feeding interval for E. affinis and the 125-minute interval for A. 

 tonsa, we believe that the reduced ingestion of cells (reduced cell 

 filtering rate) was caused by the high numbers of sediment particles 

 which filled the gut and not by any reduction in the water filtering 

 rate by the copepods. 



Reductions (approximately 50 to 60 percent) in numbers of cells 

 ingested by zooplankton in the presence of suspended nonfood 

 particles at concentrations which are typical of "high" normal back- 

 ground level in Galveston Bay (Masch and Espey, 1967), storm agita- 

 tion in the Chesapeake Bay, or during dredging and disposal 

 activities, have important biological implications. The effects 

 of a 50- to 80-percent decrease in energy flow from primary produc- 

 tion to the secondary production level would have adverse effects on 

 the nutrition and reproduction of zooplankton standing stocks as 

 these are the food supply of the larval and juvenile stages of many 

 important estuarine vertebrates and invertebrates. In addition, the 

 extreme sensitivity of these juvenile stages to suspended solids has 

 been demonstrated. 



Supporting evidence for these implications is provided by the 

 work of Paffenhofer (1972) who reported serious problems of nutri- 

 tion, survival, and reproduction when Catanus helgolandicus was 

 exposed to suspensions of "red mud" (the residue, mostly iron oxide, 

 after the extraction of aluminum from bauxite) . Mortality of C. 

 helgolandious juveniles (copepodite) was not high (9.6 to 16 percent) 

 even though they ingested these particles. However, the copepods 

 were weakened and were not able to make their characteristic sudden 

 escape movements because of reduced ingestion of phytoplankton cells 

 when red mud was present. They ingested large quantities of 

 particles, but did not obtain sufficient nutrient material to develop 

 as well as did the control organisms. There was a reduced growth 

 rate and lower weight in copepodite stages exposed to red mud. 

 Ovary development in females was much reduced because of insufficient 

 energy reserves. Energy reserves are stored as fat droplets in the 

 female. None of the females exposed to red mud had fat droplets but 

 most of the control females did (Paffenhofer, 1972). 



These results and those of Paffenhofer do not lend support to 

 Wilson's (1973) contention that selective feeding predominates in 

 A. tonsa. Most probably nonselective feeding, i.e., taking all 

 particles indiscriminately, does exist at high particle densities. 



III. SUMMARY 



Questions about the effects of suspended sediments on estuarine 

 organisms arise when dredging is planned and environmental impact 

 statements are prepared. It is difficult to assess the effects of 

 particle size and concentration of suspended solids on estuarine 

 organisms independent of, and in addition to, complicating factors 



35 



