著者

Yusuke Kondo Shoma Okada Susumu Ohtsuka Takeshi Hirabayashi Aya Adachi Makoto Urata Sho Toshino Hiroshi Miyake Nanako O. Ogawa Naohiko Ohkouchi

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.13, no.2, pp.66-74, 2018-05-30 (Released:2018-05-24)

参考文献数

50

被引用文献数

1 1

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In this study, we investigated the trophic interactions between the Japanese giant box jellyfish, Morbakka virulenta, and fish in the central part of the Seto Inland Sea, western Japan, in autumn and winter. Occurring in the surface waters at nighttime, these cubomedusae, regardless of their size (1.5 to 22.5 cm in bell height), were found to be piscivorous, feeding mainly on the Japanese anchovy, as shown by their stomach contents analysis. This finding was supported by a stable isotopic analysis and by an unchanged cnidome, irrespective of the bell height of medusae. Their nocturnal occurrence near the surface often took place around the slack tide, during which the medusae were foraging with tentacles fully extended. Other associations between the medusae and fish were also observed at this time: presumed commensalism with juvenile Japanese horse mackerel, and predation by black scraper.

著者

Ikuhiko Kin Naoto Jimi Susumu Ohtsuka Gaku Mizuno Toru Nakamura Yoichi Maekawa Yuichi Oba

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.17, no.2, pp.214-220, 2022-05-30 (Released:2022-05-31)

参考文献数

37

被引用文献数

1

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The polychaete genus Tomopteris is an important component of the zooplankton and is also known for its communication using bioluminescence. However, there have been few studies about the species diversity and ecology of Tomopteris because of taxonomic and handling difficulties resulting from the fragility of their bodies. In this study, we performed DNA barcoding and species delimitation analysis to better understand the species diversity of Tomopteris using 17 specimens collected on a research cruise conducted off the eastern Kii Peninsula, Japan. Due to damage to the detailed morphological characteristics necessary for identifications based on the current taxonomy, none of the specimens was morphologically identifiable at the species level. The analyses of the mitochondrial cytochrome c oxidase subunit I (COI) and nuclear large ribosomal subunit (28S) RNA gene sequences revealed 7–8 molecularly delimited species among them, which was greater than the number of species currently recognized in Japan. These results suggest that the traditional morphology-based taxonomy overlooks the taxonomic complexity of Tomopteris, thus a combinatory analysis of both morphology and DNA barcoding will be desirable for assessing the true species biodiversity of Tomopteris.

著者

Hayato Tanaka Susumu Ohtsuka

出版者

The Japanese Society of Systematic Zoology

雑誌

Species Diversity (ISSN:13421670)

巻号頁・発行日

vol.24, no.2, pp.217-228, 2019-10-25 (Released:2019-10-25)

参考文献数

35

被引用文献数

1

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In the present study, we describe two new marine species, Microloxoconcha toyoshioae n. sp. and M. sublittoralis n. sp., collected from the sandy bottom in the western part of Japan, from the depths of approximately 20 to 30 m and 50 m, respectively. This represents the first record of this genus from such depths, since all 10 previously described species are known from the beach interstitial waters. We suspect the two new species are most probably also inhabiting spaces between sand grains since they have very small body and have been collected with other common interstitial ostracods belonging to Cobanocythere Hartmann, 1959; Parvocythere Hartmann, 1959; Paracobanocythere Gottwald, 1983; Parapolycope Klie, 1936; and Psammocythere Klie, 1936. Owing to their small body and fragile carapace, previous studies might have overlooked the existence of interstitial ostracods from habitats other than beach interstitial. In addition, a key to all species of the genus Microloxoconcha is provided.

