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Lesson N° 4 :
Salt marshes and mangrove swamps :
Salt marshes :
Although they are limited to the innermost strip of the nearshore zone ,
higher plants have colonized marine environments . A case in point are
the tall grasses of salt marshes , which are vegetated intertidal flats.
Unlike the simple seaweeds , salt-marsh grasses possess all the
characeristics of terrestrial plants , including a root mass and a vascular
system for the circulation of internal fluids.
Because of their intertidal location, salt-marsh meadows are continually
covered and uncovered by seawater each day as tidal currents flood and
ebb.
Based on
a distinctive zonation pattern of grasses , salt marshes are
subdivided into two principal zones : the low and high marshes.
The low salt marshes extends roughly from mean low tide to the neap
high tide.
The high salt marsh , which extends from neap high tide to the level of
the highest spring tide is flooded only during unusually high tides and
during storm surges.
Therefore , unlike the low marsh the high marsh leans more toward a
terrestrial than a true marine environment.Its floral community is much
more diversified than that of the low marsh consisting of salt hay grass
Spartina Patens , saltwort grass Salicornia species, and the spring grass
Distichlis spicata.
Most marsh ecologists agree that frequency flooding plays a major role
in the distribution of plants in salt marshes. Low marshes are covered by
seawater and exposed to air repeatedly each day , Spartina Alterniflora
flourishes in this stressful environment because there is no competitive
pressure from plants that are less tolerant of such harsh environmental
conditions .By contrast , much of the high marsh is infrequently flooded
by seawater .This permits S.Patens ,Salicornia species and Distichlis
spicata to compete with and thus exclude Sparttina Alterniflora from
the High marsh.