Comparative studies on the fish-killing activities of Chattonella marina isolated in 1985 and Chattonella antiqua isolated in 2010, and their possible toxic factors

Chattonella antiqua isolated in 2010 showed extremely more potent fish-killing activities against red sea bream, Japanese horse mackerel, and blue damselfish than those of Chattonella marina isolated in 1985. Chemiluminescence and electron spin resonance (ESR) analyses suggested greater reactive oxygen species (ROS)-producing activity of C. antiqua than that of C. marina. Sodium benzoate, a hydroxyl radical scavenger, significantly suppressed the fish-killing activity of C. antiqua on blue damselfish. The chlorophyll level in the gill tissue of blue damselfish exposed to flagellate cells increased along with the exposure time, and the cell count of gill-associated C. antiqua estimated with chlorophyll level was higher than that of C. marina. These results suggest that the ROS-producing activity and affinity of Chattonella cells to the gill surface may be important factors influencing the fish-killing activity of Chattonella species.     

Assessment of EvaGreen-based quantitative real-time PCR assay for enumeration of the microalgae Heterosigma and Chattonella (Raphidophyceae)

Heterosigma akashiwo and Chattonella species (Raphidophyceae) are difficult to detect and quantify in environmental samples because of their pleomorphic and fragile cell nature. In this study, we developed a quantitative real-time polymerase chain reaction (qRT-PCR) assay for the enumeration of these algal taxa using a new DNA-binding dye, EvaGreen. Species-specific qRT PCR primers to H. akashiwo, Chattonella antiqua, Chattonella marina, Chattonella ovata, and Chattonella subsalsa were designed to target the ITS2 rRNA gene intergenic region. Primer specificities were tested via BLAST searches. In addition, specificity was verified using empirical tests, including competitive PCR. The qRT PCR assay analyzing C _t value and the log of cell number showed a significant linear relationship (r ²?≥?0.997). When light microscopy was used to monitor the population dynamics of targeted Raphidophyceae from Lake Shihwa, H. akashiwo was detected in ten samples and no Chattonella spp. were detected (70 samples collected from May, 2007 to January, 2008). In contrast, when the qRT-PCR assay was used, H. akashiwo was detected in 41 samples. C. antiqua, C. marina, and C. ovata were detected in eight samples. Most of the samples analyzed using qRT-PCR assays showed higher algal numbers than did those assayed via microscopy, suggesting that the enumeration of Raphidophyceae via classic microscopic methods most likely underestimates true algal concentration.     

Life cycle of Chattonella marina (Raphidophyceae) inferred from analysis of microsatellite marker genotypes

Red tides of Chattonella spp. have caused continuous damage to Japanese aquaculture, however, the life cycle of this organism remains incompletely understood. To further investigate this matter, we assessed genotypes at 14 microsatellite markers in three varieties of Chattonella marina, viz., C. marina var. antiqua, C. marina var. marina, and C. marina var. ovata, to establish whether Chattonella undergoes asexual diploidization or sexual reproduction. After genotyping 287 strains of C. marina, all but one of these strains was shown to be heterozygous for at least some loci, and thus, in the diploid state, suggesting that Chattonella strains undergo sexual reproduction. In addition, we performed single‐cell amplification on ‘small cells’ that are derived from vegetative cells under dark and low‐nutrient conditions. The results indicated the existence of two types of small cells. The ‘Small cell Type 1’ was found to be heterozygous, genotypically equivalent to the vegetative cells, and is therefore diploid. These small cells may change to resting cells (cysts) directly. The ‘Small cell Type 2’ was homozygous at all analyzed loci, suggesting that these small cells are haploid and may be derived by meiosis. As fusion between small cells has previously been observed, the ‘Small cell Type 2’ may be the gamete of Chattonella. We present a construct of the full life cycle of Chattonella marina based on our own and previous results.     

