UAE Mangroves



The black mangrove, Avicennia marina, is found in the lower to middle tidal zone where these are protected from intense wave energy or extremes of salinity in the coastal complex of the Emirate of Abu Dhabi. They are found in swamps lining tidal creeks flanking the barrier islands and the Dhabaiya peninsula, and the more protected shores of islands flanking the Khor al Bazam (Kinsman, 1964b; Kendall and Skipwith, 1969b; Purser and Evans, 1973).

One of the most convenient places for the geologist visiting the UAE to view these swamps is located in creeks lining the western margin of the Dhabaiya peninsula. Driving west from Abu Dhabi on the main road to Jebel Dhanna and west turn off at the sign to "Dhabiya" (note phonetic spelling). There is a gas station here and though some might not recognize it, beside the gas station is a restaurant at which many of those have visited the swamps and sabkha near by have lunched and quenched their thirst. Use the map and your intuition and you will find the creeks. Watch out for the large trucks!


Only the black mangrove, Avicennia marina, with its characteristic system of protruding roots or "pneumatophores" has been found in the Khor al Bazam and nearby islands (Kendall and Skipwith, 1969b). It occurs as small bushes and trees, either in narrow strips parallel to the shore at the very top of the intertidal flats, or in areas lining the edges of creeks draining algal flats. These areas are protected from vigorous wave action and undergo frequent tidal interchange so that the mangrove roots and lower trunk are normally covered at high water. Tanner et al. (1963) observed that a good tidal interchange is important for mangrove growth.

On the islands of Marawah and Abu al Abyad, and on the west side of the Dhubaiya Peninsula, where a series of Pleistocene outcrops protect the region from the effects of wave erosion algal flats and tidal creeks develop that are lined by mangrove stands. The larger mangroves grow on the edges of channels and diminish in height and distribution inland. Allen (1965) observed a similar relationship on the Niger delta. In the Khor al Bazam carbonate mud and silt collects around the mangroves, as it does in Florida (Vaughan, 1909) and in the Bahamas (Newell et al., 1951). In the Khor al Bazam this mud is commonly highly burrowed by crabs. Some of the mud probably precipitates in situ. These burrows stretch over the landscape like craters on the moon and locally their surface is cemented to form a beach rock.


As these channels become filled with carbonate silt and the tidal flats prograde seaward, the area becomes more restricted and is colonized by cyanobacterial mat and the mangroves die. The cyanobacterial mats tend to grow landward of the mangroves though in the higher reaches of the creeks they start to grow on banks. Here they initially take the form of the cinder like cyanobacterial mat seen on the major algal flats of the Khor al Bazam. Here this mat is often cemented to form a beachrock.

Inland, the algal mat may be marked by a superficial polygonal pattern while landward a crinkled cyanobacterial mat overlying a gypsum mush in turn supersedes this. This gypsum may be deflated from the cyanobacterial mat crinkle zone to form dunes covered by halophytes such as Arthrocnemum glaucum. These dunes can enclose the creek area.
Thus in the vicinity of Dhabaiya and other locations the sabkha can be traversed into a gypsiferous crinkled algal flat, which in turn, passes into a burrowed crab flat with some Arthrocnemum glaucum colonizing local highs, and finally to mangroves lined the tidal creeks. Cementation can be observed in the form of hardgrounds around the Arthrocnemum glaucum and extending down into the burrowed crab flats. Mud cracked zones are common here.rites of this area.

Friday, March 29, 2013
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