藤田　和彦 (フジタ　カズヒコ)

Fujita Kazuhiko

写真a

職名

教授

科研費研究者番号

00343377

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https://sites.google.com/site/reefforamslab/

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  • 併任   琉球大学   理工学研究科   物質地球科学専攻   教授  

  • 併任   琉球大学   理工学研究科   海洋環境学専攻   教授  

  • 専任   琉球大学   理学部   物質地球科学科   教授  

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  • 東北大学 -  博士（理学）  層位・古生物学

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  • 2007年04月
    -
    2012年02月

      琉球大学　理学部　物質地球科学科　海洋水圏科学講座　助教  

  • 2012年03月
    -
    2015年04月

      琉球大学　理学部　物質地球科学科　海洋水圏科学講座　准教授  

  • 2015年05月
    -
    継続中

      琉球大学　理学部　物質地球科学科　海洋水圏科学講座　教授  

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  • 海洋微古生物学

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  • 自然科学一般 / 地球生命科学

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  • 最終氷期におけるサンゴ礁島嶼環境変動

  • 気候変動下におけるサンゴ礁海岸の過去・現在・未来

  • 地球環境変動に対するサンゴ礁石灰化生物の応答

  • 第四紀熱帯海域における古環境指標の開発と検証

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  • Microscale evolution of reefal microbialites

    Sho Koyano, Fumito Shiraishi, Yosuke Yokoyama, Kazuhiko Fujita

    Coral Reefs and Sea-Level Change: Quaternary Records and Modelling ( International Association of Sedimentologists )    39 - 67   2022年12月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    Reefal microbialites are crusts and infills of microbialites developed within primary cavities of late Quaternary coralgal reef frameworks. In spite of many previous studies, factors controlling mesofabric transitions, particularly from laminated to digitate microbialites but as well as the microscale formation process in relation to microbial communities, have not yet been fully understood. Furthermore, there are still controversies regarding age differences between reef framework growth and microbialite formation. The authors have discussed the macroscale evolution of primary cavities as well as the microscale evolution of reefal microbialites obtained in a middle Holocene reef core drilled off Okinawa Island, south-west Japan, based on petrographic observations using light and scanning electron microscopy with energy dispersive X-ray spectroscopy and radiocarbon (14C) ages of corals and reefal microbialites. The authors’ petrographic observations show that coralgal reef framework growth was followed by encrusting foraminifers and metazoans, coevally with macro-bioerosion and microbioerosion of coralgal frameworks, then finally infilled with an intraskeletal and boring-filling microbialite (IBFM) and encrusted by reefal microbial crusts (RMCs), including structureless and digitate microbialites. The observed macroscale evolution was probably driven in response to progressive changes to reduced light and water circulation in the primary cavities associated with middle Holocene transgression and reef formation. The microfabric of reefal microbialites consists of primary in situ precipitated peloids (spherical micritic clots), voids (primary pores) and allochthonous detrital grains (bioclastic and siliciclastic) fallen from upper reef surfaces. IBFM geopetally infilled inside bioeroded cavities soon after the bioerosion of coralgal frameworks. RMCs have a two-layered microfabric succession, which is composed of the alternation of dense peloidal aggregates and laterally aligned voids in the lower part and the mixing of peloidal aggregates and irregularly and vertically developed voids in the upper part. The authors speculate that the repeated occurrences of laterally aligned voids in the lower part may imply the intermittent pauses of peloidal formation, while peloids accumulated on the irregular outer surfaces may result in the formation of vertically developed voids and digitate surfaces in the upper part. These peloids are probably formed by coccoid sulfate-reducing bacteria in anoxic environments developed by the degradation of bacterial biofilms and organic matters, allowing sulfate reduction and increasing alkalinity, therefore carbonate precipitation. The two-layered microfabric succession generally observed in RMCs may reflect spatial-temporal oxic/anoxic variations in interstitial water and the degree of sulfate ion supply by the gradual closing of primary cavities.