Lethal effects of ichthyotoxic raphidophytes,Chattonella marina,C. antiqua,and Heterosigma akashiwo,on post-embryonic stages of the Japanese pearl oyster,Pinctada fucata martensii

The inimical effects of the ichthyotoxic harmful algal bloom (HAB)-forming raphidophytes Heterosigma akashiwo, Chattonella marina, and Chattonella antiqua on the early-life stages of the Japanese pearl oyster Pinctada fucata martensii were studied. Fertilized eggs and developing embryos were not affected following exposure to the harmful raphidophytes; however, all three algal species severely affected trochophores and D-larvae, early-stage D-larvae, and late-stage pre-settling larvae. Exposure to C. marina (5 × 10² cells ml⁻¹), C. antiqua (10³ cells ml⁻¹), and H. akashiwo (5 × 10³ cells ml⁻¹) resulted in decreased success of metamorphosis to the trochophore stage. A complete inhibition of trochophore metamorphosis was observed following exposure to C. antiqua at 5 × 10³ cells ml⁻¹ and C. marina at 8 × 10³ cells ml⁻¹. In all experiments, more than 80% of newly formed trochophores were anomalous, and in the case of exposure to H. akashiwo at 10⁵ cells ml⁻¹ more than 70% of D-larvae were anomalous. The activity rates of D-larvae (1-day-old) were significantly reduced following exposure to C. antiqua (8 × 10³ cells ml⁻¹, 24 h), C. marina (8 × 10³ cells ml⁻¹, 24 h), and H. akashiwo (10⁴ cells ml⁻¹, 24 h). The activity rates of pre-settling larvae (21-day-old) were also significantly reduced following exposure to C. antiqua (10³ cells ml⁻¹, 24 h), C. marina (8 × 10³ cells ml⁻¹, 24 h), and H. akashiwo (5 × 10⁴ cells ml⁻¹, 24 h). Significant mortalities of both larval stages were induced by all three raphidophytes, with higher mortality rates registered for pre-settling larvae than D-larvae, especially following exposure to C. marina (5 × 10²–8 × 10³ cells ml⁻¹, 48–86 h) and C. antiqua (10³–8 × 10³ cells ml⁻¹, 72–86 h). Contact between raphidophyte cells and newly metamorphosed trochophores and D-larvae, 1-day-old D-larvae, and 21-day-old larvae resulted in microscopic changes in the raphidophytes, and then, in the motile early-life stages of pearl oysters. Upon contact and physical disturbance of their cells by larval cilia, H. akashiwo, C. marina and C. antiqua became immotile and shed their glycocalyx. The trochophores and larvae were observed trapped in a conglomerate of glycocalyx and mucus, most probably a mixture of larval mucous and raphidophyte tricosyts and mucocytes. All motile stages of pearl oyster larvae showed a typical escape behavior translating into increased swimming in an effort to release themselves from the sticky mucous traps. The larvae subsequently became exhausted, entrapped in more heavy mucous, lost their larval cilia, sank, become immotile, and died. Although other toxic mediators could have been involved, the results of the present study indicate that all three raphidophytes were harmful only for motile stages of pearl oysters, and that the physical disturbance of their cells upon contact with the ciliary structures of pearl oyster larvae initiated the harmful mechanism. The present study is the first report of lethal effects of harmful Chattonella spp. towards larvae of a bivalve mollusc. Blooms of H. akashiwo, C. antiqua and C. marina occur in all major cultivation areas of P. fucata martensii during the developmental period of their larvae. Therefore, exposure of the motile early-life stages of Japanese pearl oysters could adversely affect their population recruitment. In addition, the present study shows that further research with early-life development of pearl oysters and other bivalves could contribute to improving the understanding of the controversial harmful mechanisms of raphidophytes in marine organisms.     

A mutualistic interaction between the bacterium Pseudomonas asplenii and the harmful algal species Chattonella marina (Raphidophyceae)

Several studies on various Chattonella species have reported that bacteria may play an important role in Chattonella bloom initiation, however, no studies have described how these bacteria promote the growth of C. marina. The interaction between C. marina and bacteria was investigated for identification and characterization of potential growth-promoting bacteria. In preliminary tests, the growth promoting effect of Pseudomonas species (25 strains) was investigated and P. asplenii (≥2.27) was determined as a growth-promoting bacteria for both C. marina strains (CCMP 2049 and 2050). This bacterium exerted optimal growth-promoting effects on C. marina, causing an increase in the initial density of P. asplenii to approximately 1 × 10⁷ cells mL⁻¹, which was used as the initial density in this study. To determine whether the growth-promoting activity was direct or indirect, P. asplenii was incubated in the algal media and then a filtrate of this culture was added to both C. marina strains. The P. asplenii filtrate stimulated the growth of C. marina and maintained the growth-promoting effects after high temperature (121 °C for 20 min) and pressure (15 psi) treatment. Thus, P. asplenii is able to promote C. marina growth through the release of a heat-resistant substance, such as inorganic nutrients. A nutrient analysis indicated that this bacterium elevated the phosphate concentration. Interestingly, P. asplenii was unable to survive in phosphate-limited media but could grow in phosphate-limited media incubating C. marina. Moreover, this bacterium could secrete significantly more phosphate in the presence of C. marina (p < 0.0001). These results suggested that P. asplenii and C. marina may have a mutualistic interaction.     

