Chesapeake Bay Benthic Monitoring Program

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Monitoring Benthic Habitats

Which Benthic Habitats Do We Monitor?

Benthic organisms are collected from subtidal soft bottom habitats in the Chesapeake Bay.  Soft bottom habitats are muddy or sandy sediments and comprise 99% of the Bay bottom.  Oyster reefs and other hard bottoms are more difficult to sample quantitatively and are not included in the Benthic Monitoring Program.

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.

Benthic
Habitat
Salinity
Range (ppt)
Tidal
Freshwater
0 - 0.5
Oligohaline 0.5 - 5
Low
Mesohaline
5 -12
High
Mesohaline
12 - 18
Polyhaline 18 - 25

How Do We Monitor Benthic Habitats?

The sediments are sampled with a benthic grab, which is a mechanical device that scoops a fixed amount of bottom sediment each time it is used.  Sediments collected in the benthic grab are sieved through a screen with 0.5 millimeter openings, and animals retained in the sieve are preserved to be identified and counted.

 

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URL http://esm.versar.com/vcb/benthos/benthos/habitat.htm

Revised: February 24, 2003.