17505 research outputs found
Sort by
造礁サンゴ類ミドリイシ属における生殖隔離機構と種分化の関係に関する研究
Full text linkGene introgression has been identified as a contributing factor during the evolutionary process of the genus Acropora, a representative coral genus responsible for forming coral reefs. Approximately one-third of Acropora species participate in multi-species synchronous spawning. During this event, gametes from multiple species are mixed, creating conditions conducive to hybridization. Indeed, previous studies have demonstrated hybridization between certain species in vitro, and genomic analyses have revealed evidence of introgressive hybridization in Acropora's evolutionary history. However, reports of naturally occurring hybrids are scarce; the only documented case is A. prolifera in the Caribbean Sea. As a result, it remains unclear whether gene introgression plays a significant role in driving species diversity within Acropora.
In Chapter 2, I investigated how gamete compatibility contributes to speciation among Acropora species. Gamete compatibility is a critical factor in enabling hybridization. However, as many Acropora species spawn synchronously, and some exhibit compatible gametes, it remains unclear which species are involved in hybridization events. To address this, I focused on species that spawn three months after the multispecies synchronous spawning period. Using two morphotypes of A. divaricata (Fig. 1), I examined whether these morphotypes represent distinct species or merely morphological variations. Despite finding gamete compatibility between the two morphotypes, I observed that differences in spawning timing act as a reproductive isolation mechanism.
In Chapter 3, I focused on tabular-forming Acropora, which previous studies identified as having the highest hybridization rates, making them strong candidates for investigating the relationship between introgression and speciation. I did morphological analyses, crossing experiments, and genome analyses with single nucleotide polymorphisms (SNPs) to examine the relationship between gamete compatibility and introgression. The morphological analyses and crossing experiments show four tabular species are distinct. In addition, SNP analyses support these species boundaries. However, I found that examined tabular Acropora possesses well-established gamete recognition mechanisms that prevent hybridization. Furthermore, several gamete-composing proteins encoding genes were on the genetically divergent loci with high Fst values. Moreover, the codon evolution of these CDs is supported across Acropora, implying that adaptive evolution might have been accompanied by species differentiation. These results suggests that speciation may result from these mutations rather than introgression.
In Chapter 4, I explored how closely related species with differing distributions have diverged. A. aff. hyacinthus has long been regarded as a species complex due to challenges in morphological identification. I employed integrative species identification methods to identify species within the A. hyacinthus complex to address this. My findings suggest that mutations in genes related to environmental stress response likely act as drivers of speciation within this group.博士（学術）琉球大学University of the Ryukyu
重症大動脈弁狭窄症の日本人患者における経カテーテル大動脈弁置換術後の上腕一足首脈波伝播速度の変化と死亡率との関連：単一施設後ろ向きコホート研究
Full text linkTranscatheter aortic valve replacement (TAVR) offers a solution, especially for high-risk aortic stenosis (AS) patients. However, patient outcomes post-TAVR show variability, highlighting the need for reliable prognostic indicators. Brachial–ankle pulse wave velocity (baPWV), a measure of arterial stiffness, may predict outcomes post-TAVR. This study aims to explore baPWV’s prognostic value in relation to all-cause mortality post-TAVR. This study prospectively enrolled 212 severe AS patients undergoing TAVR between September 2015 and December 2021, focusing on pre- and post-TAVR baPWV measurements