Physiological indicators of fitness in benthic invertebrates: a useful measure for ecological health assessment and experimental ecology

Physiological indicators of fitness present a measure of an organism's response to a changing environment. An analysis of how these organisms allocate and store their energy resources provides an understanding of how they cope with such environmental changes. Each individual has to balance the investment necessary to acquire a certain resource with the energy gained by it. This trade-off can be monitored by measuring several physiological indicators of fitness such as energy storage components, metabolic state or RNA/DNA ratio. Because environmental adaptations and ecological strategies of survival are best examined within the natural environment, our research has to rely on the physiological indicators that are easily accessible in the field. The physiological indicators presented here are significant for an individual's fitness and in turn lead to reliable values in field-collected samples. Based on our own expertise and on a literature survey, the physiological relevance of the presented indicators is explained. Furthermore, some consideration to the analytical methods used to obtain the physiological indicators is given, and possible errors introduced at the sampling site and during the laboratory procedures are discussed. This work demonstrates that the integration of ecological and physiological expertise facilitates the identification of future ecological problems much earlier than separate approaches of both disciplines alone.