DAHLHOFF, E.P.: Biochemical and physiological indicators of metabolic variability in rocky intertidal organisms

Comparative physiologists have long been interested in the relationship between metabolic activity and environmental variation. Rocky intertidal animals have been central in these studies. They experience large spatial and temporal variations in a number of environmental conditions that affect physiological processes and are highly amenable to experimental manipulation. Many physiologists have demonstrated strong, positive relationships between indices of metabolic activity (such as metabolic rate, activity of metabolic enzymes, and RNA:DNA ratios) and variation in temperature or food availability under controlled (usually laboratory) conditions. Recent studies have begun to effectively use physiological measurements of metabolic processes in an ecological context. I will describe three examples of such studies. I will show that RNA:DNA ratios may be used as effective indicators of dietary status for suspension-feeders responding to rapid changes in food availability. I will discuss the use of enzyme activities to index the metabolic rate of invertebrates living in distinct rocky intertidal communities. Finally, I will describe the effects of natural and experimentally manipulated variation in temperature and food availability on the physiology of a predatory whelk. These studies illustrate the great promise, as well as underscore some key considerations, of using biochemical and physiological indicators of metabolic activity to address previously intractable questions in marine ecology.