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Life history and in situ growth rates of Alexandrium taylori (Dinophyceae, Pyrrophyta)
Abstract
Alexandrium taylori Balech is a phototrophic marine dinoflagellate. It produced recurrent blooms during the summer months (July and August) of 1994 to 1997 in La Fosca beach (NW Mediterranean). In addition to a motile vegetative form, A. taylori had two benthic forms: temporary cysts and resting cysts. Temporary cysts were a temporally quiescent stage produced from the ecdysis of the vegetative cell in both natural populations and laboratory cultures. Temporary cysts may divide to form motile cells. Resting cysts had a thicker wall than the temporary cysts and had a red accumulation body. Gametes and planozygotes were also observed in laboratory cultures. Alexandrium taylori showed in situ diurnal vertical migration with an increase of vegetative cells in the water column in the morning through midday, with concentrations peaking in the afternoon followed by lower levels at night. Most vegetative cells lost their thecae and flagella, and with them their motility, turning into temporary cysts that settled in the early evening. The number of temporary cysts in the water column rose in the evening and at night. The temporary cysts gave rise to motile cells the following morning. Synthesis of DNA occurred in vegetative cells at night, and a preferential period of cell division occurred at sunrise. The estimated division rate in the field was 0.4-0.5 vegetative cells · day-1. Temporary cysts had twice the DNA of a G1 vegetative cell. The minimum in situ division rate of the temporary cysts was 0.14 day-1. The role of the resting and temporary cyst population in the annual recurrence and maintenance of the A. taylori bloom is discussed.
... Furthermore, natural field populations of microalgae typically exist in a complex assemblage of phototrophic, heterotrophic, and mixotrophic protists that can overlap in cell size and DNA content, making a target species difficult to separate out for cell cycle analysis by FCM, particularly when the target species is not numerically dominant in the community. These factors have limited the use of FCM for cell cycle analysis of field populations of microalgae, with notable exceptions (Boucher et al. 1991;Vaulot and Partensky 1992;Liu et al. 1998), and provided the impetus for using microfluorometry instead (Vaulot and Partensky 1992;Yamaguchi 1992;Liu et al. 1997;Garcés et al. 1998Garcés et al. , 1999Gisselson et al. 1999;Van Dolah and Leighfield 1999;Garcés and Masó 2001). Microfluorometry is a microscope slide-based technique wherein a light microscope equipped with a fluorescence spectrophotometer is used to allow visual selection and quantitative measurement of stained DNA fluorescence of nuclei in single cells, one cell at a time. ...
... A closable aperture allows the operator to optically exclude nontarget cells and cytoplasmic DNA. However, this method is time consuming as it requires measurement of one cell at a time, which typically results in only 200-300 cells being measured and relatively high coefficients of variation (CV; coefficient of variation = [peak SD Ä mean] × 100) on the fluorescence peaks for G1 and G2 phases (Cetta and Anderson 1990;Garcés et al. 1998Garcés et al. , 1999Garcés and Masó 2001). ...
... While the ICM G1 peak CV (10.3%) was higher than the FCM CV (6.4%) for the field samples, it nevertheless fell within an acceptable range (< 15%) (Boucher et al. 1991;Veldhuis et al. 1997;Ormerod et al. 1998;Parrow and Burkholder 2003a). Furthermore, CVs are typically not reported for field data on bloom cell cycle phase distribution (Vaulot and Partensky 1992;Garcés et al. 1998Garcés et al. , 1999Garcés and Masó 2001). Even if that is the case, overestimation of the percentage of G1-phase cells when determining in situ growth rates would only result in a lower (i.e., more conservative) estimate of specific growth rates (μ). ...
The goal of this work was to develop and demonstrate the utility of microscope‐based image cytometry (ICM) as a method for quantifying nuclear DNA content and cell cycle phase distribution in microalgae both in culture and in natural blooms, as an alternative to flow cytometry (FCM). To do so, aliquots from the same samples of the dinoflagellate Karlodinium veneficum were examined using both ICM and FCM. ICM specimen preparation and data acquisition methods were optimized to improve precision and agreement between the two techniques. Accuracy and precision of DNA measurements by ICM were significantly higher using the DNA fluorophore DAPI compared to SYBR® Green I. Milli‐Q H2O was found to be superior to Tris‐EDTA as a staining and slide preparation solution for ICM analyses. Lower‐powered objective magnification (10x, 20x) in image acquisition for ICM produced higher precision in nuclear DNA measurements. Overall precision of ICM analysis of DAPI‐stained K. veneficum cells was comparable to FCM, with respective 1C DNA peak coefficients of variation as low as 6.2%. Cell cycle distributions of mid‐log culture samples analyzed by both ICM and FCM were in agreement (two‐way ANOVA; p = 0.93); while distributions analyzed in a field sample were similar but not identical (Z‐test; p < 0.001). Overall, the results show the feasibility of ICM as a useful tool for microalgal cell cycle analysis, with the potential for more flexible application to mixotrophic/phagotrophic species and complex field populations.
... Until recently, this interpretation was accepted (e.g. Figueroa & Bravo 2005;Garcés et al. 1998;Walker 1984). In general, a vegetative cell was divided by binary fission to form two new cells during the planktonic stage (Figueroa et al. 2007;Pfiester & Anderson 1987). ...
... However, asexual division of F. mexicanum is characterised by eleutheroschisis. This type of asexual division was reported for F. cf duplocampaniforme and other dinoflagellates, including A. taylori Balech, A. hiranoi Kita & Fukuyo, A. pseudogonyaulax (Biecheler) Horiguchi ex Yuki & Fukuyo and Kryptoperidinium foliaceum (Stein) Lindemann (Amorim et al. 2013;Garcés et al. 1998;Montresor 1995;Zmerli Triki et al. 2015). ...
... This pattern coincides with previous observations of the excystment of sexual coccoid stages controlled by diel changes (e.g. Garcés et al. 1998 1995). The ecological significance of the life history of these Alexandrium species is related to saving energy and time (Figueroa et al. 2008;Giacobbe & Yang 1999). ...
We describe the life cycle, morphology and molecular phylogenetic position of Fragilidium mexicanum, based on vegetative cells established by incubation of resting cysts isolated from sediment trap samples collected at Jinhae–Masan Bay, Korea. Resting cysts of F. mexicanum were spherical and surrounded by transparent mucilage, similar to other Fragilidium species. Germinated vegetative cells were identified as F. mexicanum based on thecal morphology and tabulation; the plate formula was Po, Pc, 4ʹ, 8″, 10c, 6s, 7ʹʹʹ, 1p, 2ʹʹʹʹ. Molecular phylogenetic analyses of sequence data for small and large subunits of ribosomal DNA genes revealed that Fragilidium species were monophyletic with high supports and that F. mexicanum formed a separate clade with Fragilidium sp. (JQ317599). Time-lapse photography was used to clarify the life history. Isolated resting cysts germinated into an unarmoured planomeiocyte and directly formed the pellicle cyst, with an armoured planomeiocyte emerging from the pellicle cyst. The armoured planomeiocyte underwent ecdysis and formed a coccoid meiocyte, with a two-celled chain emerging from the coccoid meiocyte. Like the armoured planomeicyte, vegetative cells also underwent ecdysis and then divided into two daughter cells that eventually emerged as motile vegetative cells. The life cycle of F. mexicanum has nonmotile life history stages that regularly alternate with motile stages. The nonmotile stage consists of five forms: resting cyst, pellicle cyst, asexual coccoid stage, coccoid meiocyte, and zygote. The motile stage also has five forms: unarmoured and armoured planomeiocyte, planozygote, gamete and vegetative cell.
... The inoculum can derive from several sources and may involve different life stages. [148][149][150] Smayda and Reynolds 68 summarized sources of blooms by presenting three categories: holoplanktonic, meroplanktonic, and advected sources. Holoplanktonic infers that the source population exists all year long at low concentrations and has a wide temperature tolerance; it does not however mean that there is not a sexual cycle or that the maintenance life stage is a vegetative cell. ...
... Studies on ecdysal cysts of Pfiesteria piscicida, 165 Pseudopfiesteria shumwayae, 166 and Alexandrium taylori 150 have considered this stage as part of the asexual reproduction. However, there are other studies on Pfiesteria, cryptoperidiniopsoids, and Lingulodinium polyedrum that show temporary cysts as a product of the sexual cycle. ...
... Production of ecdysal cysts could be advantageous as it allows a stock of the population to be stored in sediments. 150,168 Moreover, it has been suggested that temporary cysts in the Alexandrium genus could be a means to avoid predation or attack by viruses, bacteria, and parasites. 168 Furthermore, survival of temporary pellicle cysts of dinoflagellates in mussel and oyster feces has been proposed as indicative that such processes may serve as a means of potential dispersion of the species. ...
... G. impudicum was observed at five beaches ( Figure 5, Table 1), the majority of them in the Oristano Gulf ( Figure 5). The maximum density of G. impudicum was 7.4 Â 10 3 cells L À1 at Torregrande II (29). L. polyedrum and P. reticulatum were observed at five and seven beaches, respectively ( Figure 5, Table 1), but were not notably more common in any particular area. ...
... Most of the information about the Mediterranean coasts is derived from studies of specific species, e.g. Alexandrium taylorii [28][29][30][31][32], naked dinoflagellates [33][34], Ostreopsis species [20,35-37 and references therein], or taxa grouped by certain common characteristics, such as benthic species [38][39]. Only limited data are available on the entire set of harmful species [40]. ...
... In Sardinia, this species has been reported at Platamona [41], and its presence was confirmed at Valledoria and La Speranza beaches (C.T. Satta, personal communication). The adverse events associated with A. taylorii on beaches along the Mediterranean coast have increased in recent years [28][29][30][31][32]41]. Our results indicate that A. taylorii may be the causative agent of HABs, either alone or in mixed blooms with other problematic species. ...
The presence and distribution of harmful algal species were investigated along the coasts of Sardinia in the summer of 2012. Fourteen potentially noxious taxa were identified at 74 beaches. The majority of the recovered taxa were potentially toxic and/or high biomass producers. Alexandrium taylorii, Gymnodinium instriatum, and Ostreopsis cf. ovata were the most frequent and abundant taxa, although Barrufeta bravensis reached the highest density (4.4 × 106 cells L−1). Barrufeta bravensis, A. taylorii, and G. instriatum were responsible for intense water discoloration at two of the beaches sampled. Polymerase chain reaction (PCR) analyses supported the identification of several taxa and decisively identified B. bravensis. PCR assays increased the information available on the species distributions. The locations studied were heterogeneous in their prevailing environmental conditions and their morphodynamic profiles. Statistical analyses indicated that the distributions of harmful algal species correlated with gravel and medium-fine sand substrata. These data provide substantial knowledge on the distributions of harmful algal species on beaches, which have been poorly studied on a global scale. The apparent relationship between noxious species and grain size suggests that vegetative cells may be recruited from cyst beds in beach sediments.
... Formation of cysts in dinoflagellates is commonly associated with sexual stages of reproduction (von Stosch 1973, Yoshimatsu 1981, Pfiester and Anderson 1987; therefore, understanding the timing of these stages and environmental factors associated with the process is important in defining the potential for blooms. Stages of sexual reproduction for cyst producing species include gametes, fusion of gametes and zygote formation (Dale 1983, Garcés et al. 1998, Persson et al. 2008. Both endogenous and exogenous conditions, such as mandatory dormancy periods, or fluctuations in light or temperature, can lead to cyst germination, potentially leading to the formation of blooms (Anderson and Kiefer 1987, Ishikawa and Taniguchi 1997, Kremp and Anderson 2000, Kim et al. 2002, Moore et al. 2015. ...
... In terms of light conditions, sexual stages in dinoflagellates have been observed during the dark phase in algal culture experiments (von Stosch 1973), during short photoperiods (Sgrosso et al. 2001). In some species temporary cyst formation has been observed at night, followed by motile cell formation in the early morning (Garcés et al. 1998). Other researchers have found that higher than optimal irradiances can enhance encystment in some species (von Stosch 1964, Blackburn et al. 1989. ...
This study reports on the harmful algal bloom (HAB) dinoflagellate Akashiwo sanguinea in the upper, mid and lower Caloosahatchee estuary, Florida during monthly sample events at four sites from February 2009 through February 2010. Akashiwo sanguinea cells were microscopically quantified throughout the course of the study and scanning electron microscopy was used to confirm certain life stage observations. Water temperature and salinity were recorded for each collection. A rare observation of a major sexual reproduction event was made from water samples collected in situ during February 2009. This sample event included 600 cells ml⁻¹ of small cells, 25 cells ml⁻¹ of perpendicularly connected cells in the fusing position, 17 cells ml⁻¹ of planozygotes, cells surrounded by mucoid halos and asexual pairs. Structures consistent with a fertilization tube in the apical or sulcal regions of the small cells were also observed. A bloom of A. sanguinea vegetative cells was observed in the upper estuary in May with cell densities near 700 cells ml⁻¹ and again in June with densities greater than 300 cells ml⁻¹. Results provide insights into environmental conditions during the occurrence of reproduction stages and vegetative cell blooms of A. sanguinea.
