The crown-filament pump of the suspension-feeding polychaete Sabella penicillus: filtration, effects of temperature, and energy cost

Abstract

The energetics of the ciliary crown-filament pump was studied for the suspension-feeding polychaete Sabella penicillus. Maximum filtration rate expressed as the clearance capacity (F1, l h-1 ind.-1) as a function of body size (W, g dry wt) was: F = 13.62W0.24. The filtration rate was high and constant at algal (Rhodomonas sp.) concentrations below about 4 .times. 103 cells ml-1, but a higher conentrations the gut capacity was probably exceeded thus leading to a reduced filtration rate. Oxygen consumption (R, ml O2 h-1 ind.-1) as a function of size was: R = 0.13W0.66. The water-processing capacity of a ''standard'' 65 mg dry wt S. penicillus was estimated as 354 l of water filtered per ml of oxygen consumed. This suggests that the polychaete is adapted to live in waters with extremely low algal concentrations. Filtration rate as a function of temperature was measured in 2 size groups of worms. The relationship fitted straight lines and it was found that the viscosity effect may explain the whole correlation between filtration rate and temperatures between 5 and 20.degree. C. The operating point, Op, of the crown-filament pump was determined by equating pump characteristic and system characteristic, .DELTA.Hp = .DELTA.Hs. The system characteristic was calculated as the sum of the 2 major contributions, namely the pressure drop across the pinnule-lattice of the crown-filaments, .DELTA.Hipc, and the kinetic loss, .DELTA.Hkex, in the water leaving each crown-filament, which was regarded as one of a species of parallel ''pump units''. The calcualted operating point and components for e.g. 15.degree. C were Op = .DELTA.Hipc + .DELTA.Hkex = 0.0222865 + 0.000065 = 0.0224 mm H2O. The mechanical work done by the pump (pumping power) was 0.451 .mu.W, compared to a total metabolic energy expenditure of R = 112 .mu.W.