Monitoring Benthic Habitats

The animals that are collected are known as macrofauna, and can be divided into two groups: infauna and epifauna.  Infauna live under the sediment surface, and their numbers and kinds are reliable and sensitive indicators of benthic habitat quality.  Epifauna live on the sediment surface and are usually associated with surface structures such as shells, vegetation, or animal colonies.   Because epifauna are less exposed than infauna to toxic substances in the sediment, they are not used to assess sediment quality.

The composition of benthic communities differs substantially according to bottom salinity and sediment type.  Bottom salinity (given in parts per thousand) is the dominant factor in the Chesapeake Bay.  Benthic communities in the Bay are classified according to the salinity ranges in which they occur.  These salinity ranges (tabulated to the right) define five habitats: Tidal Freshwater, Oligohaline, Low Mesohaline, High Mesohaline, and Polyhaline.  In mesohaline and polyhaline habitats, benthic community composition also differs in muddy and sandy sediments.  Benthic community composition, however, does not change with sediment type in tidal freshwater or oligohaline habitats.