There was also some indication, based on observations of gonadal 

 condition, that oysters from the Abers had an altered reproductive cycle 

 compared to reference oysters, possibly including near complete reproduc- 

 tive suppression for one year after the spill. Sample sizes and frequen- 

 cies were not great enough to demonstrate this convincingly. 



II. Petroleum Contamination and Biochemical 

 Indices of Stress in Oysters and Plaice 



The most obvious immediate biological effect of the Amoco Cadiz 

 spill was a very large kill of benthic estuarine and coastal marine 

 organisms (Cross et al. , 1978). The rate of recovery of these benthic 

 communities would depend on the rate and success of reproduction by the 

 surviving animals in the affected area and on the success of recruitment 

 from adjacent unpolluted areas. The resident benthic fauna in the oil- 

 impacted area which survived the spill were undoubtedly severely stressed. 

 Because of the heavy contamination of the estuarine sediments with oil 

 it is highly probable that the surviving resident benthic fauna would 

 continue for some time to be stressed and potential immigrants to the 

 estuaries would be subjected to stress as they settled there. 



Considerable research has been conducted in recent years on sub- 

 lethal physiological stress responses of marine animals to oil and other 

 types of pollution (Neff et al. , 1976a; Anderson, 1977; Johnson, 1977; 

 Patten, 1977; Neff, 1979; Thomas et al., 1980; Neff and Anderson, 1981). 

 A variety of sublethal physiological and biochemical responses to 

 pollutant stress have been described. In an ecological perspective, 

 the net effect of chronic pollutant stress on marine organisms is to 

 shunt limited energy resources away from growth and reproductive 

 processes to maintenance and homeostatic functions. The result is 

 decreased growth, fecundity and reproductive success in the stressed 

 population. A variety of biochemical parameters are altered in stressed 

 animals and reflect the stress-induced changes in energy balance and 

 partitioning. These biochemical parameters can be used as an index 

 of pollutant stress in marine animals. 



Biochemical indices of pollutant stress chosen for use in this 

 investigation include hemolymph glucose concentration and adductor 

 muscle-free amino acids in oysters; and blood glucose and cholesterol, 

 liver glycogen and ascorbic acid, and muscle-free amino acids in plaice. 

 We have discussed elsewhere the rationale for using these parameters as 

 indices of pollutant stress (Thomas et al. , 1980, 1981 a,b). 



285 



