Cryptic speciation in Protoceratium reticulatum (Dinophyceae): Evidence from morphological,molecular and ecophysiological data

The cosmopolitan, potentially toxic dinoflagellate Protoceratium reticulatum possesses a fossilizable cyst stage which is an important paleoenvironmental indicator. Slight differences in the internal transcribed spacer ribosomal DNA (ITS rDNA) sequences of P. reticulatum have been reported, and both the motile stage and cyst morphology of P. reticulatum display phenotypic plasticity, but how these morpho-molecular variations are related with ecophysiological preferences is unknown. Here, 55 single cysts or cells were isolated from localities in the Northern (Arctic to subtropics) and Southern Hemispheres (Chile and New Zealand), and in total 34 strains were established. Cysts and/or cells were examined with light microscopy and/or scanning electron microscopy. Large subunit ribosomal DNA (LSU rDNA) and/or ITS rDNA sequences were obtained for all strains/isolates. All strains/isolates of P. reticulatum shared identical LSU sequences except for one strain from the Mediterranean Sea that differs in one position, however ITS rDNA sequences displayed differences at eight positions. Molecular phylogeny was inferred using maximum likelihood and Bayesian inference based on ITS rDNA sequences. The results showed that P. reticulatum comprises at least three ribotypes (designated as A, B, and C). Ribotype A included strains from the Arctic and temperate areas, ribotype B included strains from temperate regions only, and ribotype C included strains from the subtropical and temperate areas. The average ratios of process length to cyst diameter of P. reticulatum ranged from 15% in ribotype A, 22% in ribotype B and 17% in ribotype C but cyst size could overlap. Theca morphology was indistinguishable among ribotypes. The ITS-2 secondary structures of ribotype A displayed one CBC (compensatory change on two sides of a helix pairing) compared to ribotypes B and C. Growth response of one strain from each ribotype to various temperatures was examined. The strains of ribotypes A, B and C exhibited optimum growth at 15 °C, 20 °C and 20–25 °C, respectively, thus corresponding to cold, moderate and warm ecotypes. The profiles of yessotoxins (YTXs) were examined for 25 strains using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). The parent compound yessotoxin (YTX) was produced by strains of ribotypes A and B, but not by ribotype C strains, which only produced the structural variant homoyessotoxin (homoYTX). Our results support the notion that there is significant intra-specific variability in Protoceratium reticulatum and the biogeography of the different ribotypes is consistent with specific ecological preferences.     

Characterization of spirolide producing Alexandrium ostenfeldii (Dinophyceae) from the western Arctic

Toxin producing dinoflagellates of the genus Alexandrium Halim represent a risk to Arctic environments and economies. This study provides the first record and a characterization of Alexandrium ostenfeldii in the western Arctic. During a cruise along the coasts of western and southern Greenland 36 isolates of the species were established in August 2012. Plankton samples taken at three different stations from the upper water layer at water temperatures of approx. 4–7 °C, contained low amounts of A. ostenfeldii. Sequencing of SSU and ITS-LSU rDNA and subsequent phylogenetic analyses identified all Greenland strains as members of a NW Atlantic spirolide producing phylogenetic clade. Molecular results were confirmed by morphological features typical for this group (=Group 5 of a recent ITS-LSU phylogeny of A. ostenfeldii). The Greenland isolates did not contain either Paralytic Shellfish Poisoning toxins or gymnodimines, but produced several spirolides. Altogether 12 different analogs were detected, of which only SPX-1, C, 20-meG and H have been described earlier. The remaining 8 spirolides have not been identified so far. Some of them were found to dominate the toxin profiles of a number of isolates. Among the 36 investigated strains spirolide composition varied considerably, particularly isolates from western Greenland (Station 516) exhibited a high diversity of analogs, with different profiles in nearly all 22 isolates. All of the 34 tested Greenland strains showed considerable lytic capacity when exposed to Rhodomonas salina.     