著者

Susumu Ohtsuka Kazuhiko Koike Dhugal Lindsay Jun Nishikawa Hiroshi Miyake Masato Kawahara Nova Mujiono Juro Hiromi Hironori Komatsu

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.4, no.1, pp.1-13, 2009-02-25 (Released:2009-04-20)

参考文献数

91

被引用文献数

45 53

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Since marine medusae and ctenophores harbor a wide variety of symbionts, from protists to fish, they constitute a unique community in pelagic ecosystems. Their symbiotic relationships broadly range from simple, facultative phoresy through parasitisim to complex mutualism, although it is sometimes difficult to define these associations strictly. Phoresy and/or commensalism are found in symbionts such as pycnogonids, decapod larvae and fish juveniles. Parasitism and/or parasitoidism are common in the following symbionts: dinoflagellates, ciliates, anthozoan larvae, pedunculate barnacles, anuropid isopods, and hyperiid amphipods. Mutualism is established between ctenophores and gymnamoebae, and between rhizostome medusae and endosymbiotic dinoflagellates. More information on symbiotic apostome ciliates, anthozoan larvae and hyperiid amphipods is definitely needed for further studies in consideration of their high prevalence and serious damage they can inflict on their hosts. The present paper briefly reviews previously published data on symbionts on these gelatinous predators and introduces new information in the form of our unpublished data.

著者

Akane Iida Kenji Nohara Fatimah Md. Yusoff Khwanruan Srinui Tran Manh Ha Susumu Ohtsuka Ephrime B. Metillo Honorio B. Pagliawan Jun Nishikawa

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.16, no.4, pp.308-317, 2021-11-17 (Released:2021-11-18)

参考文献数

63

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The rhizostome jellyfishes, Rhopilema hispidum and Lobonemoides robustus, are two of the most abundant and commercially important species in Southeast Asia. However, information on genetic diversity and continuities among local populations remains totally unknown. We explored the genetic structure and population continuities of R. hispidum and L. robustus using genetic markers (COI & ITS1 regions) at 11 locations in four countries in Southeast Asia where fisheries were conducted. Rhopilema populations showed genetic distances (ΦST) among locations correlated positively with geographic distances, suggesting that they are in the isolation-by-distance (IBD). In Lobonemoides, molecular analysis revealed three distinct clades corresponding to sampling locations. Genetic distances among locations in L. robustus suggested that all populations maintain significant isolation. Our study reveals that these two blooming species have different phylogeographic patterns and differ in genetic diversity and continuities. Eustatic sea level changes during the Pleistocene and present ocean current systems, as well as differences in biological characteristics of these two species may explain these phylogeographic differences. Our results also suggest that jellyfish fisheries need to be carefully managed to avoid extinction of local populations and maintain the genetic diversity of these species, especially for L. robustus, which exhibits considerable genetic diversity in each location.

著者

大塚 攻 西田 周平 Susumu Ohtsuka Shuhei Nishida 広島大学生物生産学部附属水産実験所 東京大学海洋研究所 Fisheries Laboratory Hiroshima University Ocean Research Institute University of Tokyo

出版者

日本海洋学会

雑誌

海の研究 = Umi no Kenkyu (Oceanography in Japan) (ISSN:21863105)

巻号頁・発行日

vol.6, no.5, pp.299-320, 1997-10-05

参考文献数

151

被引用文献数

9

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The feeding ecology of marine pelagic copepods has been intensively studied since the 1910's. Recently, many new techniques, such as high-speed cinematography, deep-sea ROV, and SCUBA, have been introduced for direct observatios of their feeding behavior. These have clearly revealed that particle-feeders employ suspension feeding but not filter-feeding and that appendicularian houses are important food items for some pelagic calanoid, harpacticoid, and poecilostomatoid copepods. Particle-feeders commonly utilize microzooplankton such as ciliates and copepod nauplii and fecal pellets. Detritivory, strict selective predation, and gorging have been found exclusively in oceanic copepods. Five calanoid families Diaixidae, Parkiidae, Phaennidae, Scolecitrichidae, and Tharybidae with special sensory setae on the mouthparts and the poecilostomatoid Oncaea are considered to be adapted for feeding on detrital matter such as appendicularian houses. Some heterorhabdids probably inject a venom or anesthetic into prey animals to capture them. In the laboratory, predation on fish eggs and larvae by copepods, rejection of some dinoflagellates by calanoids, developmental inhibition of copepod eggs by feeding on some diatoms, and copepods' reactions to fecal pellets were demonstrated. Pelagic copepods constitute an assemblage of evolutionarily different groups. Among the 10 orders, calanoids supposedly first colonized the marine pelagic realm, and, at present, are most successfully adapted of any order to this environment by a wide variety of feeding mechanisms. They have developed a wide variety of feeding mechanisms. On the other hand, poecilostomatoids have secondarily become adapted to pelagic environments and are loosely associated with fish larvae and pelagic invertebrates, such as salps and appendicularians, for feeding. The calanoid family Heterorhabdidae consists of 2 particle-feeding, 3 carnivorous, and 2 intermediate genera. A phylogenetic analysis showed that the carnivores could have originated from the particle-feeders through the intermediate conditions, and that the mouthpart elements of the carnivores could be derived from those of the particle-feeders with modifications of the original elements and no addition of novel structures. Recent studies demonstrate that some copepods such as scolecitrichids and Oncaea can efficiently feed on nanoplankton trapped in appendicularian houses, and also suggest that suspension-feeders may transport diatom resting spores into the sea-bottom in the epipelagic zone and metals in the deep-sea bottoms through their feeding behavior, and that epipelagic carnivores may compete with fish larvae for copepod nauplii and dinoflagellates.

