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We conducted continuous mooring observation from autumn to winter of fiscal year 2020 to elucidate the mechanism of red tide development in the inner Ariake Sea, a very turbid shallow coastal water in Japan. The red tide dominated by Skeletonema spp. (mainly Skeletonema dohnii) developed at first neap tide after the annual minimum water temperature. Red tides at similar times of the year have been frequently observed here. Formation of two physical environments favorable for phytoplankton proliferation played a trigger role. One was stabilization of water column due to net heat flux transition through the sea surface from cooling to heating in mid-winter. Another was deepening of euphotic layer up to or exceeding water depth at the neap tide. Since the inner Ariake Sea has the small heat capacity due to its shallowness, the air and water temperature fluctuated almost in tandem, and reached their respective lowest values with a short time lag. The sea-surface heat flux, a main factor governing water temperature fluctuations, was dominated by latent heat and showed the highest correlation with the difference between atmospheric and sea-surface specific humidity. After mid-January, the atmosphere stabilized as the air temperature exceeded the water temperature, and the sea-surface cooling due to the latent heat weakened. With the heat flux change from negative to positive, the water column was stabilized. Then, winter bloom occurred during the neap tide when the compensation depth became deep with the decrease in suspended sediment concentration. [ABSTRACT FROM AUTHOR]

The temporal changes in the behavior of vegetative cells and cysts of the noxious red tide flagellates Chattonella (C. antiqua and C. marina) were investigated in Ago Bay, central Japan, mainly in 2013. In this study, in situ germination flux (cells m-2 day-1) was measured in May, June, and October 2013, using a 'plankton emergence trap/ chamber (PET chamber)'. Vegetative cells occurred in April and increased from May, forming a bloom in July with cyst production, and subsequently decreased thereafter. This change in the occurrence of the vegetative cells was considered to be controlled primarily by temperature and secondarily by nutrients and biotic factors. The PET chamber experiment showed that cyst germination in May contributed largely to forming the initial vegetative population to initiate blooming. An experiment to elucidate the effect of storage temperature on the germinability of cysts in the sediment showed that newly produced cysts (immature dormant cysts) mature (acquire germinability) under low storage temperature (10°C) within at least one month, indicating that cysts need to experience a cold season in the sediment for their maturation. The PET chamber experiment conducted in October before a cold season also confirmed that cysts scarcely germinated from the cyst population, containing many immature dormant cysts, in the in situ sediment. However, these cysts could act as seeds to form the initial population of the subsequent bloom in the next season, since the cysts will mature by then. Consequently, Chattonella cysts were concluded to play crucial roles in the population dynamics. [ABSTRACT FROM AUTHOR]

Isahaya Bay in Japan has suffered from severe red tides. A previous study reported that red tides continued under dissolved inorganic nitrogen (DIN) depleted conditions in the bay. One possible explanation for this phenomenon is that regenerated NH4+, through organic matter decomposition, facilitates the persistence of red tides in the bay. Direct utilization of dissolved organic nitrogen (DON) by phytoplankton isolated from other coastal ocean areas has been reported. No study has been conducted on the direct utilization of DON by the phytoplankton community in Isahaya Bay. However, if phytoplankton in the Bay can utilize DON directly, DON probably contributes more to red tide formation and persistence than previously thought. In this study, field sampling and DIN and DON (in the form of amino acids and urea) enrichment bioassays were conducted to test whether growth of phytoplankton in Isahaya Bay can be stimulated through the addition of amino acids and urea. Phytoplankton growth rates in both the presence and absence of erythromycin, a bacterial inhibitor, were stimulated by NH4+, NO3−, and urea addition. The results suggest that phytoplankton in Isahaya Bay can be stimulated urea directly and indirectly. On the other hand, concentrations of DIN and urea were often depleted in the bay station throughout study period. Thus, DIN regeneration process might be an important process supporting red tides under DIN-depleted conditions. Notably, urea might prolong red tides through contribution to the NH4+ regeneration process, as urea is hydrolyzed to NH4+ by ureases produced by bacteria. [ABSTRACT FROM AUTHOR]

In 1997, the inner part of Isahaya Bay on the west coast of the Ariake Sea was separated from the sea by dikes, leading to the formation of a freshwater reservoir. Since the Isahaya Reclamation Project began in the 1990s, red tides have become more common in the bay. Studies suggested that a non-negligible amount of NH 4 + was regenerated from organic matter decomposition in the turbid water drained from the reservoir into the bay, and this drainage water might be an important source of NH 4 + for red tides in the bay. Although labile organic matter in the turbid water might also originate from resuspended sediments in the reservoir induced by the drainage process, the potential for the resuspended sedimentary organic matter to serve as an NH 4 + source has never been evaluated. In this study, we found that sediments near the drainage gates on the dike in the reservoir contained high levels of amino acids and NH 4 +. In addition, the NH 4 + concentrations were positively correlated with amino acids concentrations. This result can be explained by increasing NH 4 + production according to labile organic nitrogen accumulation in the sediments near the dike. The result of our study suggests that the sediment resuspension near the dike induced by drainage might be a source of bioavailable nitrogen for Isahaya Bay. [ABSTRACT FROM AUTHOR]

