Makoto Yoshida

Fixation of Chattonella antiqua and C. marina (Raphidophyceae) using Hepes-buffered paraformaldehyde and glutaraldehyde for flow cytometry and light microscopy

Katano T., Yoshida M., Lee J., Han M.-S. and Hayami Y. 2009. Fixation of Chattonella antiqua and C. marina (Raphidophyceae) using Hepes-buffered paraformaldehyde and glutaraldehyde for flow cytometry and light microscopy. Phycologia 48: 473–479. DOI: 10.2216/08-102.1. Chattonella antiqua and C. marina are harmful algal species that cause massive fish kills in coastal environments. Generally, Chattonella cells cannot be preserved well by fixation because of their fragile nature. In the present study, we developed a new fixative for Chattonella. Phosphate-buffered saline, which is generally used as a buffer for fixative, caused precipitation after fixation. In contrast, Hepes or sodium cacodylate prevented the precipitation. Moreover, these buffers worked well in the fixation to preserve cell morphology. Since Hepes is not as noxious as cacodylate, we selected Hepes as the buffer for the fixative. Cell counting revealed that the decrease in cell numbers by fixation was negligible and did not start until at least 8 days after fixation. We successfully analysed the DNA amount in fixed cells of Chattonella by flow cytometry. The present study demonstrated that Hepes-buffered paraformaldehyde and glutaraldehyde are superior to other fixatives for flow cytometry and light microscopy.

Encystment and Excystment under Laboratory Conditions of the Nontoxic Dinoflagellate Alexandrium fraterculus (Dinophyceae) Isolated from the Seto Inland Sea, Japan

S. Nagai, G. Nishitani, Y. Takano, M. Yoshida and H. Takayama. 2009. Encystment and excystment under laboratory conditions of the nontoxic dinoflagellate Alexandrium fraterculus (Dinophyceae) isolated from the Seto Inland Sea, Japan. Phycologia 48: 177–185. DOI: 10.2216/08-43.1. The sexuality (i.e. encystment and excystment) of the nontoxic dinoflagellate Alexandrium fraterculus, isolated from the Seto Inland Sea, Japan, was clarified for the first time under laboratory conditions. Sexual reproduction was by conjugation of isogametes, and plasmogamy was completed in 25–60 min after the conjugation started and produced a planozygote with one transverse and two longitudinal flagella, then a cyst was formed. Cysts were round or elliptical. The cyst size was 37.5–50.0 µm in diameter. The surface of cysts was smooth, and there was no paratabulation. Encystment through sexual reproduction was observed in two of 28 pairs, which included seven self-crossings, by use of seven nonaxenic clonal strains. No planozygote formation or encystment was found in any of the self-crossings, indicating that this species is heterothallic. Successful excystment was observed when the cysts, which had been preserved at 10°C in the dark for 3 mo, were incubated under light conditions at 25°C, thus showing that this species has a similar life cycle as reported in A. tamarense/catenella/tamiyavanichii.

Effect of nutrient concentration and salinity on diel vertical migration of Chattonella marina (Raphidophyceae)

Abstract Vertical migration plays an important role in the development of Chattonella populations in the natural environment; however, this behaviour has remained largely undescribed. In the present study, the diel vertical migration of Chattonella marina in the Ariake Sea was examined along with nutrient concentrations and salinity at four sampling sites during the bloom in the summers of 2008, 2009 and 2010. Cells of Chattonella were abundant at the surface (0 m depth) in the daytime in most cases. However, when surface salinity was 9, which is the lower limit for growth, the population accumulated at a depth of 2 m, where salinity was 15, suggesting that Chattonella moves to avoid water with low salinity. Chattonella cells actively migrated, even under nutrient-replete conditions (mean DIN concentration, 12.73 µM). The present study demonstrates that Chattonella cell migration is independent of nutrient availability. In addition, Chattonella cells stop upward migration when the surface salinity is low (<u200915). These insights are important for making predictions of Chattonella population dynamics after heavy rains.

HYDRAULIC MODEL EXPERIMENTS ON SLIDING STABILITY OF CAISSON BREAKWATER WITH GROUND ANCHOR FOR REINFORCEMENT

The rise of sea levels and the increase of wave forces which has been caused by global warming will cause the failure of breakwaters. The ground anchor for reinforcement is proposed as an anti-sliding method of caisson breakwaters. In this study, we conducted hydraulic model experiments with a scale of 1 to 30 model in order to investigate the sliding stability of caisson breakwaters with the ground anchor for reinforcement against wave forces. The results show that the caisson breakwater with the ground anchor for reinforcement increases the sliding resistance and reduces the sliding distance, and the larger the initial tension of the anchor is, the more effective as an anti-sliding method.

SHAKING TABLE TEST ON DYNAMIC BEHAVIOR OF CAISSON TYPE QUAY WALL WITH GROUND ANCHOR FOR SEISMIC REINFORCEMENT

アンカーで耐震補強された岸壁の耐震性は数値解析などで確かめられてはいるが，実際の地震時挙動を確認した事例は少なく，アンカーによる耐震補強効果について十分には明らかにされていない．そこで，グラウンドアンカーによるケーソン式岸壁の耐震補強効果を明らかにすることを目的として，大型水中振動台による模型振動実験を実施した．その結果，ケーソン変位抑制時のアンカーおよび岸壁の動的挙動を明らかにするとともに，ケーソン式岸壁にアンカーを適用した場合の留意点を指摘した．さらに，本実験を対象として，ケーソンの滑動，転倒および支持力について安定計算を行った結果，耐震補強によるケーソン安定性向上への貢献度がケーソンの破壊モードに応じて異なることが明らかになった．