associated with natural sediments such as sorbed toxic metals and 

 pesticides, high BOD, and high nutrient content. The objective in 

 this study was to identify the biological effects of particulate 

 mineral solids similar in size distribution to sediments likely to 

 be found in estuarine systems but free of complicating factors, and 

 to study the effects of natural sediments. This report presents the 

 effects of suspended particles on carbon assimilation of four common 

 phytoplankton species and on the feeding rates of two common 

 copepods . 



Experimental concentrations are typical of those found in estua- 

 rine systems during flooding, storm agitation, dredging, and dredged- 

 material disposal. 



Fine silica sand was added to cultures of the common phytoplank- 

 ters M. luthevij Chlorella sp., Nannoohloris sp., and Stidhooooaus 

 sp., consequently reducing their carbon assimilation by 50 to 90 

 percent, probably by light attenuation. 



Suspensions of Fuller's earth, fine silica sand, or natural sedi- 

 ment caused reductions in the feeding rates of the two copepods 

 tested. Concentrations greater than 250 milligrams 1"-^ caused reduc- 

 tions in the ingestion of radioactively tagged M. luthevi by the 

 copepods E. affinis and A. tonsa. Evidently, nonselective feeding, 

 i.e., taking up all particles indiscriminately, does exist at high 

 particle densities in these copepods. This results in reduced 

 consumption of food particles which, if continued over a long enough 

 period, could cause a serious break in the food chain. However, 

 these experiments were designed to measure feeding rate and were not 

 designed to measure stress on the copepods. Therefore, they cannot 

 be used to predict the exposure time required to cause serious 

 population depletion. 



36 



