solution into and out of their bodies the water in the vessel was mixed, causing much of the yeast 

 to remain in suspension. Therefore, the loss of yeast from the vessels containing mussels would 

 be due largely to the intake of yeast by the mussels, and loss of yeast due to settlement and'or 

 sorption to glassware would have had a minimal effect on the yeast concentration. Modifications 

 were made to the methods including rinsing the mussels with deionized water and patting them 

 dry before placement in the yeast suspension. Also, after investigating the source of variation in 

 the data, we decided to remove the change in concentration in the yeast control from equation 1 . 

 This change resulted in the following equation: 



Fr= (Y -Y 4 )- Wt-'-h' 1 eqn.2 



where: Y = Initial yeast concentration (mg yeast • L water" 1 ) 



Y 4 = Yeast concentration after 4 h filtering period ( mg yeast • L 



water' 1 ) 

 Wt = Dry weight of mussel (g) 



h = Time (4 h) 



Fr = Mussel filtering rate (mg yeast • g mussel"'- h" 1 ) 



The removal of the yeast control from the calculation made it possible to compare filtering rates 



obtained from mussels exposed to porewaters to the filtering rates of mussels exposed to filtered 



creek water (control solution) (Table 2). Figure 3 summarizes the steps of the modified mussel 



filtering assay used in the studv. 



