Journal of Oceanography, Vol. 59 (No. 6), pp. 809-818, 2003
Hidekatsu Suzuki1*, Hiroshi Sasaki1 and Mitsuo Fukuchi2
1Department of Biotechnology, Senshu University of Ishinomaki, Ishinomaki 986-8580, Japan
2National Institute of Polar Research, Kaga, Itabashi-ku, Tokyo 173-8515, Japan
(Received 8 February 2002; in revised form 7 April 2003; accepted 10 April 2003)
Abstract: A time-series sediment trap deployment was carried out in the marginal ice zone (MIZ) of the Antarctic Ocean (64°42´ S, 139°58´ E; sea depth of 2930 m), during the austral summer. Cylindrical fecal pellets were the predominant sinking particles at 537 m in the middle of January and most of them disappeared below that depth, the loss of which were 25.3 mg C m-2day-1 in the depth range of 537-796 m. Small-sized sinking particles other than fecal pellets increased in that depth range. Analyses of fecal pellets for remnant DNA corresponding to 16S mitochondrial RNA and 28S ribosomal RNA suggested that the large cylindrical fecal pellets at 537 m were produced by Antarctic krill (Euphausia superba) and copepods. According to the presence of the DNA associated with sinking particles, E. superba fecal pellets rapidly disappeared below 537 m, while copepod fecal pellets still remained in the mesopelagic and bathypelagic layers. Small-sized amorphous sinking particles at 537 m also contained E. superba- and copepod-derived DNA. The abundance of trap-collected copepods (Oithona spp. and Oncaea spp.) which are known to be coprophagous increased at 796 m where many fecal pellets disappeared. We suggest that those rapidly sinking pellets were fragmented by copepods with intensified coprorhexy activity (fragmentation of fecal pellets) in the mesopelagic layers, reducing their sinking rates. These smaller and slower sinking particles can be important food sources for detritivorus or coprophagous animals in mesopelagic and bathypelagic layers in the MIZ.