著者

B. A. Venmathi Maran Susumu Ohtsuka Xu Shang

出版者

The Japanese Society of Systematic Zoology

雑誌

Species Diversity (ISSN:13421670)

巻号頁・発行日

vol.17, no.2, pp.201-219, 2012-11-25 (Released:2018-03-30)

参考文献数

92

被引用文献数

4 7

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Adults of caligiform copepods are often found in plankton samples, in addition to the naupliar and copepodid stages. Here, we report on adult parasitic copepods of the families Caligidae and Pandaridae from plankton samples collected in Japanese and Chinese coastal waters. The following previously described species were found in 2008: Caligus calotomi Shiino, 1954; C. orientalis Gusev, 1951; C. undulatus Shen and Li, 1959; Lepeophtheirus semicossyphi Yamaguti, 1939; Metacaligus uruguayensis Thomsen, 1949, and Pandarus satyrus Dana, 1852 in Japanese waters; and C. orientalis and C. rotundigenitalis Yu, 1933 in Chinese waters. The findings of adults of Lepeophtheirus and Metacaligus in plankton samples represent the first such a record for each genus. Two new species of Caligus are also described from plankton taken in Japanese waters in 2008 and 2010. An ovigerous female collected from off Iheya Island, Ryukyu Islands, Okinawa Prefecture is described as Caligus quadrigenitalis sp. nov., and two adult females and a male collected from the Seto Inland Sea and off Hirado Island, Kyushu, western Japan is described as Caligus ogawai sp. nov.

著者

B. A. Venmathi Maran Susumu Ohtsuka

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.3, no.4, pp.202-215, 2008-11-25 (Released:2009-02-25)

参考文献数

41

被引用文献数

13 19

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Parasitic copepods usually have one or more free-swimming larval/juvenile stages for dispersal or infection. However the present study has revealed that adults and chalimus stages of caligiform copepods have often been discovered in plankton samples collected from East Asia. This is the first report on free-swimming adults of caligiform copepods from Japanese and Korean waters. Adults of the following species have been discovered in this study. In Japanese waters: Caligus coryphaenae (4♂♂), Caligus sp. (1♂), Pandarus sp. (4♂♂, 16 chalimi) off Nansei Islands in May 2003 and 2006; C. sclerotinosus (1♀) near a fish farm, Ehime Prefecture in December 2006; C. undulatus (1♀) off Ube, the Seto Inland Sea in July 2006; and C. undulatus (1♂) in the Ariake Sea in June 2007. In Korean waters: C. orientalis (1♀, 1♂) from brackish waters of the Mankyong River and C. undulatus (1♂) from the Seomjin River in October 2006. It is interesting to point out that C. undulatus has never been recorded as a parasite infecting any host, but has been collected from plankton samples in East Asia, India and Brazil. It is also noteworthy to mention that males (80%) were found more frequently than females (20%) in this study. We considered the following possibilities for the occurrences of caligiform adults originally infecting fish: (1) escaping from irritation or diseases in the host, (2) looking for an opportunity to switch hosts, (3) change in their life mode, and (4) accidental detachment. In the case of chalimi, it could be accidental, because they would be tightly attached to the host using a special organ called the “frontal filament”, and cannot grow up to the adult stage without nutrient supply from the host.