The Influence of water flow rate on Pumping Rate in Mytilus Edulis using a Refined Direct Measurement Apparatus

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Abstract
The direct method of pumping rate measurement in bivalve mollusks separates and estimates the exhalant water current from the gills which is a function of lateral ciliary activity. This is distinct from the indirect method which measures a filtration process performed by the latero-frontal cirri and not a volume of water pumped. The effect of a small artificial pressure gradient between the inhalant and exhalant sides of the gill has a significant effect on the observed pumping rate of M. edulis in the conventional direct system. A refinement of the direct method is described which eliminates pressure bias acting in the system and allows pumping rate to be estimated reliably. This is verified by comparisons of pumping and filtration rates for similar sized specimens. The refined direct apparatus is used to show that within the limits of 2-42 l h-1 the water flow rate past the mussel has no significant effect on pumping rate.