conditions; the other population was in a cooling water discharge channel of a nuclear power plant, where the temperature and flow rate of the water were artificially higher. The life cycle was synchronous at the natural site, with sexual reproduction occurring in the winter; most of the initial cells were found in March-April. After this, a reduction in cell size occurred, and the vegetative life cycle consisted of two parts. During the first part, cell volume decreased, whereas the surface area to volume ratio increased, and during the second part of the cycle, both of these parameters decreased. No direct evidence was found for the existence of a supra-annual life cycle in D. moniliformis, as convincing modes fm large cells were lacking in the size-frequency distributions. It was concluded from extrapolations of the data that the natural life cycle of D. moniliformis probably lasts 2 or 3 years. The changes in cell proportions during the life cycle fit well with annual growth cycles of D. moniliformis at the natural site (i.e. the cells had high surface area to volume ratios during the period of optimal growth in late spring [May-June]). At the site affected by cooling water discharge, the synchronization of the natural life cycle was disrupted, but some seasonal size variation did occur. Under natural conditions, auxosporulation is probably triggered by a combination of small cell size, low water temperature (0–3° C), and rapidly increasing light intensity or daylength in late winter to early spring. When these conditions were not met (e.g. at the heated site, the required low temperature was absent), auxosporulation did not occur simultaneously. This paper also presents scanning electron photomicrographs showing the typical shape and fine structure of the initial cell of D. moniliformis. These cells are semispherical in cross section, possess a pronounced curvature along the longitudinal axis, and are bent in the perualvar plane.     

Field assessment of the potential of algicidal bacteria against diatom blooms

The possible use of algicidal bacteria for the efficient termination of natural freshwater diatom blooms with minimal adverse effects on the freshwater ecosystem was assessed under laboratory and field conditions. A field mesocosm (150 L) was dosed with a single application of isolate SK09, and monitored at Samnang jin in the lower part of the Nakdong River (South Korea) over 12 days of the winter season. We found that the tested bacterium acted against some species of Stephanodiscus- and Aulacoseira-like structures on in vitro and in vivo diatom blooms. However, this bacterium failed to fully control in vivo natural blooms of Stephanodiscus due to the low water temperatures of less than 10°C and predation activity of protozooplankton (heterotrophic nanoflagellates and ciliates). In addition, its selective inhibition indirectly affected the decrease of dissolved oxygen levels, the dramatic regeneration of N and P by the large-scale Stephanodiscus-lysing process, and a great increase in algal biomass of genera Chlamydomonas. This strongly suggests the necessity of developing an effective strategy for enhancing the activity of algicidal bacteria, and for mitigating some drawbacks to effectively and safely regulate natural diatom blooms.     

Observations on girdle bands during cell division in the diatom Stephanodiscus

The fate of old girdle bands and the formation of new bands in the centric diatom Stephanodiscus are discussed. The use of scanning electron microscopy is a great aid in such studies since it enables observation of complete cells and determination of the position and overlap of girdle bands. It appears that both parent girdle bands are lost during cell division and two new bands formed around each daughter cell.     

Phytoplankton aggregate formation: observations of patterns and mechanisms of cell sticking and the significance of exopolymeric material

