TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 66 (No. 5), pp. 673-684, 2010

Effects of the Copepod Community Structure on Fecal Pellet Flux in Kagoshima Bay, a Deep, Semi-Enclosed Embayment

Toru Kobari1*, Hiroyasu Akamatsu1, Masato Minowa1, Toshihiro Ichikawa2, Kazuo Iseki3, Ryuji Fukuda4 and Masataka Higashi5

1Fisheries Biology and Oceanography Division, Faculty of Fisheries, Kagoshima University, Shimoarata, Kagoshima 890-0056, Japan
2Department of Earth and Environment Science, Faculty of Science, Kagoshima University, Korimoto, Kagoshima 890-8580, Japan
3Graduate School of Biosphere Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8524, Japan
4Nansei-Maru, Faculty of Fisheries, Kagoshima University, Shimoarata, Kagoshima 890-0056, Japan
5Kagoshimai-Maru, Faculty of Fisheries, Kagoshima University, Shimoarata, Kagoshima 890-0056, Japan

(Received 8 May 2010; in revised form 29 July 2010; accepted 2 August 2010)

Abstract: Seasonal changes in the shape and size composition of fecal pellets were investigated with sediment trap samples from 50 and 150 m in Kagoshima Bay to evaluate how the mesozooplankton community affects fecal pellet flux. Deep vertical mixing was evident in March, and thermal stratification was developed above 50 m in June, August and November. Chlorophyll a, suspended particulate organic carbon (POC) and copepod abundance were uniform throughout the water column during the seasonal mixing and concentrated above 50 m in the stratified seasons. Calanoids were the most predominant copepods in March and poecilostomatoids composed more than 45% of the copepod community in June, August and November. Fecal pellet fluxes at 50 and 150 m were the highest in March, nearly half of POC flux. The relative contribution declined considerably in the other months, especially for less than 4% of POC flux in August. The decline was corresponded to the predominance of cyclopoids and poecilostomatoids. Cylindrical pellets dominated the fecal matters at both depths throughout the study period, while larger cylindrical pellets nearly disappeared at 150 m in June, August and November. Copepod incubation revealed that cylindrical and oval pellets were egested by calanoids and the other copepods, respectively. We suggest that cylindrical fecal pellets produced by calanoid copepods contribute to feces flux but the predominance of poecilostomatoids and/or cyclopoids decreases feces flux via the increase of oval pellets and fragmentation of larger cylindrical pellets.

*Corresponding author E-mail: kobari@fish.kagoshima-u.ac.jp

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