地衣及其内生真菌活性次级代谢产物研究进展

地衣是一种独特的菌藻共生体,能够在荒漠、高山、冻土等恶劣环境生存,具有特殊的生理结构和独特的生存环境.地衣及其内生真菌能够产生结构新颖、活性广泛的次级代谢产物,研究地衣及其内生真菌次级代谢产物对新型药用资源开发以及利用等方面都具有重要的意义.本文关注了近年来地衣及其内生真菌的次级代谢产物相关研究,并对其生物活性方面的研...     

The life history of the toxic marine dinoflagellate Protoceratium reticulatum (Gonyaulacales) in culture

Asexual and sexual life cycle events were studied in cultures of the toxic marine dinoflagellate Protoceratium reticulatum. Asexual division by desmoschisis was characterized morphologically and changes in DNA content were analyzed by flow cytometry. The results indicated that haploid cells with a C DNA content occurred only during the light period whereas a shift from a C to a 2C DNA content (indicative of S phase) took place only during darkness. The sexual life cycle was documented by examining the mating type as well as the morphology of the sexual stages and nuclei. Gamete fusion resulted in a planozygote with two longitudinal flagella, but longitudinally biflagellated cells arising from planozygote division were also observed, so one of the daughter cells retained two longitudinal flagella while the other daughter cell lacked them. Presumed planozygotes (identified by their longitudinally biflagellated form) followed two life-cycle routes: division and encystment (resting cyst formation). Both the division of longitudinally biflagellated cells and resting cyst formation are morphologically described herein. Resting cyst formation through sexual reproduction was observed in 6.1% of crosses and followed a complex heterothallic pattern. Clonal strains underwent sexuality (homothallism for planozygote formation and division) but without the production of resting cysts. Ornamental processes of resting cysts formed from the cyst wall under an outer balloon-shaped membrane and were fully developed in <1 h. Obligatory dormancy period was of ∼4 months. Excystment resulted in a large, rounded, pigmented, longitudinally biflagellated but motionless, thecate germling that divided by desmoschisis. Like the planozygote, the first division of the germling yielded one longitudinally biflagellated daughter cell and another without longitudinal flagella. The longitudinal biflagellation state of both sexual stages and of the first division products of these cells is discussed.     

Yessotoxins production during the culture of Protoceratium reticulatum strains isolated from Galician Rias Baixas (NW Spain)

Yessotoxins (YTXs) production along the culture growth of three strains of the dinoflagellate Protoceratium reticulatum isolated from seawater of Galician Rias Baixas, Spain was investigated. Quantification and toxin profile determination in both cells and culture medium along the growth curve were performed by liquid chromatography–mass spectrometry (LC–MS³) analysis. The YTX profile was very similar among strains, the three algal strains produce mainly YTX and also some YTX analogs. Among the strains the maximum toxin production ranged between 416 and 576 ng mL⁻¹. This is the first report about YTX production by P. reticulatum isolated in Galician coast, NW Spain.     

青灰叶下珠内生菌Phomopsis sp.TJ507A的化学成分及生物活性研究

为探究药用植物青灰叶下珠(Phyllanthus glaucus)来源内生真菌拟茎点霉(Phomopsis sp. TJ507A)的化学成分,本实验联合运用硅胶柱色谱、ODS柱色谱、凝胶柱色谱(Sephadex LH-20)、半制备型高效液相色谱(HPLC)等分离技术,从该菌株大米固体发酵产物的乙酸乙酯提取物中分离得到4个倍半萜化合物phomophyllin O(1)、phomophyllin P(2)、7-hydroxy-10-methoxydehydrodihydrobotrydial(3)、plorantinone D(4)和8个甾体化合物fortis-terol(5)、dankasterone B(6)、(14α,22E)-14-hydroxy-ergosta-7,22-diene-3,6-dione(7)、(14α,22E)-14-hydroxyerg-osta-4,7,22-triene-3,6-dione(8)、calvasterol B(9)、isocyathisterol(10)、ergosta-4,6,8(14),22-tetraen-3-one(11)和ganodermaside D(12)。化合物1和2为新化合物,运用现代波谱分析技术、[Rh2(OCOCF3)4]络合诱导ECD法及与文献对比等方法,鉴定了化合物1和2的结构和绝对构型。化合物1～5、7、8和10均为首次从该属真菌中分离得到。通过体外生物活性评价,发现化合物9具较强的NO生成抑制活性(IC508. 7μM)。     

