| What Lives in an Estuary?
25 September 1998
Estuaries are coastal areas where sea water mixes with
fresh water, primarily from rivers. Nutrients carried downstream
are trapped in the estuary, creating fertile ground for
the growth of a wide variety of diverse plant life. This,
in turn, supports the habitats of many different animals.
Because estuaries are protected from the wave action of
the open sea, they are also perfect nursery grounds for
a large variety of important shell and fin fish.
North Carolina has more square miles of estuarine waters
than any state on the east coast. Our estuaries vary considerably
- from broad, shallow sounds like the Albemarle and the
Pamlico, to narrow bodies of water, such as the Currituck
Sound. Different water levels, types of basins, tidal patterns,
salt levels, temperature, and types of sediment make each
estuary unique and define the types of habitats and organisms
The coastal marsh is just one habitat found in North Carolinas
Coastal marshes are valuable, productive wetlands that
are sometimes flooded, depending on the tides. There are
four kinds of coastal marsh habitats in our estuaries: low
salt marshes, high salt marshes, brackish marshes and freshwater
The low salt marsh is the foundation of the estuarine food
web and as such is relied upon in some way by most living
things in the estuary. Salt marsh cordgrass is one of the
most important plant species in this habitat. Cordgrass
is especially suited to the drastically changing salinities,
temperatures and water levels in the low salt marsh. It
stabilizes the fine particles of clay and silt that are
deposited by the estuarys slow current by creating
a network of roots and stems that hold the soft soil together.
Cordgrass also protects the mainland from erosion by slowing
down the force from incoming waves and tides.
Cordgrass is important to the animals in the low salt marsh
as well. It is one of the most important producers in the
estuarine food web. When the plant dies back each fall and
is washed into the estuary, its tissues are broken down
by bacteria into detritus. Detritus is a primary food source
for many aquatic animals.
Several types of snails live among the cordgrass, including
marsh periwinkles. They eat algae that grows on its stalks,
and they use the stalks as an escape from the rising tide.
Ribbed mussels, oysters and fiddler crabs are found in the
low salt marsh habitat. Birds and mammals also forage
in the low salt marsh. Egrets, herons, willets and osprey
are just a few of the birds that rely on the low salt marsh
for food. Racoons, meadow mice and even bats venture into
the marsh for a meal.
Fewer animals use the high salt marsh for food. High salt
marshes are the areas where daily tidal flooding in the
low salt marsh has created a build-up of fine sediment.
Soil elevation increases and shrubs gradually move into
the upland edge of these zones. Salt meadow cordgrass, salt
grass, sea ox-eye, black needlerush and glasswort become
more common. Marsh elder and wax myrtle are among the shrubs
that are prevalent in this area. Insect-eating birds like
the red winged blackbird, meadowlark and seaside sparrow
nest in the high marsh. Other common animals here include
the sand fiddler crab, marsh crab and meadow marsh.
North Carolina Division
of Coastal Management
Carolina National Estuarine Research Reserve