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Recent Ostracoda from the Northeastern part of Osaka Bay, Southwestern Japan

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Ostracodes from Osaka Bay, southwestern Japan, were quantitatively studied in order to examine the relationships between environmental factors and species distribution. At least 109 species belonging to 43 genera were identified from 31 surface sediment samples. On the basis of Q-mode cluster analysis, four biotopes (A, B, C and D) are recognized. Characteristic species of each biotope are as follows: A (central bay at 17.2-37.2 m water depth), Trachyleberis scabrocuneata, Cytheropteron miurense, Kobayashiina donghaiensis, Schizocythere kishinouyei and Krithe japonica; B (inner part of the bay at 16.3-21. 1 m water depth), Bicornucythere bisanensis (form A), Bicornucythere bisanensis (form M), Cytheromorpha acupunctata, Loxoconcha viva and Nipponocythere bicarinata; C (innermost part of the bay at 9.2-15.9 m water depth), B. bisanensis (form A), Loxoconcha tosaensis and Spinileberis quadriaculeata; D (inner part of the bay at 12.6 m water depth), C. acupunctata. These results suggest that species distribution is controlled by bathymetry. High abundance and high species diversities are found in the westernmost area. In contrast, low abundance and low species diversities are observed in the eastern area, where water masses with low dissolved oxygen content spread, especially in the summer. It is shown that the tidal current and the dissolved oxygen contents strongly influence abundance and species diversity of ostracodes in Osaka Bay.
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... 3. Yasuhara and Irizuki (2001) studied Recent ostracod assemblages from the Osaka Bay in Japan and reported males, females, and juveniles of N. bicarinata. Although the lateral view (with an exception of a slightly more arched dorsal margin), presence of the ventral keel, and the general shape of both sexes resemble this species, the lack of any ornamentation distinguishes this record from the phenotype of the type specimen of N. bicarinata. ...
... Nipponocythere bicarinata is a typical middle bay species in Japan (Irizuki et al., 2006) abundant in muddy substrates at a water depth of deeper than 10 m Yasuhara and Seto, 2006). Since its original description based on specimens collected from the Seto Inland Sea of Japan (Brady, 1880), N. bicarinata has been routinely reported in sediments from several studies of Japan's Pliocene (Iwatani and Irizuki, 2008;Tanaka and Nomura, 2009; Ozawa and Tanaka, : Brady, 1880;van den Bold, 1966van den Bold, , 1985Ishizaki, 1971Ishizaki, , 1981Ishizaki and Gunther, 1976;Ishizaki and Kato, 1976;Hanai et al., 1977;Guan et al., 1978;Hu, 1978Hu, , 1982Hu, , 1984Osario, 1978;Colalongo and Pasini, 1980;Ishizaki, 1981;Malz, 1981;Frydl, 1982;Hou et al., 1982;Gou et al., 1983;Ř íha, 1983;Ciampo, 1986;Tabuki, 1986;Bodergat and Ikeya, 1988;Paik and Lee, 1988;Ruan and Hao, 1988;Wang et al., 1988;Zhao and Wang, 1988;Liu, 1989;Yajima and Lord, 1990;Ikeya et al., 1992;Ayress and Corrège, 1993;Drapala and Ayress, 1993;Barra, 1995;Zhou, 1995;Cao, 1998;Bonaduce et al., 1994;Yamane, 1998;Lee et al., 2000;Yasuhara and Irizuki, 2001;Bodergat et al., 2002;Szczechura and Aiello, 2003;Yasuhara and Yamazaki, 2005;Irizuki et al., 2006Irizuki et al., , 2018Yasuhara and Seto, 2006;Hu and Tao, 2008;Tanaka, 2008;Ozawa, 2009;Hou and Gou, 2007;Tanaka and Nomura, 2009;Iwatani et al., 2011;Irizuki et al., 2018;Tanaka et al., 2012Tanaka et al., , 2019Hong et al., 2019;Ozawa and Tanaka, 2019. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) ...