基于超高效液相色谱-电喷雾-质谱、天然产物词典和活性筛选的艾纳香内生真菌次生代谢产物

【背景】植物内生真菌是天然活性小分子的重要来源,但由于种类繁多,导致寻找结构新颖、活性强的化合物非常困难,重复分离已成为制约新型药源小分子发掘的瓶颈。【目的】综合各种技术,快速寻找目标活性次生代谢产物。【方法】通过对菌株分子鉴定、天然产物词典(dictionaryofnatural products,DNP)数据库检索、超高效液相色谱-电喷雾-质谱(ultraperformanceliquidchromatographyquadrupole time-of-flight mass spectrometry,UPLC-QTof-MS)分析、滤纸片法抑菌实验和色谱技术跟踪获得活性单体化合物。运用质谱和单晶衍射技术对化合物结构进行鉴定,96孔板法对单体化合物进行活性评价。【结果】分离鉴定出11株艾纳香内生真菌,筛选出一株各方面表现良好的艾纳香内生菌菌株Diaporthe sp.,从其大米培养基中获得一个单体化合物Cytochalasin H,活性评价显示其对枯草芽孢杆菌具有很好的抑制活性,MIC值为32μg/mL。【结论】将多种筛选技术相结合的方法应用于艾纳香内生真菌活性代谢产物的发掘,为快速寻找活性先导化合物提供了很好的借鉴。     

Novel bioactive metabolites of dipyrone (metamizol)

Dipyrone is a common antipyretic drug and the most popular non-opioid analgesic in many countries. In spite of its long and widespread use, molecular details of its fate in the body are not fully known. We administered dipyrone orally to mice. Two unknown metabolites were found, viz. the arachidonoyl amides of the known major dipyrone metabolites, 4-methylaminoantipyrine (2) and 4-aminoantipyrine (3). They were identified by ESI-LC-MS/MS after extraction from the CNS, and comparison with reference substances prepared synthetically. The arachidonoyl amides were positively tested for cannabis receptor binding (CB(1) and CB(2)) and cyclooxygenase inhibition (COX-1 and COX-2 in tissues and as isolated enzymes), suggesting that the endogenous cannabinoid system may play a role in the effects of dipyrone against pain.     

Rotifers from the Canadian high arctic (Devon Island,Northwest territories)

Samples from eight water bodies in the region of Truelove and Sparbo Hardy Lowland, Devon Island (75 ° 30 N, 86 ° 00 W) yielded 70 taxa (4 Bdelloidea, 66 Monogononta) of rotifers, nineteen of which are new records for the Canadian High Arctic.     

Compartmentation and localization of bioactive metabolites in different organs of Allium roylei

To investigate the involvement of Allium roylei metabolites in the plant’s defenses, a comprehensive analysis of the content of cysteine sulfoxides, flavonols, polyphenols, ascorbic acid, and saponins was carried out in the various organs of this species. Metabolomics high performance liquid chromatography (HPLC), spectral-based analysis, and histochemcial studies have given important insight to the validity of saponins as a key component involved in plant protection. The root-basal stem, bulb, and leaf extracts exhibited 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity with inhibition concentration (IC₅₀) ranging from 0.649 to 0.757?mg/mL. The antimicrobial properties of the saponin and flavonoid crude extracts were evaluated. The saponin extracts demonstrated significant antifungal activity depending on the applied concentration, and the growth inhibition rate of the tested fungal pathogens ranged from 1.07 to 47.76%. No appreciable antibacterial activity was recorded in the same sample.     

