MULTIPLE-FACTOR AND SYNERGISTIC STRESSES 741 



contrast to the osmoregulatory ability of C. crangon, C. allmanni 

 showed a very high degree of osmoconformity, and no difference in 

 blood concentration was observed at different temperatures (5 to 

 15° C). Temperature and salinity did interact to influence the lethal 

 limits of this species. For example, at 5 to 7° C a salinity as low as 

 10\o could be tolerated, but at 21°C, salinities below 25% o were 

 lethal. This response is the reverse of C. crangon where lower 

 salinities were tolerated at higher temperatures. 



Spaargaren (1972) also investigated the effects of temperature 

 and salinity on the osmoregulatory ability of two species of prawns 

 from the Bay of Naples, a region of high salinity throughout the 

 year. At low temperature and high salinity, Palaemon serratus is a 

 strong regulator of osmotic concentration in the body fluids; at low^ 

 salinities conformity is noted. At high temperatures the regulation 

 range is shifted toward lower salinities. 



When comparing the response of these two species with the two 

 species of Crangon previously cited, Spaargaren concluded that 

 L. seticaudata and C. allmanni show similar osmoregulatory re- 

 sponses. Hov/ever, C. allmanni could withstand lower salinities longer 

 at low temperatures, whereas L. seticaudata tolerated reduced 

 salinities longer at high temperatures. This response pattern corre- 

 lated well with conditions normally encountered in their respective 

 habitats. Unlike C. crangon, P. serratus did not show a causal 

 connection between osmoregulation patterns and migration. 

 Spaargaren suggested that the effect of temperature on osmoregula- 

 tion is a secondary adaptation to changing seasonal conditions. 



In contrast, the differential effects of temperature on the 

 osmoregulatory ability of two closely related species of shrimp 

 influence their seasonal distribution. Both species can hyperosmo- 

 regulate in reduced salinity at those temperatures normally encoun- 

 tered during the summer, and they Eire found in estuaries. Although 

 at low temperature this ability to osmoregulate is impaired in both 

 species, Penaeus duorarum is less affected and can overwinter in the 

 cold inshore waters of the Carolina coast (Williams, 1960). 



OTHER PHYSIOLOGICAL PROCESSES 



Other physiological processes also have been studied when the 

 organism is subjected to multiple environmental factors. Duman and 

 DeVries (1974) found that temperature and photoperiod influenced 

 the production of a macromolecular substance that functions as an 

 antifreeze in the blood serum of a fish. From a biogeographic point 



