chemi luminescence, an undesirable feature of this counting fluid for- 

 mulation. After background subtraction, counts were corrected for 

 quenching by an external standard quench curve constructed from 

 counts of standard toluene carbon-14 with increasing amounts (0 to 

 400 microliters) of chloroform in a solution of 15 milliliters of 

 acidified Instagel and 1 milliliter of Soluene-100. Counting effi- 

 ciency of most samples was approximately 88 percent. 



Results are graphed as average carbon uptake (counts min hr ) 

 of the 20 zooplankters in the paired replicate bottles (10 from each 

 bottle) plotted against time from initial feeding. 



e. Determination of the Effects of Increasing Concentrations of 

 Different Sediment Types on Zooplankton Feeding Activity at Time of 

 Maximum Ingestion . Maximum ingestion (maximum uptake of carbon-14) 

 of radioactive M. lutheri cells (50,000 cells ml"-^) at 20 - 2' Celsius 

 under approximately 0.2 x 10 ergs cm sec light intensity in a 

 salinity range of 5.5 to 7.5 parts per thousand was 5 minutes for 

 adult A, tonsa and 10 minutes for adult Eurytemora affinis. 



Slurries of different sediment types were prepared and maintained 

 as outlined in Section I, except that the filtered Patuxent River 

 was not enriched with f/2 medium. Slurries of natural sediment were 

 aerated to a light tan color before use in these experiments. This 

 reduced the biochemical oxygen demand (BOD) . 



Phytoplankton, zooplankton, and scintillation vials were prepared 

 as in the preceding section with the following procedural changes: 



(1) For E. affinis^ replicated experimental sets with series of 

 increasing concentrations were conducted with the two differ- 

 ent size distributions of Si02 (see App.). Only one experi- 

 mental run with Fuller's earth was made, but all bottles were 

 replicated. Two experimental runs were made with natural 

 sediment and only the controls were replicated. 



(2) For A. tonsa, two experimental runs with replicated controls 

 were made with Fuller's earth and with Si02i (15 micrometers). 

 Only one experimental run was made with natural sediment due 

 to a shortage of adults. 



(3) The time course of the feeding experiments with increasing 

 concentrations of each sediment type was 5 minutes for A. 

 tonsa and 10 minutes for E. af finis. 



(4) After the zooplankters were placed into the bottles and ac- 

 climated for 0.5 to 1 hour as before, appropriate amounts 



(by volume) of sediment slurry were added by precision micro- 

 pipet to successive bottles (pairs in some cases) to create 

 an increasing series of sediment concentrations. The amount 



21 



