著者

池脇 義弘 牧野 賢治 西岡 智哉 平野 匠 上田 幸男

出版者

公益社団法人 日本水産学会

雑誌

日本水産学会誌 (ISSN:00215392)

巻号頁・発行日

vol.82, no.6, pp.917-922, 2016 (Released:2016-11-22)

参考文献数

23

被引用文献数

2 1

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瀬戸内海をはじめ各地の藻類養殖漁場で不足しているDINを補うための新しいタイプの施肥剤(硝酸アンモニウム溶液をゼラチンで固めたのもの)を開発した。ケースに入れない2タイプと穴の開いたケースに充填したもの2タイプを作製し,実験水槽内への溶出量を硝酸塩センサーで測定した。その結果,肥料成分60-70%の溶出に,ケースに入れないタイプはおよそ5日,ケース入りのタイプはおよそ20日を要した。このことから,施肥剤を入れるケースの穴の径と数を変えることにより肥料成分の溶出速度を調整できることが示唆された。

著者

西岡 智哉 池脇 義弘 秋山 諭 山本 圭吾 田中 咲絵 宮原 一隆 原田 和弘 山下 泰司 濱﨑 正明 長谷川 尋士 本田 恵二

出版者

日本プランクトン学会

雑誌

日本プランクトン学会報 (ISSN:03878961)

巻号頁・発行日

vol.65, no.2, pp.36-43, 2018-08-25 (Released:2018-10-26)

参考文献数

19

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A widespread bloom of the harmful raphidophyte Chattonella ovata Y. Hara & Chihara occurred for the first time in the east Seto Inland Sea in the summer of 2016. From July 11 to 17, cell densities in Hiuchi-Nada and Bisan-Seto reached 10 cells mL-1. From July 19 to 24, the highly dense distribution area expanded to Harima-Nada, and cell densities reached their peak (max. 222 cells mL-1) in all areas affected from July 25 to 31. In Harima-Nada, the species decreased rapidly, whereas the level at Hiuchi-Nada and Bisan-Seto was maintained until August. From July 11 to 18, a westerly wind had prevailed in the Takamatsu area facing Bisan-Seto while the wind was weak during other periods. That caused eastward wind-induced passage flow, and expansion of the cell distribution from Bisan-Seto to Harima-Nada. In addition, the sunlight hours were long (average 8.6 h) and the water temperature was high (approximately 25 to 29˚C).Furthermore, salinity remained at around optimum for C. ovata (approximately 28 to 31) in the east Seto Inland Sea while the species bloomed. This indicates that these environmental conditions were suitable for growth of this species, which is adapted to strong irradiance, high water temperature and high salinity. In Bisan-Seto and Hiuchi-Nada, Chattonella marina and Chattonella antiqua appeared at high cell densities in mid-July when the distribution of C. ovata expanded. However, in Harima-Nada, C. marina and C. antiqua maintained low cell densities consistently. In Harima-Nada, DIN (dissolved inorganic nitrogen) and DIP (dissolved inorganic phosphorus) remained at 0.51–1.17 µM and 0.08–0.25 µM, respectively, from July 4 to August 15. The minimum cell quotas of nitrogen for C. ovata are lower than for C. antiqua. We presumed this gave a competitive advantage to C. ovata for growth. In Harima-Nada, cell density of diatoms decreased temporarily in late-July, but the density remained above 100 cells mL-1 after August. However, in Hiuchi-Nada and Bisan-Seto, cell densities of diatoms were kept below 100 cells mL-1 through the observation period. We inferred that a low concentration of nutrients, less westerly wind, and a high density of diatoms were factors that led to the regulation of the low level of C. ovata after August in Harima-Nada. We considered that the low diatom density was one of the causes of the C. ovata bloom being prolonged in Hiuchi-Nada and Bisan-Seto.