... Kim et al. (2002) reported that exposure to light and high temperature stimulated the germination of temporary cyst of C. polykrikoides, indicating the light is one of the factors for triggering the germination of temporary cysts. In addition, the temporary cysts of other species also transform into vegetative cells within 24 h, however, in contrast to other dinoflagellates that produce single temporary cysts (Anderson, 1980;Garcés et al., 1998;Olli et al., 2004;Rintala et al., 2007), C. polykrikoides produces chain-forming temporary cysts, and the two-celled chain forming vegetative cells (germlings) develop from a single four-celled chains of temporary cysts. This indicates that C. polykrikoides can maintain a greater growth rate than other dinoflagellates. ...
... Thus, the maintenance of dense blooms in Korean coastal areas may be due to a combination of vegetative cell growth, and rapid and consecutive germination of chain-forming vegetative cells from temporary cysts. Garcés et al. (1998Garcés et al. ( , 1999 argued that a decrease of the motile bloom population of A. taylori can be compensated by rapid germination of temporary cysts within 24 h. Consequently, the formation of temporary cysts can contribute to maintenance of population size during dense blooms . ...
While the initiation and development of dense bloom of Cochlodinium polykrikoides have been shown to be related to some environmental factors, little is known about the ecological role of the formation and germination of temporary cysts, nor of their significance for the rapid expansion of dense regional-scale blooms. This study examined the factors affecting the formation and germination of temporary cysts of C. polykrikoides, and provides details about the germination process. In the laboratory experiments, C. polykrikoides produced the chain-forming temporary cysts that are immobile and surrounded by a hyaline membrane. The encystment experiment indicated that darkness induces the formation of chain-forming temporary cysts, consistent with field observation of morphology and fluxes of temporary cysts. Germination occurred twice from a single four-celled temporary cysts within 24 h after exposure to light, and the germlings appeared as two-celled chain-forming vegetative cells. The germination behavior of temporary cysts of C. polykrikoides differs from that of other dinoflagellates, and this may be a survival strategy for the maintenance of population size during dense blooms.
... Marasović (1989) found temporary cysts of Gonyaulax polyedra Stein formed in Kaštela Bay (located at the eastern Adriatic coast) when environmental conditions changed dramatically, which was important for the persistence and recurrence of the blooms of this species. Garcés et al. (1998) reported that temporary cysts could play a pivotal role in the maintenance of massive blooms of Alexandrium taylori Balech in the north-west Mediterranean coast [21,22]. ...
... Marasović (1989) found temporary cysts of Gonyaulax polyedra Stein formed in Kaštela Bay (located at the eastern Adriatic coast) when environmental conditions changed dramatically, which was important for the persistence and recurrence of the blooms of this species. Garcés et al. (1998) reported that temporary cysts could play a pivotal role in the maintenance of massive blooms of Alexandrium taylori Balech in the north-west Mediterranean coast [21,22]. ...
The harmful algal bloom (HAB)-forming dinoflagellate Karenia mikimotoi was exposed to different nitrogen (N) conditions, in order to study the population growth, temporary cyst production and cellular biochemical compositions in laboratory. The results indicated the population growth of K. mikimotoi was inhibited by different levels of N starvation but showed similar fast recovery after the resupplement of N, and temporary cysts were induced in the period of N starvation. K. mikimotoi grew well in inorganic (NO3⁻, NO2⁻ and NH4⁺) and organic (urea) nitrogen sources, but the growth parameters (K, Tp, r) showed differences when simulated by Logistic model regressions. When the cellular organic compounds were measured simultaneously, K. mikimotoi cultured in urea produced more short-chained fatty acids while K. mikimotoi cultured in NH4⁺ produced more non-fatty acids compounds, indicating the potential change of toxins production cultured by various N sources. We concluded that K. mikimotoi could adapt to fluctuating N environments typical of coastal environments including total N concentration (deficiency or recovery) and relative compositions (different N sources).
... Only analysis of Noctiluca from sam ples stored in liquid nitrogen under a fluorescence microscope made it possible to identify these objects as planktonic autotrophic dinoflagellate cysts. A more accurate identification of these cysts based on pub lished data [14,15,26] showed that the most similar in size and shape are temporary cysts of the algae genus Alexandrium (Fig. 7). There are several species of the genus in the Black Sea (A. minutum, A. tamarense, A. ostenfeldii, and A. monilatum); all of them are toxic and contain so called paralytic shellfish poison (PSP) [6,16]. ...
... Calculating the total consumption of phytoplankton production by the N. scintillans population, we took into account the contribution of cysts, as in [15] it was shown that temporary cysts of Alexandrium taylory can divide, the minimum division rate was 0.14 per day. These data indicate that temporary dinoflagellate cysts, as vegetative cells, participate in primary production pro cess, and it would be incorrect to exclude them from calculations. ...
Studies were conducted at the end of June 2011 in the coastal region of
the northeastern part of the Black Sea. The bulk of the Noctiluca
scintillans population was observed in the thermocline and reached a
density of 40000 ind./m3. Analysis of digestive vacuoles
content showed that Noctiluca could consume cells of Neoceratium tripos
and N. furca, which had been considered inedible for Black Sea
zooplankton, as well as temporary cysts of dinoflagellates, presumably
of the toxic genus Alexandrium. The Noctiluca population consumed in
total 10-30% of the abundance of temporary cysts, 2-29% of primary
production, and 2-9% of potential Calanus euxinus egg production. For
the first time, the excretion rates of ammonium nitrogen and mineral
phosphorus were measured for N. scintillans. Our calculations showed
that in summer, excretion by Noctiluca contributed from 4 to 18% and
from 15 to 53% of phytoplankton total nitrogen and phosphorus
requirements, respectively. The specific growth rate of Noctiluca
(0.17-0.35) in summer, estimated from data on the daily food intake and
respiration rate, was close to the values obtained in spring.
... Under epifluorescence, these bodies exhibited an intense red autofluorescence characteristic of chlorophyll. These orange bodies may represent incipient accumulation bodies, which are widely described in the literature on dinoflagellate cysts (von Stosch, 1973;Garcé s et al., 1998;Giacobbe and Yang, 1999;Figueroa et al., 2006aFigueroa et al., , 2007Figueroa et al., , 2008Satta et al., 2013). In our experiments, orange accumulation bodies did not seem to be associated to a particular life cycle stage. ...
... Thin-walled cysts are non-motile cells enclosed within a thin pellicle (single-layered wall) following the definition of Bravo et al. (2010). These cysts are generally considered short-term cysts and have been interpreted as non-zygotic, i.e. derived from the vegetative cycle Anderson and Wall, 1978;Garcé s et al., 1998;Delgado, 1999) or zygotic (Parrow and Burkholder, 2004;Figueroa and Bravo, 2005). Among thin-walled cysts we distinguished two types which differed for the shape, color and for the Calcofluor-White affinity of cell wall: in the first type (named 'A') the thin pellicle was not stainable with Calcofluor-White (Fig. 4A-D) and under the pellicle the typical morphology (drop shape and brownish-yellow coloration) of vegetative cells was visible (Fig. 4B); these cysts were formed through ecdysis (Fig. 4A), since we observed the presence of thecal fragments adhering to the top of the pellicle. ...
... The information regarding the potential defensive ability of dinoflagellate cysts is scarce, this is especially true for temporary cysts, which for a long time was regarded as sampling (Garcés et al. 2002) or culture artefacts, related to for instance ageing of cultures (Jensen & Moestrup 1997). However, temporary cysts have been observed in situ (Garcés et al. 1998; Xiao et al. 2001) or in large-scale mesocosm experiments (Olli 2004). Therefore, it has been suggested that temporary cysts should be considered as part of a natural life cycle of dinoflagellates (Garcés et al. 2002). ...
... Thereby, the amount of temporary cysts found in the euphotic zone during sampling represent the ones being just recently produced. On the other hand, 13-59 % temporary cysts (within a 24 h period) were observed in a natural population of Alexandrium taylori, with the highest values reported in the evening and at night when light intensities decrease (Garcés et al. 1998). This implies that the results concerning temporary cyst induction of S. trochoidea in response to low light intensities, may also be relevant in the field. ...
Many phytoplankton species have evolved a variety of different defenses to decrease losses from grazing; morphological features, changes in life-history/behavior, and production of toxins. These defenses may be associated with costs. Therefore, some phytoplankton only express the defense when needed, i.e. when grazers are present. The defense can be induced by direct contact with the grazer, or infochemicals released during grazing activities may function as reliable signals of grazer presence.
Morphological defenses were studied in the colony forming prymnesiophyte Phaeocystis globosa, in combination with varying nutrient status, such as nitrogen (N) and phosphorus (P) sufficiency, N deficiency and P deficiency. NP sufficient P. globosa remained mainly as solitary cells in response to infochemicals. The responses were more complex in the nutrient deficient experiments, due to the increased mortality of copepods observed, which may have resulted from lower food quality in nutrient stressed cells. This could affect both grazers and the infochemicals released, which could have been to weak to affect P. globosa. Morphological defenses include formation of digestion resistant gelatinous sheaths, which were examined in the chlorophyte Oocystis submarina. Direct, not indirect, exposure to copepods and cladocerans caused a shift towards cells and colonies with gelatinous sheaths. Thus, infochemicals played no role in these responses. The cyanobacterium Nodularia spumigena has two potential defense mechanisms; morphology (filament size/structure), and toxicity. These defenses are not induced by the direct or indirect presence of copepod grazers. However, N. spumigena increased the mortality of copepods, which was probably related to starvation. This may contribute to the success of N. spumigena blooms, as there could be a shift in grazing towards other phytoplankton species.
The combined effects of direct/indirect copepod exposure and low light conditions on the dinoflagellate Scrippsiella trochoidea life-history (e.g. temporary cyst formation) were examined. Induction of temporary cysts occurred in response to decreased light intensity, but not in response to copepods despite the fact that copepods showed decreased ingestion on temporary cysts. In low light situations, temporary cyst formation can be an effective tool to minimize population losses.
The results presented here contribute to the complex understanding of factors influencing phytoplankton-zooplankton interactions.
... Temporary cysts are found in natural populations of dinoflagellates, but their ecological role remains unclear (Olli 2004). Confusing matters further, some dinoflagellate species undergo asexual (Garcés et al. 1998) and sexual (Figueroa & Bravo 2005) division by ecdysis, forming cysts that closely resemble the temporary cysts caused by environmental disturbances. The function of temporary cysts as a short-term survival stage is still a hypothesis, based on laboratory findings that ecdysis is reversible: when the stress factor (nutrient, temperature , algicidal bacteria, etc.) is removed, excystment into vegetative cells occurs. ...
... Ecdysis may be an adaptation to remove colonized bacteria. In addition, a previous study of a related dinoflagellate (Alexandrium taylorii) which undergoes ecdysis as its normal cell division mechanism when nitrogen starved (Giacobbe & Yang 1999) found that temporary cysts increased in abundance during the night (Garcés et al. 1998). We tested whether bacteria-induced ecdysis also increases during periods of darkness. ...
We report the isolation of 3 novel bacterial strains from the Bacteroidetes group capable of inducing temporary cyst formation by ecdysis in the bloom-forming dinoflagellate Lingulodinium polyedrum. Phylogenetic analysis of 16S rRNA revealed that 2 of these strains are most closely related to previously identified algicidal bacteria, indicating potentially similar mechanisms of inter- action. Long-term (2 wk) co-incubations of algae and bacteria under a 12:12 h light:dark cycle resulted in decreased algal cell abundances (compared to bacteria-free controls) followed by tempo- rary cyst formation. Short-term incubations in continuous light resulted in no apparent effects of the bacteria over 2 d, but incubations in continuous darkness resulted in algal ecdysis after 24 h followed by significant decreases in total algal cell abundances after 52 h compared to controls without algici- dal bacteria. We also showed that ecdysis resulted in the removal of bacteria attached to the surface of the algal cells, demonstrating a potentially direct benefit to the algae if the bacteria are harmful. We further suggest that negative interactions of bacteria on phytoplankton may be enhanced in the absence of light.
... The initiation requires an inoculum of cells to seed the bloom. The inoculum can be from several sources and may involve different life stages depending on the organism involved (Garcés et al., 1998;. ...
Ostreopsis cf. ovata is a cosmopolitan toxic dinoflagellate that produces seasonal blooms. It is currently unknown how this organism divides or how its cell cycle is controlled. The aim of this thesis was to provide a cellular and molecular characterization of the mitotic cell cycle, which underlies cell proliferation during vegetative growth, for the dinoflagellate O. cf. ovata. Morphological classification of cells collected at different phases of the bloom, allowed to identify different phases of the O. cf. ovata vegetative cycle, including cells undergoing division. Using this classification, I showed that during blooming, O. cf. ovata divides exclusively at night. Using immuno-fluorescence and confocal microscopy, I then characterized the major changes in cytoskeletal organization associated with the O. cf. ovata cell cycle. To characterize O. cf. ovata cell cycle at the molecular level, I searched for O. cf. ovata homologues of conserved cell cycle regulators identified in model organisms, using a de novo transcriptome that I generated from cultured cells. This analysis revealed the presence of major components of the O. cf. ovata cell cycle. A differential expression analysis using meta-trascriptomic datasets corresponding to bloom samples enriched in interphase cells, pre-dividing cells and dividing, which I generated during the 2019 bloom, showed an active transcriptional control during cell division. By integrating the results obtained from the transcriptomic analysis with the cytological characterization I propose a first model of O. cf. ovata cell cycle, in which cyclins and CDK activities dictate the transition from interphase to mitosis.
