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This paper investigates behaviors that a set of initial cell densities of Heterocapsa Circularisquama (HC) and Prorocentrum Dentatum (PD) and a set of environmental factors disturbing the growth of HC and PD cells formed in their growth process, which are actually fractal phenomena. First, the calculation of the fractal dimension of the set of initial cell densities of HC and PD is given in the paper. Second, by controlling the set of initial cell density, HC and PD cells grow according to a given growth target. The approximate or same behaviors of two different sets of initial cell densities of HC and PD are realized by introducing the coupling terms. Finally, the set of environmental factors disturbing the growth of HC and PD cells is constructed by introducing real parameters. Then the result that makes HC and PD cells growing according to a given growth target is reached by a proper mathematical transform to the real parameters. The approximate or same behaviors of the set of environmental factors disturbing the growth of HC and PD cells are realized by introducing the coupling terms. [ABSTRACT FROM AUTHOR]

The dinoflagellate Heterocapsa circularisquama is highly toxic to bivalves. However, significant toxicity to finfish species has not been reported. We previously found that H. circularisquama has light-dependent haemolytic agents. Purification and chemical structural analyses revealed that the haemolytic agent H2-a is a porphyrin derivative, which exhibits light-dependent cytotoxicity toward tumour cells. To clarify the biological activity of H2-a further, its antibacterial activities against Gram-positive and Gram-negative bacteria were investigated in this study. A fraction (F5) equivalent to H2-a purified from the methanol extract of H. circularisquama showed potent light-dependent bactericidal activity toward Staphylococcus aureus , and the activity was concentration- and light illumination time-dependent; however, Escherichia coli was highly resistant to F5. Electron microscopic observation suggested that F5 induces morphological changes in S. aureus in a light-dependent manner. Further analysis using other bacterial species showed that the Gram-positive bacterium Bacillus subtilis was more sensitive than the Gram-negative bacteria Pseudomonas aeruginosa and Vibrio alginolyticus . These results indicate that F5 is a photo-induced antibacterial agent with relatively higher specificity to Gram-positive bacteria. Iodometric assay suggested that singlet oxygen was generated from light-illuminated F5. Histidine, a specific singlet oxygen scavenger, markedly inhibited the photosensitising antibacterial activity of F5 against S. aureus , suggesting the involvement of singlet oxygen in antibacterial activity. The antibacterial spectrum of F5 was evidently different from that of 5,10,15,20-tetra ( N , N , N -trimethylanilinium) porphyrin tetratosylate, a commercially available porphyrin compound with antibacterial activity. Our results demonstrate that H. circularisquama has a novel antibacterial photosensitiser, a porphyrin derivative, with relatively higher specificity to Gram-positive bacteria. To the best of our knowledge, this is the first study to discover a porphyrin derivative with antibacterial activity in marine microalga. [ABSTRACT FROM AUTHOR]

Heterocapsa circularisquama , a harmful dinoflagellate, has multiple haemolytic toxins that are considered to be involved in the toxic mechanism against shellfish and certain species of zooplankton. To evaluate the further nature of the toxins of H. circularisquama , we investigated its effects on several species of bacteria. By colony formation assay, we found that H. circularisquama had antibacterial activity toward the marine bacterium Vibrio alginolyticus in a cell density-dependent manner. When the inoculated bacterial cells were co-cultured with H. circularisquama under dinoflagellate cell culture conditions, the bacterial growth was significantly suppressed, whereas the number of live bacterial cells increased when cultured in the medium alone. Since the cell-free culture supernatant and the ruptured dinoflagellate cell suspension showed no toxic effects on V. alginolyticus , it is speculated that direct cell-to-cell contact mediated by the live dinoflagellate cells may be the major toxic mechanism. The decrease in bactericidal activity of theca-removed dinoflagellate cells may further support this speculation. H. circularisquama also showed bactericidal activities towards Escherichia coli and Staphylococcus aureus . In the dinoflagellate/bacteria co-culture system, the number of live bacterial cells declined with increasing incubation time. Light-dependent antibacterial activity of the ruptured dinoflagellate cells against S. aureus was observed, whereas no such activity was detected against E. coli . These results suggest that intracellular photosensitising bactericidal toxins, which were previously found to be porphyrin derivatives, may have specificity towards gram-positive bacteria. Based on these results together with previous studies, it is obvious that H. circularisquama possesses antibacterial activity, which may be mediated through toxins located on its cell surface. It is likely that such toxins play a role in the defence mechanism against predators and infectious bacteria. Although the exact biological significance of intracellular photosensitising toxins is still unclear, such toxins may have potential to be developed as novel photo-controllable antibiotics. [ABSTRACT FROM AUTHOR]

