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Severe damages will result in human society, when several different critical natural phenomena coincide. One example relates to the resting cysts of Alexandrium species (dinoflagellates that cause paralytic shellfish poisoning), which are preserved in surface sediments throughout Osaka Bay, Japan. These cysts have been found to accumulate particularly densely in shallow areas in the inner parts of Osaka Bay, where a tsunami caused by an earthquake could occur any time. Damage by a tsunami could cause a change of the coastal ecosystems at Osaka Bay including the resuspension of surface sediments containing resting Alexandrium tamarense cysts and the subsequent redistribution of the cysts in newly deposited sediment. Under certain environmental conditions, these cysts could germinate and form dense blooms, leading to paralytic shellfish poisoning. Such a scenario could also affect other coastal areas, including the southern coast of the Korean Peninsula.

To better understand the outbreaks of paralytic shellfish poisoning and bloom dynamics caused by Alexandrium species in Jinhae-Masan Bay, Korea, the germination and distributions of ellipsoidal Alexandrium cysts were investigated, and paralytic shellfish toxins (PSTs) profiles and contents were determined using strains established from germling cells. The phylogeny and morphological observations revealed that the germinated vegetative cells from ellipsoidal cysts collected from the surface sediments in Jinhae-Masan Bay belong to Alexandrium catenella (Group I) and A. pacificum (Group IV) nested within A. tamarense species complex. Cyst germinations of A. catenella (Group I) were observed at only 10 °C, whereas cysts of A. pacificum (Group IV) could germinate at temperature ranges of 10 to 25 °C. Maximum germination success (85%) for isolated cysts occurred at 15 °C, and the germling cells were A. pacificum (Group IV). The results indicate that the variation in water temperature in Jinhae-Masan Bay can control the seasonal variations in germination of cysts of A. catenella (Group I) and A. pacificum (Group IV). The germination rates of ellipsoidal Alexandrium cysts were different among sampling sites in Jinhae-Masan Bay, probably because of differences in distribution and abundance of A. catenella (Group I) and A. pacificum (Group IV) in the sediments. The ellipsoidal Alexandrium cyst concentrations were much higher in February than in August, however the distributions were similar. Gonyautoxins 3 and 4 (GTX-3 and GTX-4) contributed a large proportion (>90%) of the toxins produced by strains A. catenella (Group I) and A. pacificum (Group IV) established from germling cells, and the total cellular contents were higher in A. catenella (Group I) than in A. pacificum (Group IV).

Dinoflagellates are a major component of the modern plankton. Of the 2192 species of marine free-living dinoflagellates presently described, an increasing number are being shown to produce resting cysts (probably hypnozygotes) within their life cycle. With rare exception, only the resting cysts fossilize, so they are of central importance in tracing the history of dinoflagellates through geological time. Cysts of many of the more common dinoflagellate species have distinctive morphologies allowing their geographic and stratigraphic occurrences to be traced. An ever-increasing number of taxa are also being shown to produce distinctive and geologically preservable cysts, potentially enhancing our knowledge of the diverse representation of dinoflagellates through time. Here the organic-walled cysts of 73 rare, poorly known or morphologically problematic marine dinoflagellate cyst species belonging to the orders Gymnodiniales (nine species) and Peridiniales (64 species) are reviewed, described and illustrated, and their stratigraphic ranges assessed. The names Echinidinium aculeatum and Echinidinium transparantum are validated herein. © 2019 Elsevier B.V.