Coastal dolphins inhabiting areas influenced by human activities can face anthropogenic threats, so monitoring surveys to detect changes in abundance are required. Photo-identification surveys of Indo- Pacific bottlenose dolphins (Tursiops aduncus) were conducted from 2001 to 2013 in the waters south of Amakusa-Shimoshima Island, Japan, where a few dozen dolphins emigrated from the waters north of the island. We report the range, the group composition, the number of individuals, and the breeding of the dolphins settled in the new area. The dolphins were found only in narrow straits between islands. One strait was the core habitat area. Two types of groups were observed: groups with females (range of group size = 15 to 29) and those without females (range of group size = 1 to 3). The total number of dolphins gradually decreased from 31 individuals in 2001 to 18 in 2011, which was mainly attributed to the reduction in the male number from 17 to 8. Few new immigrants to the area were found. In 2009, a temporary invasion by large groups of dolphins inhabiting the northern original area occurred. After the temporary invasion started to occur, we did not observe new calves nor calves that survived to the next year. The breeding had been successful except for the first two years after the settlement. The presence of the much larger group might have negatively impacted the maternal feeding environment. It was possible that the environmental deterioration due to the red tide, which can affect fish survival, was progressing. Two females disappeared in 2011, and all the remaining dolphins disappeared in 2012. Certain dolphins were found in other areas. In the present study, the process behind the dolphins' population range expansion is examined along with factors that may have hindered the colonization process. [ABSTRACT FROM AUTHOR]

In 1997, the inner part of Isahaya Bay on the west coast of Ariake Bay, western Japan, was separated from the sea by dikes, leading to the formation of a freshwater reservoir. Since the Isahaya Reclamation Project began in the 1990s, red tides and hypoxia have become more common in the bay. Eutrophic high-turbidity water from the reservoir is frequently discharged into the bay, so NH4+ regenerated from organic matter in the discharge may be a source of nutrients for the red tides. In this work, we mixed reservoir water and seawater from the bay in experiments aimed at quantifying the NH4+ regeneration caused by the direct decomposition of labile organic matter in the high-turbidity drainage water. By comparing the results of field monitoring and mixing experiments, we estimated that the NH4+ regeneration rate under the influence of the drainage water was 192–501 μmol m−2 h−1, which was 31.5–46.8% higher than the natural NH4+ regeneration rate. This suggests that the additional NH4+ regeneration induced by the drainage water is non-negligible and that the organic matter in the drainage water may be an important source of NH4+ for red tides in the bay. This is the first study to provide data on the non-negligible amount of NH4+ regenerated upon the direct decomposition of labile organic matter in high-turbidity water drained from a reservoir on reclaimed land into the bay. [ABSTRACT FROM AUTHOR]

• Genetic relatedness of Japanese and global A. ostefeldii isolates was investigated. • Western Japanese isolates group with isolates from low-saline and shallow areas. • Northern Japanese isolates form a separate group explained by geographic isolation. • Low genetic diversity of western Japanese population implies a recent introduction. • Bloom in a shallow coastal lagoon in western Japan after a change in salinity. In recent years, blooms of toxic Alexandrium ostenfeldii strains have been reported from around the world. In 2013, the species formed a red tide in a shallow lagoon in western Japan, which was the first report of the species in the area. To investigate the genetic relatedness of Japanese A. ostenfeldii and global isolates, the full-length SSU, ITS and LSU sequences were determined, and phylogenetic analyses were conducted for isolates from western and northern Japan and from the Baltic Sea. Genotyping and microsatellite sequence comparison were performed to estimate the divergence and connectivity between the populations from western Japan and the Baltic Sea. In all phylogenetic analyses, the isolates from western Japan grouped together with global isolates from shallow and low saline areas, such as the Baltic Sea, estuaries on the east coast of U.S.A. and from the Bohai Sea, China. In contrast, the isolates from northern Japan formed a well-supported separate group in the ITS and LSU phylogenies, indicating differentiation between the Japanese populations. This was further supported by the notable differentiation between the sequences of western and northern Japanese isolates, whereas the lowest differentiation was found between the western Japanese and Chinese isolates. Microsatellite genotyping revealed low genetic diversity in the western Japanese population, possibly explained by a recent introduction to the lagoon from where it was detected. The red tide recorded in the shallow lagoon followed notable changes in the salinity of the waterbody and phytoplankton composition, potentially facilitating the bloom of A. ostenfeldii. [ABSTRACT FROM AUTHOR]