A harmful dinoflagellate, Heterocapsa circularisquama , is highly toxic to shellfish and the zooplankton rotifer Brachionus plicatilis . A previous study found that H. circularisquama has both light-dependent and -independent haemolytic agents, which might be responsible for its toxicity. Detailed analysis of the haemolytic activity of H. circularisquama suggested that light-independent haemolytic activity was mediated mainly through intact cells, whereas light-dependent haemolytic activity was mediated by intracellular agents which can be discharged from ruptured cells. Because H. circularisquama showed similar toxicity to rotifers regardless of the light conditions, and because ultrasonic ruptured H. circularisquama cells showed no significant toxicity to rotifers, it was suggested that live cell-mediated light-independent haemolytic activity is a major factor responsible for the observed toxicity to rotifers. Interestingly, the ultrasonic-ruptured cells of H. circularisquama suppressed their own lethal effect on the rotifers. Analysis of samples of the cell contents (supernatant) and cell fragments (precipitate) prepared from the ruptured H. circularisquama cells indicated that the cell contents contain inhibitors for the light-independent cell-mediated haemolytic activity, toxins affecting H. circularisquama cells themselves, as well as light-dependent haemolytic agents. Ethanol extract prepared from H. circularisquama , which is supposed to contain a porphyrin derivative that displays photosensitising haemolytic activity, showed potent toxicity to Chattonella marina , Chattonella antiqua , and Karenia mikimotoi , as well as to H. circularisquama at the concentration range at which no significant toxicity to rotifers was observed. Analysis on a column of Sephadex LH-20 revealed that light-dependent haemolytic activity and inhibitory activity on cell-mediated light-independent haemolytic activity existed in two separate fractions (f-2 and f-3), suggesting that both activities might be derived from common compounds. Our results suggest that the photosensitising haemolytic toxin discharged from ruptured H. circularisquama cells has a relatively broad spectrum of phytoplankton toxicity, and that physical collapse of H. circularisquama cells can lead not only to the disappearance of its own toxicity, but also to mitigation of the effects of other HABs. [ABSTRACT FROM AUTHOR]

The harmful alga, Heterocapsa circularisquama , causes recurrent mortalities of bivalve molluscs in Japan, with demonstrated hemolysis and cytotoxicity in rabbit erythrocytes, HeLa cells, and bivalve tissues. Nonetheless, the effects of exposure to sublethal cell densities on the physiological energetics of bivalves have not been investigated, nor the potential involvement of neurotoxicity. In the present study, two sets of experiments were conducted with adult clams, Ruditapes philippinarum . In the first set, the clearance rate (CR), respiration rate (RR), absorption efficiency (AE), ingestion rate (IR), and absorption rate (AR) were examined in clams exposed to H. circularisquama to quantify the scope for growth (SFG) as an indicative of the bioenergetic status of clams (5, 50, 2.5 × 10 2 , and 5 × 10 2 cells ml −1 ; under 15 °C and 20 °C). In the second set, the activity of the biomarker of neurotoxic exposure, acetylcholinesterase (AChE), was monitored following 3, 6, 24, and 48 h of exposure (5, 50, 5 × 10 2 , and 10 3 cells ml −1 , at 20 °C) in gills of R . philippinarum , and compared to that in Mediterranean mussels, Mytilus galloprovincialis ; a species also affected by H . circualrisquama and in which AChE activity was more extensively studied. At 15 °C, CR, IR, and AR were decreased for exposures to 50–5 × 10 2 cells ml −1 resulting in a significant decrease in the absorbed energy (A), and a significant decrease in SFG at 5 × 10 2 cells ml −1 . At 20 °C, AE was null for exposures to 2.5 × 10 2 and 5 × 10 2 cells ml −1 . RR was decreased at 2.5 × 10 2 and 5 × 10 2 cells ml −1 , CR, IR, and AR were decreased at 5–5 × 10 2 cells ml −1 , and the AE was null for 2.5 × 10 2 –5 × 10 2 cells ml −1 resulting in a significant decrease in the respired energy (R), but mainly in (A) especially at 2.5 × 10 2 and 5 × 10 2 cells ml −1 decreasing the SFG over the entire range of cell density with negative values for 2.5 × 10 2 and 5 × 10 2 cells ml −1 . The activity of AChE in both clams and mussels was significantly reduced following 3–48 h of exposure to 5–5 × 10 2 cells ml −1 . Reduction in the energy available for clams to grow and reproduce was induced mainly via decreased energy acquisition, and delayed and/or reduced functions of the digestive organs. In addition, this is the first report of decreased neuroenzymatic activity in two bivalve molluscs induced by exposure to H. circularisquama potentially via either neurotoxic compounds affecting the activity of gill cilia and/or gill muscles, and/or potentially via either neurotoxic compounds affecting the activity of gill cilia and/or gill muscles, and/or non-cholinergic affects associated with other functions; both resulting in decreased SFG. The relationship between the decreased AChE and decreased SFG should be corroborated in future research. [ABSTRACT FROM AUTHOR]