To investigate dinoflagellate cyst production and seasonality in relation to major environmental factors, such as water temperature, salinity, chlorophyll-a (chl-a) and dissolved nutrients, and to propose dinoflagellate cysts as possible biological indicators for the reconstruction of past environmental conditions, a sediment trap study was conducted for one year, from March 2011 to February 2012, in Jinhae-Masan Bay, Korea. Marked increases in dinoflagellate cyst production were documented in Jinhae-Masna Bay during two distinct seasons (summer and late autumn) characterized by different environmental conditions. Summer (July and August) was characterized by relatively high water temperature, dissolved inorganic nitrogen (DIN), and chl-a concentrations and low salinity, whereas late autumn (November and December) exhibited high dissolved inorganic phosphorus, low water temperature and high salinity, compared to those of the summer. Fourteen dinoflagellate cyst taxa were identified. These assemblages were dominated by Brigantedinium species (round brown cyst), cysts of Scrippsiella species, Spiniferites species and cysts of Alexandrium species (ellipsoidal cyst). The total flux of dinoflagellate cysts ranged from 781 cysts m −2 day −1 to 5602 cysts m −2 day −1, and the production of autotrophic dinoflagellate cysts was mainly restricted to the warmest months (July–September) and autumn. Multivariable analysis revealed that the production of major dinoflagellate cysts, excluding those of Brigantedinium species, can be enhanced by environmental conditions during summer in Jinhae-Masan Bay. In particular, the increased production of cysts of Scrippsiella species was related to increased water temperature, and the increased production of Spiniferites species was associated with lower salinity. Two peaks in cyst production of Alexandrium species in August and November corresponded with significant increases in DIN and DIP; however, no significant relationship was found between the production of Brigantedinium species and environmental factors in Jinhae-Masan Bay. These results suggest that the cysts of Scrippsiella species, Spiniferites species and cysts of Alexandrium species present in sediment samples from Jinhae-Masan Bay can be used as biological indicators to reconstruct past environmental conditions involving relatively high water temperature, low salinity and enhanced nutrient level.

A new phototrophic dinoflagellate, Grammatodinium tongyeonginum gen. & sp. nov., was established by incubating resting cysts collected from surface sediment samples from Tongyeong coastal area, Korea. The resting cysts were ovoid with a large reddish pigment body and surrounded with a thick mucous layer that incorporated attached detritus particles. The vegetative cells were 24.6–40.9 μm long and 16.4–27.3 μm wide. The cell surface was covered with prominent longitudinal equidistant furrows. The cingulum was narrow and descended two to eight times its width. The nucleus was located at the central part of the epicone. The peripheral chloroplasts were usually granular and yellow-green in culture and were distributed along the rim of the cingulum. The horseshoe-shaped apical groove ran from the end of the sulcal extension anticlockwise around the apex. The distal end of the apical groove was located next to the extension of the sulcus and more to the ventral side than the proximal end. Molecular phy...

Outbreaks of paralytic shellfish poisoning (PSP) and dense blooms caused by Alexandrium species in Jinhae-Masan Bay, Korea have been nearly annual events for many years. However, excluding some Alexandrium species responsible for PSP, there are no critical reports on the morphology of Alexandrium species in this bay. To identify the Alexandrium species based on detailed morphological features, vegetative cells collected water samples and established by the incubation of resting cysts isolated from sediment trap samples were analyzed. Four species of Alexandrium were identified: Alexandrium affine, A. fundyense, A. catenella, and A. insuetum. Morphological features of these species were basically consistent with those outlined in previous studies. However, the ventral pore and the connecting pore on the sulcal plate, which have been accepted as diagnostic characteristics for the identification of A. fundyense and A. catenella, need to be reevaluated, indicating that useful morphological features for identifying these two species should be recommended to avoid confusion in the classification of species in genus Alexandrium.

Centrodinium punctatum is a fusiform dinoflagellate with a global marine distribution. Due to a close phylogenetic relationship of one C. punctatum strain to Alexandrium species, toxin production of this C. punctatum strain was assessed using liquid chromatography coupled to tandem mass spectrometry. The paralytic shellfish toxin (PST) profile of C. punctatum was dominated by six analogs, i.e. STX (30%), GTX-1 (20%) and neoSTX (24%), followed by GTX-2 (9%), GTX-4 (9%) and GTX-3 (8%); deoxy-STX was also putatively identified while no gymnodimines, spirolides or goniodomins were detected. This is the first record of C. punctatum producing saxitoxins. The estimated cellular toxicity was rather elevated, between 91 and 212 pg cell−1 (or 259 and 601 fmol cell−1). When considering the toxicity equivalent factors, results suggest that this species can produce high cellular toxicity compared to other STX-producing dinoflagellates. Morphological details of the sulcal area and the hypotheca of Centrodinium punctatum were re-examined by scanning electron microscopy (SEM); this revealed that in the sulcal area, the left posterior sulcal plate (Ssp) is larger and longer than the left posterior sulcal plate and extended into the hypotheca. Based on the morphological observation, a revised interpretation of the sulcus and hypotheca is proposed.

