The lugworm (Arenicola marina) pump: Characteristics, modelling and energy cost

Abstract

The lugworm Arenicola manna was studied in an observation aquarium; the typical undisturbed stroke frequency of the piston pump was f = 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 μW. The respiration rate (R, μl 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 f = 7 strokes min-1. The total respiration of the 'standard' worm was R(tot) = 232 μl O2 h-1 = 1281 μW, and thus the overall pump efficiency was μ = 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.