The mussel pump: properties and modeling

Abstract

erties of the blvalve pump were assessed by investigating, in the mussel R4yhlus eduhs, effects on pump characteristics of reduced valve gape, serotonin stlrnulation of cihary activity, as well as spawning. Reduced valve gaping caused a proportional dechne both in flow rate at zero back pressure, V', and in pump pressure at zero flow, AH?,( = AH",,, the coefficient C I Z= L,.Hq2N0 remaining constant. Enhanced beating rate of lateral cilia, induced by serotonin stimulation, did not affect flow rate or pump pressure. Excessive stimulation that eliminated the laterofrontal clrri from the flow pathway had eri-atlc,non-significant effects. Pump pressure and flow rate vaned with the extension of mantle edges and expiratory siphon, as correlated with the valve gape. Retraction of mantle edges and siphon at reduced valve gape results in a reduction in width of the interfilament canals and thus in the distance between opposing bands of lateral cilia. This distance appears to be the main factor in determining pump pressure and flow rate in the mussel and other bivalves The distance tends to be maximal when mantle edges and siphon are fully extended, as they normally are in undisturbed mussels. It is concluded that the rate of water pumping constitutes an emergent property of the spatial geometry of the interfllament canals and the mantle cavlty, rather than a physiologically regulated process. Based partly on the experimental results and kartly on theoretical as_sumptionsthe pump could be modelled by the equation ,'.PI = ,'.H,2-+ C,,(V/l)' i C,,,i'(l - oc + where dimensionless quantitities are t'\.H,? = I',H,~/:".H{ ;,C,, = C,,/I^. H;,,,; V = VO/V",,,; 1 = relative valve gape; and Clrl= C,,,/iAjH~, C,:, and C,,,.are coefficients of kinetic energy loss at the exhalant siphon,hH,, and of fr~ct~onlaolss in the interfilament canals, :".H,I,.