Characterization and antimicrobial activity of the bioactive metabolites in streptomycete isolates

Twenty different streptomycete isolates were obtained from soils of southeast Serbia. Five isolates identified as Streptomyces hygroscopicus (SH100, SH101, SH102, SH103, and SH104) showed strong activity against Botrytis cinerea, a parasite found in domestic vines. These isolates were extensively studied for their in vitro antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, yeasts and fungi, and also antiviral activity against Herpes simplex. The results indicated that the obtained isolates were highly active against Botrytis cinerea, Candida albicans, and Herpes simplex, with an inhibition zone at ≥31 mm. The structure of the bioactive components was determined using elemental analysis, as well as UV/VIS, FTIR, and TLC.     

Growth responses of arctic graminoids following grazing by captive lesser snow geese

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0–180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.     

Parallel evolutionary patterns in multiple lineages of arctic Artemisia L. (Asteraceae)

Early observers of plant evolution in the Arctic have noted a floristic similarity with temperate alpine regions and a predominance of high ploidy levels. The aim of our study was to survey these and other traits in multiple closely related but independently evolved lineages of Artemisia. Our phylogenetic study was based on 133 taxa using 3'-ETS and ITS, and on data on morphology, karyology, distribution, and ecological preferences. We compared Arctic lineages with sister groups and tested whether patterns were significantly different. We found: (1) Artemisia has independently adapted to Arctic habitats 13-18 times; (2) There were no ecological preferences of putative progenitors that might determine the colonization success in the Arctic, although most sister groups were centered in steppe habitats; (3) Plant height was distinctly reduced in Arctic lineages; (4) Arctic lineages contained no more polyploids than their respective sister groups or taxa from other habitats; (5) Enlarged flower heads have evolved repeatedly, probably for better pollinator attraction. This strategy could be a substitute for polyploidy, which is typical in other Arctic taxa. Stronger pollinator attraction should result in better outcrossing and higher heterozygosity in the offspring, which is among the main effects of polyploidy.     

Effects of temperature,salinity and their interaction on growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a seafood poisoning that is widespread in tropical, subtropical and temperate regions of the world. In the main island of Japan, distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3, have been reported. To discuss the bloom dynamics of these Japanese species/phylotypes of Gambierdiscus, first we tested six culture media to optimize growth conditions and then clarified the effects of temperature and salinity and temperature–salinity interactions on growth. All strains of the species/phylotypes tested showed the highest cell yields when they were cultivated in IMK/2 medium. G. australes, G. scabrosus and Gambierdiscus sp. type 2 grew in the range 17.5–30 °C, whereas Gambierdiscus sp. type 3 grew in 15–25 °C. The semi-optimal temperature ranges (≥80% of the maximal growth rate) of the former three species/phylotypes were 19–28 °C, 24–31 °C and 21–28 °C, respectively, whereas that of the latter phylotype was 22–25 °C. Hence, Gambierdiscus sp. type 3 may be adapted to relatively lower water temperatures of ≤25 °C. In contrast, G. australes, G. scabrosus and Gambierdiscus sp. type 2 presumably possess adaptability to relatively high water temperatures. The optimal temperature for G. scabrosus was 30 °C, whereas the optimal temperature for the others was 25 °C. G. australes and Gambierdiscus sp. type 3 grew in a salinity range of 25–40 whereas G. scabrosus and Gambierdiscus sp. type 2 grew in salinity 20–40. Furthermore, the semi-optimal salinity range of G. australes, G. scabrosus, Gambierdiscus spp. type 2 and type 3 were salinity 27–38, 24–36, 22–36 and 29–37, respectively. Among the species/phylotypes, G. scabrosus and Gambierdiscus sp. type 2 grew even at salinity 20 where the others did not grow, thus possessing adaptability to low salinity waters. Our results clearly demonstrate that the optimal and tolerable temperature–salinity conditions differ among Japanese Gambierdiscus species/phylotypes. Considering these results, temperature–salinity interactions may play an important role in bloom dynamics and the distribution of the Gambierdiscus species/phylotypes in Japanese coastal waters.     

