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Gymnodinium nagasakienseの赤潮発生機構と発生予知に関する生理生態学的研究
https://fra.repo.nii.ac.jp/records/2003215
https://fra.repo.nii.ac.jp/records/200321503edf9ad-a5c1-4707-ba2f-655cfbd9139a
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2024-04-25 | |||||
| タイトル | ||||||
| タイトル | Gymnodinium nagasakienseの赤潮発生機構と発生予知に関する生理生態学的研究 | |||||
| 言語 | ja | |||||
| タイトル | ||||||
| タイトル | Physiological Ecology of the Red Tide Flagellate Gymnodinium nagasakiense (Dinophyceae) - Mechanism of the Red Tide Occurrence and its Prediction - | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | jpn | |||||
| キーワード | ||||||
| 言語 | en | |||||
| 主題Scheme | Other | |||||
| 主題 | Gymnodinium nagasakiense; Red tide; Chromosome number; Growth physiology; Growth rate; Cell cycle. | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_6501 | |||||
| 資源タイプ | departmental bulletin paper | |||||
| アクセス権 | ||||||
| アクセス権 | metadata only access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
| 著者 |
山口, 峰生
× 山口, 峰生 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | During the summer of 1965, a huge bloom of the dinoflagellate Gymnodinium nagasakiense Takayama et Adachi, named Gymnodinium type-'65 at the time, occurred in Omura Bay in Kyushu, the western part of Japan, and caused mass mortality of cultured and feral fish. Since then, G. nagasakiense red tide has frequently occurred in the coastal waters of western Japan. The present study was done to establish the biological background for the elucidation of the mechanism of Gymnodinium red tide and its prediction. The major factors involved in the red tide outbreaks were examined by a field survey, the growth responses of the organisms to physicochemical factors in culture were observed, and the cell cycle of the organism was determined to develop a technique for estimating the species-specific in situ growth rate. The chromosome number of G. nagasakiense was examined for clonal cultures from different origins; i.e., Suo-Nada, Hiroshima Bay, Uranouchi-Inlet and Gokasho-Bay. G. nagasakiense had rod-shaped chromosomes that measured about 10~20 μm long and 1.5~2 μm wide. There was no significant difference in chromosome counts for the cultures from different waters. The chromosome number of G. nagasakiense was 113±5 (mean±SD, n=105). This indicated that the chromosome number in this species was stable and should be valuable for the taxonomy of the organism. Distribution of the vegetative cells and environmental factors concerning the red tide outbreaks was investigated in Suo-Nada, western Seto Inland Sea from 1985 to 1987. Important factors causing the huge bloom of G. nagasakiense were the marked decrease of the salinity of the surface layer by heavy rainfall, increase of vertical stability caused by a development of halocline and formation of large scale anoxic bottom water. Frequent observation of the sea water from Uranouchi-Inlet, Kochi Prefecture, confirmed that vegetative cells of G. nagasakiense occurred throughout the year. The effects of temperature, salinity and irradiance on the growth of this organism were examined using axenic cultures to evaluate the relative importance of these factors on the dynamics of natural populations. G. nagasakiense grew at a low irradiance of 10 μEm -2s-1 and more and the growth was saturated at 110 μEm -2s-1. The growth response to light allowed them to dominate in the low light conditions such as subsurface layer and bad weather in the rainy season. The growth