The harmful dinoflagellate, Heterocapsa circularisquama , has been causing mass mortalities of bivalve molluscs in Japan, at relatively low cell densities. Although several studies have been conducted to determine the toxicity mechanisms, the specific cause of death is still unclear. In a previous study, in our laboratory, it was shown that H . circularisquama (10 3 cells ml −1 ) caused extensive cytotoxicity in the gills of short-neck clams, Ruditapes philippinarum . In the present study, Mediterranean mussels, Mytilus galloprovincialis , were exposed to H . circularisquama at four cell densities (5, 50, 500, 10 3 cells ml −1 ), three temperatures (15, 20, and 25 °C), and three exposure durations (3, 24, and 48 h), and the pathologies in nine organs (gills, labial palps, mantle, hepatopancreas, stomach, intestines, exhalant siphon, adductor muscles, and foot) were assessed. Foot, adductor muscles, and exhalent siphons of mussels were not affected; however, 16 inflammatory (hemocytic infiltration and aggregation, diapedesis, hyperplasia, hypertrophy, edema, melanization, and firbrosis) and degenerative (thrombus, thrombosed edema, cilia matting and exfoliation, epithelial desquamation, atrophy, and necrosis) pathologies were identified in the gills, labial palps, mantle, hepatopancreas, stomach, and intestines. The total prevalence and total intensity of pathology in each individual mussel, and the prevalence and intensity of pathology in each organ increased significantly with increased cell density, exposure duration, and temperature. The prevalence of pathology was the highest in gills, followed by the prevalence in labial palps, mantle, stomach, and intestines. Pathology was least prevalent in the hepatopancreas. The intensity of pathology was the highest in the gills, followed by the labial palps and mantle, the stomach and intestines, and the hepatopancreas. This detailed quantitative histopathological study demonstrates that exposure to H . circularisquama induces a broad cytotoxic effect in six vital organs, even at low density (5 cells ml −1 ) and low temperature (15 °C), but not in muscular organs. Combining cell density, time, and duration of exposure, the organ most affected by the harmful alga was the gill, followed by the labial palps and mantle, the stomach and intestines, and the hepatopancreas. The results of this pathological analysis show that exposure to H . ciruclarisquama severely affects the gills, the labial palps, and mantle thereby interfering with particle clearance and sorting, cleansing, and respiration, but also affects the stomach, intestines, and hepatopancreas, altering the digestive processes and possibly detoxification pathways, if mussels are able to detoxify the toxins of H . circularisquama . In the most severe cases, bivalves would most likely have died as a result of combined severe alterations of the vital functions, failure of tissue repair, and moderate to heavy hemorrhaging in both the external organs and the digestive organs concomitantly with light to moderate alterations in the detoxifying processes. [ABSTRACT FROM AUTHOR]

A bloom of non-indigenous dinoflagellate Heterocapsa circularisquama (Peridiniales, Dinophyceae) and bloom-associated shellfish mortality were detected for the first time in Kuwait's waters (Arabian/Persian Gulf, NW Indian Ocean) during June–July 2020. This species is endemic to the Asia Pacific region, and associated with shellfish kills, causing tremendous damage to bivalve aquaculture, and economic losses in western Japanese waters and Hong Kong. In Kuwait Bay, this dinoflagellate was found in bloom proportions up to 108 cells·l−1 and represented from 72 to 83% of the total phytoplankton population in red tide patches. Native bloom-forming small-sized diatoms, Thalassiosira delicatula , T. exigua , and Minutocellus polymorphus were also abundant at the time of the H. circularisquama bloom. Microalgal cell morphology was determined using light and electron microscopy for specimens from the field and cultures established by cell isolation from the bloom area. The molecular characterization of cultured Heterocapsa strains was based on the large subunit region of the ribosomal DNA sequences. The overall morphology and body scale structure of Heterocapsa from Kuwait Bay were very similar to that of the H. circularisquama described from Japanese waters. The sequences of the LSU rDNA of Kuwait's strains were identical to those of the H. circularisquama. This is the first record of H. circularisquama occurring at high abundance outside the Asia Pacific region, and it may be an indication this invasive and harmful species is now established in Kuwait's marine environment. • Heterocapsa circularisquama is discovered for the first time in the NW Indian Ocean. • Morphological and molecular data confirmed the species identity. • Bloom of Heterocapsa circularisquama caused mortality in bivalves. • Heterocapsa circularisquama represents an invasive and harmful species to Kuwait. [ABSTRACT FROM AUTHOR]