Dietary variation in arctic foxes (Alopex lagopus)-an analysis of stable carbon isotopes

We used stable carbon isotopes to analyse individual variation in arctic fox diet. We extracted collagen from bones (the lower jaw), and measured stable carbon isotopes. The foxes came from three different localities: Iceland, where both microtines and reindeer are rare; west Greenland, where microtines are absent; and Sweden, where scat analyses showed the primary food to be microtine rodents and reindeer. The Icelandic samples included foxes from both coastal and inland habitats, the Swedish sample came from an inland area, and the Greenland sample from coastal sites. The spatial variation in the isotopic pattern followed a basic division between marine and terrestrial sources of protein. Arctic foxes from inland sites had ¹³C values of –21.4 (Iceland) and –20.4 (Sweden), showing typical terrestrial values. Coastal foxes from Greenland had typical marine values of –14.9, whereas coastal foxes from Iceland had intermediate values of –17.7. However, there was individual variation within each sample, probably caused by habitat heterogeneity and territoriality among foxes. The variation on a larger scale was related to the availability of different food items. These results were in accordance with other dietary analyses based on scat analyses. This is the first time that stable isotopes have been used to reveal individual dietary patterns. Our study also indicated that isotopic values can be used on a global scale.     

Modem organic-walled dinoflagellate cysts in arctic marine environments and their (paleo-) environmental significance

The Arctic Ocean is one of the least known marine regions of the world. Because of its major influence on global climate and its hostile environmental conditions it is a fascinating area for paleoecological, paleoclimatic and paleoceanographic research. The composition of planktic microfossil assemblages, and both the trace-element and stable isotope compositions of hard parts, provide us with valuable information about the physical and biochemical parameters of surface waters in the high northern latitudes. Calcareous and biosiliceous microfossils that are traditionally used in Quaternary paleoenvironmental studies are of limited value in the Arctic Ocean because of their low abundances, low diversity and/or low preservation potential. The past several decades have seen considerable progress in our knowledge of the ecology and biogeography of dinoflagellates and their organic-walled cysts in the high northern latitudes, and these dinoflagellate cysts are now important proxies for reconstructing surface water conditions in the Quaternary. This arcticle gives an overview of the ecology of dinoflagellates and their cysts, the processes that transform the living communities into sediment communities, and the environmental gradients that may be reconstructed from fossil dinoflagellate cysts assemblages in the high northern latitudes.      

Cold-hardiness of the arctic beetle, Pytho americanus Kirby Coleoptera,Pythidae (Salpingidae)

The arctic beetle, Pytho americanus Kirby, is frost tolerant in both larval and adult stages. This is the first demonstration that an insect can tolerate freezing in more than one life stage, a situation which would be congruous with its northern distribution and allow it to spread its life cycle over a number of growing seasons. The main biochemical correlates during the cold hardening process of low temperature acclimation are increasing glycerol and decreasing glycogen concentrations. Glycerol is the only polyol to be synthesized during acclimation, and it accumulates to a maximum of 8.2 and 12.2% of the fresh body weight in larvae and adults respectively. This coincides with the peak of frost tolerance. In addition to its normally assumed roles in cryoprotection it is suggested that glycerol may further serve to minimize dehydration in the overwintering insect by increasing the level of ‘bound’ water. Evidence is presented that indicates that glycerol is synthesized mainly from carbohydrate reserves, especially glycogen, but it does not rule out the possibility that a proportion of free glycerol comes from glyceride sources.P. americanus larvae and adults have low supercooling potential and maintain their supercooling points in the region of ?4° to ?8°C. It is hypothesized that these elevated supercooling points are a result of the presence in the haemolymph of nucleating agents which ensure ice formation at high sub-zero temperatures. It is believed that this beetle overwinters in a frozen state within its microhabitat, which is under bark of fallen spruce which is, in turn, covered by an insulating blanket of snow. The advantages of this overwintering strategy are discussed.     

