THE CALCAREOUS RESTING CYST OF PENTAPHARSODINIUM TYRRHENICUM COMB. NOV. (DINOPHYCEAE)1

While investigating dinoflagellate cyst assemblages in surface sediments of the Gulfs of Naples and Salerno (Mediterranean Sea), we found a new calcareous resting cyst. This cyst has a round to oval body surrounded by a thick mineral layer, which gives it the shape of a Napoleon hat, with a flat, oval face bearing the archeopyle and a convex keel on the opposite side. The cyst shape is variable in both natural samples and clonal cultures. The organic membrane underlying the calcareous covering is resistant to acetolysis, thus demonstrating the presence of sporopolleninlike material. The cyst germinated into a motile stage having the same morphological features and thecal plate pattern as Peridinium tyrrhenicum Balech. We believe the validity of the genus Pentapharsodinium Indelicato & Loeblich should be accepted. Based on the comparative examination of the species we collected and of a similar species, Pentapharsodinium trachodium Indelicato & Loeblich, we propose Pentapharsodinium tyrrhenicum as a new combination for Peridinium tyrrhenicum. The genus Pentapharsodinium also includes P. dalei Indelicato & Loeblich (= Peridinium faeroense Dale), which produces spiny, organic-walled cysts. The presence of species forming calcareous cysts and species producing noncalcareous cysts in the same genus raises questions about maintaining the family Calciodinellaceae. This family should only include calcareous cyst-forming peridinioids, in order to maintain a unified system of classification of fossil and recent dinoflagellates.     

Examples for character traits and palaeoecological significance of calcareous dinoflagellates

The palaeoecological significance of calcareous dinoflagellate cysts is illustrated by various examples. Genetically fixed and ecologically triggered character traits are distinguished. A summary is given regarding intraspe-cific variability, cyst size and shape, wall thickness, size and shape of the calcitic wall crystals, paratabulation, and archeopyle morphology based on the knowledge, which has been accumulated during the last two decades. Diversity and characteristic cyst associations from different localities are compared. Information on sea level changes, water temperature, oceanographic distribution, and nutrient conditions can be gained from the investigated character traits of calcareous dinoflagellates.      

Pithonelloid wall-type of the Late Cretaceous calcareous dinoflagellate cyst genus Tetratropis

The late Cretaceous calcareous dinoflagellate genus Tetratropis features both a pithonelloid wall-type (evenly inclined wall-components, proven here by a polarisation optical revision) and a peridinialean paratabulation strongly suggesting a dinoflagellate origin of at least part of the Pithonelloideae. This affinity with dinoflagellates sheds more light on the palaeoecology of the Pithonelloideae (commonly termed “calcispheres”), which are characteristic of the middle to Late Cretaceous. The very short-term stratigraphic occurrence of all Tetratropis species is comparable to the distribution pattern of other calcareous dinoflagellate cyst species with a distinctive paratabulation and is thought to reflect a narrow palaeoecological niche. Tetratropis species can be interpreted either as paratabulated morphotypes of otherwise atabulate Pithonelloideae formed under exceptional palaeoenvironmental conditions or as invaders from a highly specific palaeoecological niche during short-term palaeoceanographic events probably related to the initiation of the Late Cretaceous global cooling.     

Distributions of calcareous dinoflagellate cysts in surface sediments of the western equatorial Atlantic Ocean,and their potential use in palaeoceanography

Only very few studies focus on recent calcareous dinoflagellate cyst diversity, geographic distribution and ecology, so that information on the distribution patterns and environmental affinities of individual cyst species is extremely limited. This information is, however, essential if we want to use calcareous dinoflagellate cysts for palaeoenvironmental reconstruction. Surface sediment samples from the generally oligotrophic western equatorial Atlantic Ocean, offshore northeast Brazil, were therefore quantitatively analysed for their calcareous dinoflagellate cyst content, including the calcareous vegetative coccoid Thoracosphaera heimii. Seven calcareous dinoflagellate cyst species/morphotypes and T. heimii were encountered in high concentrations throughout the area. Substantial differences in the distribution patterns were observed. The highest concentrations of cysts are found in sediments of the more oligotrophic, oceanic regions, beyond the influence of Amazon River discharge waters. Dinoflagellates producing calcareous cysts thus appear to be capable of surviving low nutrient concentrations and produce large numbers of cysts in relatively stable and predictable environments affected by minimal seasonality. To test for the environmental affinities of individual species, distribution patterns in surface sediments were compared with temperature, salinity, density and stratification gradients within the upper water column (0–100 m) over different times of the year, using principal components analysis and redundancy analysis. T. heimii and four of the seven encountered cyst species (Sphaerodinella? albatrosiana, two morphotypes of Sphaerodinella? tuberosa and Scrippsiella regalis) relate to these parameters significantly and the variations in the cyst associations appear to be associated with the different surface water currents characterising the area. The results imply that calcareous dinoflagellate cyst distributions can potentially be used to distinguish between different open oceanic environments and they could, therefore, be useful in tracing water mass movements throughout the late Quaternary.     

