著者

SAWAMOTO SHOZO MATSUMOTO RUI

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.7, no.4, pp.203-206, 2012-11-01

被引用文献数

16

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More than 50 specimens of the megamouth shark Megachasma pelagios have been reported so far, but biological observations on the species are still limited. We examined a female megamouth specimen that was captured by the bonito purse seine fishery in the Kuroshio Extension in July 2007 and donated to the Okinawa Churaumi Aquarium. The specimen was an immature female, 3,667 mm in total length and 361 kg in weight. The stomach contents measured 2,200 mL excluding the portion that was lost from the specimen before measurement. Detailed examination of a small part (14.6 mL) of the stomach contents revealed undamaged worm-like organisms, 10 partially damaged euphausiids and abundant fragmented pieces of euphausiids. The worm-like organisms were probably parasites such as tapeworms. The partially damaged euphausiids were identified as Euphausia pacifica except for one individual of Nematoscelis difficilis. Based on the number of fragmented right mandibles, which were less damaged than the other fragmented appendages, the total number of euphausiids in the stomach contents is estimated to be at least 18,000 individuals. The high abundance of euphausiids in the stomach contents suggests that the present specimen has fed on a swarm of E. pacifica in an oceanic area.

著者

Itoh Hiroshi Nishida Shuhei

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.2, no.3, pp.134-146, 2007-08-01

参考文献数

48

被引用文献数

3 14

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A 17-month field survey and laboratory experiments were conducted to investigate the life cycle, seasonal population fluctuations, and salinity tolerance in the poecilostomatoid copepod Hemicyclops gomsoensis associated with the burrows of the mud shrimp Upogebia major and the ocypodid crab Macrophthalmus japonicus in the mud-flats of the Tama-River estuary, central Japan. On the basis of sample collections in the water column and from the burrows, it was revealed that H. gomsoensis is planktonic during the naupliar stages and settles on the bottom during the first copepodid stage to inhabit the burrows of U. major and, to a lesser extent, those of M. japonicus. While females carrying egg-sacs were present throughout the year, the copepods' reproduction took place mainly during early summer to autumn with a successive decrease from autumn to winter. Occasionally the copepod populations in the burrows suffered from severe flushes of river water that led to salinity decreases in the burrow water to fatal levels, but usually the salinity in the burrow was within optimal levels and permitted recovery and maintenance of the populations.

著者

Yusuke Yamana Hayato Tanaka

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.2, pp.83-94, 2017-05-30 (Released:2017-06-06)

参考文献数

32

被引用文献数

2

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Two new taeniogyrinid sea cucumbers collected in the intertidal zone of southern Japan, Taeniogyrus verruculosus sp. nov. and Scoliorhapis sesokoensis sp. nov. are described. Both species possess a small body size (approximately 30–40 mm), light body color (translucent white in preserved specimens), ten tentacles, and numerous verrucous surfaces on the body, within which small (mostly less than 70 µm in length) sigmoid-hook ossicles are present. The two new species have a very similar external appearance to each other, however they do differ in the number of tentacle digits: T. verruculosus possesses up to eight digits, whereas S. sesokoensis possesses up to six. In both species, wheel papillae are not present. T. verruculosus possesses only a few small (mostly less than 30 µm in diameter) wheel ossicles in the anterior dorsal skin, which are not present in S. sesokoensis. Additionally, the DNA barcode sequences of two new species were determined and are available in the DDBJ/NCBI/GenBank databases under the accession numbers.

著者

Tatsuya Ishikawa Miyuki Maegawa Akira Kurashima

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.11, no.4, pp.112-119, 2016-11-25 (Released:2016-11-23)

参考文献数

30

被引用文献数

12

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This study examines the effects of the sea urchin Diadema setosum on algal composition, coverage and biomass on barren ground. In cage experiments, the effects of D. setosum density were examined at 5 levels over the range of 0–8 ind. m−2. Algal coverage and number of species, densities and lengths of Sargassum spp. on experimental blocks in each cage were measured monthly. In the cage without D. setosum, algal coverage and biomass were higher than in cages with D. setosum. For D. setosum density of 1 ind. m−2 and higher, decreased algal coverage and decreased biomass and density of Sargassum spp. were observed. D. setosum at a density higher than 2 ind. m−2 had a negative effect on algal species numbers. Consequently, algae could grow when the D. setosum density was fewer than 2 ind. m−2. This study revealed that grazing by D. setosum has a great effect on the seaweed bed ecosystems along the coast of central Japan.