To assess the algicidal effects of the thiazolidinedione derivative TD49 on the unarmored dinoflagellate Heterocapsa circularisquama and to evaluate the response of the planktonic community and the environment to this chemical, we undertook mesocosm (1,300 L) and small-scale experiments. The reduction ratio for H. circularisquama in each experiment was dependent on the concentration of TD49. At a TD49 concentration >0.4 μM, the abundance of H. circularisquama decreased by 99 % in the small-scale experiment and by 84 % in the mesocosm during the initial 2 days. At 0.2 μM TD49, the abundance of H. circularisquama decreased by up to 85 % in the small-scale experiment, whereas the abundance in the mesocosm increased, implying the absence of an algicidal effect. The decrease in planktonic organisms, including H. circularisquama, following TD49 treatment was correlated with abrupt declines in culture pH and dissolved oxygen concentration. Following addition of TD49, there was a significant increase in the abundance of diatoms and cryptophyta species, and after 8 days, the dominant species in the TD49 treatments shifted to small pennate diatoms including Cylindrotheca and Entomoneis species. The growth of some species among the zooplankton community was promoted at low TD49 concentrations (≤0.4 μM), whereas high concentrations (≥1.0 μM) had a negative effect. This study demonstrates that TD49 is an effective agent for the control for H. circularisquama blooms and that large-scale mesocosms play a crucial role in assessing the application of algicides such as TD49 in natural environments. [ABSTRACT FROM AUTHOR]

Abstract: The dinoflagellate, Heterocapsa circularisquama Horiguchi is known to cause massive marine shellfish deaths in coastal waters of Japan. During the last two decades, proliferation of H. circularisquama across western portions of Japan hampered the production of shellfish cultivation, resulting in economic consequences. In this chapter, the ecophysiology and toxicology of H. circularisquama and subsequent damage to aquaculture are discussed, with special emphasis on the effects of H. circularisquama on the physiology of shellfish. [Copyright &y& Elsevier]

Mortality of the short-neck clam Ruditapes philippinarum exposed to the toxic dinoflagellate Heterocapsa circularisquama was studied under controlled conditions to clarify the mechanisms of recurrent mass deaths of clams occurring in western Japanese coastal areas. One-week mortality tests, involving three water temperatures, six H. circularisquama concentrations, and two clam body sizes, showed a significant increase in mortality with increasing temperature, H. circularisquama concentration, exposure duration, and body size (ANOVA, P < 0.01). Clam death was observed at concentrations as low as 50 cells/ml and temperatures as low as 15°C. Prior to death, clams showed an extreme retraction of their mantle edge and siphon, along with recurrent vomiting behavior before initiating a closure reaction followed by paralysis then death. Gills of paralyzed clams showed an important uptake of dye, implying gill damage. This study is the first laboratory evidence of bivalve mortality induced by H. circularisquama at low concentrations and low temperature, and the first report of differential effects according to the body size of bivalves. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, oxygen budget was estimated for the lower layer of water column in a semi-enclosed bay, Ago Bay, Japan. Benthic oxygen consumption rates were measured directly with an in situ measurement device from 13 July to 16 August 2004. Oxygen budget was calculated based on physical, chemical and biological processes using the observed data. Along with the change of the water column structure at the time of a hit of typhoon, dominant phytoplankton species shifted from the diatom Skeletonema costatum to the dinoflagellate Heterocapsa circularisquama. During the diatom-dominating period, oxygen supply rate in the lower layer due to photosynthesis was comparable to or slightly lower than the sediment oxygen consumption rate. In contrast, during the dominance of the dinoflagellate, net oxygen budget was significantly negative in the lower layer while it was positive in the upper layer. This could be attributed to the migration behavior of the dominant dinoflagellate H. circularisquama that swim up to the upper layer and produce oxygen in daytime, and swim down to the lower layer and consume oxygen in nighttime. The results of the present study suggest that phytoplankton migration behavior can enhance the development of oxygen depleted water mass in the lower layer of eutrophic shallow coastal seas. [Copyright &y& Elsevier]