Chemotaxonomic survey of sterols and fatty acids in six marine raphidophyte algae

Fatty acid and sterol profiles allowed for clear discrimination betweentheraphidophyte genera Chattonella,Heterosigma, Fibrocapsa andOlisthodiscus, but exhibited little differentiation forindividual Chattonella species(C.marina, C. antiqua and C.subsalsa). Sterol and fatty acid profiles do not support theseparation of Chattonella antiqua and C.marina as distinct species. Ecophenotypic variations in lipidprofiles were also observed between Chattonella strainsfromdifferent geographic locations. Sterol signatures which may be useful aschemotaxonomic markers were: the absence of C₂₇ sterols (cholesteroland 24-dihydrozymosterol) in Heterosigma akashiwo; thepresence of isofucosterol in Chattonella; and theoccurrence of brassicasterol, poriferasterol and fucosterol inOlisthodiscus luteus. High levels of eicosapentaenoic acid(EPA; 17-27% of fatty acids) were present in all raphidophyte species. Lipidcomposition correlated more closely to recent molecular classification ofraphidophytes than carotenoid pigments.     

Molecular Analysis of Ribosomal RNA Gene of Red Tide Algae Obtained from the Seto Inland Sea

Eleven clones from five species of the planktonic microalgae, (Chattonella antiqua, Chattonella marina, Heterosigma akashiwo, Alexandrium catenella, and Scrippsiella trochoidea), which were collected from the Seto Inland Sea in Japan and from Thailand, were subjected to nucleotide sequence analysis of the D1/D2 domain of the large subunit (LSU) of their ribosomal RNA genes. After amplification by polymerase chain reaction using degenerated primers, whole-nucleotide sequences for the D1/D2 domains of the LSU rRNA gene of 11 microalgae were analyzed. Phylogenic tree analysis using these nucleotide sequences showed each species located in a cluster corresponding to its morphological classification. The nucleotide sequence data for Chattonella spp. suggest that multiple clones of both Chattonella antiqua and Chattonella marina are present in the Seto Inland Sea and that red tide blooms of Chattonella spp. in different years may have contained different clones. Received September 6, 1999; accepted December 16, 1999.     

Anti-Angiogenesis Activities of Novel Peptide Complexes: Mitochondria-Disruptive 9mer Peptides Conjugated with the Integrin alpha V beta 3-Homing Cyclic RGD Motif

Chattonella is one of the most toxic red tide phytoplankton and causes severe damage to fish farming. Recent studies demonstrated that Chattonella sp. generates superoxide and hydroxyl radicals, which may be responsible for the toxicity of this plankton. However, little is known about the mechanism of the production of oxygen radicals by Chattonella, and the role of oxygen radicals in Chattonella themselves is also unclear. In this study, we found that superoxide dismutase (SOD) and catalase inhibited the growth of Chattonella marina concomitant with their morphological changes. In the presence of these enzymes, the shape of vegetative C. marina cells changed from spindle to round. Furthermore, the generation of oxygen radicals by C. marina depended on the growth phase; the rate of superoxide and hydrogen peroxide generation was the highest during exponentially growing phase and subsequently decreased to one-fifth of the maximal level in the stationary growth phase. These results suggest that oxygen radicals generated by C. marina play an essential role in their own survival, especially in cell division.     

Development of microsatellite markers for the red tide‐forming harmful species Chattonella antiqua,C. marina,and C. ovata (Raphidophyceae)

We have developed 11 microsatellite markers that are specific to Chattonella antiqua, C. marina, and C. ovata, the red tide‐forming harmful phytoplanktons. The 11 loci were amplified in the three species. The number of alleles per locus ranged from 5 to 16. The three species shared most microsatellite regions, although the genetic differences in specific loci were detected among them. These markers of the Chattonella species will be beneficial for biogeographical, detailed taxonomic, studies.     

