We are here at Folgers Marsh on the island of Nantucket and
we are going to talk about what a salt marsh is. Salt marshes are
communities of grass - and the animals associated with them -
that form in quiet embayments between the high tide low tide marks.
It is an interesting habitat because it is both
an aquatic habitat - flooded with salty water -
and a terrestrial habitat. When the tide comes in
- as we see here at high tide - the water moves over the surface of the grass
and is partially an aquatic habitat.
The grasses are experiencing salty-water, which is not
a great condition for them. But these grasses are
adapted to tolerate it.
Animals move onto the marsh and get some protection from predation.
Things like little shrimp and little fish can move onto the surface
of the marsh.
There is a gradation of species on the marsh -
from this edge or this low tide or low marsh mark
to the high tide mark as you move back.
At the edge we have this species called 'Spartina alterniflora'
- or salt marsh cordgrass. It can grow
pretty tall in some areas, and as you move back
onto the marsh it stuts.
It is most covered by the tide for the longest period of time
- tides come in and out on a six hour cycle
twice a day. It can tolerate being
flooded by water because it has aerial roots.
Plants take in oxygen through air not their water.
The animals that live on the marsh however, most of them are
aquatic animals. Things like mussels and fiddler crabs.
They get oxygen from the water. I am going to talk a little about the animals
in the marsh. You can see there are birds feeding.
This is [an] important habitat for feeding
- things like egrets, herons
and osprey. The water that comes in through
the marsh channels - and flows throughout the marsh -
is [an] important habitat for crabs
and smaller juvenile fish of some commercially important species such as
bluefish. We also have smaller species that are
salt marsh creek inhabitants that provide food for the
crabs and the other larger fish. At the edge
of the marsh there is a mussel that is attached
to the substrate and to the
roots of the 'Spartina alterniflora'. This mussel called the ribbed mussel
- 'Geukensia demissa' - has a mutualistic
association with the grass. It provides
nitrogen and stabilizes the roots,
while the plant provides a place for it
to attach to - and a little bit of protection from predators.
You also find fiddler crabs. Fiddler crabs make little burrows
along the edge
- and there [are] actually three species of fiddler crab that live
in this marsh. Some live in this more sandy habitat
another species lives in more muddy habitat[s]. As you go
back through the marsh towards the road there is actually
a source of fresh water, and you get a third species that lives
in that more brackish water - or less
salty water. Fiddler crabs make burrows, and this burrow
help aerate the substrate.
One condition of a marsh is that when it is flooded you have a lot of microbial
action going on.
It depletes the water that is in the sediment of oxygen.
As you move back - if you were to dig a hole
and let it fill with water - that water would be very smelly because of the microbial
action - sulfur.
It also would have very little oxygen if any oxygen at all.
This is also a physiological stress for plants and animals.
So you can see [that] a salt marsh is a very unique
community of plants and animals that
live in this area the coast.
It is an important habitat, it is a habitat that provides a lot
of primary production. Which means the grasses take in carbon dioxide
and turn that into organic carbon.
It also is an important habitat for
the coastline behind it. It provides protection from
storm damage [as] a buffer zone between
the sea and the land.
Thirdly, it is an important habitat for
these important commercial species and juvenile fish that use the salt marshes
to grow larger - they use the food provided by the other smaller organisms
eat the detritus provided by the plants.