著者

Ilka Straehler-Pohl George I. Matsumoto Melisa J. Acevedo

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.2, pp.129-138, 2017-05-30 (Released:2017-06-06)

参考文献数

53

被引用文献数

9

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A lot of confusion (over the last 90 years) surrounds the naming of the Californian carybdeid population, sighted near La Jolla and Santa Barbara, since its first description by Stiasny in 1922. The specimens were first identified as Carybdea rastonii and later as Carybdea marsupialis but the identification was doubted by several scientists. To clear up the confusion, specimens of the Californian population were compared to specimens of all known carybdeid species. This comparison revealed that the Californian population represents an undescribed carybdeid species, named Carybdea confusa n. sp., being identified by the combination of the following characters: Gastric phacellae (single rooted, single stemmed), velarial canals (2 velarial canal roots/octant; canals multiple-branched with rounded tips) and pedalial canal (knee bend with thorn-like appendage).

著者

Minoru Ijichi Gyo Itani Hiroshi Ueda

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.3, pp.145-150, 2017-08-22 (Released:2017-08-24)

参考文献数

26

被引用文献数

4

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The life cycle and precopulatory mate guarding behavior of the poecilostomatoid copepod Goidelia japonica associated with the spoon worm Urechis unicinctus (Echiura) are described based on specimens from 19 worms collected from western Japan. A total of 676 copepods were collected from the host’s rectum (494 copepods) and body surface (182 copepods). Copepod numbers were significantly correlated with host weight. Copepods in the rectum consisted almost completely of copepodids (35%) and adult males (65%), with only one non-ovigerous adult female recorded. In contrast, those on the body surface were all adult males (24%) or females (76%), of which 58% were ovigerous. No nauplii or CI occurred. In the rectum, 36% of the adult males guarded 67% of the copepodids, consisting of CII–CV. From these results, their life cycle is considered as follows: nauplii and CI live as plankton; just before or after molting to CII, they enter the host’s rectum and females are probably soon guarded by males; they grow up to CV there; CV females guarded by males move to the body surface just before the final molt; on the body surface females molt to adults and spawn eggs. Guarding the first symbiotic stage (CII) is a unique precopulatory behavior for symbiotic poecilostomatoid copepods. This can be explained from the viewpoint of evolutionary resolution of the intersexual conflict and advantage for early copepodids in precopula.

著者

Saito Shinsuke

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton & benthos research (ISSN:18808247)

巻号頁・発行日

vol.4, no.4, pp.160-166, 2009-11-01

参考文献数

15

被引用文献数

2

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Density and adult ratio of the symbiotic harpacticoid copepod, Idomene purpurocincta, living in the colony of the compound ascidian host, Aplidium yamazii, were investigated on the specimens taken from a boulder shore of Tosa Bay, western Japan, to know how these ecological parameters of the symbiont were related to the host size. Field collection of the host ascidian was carried out during the low tide in every spring tide from December 2004 to August 2006. All of the copepods isolated from the hosts using menthol were enumerated according to ontogenetic stages. The ascidian host colonies appeared from January to June 2005 and from December 2005 to August 2006. The symbiotic copepod was found in all of the hosts with few exceptions even at the initial appearance of the hosts in each season. These facts suggest that the copepod entered the host immediately after the colony formation. The density of the copepod in a host was usually >103 individuals per gram of host in dry weight. An exponential negative correlation was seen between the copepod density and the host size, and the density varied less as the host size increased. The adult ratio of the copepod also greatly varied in small hosts and tended to converge to about 25% with increase of the host size, and was negatively correlated with the copepod density. The reason for these host size-related copepod density and adult ratio may be explained by recruitment of nauplii in a host and migration of adults among hosts.