The total dinoflagellate cyst community and the cysts of Cochlodinium polykrikoides in the surface sediments of South Sea (Tongyeong coast), South Korea, were analysed using next-generation sequencing (NGS) and morphological approaches. Dinoflagellate cysts can be highly abundant (111–4,087 cysts g−1 dry weight) and have diverse species composition. A total of 35 taxa of dinoflagellate cysts representing 16 genera, 21 species (including four unconfirmed species), and 14 complex species were identified by NGS analysis. Cysts of Scrippsiella spp (mostly Scrippsiella trochoidea) were the most dominant and Polykrikos schwartzii, Pentapharsodinium dalei, Ensiculifera carinata, and Alexandrium catenella/tamarense were common. Thus, a combination of NGS and morphological analysis is effective for studying the cyst communities present in a given environment. Although C. polykrikoides developed massive blooms during 2013–2014, microscopy revealed low density of their cysts, whereas no cysts were detected by NGS. However, the vegetative C. polykrikoides not appeared during 2015–2017 in spite of the observation of C. polykrikoides cysts. This suggests that the C. polykrikoides blooms were not due to development of their cysts but to other factors such as currents transporting them to a marine environment suitable for their growth.

A new species, Pentapharsodinium jinhaense sp. nov., was established by incubating resting cysts, which were collected from trap samples from Jinhae-Masan Bay, Korea. The resting cysts of P. jinhaense were spherical or ovoidal, with a large reddish pigment body and a thick wall covered by numerous needle-shaped calcareous crystals. The size, shape and plate tabulation of motile cells that germinated from the resting cysts were similar to those of Pentapharsodinium tyrrhenicum and Ensiculifera carinata; however, the motile cells had a spine located in the anterior sulcal plate and many pores and spines on the thecal surface. Molecular phylogenetic analysis using internal transcribed spacer and 5.8s rDNA showed that P. jinhaense was closely related to P. tyrrhenicum. Large subunit ribosomal DNA sequences also revealed that P. jinhaense was nested within Pentapharsodinium and formed a strongly supported clade with Pentapharsodinium dalei and P. tyrrhenicum.

Two morphologically distinct species, Brigantedinium majusculum and Trinovantedinium applanatum, have been suggested as a cyst stage of Protoperidinium pentagonum; however, the cyst–theca relationships are still virtually undefined. In this study, we re-examined the motile stage of B. majusculum via thecal plate analysis together with a molecular phylogenetic analysis based on partial large-subunit ribosomal DNA gene sequences. The morphological features of motile cells germinated from B. majusculum were identical to those of Pr. sinuosum, and the molecular phylogenetic analysis showed that the germinated cells and B. majusculum are closely related to Pr. pentagonum and Pr. latissimum as a sister group. Additionally, high sequence divergences were observed between the germinated cells and B. majusculum as well as Pr. pentagonum and Pr. latissimum (18.0–19.5% according to P-values and 20.7–22.9% according to Kimura two-parameter values). On the basis of these results, our study indicates that B. ...

