MULTIPLE-FACTOR AND SYNERGISTIC 

 STRESSES IN AQUATIC SYSTEMS 



F. JOHN VERNBERG 



Belle W. Baruch Institute for Marine Biology and Coastal Research, 



University of South Carolina, Columbia, South Carolina 



ABSTRACT 



Most studies on the adaptation of aquatic systems to environmental fluctuations 

 have dealt with the responses of an organism to variation in a single factor, while 

 other factors are kept constant and usually at optimal levels. This is a logical 

 approach and has resulted in a good understanding of response mechanisms of 

 the whole organism, tissues, and cellular components. However, organisms 

 typically are exposed to a complex of factors, with two or more factors varying 

 at the same time. The question is, "How does the complex machinery of either 

 an organism or a multiorganismic system deal with complex environmental 

 fluctuations?" To understand the ability of a biological system to survive in its 

 ecological setting, we must direct our attention to an analysis of multiple factor 

 effects and interactions both under laboratory conditions and in the field. To be 

 ecologically significant, experiments must be designed to simulate conditions of 

 the system's "real world." Unfortunately this is difficult to achieve because, for 

 example, (1) detailed analyses of the microenvironmental conditions experi- 

 enced by organisms or systems are, with few exceptions, lacking, and 

 (2) simultaneous vai-iation in several distinct factors is both technically difficult 

 and expensive to achieve in the laboratory. Field studies are difficult because of 

 the complexity of biological systems, the lack of undisturbed areas for long-term 

 study, and the need for a multidisciplinary team of researchers. Fortunately 

 some advances have been made v/ith the help of the sophisticated statistical and 

 computer techniques required to analyze the resultant complex data. 



Understanding the nature of the functional responses of organisms to 

 environmental changes is one of the challenges facing every new^ 

 generation of biologists. Aristotle wrote about the adaptive responses 

 of intertidal animals. Pliny the Elder was well schooled in the 

 response physiology of many species. He reported that the simplest 

 way to capture the exotic and wily unicorn was to station a virgin 



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