Chapter Three 



Application of the Indicator Evaluation Guidelines to an Index 

 of Benthic Condition for Gulf of Mexico Estuaries 



Virginia D. Engle, U.S. EPA, National Health and Environmental Effects 

 Research Laboratory, Gulf Ecology Division, Gulf Breeze, FL 



This section provides an example of how the Evaluation Guidelines for Ecological Indicators can be applied to 

 a multimetric ecological indicator - a benthic index for estuarine waters. 



The intent of the Evaluation Guidelines is to provide a process for evaluating the utility of an ecological 

 indicator in answering a specific assessment question for a specific program. This is important to keep in 

 mind because any given indicator may be ideal for one application but inappropriate for another. The benthic 

 index is evaluated here in the context of a large-scale monitoring program, specifically EPA's Environmental 

 Monitoring and Assessment Program - Estuaries (EMAP-E). Program managers developed a series of 

 assessment questions early in the planning process and focused the monitoring design accordingly. 



One of the primary goals of EMAP-E was to develop and monitor indicators of pollution exposure and habitat 

 condition in order to determine the magnitude and geographical distribution of resources that are adversely 

 affected by pollution and other environmental stresses (Messer et al. 1 991 ). In its first year of implementation 

 in the estuaries of the Gulf of Mexico, EMAP-E collected data to develop a preliminary assessment of the 

 association between benthic communities, sediment contamination and hypoxia. A benthic index of estuarine 

 integrity was developed that incorporated measures of community composition and diversity, and discriminated 

 between areas of undegraded vs. degraded environmental conditions. In this way, a benthic index would 

 reflect the collective response of the benthic community to pollution exposure or adverse habitat conditions. 



Information gained from monitoring benthic macroinvertebrate communities has been widely used to measure 

 the status of and trends in the ecological condition of estuaries. Benthic macroinvertebrates are good indicators 

 of estuarine condition because they are relatively sedentary within the sediment-water interface and deeper 

 sediments (Dauer et al. 1987). Both short-term disturbances such as hypoxia and long-term disturbances 

 such as accumulation of sediment contaminants affect the population and community dynamics of benthic 

 macroinvertebrates (Rosenberg 1977, Harper ef a/. 1981, Rygg 1986). Many of the effects of such disturbances 

 on the benthos have been documented and include changes in indicators such as benthic diversity, long-lived 

 to short-lived species, biomass, abundance of opportunistic or pollution-tolerant organisms, and the trophic or 

 functional structure of the community (Pearson and Rosenberg 1978, Santos and Simon 1980, Gaston 1985, 

 Warwick 1986, Gaston and Nasci 1988, Gaston and Young 1992). 



The search for an index that both integrates parameters of macrobenthic community structure and distinguishes 

 between polluted and unpolluted areas has been a recent focus of marine and estuarine benthic monitoring 

 programs (Warwick 1986, Chapman 1989, McManus and Pauly 1990). An ideal indicator of the response of 

 benthic organisms to perturbations in the environment would not only quantify their present condition in 

 ecosystems but also would integrate the effects of anthropogenic and natural stressors on the organisms 

 overtime (Boesch and Rosenberg 1981, Messer ef a/. 1991). 



3-1 



