the condenser cooling systems of thermal nuclear 

 power plants where they would encounter a siz- 

 able thermal shock. 



Zooplankton entrained in a power plant cooling 

 system located in a saltwater environment could 

 be subjected to an average temperature increase 

 ranging from 12° to 16°C (Coutant 1970). In some 

 plants, the increases are as high as 19°C. 

 Maximum temperatures would be reached in <1 

 min in the condenser and would be maintained for 

 at least 9 min in a diffuser discharge system and at 

 almost maximum temperature, for possibly up to 

 21 min, in a discharge canal system. Other factors 

 that could cause damage to euphausiids in a cool- 

 ing system include pressure changes, abrasion, 

 and toxic substances. 



I simulated the thermal conditions encountered 

 in a cooling system to determine the temperature 

 increases that E. pacifica could resist for short 

 periods (15 and 30 min). This information can be 

 applied to the design and operation of cooling sys- 

 tems to protect zooplankton. 



These studies were conducted at the National 

 Marine Fisheries Service's Mukilteo Field Sta- 

 tion, Washington, during 1971-74. 



Methods 



Euphausiids for these experiments were cap- 

 tured during daylight hours in Port Gardner of 

 northern Puget Sound, Washington, between 

 Mukilteo and Gedney Island. A 10-m net with 

 333- /Lim aperture Nytex^ netting was towed at a 

 depth of about 60 m at a rate of 4.6 km/h. Tows 

 were usually of a 5-min duration. A 946-ml glass 

 bottle was used as a collection receptacle to protect 

 the animals. 



As soon as the net was retrieved, the catch (con- 

 sisting mostly of euphausiids) was divided be- 

 tween two or three 18.9-1 Nalgene carboys filled 

 with fresh seawater and covered with black 

 polyethylene sheeting to exclude light. The catch 

 was taken immediately to the laboratory, usually 

 <2 km away, where the euphausiids were sepa- 

 rated from other organisms in the catch and placed 

 in 5-1 battery jars (23 x 14 x 17 cm) of fresh 

 seawater. They were then placed in a dark, low- 

 temperature incubator set at their previous am- 

 bient seawater temperature where they were held 

 before and after testing. 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



The test apparatus consisted of a series of 5-1 

 battery jars filled with seawater that were main- 

 tained at specific temperatures by immersion 

 heaters activated by temperature controllers 

 (Craddock 1976). The jars were in a primary bath 

 of running seawater at ambient temperature and 

 air was continuously bubbled into the jars to 

 eliminate stratification. 



Test containers for holding the euphausiids 

 were polyvinyl chloride boxes of 5 cm^ with two 

 opposing sides having 4-cm diameter cutouts cov- 

 ered with 333-/xm aperture Nytex netting to allow 

 free water circulation. Styrofoam glued to the 

 boxes provided flotation (Figure 1). 



The temperature-time regime to which the 

 euphausiids were subjected was designed to simu- 

 late their passage through a condenser cooling 

 system. Coutant (1970) depicted a hypothetical 

 temperature-time course for organisms entrained 

 in condenser cooling water and discharged by dif- 

 fuser or by discharge canal. An animal could be 

 subjected to maximum temperature increases for 

 up to about 10 min in a diffuser and up to about 20 

 min in a discharge canal system. Relative to his 

 study, I chose 15- and 30-min exposure tests to 

 represent the longest exposure that might be en- 

 countered. To simulate these conditions, test 

 euphausiids were subjected to a given tempera- 

 ture ranging from 14° to 29°C for 15 or 30 min, 

 starting from temperatures of 11° or 9°C. 

 Euphausiids used as controls were always kept at 

 the prevailing ambient temperature (approxi- 

 mately the same as the subsurface temperature of 

 Puget Sound). Five 15-min tests were conducted 

 during June- July 1971, four 30-min tests were run 

 during June-August 1971, and two 15-min tests 

 were made during March-April 1974. 



The euphausiids were held 18 h or longer before 

 testing to eliminate handling mortality and were 

 then counted into test containers in seawater 

 while the secondary baths were being raised to the 

 test temperatures. Either 5 or 10 euphausiids 

 were tested in each container, depending upon the 

 numbers available for that particular test. 



When all secondary baths became equilibrated 

 at the test temperatures, the boxes containing the 

 euphausiids along with a small amount of water 

 were placed in the test baths. Water in the test 

 containers was within 0.5°C of the test tempera- 

 ture in an average of 28 s after introduction. At the 

 end of the exposure period, the test boxes contain- 

 ing the euphausiids were removed from seawater 

 at the test temperature and placed in fresh seawa- 



896 