... Intriguingly, melatonin treatment or changes in photoperiod induce pellicle cyst formation, providing an intriguing connection to the biological clock [20]. Furthermore, several in situ studies have shown that there is a cycle of pellicle cyst formation, possibly related to light cycles, in which encystment and excystment appear to be controlled by light [21,22]. Thus, although pellicle cysts are common among dinoflagellate species, the factors triggering the formation of pellicle cysts from motile cells (and vice-versa) are unclear. ...
Background
Dinoflagellates are a group of unicellular organisms that are a major component of aquatic eukaryotes and important contributors to marine primary production. Nevertheless, many dinoflagellates are considered harmful algal bloom (HAB) species due to their detrimental environmental and human health impacts. Cyst formation is widely perceived as an adaptive strategy of cyst-forming dinoflagellates in response to adverse environmental conditions. Dinoflagellate cysts play critical roles in bloom dynamics. However, our insight into the underlying molecular basis of encystment is still limited. To investigate the molecular processes regulating encystment in dinoflagellates, transcriptome and metabolome investigations were performed on cold and darkness-induced pellicle cysts of Scrippsiella trochoidea .
Results
No significant transcriptional response was observed at 2 h; however, massive transcriptome and metabolome reprogramming occurred at 5 h and in pellicle cysts. The gene-to-metabolite network demonstrated that the initial transformation from vegetative cells into pellicle cysts was highly energy demanding through the activation of catabolism, including glycolysis, β-oxidation, TCA cycle and oxidative phosphorylation, to cope with cold-darkness-induced stress. However, after transformation into pellicle cysts, the metabolism was greatly reduced, and various sugars, polyunsaturated fatty acids and amino acids accumulated to prolong survival. The identification of 56 differentially expressed genes (DEGs) related to signal transduction indicated that S. trochoidea received a cold-darkness signal that activated multiple signal transduction pathways, leading to encystment. The elevated expression of genes encoding enzymes involved in ROS stress suggested that pellicle cysts respond to increased oxidative stress. Several cell cycle-related genes were repressed. Intriguingly, 11 DEGs associated with sexual reproduction suggested that pellicle cysts (or some portion thereof) may be a product of sexual reproduction.
Conclusions
This study provides the first transcriptome and metabolome analyses conducted during the encystment of S. trochoidea , an event that requires complex regulatory mechanisms and impacts on population dynamics. The results reveal comprehensive molecular regulatory processes underlying life cycle regulation in dinoflagellates involving signal transduction, gene expression and metabolite profile, which will improve our ability to understand and monitor dinoflagellate blooms.
... The light exposure duration often modulates the organic matters accumulation and energy metabolism within cells [19,20]. Previous studies showed that the photoperiod regulates gene expression [21][22][23], cell division [24,25] and growth [11,16,17], and even bloom dynamics of phytoplankton [26,27]. To date, however, only a few studies have examined the interactive effects of temperature and photoperiod upon phytoplankton physiology and metabolism [11,[28][29][30][31]. ...
Shift of phytoplankton niches from low to high latitudes has altered their experienced light exposure durations and temperatures. To explore this interactive effect, the growth, physiology, and cell compositions of smaller Alexandrium minutum and larger A. catenella, globally distributed toxic red tide dinoflagellates, were studied under a matrix of photoperiods (light:dark cycles of 8:16, 16:8, and 24:0) and temperatures (18 °C, 22 °C, 25 °C, and 28 °C). Under continuous growth light condition (L:D 24:0), the growth rate (µ) of small A. minutum increased from low to medium temperature, then decreased to high temperature, while the µ of large A. catenella continuously decreased with increasing temperatures. Shortened photoperiods reduced the µ of A. minutum, but enhanced that of A. catenella. As temperature increased, cellular Chl a content increased in both A. minutum and A. catenella, while the temperature-induced effect on RubisCO content was limited. Shortened photoperiods enhanced the Chl a but reduced RubisCO contents across temperatures. Moreover, shortened photoperiods enhanced photosynthetic capacities of both A. minutum and A. catenella, i.e., promoting the PSII photochemical quantum yield (FV/FM, ΦPSII), saturation irradiance (EK), and maximum relative electron transfer rate (rETRmax). Shortened photoperiods also enhanced dark respiration of A. minutum across temperatures, but reduced that of A. catenella, as well as the antioxidant activities of both species. Overall, A. minutum and A. catenella showed differential growth responses to photoperiods across temperatures, probably with cell size.
... Intriguingly, melatonin treatment or changes in photoperiod induce pellicle cyst formation, providing an intriguing connection to the biological clock [20]. Furthermore, several in situ studies have shown that there is a cycle of pellicle cyst formation, possibly related to light cycles, in which encystment and excystment appear to be controlled by light [21,22]. Thus, although pellicle cysts are common among dino agellate species, the factors triggering the formation of pellicle cysts from motile cells (and vice-versa) are unclear. ...
Background: Dinoflagellates are a group of unicellular organisms that are a major component of aquatic eukaryotes and important contributors to marine primary production. Nevertheless, many dinoflagellates are considered harmful algal bloom (HAB) species due to their detrimental environmental and human health impacts. Cyst formation is widely perceived as an adaptive strategy of cyst-forming dinoflagellates in response to adverse environmental conditions. Dinoflagellate cysts play critical roles in bloom dynamics. However, our insight into the underlying molecular basis of encystment is still limited. To investigate the molecular processes regulating encystment in dinoflagellates, transcriptome and metabolome investigations were performed on cold and darkness-induced pellicle cysts of Scrippsiella trochoidea.
Results: No significant transcriptional response was observed at 2 h; however, massive transcriptome and metabolome reprogramming occurred at 5 h and in pellicle cysts. The gene-to-metabolite network demonstrated that the initial transformation from vegetative cells into pellicle cysts was highly energy demanding through the activation of catabolism, including glycolysis, β-oxidation, TCA cycle and oxidative phosphorylation, to cope with cold-darkness-induced stress. However, after transformation into pellicle cysts, the metabolism was greatly reduced, and various sugars, polyunsaturated fatty acids and amino acids accumulated to prolong survival. The identification of 56 differentially expressed genes (DEGs) related to signal transduction indicated that S. trochoidea received a cold-darkness signal that activated multiple signal transduction pathways, leading to encystment. The elevated expression of genes encoding enzymes involved in ROS stress suggested that pellicle cysts respond to increased oxidative stress. Several cell cycle-related genes were repressed. Intriguingly, 11 DEGs associated with sexual reproduction suggested that pellicle cysts (or some portion thereof) may be a product of sexual reproduction.
Conclusions: This study provides the first transcriptome and metabolome analyses conducted during the encystment of S. trochoidea, an event that requires complex regulatory mechanisms and impacts on population dynamics. The results reveal comprehensive molecular regulatory processes underlying life cycle regulation in dinoflagellates involving signal transduction, gene expression and metabolite profile, which will improve our ability to understand and monitor dinoflagellate blooms.
... Goniodomin A production by A. taylorii is of importance for the Mediterranean area where dense and recurrent blooms of this species occur [7,[11][12][13][14][15][16]. For GDA producing A. monilatum, blooms have been linked to mortality of finfish and/or shellfish [50,51]. ...
Species of the dinophyte genus Alexandrium are widely distributed and are notorious bloom formers and producers of various potent phycotoxins. The species Alexandrium taylorii is known to form recurrent and dense blooms in the Mediterranean, but its toxin production potential is poorly studied. Here we investigated toxin production potential of a Mediterranean A. taylorii clonal strain by combining state-of-the-art screening for various toxins known to be produced within Alexandrium with a sound morphological and molecular designation of the studied strain. As shown by a detailed thecal plate analysis, morphology of the A. taylorii strain AY7T from the Adriatic Sea conformed with the original species description. Moreover, newly obtained Large Subunit (LSU) and Internal Transcribed Spacers (ITS) rDNA sequences perfectly matched with the majority of other Mediterranean A. taylorii strains from the databases. Based on both ion pair chromatography coupled to post-column derivatization and fluorescence detection (LC-FLD) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis it is shown that A. taylorii AY7T does not produce paralytic shellfish toxins (PST) above a detection limit of ca. 1 fg cell−1, and also lacks any traces of spirolides and gymnodimines. The strain caused cell lysis of protistan species due to poorly characterized lytic compounds, with a density of 185 cells mL−1 causing 50% cell lysis of cryptophyte bioassay target cells (EC50). As shown here for the first time A. taylorii AY7T produced goniodomin A (GDA) at a cellular level of 11.7 pg cell−1. This first report of goniodomin (GD) production of A. taylorii supports the close evolutionary relationship of A. taylorii to other identified GD-producing Alexandrium species. As GD have been causatively linked to fish kills, future studies of Mediterranean A. taylorii blooms should include analysis of GD and should draw attention to potential links to fish kills or other environmental damage.
... This indicates that the formation of the chain-forming temporary cysts without asexual or sexual reproduction may be an efficient strategy in the sense of energy expenditure for the rapid germination of M. polykrikoides. Consequently, the formation of a temporary cyst in the life cycle of M. polykrikoides could provide a competitive strategy over other dinoflagellates, allowing increase of population size or to maintain the bloom status in the field (e.g., Garcés et al. 1998Garcés et al. , 1999Shin et al. 2017). ...
Although the life cycle of Margalefidinium polykrikoides, formerly called Cochlodinium polykrikoides, has been described previously, the descriptions on asexual and sexual phases of this species collected from Korean coastal waters are strange and still unclear. We collected the resting cysts of M. polykrikoides from surface sediments and reexamined the germination process, and asexual and sexual life stages, and the mating behavior of the vegetative cells using a microscope equipped with high-resolution time-lapse digital camera. The resting cyst of M. polykrikoides had a distinct germination process; before germination, a mature cell in shape was visible within the resting cyst body, and the cell quickly emerged from the resting cyst. The asexual reproduction and cell chain formation of M. polykrikoides were generated in a slightly oblique direction at the epicone of cell and the chain-forming cells of M. polykrikoides could form the chain-forming temporary cysts without asexual or sexual reproduction. The planozygote produced by gamete fusion of M. polykrikoides may not necessarily develop to resting cysts but instead may divide into vegetative cells occasionally. In this phase, the armored cell, which was previously recorded by Kim et al. (2007), was not observed. The sexuality of M. polykrikoides had a homothallic mating behavior.
... Reference: 1, Jeong et al. (2015); 2, Lee et al. Lewis et al. (2006); 10, this study; 11, Kang et al. (2018); 12, Blossom et al. (2017); 13, Jacobson and Anderson (1996); 14, Cembella et al. (2000); 15, Fraga et al. (1989); 16, Jeong et al. (2005b); 17, Yoo et al. (2009);18, Karp-Boss et al. (2000); 19, Garcés et al. (1998); 20, Kita and Fukuyo (1988). not feed on them. ...
Mixotrophy in marine organisms is an important aspect of ecology and evolution. The discovery of mixotrophic abilities in phototrophic dinoflagellates alters our understanding of the dynamics of red tides. In the phototrophic dino-flagellate genus Alexandrium, some species are mixotrophic, but others are exclusively autotrophic. There are differences in the ecological roles of autotrophic and mixotrophic Alexandrium in marine food webs. However, of the 34 known Alexandrium species, the mixotrophic ability of >20 species has yet to be explored. In this study, the mixotrophic capabilities of Alexandrium insuetum CCMP2082, Alexandrium mediterraneum CCMP3433, Alexandrium pacificum CCMP3434, Alexandrium tamutum ATSH1609, and Alexandrium margalefii CAWD10 were investigated by providing each species with 22 diverse prey items including bacterium-sized microbeads (1 μm), the cyanobacterium Synechococ-cus sp., algal prey species, and the ciliate Mesodinium rubrum. None of the 5 Alexandrium species fed on any of the prey items. These results increase the number of Alexandrium species lacking mixotrophic abilities to 9, compared to the 7 known mixotrophic Alexandrium species. Furthermore, the Alexandrium phylogenetic tree based on the large subunit ribosomal DNA contained 3 large clades, each of which had species with and without mixotrophic abilities. Thus, the acquisition or loss of mixotrophic abilities in Alexandrium might readily occur.
... However, the role of pellicle cysts in the life cycle or reproduction of P. bahamense has not yet been fully understood in the field. Pellicle cysts of other thecate dinoflagellates A. hiranoi (Kita et al., 1985), A. pseudogonyaulax (Montresor, 1995), and A. taylori (Garces et al., 1998) were observed to undergo asexual reproduction. Garces et al. (2002) suggested that pellicle formation as seen in A. taylori served two purposes, namely reduction of population loss and increasing population stock. ...
Associated and algicidal bacteria play roles in the succession and decline of phytoplankton blooms, including those of harmful algal bloom (HAB)-forming species. Limited studies on HAB-associated bacterial ecology have resulted in our incomplete understanding of HABs dynamics. Diverse phytoplankton-bacterial interactions have also led to studies on their potential as biocontrol tools for HABs mitigation. Here, we tested 48 cultivable pelagic bacteria from three HAB-affected areas in the Philippines (Bolinao, Sorsogon, and Matarinao) against non-axenic cultures of the toxic, thecate dinoflagellate Pyrodinium bahamense. Co-incubation with live cultures of these isolates exhibited varying levels of algicidal activities suggesting that it may not be a phylogenetically conserved property. Furthermore, majority of the isolates elicited activity against the thecate test species P. bahamense, which was not present in the area where the bacteria were isolated, implying non-specificity of action. Exposure to bacterial cells resulted in Pyrodinium pellicle cyst formation. Despite this, however, cell lysis and decline in total cell abundance were still observed, indicating strong algicidal potency of the isolates. In depth understanding of the interplay between environmental factors and algicidal bacteria-microalgal interactions may provide significant insights on the management of HABs.