Abstract: The effects of the toxic dinoflagellate Heterocapsa circularisquama on the valve movements of adult Ruditapes philippinarum (Bivalvia, Veneridae) were investigated. The valve movement behaviour was continuously measured using a non invasive Hall element sensor-automated data acquisition system. Individual clams acclimated to the experimental conditions were subjected to different food regimes over a 96 h period: (1) unfed in filtered seawater for the first 24 h, (2) batch-fed1, in which clams were given one ration of non-toxic Isochrysis galbana at the beginning of the second 24 h, (3) batch-fed2, in which clams were given a mixture of I. galbana and H. circularisquama (5×104 cells ml−1) for the third 24 h, and (4) starved for 24 h in filtered seawater after exposure to the toxic alga. For each food regime, the valve activity was analyzed by quantifying: (1) the duration of valve opening (DVO, %), (2) the amplitude of valve opening (AVO, mm), and (3) the frequency of valve adductions (FVA, adductions h−1). The real-time monitoring of the clams'' valve movements proved that R. philippinarum detects H. circularisquama in the mixture of food at as low as 0.5 cells ml−1. Typically, the addition of the toxic alga induced a short and incomplete valve closure reaction. A strong correlation between the closure reaction time and H. circularisquama concentration was found (R 2 =0.91), the closure reaction occurring faster with increasing concentrations. Reopening of the valves was characterized by a significant increase in the FVA starting from 5 cells ml−1 (ANOVA, P <0.001) and a significant decrease in the AVO at 500 cells ml−1 (Wilcoxon, P <0.05). After exposure, clams transferred to clean seawater resumed normal valve adduction activity, but showed a significant increase in the DVO after exposure to 0.5 and 5 cells ml−1 (ANOVA, LSD, P <0.05), and a significant increase in the AVO (ANOVA, P <0.01). Such increase could have been associated with recovery behaviour. Our results indicate that the Manila clam is highly sensitive to the toxic H. circularisquama and detects efficiently its presence at extremely low concentrations, in mixture of food, and in a time- and concentration-dependent manner. The Manila clam and the valve movement monitor could thus be used as an early biological warning system to monitor the outbreaks of this toxic alga along marine coastal areas and in bivalve farms. However, field experiments are required to provide further evidence for the use of this monitor in natural environment where several factors may interfere with the valve movement behaviour. [Copyright &y& Elsevier]

Since the first discovery of the very high virus abundance in marine environments, a number of researchers were fascinated with the world of “marine viruses”, which had previously been mostly overlooked in studies on marine ecosystems. In the present paper, the possible role of viruses infecting marine eukaryotic microalgae is enlightened, especially summarizing the most up-to-the-minute information of marine viruses infecting bloom-forming dinoflagellates and diatoms. To author’s knowledge, ∼40 viruses infecting marine eukaryotic algae have been isolated and characterized to different extents. Among them, a double-stranded DNA (dsDNA) virus “HcV” and a single-stranded RNA (ssRNA) virus “HcRNAV” are the only dinoflagellate-infecting (lytic) viruses that were made into culture; their hosts are a bivalve-killing dinoflagellate Heterocapsa circularisquama. In this article, ecological relationship between H. circularisquama and its viruses is focused. On the other hand, several diatom-infecting viruses were recently isolated and partially characterized; among them, one is infectious to a pen-shaped bloom-forming diatom species Rhizosolenia setigera; some viruses are infectious to genus Chaetoceros which is one of the most abundant and diverse diatom group. Although the ecological relationships between diatoms and their viruses have not been sufficiently elucidated, viral infection is considered to be one of the significant factors affecting dynamics of diatoms in nature. Besides, both the dinoflagellate-infecting viruses and diatom-infecting viruses are so unique from the viewpoint of virus taxonomy; they are remarkably different from any other viruses ever reported. Studies on these viruses lead to an idea that ocean may be a treasury of novel viruses equipped with fascinating functions and ecological roles. [ABSTRACT FROM AUTHOR]

A monogalactosyl monoacylglycerol 1 and two digalactosyl monoacylglycerols 2 and 3 were isolated from a cultured marine dinoflagellate Heterocapsa circularisquama along with known (2S)-1-O-6,9,12,15-octadecatetraenoyl-3-O-β-D-galactopyranosyl]-sn-glycerol (4). On the basis of spectral analysis, the glycolipid 1 was characterised as (2S)-1-O-3,6,9,12,15-octadecapentaenoyl-3-O-β-D-galactopyranosyl]-sn-glycerol. The glycolipids 2 and 3 were characterised as (2S)-1-O-3,6,9,12,15-octadecapentaenoyl-3-O-[α-D-galactopyranosyl-(1''' → 6'')-O-β-D-galactopyranosyl]-sn-glycerol and (2S)-1-O-6,9,12,15-octadecatetraenoyl-3-O-[α-D-galactopyranosyl-(1''' → 6'')-O-β-D-galactopyranosyl]-sn-glycerol, respectively. The isolated monoacylglycerols 1-4 showed cytolytic activity towards heart and gill cells of oyster. [ABSTRACT FROM AUTHOR]