Flocculation of ‘sticky’ phytoplankton cells intorapidly sinking aggregates has been invoked as a mechanism explainingmass sedimentation of phytoplankton blooms in the ocean. Phytoplanktonstickiness, defined as the probability of adhesion upon collision,is one key factor determining the potential for aggregate formation.In the laboratory, we examined variation in stickiness in fivespecies of diatoms and two species of flagellates grown in batchcultures. We also investigated the production of paniculatemucus by phytoplankton cells and its role in aggregate formation,and we studied the effects of solute exudates on cell stickiness.Four of the five diatoms investigated were significantly sticky,while one diatom and both of the flagellates were not sticky.Stickiness varied considerably within species. In the diatomSkeletonema costatum, the typical but not entirely consistentpattern was that stickiness decreased with age of the batchcultures. We were otherwise unable to establish consistent relationshipsbetween cell stickiness and the growth stage of the algae, environmentalconcentrations of inorganic nutrients, and abundances of suspendedand epiphytic bacteria. We showed that the diatom S.costatumat times excretes a solute substance that depresses flocculation.This may reduce cell losses from the euphotic zone during thegrowth phase due to flocculation and sedimentation. We demonstratedtwo different mechanisms of phytoplankton aggregate formation.In the diatom S.costatum, the cells are sticky in themselves,and coagulation depends on cell-cell sticking and does not involvemucus. Aggregates are composed solely of cells. Cells of thediatom Chaetoceros affinis, on the other hand, are not in themselvessticky. Transparent exopolymeric particles (TEP), produced bythe diatom, cause the cells to aggregate and coagulation dependson TEP-cell rather than cell-cell sticking. Aggregates are formedof a mixture of mucus and cells. We found several species ofdiatoms and one flagellate species to produce copious amountsof TEP. TEP from some species (e.g. Coscinodiscus sp.) is stickyand may cause other, non-sticky particles to coagulate. Thisemphasizes the potential importance of diatom-derived paniculatemucus for particle flocculation in the ocean.     

Some Observation on the Alga Fragilaria crotonensis Kitton and its Parasitism by Two Chytridiaceous Fungi

It has been shown by experimentation that two morphologicallydistinct clones of Fragilaria crotonensis Kitton, isolated fromthe plankton of Windermere at approximately the same time, wereaffected quite differently by the chytrid Rhizophydium fragilariaeCanter. In one case the diatom filaments became heavily parasitizedand could be used for the maintenance of the fungus. In theother case infection was negligible. Additional clones, representative of these two morphologicalforms, from other bodies of water in the Windermere drainagebasin were tested. The same pattern of infection or relativenon-infection again ensued in direct accordance with the particulartype of filament used. Some preliminary experiments undertaken with a second, as yetlittle known chytrid parasite of F. crotonensis are reported.In this instance the fungus appeared to find its natural hoston cells belonging to the morphological form which failed tosupport the continued increase of R. fragilariae. The parasitism of morphological variants of F. crotonensis bythese fungi in the wild from Britain and else where is discussed. Fragilaria crotonensis Kitton, Rhizophydium fragilariae Canter, chytrid, diatom, parasitism, culture     

A probabilistic model of cell size reduction in Pseudo-nitzschia delicatissima (Bacillariophyta)

The pennate planktonic diatom Pseudo-nitzschia delicatissima is very common in temperate marine waters and often responsible for blooms. Due to its surrounding rigid silicate frustrule the diatom undergoes successive size reduction as its vegetative reproduction cycle proceeds. Since a long time the life cycle of diatoms has raised scientific interest and some years ago extensive samples of Pseudo-nitzschia have been taken from coastal waters. Mating and cell size reduction experiments were carried out and served us as a data basis for a probabilistic model of cell size reduction.We applied a homogenous non-stationary continuous-time Markov chain to model the development of individual diatoms from an initial size of about until cell death which occurred when the size reached its low at about . In contrast to conventional curve fitting models we are capable of calculating confidence intervals for estimates of the population ages as well as integrate the process of auxospore formation into the model. We thus propose a unique way to describe the stationary size distribution in a diatom population in terms of cell division and auxospore formation probabilities of its individuals.     

A Study of Two Morphological Variants of the Diatom Fragilaria crotonensis Kitton using Electron Microscopy

Two forms of Fragilaria crotonensis Kitton, one with flaredends to the cells, the other with ends that taper to a narrowrod-like tip, were previously distinguished by light microscopyand by their contrasting relationships with the parasitic chytridsRhizophydium fragilariae Canter and one referred to as species3. Examples of the above diatom types, taken from a number ofgeographically widely separated lakes, have been examined byelectron microscopy. Additional morphological differences aredescribed. The ocellus in flared-type cells consists of 4–5rows of pores while in rod-type cells fewer (2–3) rowsof pores are present. Valve thickenings on the mantle at theapex of rod-type cells are rarely visible whereas in flared-typecells they are usually very prominent. A rimoportula was presentin both cell types. In flared cells its external aperture liesimmediately behind the apex usually in line with the striaeand the internal aperture is often orientated with its longaxis oblique to that of the diatom cell. The rimoportula inrod-type cells opens at the centre of the valve face and theinternal aperture is orientated at 90° to the apical axisof the valve. Comparison made with type material suggests thatthe rod-form should be recognized as F. crotonensis var. crotonensisand the flared-form as var. prolongata Grunow ex van Heurck. Fragilaria crotonensis, diatom, systematics, chytrid infection, rimoportula     