Differential effects of typhoons on ichthyotoxic Cochlodinium polykrikoides red tides in the South Sea of Korea during 2012–2014

The harmful dinoflagellate Cochlodinium polykrikoides is known to cause fish death by gill-clogging when its abundance exceeds approximately 1000 cells ml⁻¹. Thus, red tides of this dinoflagellate have caused considerable loss in the aquaculture industry worldwide. Typhoons carrying strong winds and heavy rains may alter the process of red tide events. To investigate the effects of typhoons on C. polykrikoides red tides, daily variations in the abundance of C. polykrikoides, and wind speeds in three study areas in the South Sea of Korea were analyzed during the periods of C. polykrikoides red tides and the passage of 14 typhoons during 2012–2014. The typhoons differentially affected Cochlodinium red tides during the study period, and the daily maximum wind speed generated by the typhoon was critical. Four typhoons with daily maximum wind speeds of >14 m s⁻¹ eliminated Cochlodinium red tides, while three typhoons with daily maximum wind speed of 5–14 m s⁻¹ only lowered the abundance. However, other typhoons with daily maximum wind speeds of <5 m s⁻¹ had no marked effect on the Cochlodinium abundance. Therefore, typhoons may sometimes eliminate C. polykrikoides red tide events, or reduce cell abundances to a level that is not harmful to caged fish cultivated in aquaculture industries. Thus, typhoons should be considered when compiling red tide dynamics and fish-kill models.     

Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

Effects of temperature,salinity and their interaction on growth of benthic dinoflagellates Ostreopsis spp. from Thailand

Benthic dinoflagellates Ostreopsis spp. are known as producers of palytoxin and its analogs, resulting occasionally in human health problems worldwide. Although distribution of Ostreopsis spp. along the Thai coasts has been reported, little is known about their growth characteristics. To discuss the bloom dynamics of Ostreopsis spp. in Thailand, first we tested four kinds of media to optimize growth conditions and then clarified the effects of temperature, salinity and temperature–salinity interaction on the growth of strains of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade, Ostreopsis sp. 6 and Ostreopsis sp. 7. We showed that the f/2 medium was a suitable medium which gave the highest cell yields for all the strains tested. The strains of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade and Ostreopsis sp. 6 grew in the temperature range 20–32.5 °C, whereas the strain of Ostreopsis sp. 7 grew in 20–30 °C. The semi-optimal temperature ranges (≧80% of the maximal growth rate) for the former three strains were 22.7–27.4 °C, 27.9–30.8 °C and 23.5–26.4 °C, respectively, whereas that of the latter strain was 23–27.2 °C. The optimal temperature for the O. cf. ovata South China Sea subclade was 30 °C, whereas for the others it was 25 °C. All the Ostreopsis strains tested could grow in a salinity range of 20–40. The semi-optimal salinities for the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade Ostreopsis sp. 6 and Ostreopsis sp. 7 were 28.7–35, 23.8–30.8, 29.8–36 and 28–36, respectively. The optimal salinities for the O. cf. ovata Thailand subclade and O. cf. ovata South China Sea subclade were 30 and 25, respectively, whereas for Ostreopsis sp. 6 and Ostreopsis sp. 7 it was 35. In this study, our results suggested that the optimal and tolerable temperature–salinity conditions differ among the Thai Ostreopsis species/clades/subclades. Tolerances of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade and Ostreopsis sp. 6 to the high temperature of 32.5 °C may allow these organisms to be distributed in the tropical areas, where the water temperature often reaches >30 °C.     

Temperature requirements for dormancy break and seed germination vary greatly among 14 wetland Carex species

