THE EFFECT OF SUSPENSION DENSITY ON THE RETENTION OF 5µM DIATOMS BY THEMYTILUS EDULISGILL

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Abstract
The retention efficiency, E%, of the M. edulis gill for 5.0 .mu.m diatoms (Thalassiosira pseudonana) was estimated by separating the bivalve''s exhalant current through a rubber sleeve attached to the valves around the exhalant siphon. The particle concentration in the 4.4-6.4 .mu.m size range of inhaled and exhaled water was estimated with a model ZB coulter-counter. The mussel''s pumping rate, Rp, was recorded automatically. E% and Rp were observed for 11 mussels at diatom concentrations ranging from 3 .times. 103-1.1 .times. 105 cells/ml. Rp was maximal at 104 cells/ml and at 9.0 .times. 104 cells/ml decreased to about 55% of its maximum value. E% remained constantly high (about 97%) over the range of concentrations even when pseudofeces (filtered material rejected before ingestion) were produced. This supports the argument that, in general, a continuous filtering meshwork is formed over the ostia by synchrony in alternate (or alternate pairs of latero-frontal cirri on the same gill filament). Occasionally a low E% value (about 86%) was observed for an individual mussel and this was attributed to synchrony in .gtoreq. 3 adjacent cirri. Synchrony in 1 or more pairs of adjacent cirri is advanced as an explanation for published data on the retention of different sized particles.