Vertical distribution of suspended fecal pellets and production of copepod fecal pellets in the Ulleung Basin in the Japan/East Sea

Abstract

Vertical distribution of suspended fecal pellets (SFP) in water column and production rates of fecal pellets by copepod community was studied in the Ulleung Basin, Japan/East Sea in July 2005. An anticyclonic eddy existed in the center of the basin. The eddy was stratified with a seasonal thermocline and in the center of the eddy a strong subsurface chlorophyll maximum was developed at 40-50m depth. Experiments were made at three stations: D1 (located at the shelf edge and outside of the eddy), D2 (at the periphery of the eddy), and D4 (inside the eddy). The mean standing stock of SFP in the upper 150m was higher at D1 than at D2 and D4, showing highly positive correlation with mesozooplankton biomass. The SFP at D2 and D4 peaked at 30-50m depth with no clear difference between the day and night sampling. The SFP in the water column, however, peaked at 100m depth at D1, due to potential vertical migration of euphausiids and amphipods at dawn. The estimated production of fecal pellets by copepod community was higher at D4 than D2, mainly due to the higher chlorophyll a concentration in the subsurface chlorophyll maximum layer. The production rate of fecal pellets by copepod community was estimated 0.57 mgC m-3 day-1 (or 115 mgC m-2 day-1 in the upper 200m). The major controlling factors for the variability of mesozooplankton fecal pellets are discussed in the context of the potential role of fecal pellets in carbon flux in the Ulleung Basin in summer.