記述言語：日本語   出版者・発行元：Regional Studies in Marine Science  

Inflow from the Kuroshio Current into coastal areas stimulates biological production. However, to date there are no detailed reports on its temporal changes. In the target area of this study, Kagoshima Bay, Japan, the time of inflow of the Kuroshio branch current can be identified a posteriori based on water temperature data. This study aimed to determine the relationship between the Kuroshio branch current inflow from the surface layer and phytoplankton bloom at the mouth of the bay during the mixing season. Therefore, we compiled data from ship observations in the Kagoshima Bay from 2016 to 2019 to examine changes in water quality (temperature, salinity, and nutrients), microphytoplankton, and microzooplankton versus time since current inflow. In this study, significant relationships were obtained for microplankton in terms of both biomass and cell abundance, and specific growth rates (0.060–0.079 d–1) comparable to that of chlorophyll a. In addition, the current inflow provided nutrients to the surface in the absence of strong wind and waves. Over time, phytoplankton, mostly athecate dinoflagellates, as well as microzooplankton, mainly naked ciliates, proliferated and were quickly preyed upon by mesozooplankton. Over the study period, such events could be observed once every two weeks in most years, suggesting that these frequent phytoplankton blooms support the high biomass of mesozooplankton and larval fish found in this area.

DOI： 10.1016/j.rsma.2024.103576

Scopus

記述言語：日本語   出版者・発行元：社団法人 環境科学会  

<p>温室効果ガスであるCO₂排出量を減らす取り組みが世界各国で行われている。しかしこれらの取り組みで，CO₂排出量は減少するが，これまで大量に空気中へ排出されてきたCO₂の絶対量は低下せず，大気中CO₂濃度も低下しない。すなわち空気中のCO₂を除去しなければ，今後現在以上の地球温暖化の進行を招く。そのためネガティブエミッション技術（大気中のCO₂を回収・吸収し，貯留または固定化等を組み合わせることにより，正味としてマイナスのCO₂排出量を達成する技術）の利用が必要である。本研究の目的は光合成能力が高くCO₂を固定量が多いと考えられるケナフ（<i>Hibiscus cannabinus</i> L.）を栽培し，深海に貯蔵することによりケナフによるネガティブエミッション技術の可能性を明らかにすることである。CO₂回収・吸収の評価として2020年および2022年に供試品種にはEverglades 41を用い，2020年は株間が15 cmと30 cm, 2022年は株間10 cm, 20 cmで栽培し，効率的なCO₂固定のための栽植密度を明らかにした。CO₂貯留・固定化に関する実験として2018年にケナフの主茎を30 cm程度に切断し，それらを5本ずつ網袋に入れ，2019年6月に沖縄県近くの東シナ海（N27°02.634′ E125°56.632′）の水深606 mで貯留した。そして2020年9月に回収した。深海係留前の乾物重と比較して深海貯蔵による影響を調査した。その結果ケナフの茎は深海貯蔵前後で乾物重に差は見られなかった。また走査電子顕微鏡観察で，生物による食害の形跡は観察されなかったことから，生物による食害・分解は行われていないものと考えられた。以上のことから，ケナフによるCO₂の深海貯蔵の可能性が明らかとなった。</p>

DOI： 10.11353/sesj.37.131

記述言語：日本語   出版者・発行元：Science of the Total Environment  

Polystyrene foam is widely used due to its lightweight, impact resistance, and excellent thermal insulation properties. Meanwhile, weak adhesion between beads in polystyrene foam leads to fragmentation, generating a substantial amount of microplastics (<5 mm). Such polystyrene foam debris littered on beaches diminishes the aesthetic value of coastal areas, negatively impacting tourism. Due to its density lower than other plastics, polystyrene foam macroplastics float on the sea surface and, thus, they are significantly influenced by wind drag during oceanic transport. In contrast, polystyrene foam microplastics drifting beneath the sea surface are carried mostly by ocean currents. These properties of polystyrene foam macroplastics and microplastics hinder the elucidation of their transport, distribution, and fate in nature, despite their potential to adversely impact marine ecosystems. To elucidate the generation, transport, and fragmentation processes of polystyrene foam ocean plastics, we conducted concurrent visual observations and surface net towing from seven training vessels around Japan during 2014–2020. Overall, the abundances of polystyrene foam ocean plastics were higher in the Sea of Japan than in the North Pacific south of Japan. The average abundances of polystyrene foam microplastics and macroplastics were 0.33 pieces/m3 and 0.45 pieces/km, respectively, over the entire sea area around Japan. In the Sea of Japan, the peak abundances of polystyrene foam macroplastics occurred in upstream of the Tsushima Current, while the peak for microplastics occurred downstream, suggesting that continuous fragmentation occurred during transport between the two peaks. Backward-in-time particle tracking model experiments suggested that the sources of polystyrene foam macroplastics observed in the Sea of Japan included aquaculture buoys and styrene debris beached around the Tsushima Strait. The present study demonstrated that reducing the release of polystyrene foam aquaculture floats will likely diminish the abundance of ocean plastics in the Sea of Japan.

