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Habitat: Coastal fossil coral

by Monika Mufti

Lastminute-Express.de - Last Minute Reisen online

 
  Coral reefs have existed on the planet for more than 450 million years as evidence from fossil records show. Many areas of Sinai, especially Ras Mohammed, have well defined raised fossil coral platforms which are reminders of the ancient shorelines. These fossil reefs range from approx 15 thousand to 2 million years in age.
In Ras Mohammed and Nabq, where fossil reefs have eroded and been covered with silt (from wadi run-offs, wind deposits etc.), and where there is infiltration of fresh water (underground acquifer or wadi run-off), mangroves have been able to take a foothold.
Five distinct colonies have now evolved and they comprise the northernmost mangroves in the world:

the Mangrove Channel in Ras Mohammed
four locations in Nabq: El-Ghargana (Bedouin village), Marsa Abu Zabad, El-Rwaisia, and El-Monqatea.

 

Avicennia marina

with aerial roots at low tide

 
 

This colonization was made possible partly due to the fact that the northern highlands (incl. Mount St. Catherine - the highest summit in Egypt, 2641m) provide shelter against the cool northerly winds to make it a warm environment.

Mangroves in the Red Sea grow under extreme conditions of high salinity (42ppt) and low winter temperatures. Some of the Nabq mangroves have adapted to this harsh environment by becoming completely terrestrial. They now form part of the coastal marsh and dune vegetation (sabkha) and have lost their aerial roots altogether.

Mangroves are an important and sensitive ecosystem, providing an ideal environment for young fish and invertebrates as well as a nesting and resting site for migratory and resident birds.


Avicennia marina

at high tide showing
submerged aerial roots
Avicennia marina / Grey mangrove

Family: Avicenniaceae

Avicennia marina (the name was given in honour to the great physician-philosopher Avicennia is an evergreen tree growing up to 6m in height and has typical dark brown aerial roots (pneumatophores) that reach beyond the high tide mark. These roots, forming an intrinsic network which can be best seen at low tide, show as leafless branches sprouting from the ground around each tree.

The roots act as a natural desalinator, creating a barrier and filter, keeping out most of the salts from the seawater and can also assimilate oxygen from the uppermost mud layer. Commonly, the sap concentration in the tree is about 1/10 that of the surrounding sea water. Salt is partially excluded by the roots and the remainder is expelled by specialized glands in the leaves.


The tree has elliptical, leathery leaves that are dark green on the front and grayish underneath, often crusted over with salt crystals.
The tiny flowers are orange with hardy, exserted stamens.
Fruits appear as green 'nuts'. When ripe, they drop into the water and the tides wash them to new locations. Young mangrove shoots are easily identified throughout the Sinai coastline.


 

Avicennia marina
flower and fruit

This fruit was washed ashore by the tide


New mangrove seedling

 
Coastal salt marsh (sabkha) dunes in Nabq overgrown with mangroves

They have completely adapted to this unique environment and have lost their aerial roots alltogether. Scientists believe that favourable atmospheric conditions play an important role in this adaptation and make it possible for the plant to excrete all of the accumulated salt solely through the specialized glands in their leaves.

This particular set of mangroves is situated at Marsa Abu Zabad (Nabq) and is well above the high tide mark.

 

Terrestrial Avicennia marina
in the salt marsh (Nabq)
Another example of terrestrial Avicennia marina. The location of this pictureis at El-Rwaisia, close to the lighthouse. To the very left of the picture are shown clearly the intertidal salt deposits and the high tide mark is clearly discernible by a line of deposits on the shore.

Although this particular tree does get wet during high tide, no aerial roots are present.

 
 
 
 

References:

   
 

General:

Fossil coral reef: Pneumatophores:
  - Hort Purdue - Geo Cities
- Baobabfarm
- Mangrove Nus
- SBNP
       

 


 

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