exposure. Estimated LS^q values for striped bass yold-sac larvae were 785 
dynes/cm 2 and 300 dynes/cm 2 for 1 and 4 minute exposures, respectively. 
White perch yolk-sac larvae were more vulnerable, their LS^g values were 415 
dynes/cm 2 and 125 dynes/cm 2 for 1 and 4 minute exposures respectively. 
Calculated average shear force in the Chesapeake and Delaware Canal, where 
striped bass eggs occur, was only 13.8 dynes/cm~, far below the estimated 
LS 50 values. The authors (17) also related these LS 5Q values to expected shear 
forces of 72-230 dynes/cm 2 that might be present in the water box of a power 
plant cooling system. The 230 dynes/cm 2 shear approaches the 4 minute LS 5 q 
value for striped bass yolk-sac larvae and exceeds it for white perch. 
Chipman (27) reviewed literature on effects of naturally occurring ionizing 
radiation on marine animals. He found no convincing evidence to demonstrate 
that marine animals showed any response, functional or structural, to ionizing 
radiation levels present in the environment. In marine animals observable 
effects are primarily at the cellular level, and the radiation tolerance is a 
function of the dose-rate, time patterns of exposure and metabolic rate; 
consequently, effects would be most evident during embryonic development 
(27). 
FUTURE RESEARCH 
Both laboratory and transitional laboratory-field studies will extend our 
knowledge of environmental effects on larval stages of marine fish. A recent 
colloquium on larval mortality and the recruitment problem has defined some 
areas in need of research (48). Emphasis of that colloquium was to advocate 
research related to starvation and predation, the two factors that probably have 
the greatest effect on recruitment of year classes. Environmental stresses from 
man’s activities are additional threats, particularly to estuarine species or those 
found over the continental shelf. Pollution effects on embryos can cause gross 
functional and structural abnormalities that may produce yolk-sac larvae 
incapable of surviving to the exogenous feeding stage (81). Larvae can be 
equally vulnerable to deleterious effects of pollutants, and their responses to 
this stress may be reflected in impaired predator avoidance behavior and food 
capture efficiency. More subtle effects could involve functional disruptions of 
metabolism, temperature and salinity tolerance, and enzyme-substrate 
interactions. Both direct and indirect effects of environmental modification on 
recruitment need to be determined. 
The ability to culture larvae widens the possibilities for laboratory research 
which will help interpret results of field studies. The larval stage is a dynamic 
one, characterized by fast growth, sometimes spectacular developmental 
changes, and frequent shifts in behavior. Typical toxicity bioassays, where 
times to 50 percent mortality are estimated, may not be the best approach to 
194 