DOI： 10.1016/j.scitotenv.2024.171421

Scopus

PubMed

記述言語：英語   出版者・発行元：日本プランクトン学会、日本ベントス学会  

The northern Satsunan area, comprising the mouth of Kagoshima Bay and Osumi Strait, is an important spawning and nursery ground for Japanese jack mackerel Trachurus japonicus in Japan. Upwellings frequently occur at the mouth of the bay during winter and spring, and the consequent nutrient supply promotes phytoplankton blooms. This study examined how T. japonicus utilizes upwelling (Kagoshima Bay) and non-upwelling areas (Osumi Strait) as larval nursery grounds. Densities and growth rates (measured as the average width of the last three otolith increments) of T. japonicus larvae in both areas were compared to determine the upwelling influence on nursery ground formation. The mouth of the bay had lower temperature and salinity but higher chlorophyll-a concentrations and prey density than that of the strait. Densities of larvae were consistently higher in the bay than in the strait, indicating that the main nursery of T. japonicus is formed in Kagoshima Bay. No significant differences were observed in the growth rates of larvae among areas, suggesting that lower temperatures and prey availability are growth limiting factors in the mouth of the bay and the strait, respectively, and the Osumi Strait could also provide a favorable nursery area.

DOI： 10.3800/pbr.18.148

Scopus

記述言語：日本語   出版者・発行元：Journal of Marine Systems  

Seasonal variations in hydrographic conditions, nutrients, and microplankton abundance and biomass were investigated inside and outside Kagoshima Bay in the northern Satsunan area. The area is a nursery ground for the migrating fish. During the mixing season from November to April, highly saline water (>34.5) originating from a branch of the Kuroshio Current, the western boundary current of the North Pacific Subtropical Gyre, intruded from the surface layer into the bay causing extrusion of coastal bottom water. This intrusion generated vertical mixing between surface water and nutrient-rich bottom water. Consequently, chlorophyll a concentrations increased (>1 μg l−1) around the bay mouth. During the stratified season from May to August, the coastal surface water was extruded due to intrusion of saline water from the bottom layer. High chlorophyll a concentrations (>1 μg l−1) were also observed in the surface layer in July during the rainy season. Such differences in hydrographic conditions between mixing and stratified seasons were due to vertical distribution of highly saline water from outside the bay, which seasonally migrated between surface and subsurface layers. Relatively distinct redundancy analysis plots and boxplots generated from a generalized linear model showed that microplankton community structure differed between mixing and stratified seasons. The mixing and stratified seasons were characterized by high diatom abundance and low microplankton abundance, respectively, suggesting that vertical mixing increases nutrient supply and consequently increases diatom abundance. Thus, microzooplankton (mainly naked ciliates and athecate dinoflagellates) abundance was related to the abundance of prey organisms, such as diatoms, thecate dinoflagellates and cryptophyte-like flagellates, rather than hydrographic conditions. Thus, saline water intrusion from a branch of the Kuroshio Current likely governs hydrographic conditions in Kagoshima Bay and consequently affects temporal variations in abundance and taxonomic composition of phytoplankton and microzooplankton communities.

DOI： 10.1016/j.jmarsys.2022.103767

Scopus

記述言語：日本語

DOI： 10.1002/9781119428428.ch14

Scopus

開催年月日： 2017年3月

記述言語：日本語   会議種別：ポスター発表  

開催年月日： 2013年3月

記述言語：日本語  

開催地：東京  

国内学会

開催年月日： 2004年4月

記述言語：日本語  

開催地：鹿児島  

国内学会