Coral reefs are among the most important of all marine habitats and the Red Sea provides ideal environmental conditions for stony corals of which over 200 species are found in this semi-enclosed sea. The shallow shelves bordering the sea ensure sufficient light for calcification to occur and for photosynthesis in the algae on which some polyps feed. The more delicate branching corals thrive in shallow, well-lit water. More massy corals do well in deeper water and are better able to tolerate suspended sediment, which both cuts down available light and tends to clog the little polyps. Corals that are more efficient at cleaning away the sediment do better in areas of relatively high sedimentation.
Symbiotic algae that grow only on live corals produce part of the food the polyps need. Other algae growing on reef faces are food for herbivorous fish and other creatures.
Most stony corals are reef-builders, generally colonial. Each polyp builds a skeleton and the animal sits in a calcareous cup, or theca, that it has secreted. The polyps are connected to each other by an extension of the body above the level of the skeleton. Thus, the colony sits on the surface of the skeleton. In some species, the polyps are widely separated and form branching structures; others are close to each other and have thecal walls in common.
Coral polyps reproduce by means of asexual budding in
order to form and enlarge the colony, so colonies can
often extend over large areas. The growth rate for some
stony corals can be as low as 1cm a year, however, the
rate at which coral colonies grow depends on the type
of coral, the location and the amount of sunshine they
receive. Some corals grow at a rate of 20-25cm per year
in very good conditions. Others are slow growing at
4-5cm per year under very good conditions. Under normal
conditions these rates are halved. Breaking off just
a few centimeters of coral to take as a souvenir can
mean breaking off many years of growth.
Coral reefs provide habitats for many plants and animals. They form an ecological niche in which creatures can live, feed and take refuge from predators. Crustaceans, worms, starfish, and fish all benefit from the coral reef ecosystem.
Called sea grasses because
they grow in small lawns or meadows and for the long
grass-like leaves of many species, these aquatic plants
are more closely related to the pondweeds than to the
huge family of grasses. Sea grass beds occur on the
shallow coastal shelves of the Red Sea and contain eleven
of the limited number of species known worldwide. Due
to the relative lack of suitable shallow, sedimentary
habitat, the number and size of these beds is limited.
However, the ecological importance of sea grasses may
be comparable to that of the reefs as they are among
the richest and most productive of marine ecosystems.
In the Gulf of Aqaba, 49 species of invertebrates were found living in the sea grass beds, of which about 70% were mollusks. About 9% of the species living in these beds were found in no other habitat. Sea grass beds are important providers of food, shelter and protection for the juveniles of various species of commercially important fish and crustaceans and are the only source of food for the Green Turtle, Chelonia mydas, and the Dugong, Dugong dugon.
It appears that the diet of this large marine mammal consists entirely and solely of one species of sea grass, namely Halodule uninervis. It pulls out the grass, using its flippers and makes it into several stacks; it then eats the stacks in more or less serial order.
Offshore waters: Corals and sea grass beds
are found in the shallower waters of the Red Sea but
the deeper waters are also home to a great diversity
of fish that feed on plankton, invertebrates or each
other. Among these, the largest and most well known
are the sharks of which several species are found in
this zone. Cetaceans are also not uncommon in Egyptian
waters and include Risso's Dolphin, Grampus griseus,
and Bryde's Whale, Balaenoptera edeni.
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