Morphological features and viability of Scrippsiella trochoidea cysts isolated from fecal pellets of the polychaete Capitella sp.

To investigate the impact of grazing by the polychaete Capitella sp. on the two cyst morphotypes of Scrippsiella trochoidea, the typical morphotype with short calcareous spines (spiny-type cyst) and artificially induced the transparent type without calcareous spines (naked-type cyst), we examined the morphological features and germination capability of the two cyst morphotypes isolated from fecal pellets of the polychaete Capitella sp. produced in a restricted habitat. The morphological destruction was observed in both spiny- and naked type cysts after passage through the gut of Capitella sp., and this seemed to occur rapidly for naked-type cysts. In addition, the germination of both spiny- and naked-type cysts isolated from fecal pellets on day 2 of harvesting was significantly reduced and subsequently completely abolished, in contrast to previous findings from ingestion studies. Our results indicate that continual grazing by Capitella sp. within a restricted habitat can compromise the survival of S. trochoidea cysts.     

A NEW SPECIES OF ENSICULIFERA,E. IMARIENSE (DINOPHYCEAE), PRODUCING ORGANIC-WALLED CYSTS1

We describe a new organic-walled resting cyst from surface sediments of Imari Bay in western Japan. The cysts are spherical, 23–29 pm in diameter, and their surface is covered with spinous to membranous ornaments that are 5–7 μm long and 1.5–2.2 μm wide. The ornaments vary from slender and bifurcate to membranous and multifurcate distal extremities. No archeopyle was observed. The cyst shape is variable in both natural samples and clonal cultures. Vegetative cells are small and ovoid, 17–25 μm long and 14–21 μm wide, and are yellow-brown in color. The epitheca is conical with a conspicuous apical horn, and the hypotheca is hemispherical. The cingular transitional plate has a needle-like spine at its anterior right corner. The plate formula is Po, X, 4″3a, 7″, 5c, 5s 5″and 2″. Although vegetative cells of the present species correspond to Ensiculifera, it is distinct from other species in producing no calcareous cysts. No species of Ensiculifera has been reported to produce cysts composed of only an organic wall. The present species is provisionally placed in the genus Ensiculifera as E. imariense sp. nov.     

甲藻孢囊在长江口海域表层沉积物中的分布

为了了解长江口海域赤潮爆发潜势,于2002年4月至5月用采泥器采集了位于122°～123．5°E、29°～32°N之间12个站位的表层沉积物,分析沉积物中甲藻孢囊的分布．共分析鉴定出孢囊类型29种,其中自养型11种,异养型18种．每个站位的孢囊种类在10～21之间,孢囊密度为11．7～587孢囊·g-1干泥之间．远岸海域孢囊种类较为丰富,密度也较高．在调查区域内,孢囊密度及种类自西向东、自北向南逐渐增加．亚历山大藻孢囊分布广泛,最高密度为40．4孢囊·g-1干泥,其他赤潮种类的孢囊如链状裸甲藻、多边舌甲藻、锥状斯氏藻、科夫多沟藻和无纹多沟藻等都在长江口海域有分布．     

Dinoflagellate cyst records in recent sediments from Daya Bay, South China Sea

Nine sediment cores of 8–26 cm in length were collected from two basins of Daya Bay, the South China Sea, by Tokyo University Fisheries Oceanography Laboratory core sampler in August 2001 to investigate the distribution of dinoflagellate resting cysts. In the present study, 51 different cyst morphotypes representing 22 genera were identified from 65 sediment samples. Among them, there were 21 autotrophic species and 30 heterotrophic ones. Cyst species richness in each sample varied from 12 to 29, while the values of Shannon‐Weaver diversity index (H′) were between 0.15 and 4.13. There were an obvious increase in both species richness and values of H′in 2–6 cm sediments. Cyst concentrations varied from 154 to 113 483 cysts per gram dry weight sediment, and were much higher in upper sediments. Scrippsiella trochoidea was the most dominant cyst type, which took up over 90% of cyst assemblages in the upper sediments. The abrupt increase of S. trochoidea cysts in the surface sediments reflected the bloom of this species in Daya Bay in 2000. The results from cyst assemblages showed some trend of changes in water quality in this area, and indicated a typical type of pollution caused by cultural eutrophication, which started in the 1980s and greatly accelerated in the middle of 1990s. Cysts of Alexandrium, mainly those of Alexandrium catenella and Alexandrium tamarense complex, occurred frequently and abundantly in this area, with the highest concentration and relative frequency of 503 cysts per gram dry weight sediment and 22.3%, respectively. The high abundance of Alexandrium cysts provided rich ‘seed bed’ for Alexandrium blooms and was also an important source of paralytic shellfish poisoning toxins, especially in winter.     

