Organic sedimentation and macrofauna as forcing factors in marine benthic nanofagellate communities.

We investigated how benthic nanoflagellate communities in marine sediments 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 × 10(3) flagellates cm(-3) within 11 days. At the onset, this increase was paralleled by enhanced bacterial production and bacterial numbers. When bacterial production collapsed, flagellate ingestion rates, varying from 17 to 67 bact flag(-1) h(-1), were sufficient to control bacterial abundance. The presence of macrofauna accelerated the burst in flagellate densities. With macrofauna the same maximum densities were reached, but later densities dropped to relatively low levels. Macrofaunal bioturbation resulted in higher flagellate densities deeper in the sediment (up to 1200% at 3 cm and up to 460% at 6 cm deep).