The Salt Marsh
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Edge of Casuarina zone - looking back towards the road |
As we move away
from the road towards Towra Point, we come to an band of vegetation
made up almost exclusively of Allocasuarina glauca -the
Swamp Oak. This area is affected by the 'king
tide'(the highest of the spring
tides) which occur 3 or 4 times a year and which reach a height
of more than 2 metres. Allocasuarina requires fresh water
for growth but must be able to tolerate some salt round its root
system. The sharpness of the line of demarcation of the seaward
edge of the Swamp oak zone would suggest that the balance is
a 'delicate' one. The roots of Casuarinas contain nitrogen fixing bacteria (Frankia -Actinomycete) which make a significant contribution to the nutrient economy of the zone. |
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The salt marsh at high and low spring tide
The open portion of the salt marsh roughly coincides with the area which is covered by high tide at the spring tides but not covered by high tide at the neaps.
The angiosperm vegetation of the salt marsh is made up of relatively few species. Apart from the mangroves, the 6 major species are-
 (a samphire) |
 (a grass) |
 (a sedge) |
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Wilsonia backhousei is sometimes found on the Sarcocornia/Sporobolus dominated area of the salt marsh.
Some of these plants are known to have mechanisms to control their salt content. Sarcocornia quinqueflora accumulates salt in the swollen leaf bases which are progressively sloughed off, thus removing excess salt and Sporobolus virginicus has salt glands on its leaves.
Other (lower) plants which can be found on the salt marsh are the red alga Bostrychia (Which looks like a yellowish-green moss), and a film or crust of cyanobacteria and algae on the sand surface.