waste into coastal waters and the amount of 

 waste are not known. 



Radioactive waste 



The disposal of radioactive waste in the sea 

 presents a new threat to shellfish resources; the 

 concentration of radioactive materials in the bodies 

 of water-filtering mollusks may render them unsafe 

 for human consumption. Chipman (1960) showed 

 that many of the radionuclides added to sea water 

 become associated with both living and nonliving 

 particles suspended in water. Experiments at the 

 Radiobiological Laboratory of the Bureau of 

 Commercial Fisheries at Beaufort, N.C. (Chipman, 

 Rice, and Price, 1958; Rice and Willis, 1959)! 

 indicated that nearly all fission product radio- 

 nuclides, and also those of the trace metals, that 

 are added to algal cultures associate with marine 

 plankton used by shellfish. If continuously 

 available, radioactive particles may accumulate in 

 filtering organs, on the body surface, and in the 

 digestive tract of oysters and other shellfish. 



The accumulation of radioactive pollutants in 

 coastal waters is likely to become higher than it is 

 at present if the current practice of dumping radio- 

 active wastes from nuclear plants and many 

 research institutions close to shore or in the lower 

 parts of a river (Columbia River) continues 

 indefinitely. This unwelcome possibility must be 

 watched carefully, and a great deal of research 

 remains to be done before a clear picture emerges 

 of the potential dangers associated with the dis- 

 posal of low level radioactive waste and the con- 

 tamination of our fisheries resources. 



To evaluate the effect of pollution on the pro- 

 ductivity of oyster bottoms the following data are 

 needed: the type and extent of pollution in rela- 

 tion to the total volume and movements of water 

 in an estuary; the stability of the pollutant; its 

 physiological action; the effect of long-continued 

 exposure of oysters to low concentrations; and the 

 determination of the lethal concentration of a 

 pollutant killing 50 percent of a population, the 

 so-called LD 50. 



COMBINED EFFECT OF ENVIRONMENTAL 

 FACTORS 



Known effects of any single factor of tlie environ- 

 ment do not give a true picture of tlie situation 

 found in nature. Factors of the environment 

 always act jointly. One serious weakness of 

 many ecological studies of marine populations 

 is the tendency to correlate the results of biological 



FACTORS AFFECTING OYSTER POPULATIONS 



observations with one or possibly two selected 

 factors of the environment, such as temperature, 

 salinity, or hydrography, and to disregard the 

 effect of others. In reality, any factor can exert 

 its effect only in conjunction with others. It 

 is impossible to separate the effect of chemical 

 changes caused by a pollutant from the move- 

 ments of water and from the effects of the pollu- 

 tant on the food chain. Changes in the character 

 of a bottom brought about by sedimentation can- 

 not be separated from changes in sea water 

 chemistry, or the food chain. An increase in the 

 salinity of water encourages the invasion of 

 grounds by some competitors and predators, 

 while lowered salinity forms a barrier to inroads 

 by starfishes and drills. 



The combined action of several factors pro- 

 duces a far greater effect than that caused by any 

 single factor. Findings of what effects combined 

 factors have on agricultural plants (Riibel, 1935) 

 are fully applicable to conditions affecting aquatic 

 animals. So far, however, no adequate studies 

 have been made on the problem of measm-ing the 

 joint effect of several factors of aquatic environ- 

 ment. The relationship of all factors probably 

 can be expressed by a very complex formula of the 

 type developed by Riley (1947) for seasonal 

 fluctuations of phytoplankton populations in 

 New England coastal waters. The very com- 

 plexity of a formula of this type precludes its 

 usefulness for the practical purpose of evaluating 

 conditions on oyster bottoms. The oyster biolo- 

 gist is often confronted with the necessity of 

 expressing his opinion on the quality of the oyster 

 beds. His impression is given in general, non- 

 specific terms as adequate, good, very good, 

 marginal, etc., which do not disclose the reasons 

 for a particular evaluation. 



My proposed method of scoring eliminates the 

 uncertainty of personal impressions and assigns 

 to each factor a value which indicates the degree 

 of its effectiveness on a given- population of 

 oysters. The method has been applied success- 

 fully in the evaluation of oyster bottoms in New 

 England, the south Atlantic coast, and in some 

 Gulf States (Galtsoff, 1959). It has been already 

 stated above (p. 399) that the optimal condition 

 of ex-istence with reference to a single positive 

 factor can be assigned the numerical value of 10. 

 Degrees of inadequacies are given numerical 

 values in descending numbers from nine to one. 

 Negative factors are treated in much the same 



445 