Highlights • Population dynamics and species richness of sea urchins were studied for >45 years. • A larger-scale survey of urchin dynamics was done every c. 5 years for 38 years. • Developmental abnormality of one urchin species was studied for 41 years. • Effects of temperature and red tides were found. Abstract Continuous long-term monitoring is important for detecting ecological changes and understanding their causes, including anthropogenic impacts such as climate changes and eutrophication. Nonetheless, such long-term population studies have been rare, especially for sea urchins, which can affect community dynamics owing to their extensive herbivory and large population fluctuations. Here we present a long-term (from 1963 to 2014) dynamics of sea urchins in a fixed quadrat on a lower intertidal rocky flat in Hatakejima Island, southern Japan. We also conducted a complementary survey over the entire island approximately every five years from 1975 to 2013, and a 41-year assay for developmental abnormality of the sea urchin Heliocidaris crassispina using water adjacent to the island. The abundance of three commonest species in this area (H. crassispina , Echinostrephus molaris , and Echinometra spp.) and the richness of urchin species showed large variations, with high numbers in the 1960s and 1970s, followed by an abrupt decline in the late 1970s or early 1980s, and a gradual recovery subsequently. The species abundance and richness in the entire island survey showed good correlations with those in the quadrat census. Statistical analyses indicated that increasing water temperature and red tides were the major factors influencing the dynamics of abundance and species richness. Our studies reveal that anthropogenic environmental changes influence the long-term dynamics in abundance and richness of sea urchins. [ABSTRACT FROM AUTHOR]

Heterosigma akashiwo virus (HaV) is a dsDNA virus that infects the bloom-forming raphidoflagellate Heterosigma akashiwo. Both the host and its virus are phenotypically diverse in terms of infection specificity. Their relationships have been examined based on the occurrence or absence of algal lysis following virus inoculation; however, variations in the strain-level host-virus relationship regarding infectivity and lysis rates remain unclear. Therefore, we performed a series of cross-infectivity tests using 60 H. akashiwo and 22 HaV strains isolated from the coastal waters of western Japan. The host strains were divided into 5 different groups and viruses into 4 groups. Using a representative strain from each group, algal lysis was observed in 14 of the (5×4=) 20 host-virus combinations; the concentration of infectious units in each HaV suspension was then assessed using the most probable number (MPN) assay on the five host strains. Virus titers ranged between 1.1×10 1 and 2.1×10 7 infectious units mL -1 ; the titer of each viral lysate was differently estimated using distinct H. akashiwo strains as hosts. These results suggest that (1) a clonal viral lysate comprises virions with different intraspecific infection specificities and/or (2) the efficiency and error rates of each intracellular replication process vary in each host-virus combination.

The raphidophyte Chattonella and the bacillariophyte Skeletonema are representative bloom-causing organisms in the Ariake Sea, Japan. Changes in their abundance were monitored to clarify the role of river discharge in the red tides caused by these organisms in the innermost area of the sea. In late June 2010, heavy rain occurred and subsequently river discharge increased. A Chattonella bloom occurred after heavy rain on July 5, although Chattonella abundance was very low (<1 cell ml) before the heavy rain (June 29). Maximum cell density reached 4.2 × 10 cells ml at the surface. Thus, the bloom developed as the river plume extended in the estuary. During the course of extension of the river plume, the Chattonella population rapidly developed using the nutrients supplied by the river. Just after the Chattonella bloom, heavy rain occurred again and a very large quantity of river water flowed into the estuary. Consequently, the salinity of the surface decreased to 5 in the study area on July 16. Chattonella did not migrate to the surface probably because of the overlying low-salinity water; Chattonella formed a thin layer (20-50 cm in thickness) at the depth where salinity was 10. However, a Skeletonema population developed at the surface. On July 20, Skeletonema density at the surface exceeded 10 cells ml. With the decline of the Skeletonema abundance due to the nutrient limitation, Chattonella again formed bloom probably using deep-nutrient pool by their vertical migration behavior. The present study clearly demonstrates that the Chattonella can form dense bloom after the heavy rain. The seed population awaiting the river discharge is probably essential to the rapid development of Chattonella in the estuary. [ABSTRACT FROM AUTHOR]

iake Bay, Kyushu Island, has recently exhibited environmental degradation in the form of red tides and anoxic bottom water. To determine the characteristics and regional classification of the copepod community, zooplankton surveys were made throughout the bay in three cruises each in October 2004, January 2005 and March 2009 by vertical tows of a 0.1-mm-mesh plankton net. Oithona davisae was the most abundant in January and March, and Microsetella norvegica in October. Cluster analysis revealed that the copepod community from each cruise was generally separated into the inner to eastern-middle region and the western-middle to mouth region. A SIMPER analysis revealed that dissimilarity between the groups and similarity within each group were mainly due to the dominant species, but the similarities within the outer-region group in January and March were mostly contributed by Paracalanus parvus s.l. A non-metric multidimensional scaling with bubble plots of environmental variables and a BIOENV analysis showed that transparency was more different between the two groups than temperature and salinity. As compared with two similarly sized, eutrophic bays (Tokyo and Osaka Bays), Ariake Bay differs from Tokyo Bay in the dominance of M. norvegica and from Osaka Bay in the high abundance of O. davisae even in the colder season. The dominant species and the regional classification of the copepod community in the bay were similar to those in the studies in the 1970s, suggesting that the copepod community has not notably changed during the last 3 decades. [ABSTRACT FROM AUTHOR]