Serial Development of Foliar Gemmae in Tortula (Pottiales, Musci), an Ultrastructural Study

The development and liberation mechanism of foliar gemmae havebeen studied by electron microscopy in two mosses, Tortula latifoliaBruch and Tortula papillosa Wils. The gemmae develop on theadaxial surface of mature leaves from single initial cells onboth the lamina and costa in T. latifolia but only on the costain T. papillosa . Elongation of the initial cell is associatedwith the deposition of a highly extensible new wall whilst theold wall and cuticle in the apical dome rupture. The first divisionis transverse and separates a short basal cell embedded in thefoliar tissue and a distal cell, or gemma primordium, protrudingfrom the leaf surface. Subsequent divisions of the gemma primordiumgive rise to a six-to-eight-celled globose gemma with mucilaginousouter walls. During gemma development the basal cell producesa new wall and elongates again whilst the common wall with thegemma splits apart centripetally along the boundary betweenthe old and new wall in the basal cell; plasmodesmal connectionsare gradually severed and eventually the young gemma remainsconnected to the basal cell only by mucilage. After separationof the first-formed gemma, the basal cell may expand and producea second gemma by the same mechanism. The whole process maybe repeated several times resulting in the formation of a chainof gemmae stuck together by mucilage and which are liberatedonly when the leaves are fully hydrated. Accumulation of abundantlipid deposits in the gemmae after symplasmic isolation reflectsconsiderable photosynthetic autonomy. Abscission; bryophytes; cell wall formation; plasmodesmata; vegetative reproduction     

Variation in hatching success and egg production of Eurytemora affinis (Calanoida, Copepoda) from the Gulf of Bothnia, Baltic Sea, in relation to abundance and clonal differences of diatoms

We monitored the hatching frequencies and clutch sizes of Eurytemoraaffinis, and environmental variables in the Gulf of Bothnia,between May and October 2003. We tested the hypothesis thatthe hatching frequency of the copepod would be negatively affectedduring time periods with high diatom concentrations. Resultsfrom two stations showed significant differences between thedifferent sampling occasions, with the lowest observed hatchingfrequency during the spring diatom bloom. The reverse was truefor clutch size, with the highest average egg number duringthe diatom bloom. These results were not correlated to ambienttemperature, salinity or chlorophyll a (Chl a). In a separatelaboratory experiment, nine different local clones of the diatomSkeletonema costatum were used as food for adult E. affinisfemales, in order to screen for possible differences in toxicitywithin the Skeletonema community. The resulting average copepodhatching frequency varied between 5 and 75% for the differentclones, indicating that there can be large within-species variationin the toxic properties of diatoms. The significance of suchvariations in natural communities remains to be tested in futurestudies.     

Infection of Coscinodiscus granii by the parasitoid nanoflagellate Pirsonia diadema: III. Effects of turbulence on the incidence of infection

The influence of turbulence on the incidence of infection ofthe diatom Coscinodiscus granii by the parasitoid nanoflagellatePirsonia diadema was investigated experimentally with two initialhost densities. Independently of the initial diatom densitiesof 7 and 44 cells ml^–1, under calm conditions both diatomsand parasitoids became extinct within 6–9 days. Turbulence,however, led to the survival of diatoms at a reduced densityof 0.1–2 cells ml^–1 for >30 days. A population-dynamicmodel is formulated that takes into account the non-homogeneousdistribution of infecting flagellates among host diatoms. Applicationof the results to parasitoid–diatom interactions in naturalwaters suggests that, under turbulent conditions, endemic infectionsmay effectively prevent the mass development of host diatoms.     

