each culture flask was replaced with new glass fiber-filtered 

 Patuxent River water of the same salinity. At the same time addition- 

 al phytoplankton cells were added to the zooplankton culture flasks 

 to make up for (a) the amounts removed and dilution of the remaining 

 cells with new filtered Patuxent water, and (b) the amounts grazed 

 by the growing culture. 



Efforts were made to keep each culture in a state of rapid growth 

 (exponential growth phase) so a constant supply of adults of both 

 species (both sexes) would be available for experimental work. 

 Acartia tonsa tended towards cannibalism when the adult population in 

 each flask exceeded 20 to 30 individuals. As a result, the culture 

 population would boom and crash unexpectedly. This necessitated main- 

 tenance of this species in many culture flasks, and required close 

 monitoring of adult populations, available algal food supply, and 

 water quality. 



b. Phytoplankton Cultures . Cultures of the phytoplankters M. 

 lutheri and P. tvieovnutwri were maintained in an exponential growth 

 phase in filtered sterile (autoclaved) Patuxent River water enriched 

 with f/2 medium as described in the previous section. 



c. Sediments . Some physical and chemical characteristics of 

 sediment types used for experimental work in this section are pre- 

 sented in the Appendix. The sediment types and concentrations used 

 for each zooplankton species were as follows: 



Eurytemora af finis 



(1) Si02 (50, 100, 1,000, 10,000 milligrams l"'^). 



(2) -CIS, micrometers Si02 (50, 100, 500, 1,000 milligrams 



1 ). 



(3) Fuller's earth (50, 100, 500, 1,000 milligrams l'^). 



(4) Natural sediment (50, 100, 250, 500, 1,000 milligrams 



Aaartia tonsa 



(1) <15 micrometers Si02 (50, 100, 500, 1,000 milligrams 



(2) Fuller's earth (50, 100, 500, 1,000 milligrams l"-^) 



(3) Natural sediment (50, 100, 500, 1,000 milligrams l"-^), 



d. Determination of Time to Maximum Ingestion ^ Feeding experi- 

 ments were conducted using M. luthevi labeled with carbon-14. Cell 



18 