Abstract: An unarmored dinoflagellate Cochlodinium polykrikoides has formed red tides responsible for fish mass mortalities especially in coastal areas of western Japan and southern Korea almost every summer to autumn. In laboratory culture, the optimum temperature for growth of the species is ca. 27°C. Since the species cannot survive in water of temperatures of less than 10°C, it was considered to over-winter in some certain regions as a motile form or resting cyst, and expand its distribution after the temperature increases to a level tolerable for growth. To determine the over-wintering regions and migration pattern of C. polykrikoides, occurrences of the motile cells were surveyed in the coastal and offshore areas of western Kyushu, Japan and south coast of the Korean Peninsula from April 2006 to August 2008. Cells of C. polykrikoides were found at 14 sites during the investigated period. Motile cells occurred throughout the year in Usuka Bay, Hirado of West Japan. From offshore regions of the Goto Islands and off Shin-Nagasaki Fishing Port, motile cells of C. polykrikoides were first detected from late May, and continuously occurred until February in Nama Bay of the Kami-Goto Islands. This first appearance was before red tides of C. polykrikoides reported at coastal areas in western Kyushu. In Korea, this species was first observed in May and disappeared after October in 2007. These occurrence patterns imply that Usuka Bay in Hirado is one of the over-wintering regions in western Kyushu, and also this species is possibly transported into the northern part of the East China Sea by the Tsushima Warm Current every year. [ABSTRACT FROM AUTHOR]

Abstract: To elucidate the mechanism of bloom outbreaks of the ‘novel’ noxious flagellate Chattonella ovata (Raphidophyceae), we examined the growth responses of the organism with 42 different combinations of temperature (10–35°C) and salinity (10–35), and under various light intensities (0–381μmol photons m−2 s−1). The three strains, CO2, CO3, and CO8 of C. ovata isolated from Hiroshima Bay, tolerated a wide range of temperature (15–32.5°C) and salinity (10–35). The organism could grow rapidly at over 20°C and salinity of 20, and the maximal growth rates of 1.11–1.47divisionsday−1 were found in the combination 25–30°C and salinity of 25–30. These maximum growth rates and optimal temperatures and salinities of the C. ovata strains were clearly higher than those of Chattonella antiqua and Chattonella marina. A statistical analysis showed that growth rates of C. ovata were significantly influenced by temperature–salinity interaction. Furthermore, growth of the strain CO2 and CO8 was observed at the irradiance 15–45μmol photons m−2 s−1 or more and was saturated at over 300μmol photons m−2 s−1. The half-saturation constants of irradiance for the growth of C. ovata were much higher than those of C. antiqua and C. marina. These results showed that C. ovata is better adapted to higher temperature, salinity and light environments than C. antiqua and C. marina. These physiological features of C. ovata would be an ecological advantage to development of the bloom during summer seasons. [Copyright &y& Elsevier]

A multi-spectral classification scheme is proposed to identify water with red tide(s) using satellite ocean color imagery obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The study area was the eastern Seto Inland Sea in Japan, where serious red tides frequently occur. “Background Ocean Colors” (BOCs hereafter), or colors of water around a red tide or those of the water before/after a red tide, are calculated as the monthly climatological average of normalized water-leaving radiances (nLw) with 0.01 degree spatial resolution with SeaWiFS imagery. Criteria for detecting red-tide pixels are established from analyses of characteristics of the nLws (in the 443, 490, 510, and 555 nm bands) anomalies from BOCs and the nLw spectra together with the red-tide records in Osaka Bay. The proposed scheme can efficiently indicate the presence or absence of red tides for independent match-ups with 83% accuracy. Additional validations of specific events indicate that the algorithm performed well in the study area. These results suggest that the scheme is appropriate to detect red tides in the optically complex coastal water of the eastern Seto Inland Sea. [ABSTRACT FROM AUTHOR]

