Shallow Water Habitats
Human Effects - Example: Chesapeake Bay B-IBI
Benthic Invertebrates are used extensively as biotic indicators of estuarine environmental
status and trends because numerous studies have demonstrated that they
respond predictably to many kinds of natural and anthropogenic stress.
Many characteristics of benthic assemblages make them useful indicators. Exposure to hypoxia is typically greatest in near-bottom waters and anthropogenic contaminants and organic matter often accumulate in sediments where benthos live. Benthic organisms generally have limited mobility and cannot avoid these adverse conditions. This immobility is advantageous in environmental assessments because, unlike most pelagic fauna, benthic assemblages reflect local environmental conditions.
The structure of benthic assemblages responds to many kinds of stress because these assemblages typically include organisms with a wide range of physiological tolerances, feeding modes, and trophic interactions.
The Chesapeake Bay Benthic Index of Biotic Integrity (B-IBI) is a biotic indicator that helps scientists and managers to measure the "health" of Chesapeake Bay. The B-IBI allows scientists and managers to compare the relative condition of benthic invertebrate assemblages across habitat types. It combines several benthic community measures indicative of habitat "health" into a single number that measures overall benthic community condition. Community measures that are components of the B-IBI include species abundance, the Shannon diversity index, the abundance and biomass of pollution-indicative species, and the abundance and biomass of pollution-sensitive species.
The B-IBI is scaled from 1 to 5. Sampling sites with values of 3 or more are considered to meet the Chesapeake Bay Program's Benthic Community Restoration Goals. The Restoration Goals describe the characteristics of benthic invertebrate assemblages expected in non-degraded habitats of Chesapeake Bay. The index is calculated by scoring each of several measures as either 5, 3, or 1, depending on whether the value of the measure at a site approximates, is slightly different, or very different from values found at the best reference sites in similar habitats. Scores are then averaged to obtain an indicator value.
The criteria for assigning the scores are numeric and depend on habitat. Application is presently limited to samples collected during the summer, which is when environmental conditions are usually the most stressful for estuarine animals.
Because benthic communities are permanent residents of the Bay and they are highly sensitive to poor water quality and sediment quality, the B-IBI itself is a very good indicator of the overall health of the Bay. The B-IBI is used annually to characterize the Bay's regional health as well as trends in habitat conditions over time.
You can learn more about how the Chesapeake Bay and its benthic communities are doing by visiting these websites:
Chesapeake Bay Benthic Monitoring Program website