... Photoperiod is an important cyclic variable because it can regulate algal metabolic processes through responses to day-or night-lengths, light levels and spectra, individually or in combination (Helbling et al., 2003;Li et al., 2009, and can entrain the cells to a daily rhythm (Brand and Guillard, 1981;Shi et al., 2015;Li et al., 2016a,b;Xie et al., 2018). For example, the division of dinoflagellate Amphidinium carterae occurs at the onset of dark period (Li et al., 2016a,b); and the division cyst of Amphidinium hiranoi preferentially forms in the dark, settles down to sediments and releases two flagellated daughter cells in early light phase (Kita et al., 1985;Garcés et al., 1998). Yet, few studies have to date examined the interactive effects of different photoperiods and light levels upon dinoflagellate metabolism and physiology (Baeka et al., 2008;Mayfield et al., 2014;Shi et al., 2015). ...
... Photoperiod is an important cyclic variable because it can regulate algal metabolic processes through responses to day-or night-lengths, light levels and spectra, individually or in combination (Helbling et al., 2003;Li et al., 2009, and can entrain the cells to a daily rhythm (Brand and Guillard, 1981;Shi et al., 2015;Li et al., 2016a,b;Xie et al., 2018). For example, the division of dinoflagellate Amphidinium carterae occurs at the onset of dark period (Li et al., 2016a,b); and the division cyst of Amphidinium hiranoi preferentially forms in the dark, settles down to sediments and releases two flagellated daughter cells in early light phase (Kita et al., 1985;Garcés et al., 1998). Yet, few studies have to date examined the interactive effects of different photoperiods and light levels upon dinoflagellate metabolism and physiology (Baeka et al., 2008;Mayfield et al., 2014;Shi et al., 2015). ...
... This production of mucus appears to be created by collaboration of many cells, perhaps to keep the cells together and avoid dispersal (Margalef, 1997) during blooms as suggested for diatom species (Kiørboe and Hansen 1993). Aggregations of cells, particularly cysts of A. taylorii have been seen before, although these were not necessarily associated with mucus (Garcés et al., 1998(Garcés et al., , 1999. Only a small amount of H. rotundata and T. acuta cells got stuck in the mucus; however, there was no evidence of ingestion, and prey capture is thus unlikely the purpose of mucus production by A. taylorii. ...
... Quando le condizioni ritornano favorevoli, le cisti temporanee possono ripristinare la popolazione motile (vegetativa) in seguito a divisione cellulare. Le cellule vegetative di A. taylori sono capaci di migrazioni diurne verticali producendo addensamenti negli strati superficiali della colonna d'acqua in tarda mattina fino a raggiungere il massimo nel primo pomeriggio per poi ritornare verso il fondo nelle ore notturne (Garcés et al., 1998). ...
The problem of spreading in the Mediterranean Sea of invasive macrophytes
allocthonous, in particular of Caulerpa taxifolia, has important implications in terms of
preservation of biodiversity. Present studies have been undertaken, along the sicilian
coast of the Strait of Messina, on the composition and structure of macrozoobenthic
communities associated to Caulerpa taxifolia. The present research aims to give a
contribute to the problem of changes, caused by the alga spreading, in the composition
and structure of benthonic communities, with particular regard to mollusca and
polychaeta assemblages.
... However, the failure of most gene expression -based HCL support trees to resolve the difference between mid-day and afternoon triplicates of the AL3T -AL1T and AL9T -AL1T-comparisons indicate that a similar lack of phased physiological conditions might occur in other A. minutum strains grown under the same conditions, although we did not examine the timing of cell division and toxin production in the other strains in this study. Both laboratory cultures and field population of different Alexandrium species are known to be primarily in G1 throughout most of the light period or daylight time [28,81,82]. Thus, combining data from two different time-points during light phase should capture differences in the mRNA pool of toxic and nontoxic strains during PSP toxin production while excluding strain-specific differences in circadian responses not related to toxin production. ...
Background: The dinoflagellate Alexandrium minutum typically produces paralytic shellfish poisoning (PSP) toxins, which are known only from cyanobacteria and dinoflagellates. While a PSP toxin gene cluster has recently been characterized in cyanobacteria, the genetic background of PSP toxin production in dinoflagellates remains elusive. Results: We constructed and analysed an expressed sequence tag (EST) library of A. minutum, which contained 15,703 read sequences yielding a total of 4,320 unique expressed clusters. Of these clusters, 72% combined the forward-and reverse reads of at least one bacterial clone. This sequence resource was then used to construct an oligonucleotide microarray. We analysed the expression of all clusters in three different strains. While the cyanobacterial PSP toxin genes were not found among the A. minutum sequences, 192 genes were differentially expressed between toxic and non-toxic strains. Conclusions: Based on this study and on the lack of identified PSP synthesis genes in the two existent Alexandrium tamarense EST libraries, we propose that the PSP toxin genes in dinoflagellates might be more different from their cyanobacterial counterparts than would be expected in the case of a recent gene transfer. As a starting point to identify possible PSP toxin-associated genes in dinoflagellates without relying on a priori sequence information, the sequences only present in mRNA pools of the toxic strain can be seen as putative candidates involved in toxin synthesis and regulation, or acclimation to intracellular PSP toxins.
... En effet, des toxicités atypiques (c'est-à-dire une mortalité des souris injectées sans qu'aucune toxine connue n'ait pu être identifiée par des analyses chimiques) ont parfois été mises en évidence, comme cela a été le cas dans le Bassin d' (Arzul et al., 1999). (Sekida et al., 2001) : elle semble être faiblement perméable (Montresor, 1995 ;Garcés et al., 1998) et résistante à de nombreux agents chimiques (Morrill et Loeblich, 1981). Les kystes temporaires résistent par exemple à la digestion lors de leur consommation par les bivalves : ils ont été observés dans le système digestif (Laavir et al., 2007) ainsi que dans les fécès et pseudo-fécès (Hégaret et al., 2007c). ...
The effects of the toxin-producing dinoflagellate, Alexandrium minutum, upon the Pacific oyster, Crassostrea gigas, were assessed through an integrative approach including behavior, digestion cellular activities and reproduction. In a first time, physiological status of A. minutum was assessed using flow cytometry, microscopy and fluorescent dyes. This allows us to demonstrate that some experimental conditions can be stressful for this dinoflagellate. Experimental systems were adapted to minimize adverse conditions for harmful micro-algae. In a second time, oysters were exposed under laboratory conditions to A. minutum in several experiments and compared to control oysters fed Isochrysis sp. or Heterocapsa triquetra. The shell-valve behavior of C. gigas responded to A. minutum exposure with increased duration of time open and frequency of incomplete closures. Histological observations revealed myopathy in the adductor muscle (myoatrophy, wavy muscle fibers and hyaline degeneration), which is consistent with observed behavioral modifications. Furthermore, a positive correlation was observed between duration of time shell valves were open and quantity of accumulated toxins. A. minutum exposure resulted in activation of defense mechanisms. Increase in mucus production in gills, as well as an inflammatory response in the digestive gland, were observed in A. minutum-exposed oysters. Hemocyte characteristics and functions were also changed. Significant differences, in terms of phenoloxidase activity (PO) and reactive oxygen species (ROS) production of hemocytes, were observed between A. minutum-exposed and control oysters. Hemocyte responses to in vivo A. minutum exposure depended upon reproductive status and toxin accumulation, but also upon metabolic activity during the experiment. Lipid contents in the digestive gland were also affected upon A. minutum exposure. Significant decreases in monoacylglycerol (MAG) and diacylglycerol (DAG) contents, as well as a drastic decrease in phosphatidylcholine (PC) content in digestive glands of oysters exposed to A. minutum were observed. Decrease in PC along with reduction of MAG and DAG is thought to be related to a decrease in lipid synthesis because of tissue alterations in the digestive gland. Finally, male oysters exposed to A. minutum produced less-active spermatozoa (lower motility and ATP content) compared to control oysters. This reduction in gamete metabolism may have implications in term of reproduction success. As observed changes were sometimes subtle, and all measured variables were inter-connected, the integrative approach allowed a holistic vision of interactions between this harmful-algal species and the Pacific oyster. This study revealed previously unknown interactions between behavioral, morphological, and physiological characteristics of oysters, thereby allowing a better understanding of the interaction between HABs and bivalves, and the potential ecological consequences.
... All stages were observed in sibling culture and asexual division was characterized by eleutheroschisis division. This type of benthic division has been reported for other species such as A. taylori, A. hiranoi, and Kryptoperidinium foliaceum (Montresor 1995, Garc es et al. 1998). In most Alexandrium species (Alexandrium affine, A. tamarense, A. catenella, and A. peruvianum), asexual reproduction occurs naturally in the motile stage by sharing the thecal plates, a process known as desmoschisis. ...
Studies considering the biology and ecology of the toxic bloom-forming species, Alexandrium pseudogonyaulax, are rare. Our results highlight five features not described before in A. pseudogonyaulax life cycle: a) A. pseudogonyaulax gametes showed two modes of conjugation, anisogamy and isogamy b) sexual conjugation occurs either in the dark or in the light phase by engulfment or a fusion process c) the presence of planozygote and newly formed cysts in monoclonal culture suggests homothallism d) newly formed cysts have very dark vesicular content and are mostly unparatabulated when observed under light microscope and e) natural resting cysts are able to give either a planomeiocyte or two vegetative cells. Cyst viability was enhanced after five months of cold storage (4°C), with excystment rate reaching 97% after 3 d of incubation. Excystment rate was highest (43-79%) in Enriched Natural Sea Water diluted culture medium whereas few germling cells were able to survive without the culture medium (0-13%). Salinity-irradiance experiments revealed that the highest cell concentrations occur at high irradiances for all the tested salinities. Vegetative growth rates generally increased with increasing irradiance, and was less dependent on salinity variations. The relatively low growth rate, low cell densities in the laboratory and the notable capacity of producing cysts along growth phases of A. pseudogonyaulax could explain the occurrence of high resting cysts densities in the sediment of Bizerte lagoon and the relatively low abundances of vegetative cells in the water column.This article is protected by copyright. All rights reserved.
... Anderson and hypothesized that the asexual, short-lived cysts of A. tamarense (Lebour) probably do not play an important role in initiating toxic blooms, a process otherwise related to resting sexual cyst germination. However, short-lived cysts might be crucial for the blooming of other species, such as Alexandrium tailory Balech or L. polyedrum ( Garcés et al. 1998, Figueroa and Bravo 2005b). In A. taylori, a daily recruitment of temporary cysts from the sediment might be used as a strategy to avoid massive population losses during the shorewards coastal flow in protected beaches ( Basterretxea et al. 2005). ...
Sexuality and cyst formation were studied in the marine dinoflagellate species Gymnodinium catenatum Graham, Gymnodinium nolleri Ellegaard ? Moestrup, Alexandrium catenella (Whedon et Kofoid) Balech, and Lingulodinium polyedrum (Stein) Dodge. The study included the morphological characterization of sexual stages and processes, the time and description of meiosis, the study of the length and regulation of the mandatory dormancy period of resting cysts, and the relationships among parental strains and cyst progeny at phenotypic and molecular levels. In the species A. catenella, the effect of nutritional factors on the encystment and excystment of in culture were analysed. The mobile zygotes were observed to encyst significantly more in replete medium than in media depleted or half-depleted in nitrate and phosphate levels. On the other hand, the resting stage germinated faster placed in seawater than in medium replete or half-replete in nitrate and phosphate levels. For the species L. Polyedrum was described the previously unknown sexual cycle, which revealed the existence of two kinds of zygotes, since the planozygotes encysted either as a short-lived (<4 days), or as a long-lived (several months) cyst form. The sexual cycle and mating type behaviour of G. nolleri was also reported. A Principal Component Analysis provided evidence for a pattern of inheritance of the dormancy period in cysts. Furthermore, the inheritance of a short dormancy period, dominant over long and medium periods, was shown through two subsequent generations of cysts. The PCA analysis further indicated that there was an inverse relationship among genetic distance between compatible strains (calculated by means of an AFLP analysis) and viability of the offspring, and among cyst size and cyst production. In two of the dinoflagellate species (G. nolleri and G. catenatum), which do not undergo nuclear cyclosis, a meiotic process was described for the first time, that was linked to the viable division of the mobile zygote in a cyst-producing species. In both species, the encystment of the planozygote was modulated by external nutritional factors, which also affected the viability and morphology of the resting cyst. Two different mating systems were observed in G. catenatum (homothallism and complex heterothallism).The RAPD-AFLP technique found that there was intra-clonal genetic variation in G. catenatum strains, though the degree was inversely proportional to the homothallic behaviour. This fact might explain the important changes that the sexual behaviour of the siblings underwent with time, and the variable response in both cyst production and progeny viability of these strains.
