RESPONSES OF ICHTHYOPLANKTON 795 



It was assumed that the mechanical effect of entrainment could 

 be assessed by comparing samples taken at plant intakes with 

 those taken at discharges. Similarly, the stresses of temperature 

 change and biocide concentration could be isolated by sampling 

 during plant outages and during chlorination. Marcy (1973) used 

 these techniques to estimate entrainment mortality as 100% for 

 clupeid larvae at the Connecticut Yankee nuclear power plant; but 

 Lauer and co-workers (1974) showed significant mean differences in 

 survival of Morone sp. larvae of only 5 to 39% between intake and 

 discharge samples at the Indian Point nuclear power plant. 



Widely divergent estimates of entrainment mortality are caused 

 by several factors. First, standard methods for mortality evaluation 

 have not been established; second, different power-plant designs 

 result in varying stress profiles; and third, the ability of an organism 

 to tolerate stress is seasonal, age specific, and species specific. In 

 addition, the inherent temporal and spatial "patchiness" of natural 

 populations frequently precludes statistically adequate samples of 

 each species for in-plant comparison (Wrenn, 1976). Most impor- 

 tantly, collection-induced mortality (death caused by impingement 

 on collection nets) may be high enough to totally eliminate the 

 calculation of plant-induced mortality (O'Connor and Schaffer, 

 1977). 



These problems prompted laboratory investigations that sub- 

 jected plankton to simulations of the individual stresses encountered 

 during power-plant passage. Schubel, Koo, and Smith (1976) 

 exposed striped bass eggs and larvae to several thermal stress regimes. 

 Thermally induced mortalities were apparent after short-term expo- 

 sures to temperatures 15°C above an ambient of 20°C. Morgan and 

 co-workers (1976) developed a system for exposing striped bass eggs 

 and larvae to shear stress. Although their LD5 values exceeded 

 those occurring during power-plant passage, the possibility of 

 shear-induced damage to entrained bass was considered real 

 (Ulanowicz, 1975). 



Rapid pressure changes, especially exposure to subatmospheric 

 pressure, may be lethal to striped bass eggs and larvae (Beck, Poje, 

 and Waller, 1975). Gas bubble disease, caused by thermal and/or 

 pressure changes, is recognized as problematic at several existing 

 power-generation facilities (Harvey, 1975). 



Biocides, particularly the various dissolved forms of chlorine, 

 have measurable lethal and sublethal effects on phytoplankton, 

 zooplankton, and fishes (Brungs, 1973; Eppley, Renger, and 

 Williams, 1976; Zilhch, 1972). 