of the flagellate was examined in 25 different combinations of temperature (10 to 30℃) and salinity (10 to 30 ‰) under saturated irradiance. Growth occurred at temperatures from 10 to 30 °C and at salinities from 15 to 30 ‰. The highest growth rate was observed in the combination of 25℃ and 25 ‰, respectively. The tolerable salinity range of growth was relatively wide at an optimum temperature and was reduced to a much narrower range at a sub-optimum temperature. These findings indicate that G. nagasakiense is an eurythermal and euryhaline organism. These physiological characteristics presumably allow them to endure the winter as motile cells, which in turn act as the seed population for initiating the red tide in the following summer. G. nagasakiense could utilize both inorganic and organic nutrients (nitrate, ammonium and urea as N sources and orthophosphate and glycerophosphate as P sources). Minimum cell quotas (Q) for nitrogen and phosphorus of the organism were 3.7~4.0 pmol cell-1 and 0.23~0.35 pmol cell-1, respectively. On the basis of these values and in situ nutrient (DIN and PO4-P) concentrations the growth potentials of natural sea water were evaluated. The growth potentials of the seawater from Suo-Nada and Uranouchi Inlet ranged from 100 to 8300 cells ml-1. Therefore G. nagasakiense red tide may occur at the ordinary level of nutrients in a natural environment. The relationship between nutrient concentrations and growth rate followed Monod's equation. The half saturation constant for growth (Ks value) was 0.58~0.78μM for nitrogen and 0.14~0.15μM for phosphorus. These values were smaller than those of other dinoflagellates reported previously. This indicates that G. nagasakiense requires a very low concentration of nutrients for their growth, which is a characteristic allowing it to grow more abundantly than its competitors in the natural environment. The diel pattern of cell division of G. nagasakiense was examined in a laboratory experiment under various light and temperature conditions on light:dark (L:D) cycles (L=05:00 to 19:00 h). G. nagasakiense exhibited a distinct phased cell division on the L:D cycles, with the maximum frequency of 2 nuclei stage at 22:00 h and that of paired cells at 04:00 to 06:00 h. Cell division generally occurred at the end of the dark period and its pattern was independent of light intensity and temperature. On the basis of these observations, the applicability of the frequency of dividing cells (FDC) technique for estimating growth rate of G. nagasakiense was examined. The duration of cell division (Td), a parameter necessary for the calculation of growth rate, was determined for two different cell division stages; i.e., 2 nuclei and paired cells. Calculated Td value from the frequency of paired cells was 1.09±0.16 h and stable for the population grown under different light intensities. On the other hand, the Td estimated from the frequency of 2 nuclei varied markedly. The growth rate estimated by the FDC technique using Td from paired cells correlated significantly with those calculated from the increase in cell number. The Td value was affected by temperature. However, a statistically significant log-linear relationship was obtained between Td and temperature. Using the relationship, Td at the desired temperature could be obtained. To determine the phased cell division and to estimate in situ growth rate of G. nagasakiense by the FDC technique, field sampling was conducted in Suo-Nada and Hiroshima Bay. Natural populations