We evaluated dormancy loss in seeds of 14 Carex species (C. atherodes, C. brevior, C. comosa, C. cristatella, C. cryptolepis, C. granularis, C. hystericina, C. lacustris, C. pellita, C. scoparia, C. stipata, C. stricta, C. utriculata, C. vulpinoidea) under growing season and stratification conditions and determined the temperature requirements for germination. Seeds were germinated for 1 year at a diel temperature regime (5/1 °C, 14/1 °C, 22/8 °C, or 27/15 °C) or a seasonal regime (seeds moved among the four diel regimes to mimic seasonal temperatures). All species had conditionally dormant seeds at maturity. The optimal temperature for germination of most species was 27/15 °C. The 14 species were grouped by their seed viability, dormancy, and germination with a Seed Regeneration Index (SRI; range 0–1) using the results of this study and a previously published paper on stratification effects on Carex seed dormancy and germination. The eight species that had an SRI value >0.5 (C. brevior, C. comosa, C. cristatella, C. cryptolepis, C. hystericina, C. scoparia, C. stipata, C. vulpinoidea) had high seed viability (>60%) and required little to no stratification to germinate readily over a broad range of temperatures. The six species with an SRI value <0.5 (C. atherodes, C. granularis, C. lacustris, C. pellita, C. stricta, C. utriculata) generally had low seed viability (<50% and often <1%) and required stratification or particular temperatures (35/30 °C or 5/1 °C for C. stricta; 35/30 °C for C. utriculata; 27/15 °C for C. atherodes, C. lacustris, C. pellita; 5/1 °C for C. granularis) for germination ≥50%. These six species will require more attention from restoration practitioners to ensure that there are sufficient viable seeds to meet revegetation goals, that dormancy break is achieved, and that seeds are sown when temperatures are optimal for germination. The different seed germination syndromes that we found for these Carex species likely contribute to variable seed bank formation and emergence patterns, and species coexistence.     

Mortality in the initial ontogeny of Paralabrax maculatofasciatus (Actinopterygii, Perciformes, Serranidae) caused by Chattonella spp. (Raphidophyceae)

Fish are particularly sensitive to metabolites produced by Raphidophyte species and these have caused intensive fish kills in several countries. However, the effects on embryos of marine fish are unknown but could probably provoke an important impact on new stock recruitment and hence on fisheries. We evaluated the toxic effects of Chattonella spp. strains from the Gulf of California on three development stages of spotted sand bass (Paralabrax maculatofasciatus): embryo in segmentation stage (ES), embryo (EM), and eleutheroembryo (EL). Embryos (ES) were exposed to different cell concentrations of Chattonella subsalsa, Chattonella marina, Prorocentrum micans, and f/2 medium as control. Also, one set of embryos was tested with cell-free media for C. subsalsa cultures. Incubation lasted until embryos reached apterolarva phase. The ES was the most sensitive stage reaching 98% mortality with C. subsalsa, followed by cell-free media of C. subsalsa cultures, with mortalities close to 90%, whereas EM and EL phases presented mortalities below 60%. This work demonstrates that larval stages of P. maculatofasciatus are highly sensitive to short time exposure to all Chattonella spp. strains tested, that direct physical contact with cells is not required to cause mortality, and that the toxic effect is more pronounced when embryos hatch.     

Physiological responses of Ostreopsis ovata to changes in N and P availability and temperature increase

Ostreopsis ovata is a benthic dinoflagellate that produces palytoxin and ovatoxins. Blooms of O. ovata causing human health problems and mortality of benthic fauna have been reported from many tropical and temperate marine waters. In the present study we examined the combined effects of temperature and different nutrient conditions on the biochemical composition, growth, toxicity and carbohydrate production of an O. ovata strain originating from the Tyrrhenian Sea. O. ovata cultures with N:P ratios of 1.6, 16 and 160 (N deficient, NP sufficient and P deficient, respectively) were grown at 20 °C and 30 °C. Biomass accumulation, growth rates, cell volumes, biochemical composition, cell toxicity and carbohydrate production in each treatment were studied. Results indicated that under nutrient sufficiency O. ovata biomass accumulation increased significantly compared to N and P deficiency and also that N limitation severely affected growth. The highest growth rates were recorded at 30 °C. Cellular contents and the atomic ratios of C, N and P were higher in the cells grown at 20 °C than in those grown at 30 °C. O. ovata cell volumes increased at 20 °C. N deficiency significantly increased cell toxicity. Toxicity per cell was higher at 20 °C, but per carbon was highest at 30 °C. The highest carbohydrate production was found in conditions of N deficiency and at the lower temperature.Our study suggests that temperature increases due to global warming and nutrient enrichment of coastal waters stimulate the proliferation of O. ovata, particularly for the strains that have become adapted to warm temperate waters.     