... El «mare sporco» italiano, una ingente producción de fitoplancton con gran secreción de compuestos mucilaginosos (Herndl, 1992), causó pérdidas millonarias en el sector turístico de las costas de Emilia Romagna (noroeste del Mar Adriático) en 1989, y produjo atascos en las agallas de los peces y daños a la flora y fauna silvestre . El color pardo-verdoso de las manchas, totalmente inocuas, del pequeño dinoflagelado Alexandrium taylorii en algunas playas de Cataluña (España), en el Mediterráneo occidental (Garcés et al., 1998), es interpretado (erróneamente) por los turistas como una señal de contaminación y de aportes de aguas residuales; el abandono de las playas con manchas por los visitantes estivales causa así importantes pérdidas de ingresos a los pequeños hoteles de la zona. Las floraciones de Chaetoceros concavicornis han provocado mortandades de salmones en jaulas en la costa noroeste de Estados Unidos por la fricción mecánica de las setas espinosas de esta diatomea, que irritan las agallas, provocan segregación de mucus y acarrean hipoxia en la sangre de los peces (Bell, 1961; Rensel, 1993). ...
... Whereas many species of Gonyaulax (Entz 1904, Kofoid 1911, Hickel and Pollingher 1986, Dodge 1988, Amylax (Dodge 1988), Alexandrium (Tomas 1974, Walker and Steidinger 1979, Figueroa et al. 2007, 2008, Ceratium (e.g., Entz 1904, Elbrächter 1973, Happach-Kasan 1982, as well as other genera of Gonyaulacales such as Ceratocorys (Entz 1904, Netzel et al. 1978, Protoceratium (Braarud 1945), Pyro dinium (Buchanan 1968), or Goniodoma (e.g., Williams 1970, Netzel 1982) have been shown to divide by desmoschisis, a number of exceptions are found among the Gonyaulacales. These include eleuteroschisis in Pyrophacus ( Montresor andMarino 1994, Pholpunthin et al. 1999) and in division cysts of Alexandrium pseudo gonyaulax (Biecheler) Horiguchi ex Kita et Fukuyo ( Montresor 1995), A. hiranoi Kita et Fukuyo (Kita et al. 1993), and A. taylori Balech (Garces et al. 1998). Cell division in a division cyst after ecdysis has also been reported in the genus Fragilidium (von Stosch 1969, Skovgaard 1996. ...
Azadinium spinosum is a planktonic dinoflagellate, and a source of azaspiracids, a group of lipophilic
toxins of human health concern. Little is known about the biology of this genus, and its phylogenetic position
within the Dinophyceae is not yet fully resolved. Here, we present detailed observations regarding its vegetativecell division. As a first sign of cell division, the round interphase nucleus enlarges and becomes elongate in a slightly oblique orientation. The nucleus then divides along its longitudinal axis. Cytokinesis of A. spinosum occurs in motile cells and is of the desmoschisis type, i.e., the parental theca is shared between the two sister cells. Divided cells completely separate before the thecal plates are fully replaced. The anterosinistral daughter cell keeps the parent cell’s apex, including the apical pore complex and all the apical and epithecal intercalary plates, whereas the posterodextral daughter cell keeps, among others, both antapical plates. In general, the course of the fission line follows the plate overlap pattern and is, with a few exceptions, similar to other species of the Gonyaulacales. A literature survey shows that both desmoschisis
and eleuteroschisis have been described for Gonyaulacales and Peridiniales, which suggests that mode of division may not be a good ordinal criterion for classification.
... As unicellular organisms, the growth of phytoplankton population results directly from the completion of the cell cycle. Therefore, cell division cycle analysis provides a promising method (the Cell Cycle Approach) to study in situ growth rate Carpenter, 1988, 1991;Garcé s et al., 1998) when one or more cell cycle markers are available (Vaulot, 1995). ...
... Over the subsequent 10 days both stages tended to have similar densities. Temporary cyst formation has usually been associated with unfavourable environmental conditions but for A. taylori the temporary cyst is an intrinsic stage of its life cycle (Garcés et al., 1998). The sticky nature of the temporary cyst of A. taylori facilitates the formation of clusters (Fig. 2d), that permit the population to remain at the bottom and overcome short-term unfavourable meteorological conditions (Garcés et al., 2002). ...
Macroscopic observations of floating plastic debris collected at several places along the Catalan coast (northwestern Mediterranean) showed conspicuous green-yellow patches adhered to them. The microscopic examination of these patches showed that they were constituted mainly of benthic diatoms and small flagellates ( Ostreopsis sp. and Coolia sp., resting cysts of unidentified dinoflagellates and both temporary cysts and vegetative cells of Alexandrium taylori were also found. Plastic debris is considered to be one of the most serious problems affecting the marine environment. We suggest drifting plastic debris as a potential vector for microalgae dispersal.
... The reason for this consistent difference in encystment behavior between the CCMP2357 isolates and the others was unknown. Active clustering of cells during temporary encystment occurs for unknown reasons and by unknown mechanisms in several genera of dinoflagellates (Lombard & Capon 1971, Ucko et al. 1997, Garcés et al. 1998, Parrow et al. 2002, Parrow & Burkholder 2003a. ...
Geographically distinct strains of the heterotrophic dinoflagellate Pfiesteria shumwayae were cultivated on a fish cell line in the apparent absence of bacteria and other microbial contaminants. Cultures were established with a high rate of success by inoculating single purified P. shumwayae cells into fish cell cultures containing a simple saltwater medium suitable for both cell types, and resulting isolates were serially cultivated on fish cells for months without visible signs of abnormality or reduced viability. P. shumwayae fed phagocytically on the fish cells and exhibited higher cell production than reported using other culturing methods. Compared to previous methods of studying the interaction between Pfiesteria spp. and fishes, this system enabled closer and more direct observation of the dinoflagellates and was also more economical and sustainable as a culturing method. The absence of bacteria and other contaminating microorganisms should facilitate important physiological and biochemical investigations. The methods used were inadequate for cultivating strains of P. piscicida, suggesting a possible difference in nutritional requirements between the 2 Pfiesteria species.
... In addition, the model permitted the calculation of meaningful S. lachrymosa vegetative cell growth and encystment rates. The model should be tested with other species of dinoflagellates and must be extended if temporary cysts, or hypnospores , are part of the life cycle (van den Hoek et al. 1995, Garces et al. 1998) or when the duration of the planozygote stage is too long to be neglected. In contrast to batch cultures, net cell growth rates as well as encystment rates in the sea cannot be measured accurately from counts due to dispersion, sedimentation and natural losses such as grazing. ...
An intriguing case of encystment of the dinoflagellate Scrippsiella lachrymosa in culture has recently been presented: cyst concentrations still increased after the abundance of the vegetative cells had decreased to very low numbers. To account for this apparent time lag, and using a model with an encystment rate equation in which vegetative growth and encystment rates were coupled, the calculated growth and encystment rates had to be 8 to 12 d(-1), values which were considered 'not biologically meaningful'. Here a new model of dinoflagellate growth and encystment is presented in which the mitotic cycle (vegetative growth) is coupled quantitatively to the sexual cycle (cyst formation) by having 4 gametes emanate from 1 vegetative cell, but without directly coupling the rates of vegetative growth and encystment. Calibrated on literature data of S. lachrymosa cultured in f/4 medium, this model satisfactorily describes motile cell (vegetative cells and gametes) and cyst development with correlations between log-transformed model and experimental data of r(2) = 0.80 (motile cells) and r(2) = 0.94 (cysts) and with typical maximum rates in the exponential growth phase of mu(cell) = 0.55 d(-1) (gross vegetative cell rate), mu(gamete+cell) = 0.38 d(-1) (net motile cell growth rate), epsilon = 0.42 d(-1) (encystment rate). All these rates declined in the stationary growth phase. Sample sonication is suggested as the cause for low motile cell concentrations in the original experiment when cyst production was high. Inorganic carbon limitation due to low inorganic carbon to nitrogen concentrations in the growth media is probably the reason why cysts in f/4 medium stopped making calcite covers in later stages of the experiment and why cyst yield in f/2 medium was not double the yield in f/4. A new method for measuring in situ encystment rates of dinoflagellate populations with a phased sexual cycle is proposed.
... Overall, however, there is a clear tendency for the holococcoliths to occur in the upper water column with the heterococcoliths somewhat lower. So, it seems likely that as in other protists, such as dinoflagellates (Garcés et al., 1998) or Phaeocystis (Lancelot and Rousseau, 1994), the various life-cycle phases will prove to have distinct ecological adaptations and so allow the species to survive under and exploit a range of ecological conditions. Thomsen et al. (1991) noted that whereas Papposphaeraceae had been studied from numerous Arctic localities combination coccospheres had only been recorded in one locality, Disko Bay on the West Greenland Coast. ...
Recently discovered coccospheres with combinations of coccoliths normally considered to belong to different taxa are presented here. By analogy with other coccolithophorids especially Coccolithus pelagicus we can hypothesize that these associations probably represent moments of phase change in a complex, possibly haplo-diplontic, life-cycle. Seven of these associations are composed of heterococcoliths with holococcoliths; five of them are presented here for the first time: Helicosphaera carteri with Syracolithus catilliferus, Syracosphaera pulchra with Calyptrosphaera oblonga, Syracosphaera anthos with Periphyllophora mirabilis, Acanthoica quattrospina with holococcolithophorid sp. and Syracosphaera sp. with Corisphaera sp. type A (see Kleijne, A., 1991. Holococcolithophorids from the Indian Ocean, Red Sea, Mediterranean Sea and North Atlantic Ocean. Mar. Micropaleontol. 17, 1–76); the other two are Coronosphaera mediterranea with Calyptrolithina wettsteinii, found previously by Kamptner (Kamptner, E., 1941. Die Coccolithineen der Südwestküste von Istrien. Naturhistorischen Museum in Wien. Annalen 51, 54–149), and Syracosphaera nana with undescribed holococcoliths, figured previously by Kleijne (1991) as Syracosphaera sp. type A. In addition the association of Neosphaera coccolithomorpha and Ceratolithus cristatus, recently presented by Alcober and Jordan (Alcober, J., Jordan, R.W., 1997. An interesting association between Neosphaera coccolithomorpha and Ceratolithus cristatus (Haptophyta). Eur. J. Phycol. 32, 91–93) is verified by discovery of a further example. A further five combinations of heterococcoliths and holococcoliths are shown, these probably mostly represent life-cycle combinations but the evidence in each case is insufficient to consider these as definite associations although in these collapsed coccospheres the association of different species is less certain. Two examples of holococcolith–holococcolith associations are presented: S. catilliferus with Syracolithus confusus, and Zygosphaera bannockii with Corisphaera sp. type A. These are probably examples of intra-specific variation.A new species, Syracosphaera delicata sp. nov., is described.
... The red bodies observed in both O. ovata and C. monotis field cells in combination with their absence or low abundance levels at low water temperatures during winter could possibly reflect the presence of a resting and/or temporary cyst in their life cycle as suggested for other dinoflagellates (Faust, 1992;Garcés et al., 1998;Kim et al., 2002). A sexually produced resting cyst has been described for C. monotis by Faust (1992); however, for Ostreopsis species (O. ...
The examination of macrophyte, water and sediment samples, collected at depths less than 1.5m from 50 different sites along the North Aegean coasts, has revealed, for the first time in Greek coastal waters, the presence of two Ostreopsis species (O. ovata and O. cf. siamensis) and Coolia monotis in the majority of the sampling sites (94% and 100%, respectively). Other epiphytic dinoflagellates of the genera Prorocentrum and Amphidinium and diatoms were accompanying species in this epiphytic community. Morphometric features, plate formula and thecal ornamentation were used for species identification. O. ovata cells were smaller in dorsoventral (DV) diameter and width (W) (26.18–61.88μm and 13.09–47.60μm, respectively) in comparison with O. cf. siamensis (35.70–65.45μm and 23.80–49.98μm, respectively). In contrast, the anterioposterior (AP) diameter of O. cf. siamensis was smaller (14.28–26.18μm) resulting in DV/AP≈3, whereas the above ratio for O. ovata was less than 2 (AP ranging between 14.28–35.70μm). Moreover, the theca of O. ovata cells was ornamented with scattered pores, which fluctuated in a wider range (0.07–0.32μm) than those of O. cf. siamensis (0.23–0.29μm). Coolia monotis cells were almost round with average DV diameter 26.88μm, AP 25.66μm and width 26.76μm. Small and large cells were recorded in both field and culture populations of Ostreopsis spp. and C. monotis, while hyaline cysts were observed for O. ovata. The presence of O. ovata and O. cf. siamensis exhibited a clear seasonal pattern dominating (maximum abundance up to 4.05×105cellsgr−1fwm) the period from midsummer to late autumn in years 2003 and 2004, while C. monotis was found also in winter and spring months.
... The dinoflagellate genus Alexandrium includes a number of cyst-forming species that have been studied extensively because many are linked to dangerous and destructive blooms as a result of the toxins they produce (Anderson 1998). Given the importance of cyst and motile cell dynamics in the bloom process, there have been a number of studies of the encystment, dormancy, excystment, growth, and toxicity of many of these species (e.g., Watras et al. 1982, Anderson et al. 1983, 1984, Kita et al. 1993, Blanco 1995, Jensen and Moestrup 1997, Garcés et al. 1998). To date, however, studies of tropical or subtropical Alexandrium species are few, as are investigations of non-toxic Alexandrium. ...
