COPPER SENSITIVITY OF ADULT PACIFIC OYSTERS 303 



body masses were typically between 30 and 60 g. Oysters were 

 scrubbed before random selection for placement in the bioassay 

 system. 



Toxicity Experiments 



Bioassay System 



Animals were exposed to copper in a flow-through bioassay 

 system. The exposure solutions were introduced by gravity from a 

 mixing chamber into 10-liter 5- by 40- by 48-cm plastic trays 

 containing 10 oysters placed hinge side up at known locations. 

 Filtered seawater and CuCh solutions were pumped into the mixing 

 chambers at predetermined rates to provide the desired copper 

 concentrations. The volume of water in the exposure tray was 

 maintained constant with an outflow siphon. The flow of seawater 

 from the trays was 6.6 liters/hr. Replacement of 90% of the seawater 

 in the tray required approximately 3.4 hr. 



Gentle streams of bubbles from outlets arranged in a 5- by 15-cm 

 grid at the bottom of the trays aerated and mixed the seawater in the 

 exposure trays. All exposure trays were immersed in a water bath 

 whose temperature was monitored and maintained at 12.8 ± 1°C. 

 Continuous illumination was provided because we observed that 

 some oysters responded to abrupt changes in light intensity by 

 closing the valves of their shells. The salinity and pH of the bioassay 

 water were 31.1% o and 8.08 ± 0.05, respectively. 



During the 10- to 12-day experiments, observations were made at 

 4-hr intervals from 8:00 a.m. to 12:00 p.m. (no observations were 

 made at 4:00 a.m.). At each observation the amount of valve 

 separation of the shell was recorded. Gaping oysters (having a 

 separation of ~1 cm between the v£ilves) were gently tickled with a 

 blunt, soft, plastic probe to check for muscular responses. Animals 

 that did not respond were considered dead and were removed from 

 the bioassay system. At the termination of the experiment, oysters 

 alive in the 230 idg Cu/liter and control trays were sacrificed. 



Copper Analyses of Oysters 



Oysters were weighed intact; the bodies were removed from the 

 shells; and the soft tissues were weighed before freezing for later 

 dissection. To prepare for copper analyses, we dissected the animals 

 while they were still partially frozen into gills, digestive glands and 

 stomachs, and remaining tissues. Tissues were dried at 100°C, ashed 

 at 450°C, and wet ashed in a mixture of HCl and HNO3 for copper 

 analysis on an atomic absorption spectrometer. 



