Salt Marsh and Intertidal Mudflat Ecosystems
Structure of salt
Salt marshes are
composed mainly of emergent vascular
plants that are distributed across the intertidal. How does this differ from seagrass
does it change?
Salt marsh vegetation is
interupted by tightly meandering tidal creeks and salt pannes.
Why doesn't vegetation grow on salt pannes?
webs and energy flow in salt marsh ecosystems
systems are extremely
productive (both primary and secondary). Why are these systems so productive?
Yet, as with seagrasses, there are limited
number of animal species consuming living salt marsh grass tissues
(blades are toughened with cellulose and silca, and may contain
can secondary production (i.e.
consumer production) be high if few species are consuming salt marsh
Other pathways of energy flow:
- Micro-algae (especially diatoms) on stem and mud surfaces (about
1620 g/m-2/yr-1 for example in Louisanna marshes). Macroscopic
epiphyte, as seen on seagrass blades, are generally absent on salt
- As in most aquatic
organisms also contribute to production in marshes (though a
relatively small percentage). What
is the source of their energy?
- Invertebrates such as
wharf crabs, grasshoppers, leafhoppers, and beetles grazing on living
- Invertebrate fungus 'farmers'!
So, what would a food web/energy
diagram look like for a salt marsh ecosystem?
Ecology of salt marsh
cordgrass (Spartina alterniflora
), forms a near monoculture in
the lower marsh and is responsible for much of the marsh's
considered an invasive
other parts of the world. Further north along the eastern coast
of North America, another species of Spartina
) becomes more common in the upper marsh.
Spartina grows better when
cultivated in freshwater, so why isn't abundant in freshwater marshes?
can also form entensive meadows in areas within the marshes of Georgia.
Overall, diversity of plants is relatively low. What are the major stresses affecting salt
- Like desert plants, many marsh plants have narrow leaves and
sunken stomata to reduce water loss. Plants
adapted to saltwater (halophytes) remove excess salt by various
strategies. For example, Spartina
alternaflora has glands through which salt is excreted
leaving visible crystals of salt on its leaves. Salicornia sends salt to
its tips and, in the autumn, these compartments dry up and break off at
- Salt marsh plants must also cope
oxygen in sediements due to continual submergence The light
around the roots reveals this oxidation process. In
marsh oxygenation by the rhizoshperes of nearby plants results in
stimulation of con-specifics
Nitrogen tends to be the limiting nutrient in marshes, and changes in
supply can alter competitive outcomes among marsh plant species
Important marsh animals
include crabs, snails, and amphipods as well as deposit feeders such as
polychaetes and shrimp.
are also abundant (why?
) and include the ribbed mussel
(it's Geukensia demissa
, you Donax
) and the american oyster
include the blue crab
limit the lower distribution of ribbed mussels, and force migration of
Do excessive nutrients in water pose the
same threat to salt marshes as they do seagrasses?
Over 50% of salt marshes in the U.S. have been
destroyed, mostly due to filling
of marshes to create more land area for
industry and agriculture and by ditching
for mosquito control and diking.
An invasive species
, the common
spp.), has displaced native species in some regions.
subtidal estaurine bottoms, deposit
feeders and suspension/filter
feeders are common on and in the sediment of
mudflats. In fact, there is surprisingly little vertical zonation
in soft-sediment communities (relative to rocky intertidal and marsh
communities). Why might
organisms living within sediments not be as strongly influenced by
Diversity often appears low, but sampling with shovel and sieve will
often reveal numerous taxa.
What is the source of primary
production in intertidal mudflats?
on soft-sediment organisms:
are microscopic invertebrates (42-500 µm) that live between
sediment grains (up to 2 billion individual/m2
) and feed on
detritus, bacteria, and protozoans.
such as bivalves, link water
column and benthic process by filtering plankton and detritus, and by
expelling regenerated nutrients back to the water column.
such as polychaetes, amphipods, sea cucumbers, and snails utilize a
wide range of foods including decaying plant material, bacteria,
protozoans, diatoms, fungi, and meiofauna. Many deposit feeders
process a large volume of sediment (up to 10 times the body weight
daily) and the result is bioturbation
of sediments enhancing sediment resuspension which may stimulate
Not only do intertidal organisms have
to deal with anoxic sediments, but also with dissecation at low
high relative to subtidal soft-sediments and to marshes and
seagrass beds. Why?
Primary source: Bertness MD. 1998.. The Ecology of Atlantic
Shorelines. Sinauer Associates Inc. Sunderland, MA