... (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 2019), Middle to Late Pleistocene (Irizuki et al., 2009), and Holocene/ Recent (Bodergat and Ikeya, 1988;Ikeya et al., 1992;Ikeya and Cronin, 1993;Yamane, 1998;Yasuhara and Irizuki, 2001;Yasuhara and Yamazaki, 2005;Irizuki et al., 2006;Yasuhara and Seto, 2006;Tanaka et al., 2012Tanaka et al., , 2019. The species has also been reported from China Hong et al., 2019) and Korea (Lee et al., 2000), but only from the Holocene. ...
Article
For the first time, soft body parts of ostracod genera, Nipponocythere Ishizaki, 1971 from the family Loxoconchidae and Ambtonia Malz, 1982 from the family Trachyleberididae, both belonging to the superfamily Cytheroidea, are described and illustrated. The specimens are male representatives of the species Nipponocythere bicarinata (Brady, 1880) and Ambtonia obai (Ishizaki, 1971), collected from Wando Island, Korea. Their soft body morphology does not completely conform with the latest identification key to cytheroid families, which urges the need for a comprehensive revision. A revised diagnosis for the type species of both genera, Nipponocythere asamushiensis Ishizaki, 1971 and Ambtonia glabra Malz, 1982 is given. Stratigraphic ranges and ecological and paleoecological significance of families Loxoconchidae and Trachyleberididae are being discussed. Published records of N. bicarinata that provide an illustration and/or SEM have been taxonomically reviewed and a list of morphological variations is given. Spatial distribution data for both target species, N. bicarinata and A. obai, as well as their respective genera, were compiled separated by time: recent (i.e., Holocene) versus fossil (older than Holocene). With respect to the detected eco-phenotypes of N. bicarinata, a re-evaluation of its spatial distribution is given. We found that by excluding these morphological variations, its assumed spatial distribution is significantly altered, shifting its southernmost distribution margin, previously reported from the South China Sea, north to the northernmost region of the East China Sea.
... Genus Pistocythereis Gou in Gou et al., 1983 Pistocythereis bradyi ( Ishizaki, 1968 ) Modern distribution: Malacca Straits ; Java Sea ( Dewi, 1993( Dewi, , 1997( Dewi, , 2000; Malaysia (e.g., Ramlan & Noraswana 2009 ;Noraswana et al., 2017 ); Japan ( Ishizaki, 1968 ;Hanai et al., 1977 ;Irizuki et al., 2006 ;Yasuhara & Irizuki 2001 ;Yasuhara & Seto, 2006 ); South China Sea ( Guan et al., 1978 ;Ishizaki, 1981 ); Korea ( Abe & Choe, 1988 ); Hong-Kong ; Vietnam ( Niiyama et al., 2019 ); southwestern coast of Peninsular Thailand, Ao nun, Satun Province, Andaman Sea (present study). ...
... Remarks: Hong et al. (2019) showed that Pistocythereis bradyi prefers relatively high salinity ranging from middle muddy bay in Japan ( Irizuki et al., 2006 ;Yasuhara & Irizuki, 2001 ;Yasuhara & Seto, 2006 ), opens bays in Korea ( Abe & Choe, 1988 ) and Malacca Strait to deeper water on the inner continental shelf of Hong-Kong . This species is also sensitive to metal pollution . ...
Article
An inventory of 35 species of ostracods (Crustacea) recovered from sediment samples from a shallow embayment nearby the Mu Koh Phetra National Park in the southwestern coast of Peninsular Thailand, Andaman Sea is given. Most of the species are well-known from the Indo-Pacific area and some others are kept in open nomenclature or compared to already know species because because only few specimens were found. Several species may be new to science but have also to be kept in open nomenclature until new material is obtained. The very abundant specimens of this assemblage are mainly disarticulated valves. This contribution adds to our knowledge of the distribution of ostracods in the Andaman Sea and the degree of ostracod relationship between the Indonesian, Indian and West Pacific areas. ésumé Un inventaire de 35 espèces d'ostracodes (Crustacea) provenant de sédiments d'une baie peu profonde près du Parc National Mu Koh Phetra sur la côte sud-ouest de la péninsule de Thïlande, Mer d'Andaman, est donné. La plupart des espèces sont bien connues de la zone Indo-Pacifique et certaines sont conservées en nomenclature ouverte ou comparées à des espèces déjà connues en raison du faible nombre de spécimens collectés. Plusieurs espèces semblent nouvelles mais sont aussi conservées en nomenclature ouverte jusqu’à l'observation de nouveau matériel. Les très abondants spécimens qui composent cet assemblage sont principalement des valves désarticulées. Cette contribution accroit notre connaissance de la distribution des ostracodes dans la Mer d'Andaman et de la relation entre les ostracodes des zones indonésiennes, indiennes et ouest-pacifiques.
