211 

 EUGENE P. HAYDU 

 development of these larvae are adversely affected by 

 even very low concentrations of SWL. The report goes on 

 to suggest that other forms of aquatic life, some of which 

 are closely related, others not so closely related, are 

 similarly affected. The report does not provide data to 

 support this suggestion, however. It has been proposed 

 that due to its sensitivity and reproducibility the oyster 

 larval test be adopted as a standard test for establish- 

 ing the toxic levels of all suspect pollutants. Such a 

 proposal ignores the general experience of biologists of 

 the great diversity in the sensitivity of various species 

 to environnnental change, whether natural or induced. An 

 example of this can be shown by the range of A8-hour 



median tolerance limit values found for an organophos- 

 phorus insecticide. 



For shrimp, the median tolerance limit 

 value was 0.0002 parts per million. For fish it was 0.01 

 parts per million. And for the oyster it was 0.3 parts 

 per million. This represents a one thousand five hundred- 

 fold difference in the response of three different species 

 to the same material. 



In long-term laboratory studies of the 

 oyster-mud flat community which I carried out during the 



1950's, the productivity of clams from the larval stage 



