Short-term sedimentation pattern of zooplankton, faeces and microplankton at a permanent station in the Bjornafjorden (Norway) during April-May 1992

Abstract

Sedimentation rates were determined daily over a 2 wk period (late April -early May 1992) under post spring bloom conditions at a permanent station in the Bjernafjorden, Norway. Samples collected using floating sediment traps deployed at 50 and 100 m depth showed that sedimented seston, particulate organic matter, carbonate and lithogenic + opal fractions were, on average, twice as high at 100 m (221, 99, 51 and 76 mg m-2 d ', respectively) as at 50 m (119, 62. 27 and 34 mg m-2 d ' l , respectively). Faecal pellets made up the bulk of sedimenting matter, accounting for 87 and 92% of the average total organic carbon recorded at 50 and 100 m, respectively. The remaining sedimented matter consisted mainly of tintinnids. Diatoms cells and resting spores, coccolithophorids and flagellates contributed a minor fraction. It is postulated that the vertical flux of faecal pellets was determined by a combination of 3 factors: (1) relatively high standing stock of actively grazing mesozooplankton dominated by calanoid copepods and appendicularians, which are known for t h e ~r high faeces production rates; (2) a relatively high abundance of the cyclopoid copepod Oithona s~rnllls, which is reported to feed on faecal pellets produced by calanoid copepods, suggesting that coprophagy in the water column was high; (3) a phytoplankton community dominated by diatoms and coccollthophorids, whose mineral skeletons accelerate sinking rates of faecal pellets.