To determine the process of population expansion and ascertain the origin of the Sea of Japan population, in a noxious red tide forming dinoflagellate Cochlodinium polykrikoides, 13 samples, isolated from 11 different localities in Japanese and Korean coasts, were analysed using 10 polymorphic microsatellites. Analyses by nonmetric multidimensional scaling plots of pairwise FST, globalamova, and genetic admixture analysis identified three clusters ¿ the Sea of Japan populations, Yatsushiro Sea (Kumamoto Pref.) populations, and other populations ¿ indicating genetic structuring of the 13 samples into three distinct populations. In the proportion of shared alleles by pairwise individuals ( PSAxy) analyses between the Sea of Japan and the other samples, PSAxy was extremely low compared with that among the Sea of Japan or among other samples, indicating that a large genetic barrier has occurred between the populations. No significant relationship of isolation-by-distance patterns and almost no genetic distance were detected between pairwise samples of the Sea of Japan, although there is a maximal distance of > 600 km between samples. In addition, PSAxy data among the samples were extremely high compared with those among other samples, clearly showing that a large-scale transfer from west to east has occurred via the Tushima Warm Current. In the PSAxy data of the Seto Inland Sea and Pacific samples, individuals showing relatively high PSAxy were concentrated in the three areas of Nagasaki, Harima, and Mie, suggesting that frequent transfer may have occurred by human-assisted dispersal, although Nagasaki and Mie are separated by a distance of approximately 700 km. [ABSTRACT FROM AUTHOR]

Abstract  Remote sensing reflectance [R rs(λ)] and absorption coefficients of red tides were measured in Isahaya Bay, southwestern Japan, to investigate differences in the optical properties of red tide and non-red tide waters. We defined colored areas of the sea surface, visualized from shipboard, as “red tides”. Peaks of the R rs(λ) spectra of non-red tide waters were at 565 nm, while those of red tides shifted to longer wavelengths (589 nm). The spectral shape of R rs(λ) was close to that of the reciprocal of the total absorption coefficient [1/a(λ)], implying that the R rs(λ) peak is determined by absorption. Absorption coefficients of phytoplankton [a ph(λ)], non-pigment particles and colored dissolved organic matter increased with increasing chlorophyll a concentration (Chl a), and those coefficients were correlated with Chl a for both red tide and non-red tide waters. Using these relationships between absorption coefficients and Chl a, variation in the spectrum of 1/a(λ) as a function of Chl a was calculated. The peak of 1/a(λ) shifted to longer wavelengths with increasing Chl a. Furthermore, the relative contribution of a ph(λ) to the total absorption in red tide water was significantly higher than in non-red tide water in the wavelength range 550–600 nm, including the peak. Our results show that the variation of a ph(λ) with Chl a dominates the behavior of the R rs(λ) peak, and utilization of R rs(λ) peaks at 589 and 565 nm may be useful to discriminate between red tide and non-red tide waters by remote sensing. [ABSTRACT FROM AUTHOR]

Occurrence number of red tides in Osaka Bay in Japan is more than 20 cases every year. Diatom red tide was dominant in Osaka Bay, but the non-diatom red tide was dominant in early 1990s. Therefore, the material cycling in Yodo River estuary in Osaka Bay during August from 1991 to 2000 was analyzed by using the numerical ecosystem model and field observation data to clarify the reasons of change in red tide species. Year-to-year variation in calculated concentration ratio of diatom to non-diatom corresponds to the variation in observed ratio of red tide days of diatom to non-diatom. Limiting nutrient of primary production is phosphate over the period. Diatom dominated from 1991 to 1993, but it was difficult for non-diatom to grow due to the limitation by physical condition. Non-diatom was able to grow because of good physical and nutrient conditions from 1994 to 1996. And diatom dominated again under the good physical condition, and phosphorus supply was not enough for non-diatom to grow from 1998 to 2000. Phosphate concentration in the lower layer of Yodo River estuary was important to the variation in red tide species in the upper layer of Yodo River estuary. [Copyright &y& Elsevier]

Abstract: Noxious red tides of the dinoflagellate Cochlodinium polykrikoides tend to be long lasting and cause mass mortalities of cultured and natural fish and invertebrates along the western coast of Japan and the southern coast of Korea. In order to assess the tolerance of C. polykrikoides to attack by algicidal bacteria, the effects of algicidal bacteria strains on the growth of three C. polykrikoides strains were examined in laboratory culture experiments. Algicidal bacteria used were two strains of Cytophaga (J18/M01 and AA8-2, direct attack type and wide prey range), three strains of Alteromonas (S, K, D) and one strain of Pseudoalteromonas (R, indirect attack type), which were all isolated by using Chattonella antiqua as a prey organism. Neither Cytophaga strain showed any algicidal activity. In the cases of Alteromonas and Pseudoalteromonas, some cultures of C. polykrikoides were killed, but at least 10 days or more were required for the death of this dinoflagellate. C. polykrikoides survived in the presence of algicidal bacteria in concentrations up to 106–107 cellsml−1, which is enough for other red tide microalgae to be killed. On the contrary, the algicidal effects of bacteria on C. antiqua were detected clearly within a few days. These results imply that C. polykrikoides is resistant to the six algicidal bacteria examined, which may reflect the capacity for mixotrophy. This resistance of C. polykrikoides to algicidal bacteria could provide a selective advantage for survival compared to other microalgae susceptible to attack by algicidal bacteria and hence prolong red tides caused by this harmful dinoflagellate. [Copyright &y& Elsevier]