Genetic structure of Japanese Chattonella marina (Raphidophyceae) populations revealed using microsatellite markers

Chattonella marina var. antiqua and C. marina var. marina (Raphidophyceae) are red tide‐forming, harmful phytoplankton species. We investigated the genetic diversity and genetic relationship among the populations using microsatellite markers to identify putative sources of C. marina var. antiqua and C. marina var. marina in Japanese coastal populations. A positive correlation between genetic divergence and geographical distance (isolation by distance) was recognized for C. marina var. antiqua. The C. marina var. antiqua populations were established throughout a geological time scale, and genetic divergence had progressed in each population with gene flow depending on geographic distances. In contrast, isolation by distance was not observed for C. marina var. marina populations, and the genetic divergence among populations was extremely high. The Tokyo Bay population of C. marina var. marina, which was first recognized in 2008, had many private alleles but was related to the Kagoshima Bay population. The Tokyo Bay population may have been established by several invasions from the Kagoshima Bay population and other regions.     

Is inorganic nutrient enrichment a driving force for the formation of red tides?: A case study of the dinoflagellate Scrippsiella trochoidea in an embayment

Red tides (high biomass phytoplankton blooms) have frequently occurred in Hong Kong waters, but most red tides occurred in waters which are not very eutrophic. For example, Port Shelter, a semi-enclosed bay in the northeast of Hong Kong, is one of hot spots for red tides. Concentrations of ambient inorganic nutrients (e.g. N, P), are not high enough to form the high biomass of chlorophyll a (chl a) in a red tide when chl a is converted to its particulate organic nutrient (N) (which should equal the inorganic nutrient, N). When a red tide of the dinoflagellate Scrippsiella trochoidea occurred in the bay, we found that the red tide patch along the shore had a high cell density of 15,000 cells ml⁻¹, and high chl a (56 μg l⁻¹), and pH reached 8.6 at the surface (8.2 at the bottom), indicating active photosynthesis in situ. Ambient inorganic nutrients (NO₃, PO₄, SiO₄, and NH₄) were all low in the waters and deep waters surrounding the red tide patch, suggesting that the nutrients were not high enough to support the high chl a >50 μg l⁻¹ in the red tide. Nutrient addition experiments showed that the addition of all of the inorganic nutrients to a non-red-tide water sample containing low concentrations of Scrippsiella trochoidea did not produce cell density of Scrippsiella trochoidea as high as in the red tide patch, suggesting that nutrients were not an initializing factor for this red tide. During the incubation of the red tide water sample without any nutrient addition, the phytoplankton biomass decreased gradually over 9 days. However, with a N addition, the phytoplankton biomass increased steadily until day 7, which suggested that nitrogen addition was able to sustain the high biomass of the red tide for a week with and without nutrients. In contrast, the red tide in the bay disappeared on the sampling day when the wind direction changed. These results indicated that initiation, maintenance and disappearance of the dinoflagellate Scrippsiella trochoidea red tide in the bay were not directly driven by changes in nutrients. Therefore, how nutrients are linked to the formation of red tides in coastal waters need to be further examined, particularly in relation to dissolved organic nutrients.     

Newly discovered role of the heterotrophic nanoflagellate Katablepharis japonica,a predator of toxic or harmful dinoflagellates and raphidophytes

Heterotrophic nanoflagellates are ubiquitous and known to be major predators of bacteria. The feeding of free-living heterotrophic nanoflagellates on phytoplankton is poorly understood, although these two components usually co-exist. To investigate the feeding and ecological roles of major heterotrophic nanoflagellates Katablepharis spp., the feeding ability of Katablepharis japonica on bacteria and phytoplankton species and the type of the prey that K. japonica can feed on were explored. Furthermore, the growth and ingestion rates of K. japonica on the dinoflagellate Akashiwo sanguinea—a suitable algal prey item—heterotrophic bacteria, and the cyanobacteria Synechococcus sp., as a function of prey concentration were determined. Among the prey tested, K. japonica ingested heterotrophic bacteria, Synechococcus sp., the prasinophyte Pyramimonas sp., the cryptophytes Rhodomonas salina and Teleaulax sp., the raphidophytes Heterosigma akashiwo and Chattonella ovata, the dinoflagellates Heterocapsa rotundata, Amphidinium carterae, Prorocentrum donghaiense, Alexandrium minutum, Cochlodinium polykrikoides, Gymnodinium catenatum, A. sanguinea, Coolia malayensis, and the ciliate Mesodinium rubrum, however, it did not feed on the dinoflagellates Alexandrium catenella, Gambierdiscus caribaeus, Heterocapsa triquetra, Lingulodinium polyedra, Prorocentrum cordatum, P. micans, and Scrippsiella acuminata and the diatom Skeletonema costatum. Many K. japonica cells attacked and ingested a prey cell together after pecking and rupturing the surface of the prey cell and then uptaking the materials that emerged from the ruptured cell surface. Cells of A. sanguinea supported positive growth of K. japonica, but neither heterotrophic bacteria nor Synechococcus sp. supported growth. The maximum specific growth rate of K. japonica on A. sanguinea was 1.01 d⁻¹. In addition, the maximum ingestion rate of K. japonica for A. sanguinea was 0.13 ng C predator⁻¹d⁻¹ (0.06 cells predator⁻¹d⁻¹). The maximum ingestion rate of K. japonica for heterotrophic bacteria was 0.019 ng C predator⁻¹d⁻¹ (266 bacteria predator⁻¹d⁻¹), and the highest ingestion rate of K. japonica for Synechococcus sp. at the given prey concentrations of up to ca. 10⁷ cells ml⁻¹ was 0.01 ng C predator⁻¹d⁻¹ (48 Synechococcus predator⁻¹d⁻¹). The maximum daily carbon acquisition from A. sanguinea, heterotrophic bacteria, and Synechococcus sp. were 307, 43, and 22%, respectively, of the body carbon of the predator. Thus, low ingestion rates of K. japonica on heterotrophic bacteria and Synechococcus sp. may be responsible for the lack of growth. The results of the present study clearly show that K. japonica is a predator of diverse phytoplankton, including toxic or harmful algae, and may also affect the dynamics of red tides caused by these prey species.     