... Ostracoda distribution depends on environmental factors such as substrates, water temperature, water depth, salinity, and hydrochemical gradients (Smith, 1993;Yasuhara and Irizuki, 2001;Rumes et al., 2016). Ecologically, silty sand and sand are the most favorable substrates for Ostracod growth (Sridhar et al., 2002). ...
Chapter
Calcareous microfauna of Ostracoda and their diversity from continental slope sediments of Gulf of Mannar, highlighting the bathymetric and ecological variations, are examined in this chapter. Ostracoda are immensely useful and economically viable proxy for delineating ecological as well as bathymetric fluctuations. Two short core sediment samples MC-2 and MC-60 were collected at a water depth of 1,235 and 1,887 m from the study area, and the core-wise distribution of dominant Ostracoda species and their ecological implications were thoroughly investigated. A total of 33 species belonging to 23 genera in MC-2 sample and 10 species belonging to 8 genera in MC-60 sample were taxonomically identified and recorded. Of these, Ostracoda genera Krithe, Bradleya, and Acanthocythereis are dominantly present in the core sample MC-2, and the genus Krithe is abundantly present in the core sample MC-60. Ostracod fauna are found to accommodate themselves in the silty substrate in the Gulf. The relative rate of sedimentation in the Gulf has been detected from the carapaces and open-valve ratio of Ostracoda. Species diversity indices are used to determine the variations in the ecological and bathymetric conditions of Ostracoda obtained from core sediments in the Gulf of Mannar. Keywords: Ostracoda, Gulf of Mannar, Bathymetry, Ecology, Bay of Bengal
... For abundant species (i.e., Horn), we observed a distinct "Victoria Harbour + Eastern Buffer" biofacies (Figs. 6 and 7). These Victoria Harbour and "Victoria Harbour + Eastern Buffer" biofacies are characterized by sand dwellers (Cytheropteron miurense, Pistocythereis bradyformis, Loxoconcha epeterseni) and phytal taxa (Aurila, Neonesidea, Xestoleberis) ( Fig. 9; Table 2) (Yasuhara and Irizuki, 2001;Yasuhara et al., 2002). So, Mud or intermediate-level productivity may play a role not only in diversity as discussed above but also in faunal composition. ...
Article
Hong Kong is one of the most urbanized coastal cities in the world. Yet, despite extensive anthropogenic impacts, adjacent marine environments harbour tremendous biodiversity. We investigated how the diversity, taxonomic composition, and biogeography of meiobenthic ostracods in Hong Kong's coastal waters vary in response to natural and anthropogenic factors. Our regression models indicated that metal pollution and mud content were the main factors structuring meiofaunal diversity, with eutrophication also playing a role. The highest diversity was observed in the Victoria Harbour region at the center of Hong Kong's urbanized seascape, and the lowest diversities were observed in Mirs Bay, Port Shelter, and Tolo Harbour. Ostracod diversity and biogeography patterns are congruent with published studies of other soft-sediment fauna, which also identified a diversity peak in Hong Kong's urban center and a vast southern water biofacies characterized by muddy and turbid conditions. These results do not apply to organisms that prefer oligotrophic conditions, such as hard corals. For those taxa, eutrophic waters in western Hong Kong are generally not habitable and higher diversities are observed in less productive, eastern waters. Our findings indicate that meiofaunal ostracods can be used as a bioindicator for the diversity of soft sediment benthos, more broadly.
