- 著者
- Hiroshi Ueda Hiroshi Itoh Junya Hirai Kiyotaka Hidaka
- 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.221-230, 2022-05-30 (Released:2022-05-31)
- 参考文献数
- 22
The Paracalanus parvus (Claus, 1863) species complex is a common marine calanoid copepod found in the world’s oceans. Recent genetic analyses of its specimens from the world oceans revealed that the complex in the western North Pacific consists of three species, i.e., P. indicus Wolfenden, 1905, P. tropicus Andronov, 1977 and an undescribed species. We assign the last one to be Paracalanus orientalis n. sp. by comparing it with previous morphological descriptions of related species. Both sexes of the new species are fully described based on genetically identified specimens from the surface layer of the south of Japan. The new species can be reliably distinguished from P. indicus and P. tropicus by the hunchback shape of the female if it is clearly present. Among the three species, the high length:width ratio of the third exopod segment of leg 4 is also characteristic of the new species, which would be identifiable, in most cases, by having a ratio of 5.4 or more.
- 著者
- Shinji Shimode Takafumi Yamaguchi Kiyotaka Hidaka
- 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.3, pp.301-311, 2022-08-30 (Released:2022-08-30)
- 参考文献数
- 41
Calanus sinicus is one of the most dominant planktonic copepods and plays a key role as a secondary producer in the mid-latitude coastal shelf areas of the Northwestern Pacific. In this study, we investigated seasonal changes in in situ egg production rate (EPR) of C. sinicus collected from March 2014 to February 2015 in Sagami Bay, Japan. Simultaneously, we collected formalin-preserved samples to measure reproductive index (RI), which was calculated as the proportion of individuals with matured gonad to total females in each sample. Monthly averages of EPR and RI varied from 2.4 to 44.9 eggs female−1 day−1 and 0% to 75.9%, respectively. RI showed a significant positive effect on EPR. Moreover, EPR decreased with increasing temperature, which was the inverse of the effect of temperature on EPR reported in a previous study in the Seto Inland Sea. The difference between the studies suggests that the local population may adapt to different temperature environments in each location. Using a stepwise multiple regression model, EPR estimates for C. sinicus in Sagami Bay were explained by the average water temperature and RI with high probability (R2=0.71). Although local water temperature ranges must be considered before applying our model to other areas, the model would be useful to reconstruct past secondary production of C. sinicus from preserved samples collected in other neighboring coastal areas.
- 著者
- Junya Hirai Yoko Hamamoto Daiske Honda Kiyotaka Hidaka
- 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.75-82, 2018-05-30 (Released:2018-05-24)
- 参考文献数
- 38
- 被引用文献数
- 3 12
Metagenetic diet analyses of the 18S V9 region were conducted in 40 adult female Calanus sinicus during winter in Tosa Bay (Japan). The majority of prey items were small crustaceans (of Copepoda and Cirripedia) and diatoms, taxa that are dominant in the environment and have been previously reported as important prey items of Calanus. The abundance of sequences attributable to Dinophyta and Chlorophyta was significantly lower in C. sinicus gut contents than in environmental plankton communities, suggesting that C. sinicus avoids prey from these groups. Hydrozoans were also observed, and aplanochytrids (Labyrinthulea) were detected for the first time as a major prey of C. sinicus. Additionally, high proportions of unclassified eukaryote material were observed, suggesting undetected predator–prey relationships in key copepod species in marine ecosystems. The dietary importance of aplanochytrids, heterotrophic protists that accumulate unsaturated fatty acids such as docosahexaenoic acid, has been overlooked in previous research. Calanus sinicus is a key copepod species in the subtropical coastal regions of the western North Pacific, and a major food source for the larvae of commercially important fish; therefore, further investigation into novel prey items such as aplanochytrids is recommended to understand the complex food web structures in marine ecosystems.