Seasonal distribution of dinoflagellate resting cysts in surface sediments from Changjiang River Estuary

In order to understand the distribution of dinoflagellate cysts, surface sediments were collected from 15 stations in Changjiang River Estuary from 122°E to 123.5°E and from 29°N to 32°N in four cruises from May 2002 to February 2003. In the present study, 38 different cyst morphotypes representing 21 genera and 6 groups were identified, while 1 type was not identified into genus level. Species number and cell density of dinoflagellate cysts ranged from 10 to 25 species and from 12 to 587 per gram of dry weight, respectively. There were no obvious differences in cyst composition and density among seasons. However, the highest cyst species number and density were recorded in summer and winter, respectively. Cysts of heterotrophic dinoflagellates, which held 55.7% of the overall cyst density averagely, dominated cyst assemblages. Cyst density and species number increased from the west to the east, from the north to the south within the study area. Cysts of toxic dinoflagellates Alexandrium cat‐enella and Alexandrium tamarense complex distributed widely and were observed in almost all stations, with the maximum cell density of 81 per gram of dry weight.     

The chrysophycean paleocyst flora of the bottom sediments of Kortowskie Lake (Poland) and its ecological significance

The postglacial sediments of Kortowskie Lake contain well preserved chrysophycean cysts. Forty-six morphotypes were identified by scanning electron microscopy (SEM) and light microscopy (LM). Ten new morphotypes of fossil chrysophycean cysts are described. Some of the most abundant taxa show clear trends associated with the increase in lake trophic status. The cyst flora is divided into four groups: eutrophic forms (Cysta globata, C. cortoviensis, C. vermicularis); oligotrophic forms (Cysta curvicollis); cool-water forms (Cysta carinifera, C. crassicollis, C. microspinosa, C. modica and Cysta stellata), and indifferent forms (all other morphotypes which did not show a clear tendency). The percentage abundance of chrysophycean cysts wa related to climate changes, showing a considerable increase during the Subboreal period. Two factors, lake fertility and water level changes affected the abundance of the fossil cyst flora in the sediments of Kortowskie Lake.     

Chrysophyte stomatocyst assemblages associated with periphytic, high arctic pond environments

Chrysophycean stomatocysts associated with three different periphytic substrates (wet mosses, submerged mosses and rock scrapes) were investigated from ponds on Cape Herschel (78°37'N, 74°42'W), Ellesmere Island in the Canadian High Arctic. The goal of this study was to determine whether a distinct assemblage of periphytic chrysophyte cysts existed and, if so, whether assemblage composition varied with substrate and between ponds. One hundred and thirty-seven different cyst morphotypes were observed with light microscopy from 68 periphytic samples taken from 35 ponds. Twenty-six of these cysts were new morphotypes, of which 16 were identified and described using scanning electron microscopy. Significantly more cyst types with collars and hooked projections in the collar region (i.e. 'hooked'), and fewer unomamented morphotypes were recorded in the periphytic habitats as compared to the surface sediments. Wet moss stomatocyst assemblages were particularly distinct, with a high number of heavily silicified and hooked morphotypes. The morphotype richness was far greater in periphytic environments, with 86, 100 and 95 morphotypes observed in the wet mosses, submerged mosses and rock scrapes, respectively, as compared to only 35 types in the surface sediments of the ponds. Canonical correspondence analysis indicated that measured water chemistry did not account for the variation in the species data (p_{axic 1} < 0.01, 999 Monte Carlo permutations). This study suggests that distinct periphytic assemblages exist, and that cyst morphotype composition and richness varies with substrate.     

