Vertical Distribution, Community and Population Structures of the Planktonic Chaetognatha in the Western Subarctic Pacific: Insights on the Eukrohnia Species Group

• Published in: Oceans
• Main Authors: Yuya Nakamura, Haochen Zhang, Atsushi Yamaguchi
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2023
• Subjects: vertical distribution; population structure; Chaetognatha; Eukrohnia species group; Oceanography; GC1-1581; Subarctic
• Online Access: https://doi.org/10.3390/oceans4030018; https://doaj.org/article/c14d96aed1df469bae1e425fa890dac6

In the oceans, Chaetognatha can contribute significantly to the total zooplankton biomass (up to 10–30%). The genus Eukrohnia , the dominant Chaetognath genus in the western subarctic Pacific, includes E. hamata and E. bathypelagica. Although it has been pointed out that there is no genetic difference between the two species, no study has been made that treats them as the same species group. In this study, we investigated vertical distribution based on the eight vertical stratification samplings down to 1000 m depths conducted day/night at four seasons covering one year, community structure, and population structure of the three dominant Chaetognath species: Parasagitta elegans , E. hamata , and E. bathypelagica in the western subarctic Pacific. The population densities of each species at 0–1000 m water column were 0.04–0.36 ind. m −3 for P. elegans , 0.14–1.60 ind. m −3 for E. hamata , 0.24–1.54 ind. m −3 for E. bathypelagica , and 1.37–2.62 ind. m −3 for Eukrohnia juveniles. The vertical distributions were consistent both day and night, and no diel changes were observed for all species throughout the seasons. The vertical distribution of Chaetognaths evaluated by the distribution center was 61–169 m for P. elegans , 143–206 m for Eukrohnia juveniles, 134–279 m for E. hamata , and 253–612 m for E. bathypelagica . The body length of P. elegans ranged from 4 to 34 mm, and one to three cohorts were identified at each sampling occasion. While the presence of the eight stages has been reported for Eukrohnia , only one to five stages occurred, and specimens belonging to six to eight stages were not observed in the samples throughout the year. The body length of the whole Eukrohnia species ranged from 2 to 14 mm. The body length histograms of the Eukrohnia species group, including E. hamata and E. bathypelagica , and their juveniles showed the presence of two to four cohorts at each sampling date. Within the Eukrohnia species group, vertical changes in body length were present, which were characterized by the smaller ...