著者

YAMAMORI LUNA KATO MAKOTO

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.14, no.2, pp.131-134, 2019

被引用文献数

2

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<p>The rock-boring sea urchin, <i>Echinostrephus molaris</i>, excavates soft rocks, and the pits are later used by non-boring sea urchins such as <i>Echinometra mathaei</i> and <i>Anthocidaris crassispina</i>. The pits used by these non-boring sea urchins are also characteristically inhabited by a limpet-like algivorous trochid snail, <i>Broderipia iridescens</i> (Gastropoda, Trochidae). To determine how this unique symbiotic association is maintained, we observed reproduction and larval development of the snail, and performed assays to detect what induced settlement in the snail larvae. As candidates of settlement inducers, a habitat biofilm plate, the host and the non-host sea urchins, and conspecific snails were kept in separate glass bowls, and newly hatched <i>B. iridescens</i> veliger larvae were introduced to each bowl. Sixty to 80% of larvae settled in bowls that contained the non-boring host sea urchins and conspecific snails. On the other hand, only approximately 8% of the larvae settled in bowls containing the boring non-host sea urchins. This is the first report demonstrating that larval settlement of an algivore is induced not by the habitat biofilms, but by the symbiotic hosts.</p>

著者

Noriko Yasuoka Yoichi Yusa

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.1, pp.78-81, 2017-02-28 (Released:2017-02-28)

参考文献数

27

被引用文献数

2

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Two Saccostrea oysters (S. glomerata and S. cucullata) are considered to be protandric hermaphrodites based on indirect observations. However, no other information is available on the sexual systems of Saccostrea oysters and the potential for bi-directional sex change has not previously been reported in them. Therefore, the present study was undertaken to investigate the sexual systems of S. kegaki and S. mordax in western Japan, utilizing field sampling and in situ experiments. In the field sampling, shell length (SL) and sex were determined during the reproductive season of these oysters (June–October) in 2012. Then, sex change was directly observed between 2013 and 2016 by determining the sex of individuals through gonadal biopsy, re-attaching the individuals in the field, collecting the survivors in the following year, and determining their sex by dissection. In both species, the proportion of males decreased with increasing SL, although the SL of males and females greatly overlapped. Direct observations showed that both male-to-female and female-to-male sex change occurred. Thus, our results indicated that both Saccostrea species tend to be protandric, but have the ability to change sex in both directions under natural conditions.

著者

Ken-Ichiro Ishii Ryoma Kamikawa

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.3, pp.164-170, 2017-08-22 (Released:2017-08-24)

参考文献数

42

被引用文献数

7

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The non-photosynthetic diatoms Nitzschia spp. are known to have evolved from photosynthetic species to heterotrophic species by the loss of photosynthesis. We investigated their ability to tolerate wide ranges of temperatures and salinities. Nitzschia spp. were capable of surviving or thriving even at 5°C and 35°C. In addition, these diatoms were also capable of surviving at salinities of 0.5 and 12.0, while thriving at those from 1.0 to 9.0. Such tolerance to a wide range of temperatures and salinities would allow these non-photosynthetic diatoms to thrive in mangrove estuaries, where environmental conditions often drastically fluctuate. Our experiments revealed that the growth rates of the non-photosynthetic diatoms were larger than those estimated based on cell volumes and temperature, suggesting that these non-photosynthetic diatoms may be an important group of organisms contributing to material circulation by growing heterotrophically in mangrove estuaries.

著者

Kazuki Yoshida Tatsuma Sato Kaoru Narita Takeshi Tomiyama

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.1, pp.53-60, 2017-02-28 (Released:2017-02-28)

参考文献数

25

被引用文献数

2

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The moonsnail Laguncula pulchella (Naticidae, formerly known as Euspira fortunei) is an invasive species that has had a negative impact on the Manila clam (Ruditapes philippinarum) population in northern Japan. In southern Japan, few records of L. pulchella exist; furthermore, the knowledge concerning the ecology of this organism is currently limited. Unexpectedly, we found many L. pulchella individuals in the Misuji River estuary, located in Hiroshima in southern Japan, during May 2015. We conducted a field survey on the density and body size of L. pulchella at a tidal flat in the Misuji River estuary (Site H) and compared those to L. pulchella in Matsukawaura Lagoon, located in Fukushima in northern Japan (Site F). The adult population of L. pulchella in a clam fishing ground (40,500 m2) at Site H was estimated to be 2,048 individuals in 2015. Densities of both surfaced individuals and egg collars of L. pulchella were lower at Site H than at Site F. Sizes of L. pulchella individuals and their egg collars as well as the somatic weight of the individuals at Site H were significantly smaller than those at Site F. These results suggest that the biological characteristics of L. pulchella largely differ between the two sites.

