734 VERNBERG 



larval stages did not show a progressive increase in tolerance to 

 temperature or low dissolved oxygen with development, the mega- 

 lops is relatively insensitive to changes in oxygen concentration with 

 temperature. In general, these larval stages appear to have the 

 capacity to tolerate a wider range of temperature and oxygen 

 conditions than they encounter in the natural environment. 



The interaction of abiotic and biotic factors can influence 

 measures of tolerance. For example, Rippingale and Hodgkin (1977) 

 reported that the brackish- water copepod Sulcanus conflictus is 

 rarely found in salinities above 25%o. Yet in laboratory studies this 

 species will thrive in higher salinities if excess food is available. It is 

 suggested that the high energy demands for osmoregulation are not 

 met in natural field conditions. Another example of a biotic and 

 abiotic interrelationship was reported by Yocom and Edsall (1974). 

 Whitefish (Coregonus clupeaformis) were acclimated to different 

 temperatures and subjected to a thermal shock. The vulnerability of 

 these animals to the biotic factor of predation was assessed. 

 Thermally shocked fry were more vulnerable to capture by perch 

 than were unshocked specimens. Response to multiple factor 

 exposure occurs at the tissue level. This fact has been well 

 demonstrated by a comparison of effect of temperature acclimation 

 and salinity on isolated gill tissue of two estuarine species of bivalves. 

 The gill of the oyster Crassostrea virginica is more resistant to low 

 salinity than is the gill from scallops (Vemberg, Schlieper, and 

 Schneider, 1963). 



Wallis (1976) has published a simple multifactorial model using 

 response-surface analysis for studies relating to power-station cooling 

 systems. He incorporated salinity, temperature, temperature shock, 

 exposure time, and mortality responses as well as some sublethal 

 effects. 



LARVAL DEVELOPMENT AND GROWTH 



Various papers have dealt with the effects of environmental 

 factors on the development of embryos and larvae. Alderdice and 

 Forrester (1968) demonstrated that developmental abnormalities 

 occurred in Parophrys uetulus eggs when exposed to certain 

 temperature— salinity combinations (Fig. 5). The effects of cadmium 

 and salinity on the larval development of two estuarine crabs, 

 Rhithropanopeus harrisii and Callinectes sapidiis, when subjected to 

 either constant or cycling temperature, were reported by Rosenberg 

 and Costlow (1976). Cycling temperature appeared to lengthen 