An Analysis of Seed Development in Pisum sativum: IV. COTYLEDON CELL POPULATIONS IN VIVO AND IN VITRO

A method for quantifying changes in the cell population of Pisumsativum cotyledons during development is described. The methodis based on determining the frequency distribution for cellarea following the random sampling of a single-cell suspensionof cotyledon cells. The population profile of these cells changedprogressively and systematically from a single population, similarin size to meristematic cells, found in embryos less than 3.0mg in fresh weight, to a bimodal population in embryos greaterthan 100 mg fresh weight. This method was used to compare embryosof similar size from two genotypes near-isogenic except forgenes at the r locus. No significant differences were foundbetween the cell population profiles of embryos up to 30 mgfresh weight. However, a significant difference was found betweenembryos with fresh weights of 100 mg, the wrinkled (rr) linehaving a higher mean and maximum cell area (2 951 µm²and 9 240 µm² respectively) than the round (RR) line (2591µm²and 6470 µm²respectively). Comparisons were alsomade between cotyledon cell populations from round (RR) embryosgrown in vivo and in vitro. The most obvious differences werethe higher mean and maximum cell size of the large cell populationof in vitro grown embryos which were twice those found in vivo.Embryos grown to either 30 mg or 100 mg fresh weight in vitrohad a much greater proportion of large cells in the populationwith a corresponding reduction in total cotyledon cell number,compared with similar sized embryos grown in vivo. These data suggest that comparisons between different genotypes,or, between cultured and in vivoembryos, based on morphologicalsimilarities between embryos, may be invalid and subject tomisinterpretation. Key words: Pea, seed development, cell population     

Studies on the Development of the Air Pores and Air Chambers of Marchantia paleacea: 1. Light Microscopy

The ontogeny of the air pores and air chambers of Marchantiapaleacea begins with the schizogenous development of protodermalintercellular spaces of the initial apertures, and is completedwith the formation of the air pores and giant sub-epidermalair chambers bearing numerous photosynthetic filaments. Intercellularspace formation commences from the thallus surface and proceedsinwards to the first internal layer of cells. The cells amongwhich spaces develop do not originate from one mother cell.Spaces are formed only in the regions of the intersection ofthe anticlinal walls of three, four, or sometimes more successivederivatives of S₁, S₃ and S₄ segments of the apical cell, oneor two of which have been divided periclinally and the restanticlinally. Protodermal intercellular spaces appear in mostor all the corners of these cells, the anticlinal walls of whichexhibit an opposite disposition. The S₁, S₂, S₃ and S₄ segmentsare produced by definite divisions of a five-sided apical celland by a series of divisions give rise to initial cells of theinternal layers of the thallus and initial cells of the protodermaland sub-protodermal layers. The concept of a quiescent apicalcell cannot be accepted, since dividing apical cells have beenobserved, and the pattern of wall disposition of the thallusapex cannot be explained without the active participation ofthe apical cell. The air chambers are apparently of exogenous origin. They resultfrom the broadening of the bottom of the initial apertures bythe coordination of the rate of anticlinal divisions and growthof the protodermal and sub-protodermal cells surrounding theintercellular spaces of the initial apertures. The ontogenyof the pore rings starts at an advanced stage of air chamberformation not from a mother cell but from the cells which surroundthe closed entrance of the air chamber, by a shift of the planeof division from anticlinal to periclinal. Before the periclinaldivisions a new axis of growth perpendicular to the thallussurface is established in the mother cells of the pore. By a polarized growth into the air chamber followed by periclinaldivisions, the cells of the floor form initial cells of thephotosynthetic filaments. The latter divide again to form singleor branched photosynthetic filaments. Marchantia paleacea, air pore, air chamber     

Sex Ratios and Resource Allocation among Sexually Reproducing Plants of Rubus chamaemorus

