742 VERNBERG 



of view, it was interesting to note that apparent genetic differences 

 exist between Alaska and California populations of Anoplarchus 

 purpurescens in that the California fishes were unable to produce 

 antifreeze when acclimated to cold temperatures. 



Endocrine changes can result when levels of environmental 

 factors are changed. For example, McKeown and Peter (1976) found 

 that photoperiod and temperature influenced the release of prolactin 

 from the pituitary gland of the goldfish, Carassius auratus. In fiddler 

 crabs, Silverthorn (1975) reported that temperature and thermal 

 acclimation affected the production of a "hormone-like" factor, 

 which influenced oxygen consumption. Regeneration and molting of 

 fiddler crabs are influenced by light, temperature, and salinity (Weis, 

 1976). 



Most of the previous studies stressed the interaction between an 

 organism and its environment. However, an organism is part of a 

 population, which in turn is part of an assemblage of species called a 

 community. In evaluating the potential effects of altered environ- 

 ments, we need to have better techniques to predict effects on 

 communities. Recently Vemberg, McKellar, and Vernberg (1978) 

 proposed a simple population model to predict the influence of the 

 toxicity of a particular pollutant and environmental fluctuation on a 

 natural population. 



SUMMARY 



In summary, studies of multiple environmental factors and their 

 interactions have involved many diverse organisms inhabiting aquatic 

 systems. These studies have included numerous abiotic factors, both 

 natural and man-induced, and biotic factors. An organism is faced 

 with a complex environment, and it is a natural evolution in our 

 scientific thinking to investigate multiple factor effects and interac- 

 tions in terms of organismic responses. We need more coordinated 

 field and laboratory studies to answer environmentally oriented 

 questions. A better definition of the characteristics of the microen- 

 vironment in which a species lives is required to design laboratory 

 studies that simulate the environment. Experiments need to be 

 designed to help explain and describe the functional mechanisms 

 involved in an organism's responses to multiple factors. As we begin 

 to understand one level of complexity, we encounter an entirely 

 different and higher level of complexity. It is the excitement of 

 trying to understand the next higher level of complexity that forces 

 us to continue research. 