Red tides of Heterocapsa circularisquama have led to serious damage of bivalve aquacultures in western coastal areas of Japan. To understand the whole picture regarding the ecology of this species, it is essential to clarify its overwintering mechanisms. In this study, the population dynamics of H. circularisquama were investigated from February 2004 to November 2005, and overwintering cells were identified for the first time in water columns of Uranouchi Inlet, Kochi Prefecture, Japan. Heterocapsa circularisquama cells were detected by the indirect fluorescent antibody technique using monoclonal antibodies that specifically recognize and react to this species. Vegetative cells were almost always detected from the first observation in February 2004 to November 2005 with temperatures of 10.5–30.6°C. During the period from winter to spring, this species survived in areas with a temperature higher than 10°C. The overwintering cells of H. circularisquama were isolated in March 2004, and identification was made via observation of the morphology and body scales of the cultured cells. These overwintering cells were identified as H. circularisquama and reacted to the monoclonal antibody. These results indicate that H. circularisquama can overwinter and survive throughout the year in a vegetative cell state in Uranouchi Inlet. [ABSTRACT FROM AUTHOR]

We investigated the effects of specific light wavelengths from light-emitting diodes (LEDs) on the growth of the dinoflagellate Heterocapsa circularisquama, which kills bivalves, and the diatom Skeletonema costatum, which is an important food source for bivalves. Growth of H. circularisquama was obviously inhibited at 590 nm and a photon flux density less than 75 μmol quanta/m2/s. However, growth of S. costatum was not suppressed by irradiance from any LEDs tested from near-ultraviolet to near-infrared wavelengths at 75 μmol quanta/m2/s. The growth rate of H. circularisquama in an experimental treatment group with irradiance provided by both cool-white fluorescent lamps (12:12 h L : D cycle) and a 590-nm LED (continuous irradiance) was 0.43/day. In the control group with irradiance provided only by cool-white fluorescent lamps (12:12 h L : D cycle), the growth rate was 0.63/day, indicating that growth of H. circularisquama was suppressed by 590 nm (less than 75 μmol quanta/m2/s) irradiance from the LED and the continuous irradiance. The use of 590-nm LEDs in bivalve culture at irradiance levels less than 75 μmol quanta/m2/s might encourage the growth of the useful diatom S. costatum without stimulating growth of the harmful dinoflagellate H. circularisquama. [ABSTRACT FROM AUTHOR]

Abstract: We developed a system for the early detection of noxious dinoflagellate Heterocapsa circularisquama blooms by utilizing the response of Akoya pearl oysters (Pinctada fucata) to H. circularisquama cells. The system is based on valve movement activity in bivalves. The movements were measured by means of a magnet on one valve to a Hall element sensor on the other valve connected by thin cables to a recording device. In filtered sea water, valve movement activity of pearl oysters as displayed on the output screen of the detection system showed sporadic thorn-like spikes, indicating the shell closing for a short time, with a flat waveform indicating that the shell was open. The frequency of these spikes increased as the number of H. circularisquama cells in the filtered seawater increased. However, the frequency of the spikes almost immediately decreased when the water was changed to filtered seawater with no H. circularisquama. These results indicate that this system using the Hall element sensor can detect low densities of H. circularisquama cells in real time without needing complicated apparatus. [Copyright &y& Elsevier]

The responses of division rate, cell volume, cellular carbon (C) and nitrogen (N), cellular pigments and optical characteristics to changes in salinity were examined in the dinoflagellate Heterocapsa circularisquama. The physiological and optical characteristics of H. circularisquama were significantly affected by changes in salinity. When cells were exposed to different salinities, they exhibited physiological acclimation by adjusting their cellular properties associated with growth. This could be a beneficial tactic for ensuring proliferation and limiting damages induced by adverse environmental factors. The results of this study could be essential for assisting in the development of growth models for H. circularisquama. [ABSTRACT FROM AUTHOR]