Paralytic shellfish poisoning (PSP) caused the deaths of four people in coastal area of Korea, mainly Jinhae-Masan Bay and adjacent areas, in April 1986 and in 1996. The PSP outbreaks were caused by the consumption of mussels, Mytilus edulis . The organism that caused PSP was identified, from morphological data only, as Alexandrium tamarense which is recently renamed as A. catenella , however recent studies have shown that the morphological diagnostic characteristics used to identify Alexandrium species have uncertainties and molecular tools and other criteria should be considered as well. The organism that caused past PSP outbreaks and incidents in Korea therefore need to be carefully reconsidered. The aim of this study was to re-evaluate the species really responsible for past outbreaks of PSP in Jinhae-Masan Bay, Korea. The temporal production and fluxes of the resting cysts of Alexandrium species were investigated for one year (from March 2011 to February 2012) using a sediment trap, and the morphology and phylogeny of vegetative cells germinated from the resting cysts were analysed. The production of Alexandrium species peaked in August and November, when temporal discrepancies were found in the water temperature (22.4 and 22.7 °C in August, 19.1 and 19.6 °C in November) and salinity (29.5 and 26.1 psu in August, 30.5 and 31.8 psu in November). The morphological data revealed that Alexandrium species germinated from resting cysts collected in August have a ventral pore on the 1′ plate, whereas the 1′ plate in Alexandrium species germinated from resting cysts collected in November lacks a ventral pore. Molecular phylogenetic data for the vegetative cells from the germination experiments allowed the August and November peaks to be assigned to Alexandrium catenella (Group I) and A. pacificum (Group IV), respectively. This indicates that the production of resting cysts of A. catenella can be enhanced by relatively high water temperature. This result is not consistent with those of previous studies that A. catenella responsible for PSP outbreaks was found at relatively low water temperature. In addition, large subunit ribosomal sequences data revealed that A. pacificum isolates from Korea were closely related to those from Australia, Japan and New Zealand where the PSP toxicity of shellfish and blooms occurred in the 1990s, indicating that the introduction of toxic dinoflagellates were related to ballast water from bulk-cargo shipping. Based on these results, we concluded that past PSP outbreaks in Jinhae-Masan Bay of Korea could have been caused by A. pacificum rather than by A. catenella .

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.

To investigate the research state and characteristics of dinoflagellate cyst along the Korean coastal waters, this work analyzed 45 studies conducted in the Korean coasts and basin, the south of Jeju, East China Sea including some part of the Yellow Sea. It was found that the research on dinoflagellate cyst began in the later half of the 1980s in Korea, and that the research areas focused on eutrophied regions where a red tide occurred or on the seas where coastal development occurred. In other words, no research on the East Sea was found. In terms of research contents, there were various studies on analysis of cyst assemblage, tracking of the changes in marine environment like process of eutrophication, roles as a seed population in occurrence of a red tide, creation of cyst by use of sediment trip and tracking of its changes, morphological changes by the change of pH concentration in the hypoxia zone of eutrophied region, germination of a specific species, and other international-level studies. Species composition and cell density also varied in the Korean coastal waters. However, much research on dinoflagellate cyst in Korea is not systematic, and is fragmentary and individual and hencesuffers from great limitations. The research results so far have focused only on specific regions, and sporadic research had been conducted by specific research groups. Dinoflagellate cyst of surface sediments represents the accumulation index of pelagic environment in the sea and is a useful index to understand the marine environment efficiently. In conclusion, Korea requires organized human resources and collaborative research on dinoflagellate cyst which in turn should be considered as a component of marine ecosystem and as an essential aspect of marine biology.

To investigate the distribution, abundance, and species composition of dinoflagellate cysts in the Yellow Sea, surface sediment samples were collected at 37 sites, including the Korean dump site. Twenty-one dinoflagellate cyst taxa were identified, with the assemblages dominated mainly by Spiniferites bulloideus, Operculodinium centrocarpum, and cyst of Alexandrium catenella/tamarense type. A high frequency of O. centrocarpum in the Yellow Sea was observed for the first time, and it is likely that this can be attributed to the dynamics of the Yellow Sea Cold Water Mass and the Changjiang (Yangtze) River runoff. Total cyst concentrations ranged from 23 to 48 442 cysts/g dry weight, and high cyst concentrations were recorded adjacent to the dumping site. This result suggests that anthropogenic activities such as ocean dumping stimulate the growth of dinoflagellates in the Yellow Sea, which in turn leads to high levels of dinoflagellate cyst production.