of G. nagasakiense showed distinct phased cell division as in the laboratory conditions with the maximum frequencies around midnight. Using the FDC of the natural population and Td values calculated from in situ temperatures, the growth rates were estimated to be 0.12~0.14 divisions day -1 for Suo-Nada and 0.27~0.52 divisions day -1 for Hiroshima Bay populations, respectively. To improve the FDC technique, DNA synthesis and the cell cycle in G. nagasakiense were investigated by determining the relative DNA contents of individual cells using an epifluorescence microscopy-based microfluorometry system. The nuclei were stained with the DNA-specific fluorochrome 4',-6-diamidino-2-phenylindole (DAPI). Nuclear DNA contents, cell size distribution, cell density, and frequency of paired cells were determined every 2 h for 24 h using cells grown on a 12h L:D cycle. DNA synthesis and cell division were tightly phased to a particular period of the L: D cycle. DNA synthesis (S phase) occurred from 10:00 to 22:00 h and was followed by cytokinesis. The presence of such a distinct S phase strongly suggests that G. nagasakiense has a typical eukaryotic cell cycle, which makes it possible to estimate the speciesspecific in situ growth rate based on the diel pattern of DNA synthesis. To examine the effect of temperature on the cell cycle, G. nagasakiense cells were cultured at 5 different temperature conditions (10~30℃) and the DNA content was determined using microfluorometry. Patterns of the change in percentages of G1 phase cell showed a sine curve at the temperature of more than 20℃. From the time interval of the peaks of the curve, the generation time of the species was estimated to be 24 h. These patterns become obscure at low temperatures. Based on the percentages of the cell cycle phase (G1, S, G2+M) durations of cell cycle phases at various temperatures were calculated. It was concluded that all phases of the cell cycle were affected by temperature and were increased with decreasing temperature. Low temperature caused an increase in cell size. Cells with 4C DNA were observed at 10℃. This indicated that diploidy occurred at a low temperature. The natural population of G. nagasakiense was also found to grow under the same cell cycle progression as in the laboratory conditions. These findings suggest that the method for species-specific growth rate using the diel DNA synthesis cycle is applicable to the natural populations. The present study revealed that G. nagasakiense could grow under a very wide range of environmental factors (light, temperature, salinity and nutrients). Based on these growth characteristics the biological phase of G. nagasakiense red tide and the factors affecting red tide development were summarized as follows. First, the seed population of the red tide was thought to overwintered vegetative cells. They grew gradually and their number increased with increasing water temperature. The population grew at nearly the maximum growth rate (1.0 division day -1) into red tide under the favorable conditions where low salinity and supply of nutrients by heavy rainfall in the rainy season, decrease of competitors by low irradiance, increase of temperature and irradiance after the rainy season, increase of vertical stability and decrease of grazing pressure. Physical and biological accumulation might increase the cell density in the red tide. After the red tide, the vegetative cells overwinter and play an important role in initiating the red tide of the following