Inter-oceanic comparison of planktonic copepod ecology (vertical distribution, abundance, community structure, population structure and body size) between the Okhotsk Sea and Oyashio region in autumn

Atsushi Yamaguchi

doi:10.1080/00222933.2015.1022616

Abstract

Several aspects of the ecology of planktonic copepods (vertical distribution, abundance, community structure, population structure and body size) were evaluated and compared between communities in the autumn, in the Okhotsk Sea and the adjacent Oyashio region in the western North Pacific. Vertically, copepods were concentrated primarily at depths of 250 to 500 m in the Okhotsk Sea but near the surface in the Oyashio region. The abundances of most of the copepods were greater in the Oyashio region with the exception of Metridia okhotensis, which showed significantly greater abundance in the Okhotsk Sea (30 times greater) and dominated the copepod community, accounting for approximately 70% of total copepod abundance. The population structure of the dominant copepods in the Okhotsk Sea was dominated by late copepod stages, suggesting that these copepods were in the resting phase. The prosome lengths of most of the copepods were larger in the Okhotsk Sea than in the Oyashio region and the larger body size is probably due to the lower habitat temperatures. The special ecological characteristics of planktonic copepods in the Okhotsk Sea are possibly related to the development of a strong pycnocline in the Okhotsk Sea. The consequences of differences in copepod communities between regions were discussed from the viewpoints of life cycle timing and the scale of active vertical flux.

Highlights

Planktonic copepods dominate the zooplankton community of the global ocean
The vertical profiles of zooplankton biovolume in the Oyashio region and Okhotsk Sea were different; the profile peaked at the surface layer (0 m-thermocline) in the former and at a depth of 250-500 m in the latter (Fig. 3)
This study described inter-oceanic differences in the ecology of zooplankton and calanoid copepods and showed: 1) smaller zooplankton biovolume near the surface layer in the Okhotsk Sea; 2) a predominance of M. okhotensis in the Okhotsk Sea; 3)

Summary

Introduction

Planktonic copepods dominate the zooplankton community of the global ocean. They form a vital link between primary producers and higher trophic levels and can accelerate vertical flux of material (the biological pump) (cf. Mauchline 1998).Given their importance in marine ecosystems, an inter-oceanic comparison of their ecology is of special interest.Faunistic comparisons have revealed differences between the Arabian, Mediterranean and Red Seas (Halim 1984; Böttger-Schnack 1994); between the Japan Sea and North Pacific (Vinogradov 1973; Vinogradov and Sazhin 1978); and between the Sulu and Celebes Seas (Nishikawa et al 2007; Matsuura et al 2010). Planktonic copepods dominate the zooplankton community of the global ocean. They form a vital link between primary producers and higher trophic levels and can accelerate vertical flux of material (the biological pump) (cf Mauchline 1998). Given their importance in marine ecosystems, an inter-oceanic comparison of their ecology is of special interest. Faunistic comparisons have revealed differences between the Arabian, Mediterranean and Red Seas (Halim 1984; Böttger-Schnack 1994); between the Japan Sea and North Pacific (Vinogradov 1973; Vinogradov and Sazhin 1978); and between the Sulu and Celebes Seas (Nishikawa et al 2007; Matsuura et al 2010). The life cycle stages of the dominant copepods show inter-oceanic differences: Calanus and Neocalanus life stages dominate in the northern hemisphere (Conover 1988) and copepods are dominant in the Southern Ocean (Atkinson 1998)

Methods

Results

Conclusion