exist in polluted areas. Groups composed of higher-order levels of taxonomy are more often used in this 

 context than a single indicator species. The fact that indicator species are not found in certain areas may be 

 due to factors other than environmental condition {i.e., inability to disperse, seasonal absence, or biotic 

 competition; Sheehan 1984). 



Through a mathematical process of determining which components of the benthic community best discriminate 

 between degraded and undegraded sites, the benthic index is composed of the following parameters: diversity, 

 proportional abundance of capitellids, bivalves, and amphipods, and the abundance of tubificids. Each parameter 

 is directly or indirectly related to the condition of the benthic community. Each component of the benthic 

 index can be and has been used individually as an indicator of benthic community condition in various 

 monitoring programs. For our purposes, however, none of the components retains an individual relevance to 

 the management objective. The strength of an indicator like the benthic index lies in the checks and balances 

 associated with combining these components. 



The benthic index does, indeed, indicate if a site has a degraded benthic community and this index is used by 

 EMAP-E to compute the proportion of estuarine area with this subnominal condition. The benthic index was 

 intended to be part of an overall assessment of ecological condition of estuaries that incorporated indicators 

 of biological integrity, sediment and water quality, and aesthetic values. As a component of biological integrity, 

 the benthic index provides insight into one aspect of the biotic community; complementary indicators could 

 be developed for fish, zooplankton, and phytoplankton if sufficient data were available. One step in the 

 validation of the benthic index showed that the benthic index had a greater success rate in classifying degraded 

 or undegraded sites than any of its components did individually. Although the component parameters that 

 make up the benthic index are useful for specific assessments, by combining them, the benthic index provides 

 a more comprehensive assessment of benthic condition without being redundant. 



Guideline 2: Relevance to Ecological Function 



\t 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. 



Benthos are vital to ecosystem structure and function as a food resource for demersal fish and as intermediate 

 links between higher and lower trophic levels. They provide a significant transfer of carbon in the energy 

 dynamics of an estuary, and act as agents of bioturbation and nutrient regeneration (Flint et al. 1982). 

 Benthic organisms often provide the first step in the bioaccumulation of pollutants in estuarine food chains, 

 especially heavy metals. An index of environmental condition based on benthos, therefore, would provide 

 useful information for management decisions based on long-term trend analysis, spatial patterns of enrichment 

 or contamination, or the recognition of "hot spots" exhibited by total defaunation. An ideal indicator that 

 incorporates the characteristics of benthic community structure would be sensitive to contaminant and dissolved 

 oxygen stress and serve as a good integrator of estuarine sediment quality (Scott 1990). 



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