... Ostracods were picked from the coarse fraction. We identified ostracod taxa by referring to Ishizaki (1968), Yasuhara and Irizuki (2001), and Irizuki et al. (2008). We counted the number of valves and valve fragments of each taxon. ...
Article
Tsunami deposits in Kyushu Island, southwestern Japan, have been attributed to the 7.3 ka Kikai caldera eruption, but their origin has not been confirmed. We analyzed a 83-cm-thick Holocene event deposit in the SKM core, obtained from incised valley fill in the coastal lowlands near Sukumo Bay, southwestern Shikoku Island. We confirmed that the event deposit contains K-Ah volcanic ash from the 7.3 ka eruption. The base of the event deposit erodes the underlying inner-bay mud, and the deposit contains material from outside the local terrestrial and marine environment, including angular quartz porphyry from a small inland exposure, oyster shell debris, and a coral fragment. Benthic foraminifers and ostracods in the deposit indicate various habitats, some of which are outside Sukumo Bay. The sand matrix contains low-silica volcanic glass from the late stage of the Kikai caldera eruption. We also documented the same glass in an event deposit in the MIK1 core, from the incised Oyodo River valley in the Miyazaki Plain on southeastern Kyushu. These two 7.3 ka tsunami deposits join other documented examples that are widely distributed in southwestern Japan including the Bungo Channel and Beppu Bay in eastern Kyushu, Tachibana Bay in western Kyushu, and Zasa Pond on the Kii Peninsula as well as around the caldera itself. The tsunami deposits near the caldera have been divided into older and younger 7.3 ka tsunami deposits, the younger ones matching the set of widespread deposits. We attribute the younger 7.3 ka tsunami deposits to a large tsunami generated by a great interplate earthquake in the northern part of the Ryukyu Trench and (or) the western Nankai Trough just after the late stage of the Kikai caldera eruption and the older 7.3 ka tsunami deposits to a small tsunami generated by an interplate earthquake or Kikai caldera eruption.
... Deep-sea ostracods are distinctly different from the shelf and marginal marine taxa. In recent years, a lot of research works on taxonomy, distribution and ecology of Ostracoda have been carried out in the International marine environment including Atlantic, Pacific, Indian and Arctic Oceans (Gengo, 2016;Luz and Coimbra, 2015;Yasuhara et al., 2014;Hokuto et al., 2014;Dewi, 2014;Stepanova and Lyle, 2014;Noraswana et al., 2014;Piazza et al., 2014;Andrei and Gabriel, 2014;Yasuhara et al., 2012;Julio and Francisco, 2012;Lili et al., 2012;Theodora, 2012;Jessica et al., 2007;Mostafawi et al., 2005;Yasuhara and Irizuki, 2001). Comparatively, similar research works are few in number from the Indian sub-continental region (Mohammed et al., 2017;Hussain and Kuleen, 2016;Mohammed et al., 2015;Baskar et al., 2015;Baskar et al., 2013;Hussain et al., 2009;Gopalakrishna et al., 2007;Hussain et al., 2006;Sridhar et al., 2002;Hussain, 1998). ...
Chapter
Full-text available
Ostracoda, the calcareous microfauna and their diversity from continental slope sediments of Gulf of Mannar, highlighting the bathymetric and ecological variations, are examined in this chapter. Ostracoda are immensely useful and economically viable proxy for delineating ecological as well as bathymetric fluctuations. Two short core sediment samples MC-2 and MC-60 were collected at a water depth of 1,235 and 1,887m from the study area, and the core-wise distribution of dominant Ostracoda species and their ecological implications were thoroughly investigated. A total of 33 species belonging to 23 genera in MC-2 sample and 10 species belonging to 8 genera in MC-60 sample were taxonomically identified and recorded. Of these, Ostracoda genera Krithe, Bradleya, and Acanthocythereis are dominantly present in the core sample MC-2, and the genus Krithe is abundantly present in the core sample MC-60. Ostracod fauna are found to accommodate themselves in the silty substrate in the Gulf. The relative rate of sedimentation in the Gulf has been detected from the carapaces and open-valve ratio of Ostracod. Species diversity indices are used to determine the variations in the ecological and bathymetric conditions of Ostracoda from core sediments in the Gulf of Mannar.
