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  • Online Resource  (4)
  • Yamaguchi, Atsushi  (4)
  • Biology  (4)
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  • Online Resource  (4)
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  • Biology  (4)
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  • 1
    Online Resource
    Online Resource
    Seasonal and inter-species comparison of asymmetry in the genital system of some species of the oceanic copepod genus Metridia (Copepoda, Calanoida)
    Brill ; 2015
    In:  Crustaceana Vol. 88, No. 12-14 ( 2015-12-3), p. 1307-1321
    Details
    In: Crustaceana, Brill, Vol. 88, No. 12-14 ( 2015-12-3), p. 1307-1321
    Abstract: The seasonal and inter-annual changes in the asymmetry of female insemination and the male leg 5 of the planktonic calanoid copepods Metridia okhotensis and M. pacifica were investigated in the Okhotsk Sea. An inter-species comparison of both parameters was also carried out on seven Metridia species collected from oceans throughout the world. For M. okhotensis from the Okhotsk Sea, most of the females showed left-side insemination (annual average: 95.7%) and most of the males showed left-side asymmetry (99.7%) of the long inner process of the second exopodal segment in the fifth leg throughout the year. However, sympatric M. pacifica showed different ratios of asymmetry for female insemination and male morphotypes with a left : right = 1 : 2 ratio throughout the year. For the seven Metridia species from the global oceans treated in this study, ratios of asymmetry for female insemination and male morphotypes were correlated with each other. One-sided insemination (i.e., only left or only right insemination) was a common pattern for various Metridia species from global oceans, but their ratios varied by species. Previously, low hatching rates (29-68%) of eggs were reported for various Metridia spp. in laboratory experiments, but the reasons for these low rates were unclear. Because each spermatheca of Metridia spp. is connected to the oviduct on the same side, either left or right, this suggests that half of the eggs produced by unilaterally inseminated females remain unfertilized. The morphology of the genital structures and literature data of the egg hatching rates of Metridia spp. indicate that almost half of the eggs produced by females are not viable and are, thus, wasted.
    Type of Medium: Online Resource
    ISSN: 0011-216X , 1568-5403
    URL: Article
    DOI: 10.1163/15685403-00003485
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Brill
    Publication Date: 2015
    detail.hit.zdb_id: 2019267-8
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Life history and production of pelagic mysids and decapods in the Oyashio region, Japan
    Brill ; 2013
    In:  Crustaceana Vol. 86, No. 4 ( 2013), p. 449-474
    Details
    In: Crustaceana, Brill, Vol. 86, No. 4 ( 2013), p. 449-474
    Abstract: Pelagic Mysidacea and Decapoda have important roles in marine ecosystems. However, information on their life histories is extremely limited. This study aimed to evaluate the life cycles of pelagic Mysidacea and Decapoda in the Oyashio region, Japan. Production of the four dominant species was estimated by combining body mass (DM) data and abundance data. Mysidacea belonging to 5 species from 5 genera occurred in the study area. Their abundance and biomass ranged between 11.7-50.1 ind. m −2 and 1.2-7.9 g wet mass (WM) m −2 , respectively. Six species from 6 genera belonged to Decapoda, and their abundance and biomass ranged between 9.0-17.3 ind. m −2 and 3.0-17.3 g WM m −2 , respectively. Based on body length histograms, there were two to four cohorts for the three dominant mysids and one dominant decapod on each sampling date. Life histories of the two numerically dominant mysids ( Eucopia australis and Boreomysis californica ) followed similar patterns: recruitment of young in May, strong growth from April to June, and a longevity of three years. Life cycles of the two minor species (the mysid Meterythrops microphthalma and the decapod Hymenodora frontalis ) were not clear because of their low abundance. The timing of recruitment of the young and the strong juvenile growth for the two dominant mysids corresponds with the season when their prey is abundant. The annual production of the dominant mysid species was 14.0 mg DM m −2 ( B. californica ) and 191.8 mg DM m −2 ( E. australis ). Annual production/biomass () ratios ranged between 0.242 ( H. frontalis ) and 0.643 ( M. microphthalma ). Compared with other regions, the Oyashio region showed high production and low ratios. The high production in the Oyashio region may be related to the high biomass of these species. Because of the low temperature conditions (3°C), pelagic mysids and decapods in the Oyashio region may have slower growth, longer generation times and lower ratios than in other oceans.
