Language：Japanese   Publisher：Progress in Oceanography  

The Kuroshio has been long thought to be disadvantageous as nursery grounds for larval fishes due to the low plankton standing stocks under the oligotrophic conditions. Despite of the potential risk for survival and growth, early life stages of various fishes appear abundantly in the Kuroshio and its neighboring waters. Here, we report what kind of taxonomic groups establish community structure of larval fishes in the Continental shelf waters (CW) and the Kuroshio (KW). 16 orders and 78 families were classified in the present study. Mesopelagic fishes more abundantly appeared in the KW than in the CW, while larval fish abundance was not different between the two areas. Multivariate analysis demonstrated the regional difference of the taxonomic compositions, represented by Callionymidae, Bothidae, Labridae and Bregmacerotidae for the CW and Gonostomatidae, Myctophidae and Notosudidae for the KW. Abundance of fish larvae to ambient salinity exhibited significantly positive correlations for Gonostomatidae, Sigmops gracilis and Myctophum orientale predominated in the KW and negative correlations for Labridae appeared abundantly in the CW. These results suggest that mixture of advected specimens from the coastal and Kuroshio waters also contribute to larval fish community with high biodiversity and comparable abundance between the Kuroshio and its neighboring waters.

DOI： 10.1016/j.pocean.2024.103386

Scopus

Language：Japanese   Publisher：Continental Shelf Research  

In the northern Satsunan area, southern Japan, upwellings generated by the intrusion of the Kuroshio branch current into Kagoshima Bay are observed at the bay's mouth once every two weeks in winter and spring, and the resulting nutrient supply promotes phytoplankton blooms. Currently, this is a key spawning and nursery habitat for chub mackerel Scomber japonicus in Japan. This study examined how water temperature and prey density influenced the growth, mortality, and predatory effects of S. japonicus larvae in the northern Satsunan area. Recent growth (measured as the average width of the last three otolith increments) of S. japonicus larvae was positively correlated with water temperature but not with prey density, indicating that prey abundance was adequate for larvae and that water temperature controlled their growth rate in the study area. The instantaneous daily mortality rate of S. japonicus larvae was 0.322 in 2021 and 0.252 in 2022 (equivalent to 27.5% mortality d−1 in 2021 and 22.3% in 2022). The food requirements of S. japonicus larvae and mesozooplankton production were 0.00427 ± 0.00334 and 6.37 ± 3.04 mg DW m−3 d−1, respectively. S. japonicus larvae had no significant predatory impact on mesozooplankton (0.0869 ± 0.0796%). The present study suggests that none of the plankton feeders have a significant top-down regulating effect on mesozooplankton biomass in the northern Satsunan area, which provides a good food environment for S. japonicus larvae.

DOI： 10.1016/j.csr.2024.105399

Scopus

Language：Japanese   Publisher：Plankton and Benthos Research  

A new species of photid amphipod, Podoceropsis nanseiae, is described from Kagoshima Bay, Japan. The present new species can be distinguished from all the congeners in having clusters of robust setae on the male gnathopod 2 basis. This species resembles Gammaropsis laevipalmata Ren, 1992, however can be distinguished from G. laevipalmata by the presence of small accessory flagellum in antenna 1, the size of eyes, the shape of palmer margin of male gnathopod 2, and the clusters of robust setae on the male gnathopod 2 basis. The closely related species G. laevipalmata should be transferred to the genus Podoceropsis. Additionally, a partial DNA sequence of the mitochondrial cytochrome c oxidase subunit I (COI) was determined from the type specimens of P. nanseiae sp. nov. for future taxonomic studies.

DOI： 10.3800/pbr.19.141

Scopus

Language：Japanese   Publisher：The Plankton Society of Japan  

<p>It has been thought that food availability for fish larvae was poor in the Kuroshio because of the low standing stocks of plankton in the oligotrophic conditions under thermal stratification throughout the year. Despite a potential risk or disadvantage for larval survival and growth, Kuroshio and its neighbouring waters are nursery grounds for the early life stages of various fishes. Here, we compared the growth activity of fish larvae among 15 taxonomic groups, including 11 families in the Kuroshio and its neighbouring waters, based on protein synthetase activity and protein contents. Protein-specific (_spAARS), individual-based aminoacyl tRNA synthetase activities (_iAARS), and protein contents (PRO) of fish larvae ranged from 2 to 232 nmol PPi mg protein⁻¹ h⁻¹, from 1 to 21 μmol PPi ind⁻¹ d⁻¹, and from <1 to 26 mg ind⁻¹, respectively. _spAARS, _iAARS and PRO were variable among the taxonomic groups and were not classified between mesopelagic groups and the others. Compiling these measurements among all taxonomic groups, a significant negative correlation was found for _spAARS to PRO. The correlation showed no significant difference between the Kuroshio and its neighbouring coastal waters, indicating that growth activities to fish larvae body mass were comparable in the Kuroshio and its neighbouring waters. Based on nonmetric multidimensional scaling on _spAARS, _iAARS and PRO among 15 taxonomic groups, two different groups were classified for fish larvae, represented by the high _iAARS under the high PRO but low _spAARS (Group 1) and the low _iAARS under the low PRO but high _spAARS (Group 2), representing the different life strategies for larval growth among the taxonomic groups. The present findings suggest that these biochemical indices are useful for evaluating the growth activity of fish larvae among various taxonomic groups and that food availability is not poor enough to support larval growth in the Kuroshio and its neighbouring waters.</p>

DOI： 10.24763/bpsj.69.2_93

Scopus

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