... Mean grain size tended to be coarser, with moderate fluctuations and sorting showing large fluctuations in Interval I (Fig. 9). The C/N and C/S ratios were also higher during this time frame compared to other intervals Ikeya and Shiozaki, 1993;Yasuhara et al., 2003Yasuhara et al., , 2007Irizuki et al., 2011Irizuki et al., , 2015aIrizuki et al., , 2018aIrizuki et al., , 2018b Trachyleberis niitsumai 6.9 enclosed middle muddy bays and is widely dispersed in Japan Yasuhara and Irizuki, 2001 Aurila disparata 6.6 on rocks, silty gravel, sand, algae, and the seagrass Zostera Okubo, 1980;Schornikov and Tsareva, 1995 (Horn, 1966). T. Irizuki et al. (Figs. ...
Article
This study clarified the centennial-scale changes in meiobenthic bay ostracod assemblages in Japan over the past approximately 3000 years with relation to various human-induced and natural environmental factors. These factors were inferred via integrated multiproxy methods of high-resolution geological analyses of core sediments obtained from a shallow bay off a coastal plain, along with literature surveys of archeological and historical records. Five intervals were defined based on multivariate analyses of ostracod assemblages. The ostracod assemblage was stable before around the 6th century because of aggradational sedimentation related to gradual increases in sea level. Since then, the composite factors such as the development of a sandy spit near the study site, stable sea level, regional tectonics, regional centennial-scale climatic change possibly related to El Niño Southern Oscillation (ENSO), and flood mitigation by human settlement in the coastal plains triggered the formation of tidal flats and subtidal sandy areas with seagrass beds. This has markedly influenced offshore bay ostracod assemblages since around the 12th century. Anthropogenic impacts, such as reclamation and various artificial constructions since the late 20th century caused the disappearance of seagrass beds, input of coarser sediment into offshore bays, and increased nutrient loads. Therefore, ostracod assemblages have changed drastically. Ostracod assemblages near the boundary between land and sea have been affected by multiple complex factors, such as regional climate and depositional and human-induced processes during the Late Holocene.
... Other sources of uncertainties for this approach may also arise from the fact that the modern dataset of Tanaka et al. (2009) used for the eye size-water depth calibration is small in sample size (n = 50) and geographically restricted to the northwestern Pacific. In addition, the dataset includes only species with surface ornamentation since almost all smooth ostracods do not have a clearly discernable cuticular lens preserved as part of the fossilized valve (e.g., Cytherois, Propontocypris, Neonesidea, Xestoleberis) [e.g., see, Hong et al., 2017;Yasuhara et al., 2019Yasuhara et al., , 2020Yasuhara and Irizuki, 2001] and therefore do not suit the purpose of eye size-water depth calibration. However, there are indeed some smooth or nearly smooth species that have recognizable cuticular lens [e.g., Oculobairdoppilata and some species of Brachycythere (Moore, 1961;Van Itterbeeck et al., 2007)]. ...
Article
Deep-time sea-level changes associated with the Paleocene-Eocene Thermal Maximum (PETM) are of great interest to paleoceanographers and paleontologists, especially in shallow marine settings, like the Atlantic Coastal Plain PETM sections of the Eastern North American Continental Shelf. Accurate paleo-water depth reconstruction is essential to properly interpret and contextualize any PETM-associated paleoceanographic and paleoecological changes that are depth-dependent. In addition, our understanding on eustatic sea-level changes in the greenhouse world without polar ice sheets remains limited. Despite this importance of an accurate and robust paleodepth reconstruction, all water depth estimation methods applied for the shallow marine PETM sections suffer from uncertainties and intrinsic/logical flaws. It is therefore important to develop and apply an independent water depth proxy to complement and validate paleodepth estimates derived from the traditional estimation methods based on sedimentary fossil components and lithological features. Here we present the relative eye size of sighted ostracods as a taxonomy-free water depth proxy and apply it to shallow-marine PETM paleodepth reconstruction of the Mattawoman Creek-Billingsley Road (MCBR) core in Maryland, eastern USA. We identified a significant and rapid reduction in water depth of ~40 m within the carbon isotope excursion (CIE) onset consistent with the previous estimation based on benthic foraminifer species associations. This ostracod-eye-based paleodepth reconstruction improves current understanding on the regional paleobathymetry of the Salisbury Embayment and facilitates future studies on continental shelf paleoceanography and paleoecology during the PETM, a rapid, extreme global warming event under long-term greenhouse conditions, which possibly parallels with ongoing anthropogenic warming.