to explore associations with all-cause mortality. Of the 212 patients (119 females, 93 males, mean age 85 years), post-TAVR baPWV increased significantly from 1589 ± 376 to 2010 ± 521 cm/s (p < 0.001). Aortic valve (AV) peak velocity and mean pressure gradient decreased, while AV area increased, indicating procedural success. Despite this, 88% of patients experienced an increase in baPWV, with higher pre-procedure AV peak velocity and mean pressure gradient identified as predictors of increased baPWV post-TAVR. Over 23 months, 29 patients (14%) reached the primary endpoint of all-cause mortality. Notably, changes in baPWV, rather than baseline values, were significantly associated with event-free survival (HR: 0.64 per 1SD increase, p = 0.009). The study highlights the prognostic value of baPWV changes post-TAVR in predicting patient outcomes. Elevated baPWV post- TAVR may reflect a beneficial adaptation to altered hemodynamics, suggesting the need for individualized patient evaluation and the integration of baPWV measurements into clinical practice for improved post-TAVR management.博士（医学）琉球大学University of the Ryukyu
再生可能エネルギー統合と電力網安定化のための知的エネルギーシステム
No full textThe transition toward intelligent energy systems is crucial for achieving grid stability and seamless renewable energy integration in modern power networks The research addresses key challenges faced by Pakistan's energy ecosystem and proposes advanced technical solutions to improve system resilience, efficiency, and sustainability. Firstly, a novel method combining Modified Ensemble Empirical Mode Decomposition(MEEMD) and the Prony approach is introduced to improve the identification of low-frequency oscillations in power systems. By suppressing modal mixing and improving noise resistance, this method enhances the accuracy of oscillation parameter extraction, contributing to grid stability. This research further explores a hybrid microgrid model designed for Islamabad, integrating photovoltaic (PV) panels, wind turbines, hydrogen fuel cells (FCs), and battery energy storage systems (BESS). An advanced Energy Management System (EMS) is developed and optimized using metaheuristic algorithms-Moth Flame Optimization (MFO), Reptile Search Algorithm (RSA), and Transient Search (TS) algorithm. The TS algorithm outperforms others in convergence and accuracy, resulting in a 13.2% reduction in operational costs over a 25-year period fo:1; the most cost-effective system configuration Further, the research introduces a Home Energy Management System (HEMS) tailored for Pakistan's residential sector, integrating PV panels, wind turbines, Battery Energy Storage Systems (BESS), Hydrogen Storage Systems (HSS), and Vehicle·to·Home (V2H) technology. Through dynamic demand response (DR) strategies and Time·of—Use (TOD) pricing, the HEMS significantly lowers household energy costs, achieving up to 2.91% savings under advanced DR scenarios. The system also validates the superior performance of the TS optimization algorithm over RSA and MFO in resource allocation and operational efficiency. Finally, the study presents an intelligent deep learning-based visual recognition system for automated solar panel maintenance. Leveraging EANN and CNN architectures within the Halcon framework, the system accurately classifies soiling on PV panels with over 99.9% accuracy, facilitating efficient solar cleaning robotics. This enhances panel performance by minimizing unnecessary cleaning cycles and optimizing energy yield.
Overall, this research presented integrated solutions across power systems, microgrids, home energy management, and renewable maintenance automation, contributing to sustainable, cost-effective, and intelligent energy systems that strengthen grid reliability and enable large·scale renewable energy deployment.博士（工学）琉球大学University of the Ryukyu
琉球列島におけるトカゲモドキ属（ヤモリ下⽬：トカゲモドキ科）の保全⽣物学的研究
