Most estuarine and coastal systems have a variety of habitat types. When John Smith traveled in the Chesapeake Bay in the early 1600s, oyster bars were so numerous that they were hazards to navigation. These large oyster bars are mostly gone now, but they can sometimes be seen using sonar-mapping techniques. Today oysters are found in limited areas, including those used for commercial purposes.

Sea grass beds and marshes are other common habitat types found in most temperate estuaries. These vegetated areas often serve as important nursery habitats for small fish and crabs. Due to pollution and decreasing water clarity, sea grass beds are much reduced from historical levels in Chesapeake Bay.  Marshes are in decline due to human activities along shorelines.


Although oyster bars, sea grass beds and marshes among the best known shallow water habitats, soft sediment habitats are usually the most common bottom type found in most estuaries and coastal ecosystems.  These areas typically support high densities of small clams, worms, crustaceans and other benthic invertebrates. In addition, where light reaches the sediment, benthic microalgae are often abundant.

Sediment types range from sandy (large grain size) to muddy (small grain size).  The distribution of sediment types is influenced by the hydrodynamic setting, estuarine circulation and sediment supply to the estuary.  Sands are found most frequently in the intertidal and along shorelines exposed to wave energy.  Muddy sediments are found in more quiescent areas, in areas of high sediment delivery, and in areas such as the estuarine turbidity maximum, where circulation processes cause trapping of fine sediment.

For further information about benthic habitat types and how to map sediment distributions in estuarine and coastal marine habitats refer to the following:

NOAA Coastal Services Center, Benthic Habitat Mapping

OzCoast and OzEstuaries website: http://www.ozcoasts.org.au/conceptual_mods/index.jsp
http://www.ozcoasts.org.au/conceptual_mods/ about_sed_env.jsp