Abstract: We have previously found that the methanol extract prepared from Heterocapsa circularisquama, a harmful red rid dinoflagellate, showed light-dependent hemolytic activity toward rabbit erythrocytes. Interestingly, the cytotoxicity of the extract against HeLa cells was also strictly light-dependent, and no significant toxic effect was observed even at very high concentration in the dark. In this study, the hemolytic agents present in the extract were purified by several chromatographic procedures. Final HPLC analysis revealed that there are at least two hemolytic toxins with different retention times (H2-a and H3-a), which have similar absorption spectra. Although H3-a fraction was contaminated by a trace amount of H2-a, H2-a fraction gave a single peak on a three-dimensional chromatogram. The results of fast atom bombardment (FAB)–mass spectrometry (MS) and electrospray ionization quadrupole time-of-flight (ESI Q-TOF) mass spectrometry analyses suggested that the molecular weight of H2-a was 566. Since nuclear magnetic resonance analysis indicated the presence of a pyrrole ring in H2-a molecule, H2-a may be a porphyrin derivative with similar structure of pyropheophorbide a methyl ester, a well-known photosensitizing hemolytic compound. However, some structural and physicochemical differences were observed between H2-a and pyropheophorbide a methyl ester. Since H2-a showed potent photosensitizing cytotoxicity toward HeLa cells in a concentration-dependent manner as well as hemolytic activity, H2-a may be a novel porphyrin derivative with photosensitizing hemolytic cytotoxicity. [Copyright &y& Elsevier]

The composition of sterols was determined in a cultured marine dinoflagellate Heterocapsa circularisquama . Ten kinds of the sterol in H . circularisquama were identified by capillary gas chromatography-mass spectrometry. The major sterol was a 4-methyl sterol, 4α,23,24-trimethyl-5α-cholest-22 E -en-3β-ol (dinosterol) which is the common sterol in many dinoflagellates. [ABSTRACT FROM AUTHOR]

Red tides of Heterocapsa circularisquama (H. circularisquama), recently identified as a novel species of dinoflagellate, have frequently caused mass mortality of several species of bivalves in Japan, while no harmful effects of this flagellate on fish have been reported so far. We found that the cell-free ethanol extract prepared from H. circularisquama caused hemolysis of rabbit erythrocytes and demonstrated cytotoxic effects in HeLa cells and on the microzooplankton rotifer (B. plicatilis) in a dose- and time-dependent manner. Interestingly, the hemolytic activity and cytotoxic effects of the extract were completely dependent on the presence of light. When the experiments were conducted in the dark, no hemolysis was observed even at very high concentration of the extract. These results suggest that H. circularisquama has photosensitizing hemolytic toxin which can be easily extracted into ethanol. This may be the first report documenting the occurrence of photosensitizing hemolytic toxin in marine phytoplankton species. [Copyright &y& Elsevier]

Relationships between the growths of five different clonal strains of Heterocapsa circularisquama and intracellular bacteria were investigated using culture experiments. Although each H. circularisquama strain culture was established from one cell by repeated and careful washings with micropipettes, intracellular and extracellular bacteria in each strain culture were still observed under a epifluorescence microscope using the DAPI (4′,6-diamidino-2-phenylindole) staining technique. The extracellular bacteria are derived, presumably, from the inside of algal cells after the death and collapse of algal cells in culture. Using an electron microscope, bacteria were constantly observed in the cytoplasm and food vacuoles of H. circularisquama cells. The growth of five algal strains containing bacteria was compared with that of a bacteria-free strain using culture experiments under combined conditions of five different light intensities and five different strengths of culture medium. Bacteria showed no significant effect on the growth or survival of the algal cells. During the algal exponential growth phase, the intracellular bacterial cell numbers per algal cell decreased, whereas the total bacterial cell density in each algal culture increased. Final cell yield (total number) of the intracellular and extracellular bacteria varied considerably according to the algal strains. These results suggest that the intracellular bacteria of H. circularisquama grow or survive depending on the host alga, and that the alga can grow independently. [ABSTRACT FROM AUTHOR]

Heterocapsa circularisquama Horiguchi is lethal to shellfish, particularly bivalves such as pearl oysters (Pinctada fucata Gould). No detrimental effects of this flagellate on fish have been observed thus far. In this study, we found that H. circularisquama causes mammalian erythrocytes to lyse. Among the erythrocytes tested, rabbit erythrocytes showed the highest susceptibility, whereas erythrocytes from cattle, sheep, and human were relatively insensitive. Heterocapsa triquetra Stein, which is morphologically similar to H. circularisquama but not toxic to bivalves, showed no hemolytic activity toward rabbit erythrocytes. Culture supernatant or ultrasonic-ruptured cells of H. circularisquama showed only weak hemolytic activity. Hemolytic activity was found in the ethanol extract of H. circularisquama cells, suggesting that the hemolytic agents may be more stable in ethanol than in aqueous solution. Both an intact flagellate cell suspension and the ethanol extract caused morphological changes and eventual collapse of unfertilized eggs of Pacific oyster. Furthermore, the ethanol extract was lethal to the microzooplankton rotifer Brachionus plicatilis Müller, which is highly sensitive to H. circularisquama. Our results suggest that a hemolytic toxin produced by H. circularisquama may be one of the causative agents responsible for the shellfish toxicity. [ABSTRACT FROM AUTHOR]

