ORGANIC SEDIMENTATION AND MACROFAUNA AS FORCING FACTORS IN MARINE BENTHIC NANOFLAGELLATE COMMUNITIES

We investigated how benthic nanoflagellate communities in marine sedim ents respond to sedimentation of organic material and to the presence of macrofaunal organisms in controlled boxcosms. An input of 24 g C m( -2) resulted in a sharp increase in densities, from 93 to 477 x 10(3) flagellates cm(-3) within 11 days. At the onset, this increase was par alleled by enhanced bacterial production and bacterial numbers. When b acterial production collapsed, flagellate ingestion rates, varying fro m 17 to 67 bact flag(-1) h(-1) were sufficient to control bacterial ab undance. The presence of macrofauna accelerated the burst in flagellat e densities. With macrofauna the same maximum densities were reached, but later densities dropped to relatively low levels. Macrofaunal biot urbation resulted in higher flagellate densities deeper in the sedimen t (up to 1200% at 3 cm and up to 460% at 6 cm deep).