No full textThe sixth mass extinction induced by human activities causes a global biodiversity crisis. Island ecosystems often harbor many unique endemic species evolved in isolated environments and they are particularly vulnerable to the drastic environmental changes. The Ryukyu Archipelago, stretching between Kyushu, Japan and Taiwan, is a biodiversity hotspot with high endemism, yet many species are endangered, making it crucial for conservation efforts. Ground geckos of the genus Goniurosaurus, which have been found in 12 islands of the Central Ryukyus, are facing human-induced threats such as habitat loss, invasive predators, and illegal collection for the pet trades. Their taxonomy, genetic diversity, and ecological characteristics were not well understood, hindering effective conservation strategies. The aim of this dissertation is to fill the knowledge gaps through comprehensive genetic, morphological, and ecological studies of the Ryukyu Goniurosaurus geckos for conservation of them as well as utilization of the conservation measures for the geckos to other effective area-based conservation measures (OECMs). The series of studies attempt to clarify species boundaries, assess genetic diversity within and among populations, investigate life history traits, and examine habitat requirements to discuss effective conservation measures and prioritize efforts. Chapter 1 revealed significant genetic structure within G. k. kuroiwae, a subspecies distributed in Okinawajima and four nearby islands, identifying two distinct parapatric lineages. Chapter 2 confirmed this differentiation through genome-wide population genetic analyses and morphological examinations, leading to the description of a new species, G. nebulozonatus, from northern Okinawajima and Kourijima. This taxonomic revision, which elevated all subspecies to species status, resulted in the recognition of seven extant and one extinct Goniurosaurus species in the Central Ryukyus. Chapter 3 assessed genetic diversity across populations, finding lower heterozygosity in small, isolated island populations, indicating higher vulnerability to future environmental changes. Chapter 4 investigated age structure and longevity of G. kuroiwae, providing crucial information for population viability assessments. Chapter 5 reported oviposition sites in limestone caves, highlighting the importance of preserving such microhabitats. Chapter 6 examined the diet of G. kuroiwae and G. nebulozonatus, revealing that they relied on large invertebrates associated with humid forest environments. Based on these studies, a hierarchical approach to identifying conservation units for the Ryukyu Goniurosaurus geckos was proposed, considering different species, island populations, and within-island local populations. For fragmented habitats, the research emphasized the importance of preserving macro- and micro-geological structures, particularly limestone formations, and maintaining closed forest environments to support prey populations. The integration of genetic, morphological, and ecological data suggested the geckos' potential as indicator species for OECMs in the Central Ryukyus. Future research should focus on documenting population status across all the Ryukyu Goniurosaurus species, identifying primary threats, especially in small islands or highly-fragmented habitat patches, and comparing ecological parameters between species. These insights are not only important as information for conservation strategies corresponding to each Goniurosaurus species but also potentially beneficial for the conservation of other sympatric small animals, including reptiles and amphibians. This is expected to contribute significantly to biodiversity conservation in the Ryukyu Archipelago with its unique fauna.⼈類の活動によって引き起こされた第6の⼤量絶滅は地球規模の⽣物多様性の危機をもたらしている。島嶼の⽣態系は特に脆弱で、孤⽴した環境で特異な進化を遂げた固有種を多く擁している。⽇本の九州と台湾の間に広がる琉球列島は、⾼い固有性を持つ⼀⽅でその多くが絶滅の危機に瀕している⽣物多様性のホットスポットであり、⽣物多様性の保全上、きわめて重要な地域である。トカゲモドキ属（Goniurosaurus）は中琉球の12の島々に分布し、⽣息地の喪失や分断、違法なペット取引などの脅威に直⾯している。