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Far-Reaching Effects of Okhotsk Sea Ice Area on Sea Surface Heat Flux, Lower Atmosphere, and Ocean Mixed Layer
Get PDFThe impact of interannual variations in sea ice area in the Okhotsk Sea was investigated through a composite analysis of years with extensive and limited sea ice areas (referred to as heavy and light ice years, respectively), using atmospheric and oceanic reanalysis data. The comparison of heavy and light ice-year composites in February revealed a substantial decrease in upward surface turbulent heat flux in the Okhotsk Sea (∼−250 W m−2) and a notable increase in a surprisingly extensive region in the western North Pacific (30–120 W m−2), spanning 2300 km from the ice edge. These differences were consistent with the decrease in surface air temperature and specific humidity, suggesting that during heavy ice years, cold and dry air blowing from Siberia to the North Pacific via the Okhotsk Sea undergoes less modification over larger sea ice areas, remaining colder and drier in the North Pacific and thereby enhancing the heat flux. Such advection can be associated with the Asian winter monsoon and migratory cyclones. Cloud cover and surface radiation flux altered consistently with these differences, although longwave and shortwave radiation largely counterbalanced each other. Additionally, the Pacific storm track exhibited variation. In accordance with the heat flux difference, sea surface temperature decreased, and the ocean mixed layer deepened around the subarctic during heavy ice years. These findings suggest that sea ice area in the Okhotsk Sea influences the lower atmosphere and surface ocean in the North Pacific. Such impacts could further affect ocean nutrient circulation, ecosystems, and atmospheric teleconnections.journal articl
Distribution and stable isotope ratio characteristics of Japanese eel leptocephali in relation to hydrographic structure of their Pacific Ocean spawning area
Get PDFTo understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early-stage larvae were distributed south of or near the salinity front, confirming that the salinity front is an important oceanic feature to understand spawning locations of the Japanese eel. Larger size larvae tended to distribute into higher latitudes. Transport to northern latitudes with their growth would facilitate transport into the Kuroshio region, but retention in the Subtropical Countercurrent (STCC) might be detrimental. Preleptocephalus isotope ratios reflected maternal ratios, but feeding-stage leptocephali (8–56 mm) tended to have higher ∂15N values at lower latitudes typically in areas south of a salinity front. Feeding larvae quickly assimilate isotope ratios from the NEC after spawning and early growth. Large differences of ∂13C values of larvae between the NEC and STCC might vary with spatial baselines in the two currents. However, diel vertical migrations should be considered, because the isotope ratios in particulate organic matter distinctly depend on the depth. Comparisons among Japanese eel larvae and other taxa of leptocephali in the NEC illustrate the need for further studies on the trophic ecology of leptocephali.journal articl
New azaspiracid analogues detected as bi-charged ions in Azadinium poporum (Amphidomataceae, Dinophyceae) isolated from Japanese coastal waters
Get PDFLipophilic marine biotoxin azaspiracids (AZAs) are produced by dinoflagellates Azadinium and Amphidoma. Recently, several strains of Azadinium poporum were isolated from Japanese coastal waters, and detailed toxin profiles of two strains (mdd421 and HM536) among them were clarified by several detection techniques on liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-quadrupole time of flight mass spectrometry (LC-QTOFMS). In our present study, AZA analogues in seven strains of A. poporum from Japanese coastal waters (including two previously reported strains) were determined by these detection techniques. The dominant AZA in the seven strains was AZA2 accompanied by small amounts of several known AZAs and twelve new AZA analogues. Eight of the twelve new AZA analogues discovered in our present study were detected as bi-charged ions on the positive mode LC/MS/MS. This is the first report describing AZA analogues detected as bi-charged ions with hexose and sulfate groups in their structures.journal articl
Re-evaluation of nuclear mitochondrial pseudogenes (NUMTs) and heteroplasmy in the Japanese spiny lobster Panulirus japonicus