    Type of Medium: Online Resource
    ISSN: 0011-216X , 1568-5403
    URL: Article
    DOI: 10.1163/15685403-00003170
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Brill
    Publication Date: 2013
    detail.hit.zdb_id: 2019267-8
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Seasonal abundance, population structure, sex ratio and gonad maturation of Metridia okhotensis Brodsky, 1950 in the Okhotsk Sea: analysis of samples collected by pumping up from deep water
    Brill ; 2016
    In:  Crustaceana Vol. 89, No. 2 ( 2016-03-1), p. 151-161
    Details
    In: Crustaceana, Brill, Vol. 89, No. 2 ( 2016-03-1), p. 151-161
    Abstract: In the Okhotsk Sea, the calanoid copepod Metridia okhotensis Brodsky, 1950 is the dominant component of zooplankton, accounting for 61% of the annual mean total pelagic copepods. Although this organism is important, little ecological information is available for M. okhotensis in the Okhotsk Sea because of the ice cover during winter, which prevents the collection of seasonal samples in this region. Here, we report the seasonal changes in the population structure, sex ratio and female gonad maturation of M. okhotensis . The data are from samples collected using water pumped from a depth of 350 m off Rausu Harbour in the Okhotsk Sea at 2-week intervals over a 2.5-year period. Due to the mesh size of the strainer (420 μm), M. okhotensis was collected from C3 to adults. The sex ratio of C5 (female : male) was approximately 1 : 1 throughout the year. In contrast, the sex ratio of C6 (adult) showed a clear seasonality, with males (C6M) occurring only from December to May and females (C6F) dominating during the other seasons. The gonad maturation of C6F was scored using five categories, and their composition also showed clear seasonality. From January to April, gonads developed rapidly from stage I (immature) to V (spawning). During the other seasons, the majority of C6F had immature gonads. Based on these data, we conclude that this species likely has a diapause phase for C6F, with immature gonads, and C5M from June to November. Moulting from C5M to C6M began in December. Accompanying the occurrence of C6M, C6F were fertilized from December to January. C6F underwent gonad maturation from January to April and performed primary reproduction from April to May. Thereafter, M. okhotensis entered diapause from June to November.
    Type of Medium: Online Resource
    ISSN: 0011-216X , 1568-5403
    URL: Article
    DOI: 10.1163/15685403-00003516
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Brill
    Publication Date: 2016
    detail.hit.zdb_id: 2019267-8
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 4
    Online Resource
    Online Resource
    Seasonal changes in body size and oil sac volume of three planktonic copepods, Paracalanus parvus (Claus, 1863), Pseudocalanus newmani Frost, 1989 and Oithona similis Claus, 1866, in a temperate embayment: what controls their seasonality?
    Brill ; 2014
    In:  Crustaceana Vol. 87, No. 3 ( 2014), p. 364-375
    Details
    In: Crustaceana, Brill, Vol. 87, No. 3 ( 2014), p. 364-375
    Abstract: Seasonal changes in body size (prosome length: PL) and oil sac volume (OSV) of the three most numerically abundant copepods in Ishikari Bay, northern Sea of Japan, Paracalanus parvus (Claus, 1863), Pseudocalanus newmani Frost, 1989 and Oithona similis Claus, 1866, were studied using monthly samples collected through vertical hauls of a 100-μm mesh NORPAC net from March, 2001 to May, 2002. Seasonal changes in PL were common for the three species and were more pronounced during a cold spring. PL was negatively correlated with temperature, and this relationship was described well using the Bělehrádek equation. Seasonal changes in OSV exhibited a species-specific pattern, i.e., OSV was greater during a warm summer for P. parvus and was greater during a cold spring for P. newmani and O. similis . The OSV peak period corresponded with the optimal thermal season of each species. The relative OSV to prosome volume of the small copepods (0.6-0.8%) was substantially lower than that of the large copepods (20-32%). These facts suggest that the oil sac of small copepods is not used for overwintering or diapauses or during periods of food scarcity, but is instead used as the primary energy source for reproduction, which occurs during the optimum thermal season of each species.
    Type of Medium: Online Resource
    ISSN: 0011-216X , 1568-5403
    URL: Article
    DOI: 10.1163/15685403-00003287
    RVK:
    WA 15000
    Language: Unknown
    Publisher: Brill
    Publication Date: 2014
    detail.hit.zdb_id: 2019267-8
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
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