Alexandrium affine (Inoue et Fukuyo) Balech, isolated from Bahía Concepción (Gulf of California), was studied to determine the effect of environmental factors on cyst germination and vegetative growth. Alexandrium affine was homothallic and isogamous, and formed cysts in nutrient-deficient (N- or P-limiting) medium. The maturation period of newly formed cysts varied between two weeks and three months, depending on the storage temperature, with colder temperatures prolonging the process. The rate of germination increased with increasing temperature, and was not significantly influenced by light. Germination experiments suggest a broad temperature window for A. affine cysts, ranging from 5 to 25 °C. The optimal vegetative growth rates were 0.25 to 0.34 day-1 at 20-30 °C. No vegetative growth was observed below 15 °C or above 35 °C. With HPLC toxin analyses, we confirm that this species does not produce saxitoxins. These data on the dormancy, excystment, and growth characteristics seem to be regulated by the environmental constraints of this subtropical bay.
A dinoflagellate isolated from a small rainwater rockpool in Finland was found to be a new species of Baldinia, here described as B. droopii sp. nov. This is only the third formally described Baldinia species and the second described by modern methods. The new species had a complement of generic characters that clearly affiliated it to Baldinia: presence of an internal honeycomb structure, termed a lamellar body, a ventral fibre associated with the longitudinal basal body and a pentagonal resting cyst; and the absence of an apical structure, thecal plates and trichocysts. The most distinctive species-specific characters were the presence of a resting cyst with tubiform processes, a paratabulation matching the pattern of the motile cell, and a life cycle exhibiting a diel rhythm, alternating between motile and non-motile coccoid cells. Motile cells occurred during the light period, peaking after 3–4 h of light period, while practically no motile cells occurred during the dark period. LSU rDNA sequences confirmed B. droopii as a new species, showing c. 14% sequence difference compared to B. anauniensis. Asexual reproduction occurred primarily by binary fission or via a so-called division cyst. Sexual reproduction occurred in the culture indicating that D. droopii is homothallic. The zygote may form a resistant cyst with tubiform processes, but there were indications that this stage may be by-passed. Different stages of the asexual and putative sexual reproduction were observed and documented by video recordings.
This datasheet on Alexandrium minutum covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
In order to understand the strategy of Scrippsiella acuminata to cold dark environment, the antioxidant responses and the formation of pellicle cysts of S. acuminata to darkness at 8°C and 20°C were investigated. Cell densities decreased significantly after 96 h dark treatment, and no live cells were observed after 9-days dark treatments. The darkness stress generally resulted in an increase of antioxidant defenses, including soluble protein, superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde (MDA). Cellular soluble protein and SOD activity increased sharply under 20°C darkness, which protected algal cells against the oxidative stress from darkness, and resulted in relatively lower MDA levels. Soluble protein and SOD activity were enhanced under 8°C darkness as well however not in a sharp rise, and higher levels of MDA and GSH were recorded. The results suggested high SOD and protein levels protected cells against harsh darkness stress, while high GSH not only helped algae cells resist dark stress, but also played an important role in low temperature stress. Darkness promoted the formation of pellicle cysts of S. acuminata, and the maximum formation rates were 16.06% to 21.74% at 8°C and 20°C, respectively. Germination of pellicle cysts occurred within 24 h after light exposure, however pellicle cysts could not withstand long-time darkness stress, and all pellicle cysts died after 9-days darkness exposure. The results of this study suggest that S. acuminata is able to overcome temporary cold darkness through forming pellicle cysts.
La migración vertical es el movimiento que realiza el fitoplancton en la columna de agua como parte de su ciclo de vida o como resultado de condiciones medioambientales. En el presente estudio, se analizó la migración del fitoplancton durante julio del 2015 y febrero del 2017, para comprender el comportamiento del fitoplancton durante el día. Para esto, se realizaron muestreos de 24 h, registrando parámetros fisicoquímicos in situ y tomando muestras de fitoplancton a distintas profundidades (0, 5, 10, 15, 20 y 30 m) en diferentes momentos (5:00, 8:00, 12:00, 16:00, 19:00 y 22:00 h). Los grupos taxonómicos más diversos fueron las diatomeas (Bacillariophyta) y las algas verdes (Chlorophyta); y los géneros más abundantes fueron Aulacoseira sp. y Ceratium sp. Durante el 2015 se registraron 17 géneros pertenecientes a cinco grupos taxonómicos, se observó una disminución de las poblaciones de diatomeas en el tiempo y un aumento de cianobacterias alrededor de medio día y dinoflagelados en horas de la noche y en zonas más profundas. En el 2017 se registraron 20 géneros, con una dominancia mayor de 75% de diatomeas. Las abundancias de algas quebradizas, algas verdes y dinoflagelados permanecieron estables temporal y espacialmente y las cianobacterias presentaron una baja abundancia. En general, la variación espacio-temporal del fitoplancton en ambos años, se debe a las condiciones ambientales al momento del muestreo, siendo el fotoperiodo, la temperatura y la radiación solar las que determinaron su distribución.
A planktonic-benthic relationship has been described for many dinoflagellate species as part of their ecological strategy to overcome highly variable aquatic environments. Here, the phylogenetically and morphologically related marine dinoflagellates Protoceratium reticulatum and Ceratocorys mariaovidiorum were studied in relation to an unknown benthic life form. In vivo and fixed samples from cultures were analyzed in detail by light and scanning electron microscopy. In both species, a cell type with a morphology different from that of vegetative cells was observed in cultures grown until stationary phase. This cell type was always benthic, swimming sporadically only when it was disturbed. Its main feature included a strong dorso-ventral compression. These cells originated from vegetative cells whose protoplasm underwent a progressive flattening, resulting in a gradual detachment of the reticulate and thick thecal plates and the formation of very thin non-reticulated new plates with pores. When returned to fresh full strength medium, the cells recovered their spherical vegetative-like morphology, including new reticulated thick plates and subsequent cell divisions. The kinetics of flattened cell formation showed that in both species this cell type increased exponentially until the onset of the culture stationary phase and then decreased. The results of this study are discussed in the context of the planktonic-benthic coupling in dinoflagellate life cycles, including those newly appreciated to be well adapted to the benthic environment.
Applications of numerical models to predict and eventually manage the onset, duration, and consequences of toxic phytoplankton events of coastal ecosystems require knowledge of both the ecophysiological properties of the specific organisms and the biophysical processes, which allow them to accumulate large biomass, despite the presence of other competitors. Harmful algal blooms are not always just local events. Furthermore, independent in situ plankton data sets from the Gulf of Mexico (GOM) and Mediterranean Sea over six decades, together with adjunct satellite color data, other nitrogen isotope signals of plankton and sediments, extant circulation models, and phytoplankton biomarkers within sediment cores of this similar ecosystem, all confirm the complex western GOM eutrophied sequence of phytoplankton succession.
The LIFEHAB workshop was conceived as a forum for discussion among specialists on life histories of microalgal species. The main goals were to: 1) review current knowledge on the life-cycles of phytoplanktonic organisms, focusing on HAB species; 2) identify the role of heteromorphic life cycles in population dynamics; 3) define future HAB research directions to fill existing gaps in knowledge; 4) debate the most appropriate approaches and methods; and 5) promote the development of cooperative scientific initiatives.
The workshop included 25 presentations covering the most relevant aspects of life cycle studies in phytoplankton, ranging from an updated review of the information available for the major groups, to the role played by different life history stages in population dynamics, to the new tools available for addressing research questions. Discussion sessions focussed on the main gaps of knowledge and research needs. Complex, heteromorphic life cycles are a general feature of the large majority of
phytoplanktonic algae. Diatoms, dinoflagellates, haptophytes and raphidophytes are characterized by different life cycles, including stages with different ploidy levels, linked together by syngamy and meiotic events. There is increasing evidence that complex mating systems are a common feature among phytoplankton organisms. Understanding these is crucial for the taxonomic circumscription of species and for gaining insights into speciation mechanisms in these organisms.
Most taxa are characterized by an alternation between dormant/quiescent phases and growth phases. It is recognized that life history strategies (sensu latu, including formation of resistant/defense stages, colonies, encystment-excystment rates, vertical migrations, modulation of growth capabilities, etc), play a key role in the occurrence and dynamics of Harmful Algae Blooms (HABs). The alternation between different life history stages and their relationships with the physical, chemical and biological environment are very important for the success of harmful species.
In the course of the Workshop, the main gaps in knowledge and research priorities in this field were identified and discussed.
Dinoflagellates form a complex group of protists with a variety of morphologies, physiologies, and life cycles that give them a strong adaptation to all aquatic environments (marine and freshwater) and habitats (pelagic and benthic) making difficult to study their diversity and ecology. The objective of this thesis was the search for global biodiversity patterns and community structure of marine pelagic dinoflagellates across the world?s oceans. A morphogenetic sampling protocol, covering the entire spectrum of their size and an important part of their spatio-temporal variability, was developed (Tara-Oceans). Various tools for an automatic acquisition broadband data were tested. Diversity, relative abundance and geographical distribution of the genus Neoceratium were evaluated by FlowCAM in Mediterranean Sea. A study of the structure of biodiversity was conducted by metabarcoding with 18S rDNA (V9 fragment). Building a base of rDNA reference sequences (DinR2) allowed the taxonomic assignment of environmental metabarcodes. The metabarcode approach reveals a remarkable and unexpected diversity of pico-dinoflagellates (<5?m) and, regardless of the studied ecosystem and the sampling period, that abundance of different levels mainly depends to the size fractions (pico-, nano-, micro- and meso- plankton). Structuring of dinoflagellates communities in different size fractions of the photic zone was facing to some environmental factors and opens promising avenues for research
Nuclear-encoded 18S and partial 26S ribosomal DNA (rDNA) sequences of Alexandrium hiranoi, A. leei and A. satoanum were analyzed for the first time. The sequences of the 26S rDNA D1-D3 region of A. affine, A. catenella, A. fraterculus and A. tamarense were also determined. The maximum-likelihood and maximum-parsimony phylogenies on the basis of the 18S and 26S rDNA sequence data showed that the monophyletic Alexandrium was Subdivided into three main groups Of which genetic delineation was congruent to the shape of the posterior sulcal plate. Alexandrium hiranoi was genetically closely related to A. pseudogonyaulax and A. taylorii. Alexandrium leei formed the deepest branch without apparent genetic affiliation to the other Alexandrium species. Alexandrium satoanum consistently formed a sister group with A. hiranoi, A. pseudogonyaulax and A. taylorii, but was separated from them with high bootstrap supports. A Blast search of GenBank showed that A. affine, A. catenella, A. fraterculits and A. tamarense sequence data corresponded to their morphological species designation.
Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo (Gonyaulacales, Dinophyceae) is a phototrophic marine dinoflagellate that produces an unusual paratabulate resting cyst. Studies of vegetative and sexual reproduction were conducted on a clonal culture established from germination of a resting cyst from Fusaro Lagoon, Italy. Vegetative division in A. pseudogonyaulax takes place inside a vegetative cyst, from which two, or at times four, daughter cells originate. The daughter cells completely resynthesize new cell walls. Cyst formation takes place after sexual reproduction. A large biflagellate zygote is formed after a conjugation process in which one of the two gametes is engulfed by the other.
The vertical distribution of the planktonic, phototrophic ciliate Mesodimurn rubrum was monitored during a red-water event in daylight hours, over a complete tidal cycle Theoretical considerations based upon the hydrodynamics of the estuary, and upon the behaviour of the ciliate described to date, suggest that the population should not be able to resist flushing losses from the estuary. However, field observations reveal a pattern consisting of aggregation close to the surface during flood tide and high water, but dispersion away from the surface on the ebb tide, thus minimizing flushing losses due to the strong superficial currents Evidence is presented suggesting that the major cue for such migration may be the turbulence generated by shearing of surface currents, or gravita-tional (static) instability of surface water.
Gymnodinium nagasakiense is a noxious red tide dinoflagellate often associated with damage to fisheries in Japan. DNA synthesis and the cell cycle in this organism were investigated from 1989 to 1990 by determining relative DNA contents of individual cells using an epifluorescence microscopy-based microfluorometry system. The nuclei were stained with the DNA-specific fluorochrome 4'-6-diamidino-2-phenylindole (DAPI). Because photosynthetic pigment interferes with the fluorescence from the DAPI-DNA complex, the pigment was eliminated by methanol treatment as a first step in quantitative microfluorometry. Nuclear DNA contents, cell size distribution, cell density, and frequency of paired cells were determined every 2h for 24h using cells grown on a 12h light:dark cycle. DNA synthesis and cell division were tightly phased to a particular period of the light:dark cycle. DNA synthesis (S phase) occurred from 10:00 to 22:00 hrs and was followed by cytokinesis. The presence of such a distinct S phase strongly suggests thatG. nagasakiense has a typical eukaryotic cell cycle. This type of cell cycle makes it possible to estimate speciesspecific in situ growth rate based on the diel pattern of DNA synthesis.
The dinoflagellate, Goniodoma pseudogoniaulax, sometimes blooms in rockpools around the high tide level along the Pacific coast of Japan during spring and summer. Besides a motile pelagic form, this species has two nonmotile benthic stages (the resting cyst and temporary cyst). The resting cyst is dormant in winter, and possibly functions as seed for blooms in the subsequent warmer seasons. The temporary cyst is easily formed in culture and readily transformed into a motile stage. The temporary cyst often divides into two or four asexual products. Fusion of the smaller motile cells, presumed to be gametes, was observed. Diel observations of this organism in a rockpool showed that motile cells increased in number while the number of temporary cysts and the ratio of divided temporary cysts to divided and undivided ones decreased in the daytime; the variations in number and ratio were reversed at night. The number of the resting cysts remained unchanged day and night during the study period. It follows that motile cells lose their motility and settle to the bottom of a rockpool in the evening and change into the temporary cyst. The protoplast of some temporary cysts divide transforming it into a motile cell the next morning. The population of this species is thought to be maintained through the asexual reproduction of temporary cysts.
