ABSTRACT: The lugworm Arenicola marina was studied in an observation aquarium; the typical undisturbed stroke frequency of the piston pump was ƒ = 6 to 7 strokes min^-1. A new experimental setup was used for direct measurement of volume flow at zero and different imposed back pressures. The back pressure characteristic was a nonlinear function, the stroke frequency being reduced with increasing imposed back pressure, attaining a maximal pressure head of 20 cm H₂O, which is 30 to 150 times higher than previously found in filter-feeding macro-invertebrate pumps. The back pressure -volume flow characteristic was modelled. At the (assumed) normal operation pressure (5 cm H₂O) the power output from the 'standard' (0.5 g dry wt) lugworm pump was calculated to be P_p = 12.6 uW. The respiration rate (R, ul O₂ h^-1) measured in lugworms kept in glass tubes was dependent on the stroke frequency and correlated with dry weight (W, g) according to R = aWb, where a = 344 and b = 0.64 at ƒ = 7 strokes min^-1. The total respiration of the 'standard' worm was R_tot = 232 ul O₂ h^-1 = 1281 uW, and thus the overall pump efficiency was mu = P_p/R_tot = 1% which suggests that the energy cost of pumping is modest (<5%). The volume of water pumped per ml oxygen consumed was only 0.4 l ml^-1 O₂ which is >100 times lower than values previously found for true filter-feeders. This very low value shows that it is unlikely that the lugworm can live by filter-feeding.

KEY WORDS: Pumping costs . Ventilatory flow rate . Piston stroke frequency . Respiration rate . Filter-feeding

Published in MEPS Vol. 138 (1996) on July 25
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996