EFFECTS OF INCREASED WATER TEMPERATURE 



ON DAPHNIA PULEX 



Donovan R. Craddock^ 



ABSTRACT 



Techniques were developed to study the effects of increased water temperature on certain zoo- 

 plankters; specific studies were conducted on Daphniapulex, an abundant and important zooplankter 

 of the lower Colimibia River Study methods simulated prolonged exposure to constant high tempera- 

 tures in thermal discharges and short exposures to increased temperatures in condensers of cooling 

 systems. Effects were evaluated on the basis of survival and reproduction for periods ranging from 34 

 to 90 days. The time to death of 50% of the D. pulex, both mature and young, was less than 24 h at 

 temperatures above 27°C. Temperatures of 27°C and below required an exposure of at least 192 h to 

 cause 50% mortality. The young females were more tolerant of temperature increases than older 

 females. The greatest reproduction by older females was at the control temperature (15°C), 

 whereas reproduction by the young females was low at lower temperatures. No reproduction occurred 

 above 27°C. 



Two groups of D. pulex (one from the Seattle, Wash., area and the other from the Columbia River) 

 studied at increased temperatures for prolonged periods revealed similar patterns of survival and 

 reproduction, but the Columbia River group appeared less tolerant of increased temperatures. A 

 short exposure (15 min) to increased temperatures up to 30°C had little effect on survival and 

 reproduction. 



It was concluded that temperatures should not exceed 26° or 27°C for prolonged periods or 30°C for 

 more than 15 min to protect D. pulex populations in the river 



The lower reaches of the Columbia River (below 

 Portland, Oreg.) support extensive and valuable 

 commercial and sport fisheries as well as other 

 types of recreational activities. This section of the 

 river is also becoming increasingly industrial- 

 ized. Associated with the industrialization is 

 1) the extensive use of river water for cooling pur- 

 poses and 2) the discharge of heated cooling water 

 back into the river. This increasing use of the 

 river for industrial cooling has created concern 

 that the aquatic biota is endangered by thermal 

 pollution. North and Adams (1969) have de- 

 scribed thermal conditions at outfalls and in con- 

 denser cooling systems of some California plants. 

 They pointed out that increases of +10°F (5.6°C) 

 above normal are considered significant biologi- 

 cally at all seasons of the year. Coutant (1970) 

 presented a diagram of the hypothetical time- 

 course of acute thermal shock to any organism 

 entrained in condenser cooling water systems 

 that indicates they could be exposed to the 

 maximum increase (10.8°C) for at least 9 min in 

 diffuser systems and to substantial increases 



from 12 to 20 min in the discharge canal system. 

 He also noted the average temperature rise re- 

 ported is about 10.8°C but may be as great as 

 16°C. 



I studied the effect of increased water tempera- 

 tures on one of the abundant cladocerans of the 

 area, Daphnia pulex. It has been found to be 

 important in the diet of valuable stocks of 

 juvenile chinook salmon, Oncorhynchus tshawyt- 

 scha, in certain seasons of the year (Craddock et 

 al.2). Cladocerans may be thermally affected by a 

 thermal nuclear power plant where, along with 

 other zooplankton, they may be entrained with 

 intake cooling water and pass through the con- 

 denser cooling system encountering sudden and 

 sizable temperature increases. Increased cooling 

 water use by industrial and power plants may 

 increase the temperature of certain areas of the 

 river (bays and eddies) for extended periods and 

 also affect zooplankton. 



The specific objectives of the study were: 1) to 

 develop techniques for laboratory study of ther- 

 mal effects on zooplankton and 2) to assess the 



'Northwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, 2725 Montlake Boulevard East, Seattle, WA 

 98112. 



^Craddock, D. R., T. A. Blahm, and W. D. Parente, 1974. Occur- 

 rence and utilization of zooplankton by juvenile chinook salmon 

 in the lower Columbia River Unpubl. manuscr Northwest Fish. 

 Cent., Natl. Mar. Fish. Serv., NOAA, Seattle, Wash. 



Manuscript accepted October 1975. 

 FISHERY BULLETIN; VOL. 74, NO. 2, 1976. 



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