Batch culture experiments were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11.3–23.7 °C and from 10 to 40 psu. Maximum division rates of more than 0.3 divisions d−1 took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at different temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11.3–23.7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting cysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When stained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal flagellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.
A Mediterranean clone of the red-tide forming dinoflagellate Prorocentrum minimum was studied in vitro for its capacities to adapt to salinity, temperature and light. This clone is euryhaline and shows optimal growth between 15 and 35%. After adaptation, slow growth was observed at salinities as low as 5%. An apparatus generating crossed gradients of temperature and light allowed 100 combined experimental conditions to be studied. Variations in lighting between 30 and 500 µ mol photons m-2 s-1 had little effect on growth, and no photoinhibition occurred. The clone can grow between 8 and 31 °C, but is thermophilic with an optimal growth between 18 and 26.5°C. As result of large variations in temperature from 18°C down to 10°C, small spherical structures (8-10 µm) were observed; they are described as temporary cysts. These results were compared to those obtained by different authors, in vitro and in situ, notably in the Mediterranean region.
Water discolourations were observed in two localities of the NW Mediterranean (La Fosca and Palmira, Spain) during the summer
of 1994 and 1995 caused by a non-toxic dinoflagellate belonging to the genus Alexandrium, subgenus Gessnerium. The organism was identified as Alexandrium taylori Balech, although differences were encountered compared to the original description from Arcachon (France). Detailed studies
of the 1'plate were conducted on the Spanish material and compared with specimens from the type locality. Differences reported
here between the Spanish and French populations are considered to be within the range of the morphological variability of
this taxon.
Small cells are observed in dense populations of many dinoflagellatespecies, both in clonal cultures and in natural bloom populations. They range in size from 0.5 to 0.16 of the normal cell volume and have reduced nucleus and cytoplasmic components. Two possible origins are considered for such small cells: unequal cell division or budding-like division, and successive ‘depauperating’ cell divisions. Small cells, which are reported here for 34 species, can proliferate actively in the late stages of exponential growth, and may become the dominant form in cultures when nutrients are exhausted. When new nutrients are added to the exhausted growth medium, small cells increase in size and structural components, and may give rise to forms of a more typical size. Small cells may also serve as gametes. In the sexual cycle of the species studied here, gametes were morphologically indistinguishable from vegetative small cells. Fusion was isogamous in Gymnodinium splendens Lebour, Gyrodinium instriatum Freudenthal et Lee, Alexandrium lusitanicum Balech and Coolia monotis Meunier, but anisogamy was also observed in Gyrodinium instriatum. The nuclear structure of several stages of the life history was examined, including small cells. The results agree with earlier observations: the dinoflagellate nucleus is polyploid or aneuploid and the chromosomes are polytenic. The existence of small forms may have implications for dinoflagellate taxonomy.
Small cells are observed in dense populations of many dinoflagellatespecies, both in clonal cultures and in natural bloom populations. They range in size from 0.5 to 0.16 of the normal cell volume and have reduced nucleus and cytoplasmic components. Two possible origins are considered for such small cells: unequal cell division or budding-like division, and successive ‘depauperating’ cell divisions. Small cells, which are reported here for 34 species, can proliferate actively in the late stages of exponential growth, and may become the dominant form in cultures when nutrients are exhausted. When new nutrients are added to the exhausted growth medium, small cells increase in size and structural components, and may give rise to forms of a more typical size. Small cells may also serve as gametes. In the sexual cycle of the species studied here, gametes were morphologically indistinguishable from vegetative small cells. Fusion was isogamous in Gymnodinium splendens Lebour, Gyrodinium instriatum Freudenthal et Lee, Alexandrium lusitanicum Balech and Coolia monotis Meunier, but anisogamy was also observed in Gyrodinium instriatum. The nuclear structure of several stages of the life history was examined, including small cells. The results agree with earlier observations: the dinoflagellate nucleus is polyploid or aneuploid and the chromosomes are polytenic. The existence of small forms may have implications for dinoflagellate taxonomy.
October field collections from a salt water marsh maintained in the laboratory revealed stages of cell fusion and nuclear cyclosis in Amphidinium klebsii Kofoid & Swezy. Cells were observed with one enlarged nucleus and two epicones oriented at 90° to 180° relative to each other. Such a configuration is not typical of dividing cells, suggesting that these cells represent planozygotes. Over time, the two epicones fuse. The product of the fusion is a pigmented cell exhibiting the normal vegetative cell morphology but possessing two trailing flagella. These latter cells enlarge in size and exhibit nuclear cyclosis (rotation of the contents of the nucleus). This rotation has been linked to meiosis I in other dinoflagellate zygotes. Within this same field collection, cells enclosed by a smooth cyst wall composed of a single layer of electron-translucent material were observed. These encysted cells exhibited the same morphology as free-swimming forms of Amphidinium observed in the collection. Transfer of cysts into fresh media produced free-swimming Amphidinium cells which were capable of subsequently forming cysts. Representatives of Amphidinium klebsii are therefore able to cycle between a free-living stage and an encysted stage. Although mitosis in Amphidinium normally occurs in the motile stage, cysts contained up to eight daughter cells, suggesting that the cysts are vegetative division cysts.
October field collections from a salt water marsh maintained in the laboratory revealed stages of cell fusion and nuclear cyclosis in Amphidinium klebsii Kofoid & Swezy. Cells were observed with one enlarged nucleus and two epicones oriented at 90° to 180° relative to each other. Such a configuration is not typical of dividing cells, suggesting that these cells represent planozygotes. Over time, the two epicones fuse. The product of the fusion is a pigmented cell exhibiting the normal vegetative cell morphology but possessing two trailing flagella. These latter cells enlarge in size and exhibit nuclear cyclosis (rotation of the contents of the nucleus). This rotation has been linked to meiosis I in other dinoflagellate zygotes. Within this same field collection, cells enclosed by a smooth cyst wall composed of a single layer of electron-translucent material were observed. These encysted cells exhibited the same morphology as free-swimming forms of Amphidinium observed in the collection. Transfer of cysts into fresh media produced free-swimming Amphidinium cells which were capable of subsequently forming cysts. Representatives of Amphidinium klebsii are therefore able to cycle between a free-living stage and an encysted stage. Although mitosis in Amphidinium normally occurs in the motile stage, cysts contained up to eight daughter cells, suggesting that the cysts are vegetative division cysts.
Three new species of the dinoflagellate genus Alexandrium are described. Alexandrium tamiyavanichi is in the subgenus Alexandrium in which the Po and 1′ are connected. This species is closely related to A. cohorticula, but it differs by its general shape, the Po and 1′, the shape of its left sulcal list, and some sulcal plates. The other two species belong in the subgenus Gessnerium in which the Po and 1′ are completely disconnected. Alexandrium taylori has a pentagonal 1′ and a ventral pore. It differs from the closely related species A. pseudogoniaulax (Biecheler) by the shape of 1′, the position of the ventral pore, and all of the sulcal plates. Alexandrium margalefi is the only species of this genus described to date with a quadrangular 1′; it also has a ventral pore. Of the three species, only A. tamiyavanichi is known to produce paralyzing shellfish poisoning
The mitotic index method is re-examined by solving an idealized case analytically. A lower bound for the daily division rate of a phased cell population can be computed as ln[(1 + &,)I(1 + fmin)] wheref,,, andf,, are the maximal and minimal fractions of cells in a terminal phase of the cell cycle (e.g. mitosis) over a light : dark cycle. This new formula extends the previous analysis of McDuff and Chisholm to the case of slow-growing cells that spend more than 1 d in the terminal phase. It should be useful in the case of phytoplankton populations growing in oligotrophic waters. Further, the error between this lower bound and the actual value of the division rate is expressed as a function of the durations of the terminal phase and of the division burst.
The tide pool ciliate Strombidium oculatum Gruber alternates between an encysted (≈18 h) and a free-swimming (≈ 6 h) stage with a circatidal rhythm. This behaviour greatly increases the probability of remaining in a tide pool during flooding by the high tide. The functional biology of S. oculatum was studied in a series of field and laboratory experiments to analyse how this ciliate maintains a rhythm which is phased to the tide. Experiments revealed that S. oculatum responds phototaxically with a switch in polarity during the course of the free-swimming stage. The phototaxis is interpreted as a mechanism to guide the ciliates to advantageous microhabitats during the free-swimming and the encysted stages, respectively. It is suggested that the pigment spot used in phototaxis is composed of sequestered stigmata from ingested autotrophs. Encystment is gregarious and induced by a chemical factor present in both free-swimming ciliates and cyst walls; the thallus of green algae is preferred to rock surface as a substratum for encystment. The nutrition of S. oculatum is mixotrophic and sequestered plastids are found in the cytoplasm. Photosynthetic assimilation rates, measured by ¹⁴ C-label, were 17 and 55%, of cell carbon· day⁻¹ for free-swimming ciliates and cysts, respectively. Reproduction rate of free-swimming ciliates, calculated from in situ incubations, was 0.027 h ⁻¹.
Life cycles of several species belonging to the marine generaDissodinium Klebs in Pascher andPyrocystis Murray ex Haeckel are described. The two known species ofDissodinium, D. pseudolunula Swift ex Elbr. & Dreb., (=D. lunula auct. nonnull.) andD. pseudocalani (Gönnert) Drebes ex Elb. & Dreb. are ectoparasites of copepod eggs. In this genus, sporogenesis, with obligate sequence from primary cyst to secondary cyst to dinospores, occurs by palintomy.Dissodinium is placed into the order Blastodiniales Schiller and its position in this order is discussed. The asexual life cycle ofPyrocystis spp. represents an alternation between a dominating coccoid stage and a morphologically different transitory reproductive stage. The reproductive bodies may be either athecate aplanospores, athecate uni- or biflagellate planospores or thecate biflagellate planospores. Thecal morphology of thecate planospores resembles those ofGonyaulax Diesing. The occurrence of both, athecate aplanospores and thecate planospores in the same species, is discussed.Pyrocystis is regarded as belonging to the order Pyrocystales Apstein. The possible derivation from the Gonyaulacaceae Lindemann is suggested. In addition, the generaDissodinium andPyrocystis are redefined. A description ofD. pseudolunula as well as a list of synonyms and references for detailed descriptions ofP. lunula (Schütt) Schütt, not includingD. pseudolunula, is given.
A conceptual basis is established to estimate the duration of cell cycle phases from a partially synchronized population. This information, together with the time course of cell cycle phase fractions, can be applied to estimate species-specific, in situ growth rates of phytoplankton. The model adopts the paired-nuclei method of McDuff & Chisholm (1982) with the substitution of the sum of S, G2, and M phases of the cell cycle as the terminal event. Quantitative fluorescence microscopy is used to measure unicellular DNA contents through a diel cycle. The model has the advantage of avoiding bottle incubations and allows the measurement of species-specific growth rates.
Thick-walled, nonmotile cysts (termed hypnocysts) of two dinoflagellates were isolated from estuarine sediments in Cape Cod, Massachusetts, and germinated to produce their respective motile, thecate stages. Hypnocysts from Orleans district were identified as Gonyaulax excuvata (Braarud) Balech sensu Loeblich & Loeblich. Visually identical hypnocysts from Falmouth district were provisionally identified as Gonyaulax tamarensis Lebour. Both species were toxic. A geographic survey in September detected hypnocysts in only the sediments of locations where toxic blooms developed the preceding and following Spring. Laboratory incubation (16 C) of hypnocysts from sediment samples stored in the dark (5 C) for 6 mo initiated excystment by the temperature increase, with no appreciable effect from light regime, nutrient, or chelator concentrations. Motility of excysted germlings was optimum in highly chelated medium and in the presence of light. We conclude that hypnocysts of both tasa are important in seeding recurrent annual blooms, synchronizing early bloom development with vernal warning of seawater and increasing the geographic range of the species. We suggest that many red tides in New England and eastern Canadian waters are initiated through the displacement of motile estuarine populations into nearshore area by tidal advection and surface runoff, although the potential existence and importance of offshore cyst reservoirs cannot be discounted. Evidence is presented that hypnocysts are probable sexual zygotes whereas the thin-walled cysts readily formed in laboratory cultures (pellicle cyst) are asexual. Pellicle cysts are of limited durability, do not overwinter in nature, and therefore do not play a significant role in initiating toxic blooms.
