Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

The worms, clams, and crustaceans that inhabit the bottom substrates of estuaries are collectively called benthic macroinvertebrates. These organisms play a vital role in maintaining sediment and water quality and are an important food source for bottom-feeding fish, shrimp, ducks, and marsh birds. Benthos are often used as indicators of disturbances in estuarine environments because they are not very mobile and thus cannot avoid environmental problems.

The Data

Data Source: The U.S. Environmental Protection Agency’s (EPA) Environmental Monitoring and Assessment Program (EMAP) (http://www.epa.gov/emap/) collected these data. See the technical note for Contamination in Bottom Sediments for a description of the EMAP program. These data were collected as part of the EMAP for Estuaries (EMAP-E).

Data Collection Methodology: EMAP-E examined benthic samples from over 2000 sites from Cape Cod, Massachusetts, to Brownsville, Texas. All site selections were based on probabilistic designs that permit the extrapolation of the data to the entire area. Using a Young-modified Van Veen grab, three replicate grabs were collected from each site and forwarded for identification and quantification of species. Using an index developed by EMAP-E (Engle and Summers 1999, Engle et al. 1994, Van Dolah et al. 1999, Weisberg et al. 1997), the condition of the benthic community was determined for each replicate sample, each site, and the bottom surface area of U.S. estuaries. The index reflects changes in benthic community diversity and the abundance of pollution-tolerant and pollution-sensitive species. A low benthic index rating indicates that the benthic communities are less diverse than expected, are populated by more than expected pollution- tolerant species, and contain fewer than expected pollution- sensitive species. The data in this report reflect an assessment of benthic communities as “good” (high index score), “fair” (moderate index score), or “poor” (low index score). For this report, these classes were described using the terms “undegraded,” “moderate,” and “degraded.” These terms were chosen to ensure a neutral description of the index information (i.e., whether a site’s benthic community indicates that the site is degraded or not in relation to a reference site).

Data Quality/Caveats: The indices used in the three regions were developed independently and may not be comparable. Each has been demonstrated to be accurate in the region in which it was developed, but there is some question about whether they can be combined because of the different procedures used in their development.

The definition of undegraded and degraded areas also varied because the levels and types of stress differ from region to region. As a result, the indices in less disturbed areas, such as those being developed in southern California, are designed to detect smaller levels of perturbation than are indices developed for areas like the Chesapeake Bay, where hypoxia and resulting defaunation are prevalent.

Finally, some indices are closely identified with particular sampling methods, creating challenges for integration of results. For example, Gulf of Mexico and Atlantic coast indices are based on animals held on a 0.5-mm screen, while an index used in southern California is based on samples sieved through a 1.0-mm screen.

Note that in the 2002 Report, data were reported for the “moderate” category for the Mid-Atlantic incorrectly. The data have been revised to reflect the fact that analyses in both the Mid-Atlantic and the North-Atlantic assign either “undegraded” or “degraded” designations only.

Data Access: The data presented here were obtained directly from EPA.

2003 Web Site Update: Data were provided by the EPA for this indicator update.

The Data Gap

Benthic infaunal data are available from most areas of the country, but the index tools necessary to conduct regional-scale assessments of benthic condition are not available for estuaries in Alaska or Hawaii. EPA has recently issued national guidance on index development (EPA 822-B-00-024), which should facilitate development efforts in the remaining areas. The guidance document is available on the Web at http://www.epa.gov/waterscience/biocriteria/States/estuaries/estuaries1.html. In addition, few data are available on benthic community condition in coastal ocean waters (out to 25 miles).

References

Engle, V.D., and J.K. Summers. 1999. Refinement, validation, and application of a benthic condition index for northern Gulf of Mexico estuaries. Estuaries 22(3A):624–635.

Engle, V.D., J.K. Summers, and G.R. Gaston. 1994. A benthic index of environmental condition of Gulf of Mexico estuaries. Estuaries 17:372–384.

Van Dolah, R.F., J.L. Hyland, A.F. Holland, J.S. Rosen, and T.R. Snoots. 1999. A benthic index of biological integrity for assessing habitat quality in estuaries of the southeastern USA. Marine Environmental Research 48(4–5):269–283.

Weisberg, S.B., J.A. Ranasinghe, D.D. Dauer, L.C. Schaffner, R.J. Diaz, and J.B. Frithsen. 1997. An estuarine benthic index of biotic integrity (B-IBI) for Chesapeake Bay. Estuaries 20(1):149–158.