著者

Aiko Mitsuzawa Hiroyuki Miyamoto Hiroshi Ueda

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.12, no.2, pp.115-122, 2017-05-30 (Released:2017-06-06)

参考文献数

29

被引用文献数

13

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Copepod nauplii are the primary food item for early-stage marine fish larvae, but their feeding selectivity on the nauplii of different copepod species has not been well studied. This study revealed feeding selectivity in the dominant preflexion larvae of three fishes Sebastiscus marmoratus, Sebastes sp. and Ammodytes japonicus in the Seto Inland Sea, Japan, in spring and winter. Copepod nauplii and eggs numerically constituted 80–91% of the prey items in their guts. Chesson’s preference index for the nauplii of various copepod species was positive for Calanus sinicus and Paracalanus parvus sensu lato, negative for Acartia omorii, and negative or neutral for Oithona similis. This result is probably attributable to the size and swimming behavior of the prey species. The preference index in A. japonicus larvae was not significantly different between the nauplii of different species, suggesting that the larvae are less selective than the other two fishes. The preference index for Calanus eggs was very high, especially in Sebastiscus marmoratus and Sebastes sp., and most of the eggs in the guts were shrunken, probably due to digestion. In terms of volume, C. sinicus nauplii and eggs in gut contents represented 36–72% of total copepod nauplii and >80% of total copepod eggs, respectively, because of high selectivity by fish larvae and their large individual volumes compared with the dominant copepods. This indicates that C. sinicus is the most important prey species for early fish larvae despite their low abundance in the environment.

著者

A'an J. Wahyudi Shigeki Wada Masakazu Aoki Takeo Hama

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.8, no.2, pp.55-67, 2013-05-25 (Released:2014-08-30)

参考文献数

50

被引用文献数

1 6

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Gaetice depressus, a varunid crab common on intertidal boulder shores, is a potential key organism for monitoring organic matter flow through the food web. In order to elucidate its biogeochemical role, the diet source and trophic position of this crab on the boulder shore of an island off the Izu Peninsula, Japan, were estimated using three approaches: foregut content examination, stable isotope signature (δ13C and δ15N) and pigment biomarkers. The results suggest that G. depressus utilizes green macroalgae (Ulva sp., Ulvaria sp.) as its main diet source together with red macroalgae (Gloiopeltis complanata, Gl. furcata). This crab also utilizes periphytic and planktonic microautotrophs (occasionally tissues of heterotrophs) when macroalgae prove insufficient due to seasonal change. Therefore, G. depressus can be considered to be an omnivore since it consumes both autotrophs and heterotrophs, although it obtains organic matter mostly from autotrophs.

著者

Taketoshi Kodama Kazutaka Takahashi Ken-ichi Nakamura Shinji Shimode Takafumi Yamaguchi Tadafumi Ichikawa

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.10, no.1, pp.75-79, 2015-03-25 (Released:2015-03-20)

参考文献数

25

被引用文献数

1 4

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Short-term variation in the ammonium excretion rate by Calanus sinicus during the post-capture period was evaluated in 1-h incubations. Incubation water volume (13 mL vs. 100 mL) did not significantly affect the excretion rate, and the overall mean excretion rate of C. sinicus was similar to reported values from congeneric species. However, the 24-h variations in the excretion rate denoted that acclimation stress decreased the excretion rates 1–2 h after introduction to a no-food condition. The effect of presence/absence of food was not significant up to 24 h after capture.

著者

Shozo Sawamoto Rui Matsumoto

出版者

日本プランクトン学会、日本ベントス学会

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.7, no.4, pp.203-206, 2012-11-25 (Released:2013-06-18)

参考文献数

15

被引用文献数

1 16

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More than 50 specimens of the megamouth shark Megachasma pelagios have been reported so far, but biological observations on the species are still limited. We examined a female megamouth specimen that was captured by the bonito purse seine fishery in the Kuroshio Extension in July 2007 and donated to the Okinawa Churaumi Aquarium. The specimen was an immature female, 3,667 mm in total length and 361 kg in weight. The stomach contents measured 2,200 mL excluding the portion that was lost from the specimen before measurement. Detailed examination of a small part (14.6 mL) of the stomach contents revealed undamaged worm-like organisms, 10 partially damaged euphausiids and abundant fragmented pieces of euphausiids. The worm-like organisms were probably parasites such as tapeworms. The partially damaged euphausiids were identified as Euphausia pacifica except for one individual of Nematoscelis difficilis. Based on the number of fragmented right mandibles, which were less damaged than the other fragmented appendages, the total number of euphausiids in the stomach contents is estimated to be at least 18,000 individuals. The high abundance of euphausiids in the stomach contents suggests that the present specimen has fed on a swarm of E. pacifica in an oceanic area.