DSpace Collection: 2016-12-27
http://hdl.handle.net/2115/64169
2016-12-272024-03-29T07:13:12ZIron requirements of Heterosigma akashiwo(Raphidophyceae), Heterocapsa circularisquama(Dinophyceae) and two common centric diatoms
http://hdl.handle.net/2115/64176
Title: Iron requirements of Heterosigma akashiwo(Raphidophyceae), Heterocapsa circularisquama(Dinophyceae) and two common centric diatoms
Authors: Fukuzaki, Koji; Yoshioka, Takahito; Sawayama, Shigeki; Imai, Ichiro
Abstract: Iron is increasingly recognized to play a key role in the growth of microalgae in various marine systems, but there is a paucity of knowledge about the physiological iron requirements of harmful algal species. This study aimed to elucidate the halfsaturation constant for growth(Ks) and the maximum growth rate(μmax) of four phytoplankton species with regard to iron concentrations. The four species were the fish-killing raphidophyte Heterosigma akashiwo, the bivalve-killing dinoflagellate Heterocapsa circularisquama, and the centric diatoms Ditylum brightwellii(large sized) and Chaetoceros didymus(small sized). We conducted incubation experiments with axenic cultures of the four species using a chemically defined synthetic medium. Compared with Heterocapsa circularisquama(0.59 day-1) and Heterosigma akashiwo(0.50 day-1), the two diatom species exhibited high μmax values(0.68 day-1). The smaller diatom had the lowest Ks value of 7.5×10-9M, while the larger diatom had the highest Ks value of 2.1×10-7M. The Ks values of Heterosigma akashiwo and Heterocapsa circularisquama were 5.1×10-8 and 3.1×10-8M, respectively. Smaller-sized phytoplankton showed better affinity to lower concentrations of iron in the sea.2016-12-26T15:00:00ZFukuzaki, KojiYoshioka, TakahitoSawayama, ShigekiImai, IchiroIron is increasingly recognized to play a key role in the growth of microalgae in various marine systems, but there is a paucity of knowledge about the physiological iron requirements of harmful algal species. This study aimed to elucidate the halfsaturation constant for growth(Ks) and the maximum growth rate(μmax) of four phytoplankton species with regard to iron concentrations. The four species were the fish-killing raphidophyte Heterosigma akashiwo, the bivalve-killing dinoflagellate Heterocapsa circularisquama, and the centric diatoms Ditylum brightwellii(large sized) and Chaetoceros didymus(small sized). We conducted incubation experiments with axenic cultures of the four species using a chemically defined synthetic medium. Compared with Heterocapsa circularisquama(0.59 day-1) and Heterosigma akashiwo(0.50 day-1), the two diatom species exhibited high μmax values(0.68 day-1). The smaller diatom had the lowest Ks value of 7.5×10-9M, while the larger diatom had the highest Ks value of 2.1×10-7M. The Ks values of Heterosigma akashiwo and Heterocapsa circularisquama were 5.1×10-8 and 3.1×10-8M, respectively. Smaller-sized phytoplankton showed better affinity to lower concentrations of iron in the sea.Trailing the Effectiveness of a Modified Trawl Net in the Northern Java Sea, Indonesia
http://hdl.handle.net/2115/64175
Title: Trailing the Effectiveness of a Modified Trawl Net in the Northern Java Sea, Indonesia
Authors: Pramitasari, Sulistyani Dyah; Okamoto, Junichiro; Yoshimura, Mika; Kimura, Nobuo
Abstract: Overfishing has occurred in several regions around Indonesia, including the Northern Java Sea, primarily due to the large number of artisanal fishers and fishing boats, and the use of "un-environmentally friendly fishing gear", such as trawl nets. Consequently, Presidential Decree No.39 was enacted on July 1, 1980, which prohibited trawl operations in Indonesia to reduce fishing and social conflicts, and to protect resources. Fishers have responded to this government regulation by modifying their gear to elude its enforcement. However, these modifications are oriented more economic than conservation benefits. To rectify this issue, an environmentally-frendly trawl net that enables resource conservation needs to be developed and authorized. Therefore, in this study, a modified trawl net that included a flapper, selector, and square mesh was trialed and compared with a conventional trawl net following the experimental design. It was found that the modified trawl net has the potential to contribute to fishery resource preservation with no associated economic loss to fishers.2016-12-26T15:00:00ZPramitasari, Sulistyani DyahOkamoto, JunichiroYoshimura, MikaKimura, NobuoOverfishing has occurred in several regions around Indonesia, including the Northern Java Sea, primarily due to the large number of artisanal fishers and fishing boats, and the use of "un-environmentally friendly fishing gear", such as trawl nets. Consequently, Presidential Decree No.39 was enacted on July 1, 1980, which prohibited trawl operations in Indonesia to reduce fishing and social conflicts, and to protect resources. Fishers have responded to this government regulation by modifying their gear to elude its enforcement. However, these modifications are oriented more economic than conservation benefits. To rectify this issue, an environmentally-frendly trawl net that enables resource conservation needs to be developed and authorized. Therefore, in this study, a modified trawl net that included a flapper, selector, and square mesh was trialed and compared with a conventional trawl net following the experimental design. It was found that the modified trawl net has the potential to contribute to fishery resource preservation with no associated economic loss to fishers.宗谷暖流域における反時計回り非線形渦流列の励起機構
