The filtration activity of a serpulid polychaete population (<i>Ficopomatus enigmaticus</i> (Fauvel) and its effects on water quality in a coastal marina

An estimate of the total standing stock of Ficopomatus enigmaticus (Fauvel) in the Marina da Gama, Zandvlei, near Cape Town was made, and some aspects of the animals' filter-feeding behaviour investigated. Working on values of 5·23 g dry mass of worm (excluding tube) m⁻² on the submerged aquatic plant Potamogeton pectinatus L., plus 84·9 g m⁻² on the canal walls, the total standing stock of the serpulid was estimated at 2·88±2·24 t (1·4 t on Potamogeton; 1·48 t on canal walls).

At the average particle concentrations of Marina water of 5·27 mg l⁻¹, the clearnace rate of F. enigmaticus was 8·59 ml mg⁻¹ worm h⁻¹, resulting in an ingestion rate of 45·27 mg mg⁻¹ worm h⁻¹ of particles in the size range 2–16 μm. Clearance and ingestion rates both increased in direct proportion to food concentration. Using estimates of total standing stocks within the Marina, the F. enigmaticus population clears 2·47 × 10⁷ l of water h⁻¹ and consumes 1·3 × 10⁸ mg of particles h⁻¹ in the 2–16 μm size range. Thus, the entire volume of the Marina will be filtered in 26·1 h through the activities of this animal alone, illustrating its importance for the maintenance of water quality within this moderately polluted system.