Zoological Studies

Vol. 54, 2015

Spatial changes in the vertical distribution of calanoid copepods down to great depths in the North Pacific

Atsushi Yamaguchi1,*, Kohei Matsuno2, and Tomoe Homma1

1Laboratory of Marine Biology, Graduate School of Fisheries Science, Hokkaido University, 3-1-1 Minatomachi, Hakodate, Hokkaido 041-8611, Japan
2Arctic Environmental Research Centre, National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan

Abstract
Background: Despite its ecological importance, little information is available regarding the spatial and vertical changes in the calanoid copepod community over large geographical regions. This study investigated the spatial and vertical patterns in calanoid copepod abundance and community structure using zooplankton samples collected between depths of 0 and 2,615 m across the North Pacific from 0 to 56N.
Results: A total of 211 calanoid copepod species belonging to 66 genera and 24 families were identified. Calanoid copepod abundance decreased with increasing depth, and few latitudinal differences were detected. Across the entire region, species diversity peaked near 500 to 2,000 m in depth. The calanoid copepod community was separated into seven groups with distinct spatial and vertical distributions. For all groups, the number of species was low (28 to 37 species) in the subarctic region (north of 40N) and high (116 to 121 species) in the subtropical-tropical region. The deepest group in the subtropical-tropical region was composed of cosmopolitan species, and this group was also observed in deep water in the subarctic region.
Conclusions: In deep water, most of the calanoid copepod community consisted of cosmopolitan species, while an endemic community was observed in the subarctic region. Because the food of deep-sea calanoid copepods originates from the surface layer, sufficient and excess flux in the eutrophic subarctic region may be responsible for maintaining the endemic species in the region.

Key words: Zooplankton; Calanoid copepods; Community structure; Diversity; Deep-sea; North Pacific.

*Correspondence: E-mail: a-yama@fish.hokudai.ac.jp