Abundance and In-situ Feeding Habits of Neocalanus cristatus (Copepoda: Calanoida) in the Central and Western North Pacific Ocean in Summer and Winter

夏季と冬季の北太平洋中央部と西部におけるNeocalanus cristatusの南北分布および餌料

Nagasawa Kazuya

Ohtsuka Susumu

Saeki Seiji

Ohtani Shuji

Zhu Gen Hai

Shiomoto Akihiro

遠洋水産研究所研究報告

The abundance and in-situ feeding habits of copepodids of Neocalanus cristatus were investigated in the upper 150 m along south-to-north transects in the subarctic central and western North Pacific Ocean in June July 1995 and January 1996. Stage IV and V copepodids (CIV and CV) were dominant in June July, but Stage I to III copepodids (CI to CIII) exclusively occurred in January. The abundance of N. cristatus varied latitudinally, being the highest in the Transitional Domain and southern subarctic region in June July and also in the northern Transitional Domain in January. The summer latitudinal variations in abundance were caused by a difference in regional abundance of CV individuals. There was a statistically significant negative relationship between abundance of N. cristatus (both all and CV individuals) and chlorophyll-a concentration in June July. Copepodids of four stages (CII to CV) fed mainly on a wide variety of diatoms (e.g., Thalassiosira spp. and Coscinodiscus spp.) in both June July and January. Tintinnids and silicoflagellates followed diatoms in June July and January, respectively. Dinoflagellates and zooplantkers were much less frequently detected in the copepodid guts. Copepodids may also employ detritivory and feed on secretions and fecal pellets of zooplankton. It is likely that N. cristatus more actively feeds on phytoplankters and ciliates than previously suggested.

1995年6～7月と1996年1月に北太平洋中央部と西部における南北定線上の定点において表層(水深150mから海表面)で採集されたカイアシ類Neocalanus cristatusの現存量と消化管内容物を調べた. 6～7月にはコペドディド4期と5期が卓越したが, 1月にはコペドディド1～3期が多くを占めた. 本種の現存量は緯度によって変化し, 6～7月には移行領域と亜寒帯域南部で最も高く, 1月には移行領域北部で高かった. 夏季における現存量の南北分布の地域差は, コペドディド5期の現存量に原因していた. 6～7月には本種の現存量と表層のクロロフィル量との間に統計的に有意な負の相関が認められた. 本種は夏季と冬季に様々な珪藻類を主に食べており, 夏季には有鐘繊毛虫類, 冬季には珪質鞭毛虫類が珪藻類に次いだ. 消化管内に渦鞭毛藻類と動物プランクトンの出現は少なかった. また, 本種はデトリタス食性も示し, 動物プランクトンの分泌物や糞粒を食べていると考えられた. 以上の結果から, 本種は従来考えられていたよりも活発に植物プランクトンや繊毛虫類を食べると推定される.

Neocalanus cristatus

seasonal and regional abundance

feeding habits

North Pacific Ocean

Zoology [ 480 ]

eng

遠洋水産研究所

[ISSN] 0386-7285

[NCID] AN00025949

[URI] http://rms1.agsearch.agropedia.affrc.go.jp/contents/library/jnr/enyo.html isVersionOf