summer. On the basis of these biological characteristics of G. nagasakiense several plans for the prediction of the red tide are proposed. First, simulation using an ecological model is appropriate for long term predictions. Biological parameters for the relationship between growth rates and environmental factors obtained in the present study are useful for this purpose. Second, monitoring in situ growth rate of the organism by the newly developed FDC technique or cell cycle analysis might be a useful indicator for the short term prediction of the red tide. | |||||
| 言語 | en | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 海産渦鞭毛藻 Gymnodinium nagasakiense は1965年以降,西日本各地で赤潮を頻発し,しばしば数十億円に上る漁業被害を及ぼす有害種として知られている。そのため,本種による赤潮の発生機構及びそれに対する対策が切に望まれてきた。しかし,無菌株を用いた系統的な生理生態学的研究は少なく,未解明の部分が数多く残されていた。本論文は G. nagasakiense 赤潮の発生機構の解明と赤潮予知のため,現場海域における赤潮発生要因の抽出,種々環境因子に対する増殖特性の解明,現場における増殖速度の測定法の開発及びその基礎の確立等,生物学的情報を取りまとめたもので,その主な内容は次の通りである。周防灘全域を対象とした現場調査によりG.nagasakiense の遊泳細胞の出現と分布及び赤潮発生期における環境要因を調べた。大規模赤潮を引き起こす海況要因として,多量の降雨のよる表層水の著しい低塩分化,密度成層の発達による鉛直安定度の増大及び底層の貧酸素化の程度と規模が重要であることを明らかにした。また,高知県浦ノ内湾における本種の季節的助長を詳細に調査し,本種が周年にわたって栄養細胞で存在することを明らかにした。培養実験によってG. nagasakiense の増殖に及ばす光強度,水温,塩分及び栄養塩の影響を調べた。本種は10μEms1の弱光下でも十分増殖可能であることが判明した。このような光に対する増殖特性を備えることによって,本種は中層域や低日射量下でも他種に優先してその個体群の増大をはかることができると考えられた。本種は水温10~30℃,塩分15~30%の範囲で増殖可能であり,最大増殖速度は25℃,25‰で1.06 divisions day lであることが判明した。したがって,本種は広温·広塩分性種であること,さらに瀬戸内海の冬季水温に近い10℃でも十分増殖可能であるため栄養細胞で越冬でき,それが翌年の赤潮の初期個体群として重要であると考えられた。本種は窒素源として硝酸態,アンモニア態窒素及び尿素のすべてを,またリン源としては無機リン,グリセロリン酸を低濃度から高濃度にわたり利用できることが判明した。このような有機態窒素·リンの利用能を他種と比較した結果,G. nagasakiense は珪藻類及びラフィド藻よりも生態的に優位であることが判明した。本種の細胞内窒素及びリン含量はそれぞれ3.7~4.0pmol cell-1と0.23~0.35 pmol cell-1であった。この細胞内窒素·リン含量と現場海域における栄養塩濃度から海水の持つ潜在的な細胞増殖密度を計算すると100~8,300 cells mlに達することが判った。したがって,通常の現場海水の栄養塩レベルでも本種は赤潮状態にまで増殖し得ることが明らかとなった。本種の増殖速度と栄養塩濃度との関係は Monodの式に従うことが判明した。増殖の半飽和定数(Ks値)は窒素で0.58~0.78μM,リンで0.14~0.15μMであった。この値はこれまで渦鞭毛藻で報告されている中で最も小さく,本種は低濃度の栄養条件でも十分増殖できる特性を有することが判明した。本種の細胞内窒素及びリン含量はそれぞれ3.7~4.0pmol cell-1と0.23~0.35 pmol cell-lであった。この細胞内窒素·リン含量と現場海域における栄養塩濃度から海水の持つ潜在的な細胞増殖密度を計算すると100~8,300 cells mいに達することが判った。したがって,通常の現場海水の栄養塩レベルでも本種は赤潮状態にまで増殖し得ることが明らかとなった。本種の増殖速度と栄養塩濃度との関係は Monodの式に従うことが判明した。増殖の半飽和定数(K2値)は窒素で0.58~0.78μM,リンで0.14~0.15μMであった。この値はこれまで渦鞭毛藻で報告されている中で最も小さく,本種は低濃度の栄養条件でも十分増殖できる特性を有することが判明した。現場海域におけるG.nagasakienseの増殖速度測定法を開発するため,細胞分裂指数による方法を検討した。本種の細胞分裂は夜間に同調的に起こることが判った。分裂に要する時間は光強度によって影響されなかったが,温度によって変化し低温になるにつれ増加した。しかし,温度と分裂時間の間には対数直線関係があり,この関係式に基づき任意の水温における分裂時間が計算できた。分裂指数法と細胞数の増加から計算した増殖速度との間には高い相関関係が得られ,分裂指数法により増殖速度が測定できることが判明した。顕微鏡蛍光測光とDAPI 染色の組合せによる核DNA量の測定法を確立し,それを用いて細胞周期を調べた。その結果,本種は明瞭なDNA合成期(S期)を有し,他の真核生物と同様の細胞周期に基づいて増殖することが判明した。したがって,分裂指数法による増殖速度測定の際に,細胞周期のS期及びG2+M期も分裂指標として使用可能なことが明らかとなり,測定精度の向上及び試料採取回数の削減など実用面での改善が期待できた。 | |||||
| 言語 | ja | |||||
| bibliographic_information |
ja : 南西海区水産研究所研究報告 en : Bulletin of Nansei National Fisheries Research Instituite 巻 27, p. 251-394, ページ数 144, 発行日 1994-03 |
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| 出版者 | ||||||
| 出版者 | 南西海区水産研究所 | |||||
| 言語 | ja | |||||
| 出版者 | ||||||
| 出版者 | Nansei National Fisheries Research Instituite | |||||
| 言語 | en | |||||
| item_10002_source_id_9 | ||||||
| 収録物識別子タイプ | PISSN | |||||
| 収録物識別子 | 0388-841X | |||||
| item_10002_source_id_11 | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AN00181988 | |||||
| 情報源 | ||||||
| 識別子タイプ | Local | |||||
| 関連識別子 | nnf_k_27_251 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010501886 | |||||
| 言語 | ja | |||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||