Calcareous dinoflagellate cysts in South and equatorial Atlantic surface sediments: diversity,distribution, ecology and potential for palaeoenvironmental reconstruction

Several marine, peridiniphycidean dinoflagellate species produce calcareous cysts during their life cycle, which are relatively resistant to chemical and physical degradation and are therefore often found in large quantities in oceanic bottom sediments. Although the use of these calcareous cysts as proxies for palaeoenvironmental and palaeoclimatic reconstructions has seen many advances over the last decade, until now only relatively patchy and regional information was available on their recent distribution patterns and ecology, especially at the species level. In this paper, comprehensive calcareous cyst diversity and distribution data have been compiled from published and unpublished work for 167 South and equatorial Atlantic Ocean surface sediments, ranging from 20°N to 50°S, and 30°E to 65°W. The main aim has been to focus on the complex, often non-linear, relationships between individual species’ distributions and the physicochemical and trophic conditions of the overlying (sub)surface waters through the use of x–y graphs of cyst abundance vs. (sub)surface water environmental parameters, and detrended correspondence analyses. Ten cyst species and the calcareous vegetative coccoid species Thoracosphaera heimii were observed in the bottom sediments, each species showing its own characteristic distribution pattern in relation to the environmental conditions of the upper water masses above them (e.g. sea surface temperature, productivity, stratification). The sensitive reactions of various species to unique combinations of environmental parameters shows that each species has its own specific ecological traits, thus rejecting the bundled use of ‘calcareous cyst accumulation’ as a general proxy for oligotrophy or stratification in future palaeoenvironmental analyses. The acquired ‘reference’ data set of this study is large and diverse enough to allow its future application in quantitative palaeoenvironmental reconstruction models, and shows that there is still an enormous reconstruction potential concealed in many fossil calcareous dinoflagellate cyst assemblages.     

Scrippsiella trochoidea and scrippsiella regalis, nov. comb. (peridiniales, dinophyceae): a comparison

Culture experiments on dinoflagellates from the Atlantic Ocean revealed Scrippsiella regalis (Gaarder) Janofske, nov. comb., a calciodinelloid species with a spherical spiny calcareous cyst. This calcareous cyst was collected previously from plankton and sediment samples, where it was described as the coccolithophorid Discosphaera regalis Gaarder or was often mistaken for the cyst of Scrippsiella trochoidea (von Stein) Loeblich III. The morphological features of both the cellulosic theca and the calcareous cyst of S. trochoidea and S. regalis were compared with respect to their systematic position and the emendation of taxa. Both species were found to have different distribution patterns. Scrippsiella trochoidea is known only from the neritic environment, whereas S. regalis has been found mostly in oceanic samples. The preservation of these spiny calcareous dinocysts in the (fossil) sediment was dependent on the ultrastructure of the calcareous layer of the cyst wall.     

CONTROL OF GERMINATION OF ALEXANDRIUM TAMARENSE (DINOPHYCEAE) CYSTS FROM THE LOWER ST. LAWRENCE ESTUARY (CANADA)

Cysts of the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech 1992 from the lower St. Lawrence estuary were used in a test of the following hypotheses: (1) cyst germination is triggered by a change in temperature, and (2) germination rate varies throughout the year and is controlled by a circannual internal biological clock. Results show that cyst germination was not affected significantly by temperature of incubation over the range 1°–16° C, and light showed no significant stimulation of germination. This is supported by the lack of effect of cyst incubation conditions during evaluation of the seasonal changes in germination rate (two temperatures: 4° and 15° C, and two light conditions: darkness and 150 μmol photons·m^?2·s^?1). Thus, direct environmental control through short-term increases in temperature and exposure to light has no effect on the germination of the cysts tested. The rate of germination, observed monthly over a 16-month period, showed low germination (<20%) over most of the period tested, except for a maximum reaching more than 50% germination in August to October of the second year of the experiment. This pattern was observed for cysts both from monthly field collections and from laboratory-stored cysts kept under constant environmental conditions (4° C, in the dark). The peak in germination observed under constant environmental conditions (in the laboratory), the almost coincidental increase in cyst germination observed for the field-collected cysts, and the absence of effects of temperature and light during incubation could be explained either by a temperature-controlled cyst maturation period (the time-temperature hypothesis of Huber and Nipkow 1923) or by the presence of an internal biological clock. However, the large decline in the rate of germination 2 months after the maximum provides strong support for the biological clock hypothesis. The ca. 12-month maturation (dormancy) period observed for the laboratory-stored cysts is the longest reported for this species to our knowledge; this might be related to the low storage temperature (4° C), which is close to bottom temperatures generally encountered in this environment (0° to 6° C). Similar field and laboratory storage temperatures could explain the coincidental increase in germination rate in the fall of the second year if cyst maturation is controlled by temperature. A fraction of the laboratory-stored cysts did not follow a rhythmic pattern: A rather constant germination rate of about 20% was observed throughout the year. This continuous germination of likely mature cysts may supplement the local blooms of this toxic dinoflagellate, as these often occur earlier than peak germination observed in late summer. It seems that two cyst germination strategies are present in the St. Lawrence: continuous germination after cyst maturation, with temperature controlling the length of the maturation period, and germination controlled by a circannual internal rhythm.     