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  • Reef growth history at intermediate to mesophotic depths since the end of the Last Glacial period along the Great Barrier Reef shelf edge

    Marc Humblet, Jody M. Webster, Yusuke Yokoyama, Juan Carlos Braga, Kazuhiko Fujita, Yasufumi Iryu, Stewart J. Fallon, William G. Thompson

    Coral Reefs and Sea-Level Change: Quaternary Records and Modelling ( International Association of Sedimentologists )    189 - 214   2022年12月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    Reef communities at intermediate (10 to 30 m) and mesophotic (~ 30 to 150 m) depths occupy large areas of sea floor but little is known about their potential to accrete vertically, their response to sea-level change and other environmental perturbations. In this study, the authors have examined cores from two holes, M0040A and M0041A, drilled by the International Ocean Drilling Program Expedition 325 along the shelf edge of the modern GBR at 131 m water depth. The objective was to investigate reef growth history at palaeo-water depths > 20 m over a time period spanning 30,000 years, from the end of the Last Glacial period through the last deglaciation. Based on changes in lithologies and biotic components, and a robust chronostratigraphic framework supported by 47 radiometric ages, the authors have identified two episodes of reef growth, one during Marine Isotope Stage (MIS) 2 and the other at the onset of the deglaciation, both characterised by abundant microbialite crusts and distinct coral assemblages. Palaeo-water depths range from 30 to 60 m and from 20 to 30 m for the MIS 2 and early deglacial reef sections, respectively. The first episode of reef growth documented in the cores initiated at 27 to 25 ka, possibly in response to increased light availability and change in sedimentation resulting from falling sea-level between 32 and 29 ka from MIS 3 and also to low atmospheric pCO2 at the end of the Last Glacial period. Reef accretion was reduced or ceased sometime between 24 and 19 ka, coinciding with the rapid 20 m sea-level fall of the peak Last Glacial Maximum and minima of SSTs. Reef growth resumed at 19.5 to 18.5 ka, influenced by a period of moderate sea-level rise and increasing sea surface temperatures at the onset of the deglaciation. Reef growth termination at ca. 17 ka correlates with a major episode of reef demise previously identified in adjacent mid and outer terrace cores and linked to reduced water quality combined with rapid deglacial sea-level rise. Vertical accretion (VA) rates were calculated based on two methods: linear visual fitting and Bayesian modelling. The findings show that the highest VA rates are associated with microbialite boundstone. Reef ecosystems dominated by microbialite and corals developed at intermediate and mesophotic depths, and grew vertically at maximum rates of 2 to 5 mm yr-1 depending on the method used, over a period of rapid environmental change during the transition from MIS 3 to MIS 1. Further study needs to explore the potential of modern-type deep coralgal communities to cope with higher rates of sea-level rise predicted this century.

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  • Trophic niche separation of two non-spinose planktonic foraminifers Neogloboquadrina dutertrei and Pulleniatina obliquiloculata

    Toue R.

    Progress in Earth and Planetary Science ( Progress in Earth and Planetary Science )  9 ( 1 )   2022年12月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    Abstract Based on laboratory observations, planktonic foraminifers are omnivorous, feeding zooplankton and phytoplankton. Spinose species tend toward greater dependence on zooplankton prey than on phytoplankton prey, while non-spinose species are more adapted to herbivorous diets. However, the trophic activity of planktonic foraminifers in the natural environment and their trophic positions in the marine food web have not yet been fully understood. The trophic position (TP) of two non-spinose species, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, was determined by differences in the nitrogen isotopic composition between two amino acids (glutamic acid and phenylalanine). Results show that TP values of N. dutertrei were ~ 2.4, indicating dependence on omnivorous (mixed herbivorous and carnivorous) diets, while those of P. obliquiloculata were ~ 2.1, indicating dependence on herbivorous diets. Together with previous laboratory observations, these TP values suggest that N. dutertrei is a detritivore or scavenger, while P. obliquiloculata is generally a herbivore. This trophic niche separation likely allows these two planktonic foraminiferal species to live within a similar depth zone in the open water column and provides a clue for understanding causes of spatial and temporal changes in their relative abundances in living and sediment assemblages.