In this study, we investigated the relationship between seasonal/annual variation in water masses and nutrients, and the effects of nutrients on phytoplankton assemblages in the western Korea/Tsushima Strait. We collected water samples at least once per month from March 2006 to January 2008. There was seasonal variation in nutrient concentrations, with higher values in winter than in summer, and there was annual variation in chlorophyll-a concentration and phytoplankton abundance during spring, with values being approximately three and 10 times higher, respectively, in 2007 than in 2006. Phytoplankton abundance was also approximately four times higher in 2007 than in 2006 during the stratification periods. Our findings suggest that when the supply of nutrients to the upper layer is increased as a result of the Tsushima Warm Water Current and the effect of typhoons, they regulate the abundance and composition of phytoplankton assemblages in the Korea/Tsushima Strait, inducing a succession from flagellates ...

To develop a better understanding of the species composition and production of dinoflagellate cysts, including the ecological characteristics of Polykrikos species, a sediment trap study was conducted from June 2005 to June 2006 in Gamak Bay, Korea. Thirty-two dinoflagellate cyst taxa were identified in the sediment trap samples, and the dinoflagellate cyst assemblages were found to be dominated by cysts of Polykrikos kofoidii , Scrippsiella trochoidea , Protoperidinium spp., Polykrikos schwartzii , Gymnodinium catenatum and Ensiculifera carinata . The flux of dinoflagellate cysts ranged from 0.10 × 10 5 to 35.97 × 10 5 cysts m − 2 day − 1 , and the highest flux occurred during summer, and was driven completely by the flux in the production of P. kofoidii and P. schwartzii cysts. The timing of the production of cysts of Polykrikos species seemed to be related to the appearance of G. catenatum as prey. The assemblages of dinoflagellate cysts in surface sediments from Gamak Bay, and their seasonal changes, were very similar to those in the sediment trap samples, which suggested that the monitoring of dinoflagellate cysts in sediment samples can provide information on the environmental conditions in Gamak Bay.

To evaluate the algicidal impact of a newly developed algicide thiazolidinedione derivative,TD49, on dinophyceae Akashiwo sanguinea in aquatic ecosystems, tentative culture experiments for thetarget species were conducted in small (SS), middle (MS), and large scale (LS) culture vessels. When TD49was introduced at the final concentration of 2 µM in SS and MS, as well as 1 µM in LS, the abundance of A.sanguinea decreased significantly in all the treatments. On the other hand, total phytoplankton abundance,except A. sanguinea in the TD49 treatments, gradually increased with culture time, which implies that a celldestruction of A. sanguinea by TD49 is a major cause of the population growth by other phytoplanktonspecies. Also, A. sanguinea was easily destroyed, which was likely to be a source of extracellularsubstances. In particular, a pH decrease was significant in the treatments than in the control, which indicatesthat the water in the treatments has been acidified, due to an increase in the heterotrophic metabolisms ofbacteria and degradation of A. sanguinea cells. Our results indicate that the TD49 substance is the potentialagents for the control of A. sanguinea in the enclosed and eutrophic water bodies.Key words :Akashiwo sanguinea, algicidal effect, thiazolidinedione, ecosystem*Corresponding author. E-mail : yokim@kordi.re.kr

To investigate dinoflagellate cysts as indicators of salinity or eutrophication and to document the historical occurrence of ellipsoidal Alexandrium cysts in the Korean coastal areas, we studied a sediment core from Yeoja Bay. The analyzed dinoflagellate cysts include over 30 taxa commonly reported from other temperate regions. Cluster analysis based on dinoflagellate cyst assemblages indicated two main time intervals: from the mid-1990s to 2006 (Zone II) and from the early 1900s to early 1990s (Zone I). The total cyst concentration increased sharply in Zone II, to reach approximately five times the level in Zone I. The salinity in Yeoja Bay increased after 1995 (from 28 to 31 psu), possibly due to a stronger intrusion of the Tsushima Warm Current. The increase in salinity coincided with increases in the abundance of Brigantedinium spp. and Selenopemphix nephroides . In addition, ellipsoidal Alexandrium cysts have occurred since the 1980s and increased in abundance since the mid-1990s, when a paralytic shellfish poisoning outbreak and increases in ellipsoidal Alexandrium cysts were recorded in several Korean and Japanese coastal areas. This suggests that ellipsoidal Alexandrium cysts may have been carried to the Korean coast, including Yeoja Bay, by the current system, possibly the Tsushima Warm Current, and that the current system may influence the growth of Alexandrium cysts.