EVIDENCE FOR ASEXUAL RESTING CYSTS IN THE LIFE CYCLE OF THE MARINE PERIDINOID DINOFLAGELLATE,SCRIPPSIELLA HANGOEI1

Scrippsiella hangoei (Schiller) Larsen is a peridinoid dinoflagellate that grows during winter and spring in the Baltic Sea. In culture this species formed round, smooth cysts when strains were mixed, indicating heterothallic sexuality and hypnozygote production. However, cysts of the same morphology were also formed in clonal strains exposed to slightly elevated temperature. To better understand the role of cysts in the life cycle of S. hangoei, cyst formation and dormancy were examined in culture experiments and the cellular DNA content of flagellate cells and cysts was compared in clonal and mixed strains using flow cytometry. S. hangoei exhibited a high rate of cyst formation in culture. Cysts produced in both clonal and mixed strain cultures were thick‐walled and underwent a dormancy period of 4 months before germinating. The S. hangoei flagellate cell population DNA distributions consisted of 1C, intermediate, and 2C DNA, indicative of respective eukaryotic cell cycle phases G1, S, and G2M. The majority (>95%) of cysts had a measured DNA content equivalent to the lower 1C DNA value, indicating a haploid nuclear phase and an asexual mode of cyst formation. A small percentage (<5%) of cysts produced in the mixed strain culture had 2C DNA, and thus could have been diploid zygotes. These findings represent the first measurements of dinoflagellate resting cyst DNA content, and provide the first quantitative evidence for dinoflagellate asexual resting cysts. Asexual resting cysts may be a more common feature of dinoflagellate life cycles than previously thought.     

Protoperidinium tricingulatum sp. nov. (Dinophyceae), a new motile form of a round,brown, and spiny dinoflagellate cyst

A small, broadly ovoidal and heterotrophic dinoflagellate containing round, brownish, and spiny cyst was found in the water column of Huibertsplaat in the Wadden Sea off the coast of the Netherlands. This dinoflagellate had these conspicuous morphological characters: a five‐sided first apical plate (1′), only three cingular plates, and an extremely small first antapical plate. Based on these morphological features, Protoperidinium tricingulatum Kawami, vanWezel, Koeman et Matsuoka is described as a new species. The flagellar pore of P. tricingulatum is covered with a small fin, which rises from the left side of the right sulcal plate to the large V‐shaped posterior sulcal plate. This feature suggests that P. tricingulatum is assigned to the Abé's Monovela Group. The cyst stage of P. tricingulatum was positively linked to the vegetative stage by comparison of the ribosomal 5.8S rDNA, internal transcribed spacers (ITS1 and ITS2). Living cysts of P. tricingulatum are round, brownish, and covered with many slender spines bearing capitate or cauliforate distal ends. The cyst also possesses a theropylic archeopyle formed by a slit corresponding to parasutures between three apical and two apical intercaraly plates. These morphological characters indicate that this species is morphologically related to two dinoflagellate cyst‐genera Islandinium and Echinidinium.     

广东大亚湾甲藻孢囊及其与锥状斯氏藻赤潮的关系

1999年12月至2001年1月,在大亚湾澳头海域用沉积物捕捉器(Sediment trap)及TFO重力采泥器对甲藻孢囊进行每月一次的周年监测,并同时研究了浮游植物的季节变化.结果显示,晚秋孢囊形成率最高(3.48105 cysts/m2d),冬季形成率较低,年平均为1.28105 cysts/m2d.锥状斯氏藻(Scrippsiella trochoidea)是大亚湾沉积物孢囊中的绝对优势种,除个别季节外,其形成率一般占孢囊总形成率的50%以上.2000年8月至9月,该海域发生了一次较大规模的锥状斯氏藻赤潮,最高细胞密度达4.0104 cells/mL.赤潮中后期,锥状斯氏藻孢囊包括暂时性孢囊和休眠孢囊大量形成,孢囊的形成减少了水体中营养细胞数量,是赤潮消退原因之一.       

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea: distribution patterns and influence of main environmental gradients

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.