ECOLOGY OF AMORPHOUS AGGREGATIONS (MARINE SNOW) IN THE NORTHERN ADRIATIC SEA .5. ROLE OF FECAL PELLETS IN MARINE SNOW

Abundance and size classes of fecal pellets in marine snow as compared to the ambient water were investigated in the Northern Adriatic Sea during summer 1990 and 1991. Numbers of fecal pellets in marine snow varied with depth and kind of aggregates ranging from 31 to 353 000 fecal pellets 1-1 marine snow. Fecal pellets were found to be enriched in marine snow by a factor ranging from 0.3 to 3800. Small fecal pellets (< 10(5) mum3) contributed up to 68 % of the total fecal pellet volume in marine snow. Fecal pellets are a major source of carbon in marine snow (up to 37 %) and they are effectively scavenged especially by large (> 1 m) amorphous aggregates. Besides low sinking velocities, resuspension and reingestion, trapping of fecal pellets by marine snow is an efficient mechanism to keep fecal pellet-derived carbon confined to the upper layers of stratified water columns.