Feeding response and carbon assimilation by the blue mussel Mytilus trossulus exposed to environmentally relevant seston matrices

Abstract

The feedlng response of the blue mussel Mytllus trossulus exposed to environmentally relevant seston matnces were studied in the laboratory under flow-through conditions Twelve seston matnces varying In quality and quantity were prepared by mixlng 3 microalga Thalassloslra pseudonand (5, 20 and 150 X 106 cells 1 ') and 4 silt concentrations (0 5 20 and 50 m g 1 ') to represent an increasing seston organic quallty of 10 to 71 and dn increaslilg seston quantity of 1 4 to 56 6 mg I ' Clearance rates (CRs) pseudofaeces (PF) production, sorting efficiency (SEF) ingestion rates (IRs) of particulate organic matter (POhl) and particulate inorganic matter (PIM) and apparent and true carbon ass~milation efflciencies (C-AE0 ,) were determined for the varlous exposure regimes Under conditions of 0 dnd 5 mg 1 ' silt CRs decreased by 3-fold 114 4 to 4 9 1 h ' g ' dry wt (gdw ')I and 6-fold (18 0 to 3 3 1 h ' cldw ') respectively with Increasing seston quality Under condit~ons of hlgh silt loads (20 and 50 m g I-') CRs were independent of increasing seston quallty with maximum CRs (21 8 & 2 2 1 h ' gdw l ) observed at the 20 x lob cells 1 ' and 20 mg l I silt exposures PF production was dependent on seston quantity (r2 -0 63 p < 0 05) with mussels preferentially rejecting the inorganic versus the organic component of the seston This SEF was optlrnized at a seston quality of 40% organic matter As a consequence of this selective feedlng strategy, determined POM IRs under high a l g a e / h ~g h s ~l t (high quantity/quality) exposure reglmes were comparable to those of the high quality (lust algae) exposures (POM IRs of 48 0 as compaied to 38 1 and 91 3 mg h ' gdbv ' for high quality and high quantity/qual~ty respectively) In contrast mussels exposed to low quahty/quantity seston Ingested both seston components (SEF < 2 4 % ) I e the mussel was non-select~ve possibly ingesting both seston components to meet nutrient requirements Apparent C AE",, expressed as C ,,,,,,, -C , ,,,,., /C ,,,,,,, correlated with seston quality ( '0 POM) (r2 = 0 64, p < 0 05) However, carbon assin~ilation expressed as a true C-AE"o,