Guideline 2: Relevance to Ecological Function 



It must be demonstrated that the proposed indicator is conceptually linked to the ecological function of 

 concern. A straightforward link may require only a brief explanation. If the link is indirect or if the 

 indicator itself is particularly complex, ecological relevance should be clarified with a description, or 

 conceptual model. A conceptual model is recommended, for example, if an indicator is comprised of 

 multiple measurements or if it will contribute to a weighted index. In such cases, the relevance of each 

 component to ecological function and to the index should be described. At a minimum, explanations and 

 models should include the principal stressors that are presumed to impact the indicator, as well as the 

 resulting ecological response. This information should be supported by available environmental, ecological 

 and resource management literature. 



Performance Objectives 



1. Demonstrate conceptual linkages between ecosystem components and principal stressors. 



2. Demonstrate conceptual linkages between principal stressors believed to cause impairment with 

 respect to the societal value of interest, ecosystem responses to these stressors, and the indicator 

 (or its components). 



Basic relationships between major structural components and processes can be graphically represented 

 (Figure 4-1, modified from Hughes etal. 1994) to illustrate possible routes of exposure from anthropogenic 

 stressors. This diagram also points out the location and functional roles of fish assemblages to demonstrate 

 those stressor-response relationships that can be effectively monitored with a fish assemblage indicator. 

 Fish assemblages can be used to assess condition both in the water column and bottom habitats, and can 

 provide information from multiple trophic levels. 



More specific hypotheses have been developed regarding the relationship of indicator metrics with 

 anthropogenic stressors (Fig. 4-2). This approach is based on a model originally conceived by Karr et al. 

 (1 986). We have modified the model to organize it by types of major stressors (following terminology presented 

 in U.S. EPA 1997). This representation shows direct linkages between individual metrics and each type of 

 stressor, and helps to illustrate the diagnostic capability of the indicator since different scores for individual 

 components can be associated with responses to certain groups of stressors. 



The suite of candidate metrics represent those selected after a screening process to eliminate those that 

 were not responsive to hypothesized stressors of interest, were redundant in their information content, or 

 were otherwise not suited for application in the proposed monitoring framework and/or geographic region of 

 interest. The metrics shown in Table 4-5 provide information about the ecological relevance of each component 

 metric; consequently Table 4-5 could be considered one type of conceptual "model" of the indicator. It 

 demonstrates anticipated responses of component metrics to various types of stressors, based on 

 characteristics offish assemblages in environmentally degraded systems described by Fausch etal. (1990). 



Further demonstrating the diagnostic capability and potential discriminatory ability of the indicator (addressed 

 more completely as part of Guideline 1 2), Figure 4-3 shows the range of response for each individual metric, 

 based on summaries in Angermeier and Karr (1986) and Karr (1991). Some metrics {e.g., species richness) 

 will exhibit a response over the entire range of condition, while others help to discriminate either very good 

 condition (e.g., sensitive species richness) or very poor condition (e.g., proportion of tolerant individuals). 



4-7 