これらトカゲモドキ類の分類、遺伝的多様性、⽣態的特性については解明が⼗分に進んでおらず、効果的な保全戦略の⽴案が困難である。本研究の⽬的は、中琉球のトカゲモドキ属ヤモリ類の遺伝学的、形態学的、⽣態学的研究を統合し、このような知⾒のギャップを解消し、本種群の保全に貢献すること、そして、本種群の保全策を効果的な地域ベースの保全対策（other effective area-based conservation measures; OECMs）の推進に活⽤することである。このことを⽬指し、本研究では種の境界を明確にし、個体群内および個体群間の遺伝的多様性を評価し、⽣活史特性を調査し、⽣息に必要な環境条件を特定することにより、効果的な保全⽅法に関する議論を⾏い、保全上の優先順位を検討した。第1章では、沖縄島と周辺4離島に分布する亜種クロイワトカゲモドキG. k. kuroiwae内に顕著な遺伝的構造があることを明らかにし、側所的に分布する2つの系統を⾒出した。第2章では、ゲノムワイドなデータに基づく集団遺伝学的解析と形態学的分析により系統間の分化を再確認し、沖縄島北部および古宇利島から新種ヤンバルトカゲモドキG. nebulozonatusを記載した。この分類学的再検討に付随して、すべての亜種を種に繰り上げた結果、中琉球のトカゲモドキ類には7現⽣種と1絶滅種が認識されることとなった。第3章では、個体群間の遺伝的多様性を評価し、⼩⾯積かつ他の島から孤⽴した島の個体群ではヘテロ接合度が低く、将来の環境変化に対する脆弱性が⾼い可能性を⽰した。第4章では、クロイワトカゲモドキの齢構成と寿命を調査し、個体群の存続可能性評価に不可⽋な情報を提供した。第5章では、⽯灰岩洞⽳内の産卵例を報告し、このようなミクロな地理スケールでの地質学的構造の保存の重要性を⽰した。第6章では、クロイワトカゲモドキとヤンバルトカゲモドキの⾷性を調べ、湿潤な森林環境に⽣息する⼤型無脊椎動物に依存していることを明らかにした。⼀連の研究に基づいて、異なる種、島嶼個体群、島内の局所個体群を考慮した、中琉球のトカゲモドキ属の保全単位を特定するための階層的なアプローチを提案した。とくに、分断された⽣息地については、マクロおよびミクロの地質構造、なかでも⽯灰岩地形の保存と、餌⽣物の個体群を⽀える閉鎖的な森林環境の維持の重要性を議論した。遺伝的、形態学的、⽣態学的データの統合により、これらのヤモリ類が中琉球におけるOECMを進める際の指標となる可能性が⽰唆された。今後の研究では中琉球のトカゲモドキ属全種の個体群状況の記録、とくに⼩島嶼や⾼度に断⽚化した⽣息地パッチにおける主要な脅威の特定、種間の⽣態学的パラメータの⽐較に焦点を当てるべきだと考えられる。これらはトカゲモドキ類のそれぞれの種に対応する保全戦略の情報として重要であるだけでなく、同所的に⽣息する他の爬⾍両⽣類を含む⼩型動物の保全にも潜在的に利益をもたらす可能性がある。これにより、特有の⽣物相を擁する琉球列島における⽣物多様性保全に⼤きく貢献することが期待される。博士（理学）琉球大学University of the Ryukyu
沖縄の中有光層における自然撹乱下でのサンゴ群集および加入動態
Full text linkMesophotic coral communities (~30-150 m depths) are known for their unique biodiversity and refuge/reseeding roles in aid of shallow reef recovery. Disturbances are discovered at the mesophotic zone, yet many mesophotic communities are largely neglected. This dissertation aimed to know how Okinawan mesophotic coral communities respond to disturbances. It was addressed by (1) describing their vertical distribution, (2) assessing their condition under natural disturbances, and (3) examining their recruitment dynamics. For distribution, photo-quadrats were collected at 30-80 m depths among 15 sites in Okinawa. For disturbances, a coral community at 40 m depth in Shigeo reef (Motobu) was monitored by an autonomous underwater vehicle in 2017 (local bleaching event) and 2018 (three days after a typhoon). Photo-quadrats were also collected in this mesophotic site to survey coral-sponge interactions in 2022. For recruitment, tiles were deployed for 6, 15, and 26 months at 10, 20, and 40 m depths in clear water (Shigeo reef) and turbid locations (Yabu). The data showed that Zone 1 (30-49 m depths) was characterized by Acropora and Montipora/Porites whereas the deeper zones (50-80 m depths) by Leptoseris. Shigeo reef at Zone 1 had the highest coral cover (mean: 48.6%), but some deeper sites had similar or higher coral cover than many sites at Zone 1. In 2017, coral bleaching was minor (8.3% of coral cover) at 40 m depth in Shigeo reef likely due to lack of significant thermal stress. In 2018, the relative abundances of coral taxa plus growth forms were maintained in this mesophotic site. However, some coral branches were overturned and scattered, and there was a slight increase in sediment cover likely due to typhoon. In 2022, coral-killing sponge Chalinula nematifera and Terpios hoshinota had low prevalences (highest mean cover per transect at 3.8% and 1.8%, respectively) and overgrew abundant branching corals in this mesophotic site. In terms of recovery, recruit densities on mesophotic tiles were initially lower but became two-times higher at 26 months than their shallow counterparts. Based on size structure, both mesophotic and shallow tiles showed an accumulation of small and large recruits over time. However, mesophotic tiles only had small recruits at 6 months compared to large recruits on shallow tiles possibly due to later settlement or slower growth of mesophotic recruits. Comparing recruit input and survival, recruitment at 40 m depth might be influenced by larval input and/or settlement processes in Yabu and by post-settlement processes in Shigeo reef. The