Abstract: During surveillance of the distribution of the paralytic shellfish poison (PSP)-producing dinoflagellate in 2003, 2004 and 2005 along the coastlines of the Seto Inland Sea, Hiroshima Prefecture, Japan, some species of toxic phytoplankton were isolated from the eastern coasts, Bingo-Nada, the central regions of the Seto Inland Sea. It was rather unexpectedly revealed from the basis of the morphological characteristics that they were unambiguously identified as Alexandrium tamiyavanichii and Alexandrium catenella. Two strains (ATY041106, ATY051018) of A. tamiyavanichii showed a specific toxicity of 38.7×10−6 and 111.5×10−6 MU/cell, respectively. These values seemed to be several times or much higher than that of A. catenella (AC030816, AC040614), having a specific toxicity of 4.5×10−6 and 4.1×10−6 MU/cell, respectively, isolated in the same area. From the results of HPLC-furuorometric analysis, it revealed that the toxins in ATY041106 exist almost exclusively as β-epimers (C2, GTX3, GTX4), which accounted for 72.7mol%. The toxin profiles of this strain are featured by the presence of a large amount of GTX3 (59.1mol%) and a small amount (20.6%) of C1 and 2 in comparison with the PSP compositions of A. tamarense, which is isolated as the main responsible species in Hiroshima Bay, a western part of coastal sea in Hiroshima Prefecture. On the other hand, it revealed that the toxin profiles of two strains (AC030816, AC040614) of A. catenella exist almost exclusively as β-epimers (C2, GTX3, GTX4), which accounted for 81.8 and 56.5mol%, as the same manner. The toxin profiles of these two strains are featured by the presence of a large amount of C2 (80.5 and 46.3mol%) in comparison with the PSP compositions of A. tamiyavanichii. To our knowledge, this is the first record to show the distribution and harmful influence of A. tamiyavanichii and A. catenella in Bingo-Nada in Hiroshima Prefecture. Though contamination of bivalves with these PSP-producing planktons in this area has not occurred yet so far, attention should be paid to this species as well as the other causative dinoflagellate from the stand point of public health and food hygiene. [Copyright &y& Elsevier]

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]

Four species of Chattonella, which are well known to form red tides that are lethal to fish, were subjected to phylogenetic analysis on the basis of the ribosomal RNA genes (rDNA), 5.8S rDNA, 18S rDNA, 28S rDNA, and the flanking internal transcribed spacers 1 and 2 (ITS1 and ITS2). The 18S rDNA sequences of C. antiqua, C. marina, and C. ovata isolated from different regions in Japan were compared. They were found to be identical with each other in a sequence 1818 bp long. The sequences of the D1/D2 region in the 28S rDNA, 5.8S rDNA, and ITS region that are known to be more variable regions were also found to be identical. These homogeneities of the rRNA gene family revealed the extremely close relatedness of C. antiqua, C. marina, and C. ovata. The sequences of C. verruculosa were different from those of these three species , resulting in an 89.2% homology in the 18S rDNA sequences, 70.4% homology in the D1/D2 region in the 28S rDNA sequences, and an 81.5% homology in 5.8S rDNA sequences and the ITS regions. Chattonella verruculosa was grouped within a single cluster composed of Dictyochophyceae rather than the other species of Raphidophyceae. [ABSTRACT FROM AUTHOR]

The article discusses the result of the study regarding the isolation and structure determination of algicidal compounds from Ulva fasciata, in Japan. Among the seaweeds tested, the green alga Ulva fasciata showed the strongest algicidal activity. The isolation of algicidal compounds was due to the bioassay-guided fractionation of the methanol extract of U. fasciata. The structures of these compounds were determined and showed potent algicidal activity against the red-tide phytoplankton Heterosigma akashiwo.

We isolated 2 virus-like agents that suppressed growth of Gymnodinium mikimotoi from coastal waters of the Uwa Sea, Japan. The agents found in the flagellate cells, named GM6 and GM7, were filterable in a 0.22-lm-pore filter with approximately 100-nm shapes. Electron microscopic observation showed the presence of virus-like particles in severely damaged G. mikimotoi cells infected by GM6. The growth-suppression activity of the agents (GM6 or GM7) was lost by heating at 50°C, with treatments of DNase and protease, and filtration through a 0.05-lm filter. Our results suggest that the agents are DNA viruses infectious to and virulent for G. mikimotoi. This is the first report of a virus-like agent specific to G. mikimotoi. [ABSTRACT FROM AUTHOR]

Investigates temporal changes of the red tide flagellates Chattonella spp. and the algicidal bacteria Cytophaga sp. J18/M01 and Alteromonas sp. S in the Seto Inland Sea, Japan. Possible tools in reducing the impacts of harmful algal blooms; Changes in vertical profiles of water temperature, total bacteria, algicidal bacterium and microalgal biomass; Other types of algicidal bacteria existing in coastal seas.