The germination characteristics of Alexandrium minutum (Dinophyceae), a toxic dinoflagellate from the Fal estuary (UK)

The germination characteristics of Alexandrium minutum cysts from the Fal estuary were studied at different conditions of temperature (4–24 °C) and salinity (15–35‰) and in the dark and low light intensity (2 μmol^?2 s^?1). Sediment sub-samples were directly cultured and processed at the end of the experiment for counts of non-germinated cysts. A decrease in the number of cysts was interpreted as germination that was calculated by comparison of the number of cysts over time with that of initial counts. The 50% germination time (time at which 50% of the total initial number of cysts had germinated) was calculated for each condition. A. minutum did not germinate in the dark but it germinated under all other conditions studied. Highest germination occurred at salinities of 30 psu and 35 psu and temperatures from 8 °C to 24 °C (germination rate—expressed as the inverse of the 50% germination time: 1.1–1.2). Lowest germination occurred at 15 psu and 4 °C and 24 °C (germination rate: 3.9–3.8). However, little variation in germination rates occurred across the conditions studied. As these conditions represent those likely in the estuary it is probable that A. minutum cysts on the surface of the sediments represent a constant source of cells to the water column and sediment disturbance (revealing buried cysts) could rapidly inoculate the water column with vegetative cells. This data was used to develop a model for Alexandrium germination from coastal sediments.     

Factors controlling Zostera marina L. growth in the eastern and western Pacific Ocean: Comparisons between Korea and Oregon,USA

Zostera marina distribution is circum-global and tolerates a wide range of environmental conditions. Consequently, it is likely that populations have adapted to local environmental conditions of light, temperature and nutrient supply. We compared Z. marina growth dynamics over a 2-year period in relation to environmental characters at Jindong Bay, South Korea and Yaquina Bay, Oregon, USA. Water temperature in Jindong Bay showed stronger seasonal variation (summer–winter ΔT = 20 °C) than in Yaquina Bay (summer–winter ΔT < 5 °C). Underwater irradiance in Jindong Bay exhibited a winter maximum, while in Yaquina Bay underwater light exhibited a summer maximum. Integrated annual underwater irradiance during 2003 was 2200 and 1200 mol photons m⁻² year⁻¹ in Korea and Oregon, respectively. Z. marina shoot density, biomass and integrated production were not significantly different between the two study sites. Seasonal Z. marina growth in Jindong Bay appeared to be controlled by temperature and light, while the growth pattern in Yaquina Bay suggested light regulation. Several seagrass parameters were correlated to phosphate concentrations, even though nutrients did not appear limiting. Despite differences in environmental factors, relative growth rates and temporal growth dynamics between study sites, integrated annual leaf production was quite similar at 335 and 353 g DW m⁻² year⁻¹ in the Jindong and Yaquina Bay study sites. We suggest that Z. marina net productivity is acclimated to the local environmental conditions and may be a general characteristic of temperate seagrass populations.