recruit composition at 40 m depth was also Alveopora-rich in Yabu, but it shifted from Acropora at 6 months to pocilloporids at longer deployments in Shigeo reef. Although temporal variability in recruitment might be at play, this succession could indicate that recovery solely by larval recruitment may not lead to a pre-disturbed community composition. Overall, these findings show that the coral community at 40 m depth in Shigeo reef was minimally impacted by natural disturbances at present-level, thus, could be a potential refuge. However, mesophotic coral communities in clear water and turbid sites showed differential recovery capacity and they could be vulnerable to shorter recovery window caused by frequent disturbances. Understanding how mesophotic coral communities currently respond to disturbances is crucial to promote their evidence-based management and improve foresight of their persistence in an increasingly disturbed ocean.博士（学術）琉球大学University of the Ryukyu
レーダーチャートを用いた寛骨臼形成不全症に対する寛骨臼回転骨切り術前後の寛骨臼被覆の可視化
Full text linkBackground: Curved periacetabular osteotomy (CPO) is indicated for patients with developmental dysplasia of hip (DDH) to prevent progressive osteoarthritis. Patients with DDH have not only lateral acetabulum dysplasia but also anterior and posterior dysplasia. The full circumference acetabular coverage angle (ACA) of the femoral head should be evaluated preoperatively. This study aimed to determine the full circumference ACA in the patients with DDH before and after CPO compared with the coverage in normal patients.
Methods: Twenty-three patients (a total of 24 hips) with DDH undergoing CPO between February 2006 and March 2014 were included in this study. The normal group was defined as the normal side in patients with unilateral osteonecrosis of the femoral head (ONFH) and the non-collapsed femoral head side in patients with bilateral ONFH. Pre- and postoperative hip functions were evaluated using the Japanese Orthopedic Association (JOA) hip score. ACA was measured using pre- and postoperative threedimensional computed tomography (3DCT) and described as a clock using a radar chart. The ACA of the normal group was evaluated in the same manner as that for patients who underwent CPO. The ACA before CPO was compared with the ACA after CPO, the ACA before CPO was compared with that of the normal group and the ACA after CPO was compared with that of the normal group at each location.
Results: The mean JOA hip scores improved significantly from 69 preoperatively to 88 postoperatively. The superior, posterior, and anterior ACA after CPO significantly increased and the inferior ACA decreased compared with ACA before CPO. The superior, posterior, and anterior ACA before CPO were significantly smaller than ACA in the normal group. The ACA after CPO were similar to the normal group.
Conclusions: CPO improved the anterosuperior coverage of the femoral head but reduced its inferior coverage. The radar chart could visualize acetabulum full circumference and was useful for threedimensional pre-postoperative evaluation.博士（医学）琉球大学University of the Ryukyu
腐食した鋼桁端部のせん断耐力評価および補修に関する研究
No full textSteel girders are vulnerable to corrosion due to prolonged exposure to deicing agents, humidity, and inadequate ventilation, particularly at girder ends. These regions are crucial for resisting shear forces, and corrosion can significantly reduce shear strength and load-carrying capacity.
This study investigates the impact of corrosion-induced web thinning on shear strength through a numerical approach, considering several levels of corrosion damage· and the damage height. Eigenvalue analysis evaluates buckling modes and shear buckling coefficients, showing that as corrosion progresses between the web. and. lower flange, boundary conditions change, leadin to a gradual decline in buckling strength. Increasing corrosion height further accelerates reductions in both buckling and post-buckling strength.
