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Benthic Habitat Mapping
Benthic Indices
Different "benthic indices" have been developed in recent years to assess environmental conditions and benthic habitat quality in estuarine and marine systems at regional scales (Diaz et al. 2004). The growth in the number of indices has been fueled largely by the desire to distill an often-bewildering array of environmental data into a single numeric score or category, which can be readily understood by non-specialists within a "good" versus "bad" continuum. Index of Biotic IntegrityThe original "Index of Biotic Integrity" (IBI) was based on combining several different attributes or "metrics" of a given population or community into a single value indicative of habitat quality or ecosystem condition (Karr 1981). A metric was defined as an attribute of a community (e.g. number of species, number of individuals, etc.) that changes in some predictable way with increased human influence. The IBI approach placed emphasis on simultaneously incorporating several metrics that reflect different aspects of community composition, functional organization, trophic structure, or biotic interactions. By using a combination of metrics, the IBI becomes sensitive to a much wider array of human-induced stresses than any single metric by itself. The original IBI was developed to evaluate water quality and ecosystem condition in freshwater streams, using various fish community metrics. However, the principles behind the IBI have since been applied to include other taxonomic groups, especially benthic invertebrate communities. How are the IBI results determined?
As society's requirements for quantitative evaluations of ecosystem conditions have expanded, so too has the demand for broad-based approaches to habitat assessment. Since Karr's original introduction of the IBI, there has been a steady increase in the number and complexity of indices developed to evaluate ecosystem condition and habitat quality in a variety of fresh water, estuarine, and near coastal environments. A significant number of the indices designed for use in estuarine or coastal marine environments make use of benthic macroinvertebrates as indicators of habitat quality and were developed in accordance with the basic principles and methodology of Karr's original IBI. Macroinvertebrate communities are generally viewed as reliable indicators of benthic habitat quality for a variety of reasons:
In the U.S., various Benthic Index of Biotic Integrity (B-IBI) examples have been developed for the Southeastern U.S. estuaries, and the mid-Atlantic region. In addition, the Benthic Index of Environmental Condition (B-IEC) was developed for Gulf of Mexico estuaries, and the Virginian Province Benthic Index was developed for estuaries along the U.S. east coast from Cape Cod, Massachusetts, to Chesapeake Bay, Virginia (Paul et al. 2001). Although they are given different names and are calculated using slightly different methods, all of these benthic indices ultimately are based on a simple principal: variation in the structure of benthic communities (i.e., the types and numbers of organisms present) can be an effective indicator of benthic habitat quality across a region. In developing these indices, researchers in the U.S. utilized extensive datasets collected by partnerships of federal and state agencies as part of long-term, regional-scale monitoring programs. These data sets typically include both benthic community data (e.g., lists of the number of individuals of each species found in each sample) and simultaneous measurements of key habitat variables (e.g., dissolved oxygen levels, sediment contaminant concentrations) collected at relatively large numbers of sampling stations throughout a given region. The same general procedure has been utilized in the development of the various B-IBI, B-IEC, and Virginian Province benthic indices, consisting of the following five steps.
Mapping of benthic community condition using various benthic indices has proven to be an effective tool for managers to evaluate both status and trends in estuarine systems at regional scales. The Regional Monitoring case study describes an example of how these indices are incorporated in regional quality assessments. References Diaz, R.J., M. Solan, and R.M. Valente. 2004. "A Review of Approaches for Classifying Benthic Habitats and Evaluating Habitat Quality." Journal of Environmental Management. Volume 73. Pages 165 to 181. Karr, J.R. 1981. "Assessment of Biotic Integrity Using Fish Communities." Fisheries. Volume 6. Pages 21 to 27. Paul, J.F., K.J. Scott, D.E. Campbell, J.H. Gentile, C.S. Strobel, R.M. Valente, S.B. Weisberg, A.F. Holland, and J.A. Ranasinghe. 2001. "Developing and Applying a Benthic Index of Estuarine Condition for the Virginian Biogeographic Province." Ecological Indicators. Volume 1. Pages 83 to 99.
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