Get PDFThe Japanese spiny lobster Panulirus japonicus has been reported to harbor a numbers of nuclear mitochondrial pseudogenes (NUMTs) and heteroplasmy. However, distinguishing phylogenetically young NUMTs, heteroplasmy, and PCR-cloning artefacts may be challenging. In addition, greater degradation for mtDNA than nuclear DNA in elderly tissue specimens may promote amplification of NUMTs. In this study, we performed clone library-based nucleotide sequence analysis of the partial mtDNA COI gene using genomic DNA and cDNA obtained from fresh tissues of the Japanese spiny lobster and genomic DNA obtained from three crustacean and three fish species. Minor nucleotide substitutions between clones in an individual were ubiquitously observed in all species examined including the lobster cDNA, suggesting that most of these were artefacts. Rarely, a few clones were most likely to have originated from heteroplasmic copies, as they had skewed nucleotide substitutions at the third codon. The Japanese spiny lobster is more likely than others to detect NUMTs, while the detection of NUMTs may be somewhat suppressed using genomic DNA obtained from fresh tissue.journal articl
Species Identification Model of the Tiger Pufferfish Genus using eXplainable Artificial Intelligence(XAI) Based Convolutional Neural Network
Get PDFThe Tiger Pufferfish (Takifugu rubripes) is a staple in Japanese cuisine, with over ten species of the Takifugu genus found in the surrounding seas. Given that certain parts of the pufferfish are toxic, they are predominantly prepared by trained professionals. Furthermore, species within the Takifugu genus are susceptible to hybridization, leading to an increase in hybrid numbers. However, identifying these hybrids is a challenging and time-consuming task, even for experts. To address this, we developed a transfer learning model using the pretrained VGG16 model to differentiate between pufferfish species. The VGG16 model, commonly used in image recognition, is built on convolutional neural networks. We also implemented Gradient-weighted Class Activation Mapping (Grad-CAM) for visual interpretation of the model. Grad-CAM generates a heat map that highlights the areas focused on by the AI model in the image, allowing us to identify factors contributing to misjudgment and make further improvements. We used seven species from the Takifugu genus (excluding hybrids), and approximately 15 colored images of each species were prepared for machine learning. The results showed that our model was able to distinguish between pufferfish species with relatively high accuracy, although some misclassification occurred among species with imilar body patterns. The Grad-CAM results revealed that the model was able to distinguish body patterns, but some misclassifications occurred due to gravel and background objects being recognized as patterns.編集：水産大学校departmental bulletin pape
潜堤付き防波堤の波浪制御機能に関する研究
Get PDF防波堤本体工の前面の少し離れた場所に潜堤を設置する“潜堤付き防波堤”は，気候変動に対する既存防波堤の改良工法として，また，藻場造成等の環境機能を併せ持つ構造形式として有効と考えられるが，波浪制御機能について十分な知見がないのが実態である．本研究では潜堤付き防波堤を対象に，構造条件や波条件ごとの越波流量，反射率，伝達率を明らかにすることを目的とする．機能検証は水理模型実験と数値計算により行い，複数の構造条件に対して設計条件である波諸元から波浪制御機能を推定するための知見を整理した．また，潜堤付き防波堤の越波流量は波高が比較的小さい場合は“消波工付き護岸”と同等程度であるが，波高が増大すると“直立護岸”と同等程度となることを明らかにした．journal articl
Okeaniazole A: Thiazole-containing cyclopeptide from the marine cyanobacterium Okeania hirsuta with antileishmanial activity
Get PDFA macrocyclic peptide, okeaniazole A (1), was isolated from the Okinawan marine cyanobacterium, Okeania hirsuta. The planar structure was elucidated by the analyses of MS and NMR spectra. The absolute configuration of the amino acid residues was determined by a combination of ozonolysis, hydrolysis, and Marfey’s analysis. Okeaniazole A (1) and a related cyclic heptapeptide dolastatin 3 (2) exhibited antileishmanial activity, with IC50 values of 12.1 and 12.5 µM, respectively. These two compounds did not show any cytotoxicity toward L1210 mouse leukemia cells at concentrations of 100 µM.journal articl
Development of advanced maturation and spawning technology for the dissemination of artificial seedlings of bluefin tuna （Thunnus orientalis）
No full text太平洋クロマグロの資源量が緊迫する中で、完全養殖技術によって生産された人工種苗の普及・実用化が強く望まれている。しかしながら、人工種苗は同時期に採捕される天然種苗と比較して体サイズが小さく、海面生簀での育成中の生残率、特に越冬期の生残率が低いことなどから、天然種苗から人工種苗への転換が進んでいない。このため、養殖クロマグロの従来の産卵時期よりも早い時期に採卵し、天然種苗と同等の大きさの人工種苗を生産する新たな技術の開発に取り組んだ。本稿では、まず過去に開発した大型陸上水槽を用いた陸上施設での成熟・産卵技術について紹介するとともに、そこで開発した成果を基に取り組んだ早期熟成・産卵誘導技術の開発について紹介する。journal articl
持続可能性に優れた高効率な養魚飼料の開発に向けた取り組み
Get PDF養殖用配合飼料には原料として多くの魚粉が使用されており、その供給量不足と価格高騰を背景に低魚粉飼料の使用が求められている。一方、配合飼料中の魚粉を大幅に減らして代替原料を使用すると魚体内に生理異常を生じ、成長が遅れてしまう。養殖重要種であるブリとマダイを用いて魚粉代替飼料原料の消化吸収特性を評価し、代替生理への影響を詳細に解析している。消化吸収と生理状態の改善に基づく飼料原料の配合調整によって、成長効率の良い魚粉代替飼料の開発が期待される。journal articl