To assess more severe corrosion, a model was developed for web panels with through-thickness cracks between the web and lower flange, accounting for boundary continuity loss and its effect on shear resistance. Numerical and experimental results indicate that when corrosion affects more than half of the web's length, shear strength deteriorates significantly due to shifts in buckling modes and tension field action. Advanced corrosion patterns, such as web detachment from the lower flange, further reduce post-buckling strength by altering the tension field and plastic hinge locations. Furthermore, a study on real bridge conditions with even heavier corrosion damage reveals severe shear strength decline when both the web and lower flange sustain damage. Corrosion spreading transversely across the flange, combined with web panel deterioration, leads to web-flange disconnection, causing local yielding and a sudden reduction in post-buckling shear strength.
After evaluating corrosion-induced shear strength loss, this study explores CFRP as a strengthening solution with cost-effectiveness as a main parameter. CFRP's high tensile strength and lightweight properties enhance shear buckling strength, with no notable difference between full and partial.coverage for web panels without severe localized damage. The study further identifies optimal CFRP fiber orientation for restoring post-buckling shear strength.
While CFRP has been applied to repair damaged girders, this study extends the analysis to severe corrosion cases involving web detachment and lower flange damage. Results demonstrate that CFRP reinforcement effectively mitigates shear strength loss, even in extreme cases, by restoring structural capacity and preventing excessive shear deterioration when strategically applied.
Overall, this study provides insights into corrosion-induced shear strength deterioration in steel girder ends, evaluating the limitations of the average web thickness approach and severe corrosion effects. Findings highlight the progressive decline in shear strength and web detachment effects while demonstrating CFRP's effectiveness in restoring shear resistance.博士（工学）琉球大学University of the Ryukyu
Detection of PC steel strand Fracture in Full-scale Pre-tensioned Girders Subjected to Salt Damage
No full text約73万橋ある道路橋の中小橋の約46％はプレストレストコンクリート橋（以降，PC)であり，約74％ある橋長15m未満の橋梁の約半数は，PCプレテンション桁橋（以降，プレテン桁）と想定される．このうち，維持管理費や人材確保に課題のある地方自治体の道路橋が約66％を占める．このような状況下で，劣化橋梁の維持管理を適切に判断するには，劣化進行の予測に伴う残存耐力の評価は重要である．残存耐力の評価には，コンクリート内部のPC鋼材の腐食破断や断面欠損などを把握できる診断技術が必要である．供用年数の累積に伴う劣化進行を踏まえると，PC銅材の腐食状態と近接目視の状態との関連性を評価できる診断技術は必要になると考えられる．それを基に非破壊調査により，塩害腐食によるPC鋼材の破断状態を精度よく検知できれば，維持管理費を抑えつつ，残存耐力の評価精度が高まると考えられる．
本研究では，塩害劣化した実大プレテン桁における錆汁が付随した腐食ひび割れ幅とPC鋼より線の腐食損傷状態との関連性と，非破壊調査の1つである近年開発改良中の3軸磁気センサを使用した磁気計測機器による漏洩磁束法（以降，3軸磁気法）を適用してPC鋼より線の腐食状態とその位置の検知性能の検証を目的に，調査研究を行った．
塩害劣化した実大プレテン桁の診断技術の構築を目的に，約40年経過した塩害劣化した2本よりPC鋼材を使用した実大プレテンI桁を対象に，桁下面の腐食ひび割れの目視・打音調査，コンクリートを撤去してPC鋼より線の腐食損傷状態を観察し，錆汁が付随した腐食ひび割れの状態とPC鋼より線の腐食損傷状態を対比検証した．最後に，塩害劣化した7本よりPC鋼材を使用した実大プレテン桁の桁下面において，錆汁が付随した腐食ひび割れとコンクリート撤去調査によるPC鋼より線の腐食損傷状況を対比分析した．これらから，腐食ひび割れ幅とPC鋼より線の腐食破断にはおおよそ関連性があり，腐食ひび割れに付随する錆汁位置にはPC鋼より線の腐食破断があると推測できることを示した．
塩害劣化した実大プレテン桁に3軸磁気法を適用するため，PC鋼より線の腐食破断の検知性能を検証することを目的に，3軸磁気法の検知性能を検証した．初めに，PC鋼より線破断箇所とスターラップの検知原理を整理し，塩害劣化した2本よりPC鋼材の実大プレテンI桁において，磁気調査後にコンクリートを撤去し，PC鋼より線の腐食損傷状況を観察して調査結果を対比分析し，素線1本破断以上は検知できること，スターラップ近傍では破断検知が難しいことを示した．次に，適用範囲を7本よりPC鋼材に拡張するため，7本よりPC鋼材の素線破断試験体とスターラップを用いたPC桁模擬試験体の基本実験で，PC鋼より線の素線破断はスターラップ間では素線1本破断以上，スターラップ近傍では素線2本破断以上が検知できること，素線破断本数を推定できるように近似式を示した．最後に，実際に塩害劣化した7本よりPC鋼材の実大プレテンI桁で，磁気調査結果から素線破断本数を推定した後，かぶりコンクリートを撒去してPC鋼より線の損傷状況を観察して調査結果を対比分析し，素線l~2本範囲の精度で，7本よりPC鋼材の素線破断が検知できることを示した．博士（工学）琉球大学University of the Ryukyu
