Responses In feeding behaviour to wide vanatlons in the amount and composition of natural seston were studled In the green-lipped (GreenshellT\'] mussel Perna canaliculus of standard 58 + 2 mm shell length Nutnent acquisition wds pnmanlv regulated by the rate that mussels cleared water of part~cles (I h ' I , which vaned In hyperbol~c relation with the abundance of chlorophyll-rich organics, lather than with the ren~alning organic 01 inorganic components of ava~lable 5eston Maximal clearance rates of about 15 1 h ' g ' consistently occurred when chlorophyll a was available at only 1 to 2 pg 1. ' Although clearance rates decreased exponentially, rates of filtrat~on and ~ngestion (mg h ') continued to grow as the total dry part~culczte mass (TPV) of available seston increased u p to about 1000 n~g l ' The proportlon of t~ltered matter ejected a s pseudofaeces before lngestlon remained at a constant fractlon xvh~ch averaged 0 87 at seston concentrations abovcl about 40 mg TP>l l Only above about 1000 m g TPM I-' dld a decline In f~ltration rate suggest any physical ovcrload~ng of feedlng mechanisms Within particles filtered on the cten~dla significant net ennchment of up to 0 23 * 0 10 (mean + 2 SE) tlmes the organic fractlon in available seston stemmed pnnlanly from the preferential retention of particles that were nch in chlorophyll a The efficiency of such retention vaned in quadratic relat~on with seston co~npos~tlon b e~n g maximal at an optimal concentrat~on of chlorophyll a per unit total organic matter Within ingested particles, f u r t h e~ net enrichment of up to as much as 1 47 + 0 26 times the organic iractlon within filtered matter stemmed from the differential pre-ingestive relectlon of particles w~t h i n pseudofaeces Efficlencies of both these selective mechanisms increased with filtrat~on rates The combined effect was that the organic content of ingested matter (OCI) was enhanced at faster filtration rates, to as much as 7 times the organic content of available seston (OCS). Associated benefits were a m p u l e d by a positlve hyperbolic relation that was confirmed between OCJ and the net absorption efficiency from Ingested organlcs Flndlngs showed that tissue wasting occurred in P canaliculus of l g dry soft tissue feedlng upon seston that contained less than 0.86 + 0.19 pg chlorophyll a l . Maximal net organic absorption rate indicated potcntial growth of 6 S":, d ' g ' dry soft tissue, assuciated with the peak in clearance rate. A high capacity for f~ltrat~on and the ability to adjust clear,ince ratr cnabled P canaliculus to optimise particle selection and absorption efficiencies at levels that maintained organic absorption rate independent of the reduction in OCS as TPM increased to at least 1000 mg I ' Collective findings help to explain why P canaliculus~s so well-suited for cultivation, establish that reduced mussel growth within the New Zealand GreenshellT\' industry from 1996 to 1998 was due at least in part to food limitation, and suggest a potential for significant expansion of ...

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