http://hdl.handle.net/2115/64174
Title: 宗谷暖流域における反時計回り非線形渦流列の励起機構
Authors: 伊田, 智喜; 有田, 駿; 磯田, 豊
Abstract: The generation mechanism of anti-clockwise nonlinear eddy street along the Soya Warm Current is examined using the inflow-forced numerical model incorporating the simple shelf-slope topography. According to the conservation of potential vorticity, a strong positive vorticity is produced off the inflow entrance by vortex stretching as the water column is pushed out to deeper offshore. It rapidly grows up an isolated anti-clockwise circular eddy, i.e., a nonlinear eddy, during advection time traveling round the eddy. Therefore, this advection time controls the oscillated period, and each isolated eddy is periodically generated and stably advected downstream by the mean shear-flow. Such flow system accompanied by the eddy street is interpreted as the self-excited oscillation.2016-12-26T15:00:00Z伊田, 智喜有田, 駿磯田, 豊The generation mechanism of anti-clockwise nonlinear eddy street along the Soya Warm Current is examined using the inflow-forced numerical model incorporating the simple shelf-slope topography. According to the conservation of potential vorticity, a strong positive vorticity is produced off the inflow entrance by vortex stretching as the water column is pushed out to deeper offshore. It rapidly grows up an isolated anti-clockwise circular eddy, i.e., a nonlinear eddy, during advection time traveling round the eddy. Therefore, this advection time controls the oscillated period, and each isolated eddy is periodically generated and stably advected downstream by the mean shear-flow. Such flow system accompanied by the eddy street is interpreted as the self-excited oscillation.北太平洋風成循環流の季節変化に関する数値モデル実験
http://hdl.handle.net/2115/64173
Title: 北太平洋風成循環流の季節変化に関する数値モデル実験
Authors: 舘野, 愛実; 藤原, 将平; 磯田, 豊; 朝日, 啓二郎
Abstract: A two-layer model ocean with Izu-Ogasawara Ridge(IOR) and the Emperor Seamounts(ESs), driven by seasonally varying wind stress, is used to explain the observed seasonal variations of barotropic and baroclinic response in the North Pacific. Since isostasy is achieved for annual mean state, the annually averaged subarctic and subtropical surface gyres are separated without any bathymetric influence. For a short time scale such as seasonal variation, the barotropic flow is inhibited from ascending the bottom slope because of the restriction of the potential vorticity conservation, and generates the baroclinic Annual Rossby Waves(ARW) through the impinging process on the shelf slope. The most conspicuous feature in barotropic response is the southward invasion of the subarctic anti-clockwise circulation strengthened in winter into the subtropical region along the IOR and the western shelf slope. It is also found that the westward propagating baroclinic ARW from the southern ESs is appeared to be enhanced in spring by superimposing on the seasonal change of Ekman pumping. These model results are consistent with those estimatied from the observation.2016-12-26T15:00:00Z舘野, 愛実藤原, 将平磯田, 豊朝日, 啓二郎A two-layer model ocean with Izu-Ogasawara Ridge(IOR) and the Emperor Seamounts(ESs), driven by seasonally varying wind stress, is used to explain the observed seasonal variations of barotropic and baroclinic response in the North Pacific. Since isostasy is achieved for annual mean state, the annually averaged subarctic and subtropical surface gyres are separated without any bathymetric influence. For a short time scale such as seasonal variation, the barotropic flow is inhibited from ascending the bottom slope because of the restriction of the potential vorticity conservation, and generates the baroclinic Annual Rossby Waves(ARW) through the impinging process on the shelf slope. The most conspicuous feature in barotropic response is the southward invasion of the subarctic anti-clockwise circulation strengthened in winter into the subtropical region along the IOR and the western shelf slope. It is also found that the westward propagating baroclinic ARW from the southern ESs is appeared to be enhanced in spring by superimposing on the seasonal change of Ekman pumping. These model results are consistent with those estimatied from the observation.