Combined methods of size fractionation and single-cell isolation were used to investigate the seasonal variation of phytoplankton dynamics in Tokyo Bay with an emphasis on primary productivity. Red tides occurred in Tokyo Bay from spring to autumn; a diatom, Skeletonema costatum, and a raphidophycean, Heterosigma akashiwo, were the most important primary producers. Small diatoms and flagellates, including these species, were dominant and showed rapid changes of phytoplankton community structure within several days in summer. The nanoplankton (3–20 μm) fraction contributed most to chlorophyll a concentration and primary productivity during spring to autumn, whereas the microplankton (>20 μm) contribution was remarkable in winter. Picoplankton (<3 μm phytoplankton) remained relatively constant throughout the year. A significant reverse relationship was obtained between assimilation rate and chlorophyll a content for the total and nanoplankton population; the assimilation rate was high at the initial phase of the bloom, then decreased to a minimum level at the peak of the bloom. Factors controlling the reduction of assimilation rates at the peak, and changes in phytoplankton community structure, are discussed. [ABSTRACT FROM PUBLISHER]

Because riverine dissolved organic matter (DOM) has been considered less bioavailable to coastal bacteria than marine DOM produced by marine phytoplankton, nutrient regeneration from riverine DOM through marine bacterial decomposition has rarely been quantified, especially in eutrophic coastal seas. Through incubation experiments, this study aimed to compare nutrient regeneration from the decomposition of riverine and marine high-molecular-weight (HMW) DOM by coastal bacteria in a eutrophic coastal sea, namely the Ariake Sea in Japan. As an indicator of the bioavailability of DOM, carbon contained in total dissolved amino acids relative to dissolved organic carbon (DOC) was higher in marine HMW-DOM than riverine HMW-DOM in July and August, although the opposite pattern was observed in September. Another indicator of the bioavailability of DOM, the degradation index of amino acids, showed more fresh organic matter in riverine HMW-DOM than marine HMW-DOM in August and September. These results suggest that the bioavailability of HMW-DOM was comparable between the river site and marine site. NH 4 + and PO 4 3− were released in seawater incubations treated with both riverine and marine HMW-DOM. In addition, amount of riverine DOC decomposition and NH 4 + and PO 4 3− regeneration in this study were higher than those in other eutrophic sea. In July, NH 4 + and PO 4 3− significantly increased in the riverine HMW-DOM treatment, despite slow DOC decomposition. To our knowledge, this study is the first to show that riverine DOM may be comparable to marine DOM as a source of nutrients in a eutrophic coastal ecosystem. In addition, the western Ariake Sea is one of the most serious red tides area, though NH 4 + is always (NO 3 − + NO 2 − is occasionally) depleted. Thus, NH 4 + supply through riverine DOM degradation may contribute to prolong red tides in this area. • Riverine and marine high-molecular-weight (HMW) dissolved organic matter (DOM) were added to eutrophic seawater. • NH 4 + and PO 4 3− were released in seawater incubations treated with both riverine and marine HMW-DOM. • In July, NH 4 + and PO 4 3− significantly increased in the riverine HMW-DOM treatment. • The results of this study support reconsideration of the role of riverine DOM in the nutrient dynamics of eutrophic sea. [ABSTRACT FROM AUTHOR]

The article presents a discussion on effects of physico-chemical factors and nutrients on the growth of Heterosigma akashiwo, a marine raphidophycean flagellated algae. Heterosigma akashiwo has been known as a causative organism of red tides in various areas of the coastal water of Japan. In Osaka Bay, this species occurs as a summer red tide. This red tide sometimes produces a harmful effect on fishes and causes local inhabitants and fishermen to complain because they are inclined to believe that the occurrence of the red tide is due to domestic or industrial pollution.

Examines the ultrastructure of Chattonella species, a red tide chloromonadophycean alga, from Kagoshima Bay, Japan. Isolation of a chloromonad associated with red tides; Attachment of two flagella at the base of the gullet; Association of the flagella with the nucleus by a rhizoplast.

Presents a study on the effect of lectin stimulation on the generation of superoxide anion in Chatonella marina or red tide phytoplankton from Japan. Effect of lectins on oxygen production in red tide phytoplankton; Methodology of the study; Results and discussion; Conclusion.

The distribution and biomass of Peridinium bipes f. occultatum were observed in the autumns of 1991, 1992 and 1994 at the head of the Shorenji Dam reservoir (Mie prefecture, Japan). Summarizing observations and some other information, we discussed processes related to the accumulation of Peridinium biomass. In the study area biomass of Peridinium increased at a similar rate to growth day by day, and roughly 2/3 of the dally maximum biomass fluctuated in a given day. The horizontal 'import' and 'export of Peridinium biomass by flows mainly change the biomass of red tide at the upstream end of the reservoir. Flow control in the reservoir, as well as growth control, will also be important in suppressing freshwater red tide. [ABSTRACT FROM AUTHOR]