In unialgal culture, Gymnodinium pseudopalustre Schiller (G.p.) and Woloszynskia apiculata sp. nov. (W.a.) multiply respectively by binary fission in the motile state and by motionless zoosporangia, releasing 2, 4 or 8 zoospores. Both species are isogamous, but G.p. is homothallic, W.a. heterothallic. Fusion of the planogametes leads to long-lived planozygotes, which retain two posterior flagella and, while enlarging, assume specific morphologies. The motile stage of the zygotes is terminated by formation of hypnozygotes (resting spores), globular and spiny in G.p., grossly fusiform (‘horned’) and tubercled in W.a. The composition of the hypnozygote walls is described. After their dormancy has been broken by a cold treatment of several weeks in the dark, hypnozygotes of both species germinate when brought back to higher temperature and light. In so doing, those of G.p. excyst one posteriorly biflagellate swarmer as a meiocyte, which, after a stage of nuclear cyclosis or, in karyological terms, zygotene through postzygotene, undergoes two steps of binary fission in the motile stage, separated by several days. In W.a., cyclosis as well as the first meiotic cell division occur inside the closed wall of the hypnozygote (now a meiocyte); thereafter either two swarmers escape and undergo the second meiotic division in a separate zoosporangium or, alternatively, second meiotic nuclear and cell divisions also take place inside the spore wall and four swarmers are finally excysted. Some aspects of dinoflagellate life cycles and taxonomic questions are discussed.
Cytokinesis is described for the first time in a pelliculate dinoflagellate that retains its thecal plates during cell division. In Heterocapsa niei cytokinesis proceeded in a manner that differed from that described for other dinoflagellates. The thecal plates separated along the fission line before the development of a cleavage furrow. A distinct cleavage furrow developed as cytokinesis progressed. The outer membrane and the outer plate membrane expanded during division to enclose the enlarging cell undergoing cytokinesis; however, as the cleavage furrow deepened, these membranes were not continuous with the cytoplasm. The pellicle was occasionally intermittent in the region of the cleavage furrow, possibly facilitating movement of material from the cytoplasm to the developing outer membranes. Thecal plate formation occurred within the thecal vesicle from unrecognizable precursors.
The ultrastructure of the amphiesma during pellicle formation was investigated in two species of Dinophyceae, Amphidinium rhynchocephalum Anissimowa and Heterocapsa niei (Loeblich) Morrill & Loeblich using thin sections. In both species the amphiesma consists of an outermost membrane (i.e. the plasma membrane) underlain by amphiesmal vesicles. In A. rhynchocephalum the latter appear empty whereas each amphiesmal vesicle in H. niei contains a thecal plate and a thin, amorphous layer (dark-staining layer) located between, the thecal plate and the inner amphiesmal vesicle membrane. When cells of both taxa are carefully fixed, amphiesmal vesicles are always separate entities (i.e. the sutures are undisrupted). During ecdysis the following amphiesmal components are shed: the plasma membrane, the outer amphiesmal vesicle membrane, and in H. niei the thecal plates. The inner membranes of the amphiesmal vesicles then fuse with each other and form a continuous membrane (termed pellicle membrane) that remains tightly oppressed to an underlying amorphous layer (pellicular layer). In A. rhynchocephalum the pellicular layer is already present in vegetative non-ecdysed cells, whereas in H. niei it forms during ecdysis beneath the pellicle membrane. During ecdysis in H. niei, material from the dark-staining layer precipitates on the outer surface of the pellicle membrane, where it forms a characteristic honeycomb pattern. The new observations are incorporated into a revised model of pellicle formation in dinoflagellates and contrasted with earlier proposals.
Forty-five species of dinoflagellates were surveyed for the presence of a pellicular layer in the amphiesma or cell covering. Such a layer was found in 15 of the 20 genera studied. Half the pellicles tested were resistant to acetolysis and may contain a sporopollenin-like material similar to that of some dinoflagellate cyst walk. Most organisms which formed pellicles were capable of reinforcing this layer with cellulose. Pellicles of Heterocapsa niei (Loeblich) Morrill & Loeblich and Scrippsiella trochoidea (Stein) Loeblich were studied with the electron microscope. Evidence is presented indicating that dividing cells of S. trochoidea from new walls while still enclosed in the parental pellicular layer.
Cyst formation in Ceratium hirundinella (O. F. Müll.) Bergh was studied by light and electron microscopy, using material from several lakes and reservoirs and also laboratory cultures. Cells preparing to encyst build up large quantities of starch and lipid and at the same time reduce their other cell components. The cyst is released from the theca as a naked cell bounded by a double membrane. The most commonly found cyst deposits a layer of electron-dense granules containing silicon on the outer membrane and lays down a cellulose-like material between the two membranes. Cysts without the electron-dense granules are commonly formed in cultures but rarely found in lakes. These cysts appear less resistant to decay and do not show the reorganization of cell contents for dormancy. It is suggested that C. hirundinella has both a resting cyst, forming part of the life cycle, and a temporary cyst stage.
Sexuality has been established for a culture of Gonyaulax tarnarensis Lebour (strain NEPCC–71). The addition of a thick inoculum to a nitrogen–deprived medium results in the occurrence of anisogamous sexual fusion within the first three days in the new culture. Planozygotes, large “lumpy” cells recognizable by their four flagella, may persist up to 2 wk before forming a smooth–walled, oval hypnozygote. The latter resembles cysts released asexually by ecdysis but has a slightly thicker wall. Viable cysts resembling hypnozygotes (zygotic cysts), but with reduced photosynthetic pigmentation, have been isolated from natural murine sediments in Hidden Basin, British Columbia, and a culture (strain NEPCC–254) was initiated from excysted individuals. Zygotic cysts of NEPCC–71 remained encysted in the light at 17 C for 8 wk before excysting. The presence of a ventral pen with toxicity in the latter strain indicates that the taxonomy of G. tamarensis-like organisms is still in a stale of flux and the criteria for recognition of G. excavata (Braarud) Balech as a separate species are not satisfactory as presently formulated.
Dense populations of a new species of dinoflagellate, Peridinium gregarium, have been found in a limited number of small rock tidepools on the coast of southern California. The organism is present throughout the year, but during periods of low temperatures and heavy tides it remains on the bottom of the pools in small aggregations. At other seasons P. gregarium leaves the aggregations during the morning hours and collects around the upper surface of small rocks in masses held together by a mucous matrix. Oxygen bubbles accumulated in the matrix eventually float the mass to the surface of the tidepool. During the afternoon or evening, the individuals return to the bottom aggregations leaving the matrix behind. Field and laboratory studies have attempted to define the nature of this organism's tidepool habitat and factors involved in the regulation of its diurnal movements.
The dinoflagellate Peridinium cf. quinquecorne Abé forms red tide-like blooms in eutrophic shallow waters in the Philippines. The organism moves into a distinct near-surface layer when intensive solar radiation occurs, but only during the incoming tide. Shortly before high tide, regardless of light levels, the dinoflagellates seem to disappear. Simple experiments show that once intensive radiation has been reduced Peridinium quinquecorne moves out of the water column and attaches itself to solid objects away from the light. The morphology of the organism, especially as related to attachment, was studied through SEM. Its high swimming velocity and the reaction to radiation and tidal changes are described. The possibility that, superimposed on its reaction to light, this dinoflagellate may follow intrinsic tide-dependent oscillations is discussed.
The marine dinoflagellate Gonyaulax tamarensis Lebour is best known for its propensity to form blooms known as red tides in coastal waters worldwide. This paper examines the sexual cycle of this organism using light and electron microscopy. Sexual reproduction begins with contact between thecate gametes which subsequently shed their thecae to fuse along their pellicular layers. Nuclear fusion occurs well after cytoplasmic fusion and is characterized by several distinctive features: a highly vesiculate nucleoplasm without microtubules; nucleoli and V-shaped chromosomes abut the nuclear envelope distal to the region of nuclear contact; and each chromosome possesses a longitudinal line, the central chromosomal axis. Fusion results in a planozygote with numerous cytoplasmic storage products and a slightly thickened layer beneath the pellicle. Subsequent loss of thecal plates and a thickening of the sub-pellicular layer results in a non-motile hypnozygote. A newly-formed hypnozygote possesses numerous minute papillae along its outer surface, formed by the up-folding of the accumulating wall layer. Maturation of the hypnozygote wall results in a smooth three-layered wall, the outermost layer of which is the pellicular layer. Hypnozygote germination produces a large quadriflagellate plan-omeiocyte with a single nucleus and thecal plates identical to vegetative cells. Two subsequent divisions, presumably meiotic, result in Jour cells morphologically identical to vegetative cells.
Two new fluorochromes, PicoGreen® and SYTOX Green™ stain (Molecular Probes, Inc.), are useful with flow cytometry for quantitative detection of cellular DNA in a variety of marina phytoplankton. The basic instrument configuration of modern low-power flow cytometers (15 mW, 488 nm excitation) is sensitive enough to detect the DNA signal in nearly all of the 121 strains (from 12 taxonomic classes)examined. The major advantages of these dyes over others are 1)suitability for direct use in seawater, 2)green fluorescence emission of the DNA-dye complex (wavelength 525 ± 15 nm) showing no overlap with the autofluorescence of the plankton pigments in the red band, 3) high fluorescence yield of the DNA-dye complex with an increase in fluorescence > 100-fold compared to the unstained cell, and 4)dyes can be used to quantify double-stranded DNA. The high sensitivity allowed the quantification of the DNA of the smallest known phyto-plankter (Prochlorococcus) as well as bacteria found in some of the algal cultures. Of the 12 taxonomic classes tested, only the 3 Nannochloropsis spp. (Eustagmatophyceae) stained poorly, and a few members of the Chlorophyceae and Pelagophyceae showed poor staining occasionally. In general, maximal fluorescence was achieved within 15 min after addition of the dye. Although the PicoGreen dye stained some living phytoplankton species, preservation is recommended for quantitation. SYTOX Green did not stain live cells. The combination of the dyes, therefore, allows the discrimination between live and dead cells in some algal groups (Prochlorococcus, diatoms, prasinophytes, and pelagophytes). Paraformaldehyde was preferred over glutaraldehyde for fixation to avoid (induced) green autofluorescence.
The toxic red tide dinoflagellate Alexandrium tamarense (Lebour) Balech (synonymous with Protogonyaulax tamarensis (Lebour) Taylor) was subjected to iron stress in batch culture over a 24-day time course. Monitoring of life history stages indicated that iron stress induced formation of both temporary (= pellicular) and resting (= hypnozygotic) cysts. Our experimental induction of sexuality appeared to be associated with iron limitation rather than the total depletion of biologically available iron. Degenerative changes in organelle (i.e. chloroplast, mitochondrion and chromosome) ultrastructure were largely restricted to pellicular cysts, suggesting that these temporary cysts were more susceptible to short-term iron stress effects than were hypnozygotes. These results are consistent with the hypothesized ecological roles of cysts in maintaining viability over brief (pellicular cysts) and extended (hypnozygotes) exposure to adverse environmental conditions.
A dense dinoflagellate bloom of Gyrodinium aureolum Hulburt in a shallow temperate zone estuary was monitored during the summers of 1982 and 1983. The bloom was typically extremely localized, its densest part exceeding 1000g chlorophyll a liter-1 (2x104 cells ml-1). The bloom began at temperatures between 24.5 and 27C, existed at as high as 30C and terminated when water temperature dropped to between 19 and 22C. The highest specific growth rate measured was 0.90d-1 (1.3 divisions d-1) and near the termination of the bloom decreased to 0.28d-1 (0.4 divisions d-1). A diel vertical migration of the bloom was observed. A box model analysis, based on division rates, vertical migration and water circulation patterns, indicated that the bloom must move downward at the estuary mouth to maintain itself in the estuary, either by means of a convergence system or by downward swimming. High growth rate, low grazing pressure, and a stratified water column are proposed to stimulate bloom formation. Decreasing growth rate appeared to reduce the intensity of the bloom and finally allowed its disappearance by estuarine flushing and mixing.
A microscope-photometer system was used to quantify the relative DNA content of individual cells of the dinoflagellates Gonyaulax polyedra Stein and Gyrodinium uncatenum Hulburt during asexual reproduction and, for the latter species, during sexuality as well. The cell cycles of these two dinoflagellates are distinctly different although both include discrete periods of DNA synthesis. In G. polyedra, DNA synthesis and cell division are tightly phased to restricted segments of the photocycle, separated in time by distinct gap phases. All cells that replicate their DNA and enter G2 divide during the next division interval. G1 is the stage occupied by the cells most of the time. In G. uncatenum, cell division is more broadly distributed and occurs throughout half the photocycle. Cell division is thus phased only to the extent that it is restricted to the same half of the photocycle each day. G1 is very brief as DNA synthesis begins immediately after cell division. G2 is the dominant stage through time since it includes cells about to divide as well as those that just divided. G. uncatenum is the first free-living photosynthetic dinoflagellate to exhibit a pattern of DNA synthesis immediately after mitosis. The tight phasing of G. polyedra division and the restriction of G2 to cells that must divide at the end of the dark period should make it possible to calculate the growth rate of this species in mixed natural assemblages using these techniques. It should also be possible to distinguish sexual stages (zygotes) from vegetative cells. Since G. uncatenum vegetative cells often have two complements of DNA, as do zygotes following gamete fusion, these stages could not be distinguished from each other on the basis of DNA measurements alone. However, these data in combination with cell counts were used to define the onset of sexuality and to show that the gametes of this species result from two rapid divisions.
Encystment and excystment of a Portuguese isolate culture of Amphidinium carterae in culture
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Proliferacions de dinoflagel.lades a la Costa Ca-talana: estudi del creixement in situ i adaptacions per al man-teniment
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Life history and ecology of Goniodoma pseudogoniaulax (Pyrrhophyta) in a rockpool Sexual reproduction of Alexandrium hiranoi (Dinophyceae )
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Temporary cysts of Gonyaulax excavata: effects of temperature and light
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