Intro to Salt Marshes

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 flounder and 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 that eat the detritus provided by the plants.

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