Sex ratios and patterns of size variation and resource allocationwere investigated in the dioecious species Rubus chamaemorus.Sex ratios among flowering ramets varied from 6% to 40% of females.Female ramets were slightly, although not significantly, tallerthan males. It appeared that population effects (including bothgenetic population and environmental site effects) on plantsize and allocation patterns at flowering are considerably greaterthan sex effects. If both flowering and fruit production areconsidered, then female allocation to reproduction clearly exceedsmale allocation. In females, no significant relationship wasdetected between the mass of reproductive and vegetative tissues,while males did exhibit such a relationship. Reproductive effortwas less for tall males than for small males. Despite the occurrence of sexual reproduction, the main modeof reproduction in R. chamaemorus is vegetative propagation,which is the best strategy for reproduction in the unpredictableclimate of high latitudes but which leads to skewed sex ratios.As a consequence of vigorous vegetative reproduction, individualclones can grow to be large. The results of electrophoreticstudies show that the numbers of clones per population are low.Copyright1994, 1999 Academic Press Rubus chamaemorus, cloudberry, sex ratios, resource allocation, clonal structure, electrophoresis     

In situ egg production and hatching success of the marine copepod Pseudocalanus newmani in Funka Bay and adjacent waters off southwestern Hokkaido, Japan: associated to diatom bloom

. Clutch size and egg viability were examined for wild femalesof Pseudocalanus newmani collected from four different stationsinside and outside Funka Bay, southwestern Hokkaido, Japan,during pre-phytoplankton-bloom conditions in 1997, and froma single station outside the bay during the period from pre-to post-blooming seasons in 1998, to examine spatio-temporalvariability of the reproductive parameters and to detect deleteriouseffects of diatom blooms on in situ copepod reproduction. Clutchsize and hatching success in P.newmani were relatively similarat the four stations in 1997. The eggs almost always hatchedcompletely, but deformed nauplii occurred in 20–40% ofthe cases. The proportion of deformed nauplii gradually decreasedwhen the females were fed on non-diatom Pavlova sp. in the laboratory,suggesting that the occurrence of deformed nauplii was relatedto the quality of in situ food particles, including diatoms.Clutch size varied from 12 to 30 eggs female^–1 duringthe study period in 1998; more than 90% of the variation couldbe explained by the body size of the females which dependedon ambient water temperature. Hatching success also varied,from 15 to 80%, but was not related to either clutch size, femalebody size, water temperature or diatom biomass. These resultssuggest that not only egg production but also hatchability shouldbe measured routinely when estimating recruitment of the copepodinto the planktonic population, and show that neither clutchsize nor egg viability are directly affected by diatom biomass.Although we could not obtain clear evidence of in situ deleteriouseffects of diatoms on abnormal embryos and nauplii, this mightbe related to methodological problems and properties or characteristicsof prey–predator interactions. Also, deformities of copepodnauplii have not yet been observed for reasons other than feedingon diatoms.     

A daily study of the diatom spring bloom at Roscoff (France) in 1985. III. Free amino acids composition studied by HPLC analysis

The growth of a natural phytoplankton population was studiedduring a monospecific spring bloom of the diatom Rhizosoleniadelicatula at Roscoff (western English Channel). Direct examinationof the intracellular pool of 19 free amino acids (FAA) was usedas an index of the physiological status of the cells. TotalFAA in the particulate matter shows a general decrease duringthe bloom, and FAA cell content varies from 200 mM 1 cell volume^–1to 10 mM at the time of maximum biomass. FAA-N/particulate Nis <3% during the study, slightly decreasing at the timeof maximum biomass. Individual free amino acids appear reliablefor the development of the diatom biomass and good indicatorsof the growing population. At maximum biomass, major compoundsare glutamic acid (30.8 mol%), glutamine (11.7%), alanine (9.9%),isoleucine (6.6%) and lysine (6.4%). Serine, glycine, arginineand aspartic acid appear also as major components during otherperiods of the study. We suggest that the observed changes arean indication of the physiological state of the cells duringthe bloom. In particular glutamine (GLN), glutamic acid (GLU)and the GLN/GLU ratio allow the metabolic evolution of the naturalpopulation to be characterized. GLN is strictly linked to theliving biomass (Chla) while GLU is present at high percentagethroughout the study. The ecological significance of ß-alanine(BALA) is also revealed during this study, being strongly correlatedto degraded matter represented by phaeopigments. These resultsdemonstrate the validity of using individual free amino acidsas an aid in understanding the physiological status of algaein natural bloom conditions.