Heterocapsa circularisquama Horiguchi sp. nov. is described from Ago Bay, central Japan. The dinoflagellate prThe vegetative morphology and life history of Halopteris f/I/dna (Grateloup) KUtzing, collected from Korea, were examined in laboratory culture. Field plants attaining 3-5 cm in height were epilithic, tufted, yellowish- brown, and produced numerous erect axes with alter- nately distichous branches from compact basal discs. They were cultured under a 12 12 h LD photoperiod at 10°C, 15°C and 20°C to observe the influence of temperature on reproduction. At 10°C plants grew only vegetatively, whereas at 15°C and 20°C they produced unilocular sporangia. Unispores released from sporan- gia developed into monoecious, anisogamous gameto- phytes that formed plurilocular female and male gam- etangia on the same lateral branches. The zygotes, by fusion of female macrogametes and male microga- metes, developed into sporophytes bearing unilocular sporangia, whereas the unfused female gametes ger- minated parthenogenetically. This species was con- firmed to have an isomorphic life history, basically sim- ilar to the other species of Sphacelariales. oduced large-scale red tides in the bays of central and western Japan and caused mass mortality of bivalves, notably the pearl oysters. The cell is small and is composed of a conical epitheca and a hemi-spheroidal hypotheca. The chloroplast is single and is connected to the single pyrenoid. The nucleus is elongated and is located in the left side of the cell. Thecal plate arrangement has been determined as: Po, cp, 5', 3a, 7", 6c, 5s, 5"', 2" ". Heterocapsa circularisquama is morphologically very similar to Heterocapsa ilidefina and it is almost impossible to distinguish these two species at light microscopical level. The characteristics which can be used to distinguish these two species are the morphology of body scales and the ultrastructure of the pyrenoid matrix. [ABSTRACT FROM AUTHOR]

In April 1995, an unusual large-scale red tide of Heterosigma akashiwo (Hada) Hada occurred, causing massive fish kills in Kagoshima Bay, Japan. Four neurotoxic components, HaTx-I, HaTx-IIa, HaTx-IIb and HaTx-III, which corresponded to brevetoxin components, PbTx-2, PbTx-9, PbTx-3 and oxidized PbTx-2, were inferred from analysis of Heterosigma red tide toxins on TLC and HPLC. [ABSTRACT FROM AUTHOR]

• The red tide forming species noctiluca scintillans is a marine heterotrophic dinoflagellate. • We analyzed the prey organisms within natural cells of N. scintillans using two genetic methods. • Restriction enzyme digestion and blocking primer methods were applied. • DNA sequences of surprisingly diverse taxa were obtained from the natural cells of N. scintillans. • Molecular prey analyses may reveal undiscovered interactions within the plankton community. The red tide forming heterotrophic dinoflagellate Noctiluca scintillans is common in temperate to tropical waters around the world. Understanding the in situ prey of N. scintillans is essential for elucidating its role in marine microbial food webs. In this study, we applied two polymerase chain reaction (PCR)-based cloning techniques, a predator-specific restriction enzyme, and a blocking primer. The PCR of nuclear 18S rDNA was performed on single N. scintillans cells that were collected from Ishinomaki Bay, Japan, in May 2018. The maximum detection rates of non- Noctiluca sequences were 56% using the restriction enzyme method and 87% with the blocking primer method, representing a broad taxonomic range of organisms, including diatom, dinoflagellate, bolidophyte, haptophyte, euglenophyte, green algae, golden algae, ciliate, heliozoa, copepod, brown seaweed, sponge, bivalve, and polychaete. The diverse DNA was probably ingested by N. scintillans directly or indirectly through secondary predation or ingestion of marine snow or detritus containing many organisms. The application of molecular approaches to various species may reveal undiscovered interactions within the phytoplankton community, including prey-predator, or symbiotic relationships. [ABSTRACT FROM AUTHOR]

• Burkholder's goniodomin is identical to goniodomin A. • Molecular weights, melting points, solubilities and chromatographic behavior are essentially identical. • Infrared and NMR spectra and mass spectral fragmentation patterns are essentially identical. • No trace of the organism could be detected so definitive identification of the species is not possible. • This is the only report of goniodomin in the Caribbean region. In 1968 Burkholder and associates (J. Antibiot. (Tokyo) 1968 , 21 , 659–664) isolated the antifungal toxin goniodomin from an unidentified Puerto Rican dinoflagellate and partially characterized its structure. Subsequently, a metabolite of Alexandrium hiranoi was isolated by Murakami et al. from a bloom in Japan and its structure was established (Tetrahedron Lett. 1988 , 29 , 1149–1152). The Japanese substance had strong similarities to Burkholder's but due to uncertainty as to whether it was identical or only similar, Murakami named his toxin goniodomin A. A detailed study of this question now provides compelling evidence that Burkholder's goniodomin is identical to goniodomin A. Morphological characterization of the dinoflagellate suggests that it was the genus Alexandrium but insufficient evidence is available to make a definite identification of the species. This is the only report of goniodomin in the Caribbean region. [ABSTRACT FROM AUTHOR]