• Noxious HAB species were Karenia mikimotoi (China), Chattonella antiqua (Japan) and Cochlodinium polykrikoides (Korea). • In China, fish kill cases were mainly caused by Karenia mikimotoi, Heterosigma akashiwo and Chattonella spp. • In Western Japan, fish kill cases were mainly caused by K. mikimotoi, Chattonella spp., Heterosigma sp. and Cochlodinium spp. • In Korea, fish kill cases were mainly recorded by Cochlodinium polykrikoides and Karenia mikimotoi. Occurrences of harmful algal blooms (HABs) and associated fisheries damage have been continuously monitored since the 1970s along the coasts of East Asia. Fisheries damage comprises mass mortalities of fish and shellfish mainly by harmful dinoflagellates and raphidophytes (e.g., Chattonella antiqua/marina, Cochlodinium polykrikoides and Karenia mikimotoi), and contamination of algal toxins in shellfish in particular Diarrhetic Shellfish Toxins by Dinophysis spp. and Paralytic Shellfish Toxins by Alexandrium spp. Shellfish mass mortalities due to Heterocapsa circularisquama in Hong Kong and western Japan, and fish kills by Karlodinium digitatum are unique incidents for this region, whereas C. antiqua/marina, C. polykrikoides and K. mikimotoi are common also in other regions. Time series data showed that the highest bloom numbers were recorded in 1980 (Japan), in 1998 (Korea) and in 2003 (China), followed by decreasing trends in these countries. These data suggest a shift in microalgal species composition, from dominance by diatoms to dinoflagellates after 1980s in Korea, and from diatoms to small haptophytes and cyanobacteria after 2013 in eastern Russia. HAB species composition and the changes were compared among countries, for better understanding on current status and trend of HAB species in East Asia. [ABSTRACT FROM AUTHOR]

This study evaluates a novel control method for harmful algal blooms (HABs) that uses natural sediment including associated viruses. In Japan, commercial aquaculture of bivalves such as oysters, pearl oysters and clams is severely threatened by blooms of the harmful dinoflagellate, Heterocapsa circularisquama. HcRNAV is a single-stranded RNA virus that specifically infects H. circularisquama. Given that high concentrations of HcRNAV remain in bottom sediment following a H. circularisquama bloom, dispersal of sediments containing HcRNAV was expected to provide a promising tool to mitigate blooms of this dinoflagellate. A laboratory experiment demonstrated the effectiveness of a) HcRNAV alone, and b) sediments with HcRNAV, in reducing H. circularisquama densities. For the first time, a field test was implemented in an active oyster farm on Sado Island, Japan in which sediment containing HcRNAV collected from nearby waters was dispersed into 15,000 L floating mesocosms during early stages of a H. circularisquama bloom. In the treatment spraying with sediment containing HcRNAV, the density of H. circularisquama decreased significantly until it reached only ~1% of the initial after five days, while that of HcRNAV increased significantly by Day 2 (one-way ANOVA, n = 3, P <.01). These results indicate that the virus + sediment treatment was very effective in mitigating the H. circularisquama bloom under field conditions. Only a very low sediment concentration achieved these results, thereby reducing potential ecological impacts. Given the high diversity and mutation potential of HcRNAV, and the variable host response, it is recommended that field application of this mitigation strategy use indigenous sediment. This study provides the first field test of viral control of HAB worldwide and will facilitate its further practical application. • A HAB control method using natural sediments containing viruses is introduced. • The HcRNAV virus is shown to be effective in suppressing Heterocapsa circularisquama blooms. • The virus is highly specific and therefore environmental impacts on co-occurring organisms are minimized. • The dispersal of natural sediment containing HcRNAV was highly effective in suppressing blooms. • The study reports the first field test of viral control of HABs worldwide. [ABSTRACT FROM AUTHOR]

Reports the occurrence of Heterocapsa circularisquama (Dinophyceae) in a coastal area of Hong Kong, South China Sea. Observation of red samples collected in Hong Kong waters; Cell density; Findings of preliminary bioassay; Observation of thecal plate arrangement and fine structure of bioassay using mice and juvenile fishes; Technique used to identify the dinoflagellates; Importance of body scale presentation in the identification of the Heterocapsa species..