Biological Survey Design Biological surveys that measure the structure and function of aquatic communities will provide the information needed for biological criteria development. Elements of community structure and function may be evaluated using a series of metrics. Structural metrics describe the composition of a community, such as the number of different species, relative abundance of specific species, and number and relative abundance of tolerant and intolerant species. Functional metrics describe the ecological processes of the community. These may include measures such as community photosynthesis or respiration.
Biological surveys can offer variety and flexibility in application.
Indices currently available are primarily for freshwater streams. However, the approach has been used for lakes and can be developed for estuaries and wetlands. The IBI is one of the more widely used assessment methods. All 12 metric values are then summed to provide an overall index value that represents relative integrity. Several indices that evaluate more than one community characteristic are also available for assessing stream macroinvertebrate populations.