沖縄海洋⽣態系における海洋ゴミとマイクロプラスチック
Full text linkMarine litter pollution has become a threat to marine ecosystems around the world. Usually dominated by plastic materials, the consequences of the presence of marine litter in marine ecosystems include transport and transfer of alien species, smoldering and trapping of marine organisms, ingestion by marine organisms, and release of chemical contaminants into marine ecosystems. The islands of the Ryukyu Archipelago currently lack updated and substantial data on distribution of both macro- and micro-marine litter in marine ecosystems. This thesis examined the abundances and distributions of marine litter and microplastics in Okinawa marine ecosystems. First, I assessed the status of marine litter and microplastic research in Japan’s marine ecosystems, providing a summary of marine litter and microplastic research trends in Japan. This was followed by assessing distribution of marine litter on 30 beaches around Okinawa Island to provide data on abundance, sources, types and characteristics of marine litter on the beaches of the island. Marine litter assessment was also extended to urban coral reefs in Okinawa Island, comparing abundance, distribution and litter typology on urban coral reefs with those on more remote locations in Aka Island. At the micro-level, the abundance and distribution of microplastics on beaches around remote islands of Iriomote, Aka and semi-remote Kouri and Sesoko islands were also evaluated to provide data on microplastics abundance, and characteristics such as shapes, colours and dimensions. As well, the historical trends of microplastic pollution were examined with a review of microplastic ingestion by specimens collected from natural history museums around the world to evaluate microplastic pollution trends in marine ecosystems pre- and during the Plasticene as museum specimens are preserved with records of time and place of collection and rarely influenced by bioturbation and extreme natural events such as earthquakes and tsunamis. This thesis also provided the first record of marine plastic variants in the East China Sea; plastic materials in marine ecosystems that have changed form and sometimes, permeate geological records after prolonged interactions with organic and inorganic materials and long-term exposure to increased temperatures or by burning. Data on types and characteristics of plastic variants on 36 beaches around Okinawa, Ishigaki and Taketomi islands were collected, and we described plasticoral, a new plastic variant as plastic material adhered to or melted onto coral rubble. The results of this thesis show that marine litter, specifically microplastics and plastic litter variants, are more abundant in remote locations of the Ryukyus, except on coral reefs where marine litter levels recorded on urban reefs were significantly higher than those in remote locations. This thesis provides the first extensive survey of marine litter and plastic litter variants on beaches around Okinawa, while also conducting the first surveys of marine litter in Okinawa urban coral reefs, as well as microplastic occurrence data on beaches of remote islands in the Ryukyus. The results will support public policy interventions on marine litter pollution, aid mitigation efforts, and provide baseline data for subsequent studies in the Ryukyu Archipelago. Recommendations to guide future studies include extension of surveys to other remote and less populated islands, long-term monitoring rather than standing stock surveys, assessment of freshwater contributions to marine litter and research collaboration with neighbouring countries.博士（学術）琉球大学University of the Ryukyu