EFFECTS OF THERMAL EFFLUENT 565 



water sources used in the experiments. It is important to note that 

 the chemical measurements were not made continuously during the 

 experiments. 



DISCUSSION 



The simulation experiments were designed to assess combined 

 effects of temperature and other water-quality characteristics of two 

 representative thermal-effluent regimes. Absence of significant dif- 

 ferences in chemical constituents among control and thermal-effluent 

 water sources and the low concentrations of potentially toxic 

 chemicals suggest that the significant effects observed in the 

 treatment groups were caused primarily by temperature conditions. 

 The results do not rule out the possibility of direct or synergistic 

 effects involving chemical conditions, however. 



Survival of both Strongylocentrotus species was adversely 

 affected by the simulated effluent regime of station 2 but apparently 

 was not affected by the less severe effluent conditions of station 3. 

 Similarly, growth and body condition of both species were adversely 

 affected by the simulated effluent regime of station 2 and affected to 

 a lesser extent by that of station 3. 



Results of the station 2 experiment show that survival and 

 growth of large adult S. purpumtus and S. franciscanus generally 

 were affected to a greater extent than those of the smaller size 

 groups. This probably indicates more severe metabohc limitations for 

 large sea urchins at high temperatures (Johaiisen and Vadas, 1967; 

 Ulbricht and Pritchard, 1972; Ulbricht, 1973). The results also 

 indicate that all size groups of both species could not tolerate 

 temperatures consistently above 22° C. Loss of spines and failure to 

 hold the spines erect by both species, which were very common in 

 the treatment tanks following prolonged exposure to temperatures 

 above 22° C, usually preceded death of the individuals. This did not 

 occur in the control tanks. Ebert (1968) and Baker (1973) showed 

 that spine abrasion and loss affect growth markedly, and presumably 

 both are indications of poor condition. 



In a given effluent regime, effects on survival and growth 

 generally were more severe for S. franciscanus than for S. purpumtus. 

 Strongylocenti-otus purpuratus occurs in shallow subtidal and inter- 

 tidal areas, and S. franciscanus inhabits only shallow to deep subtidal 

 areas in southern California. Thus S. purpuratus might be expected 

 to show somewhat greater tolerance to high temperatures than 

 S. franciscanus because of its natural exposure. 