Growth pattern of isolated zoospores in Hydrodictyon reticulatum (Chlorococcales, Chlorophyceae)

Zoospores at various developmental stages in Hydrodictyon reticulatum were isolated from parent cells and cultured in Waris medium. Isolated zoospores grew to mature vegetative cells, and were able to reproduce zoo-spores that formed daughter hexagonal nets. Three types of shape appeared in cells 24 h after isolation: cylindrical, Y-shaped and 4-armed type. Protrusions of Y-shaped or 4-armed cells were formed at an angle of about 120° to the long axis of the cell. When cells were isolated at later stages, more cells became cylindrical in shape and fewer ceils became Y-shaped or 4-armed, Direction of cell growth also seemed to depend largely on the developmental stages of the zoospores. The later the isolated stages were, the more the cells elongated along the long axis of the zoospores.     

Molecules and morphology in concert: tests of some hypotheses in arctic Potentilla (Rosaceae)

We developed a combined molecular and morphological approach to unravel complex variation at low taxonomic levels, exemplified by some arctic members of Potentilla. Twenty-one populations from Svalbard were analyzed for random amplified polymorphic DNAs (RAPDs) and 64 morphological characters to test the hypotheses that (1) the P. nivea complex (section Niveae) consists of three taxa (P. chamissonis, P. insularis, and P. nivea), (2) three "eco-morphotypes" in P. pulchella (section Multifidae) should be considered different taxa, and (3) P. insularis originated as an intersectional hybrid (Niveae × Multifidae). Twenty-two RAPD multilocus phenotypes were observed in the 136 plants analyzed based on 35 markers. Three fairly distinct groups of RAPD phenotypes were identified in the P. nivea complex based on multivariate analyses and an analysis of molecular variance (AMOVA; 77.6% among-group variation). The variation within the P. nivea complex was more or less continuous in multivariate analyses of the morphological data. We identified, however, several individual morphological characters that separated unambiguously among the three groups of RAPD phenotypes, revealing that these groups correspond to the previously hypothesized taxa. Many identical RAPD multilocus phenotypes were observed in the "eco-morphotypes" of P. pulchella, suggesting that its conspicuous morphological variation is caused by plasticity or by genetic variation at a small number of loci. The hypothesis of the hybrid origin of P. insularis was not supported by the RAPD data. Overall, very little RAPD variation was observed within populations of the four taxa (2.1-16.7% in AMOVA analyses; average genotypic diversity, D, was 0.10-0.30). We conclude that detailed, concerted analysis of molecules and morphology is a powerful tool in low-level taxonomy.     

Temperature mediates secondary dormancy in resting cysts of Pyrodinium bahamense (Dinophyceae)

High‐biomass blooms of the toxic dinoflagellate Pyrodinium bahamense occur most summers in Tampa Bay, Florida, USA, posing a recurring threat to ecosystem health. Like many dinoflagellates, P. bahamense forms immobile resting cysts that can be deposited on the seafloor—creating a seed bank that can retain the organism within the ecosystem and initiate future blooms when cysts germinate. In this study, we examined changes in the dormancy status of cysts collected from Tampa Bay and applied lessons from plant ecology to explore dormancy controls. Pyrodinium bahamense cysts incubated immediately after field collection displayed a seasonal pattern in dormancy and germination that matched the pattern of cell abundance in the water column. Newly deposited (surface) cysts and older (buried) cysts exhibited similar germination patterns, suggesting that a common mechanism regulates dormancy expression in new and mature cysts. Extended cool‐ and warm‐temperature conditioning of field‐collected cysts altered the cycle of dormancy compared with that of cysts in nature, with the duration of cool temperature exposure being the best predictor of when cysts emerged from dormancy. Extended warm conditioning, on the other hand, elicited a return to dormancy, or secondary dormancy, in nondormant cysts. These results directly demonstrate environmental induction of secondary dormancy in dinoflagellates—a mechanism common and thoroughly documented in higher plants with seasonal growth cycles. Our findings support the hypothesis that a seasonal cycle in cyst germination drives P. bahamense bloom periodicity in Tampa Bay and point to environmentally induced secondary dormancy as an important regulatory factor of that cycle.