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  • Light is an Important Limiting Factor for the Vertical Distribution of the Largest Extant Benthic Foraminifer Cycloclypeus carpenteri

    Fujita K.

    Journal of Earth Science ( Journal of Earth Science )  33 ( 6 ) 1460 - 1468   2022年09月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

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  • The coral reef-dwelling Peneroplis spp. shows calcification recovery to ocean acidification conditions.

    Charrieau LM, Nagai Y, Kimoto K, Dissard D, Below B, Fujita K, Toyofuku T

    Scientific reports ( Scientific Reports )  12 ( 1 ) 6373   2022年04月 [ 査読有り ]

    掲載種別: 研究論文（学術雑誌）

    　概要を見る

    Abstract Large Benthic Foraminifera are a crucial component of coral-reef ecosystems, which are currently threatened by ocean acidification. We conducted culture experiments to evaluate the impact of low pH on survival and test dissolution of the symbiont-bearing species Peneroplis spp., and to observe potential calcification recovery when specimens are placed back under reference pH value (7.9). We found that Peneroplis spp. displayed living activity up to 3 days at pH 6.9 (Ω<sub>cal</sub> &lt; 1) or up to 1 month at pH 7.4 (Ω<sub>cal</sub> &gt; 1), despite the dark and unfed conditions. Dissolution features were observed under low Ω<sub>cal</sub> values, such as changes in test density, peeled extrados layers, and decalcified tests with exposed organic linings. A new calcification phase started when specimens were placed back at reference pH. This calcification’s resumption was an addition of new chambers without reparation of the dissolved parts, which is consistent with the porcelaneous calcification pathway of Peneroplis spp. The most decalcified specimens displayed a strong survival response by adding up to 8 new chambers, and the contribution of food supply in this process was highlighted. These results suggest that porcelaneous LBF species have some recovery abilities to short exposure (e.g., 3 days to 1 month) to acidified conditions. However, the geochemical signature of trace elements in the new calcite was impacted, and the majority of the new chambers were distorted and resulted in abnormal tests, which might hinder the specimens’ reproduction and thus their survival on the long term.

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      PubMed

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  • バイオミネラルがつくる島と海岸

    藤田和彦, 本郷宙軌 ( 担当: 共著 )

    ボーダーインク  2015年

  • 星砂から地球環境問題を考える

    藤田和彦 ( 担当: 単著 )

    沖縄タイムス社  2013年

  • Proceedings of the Integrated Ocean Drilling Program (IODP)

    Webster J.M., Yokoyama Y., Cotterill C., the Expedition 325 Scientists (Fujita K.) ( 担当: 共著 )

    Integrated Ocean Drilling Program Management International, Inc., Tokyo  2011年08月

  • 古生物学事典第2版

    古生物学会（藤田和彦） ( 担当: 共著 )

    朝倉書店  2010年06月

  • Proceedings of the Integrated Ocean Drilling Program, Volume 310 Expedition Reports, Tahiti Sea Level

    Camoin G. F., Iryu Y., McInroy D. B. and the IODP Expedition 310 Scientists (Fujita K.) ( 担当: 共著 )

    IODP Management International, Inc., Washington, DC  2007年04月

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学術関係受賞 【 表示 ／ 非表示 】

  • 日本古生物学会　学術賞

    2020年06月26日   日本古生物学会   大型有孔虫の生態学的・古環境学的研究  

    受賞者: 藤田和彦

  • 日本サンゴ礁学会　川口奨励賞

    2010年12月04日   日本サンゴ礁学会  

    受賞者: その他の受賞者

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  • 「海面上昇に対するツバル国の生態工学的維持」中の「海岸工学的なツバル海岸の浸食・堆積過程の解明」

    研究費種類: 財団・社団法人等の民間助成金  参画方法: その他

    研究種別: 受託研究  事業名: -

    研究期間: 2009年04月  -  2013年03月 

    代表者: 藤田　和彦  資金配分機関: 独立行政法人科学技術振興機構 理事長　北澤　宏一

    直接経費: 6,500,000（円）  間接経費: 1,950,000（円）  金額合計: 8,450,000（円）

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