Dinoflagellate cysts acquired from sediment cores were analyzed in order to reconstruct historical nutrient levels in Gamak Bay, Korea and Ariake Bay, Japan. Dinoflagellate cyst assemblages in Gamak Bay were characterized by high proportions of heterotrophic cysts such as Brigantedinium spp., Protoperidinium americanum and Polykrikos cysts, which suggested that nutrients levels may have already been high before 1970s, and then increased further to the hypertrophic conditions of the 1990s. In contrast, dinoflagellate cyst assemblages in Ariake Bay were characterized by high relative abundances of Lingulodinium machaerophorum and Spiniferites spp., which suggested that nutrient levels in Ariake Bay had increased gradually since the mid 1960s, and may have been significantly enhanced by the mid 1980s. Dinoflagellate cyst assemblages reflecting environmental changes in the two bays are contrasting, perhaps due to different nutrient enrichment mechanisms. This suggests that the indicators of nutrient levels encoded in dinoflagellate cyst assemblages may exhibit site-specific information.

In Gamak Bay, Paralytic Shellfish Poisoning (PSP) was first detected from seafoods in 2003, however the toxin source is unknown yet. In this study, we report potential PSP producers of toxic dinoflagellates, describing morphology and abundance of cysts isolated from surface sediment of Gamak Bay. The most abundant type in these cysts was characterized with ellipsoidal and transparent wall identical to Alexandrium catenella and/or A. tamarense. Germination experiment of the cysts revealed that all motile cells germinated were morphologically identified as A. tamarense. This result suggests that A. tamarense may relate to PSP contaminations in Gamak Bay. Moreover, bottom water temperature in Gamak Bay is favorable for germination of A. tamarense cysts. Further studies are required to carry out the PSP monitoring for preventing the risk of PSP events that may outbreak in future at Gamak Bay.

Distributional characteristics of dinoflagellate cysts in surface sediments were investigated in relation to environmental factors in the eastern part of Geoje Island, Korea. Samples were collected from 10 stations in February of 2004 and water temperature and salinity were measured in February, May, September and November of 2004. Total 30 taxa of dinoflagellate cysts were identified representing 19 genera, 28 species and 2 unidentified species. Among these dinoflagellate cysts,Brigantedinium spp. of which relative proportion in the total dinoflagellate cysts was 23.5%, was the most abundant at all stations except St. 1, and was followed bySpiniferites bulloideus (8.6%),Lingulodinium machaerophorum (8.2%) andDiplopsalis lenticula (6.7%). In addition, ellipsoidal cysts of the genusAlexandrium (Alexandrium catenella - tamarense type) andGymnodinium catenatum, known to be causative organisms for PSP, occurred with high concentrations.Scrippsiella trochoidea was also found; however, its cyst concentration was low. Generally, species composition in the study area was similar to these reported from Jinhae Bay and Busan Harbor and several dinoflagellate cysts reflected the eutrophic condition. Cyst distribution in the eastern part of Geoje Island seems to be influenced by the Tsushima Warm Current flowing from the southwest. The mean water temperature was 12.0°C in February, 14.7°C in May, 20.9°C in September and 17.2°C in November, which was most favorable forAlexandrium spp. growth. The abundances of dinoflagellate cysts ranged from 528 to 2,834 cysts/g dry sediment. Higher concentrations were recognized in sediments of west area of the Jisimdo than at other stations. The cyst composition of this area was closely related to these of Jinhae Bay and Busan Harbor from which currents flow into this area. Higher cyst concentration in the west area of Jisimdo might be due to formation of the gyre.

This study provides the first morphological features of resting cysts of Cochlodinium polykrikoides collected from Korean coastal sediments. Evidence for the existence of resting cysts of C. polykrikoides is based on the morphological and molecular phylogenetic data of the germinated cells and a resting cyst. The morphology of the resting cysts differed from that reported previously in sediments and culture experiments. The distinct feature is that the cyst body was covered by the reticulate ornaments and spines.