Article
This study clarified the centennial-scale changes in meiobenthic bay ostracod assemblages in Japan over the past approximately 3000 years with relation to various human-induced and natural environmental factors. These factors were inferred via integrated multiproxy methods of high-resolution geological analyses of core sediments obtained from a shallow bay off a coastal plain, along with literature surveys of archeological and historical records. Five intervals were defined based on multivariate analyses of ostracod assemblages. The ostracod assemblage was stable before around the 6th century because of aggradational sedimentation related to gradual increases in sea level. Since then, the composite factors such as the development of a sandy spit near the study site, stable sea level, regional tectonics, regional centennial-scale climatic change possibly related to El Niño Southern Oscillation (ENSO), and flood mitigation by human settlement in the coastal plains triggered the formation of tidal flats and subtidal sandy areas with seagrass beds. This has markedly influenced offshore bay ostracod assemblages since around the 12th century. Anthropogenic impacts, such as reclamation and various artificial constructions since the late 20th century caused the disappearance of seagrass beds, input of coarser sediment into offshore bays, and increased nutrient loads. Therefore, ostracod assemblages have changed drastically. Ostracod assemblages near the boundary between land and sea have been affected by multiple complex factors, such as regional climate and depositional and human-induced processes during the Late Holocene.
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Full-text available
Here, the characteristics of post-LGM (Last Glacial Maximum) in-cised valley fills and their depositional sequence were examined by analyzing the SKM core collected in the Sukumo coastal lowlands, southwestern Shikoku Island, which has been subject to extensive seismic subsidence due to the large Nankai Trough earthquakes. Here we provide results of sedimentological, radiocarbon dating, and paleoenvironmental analysis. Sediments of the SKM core show clear indications that the succession was influenced by post-glacial sea level change. The Matsuda River incised valley formed during the LGM (.-ka), and was infilled by fluvial sand and gravel in the late Pleistocene. Following postglacial transgression, sea level rose by m (a.s.l.) at. ka, and the incised valley became an estuarine environment. As sea level continued to rise, the estuarine environment was replaced by an inner bay mud bottom, and maximum water depth was reached at. ka. The. ka Kikai caldera eruption in southern Kyushu Island caused heavy K-Ah ash fall in southwestern Shikoku Island, and frequent large-scale lahars occurred immediately after the ash fall because of the proximity to the volcanic source. After the ash fall, the K-Ah secondary sediments were deposited rapidly in the inner bay environment and caused rapid sea level regression. After. ka, a delta region began to develop, which might have been due to the large K-Ah ash fall. At ka, sea level reached +. m (a.s.l.), estimated from the Sukumo midden, and is recognized as the Holocene marine limit in this area. This information on relative sea level change during the past , years suggests that the Sukumo Bay area has not subsided as a result of seismic-induced crustal deformation.
Chapter
Gamagyang Bay is located on the southern border of the Korean Peninsula. It is a geo-graphically half-closed shallow embayment with a ria-type coastal topography, which provides a variety of environments for ostracod habitation. Among the ostracod species, Pistocythereis bradyi, P. bradyformis and two members of the Keijella bisanensis species group are dominant. Although all these species crawl on the muddy bottom surface in a similar way, their main distribution ranges are limited to either the inner or the outer half of the bay. Each of the four species was recognised as having two distinct morphs within the species. Each morph has its own pattern of geographical distribution which is probably controlled by environmental factors or by the origin and history of migration of the species into Gamagyang Bay. Variation in P. bradyi, P. bradyformis and K. bisanensis occurs in the features of the mural elements, the continuity of the ventral ridge and the H/L ratio of the carapace, respectively.
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